CONTENTS
Introduction
Pickling Cucumber Variety and Weed Control Trials
Rate, Timing of Application, Source, and Placement of Nitrogen
Fertilizer on Yield of Cauliflower
Rate, Timing of Application, Source, and Placement of Nitrogen
Fertilizer on Yield of Sweet Corn
Nitrogen Rate on Yield of Green Beans, Beets, and Carrots, and
Residual Mineral Nitrogen Concentration of Willamette Silt Loam
Post-Harvest Mineral Nitrogen Status in Grower Fields
Cover Crops and N Rate on Yield of Sequential Crops of Broccoli and
Sweet Corn
Irrigation Effects on Head Rot of Broccoli
Return to:     
AUTHOR:
Dr. Delbert D. Hemphill, Jr., Professor of Horticulture, has conducted research on
vegetable crops culture and management since 1976 at Oregon State University's North
Willamette Research and Extension Center, 15210 NE Miley, Rd., Aurora, OR 97002-9543.
COOPERATORS:
Dr. N.S. Mansour is Extension Vegetable Specialist and Professor, Department of Horticulture,
Oregon State University, Corvallis, OR 97331
Dr. John Hart is Extension Soil Scientist and Associate Professor, Department of Crop and Soil
Science, Oregon State University, Corvallis, OR 97331
Dr. Richard Dick is Associate Professor of Soil Science, Department of Crop and Soil Science,
Oregon State University, Corvallis, OR 97331
Dr. Mary L. Powelson is Professor, Department of Botany and Plant Pathology, Oregon State
University, Corvallis, OR 97331
Mr. Robert B. McReynolds is District Extension Agent for vegetable crops and Associate
Professor, North Willamette Research and Extension Center, 15210 NE Miley Rd., Aurora, OR
97002-9543
Dr. John Luna is Assistant Professor and On-Farm Research Coordinator, Department of
Horticulture, Oregon State University, Corvallis, OR 97331
Introduction to the Report
We have conducted a full-time program of vegetable crop research at the North Willamette
Research and Extension Center (formerly the North Willamette Experiment Station) since 1976.
The Center, a branch of both the Oregon State University Agricultural Experiment Station and
Cooperative Extension Service, is just north of Aurora, a historic farming community 20 miles
south of Portland, Oregon. The land is provided by Clackamas County, with facilities owned and
maintained by OSU. The Center serves the vegetable, small fruit, wine grape, and nursery crops
industries and is located in an area noted for the diversity of its agriculture. Our vegetable
research emphasizes the needs of both the fresh market and processed vegetable growers in the
Willamette Valley. We also conduct research on home garden and small farm-intensive vegetable
culture.
Many of the research projects reported here involved cooperation with Experiment Station and
Extension Service colleagues at Oregon State University and their contributions are gratefully
acknowledged. The financial support of the Oregon Processed Vegetable Commission, Oregon
Department of Environmental Quality, Nalley Fine Foods, UNOCAL, the Center for Applied
Agricultural Research, and the Agricultural Research Foundation was essential to completing
these projects and is greatly appreciated.
This report is the ninth in a series of biennial reports initiated in 1979.
DISCLAIMER: The use of trade names does not constitute an endorsement by the Oregon State
University Agricultural Experiment Station. Always check pesticide labels for currently registered
uses.
Pickling Cucumber Variety and Weed Control Trials
Cooperators: N.S. Mansour, Dept. of Horticulture; Robert B. McReynolds, North Willamette Research and Extension Center
Introduction
Pickling cucumber growers and processors are interested in mechanical harvest of fruit to avoid
problems with labor cost and availability. Mechanical harvest requires changes in varieties,
number of plants/acre, and cultural practices. We have been conducting trials since 1989 to
determine the feasibility of machine harvest in the Willamette Valley. This report focuses on the
two most recent growing seasons. Our 1993 and 1994 trials included a number of varieties
screened in earlier trials as well as some varieties not previously included, and on the effect of
harvest date on maturity.
Varieties thought to have a good length/diameter ratio and processing quality were grown in
commercial-scale trials. Each variety was harvested more than once to determine days or heat
units to the optimum size distribution and the rate at which size grade increases with time.
Pickling cucumbers are graded into four sizes by diameter (See Table 1), with the smaller sizes of
greater value to the processor. Growers are paid considerably more per pound for the smaller
sizes. "Size grade" is determined from the proportion by weight of fruit falling into each of the
four size categories. As a field matures, the tonnage and size grade increase, while the value per
ton decreases. Harvest and pricing policy must be adjusted both to fit processor pack needs and
to provide adequate return for both processor and grower.
Weeds reduce yield and harvester efficiency. High weed populations may cause expensive
downtime for cleaning the harvester pickup head. Chloramben (Amiben) and naptalam (Alanap)
have been withdrawn from the market. Other herbicides have proven only partially effective or
damaging to the crop. Curbit has found a niche with some growers but inconsistency in weed
control and crop injury limits its use. Testing of alternatives has been conducted to identify
combinations of herbicides that are effective and non-phytotoxic to the crop. The 1991 and 1992
trials indicated that clomazone (Command) shows promise. Weed control was excellent but there
was some damage to the cucumber seedlings in 1991. It was apparent that more information on
crop response to clomazone, alone or in combination with other materials, was still needed. A
1993 trial indicated insignificant phytotoxicity problems, but the field was so weed-free that no
useful information on efficacy was obtained. This trial was repeated in 1994.
Methods
The variety trials were established in a commercial planting just south of Woodburn, Oregon. The
previous crops were oats (1993) and sugar beets (1994). Planting date was 8 June, 1993, and 16
May, 1994, following typical land preparation by the grower. Each variety was planted to an area
of slightly less than 1.2 acres. The area for each variety was divided into two approximately equal
and separate replicates. The planter seeded six rows at a time on 30-inch centers. Planters were
not adjusted for the slightly different seed size of each variety; thus, seeding rate varied somewhat
with variety. The goal was to produce a stand of about 80,000 plants/acre.
The entire area received a broadcast, pre-plant application of 40 pounds N and 42 pounds K/acre
and a banded application of 60 pounds N and 78 pounds P/acre at planting, for a total N
application of 100 pounds/acre. This rate appears from our previous work to be optimal for
machine-harvested cucumbers. Irrigation, cultivation, and herbicide application were provided by
the grower.
We hand-harvested all varieties three times between 6 and 10 August, 1993, and 18 and 22 July,
1994, using a once-over destructive harvest for each 90-square foot plot. The fruit was weighed
and graded on a Kerian 'SpeedSizer' mechanical grader provided by Nalley Fine Foods. The
commercial plots of all varieties were harvested by Nalley's personnel using an FMC harvester on
10 August, 1993, and 22 July, 1994. A Byron harvester was also used for one variety in 1993.
The machine-harvested samples were weighed and graded at the Nalley receiving station at
Cornelius.
The 1994 weed control plots were located at the North Willamette Research and Extension
Center to take advantage of the better control it offers for managing operations and a greater
weed population. The first of two plantings ('Flurry-M') was direct-seeded with Massey-Ferguson
International planters on 24 May, 1994. The herbicide treatments were selected to verify results
from the previous year and to establish the lower limit at which Command would be effective
when applied alone and in combination with Prefar. The preplant treatments were applied one
day before planting with a CO2 backpack sprayer (40 psi) to a dry soil surface and incorporated
to 3-inch depth with a PTO-driven power tiller. The pre-emergence treatments were applied
immediately after planting and the entire area was then irrigated with approximately 1 inch of
water.
The trial design was a randomized complete block with four replications. Four rows were planted
to a 12 x 30 foot plot. Weed control ratings represent the mean rating of the three project
leaders, each rating independently of the others. Plots were harvested on 3 August.
Commercial (Machine-Harvested) Variety Trial, 1993
It is unfortunate that the harvester could not be scheduled into the variety trial on more than one
day. Since processors want to harvest at a mean size grade near 2.5, it is apparent that 'Duke',
and to a lesser extent 'Flurry-M', 'Napoleon', and 'Quest', were harvested between one and two
days after peak maturity (Table 1). The later-maturing 'Lafayette' and the Sun line were harvested
at optimal maturity.
Fortunately, the Byron and FMC harvesters harvested several acres of 'Flurry-M' in the same field
on 6 August. This gave a basis for comparison with the hand-picked samples on the same day,
and a comparison of the two harvesters. The average grade harvested was 2.35, compared to a
hand-picked grade of 2.10 for the same date. However, the FMC harvester picked a mean grade
of 2.27 (dollar value of $155 per ton) compared to 2.43 for the Byron harvester (dollar value of
$134 per ton). Since the two machines harvested different areas of the field, we cannot be sure
whether the differences are due to the machine efficiency or to differences in the maturity of the
crop in the different areas. However, the fact that the FMC picked 9.2 percent grade 1 fruit,
while the Byron picked only 3.7 percent grade 1, leads us to speculate that the difference lies in
harvester efficiency at recovery of small fruit. We were unable to calculate dollar value per acre
since the harvested areas for each machine were not reported.
It is obvious from comparing the machine-harvest and hand-picked harvests (Table 2) of the same
varieties that machine-harvest led to higher mean grade for all varieties except the SunSeeds line,
perhaps due to poorer recovery of small fruit. The average return per acre varied from $729 for
'Duke' to $953 for the SunSeeds line (Table 1). Yields were generally comparable to those in
1992 and less than those of 1991.
Hand-Picked Variety Trial, 1993
We simulated a machine harvest three times over a five-day period (Table 2). 'Duke' was first to
reach a mean grade of 2.5 in both the hand-picked and mechanically-harvested plots. 'Napoleon'
and 'Flurry-M' were the next varieties to mature, while the SunSeeds line and 'Quest' were the last
to mature. Given the better than 0.2 change in grade per day, it may be useful to lump 'Duke',
Flurry-M', and 'Napoleon' together as the early maturing varieties, with 'Lafayette', 'Quest', and
Sun 3539 about one day later. With unusually hot weather at maturity, there was certainly no
more than a 48-hour spread between the earliest and latest varieties. 'Napoleon', and to a lesser
extent 'Sun 3539' and 'Flurry-M', were slower to increase in size grade over the harvest period
than were the other varieties. This is inconsistent with 1992 when 'Lafayette' was by far the
slowest to change size grade. The greatest return per acre, at the harvest nearest optimal
maturity, was $1347 for the Sun line and $1346 for 'Quest', but 'Flurry-M' and 'Lafayette' also
grossed in excess of $1000 per acre. 'Quest' and 'Lafayette' also performed well in the 1992
hand-picked trial.
The apparent decrease in grade for several varieties between the 9 and 10 August harvests is an
artifact. The latter harvest represented only one replicate in the generally weaker and less mature
west end of the field. The high percentage of nubs and crooks in this harvest also indicates
weakness in this area, perhaps due to low nitrogen status.
Commercial (Machine-Harvested) Variety Trial, 1994
Stands of all varieties except 'Calypso' and 'Bradley' neared or exceeded target population and
were greater than the last two years (Table 3). We experienced planter problems with the
'Calypso' pass. 'Bradley' emerged two days later than other varieties and had low seedling vigor.
At the time stand counts were taken, not all 'Bradley' seed may have germinated. The
lower-than-average yield for 'Bradley' may reflect the fact that it was harvested at low mean size
grade, rather than any deficiency in stand.
It is unfortunate that the harvester could not be scheduled into the variety trial on more than one
day. It is apparent that 'Bradley,' 'Flurry,' and the Harris-Moran line were harvested a day early.
One goal in 1994 was to obtain a high percentage of size grade #3 fruit, suitable for making
spears. The entire harvest was probably about a day early for this goal. But with an average size
grade for the 10 varieties of 2.44, the cucumbers harvested were of excellent quality.
In comparing the machine- and hand-picked harvests (Tables 3 and 4) of the same varieties,
machine-harvest produced a lower mean size grade for four varieties, essentially the same size
grade for four varieties, and a greater mean grade for only 'Calypso' and 'Neptune,' indicating
excellent recovery of small fruit. In contrast, in 1993 the FMC machine harvested a higher mean
size grade than did hand-picking.
The average return per acre varied from $854 for 'Calypso' to $1859 for 'Neptune.' Yields were
generally a little less than those in 1991, at about the same maturity, and averaged 2 to 3 tons/acre
greater than in 1992 or 1993 (mean across varieties of 10.6 tons/acre in 1994, 12.4 in 1991, 8.0 in
1992, and 7.7 in 1993). The only variety in all four trials was 'Flurry-M'. In 1991 it yielded 11.8
tons/acre, in 1992 only 3.1 tons/acre at similar mean grade. The 1993 yield was 7.1 tons/acre, but
the fruit was larger than in 1992. In 1994, at mean grade of only 2.36, 'Flurry' yielded 9.9
tons/acre.
The yields from the hand-picked plots were consistent with this trend. Average hand-picked yield
for all varieties declined from 15.1 tons/acre in 1991 to 9.2 tons/acre in 1992 and 8.4 tons/acre
when picked at nearly optimal size grade in 1993. Mean hand-picked yield in 1994 rebounded to
11.0 tons/acre, at maturity of 2.5 or less. Hand-picked 'Flurry-M' declined from 8.6 tons/acre in
1991 to 5.7 tons/acre in 1992, but increased to 9.4 tons/acre in 1993 and 9.1 tons/acre in 1994.
