CONTENTS
Introduction
Nitrogen Management in Sweet Corn
Effect of Winter Cover Crops on Vegetable Crop Yield and Leaching of
Nitrate
Impact of Cover Crop and Previous Vegetable Crop on Mold Incidence in Snapbean
Cultivar, N Rate, and Row Spacing Affect Yield of Edamame
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. John Hart is Extension Soil Scientist and Professor, Department of
Crop and Soil Science, Oregon State University, Corvallis, OR 97331
Dr. Richard Dick is Professor of Soil Science, Department of Crop and
Soil Science, Oregon State University, Corvallis, OR 97331
Dr. John Selker is Associate Professor, Department of Bioresources
Engineering, Oregon State University, Corvallis, OR 97331
Dr. Carol Miles is a Washington State University Extension Agent, 360
NW North St., MS:AESOL, Chehalis, WA 98532
Dr. Mary Powelson is Professor, Department of Botany and Plant Pathology, Oregon State University,
Corvallis, OR 97331
Dr. Neil Christensen is Professor, Department of Crop and Soil Science, 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 Oregon State University's Agricultural Experiment
Station and its 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 processed vegetable and the fresh market 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 OSU and at Washington State University. Their
contributions are gratefully acknowledged. The financial support of the Oregon Processed
Vegetable Commission was essential to completing these projects and is greatly appreciated.
This report is the eleventh 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.
Nitrogen Management in Sweet Corn
Cooperators: Dr. John Hart, Dept. of Crop and Soil Science, Oregon State University and
Dr. Carol Miles, Extension Service, Washington State University
Introduction
Vegetable growers in the Willamette Valley use high rates of N fertilizers, often exceeding 250 to 300
pounds actual N/acre per season. While growers believe 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 (Hemphill, 1997). This excess has
raised concerns that the remaining N may be contributing to nitrate pollution of ground or surface waters. We feel
that our research has contributed significantly to an understanding of the yield response of vegetables to N fertilizer
and the critical stages for N uptake, particularly as related to residual mineral N after harvest. Both research at the
North Willamette Research and Extension Center (NWREC) and a three-year survey of residual mineral N in grower fields indicates that residual N
tends to be greatest following sweet corn. For the crops that have been the major focus of our research (sweet corn,
broccoli, cauliflower), we feel that more work on rates of fertilizer application, timing, placement,and N source will
not lead to significant changes in the way we fertilize these crops.
We have recently focused on the most important remaining questions and have moved toward solutions to
the problem of high levels of residual applied N following vegetable crops. We have attempted to develop methods
to predict crop response to sidedressed N and to determine how much sidedressed N is needed, particularly in sweet
corn. Research on silage corn grown with high inputs of manures indicates that a pre-sidedress soil nitrate test
(PSNT) may be useful in determining the amount of additional N needed (Marx, 1995). In 1995, we started to
extend testing of this method to sweet corn, basing our initial efforts on the results of research in New Jersey
(Heckman and Prostak, 1992). Our preliminary evaluations of the PSNT in 1995 and 1996 (Hemphill, 1997)
convinced us that the potential exists to reduce sidedress N applications to sweet corn significantly in certain
circumstances, resulting in reduced cost to growers and reduction in leachable residual nitrate. The results reported
here continued this effort and resulted in a modification of the PSNT, which appears applicable to
sweet corn production on typical Willamette Valley soils.
Methods, NWREC Experiment, 1997
'Jubilee' sweet corn was seeded on 15 May on 30-inch row spacing. The plots had previously been fallow
for two years. Nitrogen rates of 0, 50, 100, 150, and 200 pounds/acre were applied at planting to establish five
different levels of early-season soil nitrate (Table 2). Soil samples for PSNT were taken on 7 July and sidedress N rates of
0, 30, 60, 90, and 150 pounds/A were applied to the appropriate plots on 10 July. All N was applied as urea.
Table 1 contains the complete list of treatments. One treatment (13) received 50 pounds N/acre at planting, followed
by 25-pound applications on 10, 18, and 29 July, and 12 August, for a total N application of 150 pounds/acre.
SPAD-502 chlorophyll meter (Minolta Co., Ltd., Japan) readings were taken on intact leaves on 11, 18, and 29
July, and 12 and 21 August. Harvest was on 20 August. Plots were sampled to 1-foot depth for residual soil nitrate
on 21 August.
Methods, NWREC Experiment, 1998
'Jubilee' sweet corn was seeded on 9 June on 30-inch rows. The plots had previously been fallow for two
years. Nitrogen rates of 0, 40, 80, 120, and 180 pounds/acre were applied at planting to establish five different
levels of early-season soil nitrate (Table 7). Soil samples for PSNT were taken on 21 July. Sidedress N rates of
0, 20, 60, 80, 100, 140, and 200 pounds/A were applied to the appropriate plots on 22 and 29 July, and 14 August,
to complete 11 different combinations of N rate, form of N applied, and timing of N application (Table 2). All N
was applied as urea except for applications of Greenfeed (TM) 27-0-0 liquid controlled release N solution to corn
foliage on Treatments 15 and 16 (Table 3). The Greenfeed material contains 7.1% urea plus 19.4% urea derivatives
(polymethylene urea, monomethylol urea, methylene diurea) which break down relatively slowly. SPAD meter
readings were taken on 10 intact leaves/plot at approximately weekly intervals starting on 16 July and continuing
at approximately weekly intervals through harvest. Harvest was on 14 September. Plots were sampled for residual
soil nitrate on 18 September. A second variety, GH 1703 (Rogers Sandoz), was also seeded on 9 June and treated
with only 5 rates of N (Table 3). The purpose was to compare the performance of the SPAD meter over two
varieties.
Methods, On-farm Trial of the Pre-sidedress Soil Nitrate Test (PSNT), 1997 and 1998
As in 1996 (Hemphill, 1997), the PSNT was evaluated in 1997 and 1998 at nine grower locations in which
plots of approximately 1 acre were compared to the grower practice in the remainder of the field for ear yield, stalk
nitrate-N at harvest, and soil nitrate-N at harvest. The assumption of the PSNT is that soil can be tested at about the
1-foot stage of corn growth (about 5 weeks after planting) and that sidedress fertilizer application can be reduced
when soil nitrate content exceeds a critical level. The soil was sampled to a depth of 12 inches and analyzed for
nitrate-N content. Sufficient corn was harvested from the plot area to fill a truck. The harvested area was
measured, the contents of the truck weighed, and the yield calculated. A similar procedure was followed to provide
a matching sample from an adjacent portion of the field in which the standard grower practice was followed. At
harvest, 12-inch segments of corn stalks from just above the brace roots were cut, dried, ground, and analyzed for
nitrate-N concentration. A soil sample was taken at the same time and also analyzed for nitrate-N content.
In 1997, growers limited pre-plant and at-planting N application to 50 pounds/acre. Treatments were the
grower's standard sidedress N rate and one-half this rate. Three of the sites were replicated. Sites considered
responsive to N were those where yield from the half-rate of sidedress N was less than 98% of the yield from the
full rate of sidedress N. A relative yield of 98% was chosen as the yield below which the cost of additional N
fertilizer would be recovered in additional yield. For the calculation, we assumed a price of $85/ton for corn, a
10 ton/acre yield, and a cost for N of $0.32/lb.
In 1998, our goal was to have 175 pounds available N/acre provided from a combination of the soil and
sidedress N application. The soil samples were analyzed for nitrate-N and an approximation of the amount of nitrate-N
in the soil (pounds/acre) was made using the conversion parts/million multiplied by 3.6 = pounds/acre in the surface foot of
soil. Sufficient sidedress N was applied to provide a total of 175 pounds N/acre. The fertilizer N was applied by
the growers. A relative yield level of 97.5% was chosen based on the current prices for urea fertilizer ($195/ton),
the value of sweet corn at $85/ton, and fertilizer application cost of $5/acre. At this relative yield, a yield increase
of 0.25 tons/acre would just offset the cost of an additional 75 pounds N/acre. Thus, a relative yield level of 97.5%
is a reasonable measure of success of the PSNT prediction for needed N with 1998 prices.
Results, NWREC, 1997
Our past trials indicated that the critical level of PSNT is about 25 ppm; that is, a positive yield-response
to additional N is not to be expected when the soil nitrate concentration is at this level 4 to 6 weeks after planting.
However, in this experiment, application of 100 pounds N/acre at planting resulted in a PSNT of 47 ppm (Table
2) but this level of N was not adequate for maximum yield (Table 4). This is probably because achieving this level
of available N as a result of fertilizer application does not indicate a continuing reservoir of available N coming from
mineralization of organic matter. In contrast, in the grower trials, much lower levels of N were usually applied at
planting, resulting in a better estimate of nitrate-N availability from the soil.
