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 (Figure 1) 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 shortterm
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 (even more than corn, Figure 2) 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 compactionalleviation effects of high springtime biomass cover crops.

In 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.

1) document the impacts (benefits and/or problems) of planting earlier and killing later,

2) develop and test strategies and technologies for
(a) getting cover crops established earlier, including airplane seeding, early maturing hybrids, and inter-seeding with ground equipment and
(b) letting them grow longer in spring (including planting green).

Update:
Extending the Cover Crop Growing Season by Planting Green
August 2021 Progress Report to the Maryland Soybean Board

In the spring of 2021, we began evaluating the impacts of the cover crops planted in the fall of 2020 on both corn and soybean. The biomass of the cover crops allowed to grow until soybean and corn seeds were planted in early May was far greater than for the covers terminated in early or mid-April, with about 100 kg/ha of dry matter (about 40 kg of carbon/ha) added for each extra day of growth. For the rye, crimson clover, and winter weeds present on the spring 2021 cover crops, the time of termination influenced the N content and C/N ratio of their tissues (Figure 1). The more mature plants having higher C/N ratios. However, only the rye (and weeds) reached C/N ratios > 20 which would be expected to immobilize nitrogen as they decompose. For corn planted green into cover crops in early May, we evaluated the effect on early corn growth at the V5 stage. There was a large difference between corn growth on the slowly drained silty soil compared to the well-drained sandy soil. Conditions were cold and wet just after planting for several weeks and the much wetter conditions on the silty field were probably responsible for the reduced corn growth. These conditions were aggravated by the presence of cover crop residue, especially the rye residue. The effect was much less for the three-way mixture. The no-cover V5 corn was significantly larger than the corn growing in the rye residue in both fields, but the three-way mix had the largest corn in the Sandy field and was only slightly smaller than the no-cover corn in the wet silky field. We also evaluated nitrogen uptake by the early corn growth. There was little difference in the nitrogen concentration of the corn tissue except for a small decrease due to the rye cover crop in the wet field. Multiplying these two parameters to give nitrogen uptake showed that the rye cover crop reduced nitrogen uptake as well as growth in the corn seedlings especially on the wet field. The data suggest that the growth inhibition was due to both weather conditions under the rye mulch as well as lower nitrogen availability. Stands we're not affected by the cover crop except in the silty field which had a large slug infestation that caused considerable damage to both the corn and soybean crops.
In fact, the presence of slugs in the silty soil field (7e) gave us an opportunity to study the impact of cover crop type and termination date on slug damage. We took advantage of this and conducted a study on both the corn and soybean residue plots, the results of which are in the attached PDF. The main conclusions were that the slug infestation was significantly worse in corn residue than in soybean residue, even before the crops were planted in spring. In the corn residue, where soybeans were planted, cover crops initially had little effect on the number of slugs counted. However, once the soybeans were planted, cover crops did appear to affect the damage to the seedlings. Planting green by killing the cover crop after soybean planting actually improved the survival and growth of the soybean plants slightly as compared to plots where the cover crop was killed in early-April and mid-April, weeks before soybean planting. All the plots were planted at the same time on May 6th. While all the soybeans stands were considerably reduced, stand counts taken on June 3rd show a significantly higher number of plants surviving in the late-killed (planted green) plots. While this is just one site-year, the dat do lend some support to the idea that having a living cover crop for some time after soybean planting may divert slugs and dilute their damage to the soybean crop. Clearly, this needs to be studied further.
In April 2021 the National Soybean Board published a research highlights story based on an interview with Dr. Weil: Temple, L. (2021). Get more from cover crops: Plant green. Interview with Ray Weil Part 2 of 2 United Soybean Board https://soybeanresearchinfo.com/research-highlight/get-more-from-cover-crops-plant-green/

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The overall aim of this research was 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. Planting green may also impact the risk of slug damage to soybean seedlings in no-till fields.

The aforementioned cover cropping benefits and concerns are of particular relevance 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 (even more than corn) 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. However, since most soybeans are grown in rotation with corn, this research will examine cover crop interactions with both crops. In summary, this project aims to generate important information on how to better use cover crops for improved soil quality, reduced crop stress, enhanced nutrient cycling, and profitability.

