Corn stover harvest changes soil hydrology and soil aggregation

Authors: Johnson, Jane; STROCK, JEFF - University Of Minnesota; TALLAKSEN, JOEL - University Of Minnesota; REESE, MICHAEL - University Of Minnesota

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2016
Publication Date: 4/4/2016
Publication URL: https://handle.nal.usda.gov/10113/63286
Citation: Johnson, J.M., Strock, J.S., Tallaksen, J.E., Reese, M. 2016. Corn stover harvest changes soil hydrology and soil aggregation. Soil & Tillage Research. 161:106-115.

Interpretive Summary: In 2014, three commercial-scale ethanol plants began making ethanol from crop residues. Crop residues have a lot of cellulose, which is a plant product that humans and most animals cannot digest. Cellulosic ethanol is made from crop residues like stover instead of grain. The United States grows a lot of corn grain so there is also a lot of corn stover, which may be used to make cellulosic ethanol. The term stover refers to the leaves, cobs, and stalks that are leftover when corn grain is combined. Now most stover is returned to the field but as the cellulosic industry expands more could be harvested. Sometimes stover is called "trash," but this is a misnomer in that stover is valuable either on or off the field. Keeping stover on the soil surface protects the soil from wind and water. As a result, less soil is lost to erosion. When the stover is removed, the soil is left naked and unprotected. Also keeping or removing stover may change a soil's ability to trap and retain water, and resist erosion. Soil properties change slowly over time; therefore, we studied fields where stover had be harvested at least four times. We found that in a field that was tilled, water did not move very quickly into the soil no matter whether or not the stover was harvested. The tilled field had smaller and less stable aggregate. The soil in the tilled field was exposed, more likely to erode and less likely to be able to capture rain water. The field that had not be tilled for many years could capture and store rainwater, but this was compromised if stover was repeatedly harvested. This means some of the benefits from no tilling are lost if the residue is harvested. Maybe some stover could harvested but we only looked at returning all or removing as much as possible. Even if a field is not tilled intensive stover harvest puts the precious soil resource at risk. This work will aid producers, energy industry, and action agencies to balance the pros and con of harvesting crop residues such as corn stalks for bioenergy. [REAP publication]

Technical Abstract: In the United States, commercial-scale cellulosic-ethanol production using corn (Zea Mays L.) stover has become a reality. As the industry matures and demand for stover increases, a clear understanding of how reducing the rate of stover remaining in the field impacts soil properties is critical. Stover harvest may negatively impact soil hydrological and physical properties, these impacts may differ with tillage management. This paper reports on two independent studies on a tilled (Chisel field) and untilled field (NT1995 field), respectively. Each field was managed in a corn/soybean (Glycine max [Merr.]) rotation and was subjected to two rates of stover return [only grain was harvested and all the stover was returned (Full Return Rate), and an aggressive harvest resulting in a low rate of stover returned (Low Return Rate). Specific study objectives were to measure indices of soil hydrological and aggregate stability responses to harvesting stover. Unconfined field soil hydraulic properties and soil aggregate properties were determined. Hydrological response to residue treatments in the chisel field resulted in low infiltration for both rates of residue removal. In NT1995 field, Full Return Rate had greater capacity to transmit water via conductive pathways, which were compromised in Low Return Rate. Collectively, indices of soil aggregation in both experiments provided evidence that the aggregates were less stable, resulting in a shift toward more small aggregates at the expense of larger aggregates when stover is not returned to the soil. On fields included in this study, our findings suggest that concerns of soil degradation if stover is over-harvested are warranted. Thus, harvest recommendations for sustaining these highly productive soils are needed.