In addition to weather, other factors may have contributed to the yield differences among years.
Stands were greater in 1991 and 1994 than in the other years. The plant population in 1992 and
1993 was lower than the target of 80,000/acre. Specifically for 'Flurry-M', the population was
estimated at 65,300/acre in 1991, 55,900 in 1992, 62,000 in 1993, and 94,000 in 1994.
The amount of reject material in loads delivered from the test plots was very low in both years,
indicating good weed control and excellent harvester efficiency at expelling dirt and vines.
Exceptions were 'Flurry,' which was harvested after dark and in a rush to finish up, and 'Bradley,'
a small-vined variety.
Hand-Picked Variety Trial, 1994
The ten varieties were hand-harvested three times over a five-day period (Table 4). 'Atlantis,'
'Discover,' 'Excell,' and 'Lafayette' reached a mean grade of 2.5 by the final hand-harvest, taken
only three hours before machine-harvest commenced. With unusually hot weather at maturity,
there was certainly no more than a 48-hour spread between the earliest and latest varieties. There
were again considerable differences among varieties in the rate of increase in size grade over the
harvest period (Figure 1). 'Atlantis' and 'Bradley' increased more than 0.26 mean grade/day,
contrasted with only 0.157 for 'HMX 1463.' The varieties 'Flurry' and 'Lafayette' have been
grown in each of the last three years. 'Lafayette' increased more rapidly in mean grade than did
Flurry in 1993 and 1994. The rate of change was greater in 1994 for both varieties, attributable
to the extremely high temperatures at harvest. However, relative rate of increase in grade may
not be consistent over all seasons. In 1992, 'Lafayette' was considerably slower to size than was
'Flurry.' Several years of experience and correlation with environmental variables would be
necessary to determine whether varietal differences in rate of fruit size increase are predictable.
The greatest return per acre, at the harvest nearest optimal maturity, was $1739 for 'Excell',
$1657 for 'Lafayette', and $1656 for Neptune. All varieties exceeded $1100 per acre in the
hand-picked trial.
It is apparent when comparing the percentage of nubs and crooks recorded for the last
hand-picking with the percentages recorded at the receiving station for the machine-picked fruit,
that either the harvester expels many nubs and crooks, or we grade to a higher standard than do
the receiving station personnel. Our percentage of nubs and crooks was, on the average, about
three times what the receiving station recorded. Nevertheless, most results are consistent
between our rating of hand-picked fruit and the grading at the receiving station. Both found
'Flurry' and 'FMX 4841' to have a greater than average nubs plus crooks percentage and 'Bradley'
and 'HMX 1463' to have a very low percentage.
Since all hand-harvests were near or below optimal maturity, we were not able to distinguish
among varieties in the rate at which they lose dollar value per acre when they pass optimal
maturity. All varieties except 'Discover' continued to increase in dollar return per acre between
the second and third harvests.
Modeling Cucumber Development in Response to Temperatures
We previously concluded that the number of accumulated heat units (North Carolina
State-Washington State model; sum of Tmax-15.5 oC with a 32 oC cutoff) required to reach maturity
for a given variety increased with later plantings, indicating that maturity is not a linear function of
heat unit accumulation in the Willamette Valley. Results in 1991 through 1994 were consistent
with this conclusion. In 1991, it took only 583 AHU to surpass optimal maturity for the variety
'Calypso' with a 5 June planting date. However, in 1990, 690 AHU were required for 'Calypso' to
reach a mean grade of 2.5 from a 3 July planting date. In 1994, with a 16 May planting date, only
552 AHU were required to bring 'Calypso' to a mean grade of 2.57 (machine-harvest).
From 1991 through 1994 data on 'Flurry-M', it can also be concluded that the model is not
consistent between seasons with different weather patterns. In 1991, with a relatively cool, wet
June, it took about 540 AHU to mature 'Flurry-M'. In 1992, however, with unusually high
temperatures in June, it took 600. In 1993, with an unusually cool and wet June and July, but
with very hot weather near harvest, 'Flurry-M' needed only 501 heat units to reach optimal
maturity. In 1994, temperatures were near long-term averages from planting until just a few days
before harvest. 'Flurry-M' had not reached a mean grade of 2.5 with 552 AHU. Apparently, vine
development, flowering, and fruit development in 1993 occurred normally, despite the very cool
weather, and the warmer weather in 1994 did not advance maturity.
It is now apparent that, even with the high temperature cutoff of 32 oC, the North Carolina
State-Washington State model gives too much weight to above-normal temperatures at the
pre-bloom stage of plant development. Furthermore, the model cannot anticipate any delay in
pollination and fruit set that may result from inadequate bee activity at first bloom. It is also our
belief that the base temperature of 15.5 oC used in the model is too high. Use of a 10 oC base, and
the mean rather than the maximum temperature, along with a penalty for cold weather, may
provide a superior model of plant response to temperature.
Weed Control Trial
The high rate of Command, 0.25 lb active/acre, applied pre-emergence produced yields
significantly greater than most other treatments and was the only treatment to outyield the
hand-weeded control (Table 5). Even at the lower rate, pre-emergence Command was an
excellent treatment. Pre-plant incorporation of Command resulted in significantly lower yields
and reduced weed control compared to the same rates of Command applied pre-emergence. The
high rate of Command, pre-emergence, reduced stands slightly compared to most other
treatments in both trials, but yield was not adversely affected. The combination of Command with
either Prefar or Alanap did not improve weed control or yield compared to Command alone. The
combination of Curbit and Alanap was superior to Curbit alone for both weed control and yield.
Registration of Command would provide a valuable tool for growers, particularly in view of its
low cost.
Table 1. Nalley's-OSU pickle variety trial, 1993 machine-harvest results
Variety %1s %2s %3s %4s %N&C %Rej Tot lb. Grade $/T $/A T/A
Duke 2.7z 13.4 55.6 19.7 7.8 0.8 20400 3.01 85 729 8.6
Flurry-M 3.0 28.1 55.5 8.3 4.7 0.5 17160 2.73 110 775 7.1
Lafayette 4.8 33.2 53.8 3.2 4.2 0.8 18130 2.58 123 949 7.7
Napoleon 6.4 20.8 47.6 22.2 2.5 0.6 19140 2.88 101 813 8.1
Quest 2.4 27.4 62.8 2.7 4.7 0.2 17800 2.70 113 849 7.5
Sunex 3539 3.7 44.8 46.7 1.8 2.8 0.1 17040 2.48 133 953 7.2
zSize categories are as follows: 1) 0.5-1.0 inch diameter, 2) 1.0-1.5 inch,
3) 1.5-2.0 inch, 4) over 2.0 inch. N&C=nubs plus crooks. Rej=reject material,
mainly dirt clods, stems, and roots. Grade is the weighted average of the
percentage in each size category, excluding N&C.
Table 2. Nalley's-OSU pickling cucumber variety trial, 1993 hand-picked
harvest results
Variety Harvest date %1s %2s %3s %4s %N&C Grade T/acre $/T $/acre
Duke Aug. 6z 18.7 54.7 19.6 1.0 6.0 2.03 3.9 185 715
Aug. 9 6.4 21.8 48.0 16.7 7.0 2.81 8.3 105 871
Aug. 10 4.3 18.6 48.2 8.2 20.7 2.72 8.4 98 826
Flurry-M Aug. 6 15.7 55.3 23.0 1.2 4.8 2.10 4.6 179 818
Aug. 9 3.7 25.6 54.4 8.4 7.9 2.73 9.4 108 1020
Aug. 10 3.2 29.1 45.1 9.0 13.5 2.69 9.7 107 1039
Lafayette Aug. 6 26.2 65.9 5.2 0.0 2.7 1.79 3.8 213 798
Aug. 9 4.7 39.9 44.4 3.6 7.4 2.51 9.2 128 1175
Aug. 10 9.8 30.2 47.4 3.5 9.1 2.49 6.7 132 879
Napoleon Aug. 6 12.3 55.1 27.2 3.6 1.7 2.23 3.7 176 648
Aug. 9 4.6 21.8 61.7 5.8 6.1 2.73 7.5 111 833
Aug. 10 8.7 20.6 56.4 7.4 7.0 2.67 5.7 118 677
Quest Aug. 6 26.1 64.1 6.4 0.0 3.4 1.80 3.3 214 706
Aug. 9 4.7 37.3 51.2 1.6 5.2 2.52 9.3 128 1188
Aug. 10 3.8 39.4 47.0 0.8 9.1 2.49 10.6 126 1346
Sunex 3539 Aug. 6 27.8 51.1 18.0 0.0 3.1 1.90 3.7 212 785
Aug. 9 5.2 43.5 44.3 4.2 2.8 2.49 8.5 134 1134
Aug. 10 3.5 42.9 45.7 2.4 5.5 2.50 10.4 129 1347
zHeat units accumulated for each date: Aug. 6, 457; Aug 9, 501; Aug. 10, 510.
Accumulated heat units = Sum (Tmax-15.5 oC) with a 32 oC cutoff.
Table 3. Nalley's-OSU pickling cucumber variety trial, 1994 machine-harvest results.
Variety Plants/A %1s %2s %3s %4s %N&C %Rej lb. Acres Grade $/T $/A T/A
Atlantis 101,000 5.1 40.3 49.2 0.8 3.4 1.1 8280 0.30 2.48 133 1859 14.0
Bradley 52,000 6.9 55.1 32.3 1.7 1.4 2.6 8560 0.51 2.30 146 1222 8.4
Calypso 65,000 4.5 36.3 50.3 4.0 4.0 0.9 8220 0.60 2.57 126 854 6.8
Discover 125,000 5.3 40.5 47.7 1.4 4.0 1.1 21425 1.16 2.48 133 1227 9.3
Excell 99,000 4.5 38.8 49.5 2.1 3.9 1.2 28560 1.16 2.52 129 1588 12.3
Flurry-M 94,000 6.5 43.8 37.3 0.6 7.6 4.2 2895 0.15 2.36 133 1319 9.9
FMX 4841 80,000 5.6 44.1 43.1 1.5 4.2 1.5 6815 0.29 2.43 135 1576 11.7
HMX 1463 72,000 6.1 59.7 30.9 0.2 1.7 1.4 13165 0.61 2.26 149 1609 10.8
Lafayette 83,000 5.8 44.8 44.4 0.8 3.3 0.8 26240 1.21 2.42 138 1489 10.8
Neptune 103,000 7.9 42.3 43.4 1.9 2.5 2.1 8840 0.37 2.41 140 1678 12.0
Table 4. Nalley's-OSU pickling cucumber variety trial, 1994 hand-picked harvest
Variety Harvest date %1s %2s %3s %4s %N&C Grade T/acre $/T $/acre
Atlantis July 18z 51.5 41.0 0.3 0.0 5.0 1.48 3.2 249 794
21 10.7 52.7 22.3 0.0 14.2 2.14 8.4 150 1255
22 5.4 33.0 46.0 3.3 12.3 2.54 11.8 122 1438
Bradley July 18 80.0 20.0 0.0 0.0 0.0 1.20 1.7 309 526
21 16.2 63.9 9.0 0.0 10.8 1.92 7.1 173 1230
22 6.8 47.0 35.3 0.0 10.9 2.32 10.5 137 1445
Calypso July 18 59.7 30.7 3.9 0.0 5.7 1.41 1.9 262 495
21 9.1 44.4 32.3 0.0 14.2 2.27 6.9 140 975
22 6.5 40.7 44.7 0.0 8.1 2.42 8.6 136 1170
Discover July 18 40.6 50.3 0.0 0.0 9.1 1.55 3.0 225 667
21 10.2 50.3 28.2 1.5 9.8 2.23 9.1 148 1353
22 5.0 28.7 45.6 2.2 18.5 2.55 11.8 115 1353
Excell July 18 30.5 53.0 5.3 0.0 11.2 1.72 4.8 200 964
21 7.1 43.3 37.6 1.4 10.6 2.37 10.2 136 1388
22 4.4 27.6 56.5 3.2 8.3 2.64 14.7 118 1739
Flurry-M July 18 49.4 37.8 3.6 0.0 9.3 1.50 2.5 239 602
21 10.7 42.6 26.8 2.3 17.6 2.25 6.2 138 856
22 8.0 37.3 35.4 1.5 17.8 2.37 9.1 129 1175
FMX 4841 July 18 34.6 43.0 4.2 0.0 18.2 1.63 3.4 199 688
21 4.4 50.3 21.1 0.0 24.1 2.22 7.5 126 941
22 3.3 43.5 37.7 1.8 13.7 2.44 9.0 124 1116
HMX 1463 July 18 46.2 42.3 8.2 0.0 3.3 1.61 3.5 238 837
21 7.9 70.6 16.4 4.0 1.1 2.17 9.0 159 1427
22 8.3 57.0 31.2 0.0 3.5 2.24 9.7 153 1483
Lafayette July 18 31.9 55.2 2.3 0.0 10.5 1.67 2.9 206 608
21 7.6 48.2 35.3 0.0 8.9 2.30 8.1 142 1151
22 3.7 30.2 52.7 3.2 10.2 2.62 14.1 117 1657
Neptune July 18 54.0 39.7 0.0 0.0 6.3 1.42 2.8 253 709
21 15.4 48.7 21.7 0.0 14.2 2.07 7.1 159 1130
July 22 11.1 43.5 38.1 0.0 7.3 2.29 11.1 149 1656
zHeat units accumulated for each date were: July 18, 489; July 21, 536;
July 22, 552. Accumulated heat units = Sum (Tmax-15.5 oC) with a 32 oC cutoff.