Results for 2021
While this project is ongoing, the results so far have provided some important lessons. We have shown that establishing cover crops early by interseeding into standing crops is practical using a highboy broadcast air-seeder. We also have used a special no-till drill with one out of four drill units removed to provide clearance for a young standing crop. This kind of interseeder drill did an excellent job of establishing three rows of cover crop seedlings between the rows of the cash crop. However, we soon learned that the soybean canopy is so dense that not enough light penetrates to allow these seedlings to survive the summer until soybean senescence. The system using a drill works much better in corn which allows more light to penetrate. However, we found that drilling was possible only during a very brief window and was very dependent on suitable soil moisture conditions during that window. This is essentially the same window as the time for side-dressing corn. When soil conditions were on the wet side and in a fine-textured soil, the drill caused enough disturbance to injure some of the corn crop plants and resulted in poor stands because of improper seed furrow closure. In contrast, using a highboy broadcast air-seeder, there was much more flexibility with timing, especially for corn. Good cover crop stands were established when the seed was broadcast anytime between tasseling and the beginning of grain fill in corn canopies. When conditions were dry the seeds sat and waited for the next rain so early planting increased the likelihood of a seed-germinating rain occurring before corn senescence, thus giving the cover crop a good head start. In soybeans, broadcasting cover crop seeds too early resulted in their germinating in a very dark environment and the seedlings soon died. Broadcasting into a soybean canopy was effective when it was done at the beginning of leaf fall rather than the beginning of leaf yellowing. In 2021 successful cover crop stands were established in both corn and soybean with these methods.
During the summer of 2021, our array of sensors showed that the heavier surface residue from the cover crops planted in the Fall of 2020 served to conserve moisture in the upper foot of soil. Because there was relatively good moisture throughout the season this advantage did not translate into significantly higher yields of either corn or soybeans. We expect that in dryer years yields would be advantaged. In the spring of 2021, we observed a significant slug infestation in the fine-textured, wetter field. We took advantage of this to study the impact of cover crops and cover crop termination date on slug damage to soybeans and corn seedlings. The spring of 2021 was unusually cool so the soybeans, in particular, got off to a slow start. However, we did see some significant and interesting effects. Slug numbers were not affected by the cover crop but seemed to be affected by the type of residue on the surface. The slug damage to soybean seedlings was significantly less severe where the cover crop was terminated more than a week after the soybeans were planted. While this was only one site and one year in unusually cool spring conditions, we believe that this effect is likely to be even more pronounced in a warmer spring when soybeans can get off to a faster start. In the next year, the project will continue to study the interaction between cover crop management and the degree of damage caused by slugs.

Cover crops have receive increasing attention from mainstream grain farmers across the US, with the total acres planted to cover crops increasing by 50% from 10 million in 2012 to 15 million in 2017 (USDA/NASS, 2019). Still, this is an increase from 2.8 to 4.3% of US cropland planted to cover crops. In contrast, nearly 50% of Maryland’s cropland as been planted to cover crop in recent years. Cover crops are used by most farmers in Maryland and on a greater proportion of cropland than in any other state. This high adoption rate is largely a result of the Maryland and Delaware departments of agriculture offering generous ($45-95/acre) subsidies for planting cover crops. The main purpose of these cover crop supports is the reduction cropland nitrogen losses to the Chesapeake Bay. However, these programs payout based on cover crop planting and termination, not on cover crop performance. While any cover crop is better than none, cover crop management and performance is often sub-optimal. Typically, a cereal like rye or wheat is planted in October and terminated in March with minimal achievement of ground cover, root and shoot biomass or even N capture.

The cover crop conversation in Maryland is often dominated by program payments rather than by soil health and crop production benefits that effective cover cropping could offer. As farmers can claim payments upon cover crop termination, they understandably may terminate as early as possible in spring – too early for optimal nutrient cycling, water conservation, weed suppression, soil health and crop yield enhancement. In addition, traditional recommendations suggest burn-down or plow-in be done two to three weeks before planting, ostensibly to avoid residue conditions that cause hair-pining with notill planters and also to avoid allelopathic and N immobilization inhibition of crop seedlings. This loss of potential cover crop growing degree days in April/May before cash crop planting can cut cover crop performance by more than half.

In addition, many farmers say they’d likely drop cover crops if payments ceased. Some of these farmers may lack sufficient knowledge of potential cover crop benefits and/or confidence for “dealing with” large springtime cover crop biomass, attendant N immobilization, possible soil profile water depletion, and planter performance issues. They may therefore fail to reap sustained benefits that effectively integrated cover crops could offer.