Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2018
Publication Date: 1/1/2019
Publication URL: https://handle.nal.usda.gov/10113/6471062
Citation: Johnson, J.M., Barbour, N.W. 2019. Stover harvest did not change soil nitrous oxide emissions in two Minnesota fields. Agronomy Journal. 111:143-155. https://doi.org/10.2134/agronj2018.09.0591.
DOI: https://doi.org/10.2134/agronj2018.09.0591

Interpretive Summary: In the United States one of the most common grown crops is corn. It grows quickly and produces about as much nongrain plant material as it does grain. This nongrain plant matter is comprised leaves, cobs and stalks, which collectively are called stover or residue. Because so much is produced every year, it was identified non-food material that could be used to make fuel grade ethanol. Harvesting stover can change soil properties including water content, temperature, aeration, and plant material available for soil organisms to consume. Because of the changes in soil properties, harvesting stover might also change how much nitrous oxide is released from soil. Nitrous oxide is potential greenhouse gas that contribute to global warming. We monitored the amount of nitrous oxide released from two fields. One field was managed without tillage and the other was managed by tilling with a chisel plow. Corn and soybean were planted each year in each field. Corn stover was harvested at one of three rates: none, about half and as much as possible. Nitrous oxide was released in both field after applying nitrogen fertilizer and in the early spring as the soil thawed. However, we found that the same amount of nitrous oxide was released in both fields among the three stover harvest treatments. This means that in these two fields harvesting stover did not increase nor decrease how much of this gas was released. These results are important for the bioenergy industry, feedstock producers and for modelers seeking to understand what may happen as stover harvest becomes more common.

Technical Abstract: 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 [carbon (C) and nitrogen (N)]. Thus, harvesting stover might reduce soil N2O emissions by reducing substrate and by warming and drying the soil. We hypothesized that harvesting corn stover would change emissions by altering soil properties compared to retaining the stover. 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 1) corn grain (Grain) only, 2) grain plus about 50% of the stover harvested (Grain+Moderate) and 3) grain plus harvesting as much stover as possible (Grain+Aggressive) treatments. Cumulative soil N2O emissions did not differ among treatment 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 fertilizer application. These results are valuable to modelers for enhancing estimates of the N2O component of the stover management C-footprint.