- Agronomic: corn, soybeans, wheat
- Crop Production: conservation tillage, cover crops, crop rotation, nutrient management
- Farm Business Management: budgets/cost and returns
- Natural Resources/Environment: drift/runoff buffers, wetlands
Conservation management practices are considered one of the best answers to escalating water quality deterioration by nonpoint source pollution. Integrated watershed economic model (IWEM) offers a multidisciplinary framework by addressing both the biophysical and the economic (cost and benefit) aspects of water quality improvement. An IWEM can be conceptualized as three sub-models: a watershed model, an economic model, and an optimization tool to integrate the watershed and economic models together. The present study is an attempt in this direction, by translating the three sub-models of IWEM into three essays of the dissertation. The Upper Big Walnut Creek (UBWC) watershed in central Ohio was selected for applying the IWEM framework. The modeling of the UBWC watershed was performed in the first essay. For this study the Soil and Water Assessment Tool (SWAT) was used to predict the water quality changes associated with land management practices. A dynamic programming-based economic optimization approach was used in this study, which could capture the nutrient movements in agro-ecosystems, starting from nutrient application, intake by plants and transport from the field to downstream water reservoir with possible nutrient assimilation in-between. The social cost of the pollution is parameterized with benefit estimates of water quality improvement. Model is developed for the entire watershed by considering it as a single homogeneous one hectare unit. The watershed model was used to simulate the baseline, and crop rotation and conservation technology-specific production functions. Two sets of conservation technologies were developed for the watershed. One with split nitrogen fertilizer application, cover cropping, conservation tillage and vegetative buffer stripes and the other with 25% reduction in nitrogen fertilizer, cover cropping, conservation tillage and vegetative buffer stripes. The analysis revealed that under no restriction on N loading, farmers would apply a maximum of 170.51kg/ha of N and the value function would be $7950 under C-S-W rotation. However, after introducing the social cost of pollution in objective function, the fertilizer application rate was reduced to 103 kg/ha. Additionally, within the crop-technology combination, technology Set-3(split-N application, conservation tillage, cover crop and vegetative buffer) showed the lowest pollution load to the reservoir along with higher value function.
Today, non-point source pollution (NPS) is one of the major sources of water quality impairments globally (UNEP, 2007). In the US, nutrient pollution is the leading cause of water quality issues in lakes and estuaries (USEPA, 2002). The maximum concentration of nutrients in streams is found to be in agricultural basins, and it is correlated with nutrient inputs from fertilizers and manures. This clearly shows the role of agricultural practices in water quality degradation (USGS, 1999). To improve the quality of water bodies, the United States Environmental Protection Agency (USEPA) mandates individual states to implement the Total Maximum Daily Load (TDML) (USEPA, 2002). The state and federal governments are working with several conservation programs to reduce the NPS load from agriculture (Mausbach and Dedrick, 2004). However, the ever-increasing water quality impairment by agricultural NPS in US clearly shows that the task of formulating and implementing the cost-effective policies for controlling the NPS impact on water resources is challenging.
The specific objectives of the projects are to,
1. to Identify, evaluate and prioritize the site-specific on-farm and off-farm land management strategies to reduce nitrogen loading using SWAT model.
2. to optimize the land management strategies to maximize social benefit