The overall aim of the proposed research program is to provide information that may help change the mindset about cover crop management from one of doing the minimum to qualify for payments to managing for maximal cover crop benefits for soil health and profitability. Maryland and Delaware have some of the highest proportions in the country of cropland acres cover cropped. However, farmers enrolled in the state cover crop programs typically plant cover crops after cash crop harvest, which our research shows is usually too late to effectively capture the large pool of soluble nitrogen left deep in the soil or provide enough cover to adequately control overwinter erosion. Using aerial or ground based interseeding into standing crops, choosing earlier-maturing corn and soybean cultivars, and making other adjustments to the farming system may allow earlier cover crop establishment. Many farmers also cut short cover crop growth potential in spring by terminating cover crops as early as possible, commonly in late March or early April. Such termination is too early to allow the cover crops to optimally promote soil health, water conservation and crop yield.

Delaying spring cover crop termination until optimal cash crop planting time, especially planting green instead of killing cover crops two to four weeks ahead of planting, could allow both timely cash crop planting and extended cover crop growth. Potential benefits of greater cover crop biomass growth include short term benefits such as greater nutrient cycling, better weed suppression, and more effective water-conserving in summer, in addition to longer-term benefits of increased soil organic matter and biological activity. Preliminary experience suggests that planting into living cover crops may also save time and improve stands and gain additional weed suppression advantages. The aforementioned cover cropping benefits and concerns are of particular relevancy to soybean production for several reasons. First, soybeans tend to leave a large amount of soluble N in the profile at the end of the season and soybeans tend to be harvested later than corn. These factors combine to make early cover crop establishment in fall especially important for soybean systems. Second, soybeans, unlike corn, do not tend to respond adversely to the early shading and N immobilization that may be associated with planting into living high-biomass cover crops after extended growth in spring. Soybeans therefore stand to benefit from water-conservation, nutrient-cycling (K, S, Ca, Zn, B) and compaction alleviation effects of high springtime biomass cover crops. n summary, this project will generate important information on how to better use cover crops for improved soil quality, reduced crop stress, enhanced nutrient cycling and profitability.

Our objectives are to 1) document the impacts (benefits and/or problems) of planting earlier and killing later, and 2) develop and test strategies and technologies for (a) getting cover crops established earlier, including airplane seeding, early maturing crop cultivars, and inter-seeding with ground equipment and (b) letting them grow longer in spring (including planting green).

Reports and recommendations for best management of cover crops in soybean-corn rotation systems.

Updated August 3, 2020:
This grant extension was approved on 29 May 2020. The University of Maryland began its phase 1 return to research in June 2020. Our work has been hampered by the Covid19 restrictions that have not allowed us to use undergraduate students on campus for research.

However, we have established two research field sites and established replicated plots of rye and a 3-species mixed cover crop in plots of soybean and corn crops. Giving the cover crops a head start before cash crop harvest is expected to greatly enhance the cover crop biomass produced and nutrients cycled, both of which can potentially enhance yields or reduce costs for the soybean and corn corps planted the following spring. The 3-species mixed cover crop shown in Figure 1 was photographed in mid-July. It was inter-seeded into corn and soybeans in mid-June. A special no-till drill with clearance for 30-inch crop rows was used. At a second site, the same cover crop mixture will be inter-seeded in mid-August using a hi-boy air-seeder with drop hoses. Neither type of seeding equipment is commonly owned by Maryland farmers, but if their value is proven, that could change rapidly.

Farmers will be able to use the results and recommendations from this project to increase the benefits they derive from cover crops in their soybean cropping systems.

View uploaded report

Updated February 2, 2021:
This progress report covers the period between August 1, 2020 in January 30, 2021. Reference to Figures are to graphics available in the uploaded PDF file. Covid-19 restrictions promulgated by the state of Maryland and by the University of Maryland continued to make it difficult to accomplish research objectives especially with regard to working with undergraduate students who normally constitute our main labor force. However, restrictions were relaxed somewhat in the fall semester and we are able to make good progress on several fronts.
In order to establish the early planted cover crops for this experiment we first established both corn and soybean crops in 30-in wide rows in Early May on three sites at the University of Maryland research station near Beltsville. In late June we used a Penn State University-style inter seeder drill to establish two types of cover crops in the young cash crop stands. The two cover crops established were a three-way mix of radish, crimson clover and rye and a single species cover crop consisting of just cereal rye. The Penn State interseeder worked very well on the site with sandy soil because moisture conditions were good at the time of interseeding in June and excellent cover crop stands were established at two sandy sites with both soybean and corn plots (Figure 1).