The highest yield was obtained with 200 pounds N/acre, with all the N applied at planting. Yields tended
to decline at higher N rates. Past trials have indicated greater yield with split N application. In this trial a
breakdown of fertilizer banding equipment prevented banding N below the seedline. A broadcast application of the
initial 50 lb N/acre (Treatment 14) may not have provided sufficient N during early growth. In general, our
experiments have indicated that, while it is advisable to delay the application of the bulk of crop N needs until after
rainfall has tapered off, it is critical to have adequate N present at all times. This can be seen clearly in the case
of Treatment 13 (Table 4), for which yield was much lower than other treatments with similar N rates (Trts. 4, 5, 6, 12).
Apparently, delaying the application of much of the N until relatively late in crop development meant N deficiencies
at critical earlier stages of growth.
Sweet corn yield is plotted vs. total N rate in Figure 1. Most yields clustered between 8 and 9 tons/acre,
so a smooth curve cannot be fitted to the data. However, three points stand out: the high yields at 200 lb N/acre
and the low yield of 7.6 tons/acre for Trt. 13. SPAD readings also tend to cluster (Table 5 and Figure 2) but the
relationship between SPAD and N applied can be seen in Figure 2. SPAD reading at harvest increased
linearly with rate of N applied up to about 180 pounds N/acre. After this, the SPAD reading tends to plateau and
not be responsive to more N. There is no good explanation for the one obvious outlier at 200 lb applied N. A
similar relationship existed for earlier SPAD readings.
Figure 3 demonstrates how SPAD readings tend to vary during the season. Typically, the readings start
low, increase, and then gradually decline toward harvest. The middle curve in the figure is atypical. This is the
curve for the 150 lb treatment (Trt. 13) in which the N was applied in six separate applications of 25 or 50 lb/acre.
Dribbling on the fertilizer in this fashion resulted in very steady SPAD readings but, as seen above, yield suffered.
Figure 4 indicates that there is not a simple relationship between SPAD at harvest and yield. Points are clustered
between SPAD readings of 37 and 44. This is because of the great variation in this experiment among different N
rates at planting and at harvest. The timing of the N application as well as the total amount applied affects the
SPAD reading. For SPAD to be an effective tool in sweet corn fertilization, we will need to generate more data
of the type in Figure 3 and standardize the method and timing of N application.
Both soil nitrate and ammonium concentrations were elevated at time of harvest, but only for high rates
of applied N (Table 6). The high levels of residual N at 150 pounds applied N/acre were likely due to
half the total N being applied to this treatment (#13) after the normal sidedress time. Almost 80 pounds nitrate-N/acre
were left behind in the surface foot of soil by the corn crop fertilized with 200 pounds N/acre.
Results, NWREC, 1998
As noted above, preliminary trials in 1995 and 1996 indicated that the critical level of PSNT is about 25
ppm. In this experiment, application of 120 pounds N/acre at planting resulted in a PSNT of 29.6 ppm (Table 7).
A treatment which provided a total N application of 120 lb/acre (80 at planting, 40 sidedress at mid-season) produced
maximum yield (Tables 8 and 9), indicating that a PSNT level of 2530 ppm might have produced maximum yield,
but this was not tested directly.
The highest yield of both 'Jubilee' and 'GH 1703' was obtained with 120 pounds N/acre, with 80
pounds/acre applied at planting and the remainder 6 weeks later. Yields tended to decline at higher N rates. Past
trials have indicated greater yield with split N application, but with maximum yield at 180-200 lb/acre. One
explanation for the highest yields at a lower-than-expected N rate may be seen in Table 7. Available N in the soil
before planting was unusually high, nearly 50 pounds N/acre as nitrate and 15 as ammonium. If this amount of
available N already present in the soil is added to the 120 pounds/acre applied N, then the highest yield was obtained
at 185 pounds available N/acre, very much consistent with previous trials. This serves to reinforce the importance
of the PSNT, as high concentrations of available N are occasionally present in Willamette Valley soils, even after
a high-rainfall winter like that of 19971998.
Averaged over all N rates, 'GH 1703' outyielded 'Jubilee' by 0.9 tons/acre (Table 8). However, the
difference in yield was greater at the suboptimal rates of N (Table 9). Mean ear weight and tipfill responded less
to increasing N rate for 'GH 1703' than for 'Jubilee'. The two varieties also had a strikingly different appearance
in the field. Leaves of 'GH 1703' were darker green and thicker, and the color remained dark green until harvest
even at the zero rate of N. If confirmed in future testing, the ability of a variety to produce acceptable yields at
lower rates of applied N may be of great help in avoiding leaching of nitrate and in reducing fertilizer costs.
Treatments 11 through 14 were added to compare the performance of 'Jubilee' at 180 pounds/acre applied
N, but with varying rates applied at planting versus mid-season and later sidedressings. Yields of these treatments
are seen in rows 47 of Table 10. None of these treatments produced a higher yield or quality than the standard
method of 40 pounds N/acre at planting and 140 pounds/acre sidedressed 6 weeks after planting (Treatment 7, 10.1
tons/acre, line 7 in Table 9). While applying relatively small amounts of N at several times during the season could
affect residual soil N or N leaching, it is clear from this and previous work at NWREC that there is no yield
advantage to delaying N applications past mid-season. However, note from Table 11 that treatments 11, 12, and
13 (lines 6, 7, and 8) resulted in lower residual soil N than did applying all the sidedress N at one time (line 4).
In treatments 15 and 16, we compared corn yield with all or a portion of the sidedress N applied as
Greenfeed 27-0-0 controlled-release N at 60 and 120 pounds N/acre, respectively, with the corresponding treatments
in which all sidedress was applied as urea on 22 July (compare Table 10, lines 2 and 3 with Table 9, lines 3 and
5). The use of Greenfeed 27-0-0 did not provide a yield advantage compared to the use of urea alone as N source.
SPAD readings started off higher than last year, reflecting the higher level of nitrate in the soil at planting.
At time of sidedress N application, SPAD readings did not vary with application of either 0 or 40 lb N/acre at planting
(Table 12). Differences among total N rates were not evident until two weeks later. SPAD readings for treatments
receiving suboptimal N started to decline 3 to 4 weeks before harvest. The thicker, darker green leaves of 'GH
1703' gave consistently higher SPAD readings than did 'Jubilee', indicating that separate calibration curves will be
needed for each variety. As in 1997, applying small amounts of sidedress N four times during the growing season
tended to keep SPAD readings more level over time (Table 13) but, as noted above, did not result in improved
yield.
As in 1997, both soil nitrate and ammonium concentrations were elevated at time of harvest but only for
high rates of applied N of 180 pounds/acre or more (Table 11). The residual nitrate-N level of about 40
pounds/acre for the optimal N rate of 120 pounds/acre is probably acceptable and certainly is no higher than at
planting. However, at 180 and 240 pounds N/acre, residual nitrate-N varied from 60 to 160 pounds/acre, depending
on N rate and timing of application. Residual nitrate levels were generally higher in 1998 than in 1997 for all but
the lowest rates of applied N. Residual ammonium levels did not vary significantly with amount of N applied.
Results, On-farm PSNT Trial, 1997
PSNT values ranged from 8.8 to 38.8 ppm nitrate-N, similar to those found the previous two years (Table
14). The conclusion from 1996 was that 100 pounds sidedress N/acre was sufficient for at least 98% relative yield
when the PSNT value was 18 ppm or more. Our approach in 1997 was slightly different as the sidedress N rates
varied by grower rather than being set at 100 vs. 150 pounds/acre. In addition to this variation in experimental
procedure, the analysis of the data was modified.
Relative yield was plotted vs. the sum of soil nitrate-N (as determined by PSNT) and sidedressed
fertilizer N (Fig. 5). The horizontal line in the Cate-Nelson type graph represents 98 percent relative yield. The goal of the Cate-
Nelson technique is to manipulate the vertical and horizontal lines such that the greatest number of points is located
in the upper right (I) and lower left (IV) quadrants of the graph. Points in these two quadrants are viewed
as "correct" predictions. The lower left quadrant (IV) represents situations in which the PSNT would have called
for additional N and prediction was correct. The points in the upper right quadrant (I) represent situations in which
the test indicated that available N was adequate for 98 percent relative yield and the prediction was correct.
