CONTENTS
Introduction
Nitrogen Management in Sweet Corn
Effect of Winter Cover Crops on Vegetable Crop Yield and Leaching of
Nitrate
Cultivar, N Rate, Inoculation, and Row Spacing Affect Yield of Edamame
Evaluation of Precision Planting Techniques, Flail Topping, and Multi-Row Harvesters
for Table Beet Production
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 professor, Department of Bioresource Engineering, Oregon State University, Corvallis, OR 97331.
Dr. Carol Miles is extension specialist, Washington State University Research and Extension Center, 1919 NE 78th St., Vancouver, WA 98665.
Dr. N.S. Mansour is professor emeritus, Department of Horticulture, Oregon State University, Corvallis, OR 97331.
Dr. Daniel McGrath is associate professor of horticulture and area extension agent, Oregon State University Extension Service, 3180 Center St. NE, Salem, OR 97301.
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 is located in an area noted for the diversity of its agriculture and has 10 faculty members who serve the vegetable, small fruit, and nursery crops industries. 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 twelfth 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
Cooperator: Dr. John Hart
Introduction
Vegetable growers in the Willamette Valley use high rates of nitrogen fertilizers, often exceeding 250 lb actual N/acre/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 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 3-year survey of residual mineral N in grower fields indicate that residual N tends to be greatest following sweet corn crops. 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 meaningful 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 input of manure 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 evaluations of the PSNT from 1995 to 1998 (Hemphill 1997, 1999) resulted in a modification of the PSNT that appears applicable to sweet corn production on typical Willamette Valley soils. Starting in 1998, we turned our attention to the possibility that some sweet corn varieties of acceptable yield and quality might require less applied N than does the industry standard variety 'Jubilee.' This might lead to significant reductions in the cost and environmental impact of sweet corn production.
Methods, 1999
'Jubilee,' 'GH 1703,' and 'Supersweet Jubilee' sweet corn were seeded on May 25 on 30-inch rows. The plots had previously been fallow for 2 years. Total N rates of 0, 60, 120, 180, and 240 lb/acre were applied to establish five different levels of soil nitrate. Forty lb N/acre were applied at planting to all but the zero N treatments and the remaining N was applied to the appropriate plots on July 7 (Table 1). All N was applied as urea. Stands varied among varieties, with stand of 'Supersweet Jubilee' being particularly poor. Stands were thinned to at least 6 inches between plants (27,000 plants/acre) in early July. SPADŽ (Minolta Corp.) chlorophyll meter readings were taken on 10 intact leaves/plot at approximately weekly intervals starting on July 8 until harvest, which occurred on September 7. Plots were sampled for residual soil nitrate on September 15.
Methods, 2000
'Jubilee,' 'GH 1703', 'Supersweet Jubilee,' 'Bonus,' 'Legacy,' and 'Sprint' sweet corn were seeded on June 2 on 30-inch rows. The field was fallow in 1999 and had been used for production of edamame soybean in 1998. Total N rates of 80 and 160 lbs/acre were applied to establish two different levels of soil nitrate. Eighty lb N/acre was applied at planting and the remaining N was applied to the appropriate plots on July 18 (Table 2). All N was applied as urea. Stands varied among varieties, with stand of 'Supersweet Jubilee' again being particularly poor (Table 3). Stands of 'Jubilee,' 'Bonus,' and 'Legacy' were thinned to at least 6 inches between plants in early July. SPAD chlorophyll meter readings were taken on 10 intact leaves/plot at approximately weekly intervals starting on July 27 and continuing until harvest, which occurred on September 7. Plots were sampled for residual soil nitrate during the last week of September.
Results and Discussion, 1999
The highest yield of all varieties was obtained with 120 lb N/acre. Yields tended to decline at higher N rates (Tables 4 and 5). Most of our past trials have produced highest yields at 180-200 lb N/acre, but 120 lb N/acre also produced the highest yields in 1998. As in 1998, with the relatively late planting date, available N in the soil before planting may have been unusually high. This serves to reinforce the importance of the PSNT or other method for predicting sweet corn response to applied N, as high concentrations of available N are occasionally present in Willamette Valley soils, even after high-rainfall winters like those of 1997-1998 and 1998-1999.
Just as in 1998, averaged over all N rates, 'GH 1703' outyielded 'Jubilee' by 0.9 tons/acre (Table 4). However, the difference in yield between these varieties was even greater at the suboptimal rates of N (Table 5). At optimal and supraoptimal N rates, the two varieties did not differ significantly in yield (Table 5). Most of the yield difference at low N was due to differences in mean ear weight, but at zero N, 'GH 1703' also produced more harvestable ears. As in 1998, these two varieties also had a strikingly different appearance in the field. Leaves of 'GH 1703' were darker green and thicker and the color stayed a dark green until harvest, even at the zero rate of N.
Yield of 'Supersweet Jubilee' was much lower than that of the other two varieties, mainly because of poor stands. Ear size for 'Supersweet Jubilee' actually exceeded that of the other varieties, perhaps in part because of less competition among plants (Table 4). In addition to poor emergence, many plants of 'Supersweet Jubilee' failed to develop normally and remained stunted throughout the season.
The first SPAD reading occurred on the day after the second application of N, so all N rates produced about the same reading (Table 6). This was also true 1 week later. But by 2 weeks after N application was completed, differences were evident (Table 6, July 22). In 1998, SPAD readings for treatments receiving suboptimal N had started to decline 3-4 weeks before harvest. This was not the case in 1999 as the decline, averaged over all varieties, was not noted until the last 10 days before harvest (Table 4). SPAD readings for 'Jubilee' did, however, start to decline earlier, as in 1998 (Fig. 1). SPAD readings did not differ greatly between the optimal N rate (120 lb/acre) and higher rates of N (Table 6), indicating that the excess N did not produce greater leaf chlorophyll content or greater leaf N concentrations.
As in 1998, the darker green leaves of 'GH 1703' gave consistently higher SPAD readings than did 'Jubilee,' indicating greater chlorophyll content and, perhaps, greater efficiency in uptake of applied N (Table 6). However, the latter did not appear to be the case (see below). 'Supersweet Jubilee' started out with lower SPAD readings than the other two varieties, reflecting delayed development of plants during the cool June and early July weather. But late in the season, the plants were darker green than 'Jubilee' (Fig. 2.)
As in 1998, soil nitrate concentrations were elevated at time of harvest only for rates of applied N of 120 lb/acre or more (Tables 7 and 8). The residual nitrate-N level of about 20 lb/acre for 'Jubilee' and 40 lb/acre for 'GH 1703' in the surface foot of soil at the optimal N rate of 120 lb/acre is probably acceptable and likely not too much higher than at planting. However, at 180 and 240 lb N/acre, residual nitrate-N varied from 35 to 80 lb/acre. The economic and environmental cost of the use of excessive rates of applied N should be obvious from these data, which are very consistent with those obtained in 1998. Residual ammonium levels did not vary significantly with amount of N applied. Residual soil mineral N levels were not measured in the 'Supersweet Jubilee' plots as the poor stand would have resulted in uptake atypical of a good commercial planting.
We had hypothesized that 'GH 1703,' with its darker green leaves and higher yield potential at low rates of applied N, might leave less nitrate in the soil at harvest, at least at low rates of applied N. This did not, however, appear to be the case (Table 8). Although not statistically significant, 'GH 1703' plots tended to have higher residual nitrate levels.
