Brian Caldwell1, Chris Pelzer1, and Matthew Ryan1
|1Soil and Crop Sciences Section – School of Integrated Plant Science, Cornell University
The InterSeeder is a new tool developed at Penn State University that allows for drilling of cover crops into standing cash crops (Figure 1). At the same time, liquid fertilizer and herbicides can also be applied to reduce the number of tractor passes. Three 7.5”-spaced rows of cover crops are drill interseeded in the space between 30” corn or soybean rows, allowing for excellent establishment of the cover crops. This takes place after the cash crop is established and is no longer susceptible to competition from weeds (i.e., after the critical period for weed control, which is roughly stage V5 for corn and V4 for soybeans (Hall et al. 1992). Compared to being planted after cash crops are harvested in late fall, interseeded cover crops have more time to grow before winter (Figure 2). As corn and soybean begin senescing in late summer, cover crop plants quickly add biomass before winter. In proportion to their growth in the fall and the next spring, cover crops provide a number of benefits such as recycling of nitrogen in the soil, protecting soil from erosion, and adding organic matter.
Previous research was done in New York State using other methods of interseeding into corn (Scott et al. 1987) and soybeans (Hively and Cox 2001). See also http://mysare.sare.org/wp-content/uploads/917698final.pdf. Results were promising, but problems remained with inconsistent cover crop establishment (Jane Mt. Pleasant, personal communication). Although drilling cover crops with the InterSeeder has potential to increase consistency of establishment so that cover crop benefits are achieved, there are a number of questions about the best way to implement this practice. Optimal seeding dates, cover crop species, varieties, mixtures, and soil nutrient levels have yet to be determined. Here we report on field experiments in NYS over the past two years.
On-farm cover crop interseeding trials
In 2013 and 2014, several trials were conducted in at four on-farm sites and at the Cornell Musgrave Research Farm. Five treatments consisting of two annual ryegrass varieties, tillage radish, a legume mix (hairy vetch, red clover, and crimson clover), and ryegrass + legume mix were interseeded into corn. Roundup Ready corn was used at all locations and glyphosate was applied to control weeds prior to interseeding.
Interseeded tillage radish was grown in two trials only. It produced 100-500 dry lb/acre of biomass in the fall and was killed over the winter. Performance of annual ryegrass and mixes was variable. In general, fall cover crop dry biomass was less than 700 lb/acre. In the following spring, legumes and legume mixes often produced the most biomass. Spring biomass of winter hardy species was influenced by cover crop termination date. Overwintered cover crops in New York typically grow rapidly after May 1 until they begin to reproduce in late May to mid-June. Thus early May termination can result in much lower biomass than that of cover crops terminated in late May or early June. Biomass in the fall reflects the ability of a cover crop to reduce erosion and protect soil over the winter, whereas its biomass in the spring affects soil nutrient levels. For example, depending on management practices and weather conditions, a legume cover crop biomass of 1,000 lb/a in the spring can typically provide 15 lbs/acre of nitrogen to the following crop.
In our trials, yield of the “host” crop (a cash grain crop into which the cover crops were interseeded) was not affected by the presence of an interseeded cover crop, except in one case when the interseeding was done too late and a soybean crop was damaged by equipment. However, the host crop strongly affected the interseeded cover crop. At the Cornell Musgrave Research Farm, legumes produced over 1,500 lb/acre of biomass by May 22, 2014. In contrast, at the Reed Farm in northern New York, all cover crops produced less than 250 lb/acre of biomass by May 13, 2014. Temperatures were cooler at the Reed Farm and cover crop termination was earlier, partially explaining the lower biomass levels. In addition to climate differences, the 2013 Musgrave Farm host corn crop produced less than 100 bu/acre (due to excessive spring rain and poor drainage), whereas the Reed Farm host corn crop yielded twice as much. Cover crop growth at Musgrave Farm in spring 2014 was likely more vigorous because it established under the weaker-growing 2013 host corn. Dense, tall corn such as in the Reed Farm trial, and closed-canopy soybean stands will shade and suppress cover crops interseeded into them, especially under dry conditions.
In 2013, cover crops also performed very well at the Evanick Farm, a dairy where corn was grown for silage instead of grain. Corn was planted on May 4, 2013 and cover crops were interseeded on July 2, 2013. At this site, ‘KB Royal’ annual ryegrass produced over 2,000 lb/acre of fall biomass, sampled on October 30, 2013, and the annual ryegrass + legume mix produced 1,850 lb/acre. The next spring KB Royal, legumes, and the ryegrass/legume mixture each produced about 750 lb/acre by May 1, 2014. On dairy farms such as the Evanick Farm, manure applications may result in relatively large amounts of nitrogen mineralization after silage harvest in mid-September. This, plus the early date of corn silage removal, can allow for high cover crop biomass levels in the fall, and impressive growth in spring before an early termination. Silage yield was moderate and was not affected by the interseeded cover crops.
