1. Using Long-Term Evaluations of Arkansas Cropping Systems to Reduce Nitrate Leaching and N 2 O Emissions Theodis Bunch 1, Jorge A. Delgado 2, Cal Shumway 3, LeRoy Hansen 4 and Marc Ribaudo 4 1 USDA-NRCS, National Water Management Center, Little Rock, Arkansas; 2 USDA-ARS-Soil Plant Nutrient Research Unit, Fort Collins, Colorado; 3 Arkansas State University, Jonesboro Arkansas; University of Arkansas Agricultural Experiment Station; 4 USDA-ERS, Washington, DC * For additional information, a complete list of references, questions, reprints, or requests for new tools, please email Mr. Theodis Buch at Theodis.Bunch@ar.usda.gov and/or Dr. Jorge A. Delgado at jorge.delgado@ars.usda.gov. There have been reports in the literature that nitrogen leaching losses from the Mississippi River Basin cropping systems are contributing to the transport of nitrogen loads to the Gulf of Mexico and to the resulting hypoxia problem in this area. The Arkansas Delta region has been identified as a potential source of the nitrogen entering the Mississippi Delta. To assess the effects of cropping systems and management practices on the potential leaching losses from agricultural fields located in the Arkansas Delta, we used the new Nitrogen Loss and Environmental Assessment Package with GIS Capabilities (NLEAP-GIS 4.2) that was released in 2010 to conduct a preliminary long-term analysis of a series of management scenarios for crops growing under hydrological type A and D soils. Average state yield production and recommended N inputs were used for these scenarios. Simulations were conducted for no-till and conventional systems; for each of these systems, we evaluated corn-corn and corn-soybean rotations. Factorial analyses of spring vs. fall applications, surface application vs. incorporation of N, best N rates, and 75% over-application were conducted. The analyses showed that rotations of soybeans into corn systems reduced the emissions of N 2 O across the Arkansas Delta and reduced the NO 3 -N leaching losses as well and suggest that use of best management practices and realistic N application rates can significantly contribute to decreased losses of reactive N to the environment. These analyses further suggest that NLEAP-GIS 4.2 is an effective tool for evaluating agricultural management practices. Abstract Summary References New Tools in 2010 Figure 2. The NLEAP-GIS 4.2 which has NTT capabilities and runs in Microsoft Excel® 2010, is planned to be released in November 2010. Figure 1. Advances in Nitrogen Management for Water Quality is scheduled to be published in November 2010 by SWCS and will have 15 chapters covering new tools, methods, and findings related to the management of nitrogen. Authors from ARS, NRCS, as well as authors from different universities and countries, present valuable information for practicing nutrient mangers that may potentially help them increase nitrogen use efficiency, protect water quality, and reduce losses of reactive nitrogen to the environment. The practice of applying nitrogen to farming systems has brought important benefits to the world population and the environment, as nitrogen inputs have enabled farms to maximize yields of cropping systems. The Green Revolution, in which nitrogen certainly played a major part, helped to meet the food demands that accompanied increases in the world population. However, reactive nitrogen losses to the environment can be exacerbated by nitrogen inputs to agricultural systems, which can enter the environment via loss pathways such as nitrate leaching, surface runoff, ammonia volatilization and denitrification. Emissions of trace gases such as nitrous oxide could also be increased by N inputs (Mosier et al. 1991). Managing nitrogen effectively, although difficult to do because of nitrogen’s dynamic and mobile nature, is possible. A new book, titled Advances in Nitrogen Management for Water Quality, explores how management practices may affect nitrogen dynamics and losses, and the conservational implications of nitrogen and its management. Several new tools that can be used to assess nitrogen management practices, are also discussed in the book (Figure 1). This book will be published by the Soil and Water Conservation Society (SWCS) in November of 2010. The flux of nitrogen from the Mississippi watershed has been reported to be contributing to nitrogen levels in the Gulf of Mexico; the high levels of this nutrient is thought to have a contributing role in the hypoxia problem of the Gulf of Mexico. It has also been reported that nitrogen from the Arkansas Delta is contributing to the flow of nitrogen from the Mississippi watershed. We tested the potential of the new 2010 NLEAP-GIS 4.2, which runs in the Microsoft Excel® 2010 environment, and the 2010 Nitrogen Trading Tool (NTT), which also works in the Microsoft Excel® 2010 environment, to assess nitrogen management and to find practices that may be able to increase nitrogen use efficiency and reduce atmospheric, surface and leaching losses in Arkansas soils. The NLEAP-GIS 4.2 and the NTT can effectively assess nitrogen management risk across the landscape and over multiple cropping systems. More information about these tools will be available in the upcoming book, Advances in Nitrogen Management for Water Quality (Delgado and Follett, 2010; Figure 1) and upcoming user manual for NLEAP-GIS 4.2 (Delgado et al. 2010; Figure 2). Figure 3. The new NLEAP-GIS 4.2 was used to evaluate