Points falling in the upper left and lower right quadrants are considered "incorrect" predictions. The upper
left quadrant (III) represents situations in which the PSNT called for additional N, but the relative yield indicates that
it was not needed. These incorrect predictions are of low risk to the grower as they call for an additional fertilizer
application that the grower would likely make anyway unless that grower typically uses rates that are considerably
less than most growers now apply. Yield would not be sacrificed and expenditures would be the same save for the
cost of the PSNT itself. However, these situations are potentially the most damaging to the environment because excess
N at the end of the growing season will be leached by the heavy winter rainfall typical of western Oregon.
Points falling in the lower right quadrant (II) are situations where the plots did not achieve a relative yield
of 98 percent when the PSNT indicated that N was adequate. These sites were on sandy or gravelly soils in which the
reservoir of mineralizable soil N was very low.
Yield data from both 1996 and 1997 is presented in Figure 6. The graph reveals that 98 percent or greater
relative yield was attained when the sum of the PSNT and sidedress N was greater than 175 pounds/acre. If the sum
of PSNT and sidedress N is less than 150 pounds/acre the relative yield is less than 98 percent. Between 150 and 175
pounds/acre, the relative yield is sometimes less than 98 percent and sometimes greater than 98 percent.
Assuming that the sum of PSNT plus sidedress N must be 175 pounds/acre to achieve the desired relative
yield of 98 percent, the amount of sidedress N to apply can be calculated from the formula:
Sidedress N (pounds/acre) = 175 pounds/acre - [PSNT (ppm) x 3.6] (1)
Another method to provide sidedress N rates is to group PSNT results into three categories as shown in
Table 15.
Stalk nitrate concentrations at harvest (Table 14) did not provide an adequate assessment of yield or N
treatment. The critical value of 2700 ppm that we proposed in 1996 (Hemphill, 1997) seems very low for 1997
data. In addition, a sufficient nitrate-N concentration of 10,000 ppm in stalks at harvest was found in New Jersey
(Heckman and Prostak, 1992). Our current data set shows that high stalk nitrate-N content, probably above 8,000
ppm, indicated adequate N supply, but that stalk concentrations below 8,000 ppm did not necessarily indicate
insufficient N supply.
Results, On-farm PSNT Trial, 1998
The 1998 trial was a test of the formula (1) proposed above. Yields ranged from a low of 7.2 tons/acre at site
G, which had an infestation of barnyard grass, to a high of nearly 14 tons/acre at site B (Table 16). To compare
yield from all sites, relative yield was calculated by dividing the yield of the PSNT plot by the yield from the sample
of the rest of the field and multiplying by 100 percent. For example, if yield from the field was 10.0 tons/acre and that
from the PSNT plot was 9.75 tons/acre, the relative yield is 97.5 percent.
Relative yield was lowest (92.3 percent) at site E and highest (103.8 percent) at site B. Relative yield is ranked against the sum
of sidedress N fertilizer and the soil nitrate-N level determined by the PSNT (Table 17). The lowest amount of N,
133 pounds/acre, was entirely soil N. No N fertilizer was sidedressed at this site. The plot yield was almost 96 percent
of the yield from the rest of the field which had a sidedress N application of 160 lb/acre. Four of the plots received
less than 175 pounds N/acre as a combination of soil N and sidedress N. Of these four sites, only one (A) produced
a relative yield greater than 97.5 percent and that site had a combined soil and applied N level of 170 pounds/acre.
Of the five sites with more than 175 pounds N/acre from soil and sidedress, two produced relative yields less than
97.5 percent. Site H was a sandy soil; at harvest soil and stalk nitrate-N content at site H were lower for the plot area
than for the rest of the field. Soil and stalk nitrate-N content at harvest were both low for site D. The stalk NO3-N
concentration was lower in the plot area than in the field (Table 16).
Relative yields for the last three years were plotted versus the sum of sidedress and soil N (Figure 7). The vertical
line on the right of Figure 7 represents 175 pounds/acre; the left vertical line marks 135 pounds N/acre. This line
creates a third category of data points where additional N produces additional yield about half the time i.e., between
135 and 175 pounds N/acre there are five points above, and five points below, the 97.5 percent relative yield line.
Another way to express the test outcome is "yes, maybe, no." If sidedress plus soil N is below 135 pounds/acre,
then, "yes" ‹a yield increase from additional N is highly likely. If the soil plus sidedress N is above 175 pounds/acre,
then, "no" ‹increased yield with additional N in highly unlikely except on sandy or gravelly soils. If the N level is
between 135 and 175, then, "maybe" ‹a yield increase with more N is difficult to predict. For fields in the "maybe"
category, the SPAD meter may be useful in monitoring plant N status.
For the last three years, nitrate-N content of the soil at time of PSNT ranged from 30 to 160 pounds/acre
in the surface foot. This range of available N shows the need for a test that enables growers to adjust sidedress N
application rates on a site-specific basis. Our modification of the PSNT allows many growers to make this
adjustment. Of the 30 locations reported here, a detrimental economic consequence of using the modified PSNT
occurred in only two locations.
Literature Cited
Heckman, J.R. and D. Prostak. 1992. Presidedress soil nitrate test (PSNT) recommendations for sweet corn. Rutgers
Coop. Ext. and N.J. Agric. Expt. Sta. FS 760.
Hemphill, D.D., Jr. 1997. Vegetable research at the North Willamette Research and Extension Center, 19951996.
Oregon Agric. Expt. Sta. Spec. Rep. No. 975.
Marx, E. 1995. Evaluation of soil and plant analyses as components of a nitrogen monitoring program for silage
corn. M.S. Thesis, Oregon State Univ., Corvallis.
Table 1. List of N rates (lb/acre), PSNT trial, NWREC, 1997.
Trt. Total N rate At planting Sidedress, 7/10
1 0 0 None
2 80 50 30
3 110 50 60
4 140 50 90
5 130 100 30
6 160 100 60
7 190 100 90
8 180 150 30
9 210 150 60
10 240 150 90
11 200 200 0
12 150 150 0
13 150 50 4x25
14 200 50 150
Table 2. Effect of N at planting on soil nitrate levels
and leaf SPAD readings at time of PSNT testing, NWREC, 1997.
N at planting, lb/acre Soil nitrate, ppm, 7/7 SPAD, 7/11
0 3.7 37.3
50 20.3 42.0
100 47.0 43.8
150 56.4 44.9
200 71.3 44.9
LSD (0.05) 35.5 4.2
Table 3. List of treatments in PSNT sweet corn experiment,
NWREC, 1998.
Trt. Variety Total N N at Sidedress N
applied planting 7/22 7/29 8/12
----------------lb/acre-------------------
1 Jubilee 0 0 0 0 0
2 GH 1703 0 0 0 0 0
3 Jubilee 60 40 20 0 0
4 GH 1703 60 40 20 0 0
5 Jubilee 120 40 80 0 0
6 GH 1703 120 40 80 0 0
7 Jubilee 180 40 140 0 0
8 GH 1703 180 40 140 0 0
9 Jubilee 240 40 200 0 0
10 GH 1703 240 40 200 0 0
11 Jubilee 180 40 60 40 40
12 Jubilee 180 80 40 40 20
13 Jubilee 180 120 20 20 20
14 Jubilee 180 180 0 0 0
15 Jubilee 60 40 10z 0 10z
16 Jubilee 120 40 40y 20z 20z
__________________________________________________________
zApplied as Greenfeed 27-0-0 controlled release N solution.
yApplied as one-half urea, one-half Greenfeed 27-0-0.
Table 4. Yield of sweet corn, PSNT plots, NWREC, 1997.
Trt. Total N Yield Ear length Ear wt. Tipfill
(lb/acre) (tons/acre) (inches) g/ear
1 0 3.4 8.4 249 2.3z
2 80 8.0 9.1 321 3.1
3 110 8.5 9.7 320 3.1
5 130 8.1 9.6 316 2.9
4 140 8.6 9.8 317 3.0
12 150 8.8 9.7 324 3.0
13 150 7.6 9.5 296 2.8
6 160 8.2 9.8 330 3.1
8 180 8.7 9.7 319 3.1
7 190 8.5 9.5 332 3.2
11 200 10.1 9.5 321 3.2
14 200 9.5 9.4 283 2.9
9 210 8.9 9.6 349 3.1
10 240 8.9 9.2 314 2.9
LSD (0.05) 1.6 0.5 28 0.6
zFive-point scale with 5 = perfect fill, 1 = 2 inches
or more unfilled kernels.
Table 5. Trends in SPAD readings as affected by total N application, NWREC, 1997.