Table 5. 1994 pickling cucumber herbicide trial
Treatment Rate, lb Yield Stand count/ Weed density Weed controlx Acre cost of
ai/acre kg/plot 3 row feet per sq. ft. rating chemicals
Command PREz 0.125 16.5 34 6.5 8.5 $2.84
Command PRE 0.25 19.8 26 4.5 9.4 $5.68
Command PPIy 0.125 9.0 33 19.3 4.3 $2.84
Command PPI 0.25 14.8 33 13.0 5.7 $5.68
Command PPI 0.125 13.8 34 39.8 3.6 $64.14
Prefar 6.0
Command PPI 0.125 13.5 32 8.5 7.0 $56.94
Alanap 4.0
Curbit PRE 1.5 11.8 29 9.5 5.7 $30.58
Curbit PRE 1.5 15.3 33 4.0 9.0 $84.68
Alanap 4.0
Alanap PPI 4.0 17.4 33 9.3 7.2 $115.40
Prefar 6.0
Handweeded --- 13.7 32 21.3 1.2 ----
Untreated --- 3.6 34 23.0 1.2 ----
LSD 0.05 4.6 4 14.7
zPRE: pre-emergence, incorporated with water.
yPPI: pre-plant incorporated with rotary tillage.
x0=no control, 10=complete control.
Rate, Timing of Application, Source, and Placement of Nitrogen
Fertilizer on Yield of Cauliflower
Cooperator: John Hart, Dept. of Crop and Soil Science
Introduction
Vegetable growers in the Willamette Valley use high rates of nitrogen fertilizers, often exceeding
300 pounds actual N/acre per season. While growers claim that these rates are necessary to
achieve maximum yields and quality, a considerable portion of the applied fertilizer is not taken up
by the crop. This has raised concerns that the remaining nitrogen may be contributing to nitrate
pollution of groundwater. Improved efficiency of nitrogen management in vegetable crops may
be possible if the fertilizer could be applied at the time of maximum crop need and placed for
maximum contact with the root system. Sources of nitrogen may differ in efficiency of N uptake
because of differences in volatility, degree of leaching, or crop preference for ammonium or
nitrate.
A trial in 1991 investigated broccoli yield response to a wide range of rates of nitrogen as well as
different methods of fertilizer placement. Method of placement did not affect yield. Rates of
applied N up to 250 pounds per acre did not significantly increase the soil nitrate or ammonium
concentration at the end of the growing season. Cauliflower is planted at lower populations and
with greater between-row spacing than is the norm for broccoli. In a 1992 trial cauliflower yield
increased with increasing rate of applied nitrogen up to 240 pounds/acre. Yield did not vary with
band or broadcast placement of fertilizer at planting but there was a trend toward greater yield
with the banded application. Broadcast application of sidedressed nitrogen was superior to
banded application. The purpose of these trials was to confirm results obtained in 1992 and to
investigate the effects of timing of application of sidedressed nitrogen as well as the form of the
sidedressed nitrogen. A second purpose was to study soil nitrogen accumulation as a function of
rate of applied nitrogen and presence of a winter catch crop and to monitor loss of nitrate through
the soil profile in the winter following the crop.
Methods
'Snowball Y' cauliflower was direct-seeded in a Willamette silt loam, pH 6.0, at the NWREC on
10 June in both 1993 and 1994. Rows were 12 inches apart with a plant density of about
two/inch in the row. Plot preparation included a broadcast and incorporated application of
10N-8.7P-16.7K fertilizer at 600 pounds/acre, boron at 2.0 pounds/acre, ammonium molybdate at
2 ounces/acre, trifluralin at 0.75 pounds/acre, and chlorpyrifos at 1.3 pounds/acre. On 27 July,
1993 (20 July, 1994) the seedlings were lifted with a shovel and transplanted bare-root into their
final location. Soil preparation was the same as for the seed bed. Transplants were set in rows
2.5 feet apart with 18 inches between plants in the row. Plot size was three rows, 20 feet long.
All three rows were harvested.
The initial application of 40 pounds N/acre was either broadcast as urea or banded as
calcium-ammonium nitrate solution (CAN-17) three inches to the side of the row immediately
after transplanting and irrigated in. The remaining nitrogen was broadcast or banded on the
appropriate plots on 2 September or on 2 and 21 September, 1993 (24 August or 24 August and
21 September, 1994) depending on the treatment (Table 6). Sidedress N source was either urea,
calcium nitrate (CN), or CAN-17 as appropriate for the treatment. Treatments were in
randomized complete block design with four replications. The plots were sprinkler-irrigated as
necessary and harvested on 8 and 19 October, and 2 November, 1993 (10 and 21 October, 1994).
Two sets of plots were overseeded with 'Wheeler' cereal rye on 7 September to determine the
feasibility of overseeding in cauliflower as a means of establishing a winter nitrogen catch crop.
Following the last harvest in 1993, soil in treatments 1, 2, 3, 4, 5, and 11 was sampled to 48-inch
depth in 12-inch increments. The plots were maintained through the winter in order to resample
for soil nitrogen content and cover crop biomass accumulation. Shoots were clipped to 1 inch
above the soil surface on 18 April. After weighing, subsamples were weighed, dried, reweighed,
and submitted for analysis of total N. The soil of treatments 1-5 and 10 were sampled in 1-foot
increments to 5-foot depth on 21 April. Samples were frozen and submitted for analysis of nitrate
and ammonium content.
Results and Discussion
For the plots receiving only broadcast applications of urea, yield and mean head weight increased
with increasing rate of nitrogen to a maximum at 240 pounds N/acre in 1993 and 180 pounds in
1994 (Table 7). The same trend was not true for the percentage of Grade No. 1 heads
(defect-free), as only an increase from no applied nitrogen to the lowest rate of 60 pounds/acre
caused an increase in quality in 1993 and N rate did not affect curd quality in 1994. In 1992,
quality continued to increase with increasing increments of applied N. Previous work at the OSU
vegetable farm suggested that the optimum rate of nitrogen application to cauliflower is in the
range of 150 to 200 pounds/acre, similar to the results obtained in these trials.
Banded versus broadcast application of N at planting had no significant effect on yield or quality
in 1993 (Table 8). In 1992, there was a greater trend toward higher yield and head size with a
banded application but it was also not a statistically significant effect. Apparently, even with rows
30 inches apart, enough feeder roots establish in the soil between the rows that concentrating the
fertilizer near the plant row is not a great advantage. This is in agreement with results obtained
on broccoli grown on 16 or 20-inch row spacing.
Banded versus broadcast application of the sidedressed nitrogen also did not result in significant
differences (Table 8). This is in contrast to 1992, when greater yield and mean head size occurred
with a broadcast application. However, the single greatest yield in this trial was with the
combination of broadcast fertilizer at planting, broadcast sidedress fertilizer, and a rate of 240
pounds N/acre.
Overseeding cereal rye about four weeks (1993) or seven weeks (1994) before first harvest did
not reduce cauliflower yield (Table 9). This is consistent with results obtained in 1992, even
though the rye development was greater than in 1993 and 1994 than in 1992.
Use of calcium nitrate, rather than urea, as the source for the sidedressed nitrogen had no effect
on yield for the sum of the harvests in either year (Tables 10 and 11). Calcium-ammonium nitrate,
as compared to urea, also had no effect on yield or head size in 1994 (Table 12).
Splitting the sidedressed N application such that half was not applied until eight or nine weeks
after transplanting had no effect on yield or quality (Tables 11 and 13). However, there was a
significant interaction of N source x timing of application affecting mean head weight and gross
yield in 1994 (Table 11): splitting the sidedress N application decreased yield with urea as N
source, but increased it with calcium nitrate. Further testing would be needed to determine if this
effect is reproducible and biologically significant. Number of heads harvested at either harvest
was not affected by N source or splitting the sidedress N application, indicating these factors did
not affect maturity (data not shown).
In 1993, cauliflower effectively depleted the root zone of nitrate and ammonium at all rates of
applied N except 240 pounds/acre (Table 14). Even at the high rate of N, residual soil nitrate was
comparable to that before any fertilizer was applied. Apparently, cauliflower is similar to broccoli
in N uptake efficiency, even though it was planted at a lower plant population and wider
between-row spacing. Calcium nitrate versus urea as N source had no effect on residual soil
nitrate and ammonium levels at harvest (Table 15). Splitting the sidedressed N also did not affect
residual soil N concentrations (Table 16).
Cereal rye growing on plots that had been fertilized with 120 or 240 pounds N/acre accumulated
a shoot dry weight of 0.55 and 1.19 tons/acre, respectively, on 18 April. This corresponds to
nitrogen uptake of 16 and 36 pounds N/acre, respectively. Considering that only about 45 pounds
of mineral N was present in the top foot of soil immediately after harvest of plots fertilized with
240 pounds N/acre, uptake of 36 pounds N/acre appears to represent recovery of a significant
portion of the residual mineral N. Overseeding a grain into cauliflower may be a practical
alternative for establishing an effective N catch crop in this late-harvested vegetable crop.
When re-sampled in the spring of 1994, after 24 inches of precipitation, rate of applied N had no
effect on soil ammonium concentration (Table 17). Soil nitrate concentration tended to increase
with greater rates of applied N. The nitrate concentration of the surface 10 inches of soil
decreased from those immediately after harvest, while that of the next 30 inches of the profile
increased, indicating probably of movement of nitrate with the winter rainfall. The rye cover crop
significantly reduced soil nitrate concentration at all but the 20-30 inch depth, but had no effect on
soil ammonium concentration.