At the finer textured site, conditions were quite wet during June so that the no-till interseeder drill failed to achieve good seed furrow closure and stands emergence was very spotty. We did stand counts of the cover crops to document this difference in seeding effectiveness (Figure 2).
In the sandy soil fields where the seeding was most successful we observed that survival of the interseeded cover crops was much better where the cash crop rows ran East to West than where they ran North to South (Figure 3). We speculate that this was a function of sun light penetration. In the middle of summer light penetration was continuous from early morning to late afternoon in the East-West oriented row crops. However, light penetration was effective only at midday in the corn and soybean plots with North-South oriented rows. In these plots the cash crop row to the east of the interceded cover crop strip shaded the interrow from the morning light. The cash crop row to the west of a cover crop strip shaded the interrow from the afternoon and evening light. As a result of this differential shading effect, the interseeded cover crops survived through cash crop maturity in the East-West rows but died, probably from lack of sufficient light, in the North-South rows.
For interceding into soybean with North south oriented rows, the survival of the cover crop through the summer and early fall was poor. Our speculation that this was related to competition for light is supported by the negative relationship between the cover crop percent ground cover achieved and the yield of the soybeans (Figure 4). The best cover crop stand was achieved where the soybeans grew the worst. We believe this was an effect of the soybeans on the cover crop and not the effect of the cover crop on the soybeans.
Overall, the cover crops interseeded in June had no effect on the yield of either corn or soybeans in October in either the fine textured or the coarse textured field experiment (Figure 5).

We continue to monitor the cover crop growth and condition during the winter and have observed that the radish component was severely frost damaged with temperatures around 20 oF for several nights in December and expect a complete winterkill of that species with temperature predicted to be as low as 12 oF in early February.
This Spring (2021) the cover crops will be terminated, and soybean planted into the plots that had corn in 2020 and corn planted in the plots that had soybean in 2020. Corn and soybeans will be planted in late April/early May into green living cover crops and compared to plots where cover crops will be terminated in early April, 3 weeks ahead of corn and soybean planting. The corn plots will again be drill-interseeded with cover crops in June, but the soybean will be air-seeded at leaf drop in early September because of the near total lack of survival under the soybean canopy for cover crops drill interseeded in 2020. Plant nitrogen, early growth, soil water and temperature, weeds, slugs, pests, and yields will be evaluated.

View uploaded report

Updated May 3, 2021:

View uploaded report

This final report covers the period between April 1, 2020 to March 30, 2021. Covid-19 restrictions promulgated by the state of Maryland and by the University of Maryland made it difficult to accomplish research objectives especially with regard to working with undergraduate students who normally constitute our main labor force. However, restrictions were relaxed somewhat in the fall semester and we were able to make good progress on several fronts.
To establish the early planted cover crops for this experiment we first established both corn and soybean crops in 30-in wide rows in Early May on three sites at the University of Maryland research station near Beltsville. In late June we used a Penn State University-style inter-seeder drill to establish two types of cover crops in the young cash crop stands. The two cover crops established were a three-way mix of radish, crimson clover, and rye and a single species cover crop consisting of just cereal rye. The Penn State interseeder worked very well on the site with sandy soil because moisture conditions were good at the time of interseeding in June and excellent cover crop stands were established at two sandy sites with both soybean and corn plots.

At the finer-textured site, conditions were quite wet during June so that the no-till interseeder drill failed to achieve good seed furrow closure, and stands emergence was very spotty. We did stand counts of the cover crops to document this difference in seeding effectiveness.

