The overall aim of the proposed research is to provide information that may help change the mindset about spring cover crop management from one of terminating as early as possible to get it out of the way and minimize complications at cash crop planting to managing for maximal cover crop performance for soil health and profitability. Maryland has by far the nation’s highest proportion of cropland acres cover cropped. However, farmers enrolled in the state cover crop programs typically plant a single species cereal cover crop and 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, summer 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, can 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. The longer-term benefits may include participation in emerging carbon markets which offer per-acre payments for sequestering more carbon from the atmosphere. Yet many are calling into question the ability of cover crops to reliably sequester carbon and mitigate climate change (Popkin, 2022).
Much of the uncertainty about cover crops’ effects on carbon sequestration arises from the fact that most cover crop data is simply about adoption of the practice, not about the performance of the cover crop. The emerging carbon markets are hampered by a high level of uncertainty about cover crop performance and management, and also uncertainty about models used to predict the carbon stored by cover cropping. Perhaps the biggest weakness in these models is the almost total lack of data on belowground (root) carbon contributed by various cover crops at different stages of growth. This project will measure root biomass as well as aboveground biomass since roots are known to contribute more, pound for pound, than shoots to building soil organic matter and sequestering carbon. The aim is to start providing the data needed to make reliable carbon predictions about cover crops impacts on carbon sequestration for more viable carbon markets that benefit farmers.
Preliminary experience suggests that planting into living cover crops may also save time, improve stands, gain additional weed suppression, and possibly reduce slug damage to crop seedlings. Interest in spring cover crop management has been further stimulated in recent years in Maryland since the MDA cover crop program has included an extra incentive to postpone termination to after May 1st.
The aforementioned cover cropping benefits and concerns are of particular relevancy to soybean production because 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), compaction alleviation, and slug distraction effects of high springtime biomass cover crops.
Our objectives are to 1) document the impacts (benefits and/or problems) of later termination, and 2) develop 2 and test strategies and technologies for letting cover crops grow longer in spring (including planting green). Using replicated experiments on coastal plain soils at the University CMREC research farm and collaborating commercial farms in 2017-2019 we showed that biomass carbon added to soil and N fixed by legumes was 4 times greater with early May instead of early April termination. There was no drag on yields with either practice so long as a mixture with brassicas and/or legumes was planted. We currently have 2 sites at the Beltsville CMREC research farm with excellent early-planted rye, radish and rye-radish-clover mix cover crops that are in their third year if cover crop treatment implementation. In addition, we are collaborating with commercial soybean/corn farmers on the Eastern Shore. We plan to measure nitrate leaching, cover crop biomass (including root biomass carbon) and nutrient contents, soil water fluctuations and crop growth and yield in 2023. In addition, we plan to expand our study of the impact of cover crop termination timing on slug
damage to both soybeans and corn seedlings on silty soil with restricted drainage and previous slug infestations.
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, carbon sequestration and profitability.