Tag: clover

Interseeding Cover Crops into Double-Crop Soybeans – Initial Findings

1,2Cara Peterson, 2Steven Mirsky, 1Kate Tully, 1,2Victoria Ackroyd
1Department of Plant Science and Landscape Architecture, University of Maryland
2United States Department of Agriculture, Agricultural Research Service, Beltsville

The mid-Atlantic region has the highest percentage of arable acreage in cover crops in the United States, with some reports placing Maryland and Delaware as the two states with the highest percentage of total cropland planted with cover crops (Wade et al., 2015; Hamilton et al., 2017). However, the majority of producers in the region are only using grass cover crops, since legumes require earlier planting dates in order to over-winter (Mirsky et al., 2011; Clark, 2012). Farmers in this region have success with legume cover crops when planting them after wheat harvest or frost-seeding in the spring. However, most mid-Atlantic crop rotations include double-crop soybeans planted after wheat, which limits opportunities for establishing a legume cover crop. Low legume adoption is particularly problematic as farmers could use this cover crop before corn to maximize the opportunity for nitrogen fixation benefits.

cover crop rotation schematic
Figure 1. (Top) A typical mid-Atlantic crop rotation, with double-crop soybeans in the field at the pivotal points for establishing a successful legume cover crop. (Bottom) Proposed crop rotation scheme for interseeding a cover crop between 30-inch soybeans. The cover crop over-winters and is terminated before corn planting in the spring.

Some farmers interseed cover crops into growing cash crops to overcome this timing challenge. Current options for planting cover crops into standing corn and soybean include both aerial broadcasting via airplane and adapted high-boy sprayers. However, these two techniques often result in poor establishment due to low seed-to-soil contact and seed predation by rodents and birds (Hively et al., 2001; Baker and Griffis, 2009; Wilson et al., 2013).

Interseeder
Figure 2. Interseeding cover crops with three planting units between 30-inch soybean rows.

To address the issue of planting cover crops into standing cash crops, our mid-Atlantic team ran numerous trials of an InterSeeder grain drill (InterSeeder Technologies, LLC; Fig. 2). Engineered by the Pennsylvania State University, this drill plants three rows of cover crops between 30-inch rows of standing cash crops. Field trials of this InterSeeder have been conducted in corn, as well as full-season soybeans, at various sites in the region with mixed results (Curran et al., 2018; Wallace et al. 2017). In Maryland, interseeding into full-season corn was moderately successful, whereas cover crops did not perform well in full season beans. However, exploratory research in Maryland identified wide-row double crop soybeans as a viable option for interseeding. The success of seeding grass-legume mixtures into 30-inch double-crop soybeans has led to an expanded on-station research program.

New Field Trials. Field trials with five different interseeded cover crop treatments were conducted to determine the optimal legume cover crop species to interseed in mixture with cereal rye and if interseeding a cover crop mixture affected wide-row double crop soybean yields. The five different cover crop treatments included: cereal rye alone, cereal rye independently mixed with four different legumes (hairy vetch, crimson clover, red clover, and winter pea), and a no cover crop control (Table 1).

Cover Crop Seeding Rates
Table 1. Interseeding Trial Cover Crop Seeding Rates

Double-crop soybeans planted in June were then interseeded with the cover crop treatments in early September 2017 and late August 2018. The double-crop soybeans were harvested in November for 2017 and later in 2018 (December) due to wet field conditions. The interseeded cover crop treatments grew throughout the winter and were terminated with herbicides in April 2017 and 2018 before planting corn.

In an ideal interseeding scenario, the cover crop is planted as the double-crop soybeans are beginning to reach full canopy in early September. That way, the cover crops only have to survive a few weeks under the low light conditions of a soybean canopy until leaf drop. Once the soybean canopy is gone, the cover crops continue to grow but do not interfere with soybean harvest.

