After two years of corn residue removal in poorly and well-drained soil sites, there were no significant decreases in grain yield. In general, removing residue increased grain yields due to soil warming under cold and wet conditions early in the spring. In addition, there were no significant decreases in total soil organic carbon (SOC) concentrations compared to baseline year. However, potential decreases in SOC sequestration were observed when residue was removed. The adoption of no-till and increased N rates did reduce some of the carbon (C) losses due to residue removal. However, only with adoption of no-till and nitrogen (N) rates greater than 150 lbs N per acre with very little residue removed, were there potential increases in soil C were observed. In the poorly drained soil site, approximately 15% of corn residue can be removed without seeing a net loss in potential SOC sequestration. In the well-drained site, only approximately 9% of the residue can be removed without having a net loss in potential SOC sequestration. Significant short term effects of residue removal on soil physical properties were observed. Increases of bulk density were observed with 100% residue removal regardless of tillage and increased N fertilization rate. Furthermore, decreases in soil aggregation were observed with residue removal, regardless of tillage and increased N fertilization rate. Subsequently, soil water infiltration rates were significantly reduced in the well-drained soil site. In general, the adoption of no-till over chisel plow and increased rates of N fertilization did offset some of the negative impacts of residue removal, but potential losses of SOC sequestration and deterioration of soil physical properties were still observed.
Crop residue left on the surface after harvest is a potential feedstock source for bioethanol production that may alleviate some of the United States dependence on foreign fuel and net greenhouse gas emissions (GHG). Although, it is currently more expensive to produce ethanol from lignocellulosics than from starches, it is projected that improvements in technology and scale of production will improve these costs. Additionally, the process of producing bioethanol from lignocellulosics is energetically positive; that is to say that the energy content of the ethanol is greater than the energy required to produce it. It is projected that lignocellulosic ethanol production will become a viable industry and could create an annual market for crop residue, increasing from approximately 195 million tons to 425 – 600 million tons.
The removal of crop residue, however, may require farmers to change their current tillage and fertilization practices to prevent against potential soil erosion. Crop residues play a significant role in improving soil physical and chemical properties that are essential in controlling wind and water erosion, which ultimately reduce sediment and other contaminant transport to water bodies and is critical for replenishing soil organic carbon (SOC). In addition, there is no currently published research on how various levels of crop residue removal affect crop production and its response to nitrogen (N) fertilization under various tillage systems. In order to address these issues, agronomist from Iowa State University Extension held forums and surveys to outline farmer’s concerns of crop residue removal for bioethanol production. Extension educators, crop consultants, and other agriculture professionals that work with farmers directly across Iowa have indicated four prevalent concerns; (1) the need for more economical data on bioethanol production, (2) information on the effects of residue removal on soil quality, (3) the cost of nutrients removed with different levels of residue and what it means for future production, (4) and data supporting no-till, specifically on the decomposition of residue, soil temperature, soil moisture, and stand issues (Iowa State University Extension, 2008-2010). The proposed project will address these concerns by assessing the impacts of crop residue removal under different N fertilization rates and tillage practices, and monitoring the resulting impact on corn production. This will allow us to see how much (if any) residue can be removed and still sustain high soil and crop productivity. The focus of this study is to provide research based information for farmers, agronomists, and policy makers in the decision making processes utilizing crop residue for lignocellulosic ethanol production or livestock feed for maximum economic and environmental outcomes.
The objective of this project was to establish coordinated field studies to determine the short-term and long-term impacts of varying corn residue removal and N fertilization rates and tillage systems on soil, air, and water resources. The project had four anticipated outcomes which include reliable estimates of;
(1) amount of C and nutrients removed and returned to the soil by residue,
(2) soil C and N sequestration potential with different residue management practices,
(3) amount of greenhouse gas emissions,
(4) assessing needs for supplemental fertilization of following crops and cost, and
(5) impacts on soil physical properties.
This study was established in fall of 2008 on a poorly-drained soil at the Iowa State University Agronomy Research Farm west of Ames, IA and a well-drained soil at the Armstrong Research and Demonstration Farm southwest of Atlantic, IA in continuous corn.
Three treatments were established in spring of 2009; the main treatment was tillage practice (no-till and chisel plow), which was split into three different residue removal rates (0, 50, and 100%) which then was further split into six N fertilization rate treatments varying from 0 to 250 lb N/acre.
Soil measurements are being conducted every August/September which includes soil C, N, P, K, and bulk density. Greenhouse gas emissions, CO2 and N2O, were measured on a weekly basis during the corn growing season, and monthly afterwards. After every harvest, crop measurements include harvested grain yield, and N, P, and K uptake, above-ground biomass, and root biomass.
