Surface Irrigation of Dairy Farm Effluent, Part II: System Design and Operation

Dairy farms with as many as 200 cows still handle their wastewaters and solid manures separately. Because of the large volume produced and their low nutrient load, these dairy farm effluents (DE) are costly and time consuming to land spread using conventional equipment, such as the tanker. The purpose of this study was to test the equipment and cost to determine the cost of the equipment adapted for the simplified surface irrigation of DE and to establish best management practices to reduce risks of groundwater contamination. The project was conducted on two dairy farms in South Western of Montreal, Canada, where typical DE were applied to irrigated plots of 0·5 and 0·3 ha, respectively, and the groundwater quality was compared to a control plot of the same size. Groundwater quality was monitored for nutrients (total nitrogen, total phosphorus, total potassium and pH) and bacterial counts (total coliforms, faecal coliforms, and faecal streptococci). A manure pump and conventional water irrigation pipes were satisfactory in irrigating with the DE without clogging as long as the DE was collected in a tank separate from that of the solid manure. During all applications, subsurface seepage losses occurred, but these would not be lost to the watercourse when applied in quantities respecting irrigation guidelines and on soils where the groundwater table was at or below the depth of the subsurface drains. Nevertheless, these seepage losses represented less than 1% of the total volume of DE applied, and the seepage nutrient and bacterial load was generally less than half of that of the irrigated DE. The surface irrigation system reduced the cost of land spreading DE from CAN $3·25 m−3 (conventional tanker) to CAN $1·10 m−3 (surface irrigation). The heavy total potassium load of the DE requires the rotation of the irrigation plot, on an annual basis.