Water and nitrate loss through tiles under a clay loam soil in Ontario after 42 years of consistent fertilization and crop rotation

Concerns about increasing concentrations of agricultural nitrate in water resources have led to calls for new or revised agricultural land management practices. An essential step towards developing new practices is a good understanding of longterm, or "baseline", nitrate leaching into tile drainage water, both with and without annual application of nitrogen fertilizer. Accordingly, an automated monitoring system was installed to measure nitrate levels in tile drainage water from experimental plots on a Brookston clay loam soil in southwestern Ontario that have had consistent agricultural management for 42 years. Crops included conventionally tilled continuous corn (CC, Zea mays L.), continuous bluegrass sod (Poa pratensis L.) and a corn–oat (Avena sativa L.)–alfalfa (Medicago sativa L.)–alfalfa rotation with all four crops of the rotation present each year. Fertilized and not-fertilized phases were included with each of the six crops to give a total of 12 treatments. Measurements included precipitation, tile discharge, corn yield and nitrate concentration and total nitrate loss in tile drainage water. The fertilized CC, fertilized rotation corn and second year fertilized alfalfa treatments produced 3-year flow weighted mean (FWM) nitrate concentrations in tile drainage water of 15.2, 18.0 and 16.2 mg N l?1, respectively, all of which exceed the Canadian and European drinking water guideline values of 10 and 11.3 mg N l?1, respectively. The 3-year cumulative nitrate losses were high at 82.0 kg N ha?1 for fertilized CC, 99.9 kg N ha?1 for fertilized rotation corn and 69.8 kg N ha?1 for second year fertilized alfalfa. Given that the existing fertilizer recommendations are required to achieve economic corn yields, these results indicate that current corn production practices on Brookston clay loam can potentially cause nitrate pollution of the rural environment, as well as substantial economic loss to corn producers through inefficient crop use of applied nitrogen fertilizer. There is consequently a need for new agricultural practices that can increase the nitrogen use efficiency of corn production and minimize nitrate loss to the environment.