We had hoped to generate a calibration curve that could be used to indicate N sufficiency at different times during the growing season. If this were still an industry dominated by one variety, this might be a feasible approach. But with several varieties being grown and given that other factors besides availability of N, such as moisture content and other nutrients, can affect leaf chlorophyll content, this approach has its drawbacks. At the very least, calibration curves would be needed for each variety.
We are now advocating the use of a highly fertilized reference strip in a sweet corn field. The remainder of the field could be fertilized according to PSNT or grower experience with that field. Additional fertilizer would be needed if the SPAD reading of the main portion of the field dropped below 97 percent of the reading obtained in the reference strip. For example, if the reference strip reads 55 units, and the rest of the field 53, the percentage would be 96.3 and additional fertilizer should be considered. If the crop is at silking, however, it is unlikely to have time to respond to the additional N. The SPAD reading also does not tell us how much N to add. In no case, however, should the additional application bring the total N applied to more than 200 lbs/acre. The SPAD meter might best be used in combination with the PSNT to ensure that tissue N levels remain adequate.
Results and Discussion, 2000
Averaged over all varieties, higher yield was obtained with 160 than with 80 lb N/acre (Table 3). Of the six varieties, 'Jubilee' had the highest yield, but not significantly higher than 'GH 1703.' Yield of 'Supersweet Jubilee' was lowest, attributable to poor stand. In 1998 and 1999, 'GH 1703' had outyielded 'Jubilee' by 0.9 tons/acre. But of most interest was that only 'Jubilee' and 'Legacy' responded significantly to the higher rate of applied N. This result is consistent with what we have seen with 'Supersweet Jubilee' and 'GH 1703' in previous years and indicates that not all sweet corn varieties require high rates of applied N.
Most of the yield difference between N rates was due to differences in mean ear weight. 'Jubilee' and 'Legacy' produced larger ears at the higher rate of N, but the other varieties had similar sized or even smaller ears at high N than at low N. As in 1998 and 1999, the varieties that did not respond to the higher rate of applied N had a strikingly different appearance in the field. Leaves were darker green and thicker, regardless of rate of applied N, and the color remained dark green until harvest, even at the zero rate of N.
The first SPAD reading occurred 1 week after the second application of N, so both N rates produced about the same reading (Table 10). But by 2 weeks after N application was completed, differences were evident (Table 10, 3 August). SPAD readings for 'Jubilee, 'Legacy,' and 'Sprint' varied with the rate of applied N while SPAD readings for the other varieties did not (Fig. 3). As the season progressed, differences in SPAD readings among N rates also occurred in 'Bonus.' The response of SPAD readings to the higher rate of N corresponded to a higher yield for 'Jubilee' and 'Legacy' but not for 'Bonus' and 'Sprint.'
As in 1998 and 1999, the darker green leaves of 'GH 1703' gave consistently higher SPAD readings than did 'Jubilee,' indicating greater chlorophyll content (Table 10). 'Sprint' also had higher SPAD readings than all other varieties except 'GH 1703' in 2000.
Soil nitrate and ammonium concentrations at time of harvest were higher at 160 than at 80 lb of applied N/acre and the varieties differed greatly in their effect on residual soil nitrate concentration (Tables 11 and 12). The amount of residual N appeared to be related to the stand of the six varieties rather than to any inherent difference in nitrate uptake capacity. The three varieties with optimal stands ('Jubilee,' 'Bonus,' 'Legacy') had very low levels of residual soil nitrate. Residual soil ammonium concentration did not vary significantly with variety (Table 11).
As in 1999, varieties with darker green leaves did not leave less nitrate in the soil at harvest (Table 12). Again, this may be related to the relatively poor stand of some of these varieties, but the results are consistent with those seen in 1999 when 'GH 1703' plots tended to have greater residual nitrate levels even with an optimal stand. If this trend is confirmed in future research, it will mean that one must be careful not to overfertilize these high-chlorophyll varieties.
Literature Cited
Heckman, J.R., and D. Prostak. 1992. Presidedress soil nitrate test (PSNT) recommendations for sweet corn. Rutgers Cooperative Extension and N.J. Agricultural Experiment Station FS 760, Rutgers University, New Brunswick, N.J..
Hemphill, D.D., Jr. 1997. Vegetable research at the North Willamette Research and Extension Center, 1995-1996. Oregon Agricultural Experiment Station Special Report No. 975, Oregon State University, Corvallis.
Hemphill, D.D., Jr. 1999. Vegetable research at the North Willamette Research and Extension Center, 1997-1998. Oregon Agricultural Experiment Station Special Report No. 1000, Oregon State University, Corvallis.
Marx, E. 1995. Evaluation of soil and plant analyses as components of a nitrogen monitoring program for silage corn. M.S. Thesis, Oregon State University, Corvallis.
Table 1. List of treatments in sweet corn
experiment, NWREC, 1999.
Trt. Variety Total N N at Sidedress
applied planting N
---------lb/acre-----------
1 Jubilee 0 0 0
2 GH 1703 0 0 0
3 SS Jubilee 0 0 0
4 Jubilee 60 40 20
5 GH 1703 60 40 20
6 SS Jubilee 60 40 20
7 Jubilee 120 40 80
8 GH 1703 120 40 80
9 SS Jubilee 120 40 80
10 Jubilee 180 40 140
11 GH 1703 180 40 140
12 SS Jubilee 180 40 140
13 Jubilee 240 40 200
14 GH 1703 240 40 200
15 SS Jubilee 240 40 200
Table 2. List of treatments in sweet corn
variety x N rate trial, NWREC, 2000.
Trt. Variety Total N N at Sidedress
applied planting N
---------lb/acre-----------
1 Jubilee 80 80 0
2 SS Jubilee 80 80 0
3 GH 1703 80 80 0
4 Bonus 80 80 0
5 Legacy 80 80 0
6 Sprint 80 80 0
7 Jubilee 160 80 80
8 SS Jubilee 160 80 80
9 GH 1703 160 80 80
10 Bonus 160 80 80
11 Legacy 160 80 80
12 Sprint 160 80 80____
Table 3. Main effects of rate of applied N and
cultivar on stand and yield of sweet corn, NWREC, 2000.___
Seedlings/ Yield No. of Mean ear
30 ft (tons/acre) ears/plot wt (g)
N rate (lb/acre)
80 58 7.6 45 242
160 59 8.9 50 255
Significance NS ** ** NS
Cultivar
Jubilee 70 9.5 53 251
SS Jubilee 18 6.7 35 270
GH 1703 46 9.4 49 274
Bonus 113 7.6 55 199
Legacy 74 8.5 54 226
Sprint 34 7.8 42 271
Significance *** * *** **
LSD (0.05) 8 1.5 6 40
***,**,*,NSSignificant at P = 0.1, 1.0, and 5.0 percent
levels and nonsignificant, respectively.
Table 4. Main effects of rate of applied N and
cultivar on yield of sweet corn, NWREC, 1999.___
Yield No. of Mean ear
(tons/acre) ears/plot wt (g)
N rate (lb/acre)
0 5.7 38 234
60 8.0 49 269
120 9.7 55 277
180 9.1 53 270
240 9.1 53 272
Significance *** *** *
Cultivar
Jubilee 8.3 54 239
GH 1703 9.2 53 271
SS Jubilee 7.3 41 279
Significance *** *** ***
LSD (0.05) 1.0 5 10
***,*,NSSignificant at P = 0.1 and 5.0 percent
levels, and nonsignificant, respectively.
Table 5. Interaction of rate of applied N and cultivar on
yield of sweet corn, NWREC, 1999.