Table 6. List of treatments, cauliflower N utilization trials, NWREC
No. Total N Placement Placement and timing
applied at planting of sidedress
-------------------------------lb/A---------------------------------------------
1993
1 0 0 None
2 60 40 broadcast, urea 20 broadcast, 5 weeks
3 120 40 broadcast, urea 80 broadcast, 5 weeks
4 180 40 broadcast, urea 140 broadcast, 5 weeks
5 240 40 broadcast, urea 200 broadcast, 5 weeks
6 120 40 banded, urea 80 broadcast, 5 weeks
7 120 40 broadcast, urea 80 banded, 5 weeks
8 120 40 banded, urea 80 banded, 5 weeks
9 120 40 broadcast, urea 80 broadcast, 5 weeks; overseed, 6 weeks
10 240 40 broadcast, urea 200 broadcast, 5 weeks; overseed, 6 weeks
11 120 40 broadcast, urea 80 broadcast as calcium nitrate, 5 weeks
12 240 40 broadcast, urea 200 broadcast as calcium nitrate, 5 weeks
13 120 40 broadcast, urea 40 broadcast, 5 weeks; 40 broadcast, 9 weeks
14 240 40 broadcast, urea 100 broadcast, 5 weeks; 100 broadcast, 9 weeks
1994
1 0 0 0
2 60 40 broadcast, urea 20 broadcast, 5 weeks, urea
3 120 40 broadcast, urea 80 broadcast, 5 weeks, urea
4 180 40 broadcast, urea 140 broadcast, 5 weeks, urea
5 240 40 broadcast, urea 200 broadcast, 5 weeks, urea
6 120 40 broadcast, urea 80 broadcast, overseed, urea
7 240 40 broadcast, urea 200 broadcast, overseed, urea
8 120 40 broadcast, urea 80 broadcast, calcium nitrate
9 180 40 broadcast, urea 140 broadcast, calcium nitrate
10 120 40 broadcast, urea 40 bcast, 5 weeks; 40 bcast 9 weeks, CN
11 180 40 broadcast, urea 70 bcast, 5 weeks; 70 bcast 9 weeks, CN
12 120 40 broadcast, urea 40 bcast, 5 weeks; 40 bcast 9 weeks, urea
13 180 40 broadcast, urea 70 bcast, 5 weeks; 70 bcast 9 weeks, urea
14 180 40 banded, CAN-17 140 banded, 5 weeks, CAN-17
Table 7. Effect of rate of broadcast urea nitrogen on yield,
head size, and quality of cauliflower, NWREC
N rate Mean head Grade No. 1 Total yield
(lb/acre) wt. (g) heads (%) (tons/acre)
1993
0 565 39.5 7.1
60 664 62.5 8.5
120 809 62.7 10.6
180 978 58.6 11.9
240 1002 53.9 12.4
LSD (0.05) 170 16.6 2.6
1994
0 580 41.1 6.3
60 740 60.2 8.2
120 856 56.7 10.1
180 1046 66.5 12.3
240 1043 61.2 12.1
LSD (0.05) 162 NS 2.2
Table 8. Effect of broadcast versus banded application of initial and
sidedressed nitrogen on yield, head size and quality of cauliflower, 1993
Placement Placement Mean head Grade No. 1 Total yield
at planting at sidedress wt. (g) heads (%) (tons/acre)
Broadcast Broadcast 809 62.7 10.6
Banded 924 60.2 11.3
Banded Broadcast 923 51.5 10.9
Banded 889 63.0 11.0
Broadcast at planting mean 867 61.4 11.0
Banded at planting mean 906 57.8 11.0
Significance, planting NS NS NS
Broadcast at sidedress mean 866 57.1 10.8
Banded at sidedress mean 906 61.6 11.2
Significance, sidedress NS NS NS
Table 9. Effect of overseeding cereal rye on cauliflower yield,
head size, and quality at two rates of nitrogen, NWREC
Treatment N rate Mean head Grade No. 1 Total yield
(lb/acre) wt. (g) heads (%) (tons/acre)
1993
Overseeded 120 859 66.3 10.7
240 988 54.5 11.2
Mean 924 60.4 11.0
Not overseeded 120 809 62.7 10.6
240 1002 53.9 12.4
Mean 906 58.3 11.5
Significance NS NS NS
1994
Overseeded 120 898 60.7 10.4
240 1025 60.0 11.6
Mean 962 60.4 11.0
Not overseeded 120 856 56.7 10.1
240 1043 61.2 12.1
Mean 950 59.0 11.1
Significance NS NS NS
Table 10. Effect of sidedressed nitrogen source on cauliflower yield,
head size, and quality at two rates of nitrogen, NWREC, 1993
N source N rate Mean head Grade No. 1 Total yield
(lb/acre) wt. (g) heads (%) (tons/acre)
Urea 120 809 62.7 10.6
240 1002 53.9 12.4
Mean 906 58.3 11.5
Calcium nitrate 120 857 67.7 10.2
240 972 60.2 12.2
Mean 915 63.9 11.2
Significance NS NS NS
Table 11. Effect of sidedressed nitrogen source and timing on cauliflower
yield, head size, and quality at two rates of nitrogen, NWREC, 1994
N source Timing N rate Mean head Grade No. 1 Total yield
(lb/acre) wt. (g) heads (%) (tons/acre)
Urea early 120 856 56.7 10.1
180 1045 66.5 12.3
Mean, early 951 61.6 11.2
late 120 783 61.9 9.1
180 951 62.0 10.9
Mean, late 867 61.9 10.0
Mean, urea 909 60.0 10.6
Calcium nitrate early 120 849 61.5 9.6
180 966 64.2 11.1
Mean, early 908 62.9 10.4
late 120 904 65.5 10.4
180 1092 55.1 13.4
Mean, late 998 60.3 11.9
Mean, CN 953 61.6 11.1
Significance, N rate ** NS **
N source NS NS NS
Timing NS NS NS
Source x Timing ** NS **
Other interactions NS NS NS
Table 12. Effect of urea versus CAN-17 as N source on cauliflower,
head size, and quality at 180 pounds N/acre, NWREC, 1994
N source Mean head Grade No. 1 Total yield
wt. (g) heads (%) (tons/acre)
Urea 1045 66.5 12.3
CAN-17 1063 61.4 12.3
Significance NS NS NS
Table 13. Effect of splitting the application of sidedressed nitrogen on
cauliflower, head size, and quality at two rates of nitrogen, NWREC, 1993
Timing of Application N rate Mean head Grade No. 1 Total yield
(lb/acre) wt. (g) heads (%) (tons/acre)
All at 5 weeks 120 809 62.7 10.6
240 1002 53.9 12.4
Mean 906 58.3 11.5
Half at 5 weeks, 120 966 61.5 11.8
remainder at 8 weeks 240 928 67.5 11.8
Mean 947 63.5 11.8
Significance NS NS NS
Table 14. Effect of rate of broadcast nitrogen on soil nitrate and ammonium
concentrations (ppm) following final cauliflower harvest, 11 November, 1993
N rate, lb/A
0 60 120 160 240 LSD(.05)
Depth of sample (inches)
Pre-plant -----------Post-harvest------------
Nitrate
0-10 10.9 0.3 0.6 0.6 5.8 10.8 7.9
10-20 5.2 0.6 0.4 0.3 1.3 1.4 NSD
20-30 3.3 1.3 0.5 0.6 1.0 1.2 NSD
30-40 2.3 1.4 1.2 1.1 0.8 1.3 NSD
Ammonium
0-10 5.1 2.0 2.3 2.5 3.6 5.3 2.0
10-20 4.9 1.3 1.7 1.8 2.4 2.2 NSD
20-30 3.8 1.7 1.8 2.0 1.8 1.8 NSD
30-40 3.5 1.7 1.6 1.8 1.5 1.5 NSD
Table 15. Effect of nitrogen source and rate on soil nitrate and ammonium
concentrations (ppm) following final cauliflower harvest, 11 November, 1993
Urea Calcium nitrate
Depth of sample (inches) N rate, lb/A
120 240 Mean 120 240 Mean LSD (0.05)z
Nitrate
0-10 0.6 10.8 5.7 0.6 7.9 4.3 7.9
10-20 0.3 1.4 0.8 0.4 1.4 0.9 NSD
20-30 0.6 1.2 0.9 0.9 1.2 1.0 NSD
30-40 1.1 1.3 1.2 1.0 1.3 1.2 NSD
Ammonium
0-10 2.5 5.3 3.9 2.4 3.6 3.0 2.0
10-20 1.8 2.2 2.0 1.6 1.9 1.8 NSD
20-30 2.0 1.8 1.9 1.6 1.8 1.7 NSD
30-40 1.8 1.5 1.7 1.5 1.6 1.6 NSD
zLSD for N source x N rate interaction. Main effect of N source
nonsignificant for both ammonium and nitrate at all depths.
Table 16. Effect of splitting the sidedress urea application and nitrogen rate
on soil nitrate and ammonium concentrations (ppm) following final cauliflower
harvest, NWREC, 11 November, 1993
Single sidedress Split sidedress
N rate, lb/A
Depth of sample (inches) 120 240 Mean 120 240 Mean LSD (0.05)z
Nitrate
0-10 0.6 10.8 5.7 0.8 6.0 3.4 7.9
10-20 0.3 1.4 0.8 0.4 1.6 1.0 NSD
20-30 0.6 1.2 0.9 0.9 1.6 1.2 NSD
30-40 1.1 1.3 1.2 1.2 1.3 1.2 NSD
Ammonium
0-10 2.5 5.3 3.9 2.2 6.1 4.1 2.0
10-20 1.8 2.2 2.0 2.0 1.9 2.0 NSD
20-30 2.0 1.8 1.9 1.9 1.9 1.9 NSD
30-40 1.8 1.5 1.7 1.6 1.7 1.6 NSD
zLSD for sidedress x N rate interaction. Main effect of splitting the
sidedress N application nonsignificant for both ammonium and nitrate at all depths.
Table 17. Effect of rate of applied nitrogen and a rye cover crop on
residual soil nitrate and ammonium concentrations, 28 April, 1994
Sample depth Rate of applied urea, lb/acre LSD (0.05)
(inches) 0 60 120 180 240 240 (cover)
------------------------ppm---------------------
Nitrate
0-10 0.5 1.1 1.7 0.8 2.6 0.8 1.2
10-20 0.6 1.2 1.6 2.7 5.0 3.0 0.8
20-30 0.5 1.1 1.4 4.5 4.4 3.7 2.2
30-40 0.3 0.6 0.8 2.1 4.0 2.7 1.3
Ammonium
0-10 2.4 2.0 2.5 2.1 2.3 2.2 NS
10-20 2.6 2.1 2.3 1.9 2.0 1.9 NS
20-30 2.2 2.0 2.0 2.1 1.8 2.0 NS
30-40 2.0 1.5 1.7 1.7 2.6 1.7 NS
Effect of Nitrogen Rate, Source, Placement, and Timing on Sweet
Corn Yield and Nitrogen Uptake
Cooperator: John Hart, Dept. of Crop and Soil Science
Introduction
The justification for this trial is similar to that for cauliflower, reported earlier. A sweet corn trial
in 1992 indicated that source and placement of nitrogen fertilizer had little effect on yield or
quality of sweet corn. Rates of nitrogen application greater than 60 pounds per acre resulted in
accumulation of significant amounts of nitrate-N in the soil. The purpose of these trials was to
confirm 1992 results and to determine if yield of sweet corn would be affected by source or timing
of application of nitrogen fertilizer.
Methods
'Jubilee' sweet corn was seeded into a Willamette silt loam, pH 5.9, at the NWREC on 13 May,
1993, and 25 May, 1994. Plot preparation included a broadcast and incorporated application of
potassium sulfate at 250 pounds/acre, disking and cultimulching. Triple superphosphate was
banded at 130 pounds/acre, two inches to the side and two inches beneath the seed row on all
plots. Forty pounds of nitrogen/acre as urea, ammonium nitrate, calcium-ammonium nitrate
(CAN-17), or urea-ammonium nitrate (UAN-32) was also shanked in at 2 inches beneath and 2
inches to the side of the seed row on all but the zero nitrogen treatment (Table 18). The prilled
urea and ammonium nitrate were applied in the same band as the superphosphate. The liquid
CAN-17 and UAN-32 were applied with separate shanks mounted behind the superphosphate
shanks.
Plot size was 15 feet wide (six rows) by 30 feet long. Spacing between rows was 30 inches.
Immediately after planting atrazine was applied at 2.0 pounds/acre and alachlor at 3.0
pounds/acre. The remaining nitrogen was shanked in (banded) or broadcast to the appropriate
plots at planting or on 21 June, 1993 or 29 June, 1994 (split application). Treatments consisting
of various rates, sources, and sidedress application methods were in randomized complete block
design with four replications.
The plots were sprinkler-irrigated as necessary and harvested on 24 August, 1993 and 2
September, 1994. Following completion of harvest, the stover was mowed and left in place on
the plots. The plots were sampled for residual soil nitrate and ammonium concentration on 22
October, 1993, before the onset of fall rains, and their identity was maintained over the winter so
that samples could be taken in the spring of 1994.
Results and Discussion
When all the sidedressed nitrogen fertilizer was banded as urea (Treatments 1-5), yield increased
with increasing rate of N to a maximum at 180 pounds N/acre in both years (Table 19). However,
the yields at 120 and 240 pounds N/acre were not significantly different than at 180 pounds/acre.
Mean ear weight, number of ears harvested, ear length, and tipfill also tended to be greatest at
180 or 240 pounds N/acre, but there were no significant differences among the three greatest
rates of N. Kernel moisture content was approximately 73 percent for all treatments.
The other combinations of N source and application method were at 120 pounds total N/acre in
1993 and 120 or 180 pounds N/acre in 1994. Comparisons of N utilization are based on banded
urea at planting and broadcast urea sidedress, with a split application, as the standard. Mean yield
of corn fertilized at 120 pounds N/acre did not vary significantly with nitrogen source in either
year (Tables 20 and 21). This is consistent with results obtained in 1992. Past research at NWREC
with urea, ammonium nitrate, and other solid nitrogen sources indicated no consistent differences
among nitrogen sources in effects on corn yields.
When comparing the effect of the timing of the sidedressed N application, and averaged over urea
and ammonium nitrate as N source, a split or delayed application of the sidedressed N appeared
slightly superior to applying all fertilizer at planting for yield, number of ears harvested, ear
weight, and tipfill, but the differences were not significant in either year (Table 22). An effect of
split application might have been expected in 1993 because of the greater than normal
precipitation (15.3 cm) and, thus, leaching potential, during the interval between planting and the
delayed sidedress application. However, in 1994, precipitation was only 4.5 cm during the
interval between planting and the delayed sidedress, indicating little potential for leaching.
In a 1993 comparison of broadcast versus banded application of sidedressed urea or ammonium
nitrate fertilizer (Table 23), there were no significant effects on yield or quality. However, the
number of ears/acre was greater with broadcast application of the sidedressed nitrogen.
In comparing CAN-17 with urea as N source, at 180 pounds N/acre, CAN-17 again tended to
produce greater yield, but the difference was not significant (Table 24).
Sweet corn production with zero to 120 pounds applied N/acre effectively reduced nitrate
concentration in the first 40 inches of the soil profile during the growing season of 1993 (Table 25).
However, at 180 or more pounds N/acre, soil nitrate concentrations were greatly elevated in the
surface 10 inches of soil. Soil ammonium concentrations were not greatly affected by sweet corn
fertilized with any rate of N. These results are fairly consistent with those obtained in 1992, when
levels of both nitrate and ammonium were greatly increased in the surface layer of soil by rates as
low as 120 lb N/acre. This is in contrast to soil cropped with broccoli: in 1991 and 1992 rates of
nitrogen up to 250 pounds/acre did not increase nitrate and ammonium levels beyond those
present at planting. There is very little indication in this experiment of movement of applied
nitrogen beyond the root zone. Increased nitrate and ammonium levels were generally confined to
the surface 10 inches.
Plots were again sampled for nitrate and ammonium content in the spring of 1994, following
approximately 24 inches of precipitation (Table 26). Ammonium concentration did not vary with
rate of applied N. Soil nitrate concentration again did not vary with applied N from 0 to 120
pounds N/acre. However, at the higher rates of N, nitrate concentration remained elevated,
although only at depths greater than 20 inches. This is indirect evidence for the leaching of nitrate
from the surface 20 inches of soil toward the vadose zone.
