DRAINAGE AND IRRIGATION WATER QUALITY MANAGEMENT IN EASTERN CANADA

摘要

Subsurface drainage is essential for crop production in Eastern Canada. Excess precipitationrnfrom snowmelt and rainfall must be artificially removed, in order to provide an optimum soil-airwaterrnenvironment in the crop root zone. In addition, to make optimum use of the limited heatrnunits and short growing season, it is essential that soil conditions permit field machinerntrafficability in the Spring, for seedbed preparation and planting operations. There are close to 3rnmillion hectares of subsurface drained land in the wet humid regions of Eastern Canada.rnIn recent years, there has been much concern about the water quality impacts of shallowrnsubsurface drainage. Elevated concentrations of nitrate-nitrogen and dissolved phosphorus havernbeen measured in tile drainage outlets. These high nutrient concentrations have led torneutrophication of rivers and lakes. The sources of these nutrients are fertilizers and manuresrnfrom intensive animal production operations.rnBest management practices have therefore been developed and tested to reduce the nutrientrnloadings from subsurface drainage systems. One of the practices which has widescalernapplicability is sub-irrigation. An advantage of sub-irrigation is that it uses the existingrnsubsurface drainage system to supply crop water requirements during the summer growingrnseason, when droughts may occur. In addition, sub-irrigation promotes denitrification, therebyrnreducing nitrate-nitrogen concentrations in tile drainage effluent.rnThis paper will describe the water quality impacts of tile drainage in Eastern Canada, and thernresults of our research program in reducing pollution from tile drainage systems. Best practicesrnfor improving drainage and irrigation water quality will be presented, and an analysis of thernbenefits will be discussed.