Nitrate losses in subsurface drainage and nitrous oxide emissions from a winter camelina relay cropping system reveal challenges to sustainable intensification

Sustainable intensification strategies seek to increase production while decreasing the environmental footprint of agricultural systems. In the Upper Mississippi River Basin, relay cropping of a winter oilseed crop between corn and soybean has gained interest for its potential to increase total yields and revenue while providing the environmental benefits of winter cover. In a six-year field study in central Iowa, a basic corn-soybean rotation was compared with a corn-winter camelina-soybean relay cropping system for crop yields, nitrate losses in drainage, and nitrous oxide (N2O) emissions from soil. Despite filling a niche as an overwintering crop with the potential to assimilate soil nitrogen, nitrate loads in drainage were not reduced in the camelina relay cropping system. Over the course of the study, management changes to support the camelina crop tripled cumulative N2O emissions during the camelina-soybean phase, from 3.57 kg N2O-N ha-1 in the basic corn-soybean rotation to 12.2 kg N2O-N ha-1 in the camelina relay system. Most of the increased emissions in the camelina system were associated with peak emissions events following tillage and starter fertilizer application in the fall and during the spring thaw, which may point to risks of exacerbating greenhouse gas emissions during fall management of a relay crop. Corn and soybean yields were decreased in the relay cropping system by 9.8 % and 23.3 %, respectively, as a result of management changes to the system and interspecific competition. However, combined grain dry weight of soybean and the camelina oilseed crop were similar to the soybean yield in the basic corn-soybean rotation. These findings highlight the need for careful evaluation and optimization of sustainable intensification systems to ensure environmental and production goals are met.