Cultivar Yield No. of Mean ear
N rate (lb/acre) (tons/acre) ears/plot wt (g)
0 Jubilee 4.5 37 187
GH 1703 7.3 46 247
SS Jubilee 5.3 30 269
60 Jubilee 7.7 53 229
GH 1703 8.9 52 267
SS Jubilee 7.4 41 287
120 Jubilee 10.5 62 268
GH 1703 10.1 58 274
SS Jubilee 8.5 46 288
180 Jubilee 9.9 60 261
GH 1703 9.8 55 277
SS Jubilee 7.6 44 272
240 Jubilee 9.1 57 249
GH 1703 10.1 55 288
SS Jubilee 8.0 45 279
LSD (0.05) 1.7 8 42
Table 6. Main effects of rate of applied N and cultivar on SPAD chlorophyll
measurements in sweet corn, NWREC, 1999.______________________________________
Date of SPAD measurement
8 July 15 July 22 July 30 July 5 Aug. 12 Aug. 24 Aug. 1 Sept.
N rate (lb/acre)
0 32.1 35.0 36.8 37.3 39.3 41.2 41.5 44.4
60 34.2 37.0 40.2 43.3 48.2 51.1 49.5 48.8
120 32.8 35.4 41.3 44.9 48.9 53.2 53.0 53.4
180 32.8 35.8 41.8 45.9 50.8 53.5 54.7 54.3
240 31.7 34.5 42.1 45.0 50.4 53.3 54.1 55.4
Significance NS NS *** *** *** *** *** ***
Cultivar
Jubilee 32.3 35.2 37.6 38.7 42.9 44.6 42.7 42.1
GH 1703 36.1 39.9 45.1 48.1 53.1 56.7 58.1 59.2
SS Jubilee 29.7 31.5 38.7 43.0 46.5 50.1 50.9 52.6
LSD (0.05) 1.1 1.3 1.2 1.6 2.2 3.0 2.7 1.8
Significance *** *** *** *** *** *** *** ***_
***,NSSignificant at 0.1 percent level and nonsignificant, respectively.
Table 7. Main effects of rate of applied N and cultivar on post-
harvest soil nitrate and ammonium concentrations, NWREC, 1999.
Soil nitrate-N (ppm) Soil ammonium-N (ppm)
Cultivar
Jubilee 7.0 1.5
GH 1703 10.8 1.4
Significance NS NS
N Rate (lb/acre)
0 1.0 1.5
60 2.0 1.4
120 6.0 1.5
180 14.9 1.4
240 19.6 1.5
Significance *** NS
***,NSSignficant at 0.1 percent level and nonsignificant,
respectively.
Table 8. Interaction of rate of applied N and cultivar on post-harvest
soil nitrate and ammonium concentrations, NWREC, 1999.
Cultivar N rate (lb/acre) Soil nitrate-N (ppm) Soil ammonium-N (ppm)
Jubilee 0 0.7 1.3
60 1.1 1.3
120 4.4 1.7
180 9.4 1.6
240 19.3 1.7
GH 1703 0 1.5 1.6
60 2.8 1.5
120 11.8 1.3
180 20.4 1.3
240 19.9 1.0
LSD (0.05) 9.0 NS
Table 9. Interaction of rate of applied N and cultivar on
yield of sweet corn, NWREC, 2000.
N Rate Cultivar Yield No. of Mean ear
(lb/acre) (tons/acre) ears/plot wt (g)
80 Jubilee 7.8 51 217
160 11.1 56 286
80 SS Jubilee 6.4 33 272
160 7.1 38 269
80 GH 1703 9.1 46 282
160 9.7 52 267
80 Bonus 7.5 54 197
160 7.7 55 201
80 Legacy 7.4 49 215
160 9.7 59 237
80 Sprint 7.3 39 269
160 8.3 44 272
LSD (0.05) 2.2 9 53
Table 10. Main effects of rate of applied N and cultivar on SPAD
chlorophyll measurements in sweet corn, NWREC, 2000._______________
Date of SPAD measurement
27 July 3 Aug. 10 Aug. 17 Aug. 24 Aug. 1 Sept.
N rate (lb/acre)
80 45.7 44.9 46.4 40.6 40.5 40.1
160 46.2 47.3 48.8 44.7 45.4 45.5
Significance NS * * ** *** ***
Cultivar
Jubilee 44.6 42.6 42.9 38.4 37.8 37.5
SS Jubilee 42.6 43.6 46.6 43.8 44.0 42.6
GH 1703 50.8 53.8 57.2 50.5 52.3 53.8
Bonus 43.4 41.5 41.1 37.3 35.1 36.1
Legacy 43.1 42.4 43.3 36.4 36.4 35.7
Sprint 51.1 52.9 54.8 49.6 52.0 50.9
LSD (0.05) 2.5 1.9 2.8 3.5 4.1 4.6
Significance *** *** *** *** *** ***
***,**,*,NSSignificant at 0.1, 1.0, and 5.0 percent level, and
nonsignificant, respectively.
Table 11. Main effects of rate of applied N and cultivar on post-
harvest soil nitrate and ammonium concentrations, NWREC, 2000.
Soil nitrate-N (ppm) Soil ammonium-N (ppm)
Cultivar
Jubilee 2.2 1.9
SS Jubilee 11.8 3.0
GH 1703 16.2 2.5
Bonus 4.9 5.0
Legacy 3.5 2.9
Sprint 21.6 6.6
Significance *** NS
N Rate (lb/acre)
60 6.4 2.3
180 13.7 5.0
Significance ** **
***,**,NSSignficant at P = 0.1 and 1.0 percent,
and nonsignificant, respectively.
Table 12. Interaction of rate of applied N and cultivar on post-harvest
soil nitrate and ammonium concentrations, NWREC, 2000.
Cultivar N rate (lb/acre) Soil nitrate-N (ppm) Soil ammonium-N (ppm)
Jubilee 80 1.6 1.8
160 2.8 2.0
SS Jubilee 80 8.4 1.7
160 15.2 4.3
GH 1703 80 6.0 1.7
160 26.4 3.4
Bonus 80 3.7 3.4
160 6.0 6.6
Legacy 80 2.6 2.2
160 4.6 3.7
Sprint 80 16.1 3.0
160 27.1 10.2
LSD (0.05) 9.5 4.0
Effect of Winter Cover Crops on Vegetable Crop Yield and Leaching of Nitrate
Cooperators: Dr. John Selker and Dr. Richard Dick
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 in 1990 to initiate a study of the cycling and availability of N in vegetable cropping systems. These are years 10 and 11 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 and compared 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 (Hemphill 1995). 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 1 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 (Hemphill 1997). The same plan was then followed with broccoli in 1997 and sweet corn in 1998 (Hemphill 1999).
In autumn 1993, passive capillary wick lysimeters were installed beneath the winter-fallow 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 1999 and 2000 were (1) to evaluate effects of several winter cover crops, including fall-seeded and overseeded triticale, fall-seeded triticale plus common vetch, and overseeded red clover on yield and quality of snap beans (1999) and sweet corn (2000) at three rates of applied N and (2) to evaluate the effect of these cover crops and the N applied to the vegetable crops in 1998 and 1999 on the amount of nitrate leached below the root zone.
Methods
Snap beans, 1999
During winter of 1998-1999, the plots had been fallow, in overseeded 'Celia' triticale or 'Kenland' red clover, or in fall-seeded triticale or fall-seeded triticale plus common vetch. The cover crops were interseeded into the standing sweet corn crop in July 1998 or were broadcast-seeded and harrowed into the soil in late September, 1998. No additional fertilizers or pesticides were applied to the cover crops.
