Nitrous oxide emissions with organic crop production depends on fall soil moisture

Agriculture is the major anthropogenic contributor to global nitrous oxide (N2O) emissions. Many studies have examined soil N2O emissions from synthetic nitrogen (N) fertilizer additions, however, in organic production where plough-down of forage legumes are often used as a nitrogen source, emissions are as not well understood. In the current study, the Glenlea Long-Term Organic Crop Rotation Study near Winnipeg, Manitoba, was used to compare N2O emissions of a conventional annual grain and an organic mixed forage-grain system. Static-vented chambers were used to determine N2O emissions for the 2014 and 2015 crop years; from spring planting to freeze-up and again during thaw following spring. plots monitored were spring wheat and two-cut harvest with late-summer or early-fall plough-down alfalfa for the organic system, and spring wheat and soybean for the conventional system were monitored in each study year. The organically produced alfalfa received composted dairy manure in 2014 and only conventional wheat crops received fertilizer N as urea. Cumulative emissions (g N2O-N ha−1) with organic wheat were half that of conventional management. Cumulative emissions for the legume crops in the 2014 crop year were very low (