Estimating Nitrogen Mineralization from Cover Crop Mixtures Using the Precision Nitrogen Management Model

Abstract

A gronomy J our n al • Volume 10 9, I ssue 5 • 2 017 C over crops can serve multiple beneficial functions in cropping systems including improving soil aggregate stability and infiltration, reducing soil erosion, weed suppression, and managing N (Snapp et al., 2005). The dual roles of cover crops for N management in cropping systems, both as a scavenger of excess soil N following a cash crop (often maize), and as a potential source of crop-available N to the subsequent main crop following cover crop termination in the spring, have been reported on extensively (ThorupKristensen et al., 2003). Kladivko et al. (2014) reported that, if wide spread adoption of cover crops (primarily cereal rye, Secale cereale L.) occurred in the central U.S. Corn Belt, nitrate N (NO 3 -N) loading to the Mississippi River could be reduced by approximately 20%. Despite the potentially beneficial functions of cover crops, they are used on less than 1% of cropland in the United States (Wallander, 2013). Increased costs and only minimal yield benefits with cover crops reported by farmers are among the top factors that limit their adoption (Werblow, 2015). Estimating the N contribution of cover crops to a cash crop following cover crop termination can potentially improve N management of cropping systems, increase profits and reduce N losses to the environment. The potential of cover crops to improve N management where maize is the main crop has been of particular interest because of the high N losses and relatively low N use efficiency (<40%) of maize production systems (Cassman et al., 2002).The N content, C/N ratio, chemical composition, winter hardiness, and biomass accumulation of a cover crop or cover crop mixture are important determinants of cover crop residue decomposition and N availability to the subsequent main crop due to this decomposition (Vigil et al., 1991; ThorupKristensen and Dresbøll, 2010;Weinert et al., 2002;Cabrera et al., 2005 ABSTRACTCover crops influence soil N dynamics and N availability to a subsequent crop. Dynamic simulation models, if properly calibrated and tested, can simulate C and N dynamics of a terminated cover crop and estimate crop-available N over diverse production environments. We calibrated and tested a dynamic simulation model modified to simulate C and N cover crop residue dynamics in maize (Zea mays L.) production systems. Data from a 2-yr field study of different cover crop residue mixtures, fertilizer rates, and tillage practices were used in model calibration and testing. First order rate constants governing cover crop residue decomposition were calibrated so that statistical measures of model best fit were optimized. Calibration resulted in a good fit between measured and modeled N release from the terminated cover crop mixtures (root mean square error [RMSE] = 14 kg N ha -1 ; Willmott's index of agreement (IA) = 0.92). The calibrated model performed reasonably well in the testing phase (RMSE = 25; IA = 0.88) with significantly better performance for the no-till (NT) treatments compared to t...

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