'Oregon 91G' beans were seeded on June 10 in rows 20 inches apart. Plot size was 600 ft2. Nitrogen rates were 0, 60, and 120 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 cereal rye or 'Kenland' red clover in preparation for the 2000 experiments. Harvest was on August 17.
Sweet corn, 2000
During winter of 1999-2000 the plots had been fallow or in the same cover crops as in 1998-1999. The cover crops were interseeded into the standing snapbean crop in July 1999 or were broadcast-seeded and harrowed into the soil in early September 1999.
The cover crops were plowed down in early April and 'GH 1703' sweet corn was seeded on May 23 on 30-inch rows. Plot size was 600 ft2. Nitrogen rates were 0, 50, and 200 lb/acre, with half the N applied just after seeding and the remainder applied 7 weeks after seeding. At this time the appropriate plots were overseeded to 'Celia' triticale or 'Kenland' red clover in preparation for the 2001 experiments. Harvest was on September 6.
Results
1999
Cover-crop biomass accumulation and N uptake were below average for these plots, but some interesting trends emerged (Table 1). The yield of overseeded crops was smaller than for the fall-seeded crops, probably because of poor stands. Except for the overseeded red clover, cover crop biomass and N accumulation tended to increase with increasing rate of N applied to the preceding sweet corn crop. Fallow plots had only a very light stand of weeds and were hot harvested.
Bean crop stands and early growth were very good but yields were not outstanding. Both bean pod yield and total above-ground biomass (pods plus stems and leaves) were highest following winter fallow and tended to be depressed by the overseeded cover crops (Table 2). Yield also did not respond to application of N. Apparently, soil N supplies were adequate for bean crop production without added fertilizer.
Averaged over 27 collection dates, a fall-seeded cereal rye cover crop significantly reduced the nitrate concentration of leachate reaching the 4-foot depth in the soil profile for all three rates of N applied to the previous corn crop (Table 3). The magnitude of reduction in nitrate concentration with the cover crop was somewhat lower than in previous years. The difference in nitrate-N concentration in the leachate between fallow and covered plots was larger during the spring, probably because of a more extensive cover-crop root system in the spring. For the first few sampling dates, nitrate concentrations in samples taken from beneath the fallow plots were often lower than for the plots where the cover crops were getting established (Fig. 1). Nitrate concentrations of leachates for all cover crop and N rate combinations decreased with time, a trend consistent with all years except the winter of 1997-1998.
2000
The triticale and clover cover crops did not establish well in the overseeded plots and the biomass yield of these cover crops was not measured. Fallow plots were nearly free of plants. The triticale and triticale plus vetch covers seeded after bean harvest and disking of the bean residue established well and accumulated more biomass than in recent years. However, the cover crops did not recover more N from plots that had received higher rates of applied N. This is not surprising as the rates of N applied should not have been in excess of the requirements of the bean crop. The N accumulation by the common vetch in the triticale/vetch cover crop was about 80 lb/acre, attributable to N fixation rather than recovery of residual soil N (Table 4).
Corn stand was poor and yields were lower than normal for these plots. Although not always statistically significant, yield tended to decline following any cover crop, regardless of the presence of a legume in the cover crop (Table 5). In most years, a grain cover crop tended to reduce sweet corn yield compared to fallow, but yields have tended to equal or surpass those following fallow with a legume cover crop. Consistent with past years, the sweet corn yielded better following a legume cover crop compared to a grain cover crop and following red clover compared to a triticale-vetch cover crop. The latter is surprising since the stand of clover was so poor that we did not do a biomass estimate on the clover cover crop. Mineralization of N from previous clover cover crops may have influenced yield in 2000. Yield also increased normally with increasing rate of applied N. The highest-yielding treatment combination (10.0 tons/acre) was the high rate of applied N with winter fallow (Fig. 2). Lowest yield and mean ear weight was with overseeded triticale and no applied N; the same result was obtained in 1998.
Literature Cited
Brandi-Dohrn, F.M., R.P. Dick, S.M. Kauffman, D.D. Hemphill, Jr., and J.S. Selker. 1997. Nitrate leaching under a cereal rye cover crop. Journal of Environmental Quality 26:181-188.
Hemphill, D.D., Jr. 1995. Vegetable research at the North Willamette Research and Extension Center, 1993-1994. Oregon Agricultural Experiment Station Special Report No. 944, Oregon State University, Corvallis.
Hemphill, D.D., Jr. 1997. Vegetable research at the North Willamette Research and Extension Center, 1995-1996. Oregon Agricultural Experiment Station Special Report No. 975, Oregon State University, Corvallis.
Hemphill, D.D., Jr. 1999. Vegetable research at the North Willamette Research and Extension Center, 1997-1998. Oregon Agricultural Experiment Station Special Report No. 1000, Oregon State University, Corvallis.
Table 1. Interaction of cover crop and rate of N applied to preceding
corn crop on cover crop dry biomass and N uptake, NWREC, 1999.
Cover crop N rate Cover dry biomass N uptake
---------------lb/acre----------------
Overseeded triticale 0 32 3
50 167 6
200 499 11
Overseeded clover 0 226 5
50 163 4
200 88 2
Fall-seeded triticale 0 438 10
50 602 15
200 1177 28
Fall-seeded triticale/vetch 0 1123 34
50 1091 34
200 1896 44
LSD (0.05) 317 8
Table 2. Main effects of preceding cover crop and rate of applied N on
yield of snap beans, NWREC, 1999.
Treatment Pod yield Shoot fresh biomass
(tons/acre) (tons/acre)
Cover crop (avg. over N rates)
Fallow 5.2 10.1
Overseeded triticale 3.1 6.3
Overseeded clover 3.8 7.5
Fall-seeded triticale 4.8 8.9
Fall-seeded triticale/vetch 4.6 9.6
LSD (0.05) 1.0 NS
N rate (lb/acre, avg. over covers)
0 4.4 8.6
125 4.2 8.5
250 4.3 8.4
LSD (0.05) NS NS
Table 3. Interaction of cover crop and rate of applied N
on mean nitrate concentrations in water collected from
lysimeters following the 1998 sweet corn crop, NWREC, 1999.
Cover crop N rate (lb/acre) Nitrate-N (ppm)
Fallow 0 4.9
50 6.0
200 17.6
Cereal rye 0 3.1
50 4.9
200 10.5
LSD (0.05) 3.3
Table 4. Effect of rate of N applied to previous bean crop on biomass and
N uptake of triticale and triticale/common vetch cover crops, NWREC, 2000.
N rate (lb/acre) Cover crop Biomass (tons/acre) N uptake (lb/acre)
0 Triticale 0.52 19
60 0.72 23
120 0.97 22
0 Triticale/Vetch 1.55 104
60 1.78 128
120 1.48 108
LSD (0.05) 0.50 28
Table 5. Main effects of N rate and cover crop on sweet
corn yield and mean ear weight, NWREC, 2000.
Yield (tons/acre) Mean ear wt (g)
Cover crop
Fallow 8.8 327
Overseeded triticale 6.7 295
Overseeded clover 7.7 344
Fall-seeded triticale 6.6 333
Fall-seeded triticale/vetch 7.0 314
LSD (0.05) 1.6 NS
N rate (lb/acre)
0 6.0 302
50 7.7 334
200 8.4 331
LSD (0.05) 0.9 20
NSNo significant differences (P = 0.05).
Cultivar, N Rate, Inoculation, and Row Spacing Affect Yield of Edamame
Cooperator: Dr. Carol A. Miles
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 (R6 stage). 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 edamame variety trials and is involved in a breeding program for improved varieties 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 inadequate to guide production in our area. For example, the Japanese literature recommends application of 35 to 55 lb N/acre in addition to 8 tons/acre of well-decomposed animal-waste compost, which provides an unknown amount of available nutrients. 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.