Trt. Total N, lb/acre SPAD, 7/18 SPAD, 7/29 SPAD, 8/12 SPAD, 8/21
1 0 38.5 29.5 22.9 19.5
2 80 48.7 50.8 40.9 34.7
3 110 47.3 47.7 39.7 38.0
5 130 49.8 52.4 43.9 38.9
4 140 48.1 48.8 43.3 40.3
12 150 50.8 50.0 41.8 37.7
6 160 50.3 51.8 44.4 42.5
8 180 50.2 52.5 46.3 44.5
7 190 52.0 49.8 45.2 43.4
11, 14 200 49.7 51.5 44.7 41.3
9 210 51.0 53.2 42.6 43.4
10 240 50.4 53.2 45.0 42.3
13 150z 44.0 (75) 43.4 (100) 43.0 (125) 42.7 (150)
LSD (0.05) 2.8 5.2 5.9 4.7
zTotal at end of season. Actual amounts applied before each SPAD measurement
are in parentheses after the SPAD mean.
Table 6. Effect of total N rate on residual soil N levels in the surface
foot of soil, NWREC, 1997.
Total N, lb/acre Residual nitrate, ppm Residual ammonium, ppm
0 0.9 4.6
80 2.7 6.0
110 2.9 5.2
140 4.0 6.3
150z 14.9 14.3
200 19.9 13.3
LSD (0.05) 5.2 NS
zThis treatment (#13) had a large proportion of the total N applied
relatively late in the season.
Table 7. Effect of N applied at planting on soil nitrate and
ammonium levels at time of sidedress N application, NWREC, 1998.
N rate, lb/acre Soil nitrate-N, ppm Soil ammonium-N, ppm
0 13.1 3.8
40 22.3 4.1
80 23.8 5.1
120 29.6 6.4
180 31.1 9.5
Significance *** ***
***Significant at 0.1% level.
Table 8. Main effects of rate of applied N and cultivar on yield of
sweet corn, NWREC, 1998.
Yield No. of Mean ear Tipfillz Ear length
tons/acre ears/plot wt. (g) inches
N rate, lb/A
0 7.3 55 210 2.2 7.7
60 9.2 58 251 2.6 8.3
120 10.9 62 277 2.9 8.6
180 10.4 59 275 2.8 8.5
240 10.4 59 275 2.7 8.6
Significance *** * *** * **
Cultivar
Jubilee 9.2 59 244 2.7 8.4
GH 1703 10.1 58 272 2.5 8.2
Significance ** NS *** NS NS
z5-point scale with 5 = perfect fill, 1 = 2 or more inches unfilled.
***,**,*,NSSignificant at p=0.1, 1, and 5% levels, and non-significant,
respectively.
Table 9. Interaction of rate of applied N and cultivar on yield of sweet
corn, NWREC, 1988.
N rate Cultivar Yield No. of Mean ear Tipfillz Ear length
lb/acre tons/acre ears/plot wt. (g) inches
0 Jubilee 6.3 55 179 1.8 7.6
GH 1703 8.4 54 241 2.5 7.8
60 Jubilee 8.7 58 233 2.6 8.4
GH 1703 9.7 57 268 2.5 8.2
120 Jubilee 10.7 63 265 3.1 8.8
GH 1703 11.2 60 290 2.7 8.3
180 Jubilee 10.1 59 266 3.2 8.9
GH 1703 10.8 59 284 2.3 8.0
240 Jubilee 10.4 59 276 3.0 8.6
GH 1703 10.4 59 275 2.5 8.6
LSD (0.05) 0.6 5 30 0.1
z5-point scale with 5 = perfect fill, 1 = 2 or more inches unfilled.
Table 10. Effects of total rate of applied N, proportion of N applied at planting,
split applications of N, and N source on yield of 'Jubilee' sweet corn, NWREC, 1998.
Total N applied N at planting Yield No. of Mean ear Tipfillz Ear length
lb/acre lb/acre tons/acre ears/plot wt. (g) inches
0 0 6.3 55 179 1.8 7.6
60 40y 8.9 59 237 2.7 8.3
120 40x 9.7 62 246 2.4 8.1
180 40w 9.8 61 251 2.9 8.4
180 80v 10.0 61 257 2.9 8.4
180 120u 9.5 61 244 2.7 8.5
180 180 9.5 61 245 2.8 8.5
LSD (0.05) 1.0 5 26 0.1
z5-point scale with 5 = perfect fill, 1 = 2 or more inches unfilled.
ySidedress N source: Greenfeed 27-0-0, 10 lb/acre, each, on 22 July and 12
August.
xSidedress N source: Greenfeed 27-0-0 and urea. 20 lb/acre each of Greenfeed and
urea applied on 22 July, 20 lb/acre as Greenfeed on 29 July and 12 August.
wSidedress N source: urea, applied at 60 lb/acre on 22 July, 40 lb/acre on 29 July,
and 40 lb/acre on 12 August.
vSidedress N source: urea, applied at 40 lb/acre on 22 July, 40 lb/acre on 29 July,
and 20 lb/acre on 12 August.
uSidedress N source: urea, applied at 20 lb/acre, each, on 22 July, 29 July, 12
August.
Table 11. Effects of total rate of applied N, proportion of N applied
at planting, and split applications of N on post-harvest soil nitrate
and ammonium concentrations, NWREC, 1998.
N rate, lb/acre Soil nitrate-N, ppm Soil ammonium-N, ppm
0 2.6 4.8
60 2.9 3.5
120 11.8 6.3
180 37.6 5.7
240 40.8 9.4
180z 20.5 7.9
180y 16.7 6.4
180x 21.9 9.3
LSD (0.05) 13.5 NS
zSidedress N source: urea, applied at 60 lb/acre on 22 July, 40
lb/acre on 29 July and 40 lb/acre on 12 August.
ySidedress N source: urea, applied at 40 lb/acre on 22 July, 40
lb/acre on 29 July, and 20 lb/acre on 12 August.
xSidedress N source: urea, applied at 20 lb/acre, each, on 22 July,
29 July, 12 August.
Table 12. Main effects of rate of applied N and cultivar on SPAD chlorophyll
measurements in sweet corn, NWREC, 1988.
Date of SPAD measurement
16 July 22 July 27 July 3 Aug. 10 Aug. 17 Aug. 24 Aug. 1 Sept. 15 Sept.
N rate, lb/acre
0 42.1 40.8 46.8 45.5 44.0 40.1 37.9 36.1 29.0
60 42.6 41.5 50.7 48.9 49.2 44.1 45.8 41.8 34.5
120 43.0 43.4 50.1 51.1 52.5 48.1 50.0 48.6 44.4
180 42.8 42.5 51.5 51.5 50.7 49.8 50.9 48.6 45.3
240 42.0 41.4 51.8 51.7 50.2 48.2 50.5 48.7 43.7
Significance NS NS *** *** *** *** *** *** ***
Cultivar
Jubilee 40.0 38.5 46.3 45.8 44.1 41.4 41.8 39.1 33.1
GH 1703 44.9 45.3 54.0 53.7 54.5 50.7 52.2 50.4 45.6
Significance *** *** *** *** *** *** *** *** ***
***,NSSignificant at 0.1% level and nonsignificant, respectively.
Table 13. Effects of total rate of applied N, proportion of N applied at planting, split
applications of N, and N source on SPAD chlorophyll measurements in 'Jubilee' sweet corn, NWREC, 1998.
Total N N at planting Date of SPAD measurement
applied, lb/acre lb/acre 16 July 22 July 27 July 3 Aug. 10 Aug. 17 Aug. 24 Aug. 1 Sep. 15 Sep.
0 0 39.9 37.4 42.5 41.7 37.8 33.9 29.9 29.2 20.4
60 40z 40.9 39.8 46.7 45.7 43.9 40.0 40.7 35.3 31.0
120 40y 38.5 37.7 46.1 45.2 43.9 42.6 44.6 41.7 37.7
180 40x 40.3 38.7 45.5 45.9 42.2 42.3 43.9 42.7 38.3
180 80w 39.2 39.5 46.9 45.6 42.5 41.6 43.7 42.8 38.4
180 120v 39.8 40.5 48.3 47.7 44.3 41.5 41.9 41.5 37.5
180 180 37.6 41.1 48.6 46.6 43.8 42.0 42.8 40.5 36.8
LSD (0.05) NS 2.9 2.6 3.0 4.1 4.6 5.3 4.7 4.1
zSidedress N source: Greenfeed 27-0-0, 10 lb/acre, each, on 22 July and 12 August.
ySidedress N source: Greenfeed 27-0-0 and urea. 20 lb/acre each of Greenfeed and urea applied on 22
July, 20 lb/acre as Greenfeed on 29 July and 12 August.
xSidedress N source: urea, applied at 60 lb/acre on 22 July, 40 lb/acre on 29 July, and 40 lb/acre on
12 August.
wSidedress N source: urea, applied at 40 lb/acre on 22 July, 40 lb/acre on 29 July, and 20 lb/acre on
12 August.
vSidedress N source: urea, applied at 20 lb/acre, each, on 22 July, 29 July, and 12 August.
