Establishment of Permissible Levels of Residue Removal for Corn, Wheat, and Sorghum Fields as Biofuel Feedstocks

View the project final report

• 2011 annual report
• 2012 annual report
• 2013 annual report

Commodities

• Agronomic: corn, sorghum (milo), wheat

Practices

• Crop Production: crop rotation, continuous cropping, no-till, stubble mulching, conservation tillage
• Education and Training: on-farm/ranch research
• Energy: bioenergy and biofuels
• Natural Resources/Environment: carbon sequestration, soil stabilization
• Soil Management: organic matter, soil analysis, soil physics, soil quality/health

This project was first conducted in Kansas (Kansas State Univ.) from 2011 to 2012, and then it was transferred to Nebraska (Univ. of Nebraska) in late December 2012 where it continued from 2013 to 2014. Our project goal was similar in both States. The project assessed the positive and negative impacts of crop residue removal on soil quality and crop production. The experiments in Kansas focused on wheat rotations, while those in Nebraska focused on continuous corn. In western Kansas, we selected six representative on-farm research sites under no-till management in summer 2011. At the six sites, we removed wheat straw at five different levels (0, 25, 50, 75, or 100%) in a randomized complete block design with four replications at each site. All research plots were 30 ft by 30 ft in size for a total of 120 plots (6 sites × 5 treatments × 4 replications). Soil samples were collected from each plot in fall 2011, spring 2012 and fall 2012 to assess soil properties and soil C and N. In this project, we focused more on wind erosion risks due to the prolonged drought conditions during the study period. Crop residue removal at >75% reduced soil dry aggregate size and aggregate stability, indicating that excessive residue removal increased the soil’s susceptibility to wind erosion. Due to the drought, crop yield was very low in 2012. Residue removal did not affect any other soil property. Among three crops (wheat, corn, and sorghum), wheat seemed to be the least affected by residue removal. Both sorghum and corn yield decreased with residue removal rates above 75%.

In Nebraska, we used three experiments of corn stover removal under no-till continuous corn. The first site (irrigated) was at Brule (west central Nebraska) established in 2009, while the second site (irrigated) was at Clay Center (south central Nebraska) established in 2010. We established a third site (rainfed) near Lincoln, Nebraska (Rogers Memorial Farm) in fall 2013 with five different levels of corn stover removal (0, 25, 50, 75, and 100%). The latter experiment was specifically designed to establish permissible levels of stover removal in the long term similar to the experiments in Kansas. We measured grain and biomass yields, soil organic C pools (total C, organic C, and particulate organic matter), and soil hydrologic, compaction, structural, and fertility parameters. In addition to the above soil and crop parameters, greenhouse gas (CO₂, CH₄, and N₂O) fluxes were measured using the LICOR system. Results from the sites at Clay Center and Brule showed that corn stover removal at high rates (>60%) after 4 and 5 yr, respectively, increased wind erosion potential and altered the soil structural properties near the surface. At the Clay Center site, stover removal (>60%) reduced soil water holding capacity and reduced plant available water, indicating that high rates of corn stover removal can reduce water storage and availability for crops. Other soil properties were not affected. Grain yield and greenhouse gas fluxes were not affected by corn stover removal at any site. Our results in Nebraska indicate that corn stover removal at high rates (>60%) can adversely impact soil properties after 4 or 5 yr but not in the first few years.
Overall, the main finding from both studies in Kansas and Nebraska is that crop residue removal at high rates (>60%) increases risks of soil erosion but it may not negatively affect crop yields.

Introduction:

Crop residues are considered as a potential feedstock for cellulosic ethanol production by the energy industry to meet the 30×30 goal (30% replacement of fossil fuels by biofuel by the year 2030). Production of cellulosic ethanol from renewable energy sources is a plausible goal. However, the potential adverse effects of residue removal on crop production and soil and water resources have not been adequately scrutinized in the NCR and Kansas and Nebraska in particular. Indiscriminate removal of crop residues may reduce soil organic matter and nutrient pools, jeopardize the soil quality, and increase risks of non-point source pollution of waters. Most of all, it may reduce future crop yields. By increasing soil erosion, residue removal may accelerate losses of nutrients, thereby further reducing crop yields and jeopardizing sustainable use of soil and water resources.

In some ecosystems, it may be feasible to remove a portion of crop residues for ethanol production without adversely impacting the soil organic matter pools and soil quality, but, at this point, site-specific information on maximum permissible residue removal rates is not available in the NCR. Indeed, no information is available on the effects of removal of residue from irrigated and non-irrigated crop production systems in Kansas and Nebraska. Depending on the soil, removal of a fraction of total residue produced may be beneficial to improve seed germination, facilitate planting, and reduce pest infestations. Thus, this project assessed not only the negative but also the positive aspects of crop residue removal.

This regional project conducted across Kansas and Nebraska was timely because no study had previously assessed the impacts of a partial removal of residues nor attempted to study established permissible levels of residue removal for corn, wheat, and sorghum on a regional basis in the NCR and in Kansas and Nebraska in particular. This project was also unique because it was conducted under on-farm conditions in Kansas in addition to large-scale research plots in Nebraska. Our project’s approach for assessing crop residue removal impacts under both farmers’ fields and research plots provided a superior way to achieve our objectives over other studies because it integrated results from research plots with those from on-farm sites. This information is important to better discern the impacts that residue removal may have if residues are harvested.  

The outcomes can directly benefit farmers, rural communities, extension personnel, soil conservationists, land managers, policy makers, and biofuel industry groups because the project generated timely information needed to develop decision support systems. Information collected can be particularly useful to energy entrepreneurs involved in the emerging cellulosic ethanol industry. This project addressed a relevant topic in a time when there is an intensified national interest in using crop residues for producing cellulosic ethanol as well as livestock production.

Short-term Outcomes (1-2 years)

1. Gain knowledge of the rapid positive or negative impacts of crop residue removal on soil and crop production. Specifically, farmers and other end users (extension personnel and biofuel industry groups) would learn/understand whether or not crop residue removal: 1) reduces grain and biomass yields, deteriorates soil quality, and reduces soil organic matter, and nutrient pools.
2. Determine the preliminary threshold levels of crop residue removal based on the short-term data on residue removal impacts.
3. Develop reports (e.g., journal and extension articles and conference papers) based on the short-term data and hold field days for impact evaluations.

Medium-term Outcomes (3 years)

1. Determine the soil and crop response to crop residue removal by generating 3-yr data on soil hydrologic, compaction, structural, and fertility parameters as well as crop yields (grain and biomass). These data can provide a better understanding of crop residue removal impacts compared with the short-term (
2. Establish the threshold levels of crop residue removal.
3. Share the threshold levels of crop residue removal with farmers, extension personnel, biofuel industry groups, scientific community, and others through field days, conferences, project reports, and extension and journal articles.    
4. Influence the decision making process of the farmers about crop residue management through field days and publications.