In contrast to 1992 and 1993, rate of applied N had relatively little effect on post-harvest soil
concentrations of ammonium and nitrate in 1994 (Table 27). Soil nitrate content tended to be
slightly elevated in the surface 12 inches of soil at the optimal N rate of 180 pounds/acre, but the
effect was not significant and there was no effect at all at suboptimal rates of N. At the greatest
rate of applied N, soil nitrate, but not ammonium levels, were significantly increased, but to a
lesser extent than in the previous years. Any effect of N rate at greater depth was masked by the
greater-than-normal nitrate concentrations that existed at time of planting. There was a small but
significant effect of treatment on soil ammonium concentration at 36 to 48 inches. The form of
applied N had no effect on soil nitrate concentrations at harvest, but there was, again, a small
effect on soil ammonium content at 36 to 48-inch depth.
The high levels of residual fertilizer present at rates of nitrogen needed for acceptable yields is in
contrast to the situation for broccoli and is a cause for concern. Apparently sweet corn is less
efficient at taking up applied nitrogen than is broccoli. Measurements of the nitrogen content of
the above-ground biomass of each crop support this conclusion. This indicates the need for more
research on improving nitrogen uptake efficiency in sweet corn.
Table 18. List of N application treatments, sweet corn nitrogen
utilization trial, NWREC
No. N rate N source Banded at Broadcast at Sidedress rate, methodz
(lb/A) seeding (lb/A) seeding (lb/A) (lb/A)
1993
1 0 None 0 0 0
2 60 Urea 40 0 20 broadcast
3 120 Urea 40 0 80 broadcast
4 180 Urea 40 0 140 broadcast
5 240 Urea 40 0 200 broadcast
6 120 NH4NO3 40 0 80 broadcast
7 120 CAN-17 40 0 80 banded
8 120 UAN-32 40 0 80 banded
9 120 Urea 40 80 0
10 120 Urea 40 0 80 banded
11 120 NH4NO3 40 80 0
12 120 NH4NO3 40 0 80 banded
13 180 CAN-17 40 0 140 banded
1994
1 0 None 0 0 0
2 60 Urea 40 0 20 broadcast
3 120 Urea 40 0 80 broadcast
4 180 Urea 40 0 140 broadcast
5 240 Urea 40 0 200 broadcast
6 120 NH4NO3 40 0 80 broadcast
7 120 CAN-17 40 0 80 banded
8 120 UAN-32 40 0 80 banded
9 120 Urea 40 80 0
10 120 NH4NO3 40 80 0
11 180 Urea 40 140 0
12 180 NH4NO3 40 140 0
13 180 NH4NO3 40 None 140 broadcast
14 180 CAN-17 40 None 140 dribble band
15 180 UAN-32 40 None 140 dribble band
zNitrogen sidedressed on 21 June, 1993 and 29 June, 1994.
Table 19. Effect of rate of urea-nitrogenz on the yield of sweet corn,
NWREC, 1993 and 1994
N rate Yield No. ears Ear wt. Ear length Tipfilly
(lb/A) (T/A) per acre (g) (inches)
1993
0 2.7 10680 241 8.2 2.9
60 5.8 20060 268 8.7 2.9
120 7.5 25400 268 8.9 3.1
180 7.7 25960 272 8.8 3.3
240 7.5 25510 268 9.0 3.4
LSD (0.05) 1.5 6330 NSD 0.3 0.4
1994
0 7.2 37020 198 8.6 3.0
60 10.6 37333 263 9.4 3.8
120 11.6 38990 271 9.3 3.9
180 12.5 42040 275 9.5 4.2
240 10.5 35830 268 9.4 3.8
LSD (0.05) 2.1 NS 50 0.3 0.5
zForty pounds N/acre banded at planting, remainder broadcast five
weeks later.
yFive-point scale with 5=perfect fill.
Table 20. Effect of four nitrogen sources, at 120 pounds N/acrez,
on the yield of sweet corn, NWREC, 1993 and 1994
N source Yield No. ears Ear wt. Ear length Tipfill
(T/A) per acre (g) (inches)
1993
Urea 7.1 22670 286 8.9 3.3
NH4NO3 7.0 23980 271 8.9 3.5
CAN-17 7.3 24960 267 8.9 3.3
UAN-32 6.7 22560 269 8.7 3.2
LSD (0.05) NS NS NS NS NS
1994
Urea 11.6 38990 271 9.3 3.9
NH4NO3 11.3 33210 307 9.5 4.1
CAN-17 11.2 39970 267 9.4 4.1
UAN-32 11.1 40030 266 9.2 3.7
LSD (0.05) NS NS NS NS NS
zForty pounds N/acre banded at planting, 80 pounds N/acre banded
five weeks later.
Table 21. Effect of four nitrogen sources, at 180 pounds N/acrez, on the
yield of sweet corn, NWREC, 1994
N source Yield No. ears Ear wt. Ear length Tipfill Moisture
(T/A) per acre (g) (inches) (%)
Urea 12.5 42040 275 9.5 4.2 71.3
NH4NO3 12.2 39750 284 9.3 4.2 71.4
CAN-17 11.7 42250 253 9.5 3.8 74.2
UAN-32 10.6 37350 256 9.4 4.1 73.6
LSD (0.05) 1.6 NS NS NS NS NS
zForty pounds N/acre banded at planting, 140 pounds N/acre banded five
weeks later.
Table 22. Interaction of nitrogen source and timing of sidedress nitrogenz
application on the yield of sweet corn, NWREC, 1993 and 1994
N source Timing Yield No. ears Ear wt. Ear length Tipfill
(T/A) per acre (g) (inches)
1993
Urea planting 7.0 24310 265 8.9 3.0
Urea 5 weeks 7.5 25400 268 8.9 3.1
NH4NO3 planting 7.3 24850 269 8.8 3.1
NH4NO3 5 weeks 7.7 26270 271 8.8 3.3
NS NS NS NS NS
1994
Urea planting 11.2 38880 264 9.3 3.9
Urea 5 weeks 12.0 40510 273 9.4 4.1
NH4NO3 planting 11.2 35070 292 9.4 4.2
NH4NO3 5 weeks 11.8 36480 295 9.4 4.2
LSD (0.05) NS NS 21 NS NS
zRate of nitrogen = 120 pounds/acre in 1993 with 80 pounds/acre
sidedressed. Mean of nitrogen applications of 120 and 180
pounds/acre in 1994. Sidedress application average of 80 and
140 pounds/acre in 1994.
Table 23. Effect of banded versus broadcast sidedress nitrogenz
application on sweet corn yield, NWREC, 1993
N source Sidedress Yield No. ears Ear wt. Ear length Tipfill
method (T/A) per acre (g) (inches)
Urea Band 7.1 22670 286 8.9 3.3
Urea Broadcast 7.5 25400 268 8.9 3.1
NH4NO3 Band 7.0 23980 271 8.9 3.5
NH4NO3 Broadcast 7.7 26270 271 8.8 3.3
LSD (0.05) NS 2950 NS NS NS
zRate of applied nitrogen = 120 pounds/acre. Sidedressed five
weeks after planting.
Table 24. Effect of CAN-17 versus ureaz as N source on the
yield of sweet corn, NWREC, 1993
N source Yield No. ears Ear wt. Ear length Tipfill
(T/A) per acre (g) (inches)
CAN-17 8.3 28890 260 9.0 3.3
Urea 7.7 25980 272 8.8 3.3
LSD (0.05) NS NS NS NS NS
zNitrogen applied at 180 pounds/acre.
Table 25. Effect of rate of nitrogen on post-harvest soil nitrate and
ammonium concentrations, 25 October, 1993
Sample depth Rate of applied urea, lb/acre LSD (0.05) Pre-plant
(inches) 0 60 120 180 240
----------------------ppm------------------------
Nitrate
0-10 2.6 2.9 2.9 7.1 22.2 4.7 3.6
10-20 1.3 1.0 1.4 2.1 7.0 3.1 2.2
20-30 1.4 2.2 1.8 2.3 4.0 NS 2.3
30-40 1.9 1.9 2.4 2.7 3.1 NS 3.1
Ammonium
0-10 2.6 2.1 1.9 3.3 2.9 NS 3.1
10-20 1.9 1.6 1.3 1.8 2.0 NS 3.6
20-30 1.8 2.0 1.9 2.0 2.1 NS 1.9
30-40 1.9 1.7 2.2 2.4 1.9 NS 2.3
Table 26. Effect of rate of nitrogen on residual soil nitrate and
ammonium concentrations, 28 April, 1994
Sample depth Rate of applied urea, lb/acre LSD (0.05)
(inches) 0 60 120 180 240
-----------------ppm--------------------
Nitrate
0-10 1.2 0.9 1.4 0.9 1.6 NS
10-20 1.5 1.5 2.2 2.1 2.9 NS
20-30 1.7 1.7 2.8 3.9 5.2 1.2
30-40 1.6 1.6 2.6 4.6 6.1 2.5
Ammonium
0-10 3.1 2.7 3.0 3.1 3.3 NS
10-20 2.6 2.5 2.5 2.3 2.3 NS
20-30 3.1 2.3 2.6 2.3 2.2 NS
30-40 2.7 2.1 2.5 2.5 2.4 NS
Table 27. Effect of rate of nitrogen on post-harvest soil nitrate
and ammonium concentrations, 9 September, 1994
Sample depth Rate of applied urea, lb/acre LSD (0.05) Pre-plant
(inches) 0 60 120 180 240
----------------------ppm-------------------------
Nitrate
0-12 0.3 0.4 0.8 4.6 10.9 8.6 0.6
12-24 1.4 3.0 1.5 8.7 7.9 NS 8.2
24-36 9.2 7.6 3.8 9.7 6.2 NS 14.0
36-48 8.7 8.7 5.0 7.1 8.0 NS 2.3
Ammonium
0-12 2.1 2.2 2.5 2.2 5.4 NS 2.1
12-24 2.1 2.4 2.8 2.2 5.2 NS 1.8
24-36 2.5 2.3 2.9 2.3 6.5 NS 1.8
36-48 2.0 2.2 2.4 1.6 4.0 1.4 1.6
Table 28. Effect of nitrogen source on post-harvest soil nitrate and
ammonium concentrations at 180 pounds applied N/acre, 9 September, 1994
N source
Sample depth (inches) Urea NH4NO3 CAN-17 UAN-32 LSD (0.05)
------------------ppm-------------------
Nitrate
0-12 4.6 0.4 0.8 4.6 NS
12-24 8.7 3.0 1.5 8.7 NS
20-36 9.7 7.6 3.8 9.7 NS
36-48 7.1 8.7 5.0 7.1 NS
Ammonium
0-12 2.2 3.5 3.0 3.8 NS
12-24 2.2 3.0 3.5 2.6 NS
24-36 2.3 2.8 2.8 2.8 NS
36-48 1.6 3.5 2.7 2.5 1.4
Nitrogen Rate on Yield of Green Beans, Beets, and Carrots, and Residual Mineral Nitrogen
Concentration of Willamette Silt Loam Soil
Cooperator: John Hart, Dept. of Crop and Soil Science
Introduction
A survey of grower fields was initiated in 1993, in which 30 fields were sampled for nitrate and
ammonium-N concentrations before fertilization and were then cropped to beans, beets, broccoli,
carrots, cauliflower, and sweet corn. At the end of the growing season, the fields were tested for
residual nitrate and ammonium concentration. This survey was repeated in 1994 on 34 fields. To
provide a basis of comparison with the grower fields, crop yield and residual mineral N were
measured in NWREC trials as a function of applied N for beans, beets, carrots, cauliflower, and
sweet corn. The cauliflower and sweet corn trials involved other factors such as N source and
timing of N application and results are presented elsewhere. The bean, beet, and carrot results are
presented here.
Methods
All crops were seeded to a Willamette silt loam, pH 6.1, at NWREC. Plot preparation for all
crops included a broadcast and incorporated application of potassium sulfate at 250 pounds per
acre, disking and cultimulching. Pre-plant soil samples were obtained to four-foot depth, in
one-foot increments, on 21 April. The samples were frozen and submitted to the OSU Central
Analytical Lab for analysis of nitrate and ammonium content. The N source for all trials was urea.
Post-harvest soil samples were obtained on 14 September.
Beans
The plot area received a broadcast, incorporated application of 0.75 pounds trifluralin, 2.0 pounds
EPTC, and 1.2 pounds chlorpyrifos/acre. 'Oregon 91G' green beans were seeded at 65
pounds/acre on 9 May with four rows per plot on 30-inch centers. Triple superphosphate (130
pounds/acre) was banded at planting two inches beneath and two inches to the side of the seed
row. The first 40 pounds N/acre was broadcast at planting; the remaining N was broadcast on 6
June. Plots were sprinkler-irrigated and cultivated as necessary and harvested on 25 July. Plants
were mowed to simulate machine-harvest and minimize further N uptake.