Table 14. Sweet corn yield and soil and stalk nitrate-N concentrations as
affected by N rate, on-farm PSNT trial, 1997.
N fertilizer Soil nitrate-N Stalk Corn
Total rate Sidedress Preplant PSNT Harvest nitrate-N yield
Grower ------lb/acre------- --------------ppm---------------------- tons/acre
A 130 70 9.1 13.5 4.9 3010 9.48
A 130 70 9.1 10.9 4.5 10000 9.09
A 130 70 9.1 8.8 4.5 9010 8.84
A 200 140 9.1 13.1 11.0 9550 9.53
A 200 140 9.1 10.0 11.7 11180 9.05
A 200 140 9.1 12.2 8.9 11880 9.42
B 135 85 22.0 33.3 20.1 13080 9.24
B 230 190 22.0 32.6 34.1 12120 9.31
C 116 64 38.2 35.4 8.9 2398 8.96
C 180 123 8.2 38.8 19.0 7129 8.89
D 140 80 7.3 15.6 7.5 8130 7.17
D 220 160 7.3 13.1 7.3 6250 6.97
E 140 88 10.4 22.9 8.3 8545 10.30
E 140 88 10.4 23.5 8.6 5801 8.94
E 140 88 10.4 25.4 14.0 6935 8.95
E 200 148 10.4 23.2 21.6 7501 10.59
E 200 148 10.4 26.7 21.5 7161 9.63
E 200 148 10.4 27.0 12.7 7143 9.35
F 107 56 13.8 23.6 6.5 4926 10.48
F 107 56 13.8 22.9 7.2 4035 10.28
F 107 56 13.8 22.5 8.5 3144 10.07
F 145 94 13.8 21.2 13.2 4003 10.72
F 145 94 13.8 23.3 5.9 2904 10.08
F 145 94 13.8 21.1 13.2 2983 10.67
G 120 80 14.4 22.5 6.4 5372 10.65
G 200 160 14.4 19.9 2.5 10275 12.10
H 130 64 8.5 15.9 1.7 223 11.34
H 195 129 8.5 15.0 5.3 1574 11.83
I 140 90 1.4 12.2 12.1 7440 8.08
I 227 177 1.4 24.7 24.7 10950 9.66
Table 15. Sidedress N rate for sweet
corn based on 19951996 PSNT trials.
PSNT Sidedress N
ppm lb/acre
<18 150
18 to 22 100
>22 50 to 80
Table 16. Fertilizer, PSNT, yield, and soil and corn stalk nitrate-N concentrations in grower
fields, 1998.
Grower N at PSNT PSNT N applied PSNT plus Yield Relative Nitrate at harvest
planting sidedress sidedress N yield Stalk Soil
lb/acre ppm lb/acre lb/acre lb/acre tons/acre % ppm ppm
A field 40 43 155 90 245 10.52 -- 20
plot 40 35 125 45 170 10.82 102.9 -- 19
B field 66 27 97 116 213 13.47 12916 17
plot 66 27 97 88 185 13.98 103.8 11729 19
C field 40 32 115 40 155 11.56 11637 22
plot 40 32 115 25 140 10.00 86.5 11921 41
D field 47 15 53 155 208 11.22 3014 11
plot 47 17 60 120 180 10.58 94.3 2370 12
E field 50 25 88 160 248 10.05 7306 48
plot 50 24 85 80 165 9.28 92.3 7015 20
F field 39 39 142 120 262 11.72 9990 37
plot 39 35 126 48 174 11.64 99.3 10890 41
G field 45 33 117 160 277 7.55 2461 19
plot 45 37 133 0 133 7.24 95.9 4047 52
H field 50 22 79 150 229 10.44 8197 17
plot 50 21 76 100 176 9.67 92.6 6637 10
I field 30 44 160 75 235 8.63 8923 67
plot 30 43 155 50 205 8.48 98.3 8117 23
Effect of Winter Cover Crops on Vegetable Crop Yield and Leaching of Nitrate
Cooperators: Dr. John Selker, Dept. of Bioresources Engineering, and
Dr. Richard Dick, Dept. of Crop and Soil Sciences, Oregon State University
Introduction
Nitrate pollution of groundwater from the application of high rates of N fertilizers to vegetable crops is a concern
in the Willamette Valley. Excess N not taken up by the crop remains in the soil and can be leached to groundwater
during the wet winter months. Such concerns led us to initiate in 1990 a study of the cycling and availability of
N in vegetable cropping systems. These are the eighth and ninth 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 comparison to a winter-fallow control. In 1994, sweet corn
was grown on these long-term rotation plots at NWREC and fertilized at three rates of N. Following harvest the
plots were seeded to cereal rye or a mixture of cereal rye and Austrian winter pea. In 1995, broccoli was grown
on these plots at three rates of N to determine the cover-crop contribution to broccoli yield and N uptake.
Following harvest, the plots were again disked, harrowed, and seeded (drilled) to triticale or a mixture of triticale
and Austrian winter pea. In addition, other plots in both years were overseeded (relay intercropped) to cereal rye,
triticale, or red clover about one month after sweet corn or broccoli emergence. These cover crops were permitted
to grow through the winter. In 1996, sweet corn was again grown on the plots and fertilized with three rates of
applied N.
In autumn 1993, passive capillary wick samplers were installed beneath the winter-fallowed plots and fall-planted
cereal rye (later triticale) plots. All three N rates were also represented. The samplers have allowed us to collect
leachate on a continuous basis and determine both the nitrate concentration of the leachate as well as the total nitrate
loss on an area basis. Details of the installation and use of the capillary wick samplers can be found in Brandi-Dohrn
et al., 1997.
Objectives in 1997 and 1998 were 1) to evaluate effects of several winter cover crops, including fall-seeded
and overseeded triticale, fall-seeded triticale plus winter pea, and overseeded red clover on yield and quality of
broccoli (1997) and sweet corn (1998) at three rates of N and 2) to evaluate the effect of these cover crops and the
N applied to the vegetable crops in 1996 and 1997 on the amount of nitrate leached below the root zone.
Methods, Broccoli, 1997
During winter, the plots had been fallow or in the cover crops listed under Objectives. The cover crops
had been overseeded into standing sweet corn in July 1996 or were broadcast-seeded and scratched into the soil in
early October, 1996. While we did not consider this an outstanding cover crop in terms of biomass accumulation,
the plots seeded to cover crops in October had significantly (P=0.01) greater ground cover than did fallow plots, when
measured in January (Table 1).
'Packman' broccoli was seeded on 3 July in rows 30 inches apart. Two previous seedings of 'Pirate' failed
because of inadequate stands. Plot size was 600 square feet. Nitrogen rates were 0, 125, and 250 pounds/acre, with
half the N applied just after seeding, and the remainder applied 5 weeks after seeding. At this time, the appropriate
plots were overseeded to 'Celia' triticale or 'Kenland' red clover in preparation for the 1998 experiments. Harvest
was on 16 September.
Methods, Sweet Corn, 1998
During winter the plots had been fallow or in the cover crops listed under Objectives. The cover crops
had been overseeded into the standing broccoli crop in July 1997 or were broadcast-seeded and harrowed into the
soil in early October, 1997. 'Jubilee' sweet corn was seeded on 1 June in rows 30 inches apart. The stand was
thinned to 67 inches between plants in the row. Plot size was 600 square feet. Nitrogen rates were 0, 50, and 200
lb/acre, with half the N applied just after seeding and the remainder applied 5 weeks after seeding. At this time the
appropriate plots were overseeded to common cereal rye or 'Kenland' red clover in preparation for the 1999
experiments. Harvest was on 9 September.
Results, N Rate and Cover Crop on Broccoli Yield, 1997
Both yield and mean head weight tended to decline following an overseeded triticale cover crop, regardless
of N rate (Table 2). This result is consistent with those dating back to 1990 for both triticale and cereal rye cover
crops (Hemphill, 1993, 1995, 1997). The overseeded clover cover crop tended to increase yield but the effect was
not statistically significant. However, mean head weight was significantly increased with the overseeded clover.
Yield with fall-seeded triticale tended to be higher than following fallow, and mean head weight was significantly
improved by the fall-seeded triticale. In past years, fall-seeded cereal cover crops have tended to depress yield.
