Nitrogen dynamics and yields of fresh bean and sweet corn with different cover crops and planting dates

Abstract

Cover crops are recommended to mitigate N losses but effects on crop productivity have been variable and often negative. A better understanding of management-specific cover crop systems may lead to yield improvements. In 2011–2014, a split–split-plot factorial field experiment, with four replicates assessed the impact of cover crop (five species and no cover crop controls) and planting date (August vs. September) on crop yield and N dynamics. Fresh bean (Phaseolus vulgaris L.) and sweet corn (Zea mays L. var. rugosa) were grown with 45 and 101 kg N ha−1 fertilizer, respectively, except for the no cover crop without fertilizer control (Nocc-NoN). Although there was a cover crop by planting date interaction (P < 0.05) for cover crop biomass and N accumulation in the fall and spring, this interaction was not observed in main crop yield nor N concentration and accumulation, suggesting that simply growing a cover crop and below-ground effects may be more influential than the quantity and quality of above-ground biomass. Based on greater yields (6.9%) than the no cover crop with fertilizer (Nocc+N) control, all cover crops tested were recommended before corn but only the oat cover crop increased fresh bean yield (by 10.5%), which suggests crop-specific recommendations are needed. Yield improvements could not be attributed to N fertility alone, suggesting another mechanism was involved. The increased productivity with cover crops while minimizing potential for N losses in the non-growing season has important implications for sustainable agroecosystems and food security.