In the sandy soil fields where the seeding was most successful, we observed that survival of the interseeded cover crops was much better where the cash crop rows ran East to West than where they ran North to South. We speculate that this was a function of sunlight penetration. In the middle of summer, light penetration was continuous from early morning to late afternoon in the East-West oriented row crops. However, light penetration was effective only at midday in the corn and soybean plots with North-South oriented rows. In these plots, the cash crop row to the east of the interceded cover crop strip shaded the interrow from the morning light. The cash crop row to the west of a cover crop strip shaded the interrow from the afternoon and evening light. As a result of this differential shading effect, the interseeded cover crops survived through cash crop maturity in the East-West rows but died, probably from lack of sufficient light, in the North-South rows.

For interseeding into soybean with North south-oriented rows, the survival of the cover crop through the summer and early fall was poor. Our speculation that this was related to competition for light is supported by the negative relationship between the cover crop percent ground cover achieved and the yield of the soybeans (Figure 4). The best cover crop stand was achieved where the soybeans grew the worst. We believe this was an effect of the soybeans on the cover crop and not the effect of the cover crop on the soybeans. Overall, the cover crops interseeded in June did not affect the yield of either corn or soybeans in October in either the fine-textured or the coarse-textured field experiment.

We continued to monitor the cover crop growth and condition during the winter and have observed that the radish component was severely frost-damaged with temperatures around 20 oF for several nights in December. Complete winterkill of radish was not achieved despite nighttime temperatures as low as 17 oF in early February. Therefore, scattered radish plants began to flower in late March. The large roots from early-planted radishes did die and were partially decomposed by the end of March. Cover crop biomass and green groundcover percentage was measured on 02 April and 18-22 April 2021, just before the early- and mid-kill dates. The percent green groundcover in each field for each cover crop treatment just before the mid-kill date showed that the three-species mix had produced significantly more green cover (and biomass) on the sandy soil than the other treatments. Also, as expected, the no cover control had less green cover than either cover crop on both soil.

These measurements of green groundcover were made using an open-source smart phone app called CANOPEO. The app analyzes photographs or video taken vertically from about 5 ft above the ground and separated the image into shade of green living vegetation and black for all other materials (soil, dead residue, etc.). This non-destructive, rapid technique is useful for estimating the growth of cover crops, especially young, small plants. For the large inter-seeded plots of cover crops we walked diagonally across a plot from one corner to the opposite corner while the app analyzed 30 video images. The percent cover from this image analysis was closely related to the biomass dry matter determined by clipping vegetation close to the ground, then washing, oven-drying and weighing the material.

A total of 48 tension lysimeters were installed in the silty clay loam field to sample the drainage water as it percolated past 2ft or 3 ft depths as an indication of the nutrient loss by leaching. Combining samples from four sampling dates between 25 February and 20 April and averaged across both depths we observed nitrate-N concentrations about three times as high under the control plots as under either cover crop when averaged across soybean and corn crop residues (Figure 8, left). When averaged across all cover crop treatments, nitrate-N was about three times as concentrated under soybean residue and under corn residue. However, all values for nitrate-N were quite low, being less than 1 mg/L (1 ppm).

This Spring (2021) the cover crops will be terminated, and soybean planted into the plots that had corn in 2020 and corn planted in the plots that had soybean in 2020. Corn and soybeans will be planted in early May (05 May target date) into green living cover crops and compared to plots where cover crops were terminated ~4 weeks and ~2 weeks ahead of corn and soybean planting. Slugs will be counted periodically for a week before and two weeks after soybean planting using shingles pinned to the ground in 40 plots of Field 7e (silty clay loam) where slugs have been observed during the winter. After emergence, slug damage to soybean will also be scored and recorded. Surface temperature and soil moisture will also be recorded with slug counts. The effect of cover crop kill date (4 or 2 weeks prior to planting or 1 week after planting) will be determined for rye, three-way mix and no-cover (weedy) treatments. The corn plots will again be drill-interseeded with cover crops in June, but the soybean will be air-seeded at leaf drop in early September because of the near-total lack of survival under the soybean canopy for cover crops drill interseeded in 2020. Plant nitrogen, early growth, soil water and temperature, weeds, slugs, pests, and yields will be evaluated.

Farmers will be able to use the results and recommendations from this project to increase the benefits they derive from cover crops in their soybean cropping systems

Establishment of field sites, submission of reports, publication of results and recommendations.