Results from this year may indicate that soil available N content has increased sufficiently with continuous cover-
cropping to provide some yield boost to the following vegetable crop. Initial pea stand in the triticale/pea cover
crop was adequate, but the stand was lost during the late winter. Consequently, yield did not increase with this cover
crop over that obtained with triticale alone. There was no response to the rate of N applied when averaged over cover
crop treatments. The highest-yielding treatment combination was the intermediate rate of applied N following the
fall-seeded triticale/pea cover, with 5.2 tons/acre (Figure 1). Largest mean head size was obtained with the
combination of fall-seeded triticale and no applied N (Figure 2). Lowest yield and head weight were with
overseeded triticale and no applied N.
Winter Cover Crop on Nitrate Leaching, 1996-1997
A fall-seeded triticale cover crop significantly reduced the nitrate concentration of leachate reaching the 4-
foot depth in the soil profile following the 1996 corn crop (Figure 3). The difference in nitrate-N concentration in
the leachate was small during the high-rainfall months of December and January, but the amount of water percolating
past the root zone was also reduced by the cover crop, resulting in a dramatic effect on the amount of nitrate being
leached (Figure 4). By April, the amount of nitrate lost from the root zone was 33 pounds N/acre for the fallow
plots versus 18 pounds/acre for the cover crop plots at the high rate of N applied to the previous vegetable crop. This is very
consistent with results obtained in the winters of 199293 through 199596 (Hemphill, 1995, and 1997). Over the
five winters that we have obtained data from the passive capillary lysimeters, the reduction in mass of nitrate leached
has averaged 45 percent. This demonstrates the ability of even a relatively sparse cover crop to significantly improve
ground and surface water quality.
Cover Crop Yield and N Uptake, 19971998
While the cover crops, again, were rather sparse and slow-growing, all plots seeded to cover crops had
significantly (P=0.01) greater ground cover than did fallow plots when measured in February (Table 3). In addition, most
of the biomass on fallowed plots was attributable to annual bluegrass, which is shallow-rooted and does not recover
much N. Cover-crop biomass accumulation and nitrogen uptake were below average for these plots, but some
interesting trends emerged. The yield of overseeded crops was generally larger than for the fall-seeded crops, a
reversal of the previous trend (Table 4). This may have been due to the late planting date of the fall-seeded crops,
saturated soil during much of the winter, and a soil pH which was getting lower than desired. Except for the
overseeded red clover, cover-crop biomass and N accumulation did tend to increase with increasing rate of N
applied to the preceding broccoli crop.
N Rate and Cover Crop on Sweet Corn Yield, 1998
Although not statistically significant, yield, mean ear weight, ear length, and tipfill tended to decline
following an overseeded triticale cover crop, regardless of N rate (Table 5). This result was consistent with those
dating back to 1990 for both triticale and cereal rye cover crops. In past years, fall-seeded cereal cover crops have
also tended to depress yield, but this was not the case in 1998, perhaps because of the poor stand and growth of the
fall-seeded triticale. Initial pea stand in the triticale/pea cover was adequate, but the stand was lost during the late
winter because of a root disease. Therefore, yield did not increase with this cover crop over that obtained with triticale
alone. The response to rate of N applied was normal when averaged over cover crop treatments. The highest-yielding
treatment combination (10.0 tons/acre) was the high rate of applied N following the overseeded clover cover,
indicating some N contribution from the clover, despite the relatively low N uptake (Table 3) of this cover. This
treatment combination also produced the largest mean ear size. Lowest yield and mean ear weight was with
overseeded triticale and no applied N.
Winter Cover Crop on Nitrate Leaching, 1997-1998
Averaged over rates of N applied to the preceding broccoli crop, a fall-seeded triticale cover crop
significantly (P=0.05) reduced the nitrate concentration of leachate reaching the 4-foot depth in the soil profile for two
sampling dates and tended to do so for all but the last sampling date (Table 6). The difference in nitrate-N
concentration in the leachate between fallow and covered plots was larger during the fall and early winter months
than in late winter. In fact, at the high rate of applied N, but not at the zero and intermediate rates, nitrate
concentrations were higher in leachate collected beneath the triticale cover crop than below fallow plots for the last
four sampling dates (Figures. 57). This is a reversal of the trends seen in previous years (Hemphill, 1997). In
past years, nitrate concentrations of collected leachate have varied up and down during the rainy season but in 1997
1998, the concentrations tended to increase steadily during the winter. The reason for this is not known, but perhaps
significant mineralization of organic N was occurring during the mild winter.
Summary
Consistent with past results, winter cover crops reduced leaching of nitrate from the root zone in the winter
of 19961997. Leguminous cover crops made N available to the following vegetable crop, but a cover crop consisting
only of an overseeded winter grain tended to depress yield of the following broccoli crop. In contrast to previous
years, a fall-seeded triticale cover crop tended to increase broccoli yield.
In the winter of 19971998, a triticale cover crop reduced nitrate concentrations in leachate consistently at
the zero and intermediate rates of applied N, but not at the high rate of N. This is in contrast to results for the
previous five winters. A clover cover crop made N available to the succeeding sweet corn crop in 1998, but a cover
crop consisting only of an overseeded winter grain tended to depress yield of the following sweet corn crop.
Literature Cited
Brandi-Dohrn, F.M., R.P. Dick, M. Hess, S.M. Kauffman, D.D. Hemphill, Jr., and J.S. Selker. 1997. Nitrate
leaching under a cereal rye cover crop. J. Environ. Qual. 26:181188.
Hemphill, D.D., Jr. 1993. Vegetable research at the North Willamette Research and Extension Center, 19911992.
Oregon Agric. Expt. Sta. Spec. Rep. No. 908.
Hemphill, D.D., Jr. 1995. Vegetable research at the North Willamette Research and Extension Center, 19931994.
Oregon Agric. Expt. Sta. Spec. Rep. No. 944.
Hemphill, D.D., Jr. 1997. Vegetable research at the North Willamette Research and Extension Center, 19951996.
Oregon Agric. Expt. Sta. Spec. Rep. No. 975.
Table 1. Effect of cover crop on percentage of ground covered, as
determined by the string method, 6 January, 1997.
Cover crop % Triticale % Legume % Weeds % Total
Fallow 0 1 34 35
Overseeded triticale 12 0 30 42
Overseeded clover 0 21 25 46
Fall-seeded triticale 36 1 30 67
Fall-seeded triticale/pea 20 29 18 66
LSD (0.05) 14 7 15 17
Table 2. Main effects of preceding cover crop and rate of
applied N on yield of broccoli, NWREC, 1997.
Treatment Yield Mean head wt.
tons/acre (g)
Cover crop (avg. over N rates)
Fallow 3.5 349
Overseeded triticale 2.6 236
Overseeded clover 4.3 407
Fall-seeded triticale 4.1 466
Fall-seeded triticale/pea 4.4 408
LSD (0.05) NS 22
N rate, lb/acre (avg. over covers)
0 3.8 383
125 4.0 375
250 3.9 361
LSD (0.05) NS NS
Table 3. Effect of cover crop on percentage of ground covered, as
determined by the string method, 4 February, 1998.
Cover crop % Triticale % Legume % Weeds % Total
Fallow 0 0 34 34
Overseeded triticale 28 9 51 88
Overseeded clover 0 28 68 96
Fall-seeded triticale 26 2 25 53
Fall-seeded triticale/pea 34 19 21 74
LSD (0.05) 12 9 12 10
Table 4. Interaction of cover crop and rate of N applied to preceding
broccoli crop on cover crop biomass and N uptake, NWREC, 1998.
Cover crop N rate Cover dry biomass N uptake
----------------lb/acre----------------
Overseeded triticale 0 1712 26
125 3090 46
250 3759 58
Overseeded clover 0 1893 46
125 2141 37
250 2249 38
Fall-seeded triticale 0 796 17
125 743 16
250 1128 28
Fall-seeded triticale/pea 0 716 13
125 607 10
250 1054 20
LSD (0.05) 700 14
Table 5. Main effects of preceding cover crop and rate of applied N on
yield of sweet corn, NWREC, 1998.
Treatment Yield Mean ear wt. Ear length Tipfill
tons/acre (g) (inches)
Cover crop (avg. over N rates)
Fallow 7.5 203 8.2 2.1
Overseeded triticale 5.6 164 8.0 1.6
Overseeded clover 7.3 210 8.1 1.9
Fall-seeded triticale 7.5 210 8.1 2.3
Fall-seeded triticale/pea 7.0 198 8.1 2.2
LSD (0.05) NS NS NS NS
N rate, lb/acre (avg. over covers)
0 4.5 140 7.3 1.2
125 7.6 206 8.2 2.0
250 8.9 245 8.8 2.9
LSD (0.05) 0.8 20 0.2 0.3
Table 6. Main effects of rate of N applied to 1997 broccoli crop and a
triticale cover crop on nitrate concentration of leachate collected during
the 19971998 rainy season.