Beets and Carrots
The plot area received a broadcast, incorporated application of EPTC at 2.0 pounds/acre (beets)
and 150 pounds triple superphosphate/acre. Carrot plots were treated with linuron at 1.25
pound/acre one day after seeding. 'Detroit Dark Red' table beet and 'Orlando Gold' carrot were
seeded on 5 May with three rows on a five-foot bed. The first 40 pounds N/acre was broadcast
on the planting date; the remaining N was broadcast on 10 June. Plots were sprinkler-irrigated
and cultivated as necessary and harvested on 25 July (beets) and 16 August (carrots). The
remaining beet plants were pulled to minimize further N uptake.
Results and Discussion
Green beans responded with a yield increase to the first increment of applied N, but yield did not
increase further with rates of N application greater than 40 pounds/acre (Table 29). This is
somewhat unusual, as most experience with this crop indicates increasing yield up to 100 pounds
applied N/acre. Carrot yield responded as expected, with the greatest yield at 120 pounds N/acre
(Table 29). This is consistent with results previously obtained at NWREC. Beet yield increased markedly with the first increment of applied N and continued to increase in quadratic
fashion with the maximum at 240 pounds N/acre (Table 30). This is also consistent with our
previous research and with grower experience.
Soil nitrate concentration after bean harvest increased approximately linearly with increasing rate
of applied N at the 1 and 2 foot depths, but the effect was significant only in the surface foot of
soil. Soil ammonium content also increased with increasing applied N for the surface foot of soil
(Table 31).
Soil ammonium concentration did not differ with rate of applied N for beet and carrot, but in each
case soil nitrate concentration increased at higher rates of applied N for the first two feet of the
soil profile (Tables 32 and 33). For carrot, there was no increase in soil nitrate content in the
surface foot of soil until the applied N reached the optimal level for yield (Table 33). In the beet
plots, the greatest soil nitrate content in the surface two feet of soil was with 180, rather than 240,
pounds applied N/acre (Table 32). The same trend, although not significant, was apparent in the
residual soil ammonium content in the beet plots. Further research will be needed to determine
whether this observation was simply due to chance.
Table 29. Effect of rate of urea-nitrogen on the
yield of green beans and carrots, NWREC, 1994
N rate Bean Carrot
(lb/A) (T/A) (T/A)
0 4.5 15.8
40 7.5 21.0
80 6.8 23.1
120 6.7 26.0
160 7.3 24.0
Significance L*Q* L*Q*
L=linear, Q=quadratic, *significant, p=0.05.
Table 30. Effect of rate of urea-nitrogen
on the yield of table beets, NWREC, 1994
N rate Yield
(lb/A) (T/A)
0 3.7
60 13.6
120 16.4
180 17.6
240 18.0
Significance L**Q*
Table 31. Effect of rate of broadcast nitrogen on soil nitrate and ammonium
concentrations (ppm) at four depths following bean harvest, NWREC, 1994
N rate, lb/A
Sample depth (inches) 0 40 80 120 160 LSD(.05)
Pre-plant --------Post-harvest--------
Nitrate
0-12 0.7 1.6 7.7 10.2 9.9 16.4 14.1
12-24 0.7 1.0 2.7 3.9 3.7 5.3 NSD
24-36 1.6 1.3 2.3 5.5 3.4 3.8 NSD
36-48 2.3 1.3 2.3 5.0 3.9 3.1 NSD
Ammonium
0-12 1.9 3.4 4.8 3.9 6.0 7.0 2.0
12-24 1.9 2.7 2.3 3.1 2.9 3.2 NSD
24-36 2.0 2.9 1.7 4.9 2.6 2.7 NSD
36-48 1.8 3.0 1.7 4.0 3.6 2.7 NSD
Table 32. Effect of rate of broadcast nitrogen on soil nitrate and ammonium
concentrations (ppm) at four depths following beet harvest, NWREC, 1994
Sample depth (inches) N rate, lb/A
0 60 120 180 240 LSD(0.05)
Pre-plant --------Post-harvest-------
Nitrate
0-12 1.5 0.8 1.4 3.0 6.6 3.9 1.7
12-24 1.2 0.3 0.6 1.0 1.9 1.6 0.6
24-36 1.1 0.9 1.2 2.0 1.6 1.9 NSD
36-48 1.0 1.9 2.9 3.3 2.2 4.4 1.9
Ammonium
0-12 0.8 2.6 3.0 5.3 6.1 4.1 NSD
12-24 2.7 3.1 2.5 3.2 5.5 3.2 NSD
24-36 3.7 3.2 2.4 3.6 4.2 2.0 NSD
36-48 3.3 3.3 2.4 3.8 2.7 2.0 NSD
Table 33. Effect of rate of broadcast nitrogen on soil nitrate and ammonium
concentrations (ppm) at four depths following carrot harvest, NWREC, 1994
N rate, lb/A
Sample depth (inches) 0 40 80 120 160 LSD(.05)
Pre-plant --------Post-harvest--------
Nitrate
0-12 1.5 0.8 0.4 0.9 5.5 8.2 6.6
12-24 1.2 0.4 0.5 1.6 1.9 1.5 1.0
24-36 1.1 1.6 1.7 3.8 3.8 2.8 NSD
36-48 1.0 2.1 2.9 3.7 3.2 3.0 NSD
Ammonium
0-12 0.8 2.3 3.2 2.8 2.7 2.4 NSD
12-24 2.7 2.6 3.5 2.3 2.9 2.4 NSD
24-36 3.7 2.5 3.5 2.0 3.9 2.8 NSD
36-48 3.4 2.7 4.9 2.4 2.6 2.6 NSD
Post-harvest Mineral Nitrogen Status in Grower Fields
Cooperators: John Hart, Department of Crop and Soil Science
N.S. Mansour and John Luna, Department of Horticulture
Introduction
This grower trial was undertaken to determine whether residual nitrate and ammonium levels in
grower fields were similar to those found in our experiments at NWREC. The data should be
useful in indicating which of the major processed vegetable crops leave significant quantities of
residual mineral N in the soil at harvest and the extent to which grower cultural practices,
particularly fertilizer application, influence the amount of residual N that is available for leaching
by heavy winter rainfall.
Methods
Soil samples were taken in one-foot increments to a depth of 5 feet both before and after crops of
green beans, beets, broccoli, carrots, cauliflower, and sweet corn, for determination of mineral N
(ammonium-N and nitrate-N) content. Thirty fields were sampled in 1993 and 34 in 1994,
representing 15 growers and 7 soil types. The growers were interviewed to determine field
history and cropping and fertilization intentions and they kept records of fertilizer applications and
irrigations.
Results and Discussion
Mean pre-plant nitrate and ammonium concentrations for 1993 are seen in Tables 34 and 35,
respectively. Corresponding data for 1994 are in Tables 36 and 37. In order to preserve anonymity,
only means are presented. However, there were few surprises in the pre-plant data. The
relatively heavy rainfall during the late winter and spring resulted in low levels of nitrate in most
fields in both years. Most individual cases of higher levels of nitrate or ammonium could be
explained by a past history of manure application or by the presence of a legume cover crop.
Mean nitrate and ammonium levels at harvest varied by crop (Tables 34-37) and grower cultural
methods (data not shown). For example, in top foot of the soil, nitrate concentrations were
greater for sweet corn than for cauliflower or broccoli, although the mean N application to these
crops was 203, 226, and 262 pounds/acre, respectively, in 1993 and 193, 223, and 253
pounds/acre, respectively, in 1994 (Tables 34 and 36). Nitrate levels were generally elevated for
sweet corn, not only in the surface foot of soil, but also at greater depths. This contrasts with our
experience at NWREC and may indicate movement of nitrate as a result of the unusually wet late
spring and early summer, or may indicate that improvements could be made in grower irrigation
practices. For carrots, the elevated nitrate levels at the 12 to 36-inch depths may indicate soil
mixing during digging. Post-harvest ammonium concentrations varied much less between
pre-season and post-harvest sampling than did nitrate (Tables 35 and 37). Presumably, this is due to
conversion of urea and ammonium-N to nitrate during the growing season.
Table 34. Mean post-harvest nitrate concentration (ppm) in grower
fields as a function of crop and depth in the soil profile, 1993
Crop Depth of sample (inches)
0-12 12-24 24-36 36-60
Pre-plant 4.2 2.7 2.5 2.5
Beans 13.9 8.0 6.4 5.7
Beets 15.3 4.4 2.8 3.2
Broccoli 10.4 3.9 2.5 2.7
Carrots 9.2 11.8 7.1 4.3
Cauliflower 15.3 6.8 5.0 5.5
Sweet corn 21.9 10.0 8.8 7.2
Table 35. Mean post-harvest ammonium concentration (ppm) in grower
fields as a function of crop and depth in the soil profile, 1993
Crop Depth of sample (inches)
0-12 12-24 24-36 36-60
Pre-plant 3.6 2.9 2.6 2.6
Beans 4.8 3.2 3.1 2.7
Beets 4.6 3.1 3.1 2.7
Broccoli 4.8 5.0 3.1 3.4
Carrots 1.0 0.3 0.3 0.1
Cauliflower 6.7 4.1 3.5 3.8
Sweet corn 4.3 3.2 3.3 3.8
Table 36. Mean post-harvest nitrate concentration (ppm) in grower
fields as a function of crop and depth in the soil profile, 1994
Crop Depth of sample (inches)
0-12 12-24 24-36 36-60
Pre-plant 5.0 4.6 5.5 5.2
Beans 20.2 5.8 7.1 6.6
Beets 13.3 6.1 4.1 3.2
Broccoli 7.2 3.0 2.3 1.9
Carrots 12.8 7.5 7.4 6.3
Cauliflower 9.9 6.9 6.9 6.8
Sweet corn 22.2 9.1 9.6 8.0
Table 38. Mean post-harvest ammonium concentration (ppm) in grower
fields as a function of crop and depth in the soil profile, 1994
Crop Depth of sample (inches)
0-12 12-24 24-36 36-60
Pre-plant 4.2 3.9 3.0 4.1
Beans 7.4 3.5 4.0 3.6
Beets 4.5 3.6 3.0 2.2
Broccoli 6.0 4.7 3.5 3.0
Carrots 3.1 2.5 1.9 1.5
Cauliflower 7.2 3.6 3.2 4.0
Sweet corn 4.7 3.1 2.6 2.7
Effect of Nitrogen Rate and Cover Crops on the Yield of Sequential Crops of Broccoli
and Sweet Corn
Cooperator: Richard Dick, Dept. of Crop and Soil Science
Introduction
Nitrate pollution of groundwater from the application of high rates of nitrogen fertilizers to
vegetable crops in an increasing concern in the Willamette Valley. Excess nitrogen not taken up
by the crop remains in the soil and can be leached to groundwater during the wet winter months.
These concerns led us to initiate a study of the cycling and availability of nitrogen in vegetable
cropping systems. These are the fourth and fifth years of a study in which winter cover or "catch"
crops have been seeded following vegetable crops and in which the N uptake of the cover crop
and its contribution to a succeeding vegetable crop has been measured. In 1991, broccoli was
grown on the long-term rotation plots at NWREC and fertilized at three rates of nitrogen.
Following harvest the plots were seeded to cereal rye or a mixture of cereal rye and Austrian
winter pea. In 1992, sweet corn was grown on these plots at three rates of nitrogen to determine
the cover crop contribution to sweet corn yield and nitrogen uptake. Following harvest, the plots
were again disked, harrowed, and seeded (drilled) to the above cover crops. In addition, other
plots were overseeded to cereal rye or red clover about one month after sweet corn emergence.
These cover crops were permitted to grow through the winter. In 1993, broccoli was again
grown on the plots and fertilized with two or three rates of applied nitrogen. In 1994, we again
grew sweet corn following the 1993 broccoli crop and cover crops as well as following spring and
fall-plowed clover.
Methods
The overseeded cover crops of 'Kenland' red clover and 'Wheeler' cereal rye were broadcast on 1
July, 1992, and 15 July, 1993, into four plots each of the standing sweet corn (1992) or broccoli
(1993) crops. The direct-seeded cover crops were seeded on 14 October, 1993, and 7 October,
1994, after disking and harrowing to form a seedbed. These plots had been cropped to sweet
corn in 1990, broccoli in 1991, and sweet corn in 1992, with N rates of 0, 50, and 200
pounds/acre for sweet corn and 0, 125, and 250 pounds/acre for broccoli. Four plots (30 x 60
feet) were planted to 'Wheeler' cereal rye at 65 pounds/acre. The other four plots were planted to
a mixture of 'Wheeler' rye at 35 pounds/acre and Austrian winter pea at 100 pounds/acre. No
fertilizers or pesticides were applied to the cover crops. Nitrogen rate subplots of 600 square feet
each were determined by the nitrogen applied to the vegetable crop. The identity of the three N
rate subplot treatments was maintained from year to year.
On 14 April of both years, samples were taken from all subplots for determination of shoot dry
weight and nitrogen uptake. The shoots were clipped about one inch above ground. All cover
crops were mowed down on 5 May, 1993 and 15 April, 1994. The plots were plowed, disked,
and harrowed in early May. In addition, plots which had been in 'Kenland' red clover as a seed
crop were either fall- or spring-plowed and prepared for planting broccoli or sweet corn.
