APEX model application to assess the impact of best management practices on runoff, erosion, and phosphorus export in NE Wisconsin, USA

Author / Creator

Holley, Garek, author

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Summary

Agroecosystems produce food and grain products for a growing global population. With new available land for farming finite, agriculture field management practices have become more intense. However,...

Agroecosystems produce food and grain products for a growing global population. With new available land for farming finite, agriculture field management practices have become more intense. However, greater yield intensity requires increased fertilizer and pesticide inputs to cropping systems, potentially leading to unintentional, negative impacts to the environment. Additionally, tillage practices that decrease soil structure, and post-harvest management routines that leave the soil uncovered, collectively increase field susceptibility to erosional losses to adjacent surface waters. The influx of both free and sediment-bound nutrients into water bodies drives algal blooms, and ultimately, following algal death, oxygen depletion from the water column. The net result of these management choices on surface water bodies is a reduced aesthetic appeal for recreation and the reduction of aquatic biodiversity. The objective of my thesis was to evaluate best management practice (BMP) effectiveness at reducing surface runoff, sediment erosion, and phosphorus export from fields using a calibrated and validated Agricultural Policy/Environmental eXtender (APEX) model. Alternative management practices that I investigated included no-till, inclusion of a standard dairy rotation, planting of cover crops (rye), and implementation of grassed waterways. Each alternative practice was analyzed against common routines such as continuous corn, chisel plowing, and fallow soil post-harvest. The greatest percent reduction in erosion and nutrient exports occurred when fields were transitioned from continuous corn with conventional tillage to no-till. Alternatively, use of multiple BMPs together provided the greatest total reduction of runoff, sediment losses and phosphorus export. The modeled BMP that produced the greatest absolute reduction of phosphorus, sediment, and runoff losses was a standard dairy rotation with cover crops planted in the fall, and inclusion of a grassed waterway. This study is unique, in use of technically advanced edge-of-field monitoring stations to collect surface and subsurface runoff, sediment, and nutrient export from agricultural fields. Calibrated APEX models were found to be effective at demonstrating constituent losses from these fields, and capable of modeling various BMP scenarios. Specifically, this study showed that land managers and farmers would help reduce field losses by implementing BMPs which extend cover, living or non -living, to agricultural cropland soils (i.e. cover crops, and no-till).

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