the long-term effects of management practices on NO 3 -N leaching. Incorporation of soybeans (S) into the corn (C) rotations resulted in decreases in NO 3 -N leaching from these irrigated systems. Only the corn in the corn-corn (CC) and corn-soybean (CS) rotations received a spring application using the incorporation method and best nitrogen application rate. For the soybean, no fertilizer was used for the above scenarios, which are shown in this graph. (Units are in lb N/acre. Units can be converted to kg N /ha by multiplying by 1.12). Figure 4. The new NLEAP-GIS 4.2 was used to evaluate the long-term effects of management practices on N 2 O emissions. Incorporation of soybeans (cs) into the corn-corn (cc) rotations resulted in decreases in N 2 O emissions from these irrigated systems. Only the corn in the corn-corn (CC) and corn-soybean (CS) rotations received a spring application using the incorporation method and best nitrogen application rate. For the soybean, no fertilizer was applied for the above scenarios, which are shown in this graph. (Units are in lb N/acre. Units can be converted to kg N /ha by multiplying by 1.12). Table 1. Total nitrogen losses (kg N ha -1 ) via nitrate (NO 3 -N) leaching (NL) and denitrification (Den) for different crop rotations. Crops were grown on a Hydrology A, Bruno soil and a Hydrology D, Sharkey clay soil in Arkansas ¶ under different best management practices (BMP). ¶ Con = Conventional tillage; NT = No-till; CC = corn-corn rotation; CS = corn- soybean rotation; BMP-t = application of nitrogen fertilizer in the spring; BMP-m = incorporation of N when applied, BMP-r = recommended N rate using Espinoza and Ross (2008) approach; BMP- = no BMP is applied (fall, surface application with an N rate 75% higher than best rate); BMP-tmr = all BMPs used (spring, incorporated application with best nitrogen application rate). ------------ Hydrology A --------- ---------- Hydrology D ---------- Delgado, J.A., C.M. Gross, H. Lal, H. Cover, P. Gagliardi, S.P. McKinney, E. Hesketh and M.J. Shaffer. 2010. A new GIS nitrogen trading tool concept for conservation and reduction of reactive nitrogen losses to the environment. Adv. Agron. 105:117-171. Delgado, J.A., and R.F. Follett, Eds. 2010. Advances in Nitrogen Management. 2010. SWCS, Ankeny, IA (in print) Mosier A.R., D. Schiemel, D. Valentine, K. Bronson and W. Parton. 1991. Methane and nitrous oxide emissions fluxes in native, fertilized and cultivated grasslands. Nature (London) 350:330–332. Delgado, J. A., A.R. Mosier, R.H. Follett, R.F. Follett, D. Westfall, L. Klemedtsson, and J. Vermeulen. 1996. Effect of N management on N 2 O and CH 4 fluxes and N recovery in an irrigated mountain meadow. Nutr. Cycl. Agroecosyst. 46:127-134. Delgado, J.A., P.M. Gagliardi, D. Neer, and M.J. Shaffer. 2010. Nitrogen Loss and Environmental Assessment Package with GIS Capabilities (NLEAP- GIS 4.2) (USDA-ARS-SPNR User Manual for NLEAP-GIS 4.2) Delgado, J.A., M.J. Shaffer, H. Lal, S. McKinney, C.M. Gross, and H. Cover. 2008. Assessment of nitrogen losses to the environment with a Nitrogen Trading Tool (NTT). Comput. Electron. Agric. 63:193-206. Incorporation of nitrogen fertilizer minimized nitrogen losses via ammonia volatilization. Incorporation of nitrogen fertilizer lead to increased nitrogen losses from nitrate leaching and denitrification. Reduction of nitrogen fertilizer lead to decreases in nitrogen losses for all loss pathways. The best combination of management practices for reducing leaching was the reduction of nitrogen fertilizer, which was incorporated into the soil and applied in the spring (Table 1). Adding a leguminous crop reduced N 2 O emissions and nitrate leaching. We conducted an NLEAP-GIS 4.2 Nitrogen Trading Tool (NTT) analysis (data not shown) and found that this tool can be used to estimate potential reductions in N losses by pathways such as NO 3 -N leaching and N 2 O emissions, and to evaluate the potential to trade net reductions in N loss as direct and indirect carbon sequestration equivalents, in agreement with Delgado et al. (2008, 2010). The NTT evaluations demonstrate its usefulness in evaluating potential benefits to be gained from better management relative to a baseline scenario. The NTT analyses also demonstrate that there are potential benefits to water and air quality if we implement BMPs that reduce nitrogen losses across this region, and that the NTT can potentially be a useful approach to assessing management practices in the Arkansas Delta region. Nitrate leaching was higher for fall applications than for spring applications. Ammonia volatilization losses were higher for spring applications than fall applications. Spring applications also increased N 2 O emissions, in agreement with Delgado et al. 1996. Nitrogen use efficiency was higher for the spring application than the fall application. Nitrate leaching was higher for soils of hydrology type A than hydrology type D. Denitrification and N 2 O emissions were higher in the Hydrology D soil. Disclaimer: Manufacturers’ names are necessary to report factually on available data, however the USDA neither guarantees nor warrants the standard of the product; and the use of a given name by the USDA does not imply approval of that product to the exclusion of others that may be suitable. The views expressed here are those of the authors and do necessarily reflect those of the US Department of Agriculture or the Economic Research Service