Nitrogen in potato rotations with cover crops: Field trial and simulations using DSSAT

Abstract

AbstractA 2‐yr field trial was conducted in 2014−2015 in northern California to determine the N availability from different legume and grass cover crops grown during the summer and incorporated in fall. Russet Norkotah potato (Solanum tuberosum L.) were planted the following spring. The objectives of this study were to determine whether potato yield can be successfully predicted with the Decision Support System for Agrotechnology Transfer (DSSAT) model for different cover crop treatments and to assess the risk of nitrate (NO3−) leaching losses with winter precipitation. The total amount of N in the aboveground biomass of the legumes ranged from 73 to 253 kg ha−1. The potato yield of the unfertilized control reached 39 Mg ha−1, while it ranged from 34.8 to 47.9 Mg ha−1 in the cover crop treatments. The DSSAT model considerably underestimated the soil mineral N content before potato was planted in the treatments with legume cover crops. The results suggest that the legumes likely covered a larger proportion of their N requirements through N2 fixation and less through uptake of soil mineral N than predicted by the model. The inaccurate simulation of cover crop soil N uptake contributed to a poor prediction of potato yields for individual treatments. In contrast, the model was successful in simulating N mineralization from cover crop residues. Using weather data from a 30‐yr period revealed that NO3− leaching below the root zone of the subsequent potato crop is minimal in most winters.