Replacing Chemical Fallow with Cover Crops in No-till Cropping System: Effects on Nitrous Oxide Emissions.

The utilization of cover-crops (CCs) in rotation with cash-crops has been proposed to reduce soil nitrous oxide (N₂O) emissions by scavenging excess mineral nitrogen (N) after cash-crop harvest and by reducing N fertilizer requirements for the following cash-crop. This study aimed to evaluate the long-term effects of fallow management [chemical fallow vs. double-crop soybean (Glycine max), sorghum-sudangrass (Sorghum vulgare var. sudanese), daikon radish (Raphanus sativus)] and N fertilization (0, 90 and 180 kg ha^-1) on N₂O emissions on a moderately well-drained Wymore silty clay loam in northeastern Kansas. Soil N₂O fluxes were measured by the closed-static chamber method during the 2014-15 and 2015-16 growing seasons in a three-year winter wheat (Triticum aestivum)/cover crop – sorghum [Sorghum bicolor (L.) Moench] – soybean rotation. Cumulative and yield-scaled N₂O emission (YSNE) values were calculated based on the CC through sorghum harvest emissions to evaluate the overall cropping system effects. Cumulative N₂O emissions was higher for the system managed with double-crop soybean (4.47 g N₂O-N ha^-1), but not significant different from sorghum-sudangrass (4.1 N₂O-N ha^-1) and chemical fallow (3.55 N₂O-N ha^-1); whereas system with daikon radish had the lowest emission of 2.87 g N₂O-N ha^-1. The YSNE was lowest after daikon radish (17.8 g N₂O-N kg^-1 N uptake), but not different from chemical fallow and double-crop soybean (18 and 22.9 g N₂O-N kg^-1 N uptake, respectively). These results suggest that double-crop soybean and daikon radish as fallow management with optimum N rate can have the potential to be mitigate N₂O emissions while sustaining grain sorghum production.