1a.Objectives (from AD-416):
To provide biomass suppliers with accurate guidelines for management of biomass removal and maintenance of soil quality.
1b.Approach (from AD-416):
Develop regionally applicable biomass feedstock harvest guidelines based on empirical and model analysis utilizing and enhancing available models; validate guidelines and recommendations through on-farm research trials; conduct regional sustainable biomass harvest round-table sessions with producers; characterize biomass feedstock and ash; assess impact of ash on plant growth and soil properties.
The overall goal of this project is to develop the data and tools necessary to assess long-term agronomic sustainability of removing corn stover residue for energy production. It is directly related to Objective 1 of the parent project: determine crop residue needs to protect soil resources and identify management strategies that enable sustainable production of food, feed, and biofuel and Objective 2: develop options for managing crop systems to reduce greenhouse gas (i.e., nitrous oxide) emissions and increase soil carbon storage. Harvesting corn stover on fields with little or no tillage increases the risk of soil erosion by leaving the soil surface exposed by increasing the fraction of small erodible soil aggregates compared to when all stover is returned. Particulate organic matter is a soil assessment tool to detect early changes in soil organic matter. Particulate organic matter results indicated that gains in soil organic matter through no-till management can be undermined by harvesting stover. Current stover yields in West Central Minnesota are insufficient to sustain soil organic matter if any stover is harvested for bioenergy. Based on these on-farm and plot-scale trials, if a producer chooses to harvest stover, it likely would not cause an immediate reduction in crop yield. Feedstock pricing should include the value of nutrients harvested, while fertilizer management should be based on appropriate soil tests as the impact of stover harvest will vary by soil type, and crop rotation. Finally, producers who routinely harvest stover or cobs crops should monitor for micronutrient (e.g., Zn) deficiency symptoms as nutrient previously recycled in the residues will be removed. Results from the research plots were similar to the on-farm studies especially at the Donnelly farm site. Negative corn and soybean yields were not detected on the Swan Lake research field in response to harvesting cobs or other amounts of corn stover. As discussed by Johnson et al. (2013), yield responses to residue harvests are expected when stover harvest alters microclimate or cause a fertility imbalance. Harvesting stover leaves more of the soil exposed to erosive forces (i.e., wind and rain). Furthermore, reducing biomass inputs shift the distribution of aggregates toward smaller and more erodible aggregates. The lack of soil coverage and the change in aggregate size highlights the potential for increased erosion risk. On a field managed without tillage, which was reaping a soil quality reward due to limited tillage, harvesting stover undermined the no tillage benefits of increasing soil organic carbon and particulate organic matter. Soil organic carbon and particulate organic matter declined in the moderate and aggressive harvest treatments in the field managed without tillage compared to the baseline. Collectively, the results caution against repeated aggressive harvest or even moderate harvest in a corn/soybean rotation even without tillage. Although mitigation strategies (i.e., use of cover crops) may compensate for residue harvest, it is the topic of continued and future research.