Recent research by Chatterjee et al. (2015) and Aher et al. (2016) have shown that significant levels of crop residues can accumulate in crop rotations in which high residue crops such as wheat or corn are frequent component crops. This residue accumulation is partly due to the relatively cool climate in the northern Great Plains of the U.S. High residue producing crops often have high N requirements. N fertilizer is a major input in the cost of crop production, but little information is available in the literature about the rate of N mineralization and the N contribution of residue decomposition to the N requirements of subsequent grain crops in long-­term no-till culture. We have just completed laboratory research that shows that most crop residues after harvest have wide C:N ratios which encourage N immobilization rather than N mineralization. We have also noted that adding a high N-mineralizing cover crop such as forage radish may negate the immobilization through supplementing microbial N needs during the rapid growth phase of crop development. Since this previous work was done under optimum laboratory temperature and moisture conditions, we need to validate our findings under field conditions. Knowledge of the mechanisms of N cycling from post-harvest crop residues in combination with effects of cover crops in long-term no-till culture will information growers on improved decisions about the most efficient use of their fertilizer N applications.

(a) evaluate and validate our laboratory research on N-mineralization/immobilization processes in a field environment.
(b) determine how varying temperature and moisture conditions in a field environment affect crop residue decomposition and N mineralization under a no-till culture, and
( c) evaluate whether a cover crop ( e.g. radish) can help mitigate N immobilization under field conditions.

This study is currently providing information on soil moisture and temperature changes during the growing season. Soil sampling during the season will provide information on soil plant­ available N related to the residue(s) accumulating on the soil surface. This information will be presented at farmer/grower workshops and incorporated in research and extension publications providing farmers with information to make sound fertilizer management decisions.

Updated November 30, 2022:

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Most soybean growers grow the soybean in rotation combinations with other crops (spring wheat, corn) as a means of providing crop diversity to control weeds, insects and diseases as well as providing an N credit for their subsequent crop's fertility needs. Our research shows that heavy crop residue accumulation in long-term no-till culture may be responsible for N immobilization in subsequent crops. Soybean can lend itself to seeding a fall cover crop after harvest that may help offset N immobilization and mitigate the immobilization by the residue. However, soil moisture and temperature are variables that cannot be controlled under field conditions. This work will provide a clearer picture of how the crop cam be managed to improve N availability to subsequent crops.