Location: National Soil Erosion Research Lab
Title: Application of a calibrated/validated APEX model to assess sediment and nutrient delivery from the Wildcat Creek MRBI-CCPI Authors
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 13, 2014
Publication Date: N/A
Interpretive Summary: Given the difficulty and cost associated with monitoring conservation practices for water quality purposes, computer generated hydrologic models such as the Agriculture Policy/Environmental eXtender (APEX) can be implemented to estimate sediment load and nutrient transport from agricultural fields and small watersheds. Taking advantage of the water quality monitoring effort at the St. Joseph River watershed by the USDA-ARS National Soil Erosion Research Laboratory, the incorporation of six conservation agricultural practices incorporated at Wildcat Creek watershed was assessed. Prompted by the Mississippi River Basin Initiative program and through a special partnership agreement (Cooperative Conservation Partnership Initiative-CCPI), the Greater Wabash River Resource Conservation and Development Council (RC&D) facilitated the incorporation of the agricultural conservation practices at the Wildcat Creek watershed. The results indicate that cover crops are not only the conservation practice favored by farmers, but are also able to significantly reduced sediment and nutrient loads at the field scale (second only to forage and biomass planting). The present study not only helped evaluate a government promoted conservation project, but also serves as a case study and helps validate the use of APEX modeling for water quality research.
Technical Abstract: The Wildcat Creek, a tributary to the Wabash River was identified by the USDA Natural Resources Conservation Service (NRCS) as a priority watershed for its high sediment and nutrient loading contributions to the Mississippi River. As part of the Mississippi River Basin Initiative (MRBI), the incorporation of conservation practices was implemented through a Cooperative Conservation Partnership Initiative (CCPI) agreement using existing USDA programs. To evaluate the impact of conservation practices incorporated at Wildcat Creek MRBI-CCPI on water quality, seven output variables (surface runoff, subsurface flow, sediments, total phosphorus, soluble phosphorus, soluble nitrogen and soluble nitrogen in tile) were compared for four different row-crop conservation practices (residue and tillage management, no-till; residue and tillage management, mulch till; cover crops; and forage and biomass planting), and two waste application scenarios. Using the APEX model, calibrated and validated for a field within the St. Joseph River watershed, a modeling assessment was developed for current conservation practices incorporated at a similar watershed, Wildcat Creek. Mean value comparisons using the Kruskal-Wallis analysis of variance and the Wilcoxon signed-rank test, identified significant differences between forage and biomass planting and all other row-crop management practices (except cover crops), and between the waste application scenarios. Cover crops consistently reduced sediment and nutrient loads in runoff by more than 50% compared to conventional tillage practices, and the incorporation of waste utilization conservation practices reduced total and soluble phosphorus by about 75% to 92% (respectively). When extrapolating the edge-of-field values predicted by the model to the area occupied by each conservation practices throughout the duration of the contracts at the Wildcat Creek watershed, the total reductions were estimated to be almost 8,000 Mg of sediment (62% decrease), 10,000 kg of total phosphorus (64% decrease), 2,000 kg of soluble nitrogen in runoff (46% decrease), and 72,000 kg of soluble nitrogen in tile flow (25% decrease). APEX modeling is a useful tool for predicting sediment and nutrient loading information at the field-scale, which can be used to calculate the relative impact of conservation practices at the watershed scale when monitoring data is not available. The estimated results confirm the positive impact of these conservation practices and of the MRBI-CCPI initiative at improving water quality at the edge-of-field, and potentially at the Wildcat Creek, the Greater Wabash River Basins, and ultimately the Mississippi River Basin.