In our trial in 1998, the cultivars 'Shironomai' and 'Butterbeans' had better yield and quality than did 'White Lion.' Yield of all three cultivars increased with increasing rate of N, with no indication that the highest rate of applied N, 72 lb/acre, was sufficient for maximum yields. Yield per unit area was higher at 20- than at 30-inch between-row spacing (Hemphill 1999).
The purpose of the 1999 trial was to investigate the effects of two between-row spacings and four rates of applied N on the two edamame cultivars that had the higher yields in 1998. In the 2000 trial the objectives were to investigate the interaction of N rate and rhizobium inoculum on yield of edamame and to conduct a yield trial of promising varieties.
Methods
1999
Non-inoculated 'Butterbeans' and 'Shironomai' edamame were seeded to a winter-fallowed Willamette silt loam, pH 5.8, at the NWREC on June 2. Plot preparation included plowing, disking, a broadcast and incorporated application of triple superphosphate and sulfate of potash, each at 200 lb/acre, and harrowing to form a seedbed. The two cultivars were seeded on 20 and 30-inch rows, with 3-inch within-row spacing. Metolachlor (1.5 lb/acre) was applied after planting for weed control. Escaped weeds, mostly lambsquarters, Canada thistle, and red-root pigweed, were controlled by hand-hoeing. Nitrogen rates applied were 0, 36, 72, and 108 lb/acre as ammonium nitrate, with half the N applied 1 week after seeding and the remainder on July 14. The experimental design was a randomized complete-block split plot, with cultivar x spacing combinations as main plots and N rates as subplots and four replications of each treatment combination. Subplot size was 15 x 20 feet. Plots were sprinkler irrigated as necessary, usually 1 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 (lacking developed beans). Cultivars differed slightly in days to optimal maturity, with 'Shironomai' harvested on September 10 and 'Butterbeans' on September 13.
2000
Both non-inoculated and inoculated 'Butterbeans' edamame were seeded on 20-inch rows to a winter-fallowed Willamette silt loam, pH 5.8, at the NWREC on June 1. Plot preparation included plowing, disking, a broadcast and incorporated application of triple superphosphate and sulfate of potash, each at 200 lb/acre, and harrowing to form a seedbed. Metolachlor (1.5 lb/acre) was applied immediately after planting for weed control. A few escaped weeds, mostly lambsquarters, subterranean clover, and red-root pigweed, were controlled by hand-hoeing. Nitrogen rates applied were 0, 36, 72, and 108 lb/acre as ammonium nitrate, with half the N applied 1 week after seeding and the remainder on July 21. The experimental design was a randomized complete-block split plot, with inoculum as main plot and N rates as subplots. Subplot size was 15 x 20 feet. Plots were sprinkler irrigated as necessary, usually approximately 1 inch/week. SPAD chlorophyll meter readings were taken on the leaves of 10 plants per plot at approximately weekly intervals. Yields were estimated by harvest of a 10-foot section of one of the centermost rows of each subplot on September 12. Pods were harvested as in 1999.
Results
1999 Cultivar
The two cultivars differed significantly in plant development (Table 1). Stand of 'Shironomai' was 27 percent less than that of 'Butterbeans,' very consistent with results from 1998. Canopy height and width did not vary between cultivars. 'Butterbeans' had slightly greener leaves, as measured by the Minolta SPAD meter, on August 12. The two cultivars did not differ in flower development (data not shown).
Despite its relatively poor early stand, 'Shironomai' produced a higher yield/acre, higher yield of marketable pods (2 or more beans), greater mean pod weight, larger pod weight/plant, and larger mean bean weight than did 'Butterbeans' (Table 2). The number of plants harvested did not vary by cultivar. Apparently, late-emerging plants of 'Shironomai' made up for the early deficiency in stand. The number of plants harvested for both cultivars represented about 60 percent of the intended stand.
Although there were significant interactions of cultivar and N rate affecting total yield/plot and weight of 100 pods (Table 3), 'Shironomai' was superior at each N rate. The mean weight of 100 pods and the total weight harvested/plot was highest at 72 lb applied N/acre for 'Butterbeans,' but at 108 lb N/acre for 'Shironomai.' Mean bean weight of 'Butterbeans' was more responsive to rate of applied N than was that of 'Shironomai' (Table 3). Mean bean weight of 'Shironomai' significantly exceeded that of 'Butterbeans' in the absence of applied N, but not in the presence of N fertilizer (Table 3).
Cultivar and between-row spacing interacted on marketable pod weight/plant and the weight of 100 marketable pods (Table 4). For weight of 100 pods, 'Shironomai' was the better variety at 20-inch, but not at 30-inch spacing. Marketable pod weight was higher for 'Shironomai' at both spacings. Marketable pod weight/plant was higher at 30-inch spacing for 'Shironomai' but not for 'Butterbeans.'
1999 Spacing
Spacing did not affect canopy size when measured on July 29. Leaf chlorophyll content was slightly higher at the 20-inch spacing when measured on August 12. (Table 1).
The 20-inch spacing, as in 1998, produced a lower yield per foot of row, lower mean pod weight, and lower total and marketable yield/plant than did the 30-inch spacing. However, also as in 1998, the yield per unit area was higher with the 20-inch spacing as the larger number of plants more than offset the higher yield/plant obtained with the wider spacing (Table 2).
Spacing and rate of applied N interacted on yield of marketable and total pods/plant (Table 5). In each case, the yields increased between 72 and 108 lb N/acre for the 20-inch spacing, but not for the 30-inch spacing.
1999 N rate
As in 1998, rate of N had no effect on stand, but canopy height and width increased linearly with increasing N (Table 1). Increasing N had no effect on flowering in 1999 but leaf chlorophyll content increased linearly with increasing rate of applied N.
As in 1998, total weight harvested/plot, yield/unit area, weight of marketable pods/plot, mean pod yield/plant, and mean marketable pod weight/plant increased linearly with increasing rate of N (Table 2). In contrast to 1998, mean weight of the individual pod also increased linearly with increasing applied N. Also in contrast to 1998, the mean bean weight increased quadratically with increasing rate of applied N. The number of beans/pod, the yield of unfilled pods, and the number of plants harvested per plot did not vary with N rate (Table 2). Also as in 1998, there were no 3-way interactions of N rate, spacing, and cultivar affecting plant development or yield.
2000 N rate
As in 1998 and 1999, leaf chlorophyll content, as estimated by SPAD readings, increased linearly with increasing rate of applied N on each of six dates of measurement (Table 6). For the last two measurement dates, presence of inoculum greatly increased SPAD readings at the two lower rates of applied N, but this was not true at the two higher rates of N application (Table 7). This trend also occurred earlier in the season but the interaction of inoculum and N rate was significant only on the last two dates that SPAD readings were taken.
Rate of applied N did not affect the number of plants harvested. In a strong departure from results obtained in 1998 and 1999, yield of marketable pods, yield of pods containing two or more beans, and total weight, averaged over the presence and absence of inoculum, was greatest at only 36 lb applied N/acre (Table 8). However, this yield was not significantly greater than with no applied N. Yield of pods containing only one bean, yield of unmarketable pods, weight of 150 pods, total pod weight per plant, number of beans from 25 pods, and mean bean weight did not vary with N rate. Weight of beans from 25 pods declined linearly with increasing rate of N.