When determining whether management practices were a sink or a source for soil C and CO2, a C budget approach was used to estimate net ecosystem productivity (NEP):
NEP = (ANPP + BNPP) – Rh
where, ANPP is potential C content input from above-ground plant biomass, BNPP is potential C content input from below-ground root biomass, and Rh is C loss as CO2 due to microbial decomposition. These measurements provide insights into whether management practices are potentially increasing SOC and whether they are a sink or a source for CO2.
Annual field days, training workshops, and other educational events were held with approximately 200 farmers and 50 agriculture professionals in the Iowa State University Agronomy Research Farm (North Central Iowa) and the Armstrong Research and Demonstration Farm (Southwest Iowa). Training, PowerPoint presentations, and poster displays were presented during these annual events. In addition, fact sheets, extension bulletins, and newsletter articles will be developed utilizing the Iowa State University publication system. The focuses of hosting these events are to provide basic information and hands-on training on residue management practices to meet the farmer’s needs for sustainable cropping practices. In addition, evaluation surveys were developed to qualitatively and quantitatively measure farmers’ and other agriculture professionals’ familiarity with the project’s stated outcomes during field days and workshops.
Corn Yield Response to Residue Removal
Corn yield response due to residue removal by N rate is summarized in Figure 1. In 2009, there was generally no significant effect of residue removal on corn yields. The only exception is when no N was applied, removing residue increased corn yields. Both the poorly and well-drained sites had unusually cold and wet spring prior to June. In 2010, there was a significant residue removal effect on corn yields as affected by different N rates and tillage. Corn yields were much lower in 2010 due to a cold and wet spring similar to 2009 yields. In the well-drained soil, corn yields were higher when 50 and 100% of the corn residue was removed across all N rates. In the poorly drained soil, corn yields were also higher when 50 and 100% of residue was removed at N rates ranging from 50 to 200 lbs N ac-1. Corn yields were also affected by tillage (Figure 2). The lowest corn yields occurred when no residue was removed and under no-till. Hence, the highest corn yield occurred when 50 and 100 % of corn residue was removed under chisel plow. Increases in corn yield due to residue removal may be attributed to higher soil temperatures increasing potential organic mineralization resulting in greater biomass and grain production.
Residue Removal effects on Total Soil Carbon
After two years of residue removal and under different N rates and tillage practices, there were no significant differences in total soil C compared to the baseline year in 2008 for both sites (Figure 3). This was not entirely unexpected, since total soil C in these sites are relatively high and ranged from 2.3 to 4.5 %. Any changes in total soil C would be difficult to detect after only two years, where maximum increases in total soil C have been recorded to be as high as 0.06 % in one year. This is often masked by natural soil variability which in these sites, total soil C varied by 0.5 %. Residue removal effects on labile (new, easily decomposable) soil C pool are greater and much easier to detect. Soil microbial biomass-C is used as an indicator for labile C in the soil, and was done in this study, although lab analysis is not completed.
Residue Removal effects on Potential Soil Organic Carbon Sequestration
A carbon budget approach by estimating net ecosystem productivity was used to determine if residue removal under different N rates and tillage management had net gains or losses in potential C sequestration (Figure 4.). Results from the C budget show that only under high N rates and no-till with very little residue removal, there were potential gains in soil organic C (SOC) in poorly and well-drained soils. In the poorly-drained soil site, approximately 15 % of the residue can be removed without having a net loss in potential SOC sequestration. In the well-drained soil site, only approximately 9 % of the residue can be removed without having a net loss in potential SOC sequestration. Under typical N rates in Iowa (150 lbs N ac-1) with continuous corn, even when no residue was removed and under no-till, it was observed a potential net losses of SOC. Furthermore, potential losses of SOC sequestration were greatly increased when residue was removed. The adoption of no-till did lessen the potential losses of SOC due to residue removal in the poorly-drained soil site, but to a lesser extent in the not in the well-drained soil site. Potential losses of SOC sequestration were greatest under management practice with high residue removal, no N application, and chisel plow. To have an understanding of the potential removal of C and N content by residue removal. The effect of N fertilizer rate on corn biomass N and C content at plant maturity across sites and year (2009-2010) is show in Table 1 (Pantoja and Sawyer, 2011).
