Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Natural Resource Ecology and Management


Sustainable Agriculture; Environmental Science

First Advisor

Lisa A. Schulte

Second Advisor

John C. Tyndall


One of the most striking features of the US Cornbelt is the degree to which it has been designed, constructed, and intricately managed by humans for the production of agricultural products – primarily row-crop corn and soybeans. The production of provisioning ecosystem services, such as row-crop corn and soybeans, often comes at a tradeoff to other ecosystem services, such as enhanced water quality for aquatic life, recreation, and human consumption. Best management practices (BMPs) are tools that landowners can implement and manage as a way to co-produce row-crop corn and soybeans and enhanced water quality in extensively managed agricultural landscapes. Yet, selecting how and where to locate BMPs to impact aggregate ecosystem service outcomes, such as enhanced water quality, is a complex decision-making process that often involves multiple stakeholders and objectives. This research evaluates opportunities to improve the efficiency of BMP placement and management within and among crop fields and within watersheds to co-produce provisioning and regulating ecosystem services (ES), specifically row-crop corn and soybeans and enhanced water quality, in the US Cornbelt. This dissertation includes three distinct studies across three, nested scales (sub-field, field, and watershed) to examine environmental, economic, and social opportunities and tradeoffs associated with the implementation and management of BMPs designed to reduce nitrate loss to surface waters in central Iowa.

To assess nitrate-nitrogen (hereafter nitrate) retention in vegetative BMPs, the relationship between nitrate retention and plant species composition was examined in nine different monocultural and polycultural communities in a plot-based experiment. Results show a small, but significant difference between monocultural and polycultural plant communities in their ability to retain nitrate. On average, polycultural communities retained 31.5% (95% CI – 1.0%, 53.2%) more nitrate than monocultural communities. This difference was driven largely by alfalfa, which was planted as a monoculture in this experiment; alfalfa retained 63.0% (95% CI – 32.9%, 80.0%) less nitrate than the polycultural communities. Among polycultural communities, which varied in species richness (2-14 species per community), no impact was found of plant diversity on nitrate retention.

To understand farmers’ and farmland owners’ willingness to participate in new spatially targeted conservation planning frameworks designed to increase BMP efficacy, 18 farmers and farmland owners whose fields were identified via a spatial targeting technique focusing on soil and nutrient loss were interviewed in two watersheds in central Iowa. Results suggest that farmers and farmland owners often recognized the importance of producing a diverse suite of on- and off-farm ecosystem services, but lacked the context, information, certainty, and incentives to manage for them. Farmers and farmland owners were receptive to using technologies to target BMPs to areas with known resource concerns, but expressed concerns about applications in their fields, and perceived challenges related to cost, management complexity, coordination with government programs, and loss of autonomy. For broad acceptance, a spatially targeted conservation approach would need to be paired with expanded partnerships, trusted technical service, and adaptation incentives to reduce farm-level economic tradeoffs.

To evaluate the cost and effect on water quality from nitrate loss under spatially targeted alternative land management scenarios, an innovative spatially targeted conservation protocol, coupled with a GIS-based landscape planning tool, was developed, applied, and evaluated in an Iowa watershed. We found large reductions in watershed-level nitrate loss could be achieved through coordinated placement of BMPs on high-contributing parcels with limited reduction of cultivated land, resulting in improved surface water quality at relatively low economic costs. For example, one landscape scenario with wetlands, cover crops, and saturated buffers removed less than 5% of cultivated area and reduced nitrate loss by an estimated 49%, exceeding the Iowa Nutrient Reduction Strategy goal for enhancing water quality. Annualized establishment and management costs of landscape scenarios that met the nonpoint source nitrogen reduction goal in the watershed varied from $3.16 to $3.19 million (2017 USD). These results highlight the potential to minimize land-use tradeoffs by coupling targeted conservation and planning tools to help stakeholders achieve aggregate surface water quality outcomes within agricultural landscapes.

Taken cumulatively, this research suggests opportunities for improving the design, implementation, and management of BMPs to produce row-crop corn and soybeans while enhancing water quality in agricultural landscapes. Innovative and purposeful BMP design, stakeholder collaboration, and decision tools, programming, and incentives will be important components of conservation planning and water quality achievements.

Copyright Owner

Emily K Zimmerman



File Format


File Size

154 pages