2000 Inoculum
Leaf chlorophyll content did not respond to the presence of inoculum with the seed during much of the growing season, but higher SPAD readings were obtained from inoculated plants late in the growing season. SPAD readings declined in the absence of inoculum (Table 6).
The presence of inoculum reduced the number of plants present at harvest by 15 percent (Table 8). Averaged over N rates, inoculum had no effect on yield of pods containing two or more beans, yield of pods containing one bean, unmarketable yield, total yield, weight of beans from 25 pods, number of beans from 25 pods, marketable yield per plant, and average bean weight. However, the weight of 150 pods and total pod yield per plant increased with inoculum. There were no significant interactions of N rate and inoculum affecting any component of yield.
Discussion and Conclusions
For the purposes of these experiments, 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 two or more beans responded similarly to treatment.
Given that complete canopy closure was not obtained with the 30-inch spacing, and that mean bean weight and weight of 100 marketable pods was not affected by spacing in 1999 and only slightly reduced at 20 inches in 1998, 20 inches appears to be a reasonable between-row spacing for these cultivars on this Willamette soil.
Although the number of beans/pod, mean bean weight, and total and marketable pod yield/plant did not increase between the two highest rates of N, yield/plant and per unit area did increase between 72 and 108 lb applied N/acre in 1999, indicating that the latter rate is needed 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. In 1998 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. This was not the case in 1999. Inoculated seed might have responded differently to the N rate.
We have no explanation for the failure of the crop yield to respond to N rate in 2000 as it had in 1998 and 1999. SPAD readings indicated a large response to applied N. Plant biomass was not measured but perhaps the extra N resulted in larger plants but did not increase the set of pods that reached marketable size before harvest. High rates of N also delay maturity and it may be that a later harvest date would have resulted in higher yields at the higher rates of N. Inoculum was expected to increase yield at low rates of applied N but not a the higher rates. However, this interaction did not occur as the best yields were obtained with zero or the low rate of applied N, regardless of the presence or absence of inoculum.
Literature Cited
Hemphill, D.D., Jr. 1999. Vegetable research at the North Willamette Research and Extension Center, 1997-1998. Oregon Agricultural Experiment Station Special Report No. 1000, Oregon State University, Corvallis.
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, 1999.
Seedlingsz/ Canopy heighty Canopy widthy SPAD Units
20 ft inches inches 29 July 12 Aug.
Cultivar
Butterbeans 44 14 15 33 33
Shironomai 32 14 15 32 32
Significance *** NS NS NS *
Spacing
20 inches 38 14 15 33 33
30 inches 38 14 15 32 32
Significance NS NS NS NS *
N rate (lb/acre)
0 37 12 13 27 27
36 39 13 15 32 30
72 37 14 16 34 34
108 39 15 16 36 37
Significance NS L** L*** L*** L***
zCounts made 17 June.
yMeasured 29 July.
***,**,*,NSSignificant at 0.1, 1.0, and 5.0 percent probability level and
nonsignificant, respectively. L = linear.
Table 2. Main effects of cultivar, between-row spacing, and rate of applied N fertilizer on edamame yields,
NWREC, 1999.
Total wt Unfilled 1 bean/ 2+ beans/ Wt 100 No. of Mean bean No. of Pod wt./ Marketable
(g/ (tons/ pods pod pods pods beans/ wt plants/ plant pods/plant
plot) acre) (g/plot) (g/plot) (g/plot) (g) 25 pods (g) 3 m (g) (g)
Cultivar
Butterbeans 1,198 2.8 55 403 740 194 55 0.44 24.6 49 31
Shironomai 1,648 3.8 57 513 1,078 263 54 0.51 24.0 70 46
Significance *** *** NS ** *** *** NS ** NS *** ***
Spacing
20 inches 1,337 3.8 47 414 876 227 54 0.48 24.9 54 36
30 inches 1,509 2.9 66 501 942 230 55 0.47 23.7 65 41
Significance ** ** NS * NS NS NS NS NS ** *
N Rate, lb/acre
0 880 2.0 49 318 512 204 55 0.41 24.4 37 22
36 1,350 3.1 56 402 892 223 54 0.45 24.4 56 37
72 1,683 3.9 67 526 1,089 240 54 0.53 23.7 73 47
108 1,780 4.1 52 585 1,143 247 55 0.52 24.8 73 46
Significance L*** L*** NS L*** L*** L*** NS L***Q* NS *** ***
***,**,*,NSSignificant at 0.1, 1.0, and 5.0 percent probability level and nonsignificant,
respectively.
L = linear, Q = quadratic.
Table 3. Interaction of rate of applied N and cultivar, averaged
over two spacings, on weight of 100 marketable pods, total pod
weight/plot, and mean bean weight, NWREC, 1999.
Applied N Cultivar Wt of 100 pods Total wt/3 m Mean bean wt
(lb/acre) (g) (g) (g)
0 Butterbeans 161 772 0.32
Shironomai 248 988 0.50
36 Butterbeans 187 1,177 0.44
Shironomai 259 1,523 0.46
72 Butterbeans 222 1,456 0.53
Shironomai 259 1,910 0.52
108 Butterbeans 207 1,386 0.49
Shironomai 286 2,173 0.55
LSD (0.05), Significance 29* 219** 0.09*
**,*Significant at 5.0 and 1.0 percent probability levels, respectively.
Table 4. Interaction of between-row spacing and cultivar, averaged over
four rates of applied N, on the weight of 100 marketable edamame pods and
marketable yield per plant, NWREC, 1999.
Row spacing, inches Cultivar Wt of 100 pods Marketable pod wt/plant
------------------g---------------------
20 Butterbeans 185 30
Shironomai 203 41
30 Butterbeans 270 31
Shironomai 256 51
LSD (0.05), Significance 18* 7*
*Significant at 5 percent level.
Table 5. Interaction of between-row spacing and rate of
applied N, averaged over two cultivars, on yield of
marketable pods and total pods of edamame, NWREC, 1999.
Spacing (inches) N rate (lb/acre) Marketable Total
------g/3 m------
20 0 426 722
36 827 1,249
72 990 1,558
108 1,262 1,819
30 0 599 1,038
36 957 1,450
72 1,188 1,808
108 1,025 1,741
LSD (0.05) Significance 200** 219*
**,*Significant at 5 and 1 percent levels, respectively.
Table 6. Main effects of inoculum and rate of applied N on SPAD readings
in edamame, NWREC, 2000.
27 July 3 Aug. 10 Aug. 17 Aug. 28 Aug. 11 Sept.
Inoculum
Without 31 30 31 29 29 21
With 31 32 32 31 33 30
Significance NS NS NS NS *** ***
N rate (lb/acre)
0 27 27 28 27 27 18
36 32 30 31 30 30 24
72 33 32 32 31 32 28
108 34 35 36 33 35 33
Significance L*** L*** L*** L** L*** L***
***,**,NSSignificant at 0.1 and 1.0 percent probability level and
nonsignificant, respectively; L = linear.
Table 7. Interaction of inoculum and rate of applied N
on SPAD readings in edamame on two dates, NWREC, 2000.
Date Inoculum Rate of applied N (lb/acre)
0 36 72 108
28 Aug. Without 22 28 31 35
With 33 32 32 36
11 Sept. Without 10 19 25 32
With 25 30 32 34
LSD (0.05) for any two means = 4 for 28 August and 8
for 11 September.
Table 8. Main effects of inoculum and rate of applied N fertilizer on edamame yields, NWREC, 2000.