Comparing interseeded cover crop species in soybean
In 2013, 11 cover crop species and mixes were drill interseeded into soybeans at the Cornell Musgrave Research Farm in Aurora, New York and their performance was compared. Again, Roundup Ready soybeans were planted and glyphosate was applied for weed control prior to cover crop interseeding. Cover crops were drill interseeded into soybeans on July 16, which resulted in good establishment. Soybean yields averaged 53 bu/acre across interseeded cover crop treatments. Fall 2013 cover crop biomass, sampled after soybean harvest on November 19, 2013, was high for crimson clover, the legume mix, perennial ryegrass, cereal rye, and annual ryegrass. Red clover and tillage radish produced intermediate amounts of biomass. Orchardgrass, yellow sweet clover, ladino clover, and Kentucky bluegrass produced a low amount of fall biomass (Figure 3).
The following spring, several species grew well before termination on May 22, 2014. Cereal rye produced 2,000 lb/acre and medium red clover produced over 1,200 lb/acre. Yellow blossom sweet clover, perennial ryegrass, and orchardgrass also produced around 1,000 lb/acre. Annual ryegrass, Kentucky bluegrass, and ladino clover performed poorly, and winter survival of crimson clover and tillage radish was very low (Figure 3).
In the 2014-15 soybean trial, results were quite different. Weather conditions during the 2014 growing season were more challenging and cover crops were not interseeded until August 11, almost a month later than in 2013. Soybean yields were lower at 38 bu/acre, and again no differences in soybean yield were observed between treatments. Fall 2014 cover crop biomass was visibly much lower than in 2013, but cover crops were not sampled. In spring 2015, annual ryegrass produced the greatest biomass, which was similar to the amount of annual ryegrass produced in the spring of 2014. However, the other cover crop treatments did not perform as well as in the previous year (Figure 4).
Interseeding cover crops into soybeans has potential, but this practice needs more research. We observed that earlier-seeded cover crops could establish well and produce more fall and spring biomass than later-seeded cover crops, without impacting soybean yield. In both years of the experiment, red clover, orchardgrass, and the ryegrass treatments were among the top producers of biomass.
Interseeding cover crops into corn and soybeans can be a successful strategy to improve cover crop performance without decreasing host cash crop yields. Despite variable results, our findings indicate that: 1) interseeding cover crops too late can reduce cover crop establishment and limit biomass production; and 2) delaying cover crop termination until the second half of May can increase biomass production substantially. Interseeding cover crops in silage corn (rather than grain corn) results in better cover crop growth because corn silage is harvested earlier than corn grain, thus allowing for unobstructed cover crop growth for about an extra month in the fall.
We suggest that a reasonable interseeding program may be to establish a mixed ryegrass and legume cover crop under soybeans before next year’s corn; or ryegrass alone under corn before next year’s soybeans. Cover crops should produce a fall biomass of 200 to 500 lb/acre and protect the soil over winter. The following spring, delaying cash crop planting until late May can allow production of 2000 lb/acre cover crop biomass. Increased duration of spring cover crop growth could increase nitrogen content of biomass to 60 lb N/acre, in addition to cycling other nutrients and adding organic matter to the soil. There would likely be a minor 2nd year corn yield loss with this approach due to late planting date, but this could be offset by a reduction in corn nitrogen fertilization costs. Research is needed to better understand tradeoffs with yield potential and fertilizer costs associated with delaying cover crop termination in the spring.
The InterSeeder was designed by Bill Curran, Corey Dillon, Chris Houser, and Greg Roth at Penn State and they have developed additional guidelines and herbicide recommendations for cover crop interseeding. For more information about this practice and the InterSeeder see:
This work was supported by a joint research and extension program funded by the Cornell University Agricultural Experiment Station (Hatch funds) and Cornell Cooperative Extension (Smith Lever funds) received from the National Institutes for Food and Agriculture (NIFA) U.S. Department of Agriculture (Project: 2013-14-425). Partial support was also provided by the Northern New York Agriculture Development Program (Project: The early interseeded cover crop gets the worm) and the USDA NRCS CIG program (Project: Maximizing conservation in the Chesapeake Bay Watershed with an innovative new 3-way interseeder for early establishment of cover crops in no-till corn and soybean). Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture.
Hall, M.R., C.J. Swanton, and G.W. Anderson. 1992. The Critical Period of Weed Control in Grain Corn. Weed Science. 40:441-447.
Hively, W. D. and W. J. Cox. 2001. Interseeding Cover Crops into Soybean and Subsequent Corn Yields. Agron. J. 93:308–313.
Scott, T. W., J. Mt. Pleasant, R. F. Burt, and D. J. Otis. 1987. Contributions of Ground Cover, Dry Matter, and Nitrogen from Intercrops and Cover Crops in a Corn Polyculture System. Agron. J. 79:792-798.