Insights from Interseeding Trials

  • Cereal rye + crimson clover produced the highest average cover crop biomass. The cereal rye + crimson clover fall 2017 seeding produced an average of 4,980 lbs per acre of biomass while the 2018 seeding produced 3,950 lbs per acre by the spring of 2019. Cereal rye + hairy vetch and cereal rye + winter pea reached similar levels of biomass in two out of the three field sites where the cover crops survived under the soybean canopy.
  • Interseeding did not decrease yield. There was no pattern of soybean yield differences between the 30-inch wide row double-crop soybeans that had or hadn’t been interseeded. Likewise, there were very minimal differences in soybean yields between the cover crop treatments.
  • Interseeding did not affect soybean grain quality. Green cover crop plant material was not found in any soybean grain subsampling. Moisture levels remained consistent, with very slight variance across the field as expected in a normal cropping system.
  • Row orientation matters. Out of the five trial sites, two of the cover crop plantings did not survive under the soybean canopy. Interestingly, the three field sites with strong cover crop survival rates had rows oriented in roughly the same direction: East-West or Southeast-Northwest. The two field sites where the cover crops sprouted but did not survive under the soybean canopy in the fall were on a perpendicular row orientation of Northeast-Southwest. 

Row Spacing Considerations. The InterSeeder requires a 30-inch row spacing, while most double-crop soybean fields are planted in narrower rows of 15 inches or less. To account for the differing production practices, these field trials also included simple yield comparisons of 30- and 15-inch row double-crop soybeans. In the row spacing (15- vs 30-inches) trial, results were mixed. There was a yield penalty for wide row spacing in 2017, but not in 2018.

While the benefits of narrow row spacing have been well documented in full season beans, less is known about the potential advantages in double crop soybeans. We speculate that optimal production years enhance the effect of row spacing. For example, 2017 was a better soybean year compared to 2018 across the mid-Atlantic region. Higher levels of precipitation in 2018 than 2017 could have damaged yields. Previous research indicates that in lower yield years or for late-planted soybeans, the benefit of planting in 15 inch rows over 30 inch rows is lost (Alessi and Power, 1982; Hodges et al., 1983; Boquet, 1990; Weaver et al., 1990, Oplinger et al., 1992; Pederson and Lauer, 2003, Whaley et al., 2015).

Future Research. Nitrogen content analysis of the interseeded cover crop biomass is currently underway. Next, the research team will analyze how the following year’s corn crop responded to the interseeded cover crop mixtures.

References

Alessi, J., and J.F.  Power. 1982. Effects of plant and row spacing on dryland soybean yield and water-use efficiency. Agronomy Journal 74:851–854. D.o.i.:10.2134/agronj1982.00021962007400050019x

Baker, J. M., and T. J. Griffis. 2009. Evaluating the potential use of winter cover crops in corn-soybean systems for sustainable co-production of food and  fuel. Agricultural and Forest Meteorology, 149(12), 2120–2132. D.o.i.:10.1016 j.agrformet.2009.05.017

Boquet, D. J. 1990. Plant population density and row spacing effects on soybean at post-optimal planting dates. Agronomy. J.: 59–64. D.o.i:10.2134/agronj2009.0219.

Clark, A. (Ed.). 2012. Managing cover crops profitably (Third ed.). College Park, MD: Sustainable Agriculture Research and Education.

Curran, W.S., R.J. Hoover, S.B. Mirsky, G.W. Roth, M.R. Ryan, V.J. Ackroyd, J.M. Wallace, M.A. Dempsey and C.J. Pelzer. 2018. Evaluation of cover crops drill interseeded into corn across the mid-Atlantic region. Agronomy Journal 110, 435–443. D.o.i.:10.2134/agronj2017.07.0395

Fisher, K. A., B. Momen,, and R.J. Kratochvil. 2011. Is broadcasting seed an effective winter cover crop planting method? Agronomy Journal, 103(2), 472–478. D.o.i.:10.2134/agronj2010.0318

Hively, W.D. and W.J. Cox. 2001. Interseeding cover crops into soybean and subsequent corn yields. Agronomy. J. 93:308-313. D.o.i.:10.2134/agronj2001.932308x

Hodges, H.F., F.D. Whisler, N.W. Buehrig, R.E. Coast, J. Mcmillian, N.C. Edwards, and C. Hovermale. 1984. The Effect of Planting Date Row Spacing and Variety on Soybean Yield in Mississippi (Bulletin 912). Report prepared for the Mississippi Agricultural and Forestry Experiment Station.