Total Unfilled 1 bean/ 2+ beans/ Wt 150 No. of Mean bean No. of Pod wt/ Marketable
wt pods pod pod pods beans/ wt plants/ plant pods/plant
(g/plot) (g/plot) (g/plot) (g/plot) (g) 25 pods (g) 3 m (g) (g)
Inoculum
Without 892 122 268 502 343 54 0.52 23.6 38 33
With 917 140 280 497 366 56 0.50 20.2 47 40
Significance NS NS NS NS * NS NS * * *
N Rate (lb/acre)
0 957 116 267 573 338 57 0.52 21.0 46 41
36 1,041 121 314 606 359 56 0.52 21.6 50 43
72 829 151 253 425 364 56 0.49 22.8 38 32
108 790 136 262 392 358 51 0.50 22.3 36 30
LSD (0.05) 152 NS NS 107 NS NS NS NS NS *
*,NSSignificant at 5 percent probability level and nonsignificant, respectively.
Evaluation of Precision Planting Techniques, Flail Topping, and Multi-Row Harvesters for Table Beet Production
Cooperators: N.S. Mansour, Daniel McGrath, and the Stayton Canning Company
Introduction
The Oregon table beet industry has long used the variety 'Detroit Dark Red Morse Strain,' Scott Viner-type single-row harvesters owned by individual growers, and between-row spacings of 20 or more inches. Preliminary trials in 1998 indicated that beet yields and grades might be improved with a combination of closer row spacings within a bed, hybrid varieties, precision planters, and bed-oriented, multi-row mechanical harvesters. These faster, higher-capacity harvesters would likely be owned by beet processors rather than by individual growers because of their high cost. Our objectives in 1999 were (1) to test the hybrid variety 'Red Ace' against the standard 'Detroit Dark Red' to see if the expected greater vigor and uniformity of the hybrid might have some advantages in a close-row system where plants would be subject to more between-plant competition than at the standard wide row spacings; (2) to again evaluate the 12-inch-row configuration using Oregon State University's Gaspardo precision planter in comparison with grower planters such as the John Deere 71 Flex Planter and the Planet Jr; and (3) to observe the efficiency of harvesting with an AMAC ZR-2 multi-row harvester compared to a single-row Scott Viner harvester.
Methods
Two sites were used: the first was in the north Willamette Valley, southwest of Forest Grove, the second in the central Willamette Valley just west of Dayton, Oregon. The growers agreed to plant large plots, sufficient for truckload quantities of beets at harvest. Several planters were to be tested by different growers to compare with a precision planter used by the OSU researchers. Topping and harvesting included a preliminary topping with a steel-fingered flail topper to remove most foliage, followed by a Parma three-drum, rubber-finger topper, and an AMAC ZR-2 harvester. In-plant cleaning by Stayton Canning Company was conventional.
The same 1.4-sprout-per-seedball seedlot of 'Red Ace' that was used in 1998 was also used in this study. Seeding was on April 23 at Forest Grove and on April 30 at Dayton. The 'Detroit Dark Red' seedlots were those being used by the growers for their commercial plantings.
The research plots at both locations were planted using a Gaspardo SV255 precision, multiple-row vacuum planter set up to plant four rows to a bed. The rows were spaced 12 inches apart on beds spaced on 60-inch centers, giving an average spacing of 15 inches. This planter was used for 'Red Ace' and the growers' 'Detroit Dark Red'. Due to the design of the planter, the vacuum seed plate did not need to be changed among seedlots despite the large differences in seed size between the 'Red Ace' (35,287 seeds/lb) and the two lots of 'Detroit Dark Red' (51,446/lb at Forest Grove and 24,140 at Dayton). Seeding rate was approximately 25 lb/acre for both varieties.
At Forest Grove, the grower used a Planet Jr. configured to plant rows 7 inches apart for an even closer spacing, and a grass seed planter configured to plant beets in a solid mat in beds 60 inches on center. At the Dayton site, the grower used a John Deere 71 Flex Planter to plant his conventional rows on 22-inch centers. This same planter was then reconfigured to plant rows 12 inches apart in 4-row beds on 60-inch centers. The latter planting occurred 1 week after the other three treatments were seeded.
Cultural practices were those normally used by the grower in his table beet production. At Dayton the grower conducted one mechanical cultivation and one hand weeding in addition to his standard herbicide program. No cultivation or hand weeding was done at Forest Grove.
Stands were evaluated on May 14 (Forest Grove only), May 26, and on June 28, 1999. Counts were made for three randomly chosen 1 ft x 4-row (5 ft for bedded plantings) quadrats for each planting treatment. The first stand count includes only the Forest Grove plantings as the Dayton planting had not emerged.
We conducted hand-harvests at the Dayton site on August 18, 1999 and September 2, 1999. The September 2 hand-sampling date was 1 day before the plots were mechanically harvested. Hand-harvest consisted of pulling all beets from 4 lineal ft of each of four rows of each treatment on August 18 and from 3 lineal ft of each of four rows on September 2, 1999. The hand-harvests were replicated three times over different planter passes for each treatment. The replicate areas were 20 and 15 ft2 for each of the three samples taken from 12-inch-row treatments, and 26.67 and 20 ft2 for each of the three replicates for the 20-inch spacing on the August 18 and September 2 dates, respectively. This represents a total of 60 and 45 ft2 and 80 and 60 ft2 for each of the 12-inch and 22-inch-row treatments on the two dates, respectively. All beets were hand-topped and taken to Stayton Canning Company for grading by their staff.
Mechanical harvest was on September 3, 1999 at the Dayton site. Topping was done just ahead of harvest. Truckload quantities of beets were harvested from each treatment. We then measured the area harvested to fill each truck.
Results
Beet Stands
The May 26 stand counts included both the Forest Grove and Dayton sites (Tables 1 and 2). Later stand counts were fairly consistent with the first count and did not show the large mortality experienced in the 1998 season following 6 weeks of rain. The final count on June 28 involved pulling all developing plants in the quadrat. This stand count is reported and forms the basis for stand discussion.
The grass-seed planter used by the grower in the Forest Grove site produced stands that were very poorly distributed across the bed. A chain used to drag the beds immediately after the seed was dropped tended to windrow the seeds to the edges of the beds, and the plants across the bed were often clumped, unevenly spaced, and planted at various depths. The stands from the Planet Jr. were also very uneven. The scatter shoes and seed plates used with this planter tended to distribute the seed in clumps or with uneven spacing. Plants from both these planters tended to emerge at different times depending on their depth of planting.
The two treatments with the Gaspardo were very uniform in emergence and distribution down the row. Most obvious was the uniform seedling size due to uniform emergence and the uniform distribution down the row.
With only two exceptions, stands increased slightly at later counting dates. Emergence weather was good, and there was little reason to expect any unusual mortality. Stands tended to be slightly higher at Dayton than at the Forest Grove site for the two Gaspardo treatments.
Hand-harvests
Due to plant and equipment scheduling needs of the processor, other growers using the equipment, and difficulties with weed control and other limiting factors, the Forest Grove site was not harvested. Yield data from the Dayton site only are reported here.
The processor pay scale is $81/ton for Grade 1 (the smallest marketable beets), $73/ton for Grade 2 (intermediate size), and $16/ton for Grade 3 (oversize). Based on this scale, the dollar values per acre increased about $48/day over the 16 days between August 18 and September 2, an average of about $773/acre across all treatments. The range was from $658/acre for the John Deere 22-inch-'Detroit Dark Red' to $854 for the Gaspardo-'Red Ace' (Tables 3 and 4). Dollar values per acre were similar for the John Deere, 22-inch and the Gaspardo, 12-inch 'Detroit Dark Red' treatments at each harvest. Yields and dollar values of the grower-planted 'Detroit Dark Red' on 12-inch spacing lagged because of the later planting date. 'Red Ace' had a slightly higher yield and dollar value than did 'Detroit Dark Red.'
