Heterogeneous Nitrogen Losses: Cost-Effectiveness Analysis of Changes in Management Across South Dakota

The loss of nitrogen fertilizer into the atmosphere and waterways is of increasing concern for citizens and policy makers. This is particularly relevant for hypoxia in rivers, lakes, and oceans, but also relevant for policy makers in reducing the increasing concentration of greenhouse gases (GHG) in the atmosphere. GHGs trap heat in the atmosphere and include: carbon dioxide, methane, nitrous oxide and fluorinated gases. Overall, the estimated contribution from the agricultural sector to GHG emissions was 9% in 2013 (EPA, 2013). Further, the addition of nitrogen to the soil through the use of synthetic fertilizers is a main contributor to nitrous oxide (N20) emissions. Approximately 74% of U.S. N2O emissions were from synthetic fertilizer applications according to the EPA (2013). However, these emissions are not spatially homogenous, nor homogenous across crop production systems. The objective of this study is to begin to spatially account for the heterogeneous nitrogen losses from nitrogen fertilizer applications on South Dakota farms. This study conducts a cost-effectiveness analysis (CEA) to determine the best strategies, and areas, to reduce GHG emissions from nitrogen application in South Dakota. This form of analysis is done by spatially comparing the amount of emissions reductions per acre across the state, assuming alternative mitigation strategies and adoption rates. Using the environmental factors (climate type, soil texture, soil organic carbon, soil drainage, soil pH and crop type), and management decisions (no till, conventional till, and reduced till, crop rotations, and application timing), we assess the areas and methods in South Dakota that can be targeted for considering management changes to gain the most cost effective continuous improvement in stemming nitrogen losses. The purpose is to minimize costs from changes in management, but provide the maximum reduction in nitrogen losses. Spatial heterogeneity in GHG Emissions can vary considerably. For example, the coefficient of variation for N2O emission measurements typically range between 100 to 300% (Thornton and Valente, 1996; Snyder, C.S. et al., 2009). A switch from conventional tillage to reduced tillage and to no-till is expected to mitigate GHG emissions across all areas. However, it is important to spatially examine the heterogeneous effect on emissions reduction from mitigation efforts, given factors that contribute to heterogeneous GHG flux. This is particularly relevant in light of efforts to develop standardized metrics for determining GHG rates, and reductions from baseline, that may be used by agri-businesses and retailers for sourcing agricultural inputs. The intent of such effort is to provide an efficient method to promote food products and verifiable, sustainable marketing claims to consumers (Field to Market 2012 V2). Consequently, universally accepted management mitigation metrics may result in heterogeneous impacts to reducing emissions and costs, depending on site-specific environmental and soil factors that cannot be altered. Findings from this study will aid land grant extension personnel in targeting educational programs to areas where it is cost effective to enhance sustainable agriculture and mitigate GHG emissions from nitrogen fertilizer application. Results of the study will also inform stakeholders of the costs and trade-offs of changes in management decisions, such as timing of fertilizer application and fertilizer efficiency improvement methods (e.g. Brink et al., 2005). Management techniques, yields, and fertilizer applications data used for this study have been retrieved from USDA-ARMS data. Soil characteristics were obtained from NRCS soil data (GSSURGO), and crop rotations and locations were derived from USDA-FSA certified acres and the National Land Cover Database (NLCD). Arc-GIS software was used to combine the multiple data sets, into spatially homogenous response units. The Environmental Policy Integrated Climate (EPIC) model was used to simulate the homogenous response units to calculate all emission values. Simetar was then used to derive certainty equivalence values for changes in management and nitrogen runoff, which helped determine most effective management practices and the costs from our management control