Hamilton, A. V., D.A. Mortensen and M.K. Allen. 2017. The state of the cover crop nation and how to set realistic future goals for the popular conservation practice. Journal of Soil and Water Conservation. 72(5), 111-115A. DOI: 10.2489/jswc.72.5.111A

Mirsky, S.B., W.S. Curran, D.A. Mortensen, D.L. Shumway, and M.R. Ryan. 2011. Timing of cover crop management effects on weed suppression in no-till planted soybean using a roller-crimper. Weed Science 59:380–389

Oplinger, E.S. and B.D. Philbrook. 1992. Soybean planting date, row width, and seeding rate response in three tillage systems. Journal of Production Agriculture. 5: 94-99. DOI:10.2134/jpa1992.0094

Pedersen, P. and J.G. Lauer. 2004. Soybean growth and development response to rotation sequence and tillage system. Agronomy Journal 96(4), 1005–1012. D.o.i.:10.2134/agronj2004.1005

Wade, T., R. Claassen and S. Wallander. 2015. Conservation-Practice Adoption Rates Vary Widely by Crop and Region, EIB-147, U.S. Department of Agriculture, Economic Research Service. Available at https://www.ers.usda.gov/webdocs/publications/44027/56332_eib147.pdf?v=42403

Wallace, J.M., W. S. Curran, S. B. Mirsky, M.R. Ryan. 2017. Tolerance of interseeded annual ryegrass and red clover cover crops to residual herbicides in mid-Atlantic corn cropping systems,” Weed Technology, 31(5), 641-650.

Weaver, D.B., R.L. Akridge, and C.A. Thomas, C.A. 1991. Growth habit, planting date, and row-spacing effects on late-planted soybean. Crop Science (31) 805-810

Whaley, C., J. Adkins and P. Sylvester. 2015. Final report to Delaware soybean board: Evaluating the response of full season and double-cropped soybeans in narrow and wide rows to various soil moisture levels.

Wilson, M. L., J.M. Baker, and D.L. Allan. 2013. Factors affecting successful establishment of aerially seeded winter rye. Agronomy Journal, 105(6), 1868–1877.

 

Effective Cover Cropping in Extremes of Weather

Catherine Gaudlip2, Nathan Sedghi2, Rebecca Fox2, Leslie Sherman and Ray Weil1
1University of Maryland and 2Washington College

Thanks, in part, to the Maryland Agriculture Cost Share (MACS) incentive program, Maryland farmers have long led the nation in cover crop adoption. Over the past few years, many farmers have graduated from single-species to multiple-species cover crops that can increase biodiversity, soil health and resilience in the face of unpredictable weather extremes. Fine-tuning cover crop management as part of the whole farm system can enhance the benefits that cover crops provide to farmers and the Bay. For example, waiting until harvest is completed to plant cover crops in fall (hopefully by the last MACS deadline) and then terminating the covers as early as possible in spring is still a common approach that severely limits the benefits derived from multi-species cover crops. To perform effectively in preventing nitrogen leaching over the winter, cover crops need to get as early a start as possible so their roots will clean up the mobile nitrate from the deep soil layers where it is most susceptible to being lost to the Bay. Accomplishing this requires finding innovative ways to provide sufficient growing degree days (GDD) in fall. The same cover crop that prevented nitrogen leaching over the winter can pivot to providing nutrient cycling, weed suppression and soil and water conservation during the spring and summer if – and this is a big if – it is allowed to produce a large diverse biomass before it is terminated.