On 19 May, 1993, 1.3 pounds chlorpyrifos and 10.0 pounds Solubor/acre were applied to the
plots which had been overseeded. The plots which had been in drilled rye or rye plus plea or were
fallowed or had been in clover as a seed crop were treated with the above plus trifluralin at 0.75
pounds/acre. The pesticides were rototilled into the surface three inches of soil. 'Gem' broccoli
was seeded in 20-inch paired rows on 9 June. The distance between pairs of rows was 40 inches.
On 16 June, 1993, nitrogen was applied as urea in a surface band between the paired rows at rates
of one-half the total N rates of 0, 125, and 250 pounds/acre. Subplots of the clover seed crop
plots received only the 0 and 250 pound rates of total N. Drip irrigation tubing was then installed
between each pair of rows. On 28 June, the broccoli was thinned to a stand of 10 inches between
plants in the row. The remainder of the urea was sidedressed on 21 July, at which time the
appropriate treatments were again overseeded with rye or clover, using a whirly-bird fertilizer
spreader. The seed was scratched in with a garden rake.
Plots were tractor-cultivated on 13 July, 1993, and hoed as necessary later in July. All plots were
harvested on 19 August and again on 30 August from 15 feet of two inner rows of each subplot.
Following harvest, the appropriate plots were again prepared for planting of cover crops.
On 23 May, 1994, 'Jubilee' sweet corn was seeded in 20-inch paired rows with 40 inches between
pairs of rows. Phosphorus was banded at 60 pounds P2O5/acre two inches to the side and two
inches beneath the seed row. Plots which had been in overseeded rye or clover were treated with
EPTC at 3.0 pounds/acre, which was incorporated before planting. All other plots received a
broadcast application of 2.0 pounds atrazine and 3.0 pounds alachlor/acre immediately after
planting.
On 6 June, 1994, nitrogen was applied as urea in a surface band between the paired rows at rates
of one-half the total N rates of 0, 50, and 200 pounds/acre. Subplots of the clover seed crop plots
received only the 0 and 200 pound rates of total N. All N rate subplots were in the same location
as the corresponding N treatments on the previous vegetable crops. Drip irrigation tubing was
then installed between each pair of rows. The remainder of the urea was sidedressed on 1 July, at
which time the EPTC-treated plots were again overseeded with rye or clover, using a whirly-bird
fertilizer spreader. EPTC-treated plots were hand-hoed as necessary before overseeding.
Harvest on 31 August was from 15 feet each of the two innermost rows of each subplot.
Following harvest, the appropriate plots were again prepared for planting of cover crops.
Results and Discussion
Both increasing the fertilizer rate on the preceding vegetable crop and the presence of peas in the
cover crop increased total cover crop yield and nitrogen uptake (Tables 39 and 40). In 1994, the
dry matter yield of overseeded rye or overseeded clover was approximately one-half that of drilled
rye. This is in contrast to 1993, when the overseeded crops yielded about the same as the drilled
cover crops. In 1993, the greatest cover crop biomass occurred on clover plots which had been
harvested for a seed crop and allowed to regrow since the summer of 1992 (clover green
manure). In 1994, however, the yield of a clover green manure was comparatively poor, due to a
poor stand of the seed crop. Nitrogen uptake in 1993 was greatest for the clover green manure
and least for rye. Nitrogen uptake by rye increased with increasing rate of nitrogen applied to the
previous vegetable crop in 1993, particularly for the high rate of nitrogen (Table 39). Legume
nitrogen uptake did not vary with rate of applied N in 1993. Peas contributed relatively little N
uptake to the total for plots seeded to rye plus plea; however, rye N uptake also increased in the
presence of peas. Nitrogen uptake of the overseeded clover did not vary with rate of applied N in
1994 (Fig. 1). Yield of overseeded clover also did not vary with preceding N rate (data not
shown).
A rough estimate of the amount of residual fertilizer N left over from the broccoli crop that was
recovered by the rye cover crop can be obtained by examining the rye-only uptake at the three
fertilizer rates as shown in Figures 2 and 3. For 1993, subtracting the amount of N taken up by
the drilled rye grown on non-fertilized subplots from the N taken up at the other two N rates
suggests that only 5 pounds N/acre (1 pound for overseeded rye) was taken up from the
intermediate rate of N and 29 pounds/acre (25 for overseeded rye) from the high rate of N.
Likewise, in 1994, this process suggests that about 20 pounds N/acre (6 pounds for overseeded
rye) was taken up from the intermediate rate of N and 28 pounds/acre (29 for overseeded rye)
from the high rate of N. This nitrogen would have been available for leaching. Of course, an
undetermined amount of nitrogen may have leached before the cover crops were well established.
The overseeded rye did not achieve much germination or growth until after the vegetable crop
was mowed down and the onset of fall rains. Stands were poor. Thus, it is not surprising that the
yield and N uptake for the overseeded rye are less than for the drilled rye in 1994. Cover crop N
recovery in 1993 was similar, except that stands of overseeded covers were better and yield and N
uptake was about equal at all N rates.
 
Broccoli yield in 1993 varied significantly with cover crop and nitrogen rate (Table 41). Yield of
broccoli on plots which had been in rye was slightly depressed compared to plots which had been
winter fallowed. This is consistent with results obtained in 1991. Among possible explanations
are the possibility of allelopathy from the rye residue, immobilization of mineral N by the
decomposing rye straw, or an adverse effect of cereal rye on soil tilth. When a legume was
present in the cover crop, broccoli yields tended to be greater than for the winter fallow, but the
differences were not significant. Greatest yield and mean head weight were from plots which had
been in overseeded clover.
In contrast to sweet corn and broccoli yields in 1990 through 1992, the yield of broccoli did not
tend to increase from the intermediate to the highest rate of nitrogen. This was the case for nearly
every combination of cover crop treatment and N rate (Table 42). A buildup of soil organic N due
to cover cropping, thus eliminating the need for high rates of nitrogen might be an explanation for
the lack of response to a rate of N previously found to be optimal for broccoli at this site.
However, since the plots which had been winter fallowed for four years responded similarly, this
does not appear to be a valid explanation. The greatest yield recorded in this trial was for the
combination of an overseeded clover cover crop and the intermediate rate of N.
Sweet corn yield in 1994 also varied significantly with cover crop and nitrogen rate (Table 43).
There were no significant interactions of cover crop and N rate affecting any component of yield
or quality, so only main effects of cover crop and N rate are shown. As in 1993, yield from plots
which had been in drilled rye was depressed compared to any other treatment except the
overseeded rye. The combination of cereal rye and winter pea produced yield equal to that
following winter fallow and the greatest mean ear weight, while overseeded clover or a
spring-plowed clover seed crop significantly increased yield compared to winter fallow,
presumably due to the nitrogen contribution from the clover.
Sweet corn yield, number of ears harvested, ear length, tipfill, and mean ear weight all increased
with each increase in rate of applied N, regardless of cover crop treatment (data not shown). This is consistent with
results obtained in 1990 through 1992 for sweet corn and broccoli. However, in 1993, broccoli
yield did not increase from the intermediate to the highest rate of N. In 1994, the greatest yield
(8.8 tons/acre), number of ears harvested (28,170/acre), tipfill (3.5), and mean ear weight (284 g)
were with the combination of overseeded clover and the greatest rate of applied N.
The contribution of a cover crop legume to broccoli or sweet corn yield can best be appreciated
by comparing yield at zero applied N (Fig. 4 and 5). While the broccoli yield from the rye
cover crop plots was the same or slightly depressed compared to fallow, the rye plus pea,
overseeded clover, and spring-plowed clover green manure crop all significantly increased yield.
 
The difference in yield between corn on fallowed plots with no applied N and that from fallowed
plots with 50 pounds fertilizer N/acre was 4.0 tons/acre. The plots which had been in overseeded
clover, but which received no fertilizer, produced 3.5 tons/acre greater yield than did the
unfertilized fallowed plots. Assuming linear response to available N over this range, the yield
increase of 3.5 tons/acre indicates 44 pounds N/acre were provided by the overseeded clover.
Similarly, the spring-plowed clover seed crop provided an estimated 34 pounds N/acre. The rye
or rye-pea cover crops did not appear to provide N to the sweet corn crop.
Table 39. Main effects of cover crop species and nitrogen rate on previous sweet
corn crop on the yield and nitrogen accumulation by cover crops, NWREC, 1993
Treatment Dry yield Rye N uptake Legume N uptake Total N uptake
-------------------------lb/acre---------------------------
Cover crop
Drilled rye 2421 34 0 34
Drilled rye+pea 2904 45 12 57
Overseeded rye 2593 38 0 38
Overseeded clover 2510 0 62 62
Clover green manure 3548 0 105 105
LSD (0.05) 601 10 15 12
N rate (lb/A)z
0 2167 27 38 39
50 2325 32 34 41
200 3329 58 37 62
Significance ** ** NS **
zDoes not include means for the clover green manure crop, to which N was
not applied.
Table 40. Main effects of cover crop species and nitrogen
rate on previous broccoli crop on the yield and nitrogen
accumulation by cover crops, NWREC, 1994
Treatment Dry yield N uptake
-------lb/acre-------
Cover crop
Drilled rye 1915 32
Drilled rye+pea 2135 50
Overseeded rye 1067 20
Overseeded clover 996 34
Clover green manure 740 27
LSD (0.05) 547 10
N rate (lb/A)z
0 1032 25
125 1621 33
250 1932 44
Significance ** **
zDoes not include means for the clover green manure
crop, to which N was not applied.
Table 41. Main effects of preceding cover crop, and rate
of applied N on yield and quality of broccoli, NWREC, 1993
Treatment Yield Mean head
(T/A) wt. (g)
Cover crop
Fallow 3.3 202
Rye 2.8 180
Rye + pea 3.6 208
Overseeded rye 3.1 203
Overseeded clover 3.7 241
Fall-plowed clover 3.1 197
Spring-plowed clover 3.6 221
LSD (0.05) 0.6 35
N rate (lb/A)
0 2.4 149
125 3.9 233
250 3.7 238
LSD (0.05) 0.4 27
Table 42. Interaction of preceding cover crop and rate of
applied N on yield and quality of broccoli, NWREC, 1993
Cover crop N rate Yield Mean head
(lb/A) (T/A) wt. (g)
Fallow 0 1.9 124
125 4.1 246
250 3.9 236
Rye 0 1.6 111
125 3.4 208
250 3.3 221
Rye + pea 0 3.5 184
125 3.7 210
250 3.7 229
Overseeded rye 0 2.0 138
125 3.5 221
250 3.7 249
Overseeded clover 0 2.9 190
125 4.5 277
250 3.7 256
Fall-plowed clover 0 2.4 157
250 3.8 237
Spring-plowed clover 0 3.2 188
250 3.9 254
LSD (0.05) 1.1 61
Table 43. Main effects of preceding cover crop, and rate of applied nitrogen
on yield and quality of sweet corn, NWREC, 1994
Treatment Yield No. ears Mean ear Ear length Tipfill
(T/A) harvested/A wt. (g) (inches)
Cover crop
Fallow 5.1 22120 205 8.0 2.7
Fallow, clover in 1992 5.1 23090 201 7.8 2.6
Rye 3.7 18050 177 7.6 2.2
Rye + pea 5.2 23620 256 8.4 2.9
Overseeded rye 4.4 20720 172 7.5 2.1
Overseeded clover 7.1 24880 192 8.0 2.4
Fall-plowed clover 5.8 21930 228 8.4 2.9
Spring-plowed clover 6.3 23670 230 8.4 2.8
LSD (0.05) 1.1 2460 37 0.5 0.5
N rate (lb/A)
0 3.3 18000 156 7.4 1.9
50 5.2 23380 211 8.0 2.5
200 7.1 25830 253 8.6 3.3
LSD (0.05) 0.7 2590 18 0.3 0.3
Effect of Frequency and Timing of Irrigation on Yield and Head Rot of Broccoli
Cooperator: Mary L. Powelson, Dept. of Botany and Plant Pathology
Introduction
Bacterial soft rot, caused by Erwinia carotovora and possibly by Pseudomonas species, often
affects broccoli production in the Willamette Valley. The rot can affect floret or stem tissue and
occurs mainly during periods of moderate temperatures and high humidity or rainfall. Chemical
controls are ineffective and resistance has not been identified in varieties well-adapted to the local
climate and acceptable to processors. While reductions in planting density may somewhat reduce
disease incidence, the decreased disease incidence is not sufficient to offset the loss in number of
heads harvested.
Previous work at NWREC (R. Ludy, M.S. thesis, Oregon State University, 1990) indicated that
the amount of water applied to a broccoli crop did not affect floret soft rot (head rot) incidence or
severity, at least within a range of applied water that allowed for economic yields. However, in
non-replicated observations of the effect of irrigation frequency (once versus three times per
week), head rot incidence more than doubled under the greater frequency. We propose that the
incidence of rot is affected by the frequency and duration of water droplets on the floret and stem
tissue. The purpose of these trials was to determine the effects of two or three frequencies of
irrigation and the time of day of the irrigations, at equal amounts of applied water, on yield and
head rot incidence in broccoli.
