Database Research Summaries2018 Indiana Watershed Initiative: continued quantification of water quality, soil health and economic benefits from the watershed-scale pairing of cover crops and the two-stage ditch
The focus of this project is to robustly quantify the benefit of two important conservation practices in two Indiana watersheds in a manner that is meaningful to farmers, managers, and researchers.
- Quantify the water quality and quantity benefits of pairing cover crops and the two-stage ditch implemented at the watershed scale, through monitoring of the Shatto Ditch Watershed (SDW; 3300 acres) and Kirkpatrick Ditch Watershed (KDW; 6373 acres).
- Quantify the benefits of winter cover crops on improving soil health via increased nutrient retention as well as expected improvements in soil organic matter over the four years of the IWI RCPP.
- With our partners at the USDA Agricultural Research Service (ARS), we will use: 1) USDA-ARS Agricultural Conservation Planning Framework (ACPF) tool for conservation scenario planning, and 2) the process-based Soil Water Assessment Tool (SWAT) model to predict the benefits of watershed-scale cover crops and the two-stage ditch implemented regionally across other watersheds.
- Quantify the economic benefits for producers and the environment of the watershed-scale implementation of the cover crop/two-stage ditch pairing including the costs and benefits to the producers as well as the ecosystem service of increased watershed nutrient retention.
- For SDW, export during elevated flows was 18-22% lower for nitrate (Hanrahan et al. 2018) and 30% lower for SRP (Hanrahan et al. in preparation) during the first 3 years with watershed scale cover crop planting (2014-2016) compared to years without (2007-2012). However, in 2017 storms were more frequent and both runoff and nitrate export were ~40% higher than in the water year prior to cover crop saturation (2013). For KDW, annual export of water, nitrate, and SRP were higher than for SDW, likely due to KDW having both 2x higher watershed area and less cover crops (<25% of watershed area) than SDW.
- Cover crops reduced soil N content in both watersheds but had limited effects on other soil properties. For both watersheds, we found that soil NO3-N was consistently lower at both depths (0-5cm and 5-20cm) in cover crop fields compared to those without cover crops. Cover crops did not significantly alter other soil properties such as organic matter and cation exchange capacity, which can influence whether N and P will remain bound to soils or leach during storms.
- We used the SWAT tool to evaluate the nutrient reduction potential of various SDW land use scenarios (including current cover crop coverage) and estimate annual cost across a series of cover crop scenarios. We have worked with partners at the USDA Agricultural Research Service (ARS) to develop a new module for the SWAT model. This module predicts nitrate and total phosphorus reduction resulting from two-stage ditches. Data from 9 Midwestern two-stage ditches were used for the module creation phase.
- Generalizable information about the net private economic benefits of cover crops is decidedly scarce. To fill this gap, we are working with farmers to track changes in costs and revenues between rotations. This farm-level economic data will be incorporated into the various watershed-scale cover crop scenarios so as to estimate aggregate privately experienced economic outcomes. This preliminary analysis emphasizes the long-term nature of economic outcomes associated with cover crop usage.
The paired practices we propose here will allow producers to take proactive steps to reduce nutrient loss from agricultural lands. If adopted on a widespread scale, cover crops and the two-stage ditch could circumvent costly future regulatory actions to reduce agricultural nutrient loading to local or downstream surface waters.
For more information about this research project, please visit the National Soybean Checkoff Research Database.
Funded in part by the soybean checkoff.