Figure 1. Daily precipitation in fall during cover crop planting time. Fall 2017 was very dry while fall 2018 was extremely wet.

A common practice in Maryland is to drill a cover crop after harvest, which would typically be in October or November, and then kill it as early as mid-March to early April in the spring. We are conducting research that compares this common practice to a cover cropping season that is extended both in fall and in spring. There are many innovations that farmers are devising to extend the cover cropping season, but the most common and simplest are; 1) flying cover crop seed into standing crops weeks or even months ahead of harvest in the fall and 2) delaying cover crop termination right up to or even beyond cash crop planting in the spring using a technique known as “planting green.” Flying on cover crop seed may have the advantage of giving the covers a head start; however, it is more weather-dependent, can less reliably establish a good stand, and may produce less even stands than drilling after harvest. Planting green has been practiced successfully for almost a decade by a few innovative farmers in Maryland and elsewhere, but there is little research yet to document its performance. The strikingly different weather patterns of the past two years has allowed our research to assess how well these cover crop season-extending practices perform under a wide range of conditions.

Our study was conducted in collaboration with four farmers in Talbot and Kent Counties for two years. Seven fields (5 corn and 2 full season soybean) were used in fall 2017, and six fields (1 corn and 5 full season soybean) in fall 2018. Each field received two different cover crop planting treatments using a mix that included a brassica, legume, and cereal. The idea was to compare typical current cover crop management to an experimental extended-season cover crop. Therefore, cover crops were seeding either 1) by airplane into standing corn or soybeans between late August and the end of September, or 2) by drilling the seed after cash crop harvest (usually in October or November). In fall 2018, a third treatment, a no-cover control strip, was also included in each field. In spring the entire field was planted to a cash crop (corn or soybeans) on the same date, but the drilled cover crop was terminated at the farmer’s earliest convenience (2-4 weeks before cash crop planting), while the flown-on cover crop was planted green and terminated simultaneously with, or shortly after, cash crop planting.

Cover crop above-ground biomass (including the above ground portion of radish tuber) was harvested at random locations, separated by species, and weighed during the late fall, just before radishes were winter killed. Spring cover crop biomass was harvested just before herbicide application on the early killed treatment, and just before cash crop planting on the treatment that was planted green. Cover crop biomass was recorded by plant family, and the effects of planting/termination treatment was analyzed. We also analyzed the relationship between cover crop biomass and local weather conditions. Air temperature of 4 ᵒC (39 ᵒF) was used as the base in GDD calculations for the cover crop. The number of GDDs between cover crop planting and December 1st was determined for each treatment on every field, representing the number of growing degree days available to each cover crop. Cumulative daily rainfall for September and October was also analyzed to differentiate fall cover cropping conditions between the two years.

The amount of rainfall during September and October, when cover seeds were flown or drilled, differed greatly between 2017 and 2018. The fall of 2017 was hot and dry (Figure 1), with approximately 2” of rainfall for the entire month of September, and no autumn day having greater than 1” of rainfall until October 12th. In September and October of 2018 there were several rainfall events of greater than 1”, and there was no two week period without a daily rainfall of at least 0.5”. Unless irrigation is applied (a practice worth considering if available) the effectiveness of aerially seeding a cover crop is highly dependent on timely rainfall to germinate seeds that are broadcast without much seed-to-soil contact. On the other hand, excessively wet conditions can delay harvest operations and push cover crop drilling dates into November or beyond.

The contrast between fall 2017 and fall 2018 was dramatic. In 2017, harvest was on-time and some cover crops were drilled before the end of September, leading to only a two week difference, on average, between flown and drilled cover crops in our study. The flown cover crop stands were not very uniform and stand establishment was not always successful, likely due lack of rain after seeding causing late germination. In 2017, two fields were excluded from data collection because the flown cover crop failed to establish. The higher uniformity of the drilled cover crop resulted in a strong correlation between available growing degree days and total cover crop biomass (Figure 2, upper).

