Understanding Cereal Rye Nitrogen Decomposition and its Transition into Inorganic and Organic Soil Nitrogen Pools

View the project final report

Commodities

• Agronomic: corn, rye, soybeans

Practices

• Crop Production: catch crops, cover crops, nutrient cycling, nutrient management
• Soil Management: nutrient mineralization, soil analysis, soil chemistry, soil microbiology

The incorporation of cover crops (CC) in agricultural cropping systems has increased by 422% over the past eight years. This rapid increase in adoption is primarily driven by producers' knowledge of the ability cover crops to reduce sediment, increase soil heath, and to reduce nitrogen (N) loss from the landscape. The ability of cover crops to scavenge N has been well documented within the scientific community, and the decomposition and release of this N has garnered more interest amongst researchers in recent years. While the rate at which cover crop shoot biomass decomposes has been investigated, what remains unknown information is the partitioning of cover crop residue N in to soil N pools after release and the bioavailability of decomposed cover crop N across the growing period of subsequent crops. Therefore the proposed objectives of this study are to use 15N labeled isotope techniques to I.) investigate the decomposition rates of cereal rye shoot and root biomass, II.) investigate the synchrony of cover crop N release with peak N demand growth stages for maize, III.) determine the partitioning of decomposed cover crop N amongst the soil inorganic, organic, and microbial biomass N pools; among three of the most common soil orders within the North Central region. 15N labeled cereal rye root and shoot biomass will be used to track cover crop biomass N into the various soil N pools. Results from this study will enhance the knowledge surrounding cover crop root and shoot biomass decomposition and N availability, potentially allowing for producers across the North Central SARE region to advance their understanding of how cover crops affect N availability to cash crops after termination, which could lead to more effective adaptive fertilizer management.

The incorporation of cover crops into agricultural cropping systems across the North Central region has been steadily increasing over the past ten years. However, the portion of acres under cover crop production remains relatively low compared to the total number of cultivatable acres across the region. While there is ample knowledge surrounding cover crop environmental benefits such as nitrogen (N) scavenging, reduction of surface water contamination, and erosion control, hesitation in cover crop adoption could be linked to the lack of knowledge surrounding agronomic benefits provided by cover crops, specifically the release and bioavailability of N scavenged during cover crop growth. Therefore, the learning outcomes of this study are to 1.) elucidate the transition of decomposed cover crop N into the soil inorganic, organic, and microbial biomass N pools, 2.) to determine the bioavailability of that N over the duration of maize and soybean growing seasons, and 3.) investigate the synchronicity of bioavailable cover crop N with periods of peak growth and N demand in maize and soybean cropping systems. Accomplishing our learning outcomes could lead to the education of producers, trainers (i.e. certified crop advisors, government agency training officers), and the scientific community on the bioavailability of cover crop N to subsequent cash crops. Finds from this project will increase the knowledge of crop production in agricultural systems including cover crops and potentially allow for more effective adjustment of fertilizer management plans to account for bioavailable N released during cover crop decomposition and more positive economic cover crop experiences.