Collection date
Nov. 5 Dec. 3 Dec. 19 Jan. 9 Jan. 21 Feb. 13 Mar. 24
-----------------------ppm Nitrate-N-------------------------
Cover crop
Triticale 3 4 6 7 10 15 20
None 6 7 9 9 12 16 18
Significance NS ** * NS NS NS NS
N rate, lb/acre
0 3 3 3 4 4 6 7
125 4 4 6 6 9 13 16
250 8 10 13 15 19 28 34
Significance * ** ** ** ** ** **
**,*,NSSignificant differences at 1% and 5% probability levels, and no
significant differences, respectively.
Impact of Cover Crops on Mold Incidence in Snapbeans
COOPERATOR: Dr. Mary Powelson, Dept. of Botany & Plant Pathology, Oregon State University
Introduction
Limited fungicide options and the tentative state of continued registration of vinclozolin for snapbeans require
development of additional management strategies for suppression of white mold (Sclerotinia sclerotiorum). One
encouraging technique for suppression is to eliminate or reduce spring tillage and leave a straw mulch derived from
a cover crop. In 1993, weed emergence was greatly reduced and white mold incidence was reduced nearly 98 percent
when beans were planted through a barley cover-crop residue. Snapbean yields were not affected by the cover-crop
residue. This mold reduction may have been due to the presence of the barley residue acting as a physical barrier
between the white mold apothecia and the bean canopy. In addition, several compounds that have antifungal
properties have been isolated from both cereal and cole crop residues. Crop residues may also influence the
survivability of sclerotia by stimulating soil microbes which act as predators of sclerotia. Alternatively, actively
growing cover crops may induce germination of the sclerotia before bean planting and reduce survivability of the
sclerotia.
Integrated management of snapbean diseases depends on the availability, understanding, and potential
application of several concurrent strategies. Both white and grey mold are diseases that must
be effectively controlled. Our past research has indicated that both white and grey mold development may be
affected by changes in tillage systems, vegetative management, and the preceding cover crop or cash crop.
The objective for 1997 was to evaluate the impact of a cover crop and the preceding vegetable crop on the
incidence of white mold and grey mold in snapbean.
Methods
A field was divided into 15 ´ 60-foot plots of 'Jubilee' sweet corn, 'Gem' broccoli, or summer fallow during summer 1996.
White mold sclerotia were buried in mesh bags in each plot. Sclerotia survival was extremely low. In the late
summer of 1996, these plots were flailed and disked and then split by a winter fallow treatment or a cover crop
of triticale plus Austrian winter pea. Treatment combinations were replicated five times. In late May 1997, after taking
samples for biomass, the cover crops were mowed and disked several times, and the plots were seeded to Oregon 91 beans, with three rows/5-foot bed. No
herbicides were used. A total of 160 pounds N/acre was applied to the bean crop, which along with the high
seeding rate, created favorable conditions for development of white mold. Laboratory-grown sclerotia were applied
to 9-square-foot sections at the center of each plot. White and grey mold ratings were made on 18 September, and
plots were harvested on 24 September, 1997.
Results
Greater cover-crop/weed biomass accumulated on plots which had been in broccoli or summer fallow
compared to those which had been in sweet corn (Table 1). Although herbicide residue may have played a role in
this effect, the most likely explanation is that corn residue interfered in the drilling of the cover crop. Sweet corn
dry biomass was 6.3 tons/acre compared to 2.2 tons/acre for broccoli. Bean yield and number of plants/plot did
not vary significantly with previous crop/cover crop.
The number of plants with white mold also did not vary with
treatment although there was a tendency for higher white mold incidence in plots planted into cover crop residue.
The number of infected pods recovered per plot also tended to be higher following a cover crop. The previous vegetable
crop had no influence on white mold. Expressed as a percentage of the total number of plants/plot, treatments did
not affect white mold. The cover-crop residue obviously did not provide a barrier between sclerotia on the soil
surface and the bean plants. This may be because the sclerotia were applied after planting and may not have
remained in or on the residue. It is also doubtful that the white mold incidence was related to sclerotia applied to
the plots: incidence did not appear to be higher in the portion of the plot that had sclerotia applied. The high plant
density, rank growth, and over-irrigation probably caused the high incidence of white mold in this study. A straw
residue on the surface might actually have favored white mold development by contributing to greater surface
moisture and humidity in the plant canopy.
The number of plants infected with grey mold was decreased in plots that had been in broccoli the previous
summer and tended to be increased in plots with cover crop residue. The number of infected pods per plot also
tended to decrease following broccoli and to increase following the cover crop. The percentage of plants affected
by grey mold was more than halved following broccoli.
Table 1. Main effect of previous vegetable crop and winter cover crop on yield,
white mold incidence, and grey mold incidence in snapbean, NWREC, 1997.
Treatment Cover dry Yield White mold incidence Grey mold incidence
mass, g/m2 tons/acre # plants % plants # pods # plants % plants #pods
________________________________________________________________________________________
1996 crop
Summer fallow 302 11.4 17.3 22.2 29.5 8.8 12.3 10.2
Sweet corn 180 13.1 19.5 29.2 22.1 8.3 12.3 9.4
Broccoli 245 11.3 19.5 28.2 20.9 3.9 5.4 4.7
Significance * NS NS NS NS * * NS
Cover crop
None (weeds) 89 12.0 14.6 20.3 19.1 5.5 8.4 6.3
Triticale/pea 362 11.8 23.2 32.7 29.3 8.5 11.6 9.9
Significance ** NS NS NS NS NS NS NS
**,*,NSSignificant at 1% and 5% levels, and non-significant, respectively.
Cultivar, N Rate, and Between-Row Spacing on Yield of Edamame
Cooperator: Dr. Carol A. Miles, Cooperative Extension, Washington State University
Introduction
Edamame or vegetable soybean (Glycine max [L.] Merrill) is a specialty soybean that is harvested as a
vegetable when the seeds are still immature. It is usually sold as pods or as whole harvested stems but occasionally
as shelled beans. The seeds are usually boiled in the pod, shelled out, and eaten as a snack, as a vegetable with
meals, or added to soups or confections. When eaten as a vegetable, the seeds are added to salads, stir-fried, or
combined into vegetable medleys. As a sweet, the beans are ground to a paste, sweetened, and used as a topping
for sticky rice. Most production and consumption is in China, Japan, Taiwan, and Korea. Most production
research, variety development, and production guides originate in Taiwan and Japan.
Washington State University has conducted variety trials and is involved in a breeding program for
improved varieties of edamame for the Pacific Northwest. Very little information on production techniques for the coastal areas
of the Northwest is available. Information derived from the Asian literature is often an inadequate guide to
production in our area. For example, the Japanese literature recommends application of 35 to 55 pounds N/acre
in addition to 8 tons/acre of well-decomposed animal-waste compost which provides an unknown amount of available
nutrients (O'Rourke, 1994). Recommendations for plant populations are not consistent. If this crop is to be grown
in the Pacific Northwest, which appears to have a good climate for production of high yields and quality, we will
need to develop recommendations based on the soil types and cultural methods likely to be used in this region. The
purpose of this trial was to investigate the effects of two, between-row spacings and three rates of applied N on three
edamame cultivars previously determined by Carol Miles to have the potential for high yield west of the Cascades.
Methods
Non-inoculated 'Butterbeans', 'Shironomai', and 'White Lion' edamame were seeded to a winter-fallowed
Willamette silt loam, pH 5.8, at the NWREC on 3 June. Plot preparation included plowing, disking, a broadcast
and incorporated application of triple superphosphate and sulfate of potash, each at 200 pounds/acre, and harrowing to form
a seedbed. The three cultivars were seeded on 20 and 30-inch rows, with 3-inch in-row spacing. Metolachlor, 1.5
pounds/acre, was applied after planting for weed control. Escaped weeds, mostly sowthistle, prickly lettuce, groundsel,
and red-root pigweed, were controlled by hand-hoeing. Nitrogen rates applied were 0, 36, and 72 pounds/acre as
ammonium nitrate, with half the N applied one week after seeding and the remainder on 8 July, near first bloom.
The experimental design was a randomized complete block split plot, with cultivar ´ spacing combinations as main
plots and N rates as subplots. Subplot size was 15 ´ 20 feet. Plots were sprinkler irrigated as necessary, usually
approximately one inch/week. Yields were estimated by harvest of a 10-foot section of one of the centermost rows
of each subplot. Pods were stripped by hand, separated into categories of two or more beans/pod, one bean/pod,
and unmarketable (mostly lacking developed beans). Cultivars differed in maturity with 'White Lion' harvested
on 8 September, 'Shironomai' on 16 September, and 'Butterbeans' on 21 September.
