Simulation of Nitrate-Nitrogen Dynamics for Cropping Systems with Different Rooting Depths

sults in predicting residual soil NO 3 –N (Shaffer et al., 1991; Follett et al., 1994; Shaffer et al., 1995). These Most agricultural systems in the San Luis Valley of south-central researchers used the previous 1.10 version of NLEAP Colorado include rotations that have crops with different rooting that was capable of simulating the effect of management depths. The previous version of Nitrate Leaching and Economic Analysis Package (NLEAP), 1.10, was only capable of simulating the effect practices on RSN for the root zone of the simulated of management practices on the rooting zone of each crop to the crop. Additionally, NLEAP 1.10 conducted simulations nearest 0.30-m increment. Therefore, a new version of NLEAP was for the rooting zone of a crop, entered to the nearest needed to simulate the effect of best management practices (BMPs) 0.30-m increment, (e.g., 0.30, 0.61, 0.91, 1.22, or 1.52 m). on residual soil NO2 3 –N (RSN) for the root zone of each crop grown For crops such as potato, with maximum rooting depths in the region and for a similar soil depth for these systems (e.g., 0–0.91 of 0 to 0.40 m, NLEAP 1.10 capabilities are to simulate m). The improved NLEAP version 1.20 simulates maximum rooting the rooting zone to 0 to 0.30 or 0 to 0.61 m. By having depth to the nearest 0.03 m and RSN in multiple soil depths. These a 0.30-m resolution, the simulations of N and water new features allowed us to simulate the effect of BMPs on RSN for budgets with the previous 1.10 version were either overthe root zones of shallower-rooted crops such as lettuce (Lactuca or underestimated. sativa L.) (0–0.37 m), potato (Solanum tuberosum L.) (0–0.40 m), and deeper-rooted crops such as small grains (0–0.61 to 0–0.84 m). Since NLEAP 1.10 is not capable of simulating rotaNLEAP simulated RSN for a soil depth identical for all of these tions on a similar soil depth for crops with different cropping systems (0–0.91 m) (P , 0.001). This new version can be rooting zones such as lettuce (0–0.37 m) and spring used by extension agents, farmers, consultants, and others to evaluate wheat (Triticum aestivum L.) (0–0.84 m), a new version, the effect of BMPs on soil NO2 3 –N dynamics for different rooting 1.20, was developed (Delgado et al., 1998). With the zones and for similar soil depths in the agricultural system, a capability previous NLEAP 1.10, simulations would have been that was not available with the previous version of NLEAP. conducted for lettuce at 0 to 0.30 m and for spring wheat at 0 to 0.91 m. Comparisons on the effects of BMPs on RSN for these systems must be conducted for the root T is potential to use new computer models as zone of each crop and for a similar soil depth for the technology transfer tools to assess the impacts of agricultural system. NLEAP 1.20 can simulate RSN for agricultural practices on residual soil NO 3 –N (RSN) the root zone and RSN from the bottom of the rooting that is available to leach. The Nitrate Leaching and depth (BRD) to a maximum soil depth desired that can Economic Analysis Package (NLEAP) permits a rapid be a similar soil depth for the agricultural system. This site-specific evaluation of a series of best N and irrigamaximum soil depth can be set from a minimum of 0.3 tion management practices for a farmer’s field (Shaffer m to a maximum of 1.5 m, by 0.03-m increments. It also et al., 1991). To simulate different management scenarcould be set to be equal to the BRD of the crop with ios and their effects on residual soil NO 3 –N, NLEAP the deepest rooting system in the rotation. uses a regional configuration file that contains crop N This new capability is important for NLEAP simulauptake indices and other plant and soil parameters. The tion of the NO 3 –N dynamics in these agricultural sysplanting and harvesting dates, water management inputs tems. For example, the NO 3 –N that is below the root and timing, soil and climate information, and measured zone of the lettuce crop (0.37–0.91 m), although not crop yields need to be supplied. Development of the assessable for lettuce, can be scavenged by the spring model is presented in more detail in Shaffer et al. (1991). wheat, which has a deeper rooting zone (0–0.84 m). Khakural and Robert (1993) and Beckie et al. (1994) This is why simulation on a similar soil depth must be reported that the NLEAP 1.10 model has been found conducted when evaluating the effect of management to perform similarly in predicting residual soil practices on RSN. Additionally, NLEAP 1.20 was imNO 3 –N, water content in the rooting zone, and proved to simulate maximum rooting depth to the nearNO 3 –N leaching to other models such as Crop Estimaest 0.03 m from a minimum root depth of 0.30 m to a tion through Resource and Environment Synthesis maximum of 1.52 m. This new 1.20 version can simulate (CERES; Ritchie et al., 1985), the Erosion/Productivity lettuce and spring wheat root zone. It can also simulate Impact Calculator (EPIC; Williams et al., 1983), the below the root zone of lettuce (0.37–0.91 m) and the Nitrogen Tillage Residue Management (Shaffer and spring wheat (0–0.84 m). Larson, 1987), and LEACHM-N (Wagenet and Hutson, Since most agricultural systems include rotations that 1989). Other researchers have also obtained similar rehave crops with different rooting depths, this new version of NLEAP is an improvement and needs to be Jorge A. Delgado and Ronald F. Follett, USDA-ARS, Soil Plant validated and calibrated for these cropping systems. This Nutrient Research Unit, Federal Bldg., P.O. Box E, 301 S. Howes, Fort Collins, CO 80522; Marvin J. Shaffer, USDA-ARS, Great Plains Abbreviations: BMPs, best management practices; BRD, bottom of Systems Research, Fort Collins, CO 80522. *Corresponding author the root depth; NLEAP, Nitrate Leaching and Economic Analysis ([email protected]). Package; RSN, residual soil NO2 3 ; SLVWQDP, San Luis Valley Water Quality Demonstration Project. Published in Soil Sci. Soc. Am. J. 64:1050–1054 (2000).