Methods
'Gem' broccoli was seeded to a Willamette silt loam, Ph 6.0, on 7 July, 1993 and 6 July, 1994. In
1993, the experimental design was a split-plot with a 2x2 factorial combination of irrigation
frequency (every second and every eighth day) and timing (morning and evening) as main plots
and harvest as subplot treatments. In 1994, the design was a factorial combination of three
frequencies (every second, fourth, and eighth day) and the same timings. The main plots in 1993
consisted of 12 30-foot rows (18 in 1994), with three rows on a 60-inch bed. The subplots
consisted of individual three-row beds. Main plot treatments were replicated four times in a
completely random design. Plot preparation included a broadcast and incorporated application of
1000 pounds 10-20-20 fertilizer/acre, 0.75 pounds trifluralin, 1.3 pounds chlorpyrifos, and 10.0
pounds Solubor/acre. The area was then rototilled and cultimulched to form a seedbed. Plots
were seeded with a gang of three tractor-mounted Planet Jr. planters. Broccoli was thinned to
about 10 inches between plants during the last week of July. Diazinon was applied at 2.0
pounds/acre for maggot control in early August. In 1993, eighty pounds N/acre, as ammonium
nitrate, was sidedressed on 17 August. In 1994, 100 pounds N/acre, as urea, was sidedressed on
2 August and an additional 50 pounds N/acre was sidedressed on 1 September.
Plots were irrigated uniformly as needed, about 4 cm/week, until 17 September, 1993 (8
September, 1994) when the irrigation treatments were initiated. Most plants had 1-inch diameter
heads at this date. The irrigation system was constructed such that each of the treatment
combinations was controlled by a separate valve with flexible hose used to connect the four plots
making up the replicates of each treatment. Water was applied from a sprinkler located at each
end of the main plots. Main plots were isolated from each other by 30 feet in all directions.
Sprinklers were set to water a 180-degree pattern.
A spontaneous mutant of Erwinia carotovora subsp. carotovora (EccW3C105) was obtained from
J.E. Loper, USDA, Corvallis, OR and selected for field trials. It was resistant to 100 g/mL
nalidixic acid and phenotypically similar to the parental strain. Lawns of the Erwinia isolate were
grown on Lauria Bertani (LBnal) media (10 g Bacto tryptone, 5 g Bacto yeast extract, 10 g NaCl,
20 g Bacto agar in 1.0 liter of distilled H2O with the addition of 100 g/mL nalidixic acid) for 3
days. The bacteria were washed from plates and the concentration of inoculum was adjusted to
107 cells/mL. On 16 and 23 September at 8 am and 7 pm, respectively, plots were sprayed with
the bacterial suspension in 25 gal water/acre using a CO2-pressurized boom sprayer with three
flat fan nozzles.
To determine the survivability of Erwinia over time, broccoli florets were sampled every other day
at 9:00 am from 17 September to 8 October, 1993. Additionally, florets were sampled two hours
after the first bacterial application and the morning following the second application. A five-foot
section across each main plot (approximately 48 plants) was used for sampling. Five samples
(approximately 0.2 g of floret tissue) per head were collected from three heads in each plot.
Individual samples were placed in separate test tubes containing 2.24 mL of sterile potassium
phosphate buffer (ph 6.5, 0.05 M). Test tubes were agitated and then racks of test tubes were
sonicated for 5 min. After agitating again, a 0.01 ml aliquot of the wash and a 1:22.4 dilution of
the wash were each plated on separate halves of plates filled with LBnal medium. Minimum
detection limits for bacteria in the wash and the dilution were 2.24 x 102 and 5.0 x 103,
respectively. Bacterial populations were counted three days after plating.
The duration of the irrigation treatments, one-half, one, or two hours, was intended to deliver 1
cm of water for the 2-day frequency, 2 cm for the 4-day, and 4 cm for the 8-day frequency,
respectively. Rain gauges were located in the center of each main plot; actual water accumulation
was measured immediately after each irrigation. Preliminary measurements at less than 1 knot
winds indicated excellent uniformity of water application (less than 0.1 cm variation) both among
plots of the same treatment and within main plots. The half-hour irrigations commenced at 8:30
a.m. (morning) or 6:30 p.m. (evening). The longer irrigations commenced at correspondingly
earlier times, with all irrigations terminating at 9 a.m. or 7 p.m.
Soil moisture content of the surface 15 cm of the soil profile, as a percentage, was measured by
time-domain reflectometry at about 2 p.m. each day from 17 September until 1 October, 1993 and
on 19 and 21 September, 1994. Leaf wetness duration was measured with a Campbell Scientific
21X micrologger (Campbell Scientific, Logan, UT) in four plots representing each treatment.
Four replicate sensors attached to ringstands were placed in each plot in the center of the canopy.
Sensors were sampled at 30-minute intervals and wetness duration was computed as the
percentage of the interval that the sensor was wet.
Visual disease ratings were made at four-day intervals in a three-row
subplot in each plot. Heads were harvested from the appropriate subplots on 28 September, and
4 and 8 October, 1993 (19 and 29 September, 1994), counted, weighed, and checked for disease
incidence.
Results and Discussion
In 1993, mean weight of broccoli heads at the first harvest was greater for the 2-day irrigation
interval than for the 8-day interval and tended to be greater for the morning as opposed to
evening irrigation (Table 44). At the second harvest mean head weight was nearly identical
between frequencies, but was greater for the evening irrigation (Table 45). Most of these
differences appeared to be due to delayed maturity and small heads for one replicate of the 8-day
x morning treatment combination. The same trend was not observed at the third harvest (Table 46)
and mean head weight did not vary with treatment for the sum of all harvests (Table 47). Since
there were no significant interactions of irrigation frequency and timing affecting yield or rot
incidence, only main effects have been presented in the tables.
The incidence of head rot in 1993 was very low, less than 10 percent. Irrigation treatment had no
effect on rot incidence at the first harvest, but there was a greater incidence of rot with the
evening irrigations at the second harvest. At the third harvest, the 2-day interval produced more
rotten heads and, although not significant, the evening irrigation still tended to produce more rot
than did the morning irrigation. For the sum of all harvests, only the effect of irrigation interval
was statistically significant. In the observational sub/plots that were not harvested, only three
heads were observed with head rot on 4 October. Four days later, on 8 October, the number and
percentage of heads with rot was significantly greater in the 2-day irrigation interval treatment
compared with the 8-day interval. The incidence of head rot did not differ significantly between
morning and evening irrigations, although incidence was greater in the evening-irrigated plots.
Populations of the Erwinia mutant were recovered from all of the heads sampled two hours after
the first inoculation and varied from 102 to 105 colony forming units (cfu)/g fresh weight of
tissue. Two and four days later, colonies were recovered from only 2 and 3 plots, respectively.
After the second inoculation, bacteria were recovered from most of the heads with populations
ranging from 102 to 105. Recovered Erwinia populations immediately began to decline. Two,
four and six days later, bacteria were recovered from 29, 12 and 10% of the heads, respectively.
No bacteria were recovered after 30 September. Several possible reasons for the sharp decline
are proposed. Environmental conditions were unfavorable to establishment and survival of the
bacteria at the time of and immediately following application. Weather conditions prevalent
during the sampling period were characterized by dry and warm days. Bacteria applied to aerial
portions of plants are susceptible to desiccation. The ability of the Erwinia mutant to survive in
situ has not been fully investigated. Due to the poor survival of the applied mutant, an analysis of
treatment effect on survival of bacteria could not be made.
Several bacteria were isolated from diseased heads, including several Psuedomonads and
undetermined isolates, but no Erwinia. These bacteria will be tested for their ability to cause head
rot on broccoli.
Total precipitation between seeding and initiation of the irrigation treatments was 8 cm in 1993.
During the irrigation treatments only 0.15 cm precipitation was recorded and probably had little
influence on the treatments. The weather was unusually warm and dry during most of the
treatment period. However, temperatures returned to normal seasonal averages during the last
week of the experiment, with mostly cloudy skies.
Averaged over the length of the treatments, soil moisture did not vary with treatment if only the
measurements taken on the no-irrigation days are used (Table 48). Since the soil moisture readings
were taken midway between the morning and evening irrigations, the readings were greater for
morning than for the evening-irrigated plots, if measured on the day of irrigation (data not
shown). Soil moisture for the 2-day irrigation interval tended to be fairly constant over time,
although there was an increase late in the experiment, perhaps related to greater cloud cover,
reduced temperatures, and reduced evapotranspiration (Fig. 6). For the eight-day interval, soil
moisture was much less constant. Soil moisture readings were terminated on 1 October because
of instrument failure.
The lack of a consistent treatment effect on yield, and the lack of effect of treatment on soil
moisture and average amount of water applied to each plot, indicate that the effects of treatment
on head rot incidence are due to frequency or timing of irrigations rather than to the amount of
water applied. Although timing and frequency did not affect the total amount of water applied or
average soil moisture, it did affect leaf wetness duration. Mean hours of leaf wetness per day
over the course of the study was greater in the two-day irrigation interval compared to the
eight-day irrigation interval. The effect of timing was not significant, although plots irrigated in
the evening tended to have greater average daily hours of leaf wetness (Table 49). Across all
treatments, average daily hours of leaf wetness increased as the season progressed. The last three
days of September, leaf wetness averaged 12.9 hours per day and by the final three days of the
study leaf wetness averaged 19.9 hours per day.
In 1994, the amount of water (0.68 cm/day) applied to the plots during the treatment period
slightly exceeded the goal of 0.5 cm/day. However, this included two occurrences of
precipitation, averaging 0.07 cm/day. The amount of water applied did not vary significantly with
treatment. Mean soil moisture also did not vary with treatment (Table 50).
Mean weight of broccoli heads and yield per unit area in 1994 did not vary with either frequency
or timing of irrigation at either harvest (Tables 51 and 52). The first harvest occurred during a
period of unusually hot, dry weather and no rot was observed. Since there were no significant
interactions of irrigation frequency and timing affecting yield or rot incidence, only main effects
have been presented in the tables.
The incidence of head rot was fairly high at the second harvest, averaging 22 percent for all
treatments (Table 52). As in 1993, incidence of rot decreased with increasing interval between
irrigations but timing of the irrigation had no effect.
Taken together, the 1993 and 1994 results support the hypothesis that development of disease is
related to the availability and duration of free moisture. The data also provide evidence that
irrigation practices may be useful in disease control. Avoiding frequent irrigation and timing
irrigations to allow rapid drying of plants may reduce rot incidence.
Table 44. Main effects of frequency and timing of irrigation on yield and
head rot incidence in broccoli at first harvest, NWREC, 1993
Treatment No. heads harvested Yield Mean head No. rotten
per plot kg/plot wt. (g) heads per plot
Frequency
2-day interval 50.0 11.5 231 0.2
8-day interval 45.7 8.2 182 0.0
Significance NS NS * NS
Timing
morning 46.5 10.2 220 0.0
evening 49.2 9.4 194 0.2
Significance NS NS NS NS
Table 45. Main effects of frequency and timing of irrigation on yield and
head rot incidence in broccoli at second harvest, NWREC, 1993
Treatment No. heads harvested Yield Mean head No. rotten
per plot kg/plot wt. (g) heads per plot
Frequency
2-day interval 61.1 18.1 296 1.9
8-day interval 60.8 18.2 299 0.5
Significance NS NS NS NS
Timing
morning 62.9 17.1 272 0.3
evening 59.0 19.2 325 2.2
Significance NS NS * *
Table 46. Main effects of frequency and timing of irrigation on yield and
head rot incidence in broccoli at third harvest, NWREC, 1993
Treatment No. heads harvested Yield Mean head No. rotten
per plot kg/plot wt. (g) heads per plot
Frequency
2-day interval 56.0 23.2 415 12.3
8-day interval 54.5 22.1 403 5.5
Significance NS NS NS *
Timing
morning 59.0 23.9 409 8.1
evening 51.5 21.4 410 9.7
Significance NS NS NS NS
Table 47. Main effects of frequency and timing of irrigation on yield and
head rot incidence in broccoli, sum of all harvests, NWREC, 1993
Treatment No. heads harvested Yield Mean head No. rotten
per plot kg/plot wt. (g) heads per plot
Frequency
2-day interval 167.1 52.7 317 14.4
8-day interval 161.0 48.5 300 6.2
Significance NS NS NS **
Timing
morning 168.4 51.2 303 8.6
evening 159.7 50.1 313 12.0
Significance NS NS NS NS
Table 48. Main effects of frequency and timing of irrigation on the
mean amount of water applied per day and on the mean percent soil
moisture during the course of the experiment, NWREC, 1993
Treatment Water applied, cm/day Soil moisture (%)
Frequency
2-day interval 0.51 14.9
8-day interval 0.51 14.3
Significance NS NS
Timing
morning 0.53 14.0
evening 0.50 15.1
Significance NS NS
Table 49. Main effects of frequency and timing of irrigation on mean
daily hours of leaf wetness and the number and percentage of heads
with rot on 8 Oct, 1993, NWREC
Treatment Rotten headsz Rotten heads Leaf wetness
Number/plot % mean daily hours
Frequency
2-day interval 5.7 11.4 15.1
8-day interval 2.3 4.4 13.0
Significance ** ** *
Timing
morn |