Stover Harvest did not Change Nitrous Oxide Emissions in Two Minnesota Fields

Abstract

Core Ideas Nitrous oxide (N2O) emission varied among years and between crops. The N2O emissions were the same with or without stover harvest in a field without tillage. The N2O emissions were the same with or without stover harvest in field with tillage. The N2O emissions occurred after N fertilizer application in a tilled and no‐till field. The N2O emissions occurred during spring freeze‐thaw in a tilled and a no‐till field. Corn (Zea mays L.) is grown across vast acreages producing massive quantities of stover making corn a desirable cellulosic bioenergy feedstock. Nitrous oxide (N2O) is a potent greenhouse gas (GHG) so small changes in direct soil N2O emissions may have substantial influence on global warming potential (GWP) from the agricultural sector. Harvesting stover alters soil properties such as soil moisture, oxygen availability, temperature, and substrate availability (C and N). Thus, harvesting stover might reduce soil N2O emissions by reducing substrate and by warming and drying the soil. The goal of the study was to determine how harvesting corn stover altered soil N2O emissions. Therefore, soil N2O emissions were measured for four crop‐years (planting to planting) in two independent studies, one in a field managed without tillage (NT1995) and the other was in a field tilled annually with a chisel plow (Chisel). Each field was in a corn–soybean (Glycine max L. [Merr.]) rotation, with (i) corn grain (Grain) only, (ii) grain plus about 50% of the stover harvested (Grain+Moderate), and (iii) grain plus harvesting as much stover as possible (Grain+Aggressive) treatments. Cumulative soil N2O emissions did not differ among treatments in either field during any of the crop‐years monitored. Flux events occurred corresponding to fertilizer applications and to spring freeze‐thaw events. Cumulative fertilizer stimulated emissions tended to be greater for corn than soybean because of N‐fertilizer application. These results are valuable to modelers for enhancing estimates of the N2O component of the stover management C‐footprint.