Innovative Nitrogen Management Strategies to Reduce Groundwater Impacts in Drinking Water Source Protection Areas
University of Waterloo
A two-year field experiment comparing different nitrogen management practices was established for a corn crop in Ontario, Canada, starting in 2009. This work is part of an ongoing effort to reduce the amount of nitrates leaching from agricultural fields located within the well head protection area of a municipal well field currently impaired by elevated levels of nitrate. The municipality has purchased the surrounding land and maintains agricultural productivity under a farmer lease agreement. Results from the first year of the study will be presented. The random-block experiment encompassed 2 blocks each comprised of 5 fertilizer applications with 3 trials. One block was planted on wheat stubble residue and the other on wheat stubble with red clover (legume) residue. The 5 nitrogen fertilizer application treatments included a polymer coated nitrogen fertilizer and a conventional urea fertilizer applied in the spring, a conventional rate and calculator rate side dress application and a control. Fertilizer rates were determined using a soil nitrate test and a corn nitrogen calculator developed by the Ontario Ministry of Agriculture, Food and Rural Affairs. Plots with the legume cover crop were given a nitrogen credit to account for the additional residual soil nitrogen fixed by the plants. Environmental monitoring included a chemical tracer applied to the soil surface, soil solution samplers installed below the root zone, a neutron moisture meter, and an on-site meteorological station. The top 0.3m of soil were also routinely sampled for nitrate nitrogen, and 4.5m soil cores were taken at the beginning and the end of the growing season in order to establish the extent of vertical nitrate migration of each fertilizer application. Crop yield results for the spring applied polymer coated and urea fertilizers were similar, while soil nitrate samples show that there was a delay in release of nitrogen for the polymer coated product. This has the environmental benefit of releasing nitrogen closer to when plants can take it up, reducing the risk of leaching losses in the wetter period of the spring. The delayed application of nitrogen at side dress time using a lower rate from the nitrogen calculator had comparable yields to spring nitrogen applications (polymer coated nitrogen and urea). Plots with a red clover cover crop that received reduced nitrogen application rates using the nitrogen calculator had similar yields to plots without a cover crop. Overall, the initial results suggest that the polymer coated fertilizer product may provide significant environmental benefits related to reduced nitrogen leaching, yet still achieve acceptable crop yields. In addition, the use of a legume cover crop permits reductions in total nitrogen application, subsequently reducing associated environmental risk.