Figure 2. Total cover crop biomass harvested in late fall by treatment, correlated with growing degree days left in the season at the time of planting (avg. temp of each day added together). Upper graph shows the average of 7 fields for the flown treatment and 6 fields for the drilled treatment for fall 2017. Lower graph shows the average of 6 fields for both the flown and drilled treatments.

In 2018, by contrast, wet conditions led to timely germination and lush, fairly uniform stands on the flown cover crop treatments. However, the wet conditions delayed cash crop harvest, delaying and reducing the effectiveness of post-harvest cover crop drilling. The delays led to the drilled cover crop stand being a failure in one field and the time difference between flying-on and drilling cover crop seed was about 4 weeks, on average. In 2018, available growing degree days correlated closely with fall biomass achieved for flown-on cover crops, but the correlation was weak for drilled cover crops (Figure 2, lower).

Figure 3. Cover crop biomass by type in fall 2017 and spring 2018 on the same fields. The previously drilled cover crop was killed in early April, and the previously flown cover crop being killed in late April.

While there were several individual fields with higher drilled than flown cover crop biomass in 2017, the overall average winter biomass did not differ between the two seeding methods. The cover crop biomass was not evenly distributed among the species planted. The majority of biomass in the drilled treatment came from cereals. Cereals, more than legumes and brassicas, germinate and grow well in the cooler conditions of late fall. The majority of fall 2017 biomass in the flown treatment was from brassicas (rapeseed, radish). The brassicas are very quick to germinate and grow aggressively in the warmer condition of early fall/late summer, crowding out the cereals, but apparently co-existing with the legumes. In the spring of 2018, the same pattern was observed. The drilled cover crop, which was also killed in early April, consisted almost entirely of cereals. Cereals were also made up about 60% of total biomass in the flown and planted green treatment, but there was much higher clover biomass in this treatment than in the drilled and killed early treatment (Figure 3). Cereals are good at reducing nutrient leaching, but also tend to tie up nutrients for the spring cash crop. In the wet fall of 2018, the flown biomass was substantially higher and more diverse (Figure 4). Brassicas dominated the flown biomass, but the clover biomass was almost as high as the cereals. In the drilled treatment, cereals provided almost all the biomass, but this was still lower than the cereal biomass in the flown treatment. In spring 2019, cereals still dominated the drilled and killed early treatment, but there were more weeds than either clover or brassicas. The flown and planted green cover crop biomass was approximately 45% clover. This high proportion of clover can be expected to eliminate nitrogen tie-up and may allow some reduction in fertilizer nitrogen application for the following cash crop. High weed biomass in the spring of the no cover treatments indicate that the cover crops in both management systems substantially suppressed weed growth.

Figure 4. Cover crop biomass by type in fall 2018 and spring 2019. These were collected from the same fields, with the previously drilled cover crop being killed in early April, and the previously flown cover crop being killed in mid-late April or early May.

We can draw some preliminary conclusions from these data. While drilling a cover crop stand resulted in greater uniformity in the dry year, this did not necessarily produce greater cover crop biomass. Waiting until after harvest to drill a mixed species cover crop reduced the relative and absolute amount of brassica and clover growth. A cover crop dominated by cereals in the fall can lead to nitrogen tie up in the spring. In the wet year, flying a cover crop early was substantially more effective than drilling a cover crop, leading to higher biomass produced and greater diversity in mixed stands. These observed benefits are increased by delaying kill time in the spring. While there’s always a possibility that a cover crop stand can fail, our data suggest that even in a dry fall when weather conditions favor drilling, flying a cover crop on before harvest can still be an effective practice, on average. In the extremely wet year, flying on the seed early was far more effective, on average, than drilling after harvest. While more site-years of data are needed, these data are encouraging for inter-seeding, especially for mixed-species cover crops.

Note: This research is generously supported by ShoreRivers, Inc. and the Maryland Soybean Board.