Effect of conservation practices implemented by USDA programs at field and watershed scales

Authors: HER, YOUNGGU - Purdue University; CHAUBEY, INDRAJEET - Purdue University; FRANKENBERGER, JANE - Purdue University; Smith, Douglas

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2016
Publication Date: 5/1/2016
Citation: Her, Y., Chaubey, I., Frankenberger, J., Smith, D.R. 2016. Effect of conservation practices implemented by USDA programs at field and watershed scales. Journal of Soil and Water Conservation. 71(3):204-221.

Interpretive Summary: The evaluation of conservation practices is important to ensure that Farm Bill conservation payments have the desired effect of improving water quality. The objective of this study was to evaluate the effects of conservation practices that were applied to the St. Joseph River Watershed, part of the Western Lake Erie Basin. The Soil and Water Assessment Tool was used to model the load reduction effectiveness of more than 5,500 conservation practices implemented by NRCS in this watershed, which covers parts of Michigan, Ohio and Indiana. Model results indicate that many of the practices likely reduced pollutant loads between 10 and 50% at the field scale; however, when the conservation efforts were studied for the entire watershed scale, there may have been less than a 1% improvement in the pollutant loads. It is important to note that the estimated load reductions were still significant and the cumulative effect over time will help to improve water quality of receiving waters. Comparison of the spatial distributions of conservation practices and pollutant loads suggests that conservation in this watershed was not targeted to areas where greater pollutant loads would be expected. Applying conservation to these areas should result in improved load reductions. Watershed scale water quality improvement relies on identifying the proper sites for conservation to be applied, the field-scale effectiveness of practices, and the placement of practices. The impact of this research is to inform conservation planners about the impacts of Farm Bill conservation efforts in the St. Joseph River watershed, and to form a basis for future assessments and conservation planning efforts.

Technical Abstract: The objective of this study was to evaluate effects of conservation practices actually implemented in reducing sediment and nutrient loads at field and watershed scales. The Soil and Water Assessment Tool (SWAT) was used to model the load reduction effectiveness of more than 5500 conservation practices implemented by NRCS in the St. Joseph River Watershed. Model results indicated that many of the practices likely reduced pollutant loads between 10% and 50% at field scale, with high variability in load reductions among the practices. Most conservation practices reduced less than 1% of the loads when calculated for the entire watershed, but amount of the load reduction was still large and thus their cumulative long-term effects were expected to be significant. Conservation crop rotation and no-till, which were the most widely applied conservation practices in the study watershed, provided the greatest sediment load reduction, while conservation crop rotation and cover crop reduced the greatest amount of nutrients. Conservation crop rotation, cover crop, no-till, and mulch-till sometimes increased loads of soluble nutrients, resulting in the overall decrease in their effectiveness. Comparison of the spatial distributions of the selected conservation practices and simulated pollutant loads showed existing conservation practices were not targeted for areas producing relatively greater loads. The findings of this study demonstrated different effectiveness of conservation practice are at the different spatial scales, suggesting application area, field scale effectiveness, and placement of the practices are all critical in achieving watershed scale water quality improvement.