Residue Removal effects on Soil Physical Properties after Two years of Residue Removal
After two years of residue removal and under different N rates and tillage practices, there were significant differences in bulk density compared to the baseline year in 2008 for both sites (Figure 5). In the poorly-drained soil site, bulk density was significantly greater when 100% of the residue was removed under both tillage systems. Similar results were observed in the well-drained soil site, except there were also significant increases in bulk density under no-till when 50% of the residue was removed. In addition, the lack of N application also significantly increased bulk density under both sites and tillage practices, where significant reduction in root biomass took place which has direct impact on soil structure and bulk density (data not shown). Corn residue removal also negatively impacted soil aggregation after only two years (Figure 6). In general, the greatest soil aggregation occurred under no-till and when no residue was removed. Significant decreases in soil aggregation occurred when 50% of residue was removed compared to 0%, and tended to further decrease with 100% residue removal, although not significantly different. The addition of higher N rates did not appear to significantly affect soil aggregation. However when no N was applied, significant decreases in soil aggregation were observed. The results of higher bulk density and lower soil aggregation due to residue removal and subsequently reduced steady water infiltration rates (SWIR) in the well-drained soil site only (Figure 7). These decreases in SWIR were only observed under chisel plow and 100% residue removal. Consequently, the adoption of no-till did help maintain SWIR when corn residue was removed. In the poorly-drained soil site, SWIR were already low, with only 17% of the water infiltrated into the soil and 83% as runoff when simulated rainfall rates of 0.42 cm per minute were used.
Residue Removal effects on Greenhouse Gas Emissions
Sites for this study were a significant net sink for atmospheric CO2-C, even when corn residue was removed and under different tillage and N fertilization (when applied) management (Figure 8). This could be attributed to the large biomass production of corn (Table 1) being much greater then C losses from microbial decomposition. Potential C losses from microbial decomposition were greater under chisel plow compared to no-till especially during early in the growing season (Figure 9). During this period, soil temperatures in the top 6 inches were greater in chisel plow compared to no-till, until the corn canopy completely cover the soil surface, resulting in no difference in soil temperature or slightly greater in no-till. Emissions of N2O-N in 2009 and 2010 were also slightly greater in chisel plow compared to no-till (Figure 10). This was a bit surprising since current literature cites that no-till systems typically have higher N2O-N emissions due to soils being more frequent to be under anaerobic conditions compared to conventional tillage systems. However for this study in 2009 and 2010, both years were very wet, which may explain why chisel plow treatments had higher N2O-N emissions. In general, removing corn residue lowered N2O-N emissions, but was only significantly different when the entire corn residue was removed, due to soils having less water content. Applications of N had the largest effect on N2O-N emissions, typically the more N fertilizer that was added, the greater the N2O-N emissions (Figure 11).
Educational & Outreach Activities
Training and educational materials for extension educators, crop consultants, other agriculture professionals, and local farmers
Annual field days, training workshops, and other educational events were organized in September of 2010 and June 2011 for agricultural professionals and farmers at the Iowa State University Armstrong Research and Demonstration Farm (Southwest Iowa) and at the Agronomy Research Farm in Boone County. Training sessions, PowerPoint presentations, and educational materials were presented during these events. In addition to field days, initial findings of this research were shared with other colleagues and agricultural professionals through newsletter articles, American Society of Agronomy (ASA) annual meetings, presentation at the regional committee meeting, and presentation to extension educators and other agricultural professionals during various events such as the Integrated Crop Management (ICM) conference in Iowa in 2011. The ICM conference is organized annually and approximately 1,000 agricultural professionals attended the conference.
Future PhD dissertation and journal publications
Findings from field experiments will provide significantly needed information currently not available to farmers and will make a significant contribution to the scientific literature. It will also provide additional needed information for issues partly investigated, such as impacts of crop harvest on C sequestration and potential soil erosion to help decision makers, producers, agriculture professionals, and policy makers, to make the proper decisions in exploring corn residue utilization. A PhD dissertation will be completed in summer of 2012 and future journal publications related to soil C dynamics, greenhouse gas emission, soil fertility, nutrient management, and soil hydrology will be prepared. Questions that this project will address are how much corn residue can be removed without degrading soil and environmental quality, soil organic C sequestration, and agronomic sustainability in Iowa and the Midwest region.
See Publications/Outreach section.
Work is still being conducted for the economic analysis component. Completion is expected once dissertation is complete late summer 2012.
Evaluation surveys and adoption of residue removal management practices
Work is still being conducted for the farmer adoption component. Evaluation surveys were developed to qualitatively and quantitatively measure farmers’ and other agriculture professionals’ familiarity with project’s stated short and long-term outcomes during field days and workshops. These evaluation surveys include farmers’ current residue, N, and tillage practices and their willingness to adopt practices discussed in field days and workshops. Findings from surveys are expected by the end of summer 2012. After three years, increases in awareness and adoption of recommend practices for farmers that remove corn residue in their fields are expected.
Areas needing additional study
This research is in its third year and will continue for another two years to provide critical information on corn residue removal management that is not available or is deficient at this time.