Results
Cultivar. The cultivars differed significantly in plant development (Table 1). Stand of 'Shironomai' was nearly 30 percent
less than that of 'Butterbeans' or 'White Lion'. 'Butterbeans' and 'White Lion' produced plants from about 63 percent
of the planted seed, while the establishment rate for 'Shironomai' was only 44 percent. 'White Lion' produced a slightly
shorter and narrower canopy (measured 30 July) and bloomed earlier than the other two cultivars. Canopy height
of 'White Lion' did not increase with increasing rate of N to the same extent as for the other cultivars (Table 2).
Despite its relatively poor stand, 'Shironomai' produced a higher yield/acre, higher yield of large pods (2
or more beans), and larger pod weight/plant than did the other cultivars (Table 3). A greater pod weight/plant more
than offset the reduced stand. 'Shironomai' also tended to have the heaviest pods. 'White Lion' produced the
smallest total and marketable yield.
Although there were significant interactions of cultivar and N rate affecting total pod weight/plant and
marketable pod weight/plant (Table 4), 'Shironomai' was the highest yielding cultivar at each N rate. The
interaction of between-row spacing and cultivar also affected total and marketable pod weight/plant (Table 5) but
'Shironomai' was the highest yielding at both spacings.
Spacing. The 20-inch spacing produced a greater stand per meter of row than did the 30-inch spacing (Table 1).
This is because one of the two planters per bed was not properly covering seed and stand was reduced on this row
for the 30-inch spacing. With 20-inch spacing, only one of three planters did not adequately cover the seed, so
mean stand was greater. The main effect of spacing on canopy development on 30 July and on bloom was not
significant. However, spacing and N rate interacted to affect bloom (Table 6). Bloom was advanced at the lowest
rate of N for 20-inch but not for 30-inch spacing.
The 30-inch spacing produced a higher yield/plot (per meter of row) but a lower yield on an area basis
(Table 3). Mean weight of individual pods was higher at 30-inch spacing as was total and marketable pod
weight/plant. But the nearly 50 percent higher number of plants/unit area at the 20-inch spacing offset the greater per-
plant yield obtained with the wider spacing.
N Rate. Rate of N had no effect on stand, but canopy height and width increased linearly with increasing N (Table
1). Increasing N also delayed flowering.
Total weight harvested/plot, yield/unit area, weight of marketable pods/plot, mean pod weight/plant, and
mean marketable pod weight/plant increased linearly with increasing rate of N. However, mean weight of the
individual pod did not increase from the intermediate to the highest rate of N. The number of beans/pod, mean bean
weight, and number of plants harvested per plot did not vary with N rate (Table 3).
Although the main effect of N rate on total and marketable pod weight/plant was a linear increase with
increasing rate of N, not all cultivars were consistent in their response to N (Table 4).
There were no 3-way interactions of N rate, spacing, and cultivar affecting plant development or yield.
Conclusions and Discussion
For the purposes of this experiment, marketable yield was defined as those pods acceptable for fresh
marketing in-pod. However, pods with only one bean may be marketable as shelled green edamame or as seed for
planting. Yields of both one-bean pods and pods with 2 or more beans responded similarly to treatment.
Given that complete canopy closure was not obtained with the 30-inch spacing, that mean bean weight was
not affected by spacing, and that mean pod weight was only slightly lower at the 20-inch spacing, 20 inches appears
to be a reasonable between-row spacing for these cultivars on this Willamette soil. Although mean pod weight,
number of beans/pod, and mean bean weight did not increase between the intermediate and high rates of N,
yield/plant and per unit area did increase between the intermediate and high rates, indicating that 72 pounds/acre may not
be sufficient for maximum production in a situation where the seed was not inoculated, the soil had not recently been
used for production of legumes, and there was not a history of application of manures or composts. Although not
quantified, we noticed a strong tendency for a high proportion of the plants to have nodules at the zero N rate, but
not at other N rates. These plants, although dark green in color, did not exceed non-nodulated plants in size.
Inoculated seed might have responded differently to N rate.
Literature Cited
O'Rourke, A.D. 1994. Edamame: the vegetable soybean. p. 173199. In: A.D. O'Rourke (ed.). Understanding the Japanese
food and agrimarket, a multifaceted opportunity. Haworth Press, New York.
Table 1. Main effects of cultivar, between-row spacing, and rate of applied N
on stand, plant height and width, and flower development in edamame, NWREC, 1998.
Seedlingsz/ Canopy heighty Canopy widthy Plants in bloom
6 m inches inches 23 July 30 July 6 Aug.
Cultivar ----------%----------
Butterbeans 49 19 17 0 32 96
Shironomai 35 19 17 26 15 97
White Lion 50 17 15 0 73 99
Significance *** *** *** *** *** NS
Spacing
20 inches 48 18 16 9 44 98
30 inches 42 18 17 8 35 98
Significance *** NS NS NS NS NS
N rate, lb/acre
0 45 17 15 12 52 99
36 44 18 17 7 35 98
72 45 19 18 8 32 96
Significance NS *** *** NS *** NS
***,NSSignificant at 0.1% level and nonsignificant, respectively.
zCounts made 18 June.
yMeasured 30 July.
Table 2. Interaction of cultivar and rate of applied N, averaged
over two spacings, on canopy height of edamame, NWREC, 1998.
Cultivar N rate, lb/acre Canopy height, inches
Butterbeans 0 16.1
36 19.5
72 19.9
Shironomai 0 17.9
36 18.9
72 19.4
White Lion 0 16.4
36 16.5
72 17.0
LSD, Significance 1.0***
***Significant at 0.1% level of probability.
Table 3. Main effects of cultivar, between-row spacing, and rate of applied N fertilizer on edamame yields,
NWREC, 1998.
Total wt. Unfilled 1 bean/ 2+ beans/ Wt. 100 No. of Mean No. of Pod wt./ Marketable
g/ tons/ pods pod pod pods beans/ bean wt. plants/ plant pods/plant
plot acre g/plot g/plot g/plot g 25 pods g 3 m g g
Cultivar
Butterbeans 1353 3.1 56 433 864 259 57 0.60 26.5 53 34
Shironomai 1551 3.6 137 431 974 278 54 0.52 17.7 91 58
White Lion 1136 2.6 56 340 718 251 NR NR 25.0 46 29
Significance *** *** *** ** *** NS * * *** *** ***
Spacing
20 inches 1154 3.3 60 338 745 249 56 0.55 22.1 54 35
30 inches 1539 2.9 106 464 958 276 56 0.58 24.0 72 45
Significance *** ** *** *** *** * NS NS NS *** **
N Rate, lb/acre
0 1101 2.5 42 325 726 251 57 0.55 21.8 53 35
36 1400 3.2 86 433 874 269 55 0.57 24.5 65 41
72 1539 3.5 120 446 956 269 56 0.56 22.9 71 45
Significance *** *** ** *** ** * NS NS NS ** *
*,**,***,NSSignificant at 5, 1, and 0.1% probability level, and non-significant, respectively.
Table 4. Interaction of rate of applied N and cultivar, averaged
over two spacings, on mean pod weight per edamame plant, NWREC, 1998.
Applied N, lb/acre Cultivar Total pod wt./plant Marketable pod wt./plant
---------------------g-----------------------
0 Butterbeans 51 36
Shironomai 70 44
White Lion 38 24
36 Butterbeans 44 27
Shironomai 105 65
White Lion 48 30
72 Butterbeans 63 38
Shironomai 100 63
White Lion 51 32
LSD, Significance 16* 11*
*Significant at 5% level.
Table 5. Interaction of between-row spacing and cultivar, averaged over three
rates of applied N, on the mean pod weight per edamame plant, NWREC, 1998.
Row spacing, inches Cultivar Total pod wt./plant Marketable pod wt./plant
---------------------g-----------------------
20 Butterbeans 47 31
Shironomai 72 45
White Lion 44 29
30 Butterbeans 59 37
Shironomai 111 70
White Lion 47 29
LSD, Significance 13** 9*
**,*Significant at 1 and 5% levels, respectively.
Table 6. Interaction of between-row spacing and rate of applied N, averaged
over three cultivars, on flower development of edamame, NWREC, 30 July, 1998.
Spacing, inches N rate, lb/acre Plants in bloom, %
20 0 64
36 33
72 35
30 0 39
36 37
72 29
LSD, Significance 15*
*Significant at 5% level.
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