Machine Harvest
Truckloads and machine-harvested area for the different treatments were 15,940 lb from 0.248 acres for the 12-inch-row 'Detroit Dark Red' Gaspardo planting; 46,800 lb from 0.551 acres for the 12-inch-row 'Red Ace' Gaspardo planting; 28,780 lb from 0.431 acres for the 'Detroit Dark Red' 22-inch-row conventional John Deere 71 planting, and 23,960 lb from 0.368 acres for the truckload of the 'Detroit Dark Red' 12-inch planting that was harvested at the same time as the other three treatments but planted 1 week later.
Yield, grade, and dollar value data are presented (Tables 5 and 6) for one truckload mechanically harvested from each of the treatments at the Dayton location. Truck weights are as reported by the processor. The machine-harvested truckloads of beets were graded by the processor. The dollar values in Table 5 were obtained by applying the grades from the final hand sampling (Table 4) to the machine-harvest yields. The dollar values in Table 6 were obtained using the grade reported by the processor for each truckload.
Machine-harvest yields for the John Deere 12-inch spacing and the 'Red Ace' planting were considerably higher than for the final hand sample, but the yields for the John Deere 22-inch rows and the 'Detroit Dark Red' Gaspardo planting were very similar to those determined by hand harvest. 'Red Ace' clearly outperformed 'Detroit Dark Red.'
Since the processor pays similarly for Grade 1 and Grade 2 and relatively little for Grade 3 ($16/ton), the difference in using the truckload grade and the hand-harvest grade to compute value/acre is very small and does not affect the rank of the treatments. All three 'Detroit Dark Red' treatments produced similar dollar value in the machine harvest, indicating that the close row treatments do not sacrifice yield or dollar value compared to conventional spacing. As harvest efficiency is higher for the AMAC bed harvester than for the Scott-Viner single-row harvester, despite the extra topping operation required by the AMAC, the net returns may be higher for the 12-inch spacing.
Using the cannery truckload grades to judge the comparative maturity of plants in each treatment (Table 6), one can see that the 12-inch-spacing treatments were somewhat behind the 22-inch spacing treatment in beet root development. Note especially the higher percentage of Grade 3 beets for the 22-inch spacing. It is interesting to speculate what the dollar value might have been for the 12-inch spacings if they had been harvested at the same percentage of Grade 3 beets. In our opinion, the 12-inch spacings would have benefited from another week's growth. As in 1998, if we accept the grades reported in Table 6 as accurate assessments of the loads, the closer spacings retarded development of Grade 3 beets.
Recommendations
Based on observations made throughout the season and at harvest, and from the cannery grade sheets for truckloads of high-density beets which were not a part of this study, we feel that it is important that growers considering a shift to high-density beets consider the following:
1. Soil type. Sandy loam soils that will easily separate from the beets at harvest are likely to be the best for this system.
2. Soil moisture at harvest. Excessive amounts of soil may be delivered with the loads of beets from soils that are either too wet or too dry. Muddy beets result from wet soils and clods are a problem with excessively dry soils. Growers may need to irrigate a few days before harvest to ensure that clods are not a problem. Also, this system probably should not be used in fields scheduled for a late harvest when fall rains may be a problem.
3. Weed control. Growers need to select fields with the fewest weed problems and set up suitable cultivators to be used if chemical weed control is not adequate. Failure to adequately control weeds will be a serious problem in this system.
Table 1. Stand counts at Forest Grove, Oregon, 1999.
Planting method May 14 May 26 June 28
Per acre Per bed-ft Per acre Per bed-ft Per acre Per bed-ft
Grass planter 4 mph 278,784 32 331,056 38 412,368 47
Grass planter 5 mph 574,992 66 653,400 75 740,520 85
Grass planter 6 mph 252,648 29 314,432 36 331,056 38
Gaspardo 'Red Ace' 679,536 78 714,384 82 772,464 89
Gaspardo 'Detroit' 749,232 86 734,712 84 728,904 84
Planet Jr. 'Detroit' 574,990 66 860,310 78 665,016 76
Table 2. Stand Counts at Dayton, Oregon, 1999.
Planting method May 26 June 28
Per acre Per lineal-ft Per bed-ft Per acre Per lineal-ft Per bed-ft
Gaspardo 12 'Detroit' 967,032 27.8 111 1,059,960 30.4 122
Gaspardo 12 'Red Ace' 755,040 21.7 87 923,472 26.5 106
John Deere 22 'Detroit' 520,742 21.9 88 487,082 20.5 82
Table 3. Yield and dollar value of beets hand-harvested at Dayton, Oregon, 18 August, 1999.
Planting method Yield of payable Grade 1 Grade 2 Grade 3 Total value
beets, tons/acre % $/acre % $/acre % $/acre ($/acre)
John Deere 12-inch 16.1 41.3 539 27.2 320 0.7 2 881
John Deere 22-inch 19.9 35.0 565 42.9 624 3.5 11 1,200
Gaspardo 'Detroit' 12-inch 21.0 40.3 686 39.8 610 1.9 6 1,302
Gaspardo 'Red Ace' 12-inch 24.1 43.6 851 33.0 581 1.3 5 1,437
Table 4. Yield and dollar value of beets hand-harvested at Dayton, Oregon, 2 September, 1999.
Planting method Yield of payable Grade 1 Grade 2 Grade 3 Total value
beets, tons/acre % $/acre % $/acre % $/acre ($/acre)
John Deere 12-inch 21.7 43.0 966 35.0 709 0.0 0 1,675
John Deere 22-inch 25.2 30.5 738 50.5 1,102 3.3 18 1,858
Gaspardo 'Detroit' 12-inch 28.7 34.5 974 42.0 1,068 5.7 30 2,042
Gaspardo 'Red Ace' 12-inch 29.9 36.7 1,089 45.3 1,202 0.0 0 2,291
Table 5. Yield and dollar value for beets harvested by machine at Dayton, Oregon, 3 September, 1999,
using the hand-sample grade. Dollar values computed using the grades from the September 2 hand-harvest.
Planting method Yield of payable Grade 1 Grade 2 Grade 3 Total value
beets, tons/acre % $/acre % $/acre % $/acre ($/acre)
John Deere 12-inch 27.0 43.0 1,133 35.0 831 0.0 0 1,964
John Deere 22-inch 27.4 30.5 750 50.5 1,117 3.3 16 1,883
Gaspardo 'Detroit' 12-inch 26.7 34.5 897 42.0 985 5.7 30 1,912
Gaspardo 'Red Ace' 12-inch 36.5 36.7 1,262 45.3 1,406 0.0 0 2,668
Table 6. Yield and dollar value for beets machine-harvested at Dayton, Oregon, 3 September, 1999,
using the truckload grade. Dollar values computed using the grades determined on the cannery sample
taken from each truckload.
Planting method Yield of payable Grade 1 Grade 2 Grade 3 Total value
beets, tons/acre % $/acre % $/acre % $/acre ($/acre)
John Deere 12-inch 27.0 31 817 41 1,093 3 16 1,926
John Deere 22-inch 27.4 22 541 54 1,197 13 63 1,801
Gaspardo 'Detroit' 12-inch 26.7 24 624 50 1,173 6 31 1,829
Gaspardo 'Red Ace' 12-inch 36.5 25 860 58 1,298 2 14 2,672
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