Effect of Wetland-Treated Dairy Wastewater Subirrigation on Nutrient Uptake in Maize and Soybean.

Agricultural systems are often implicated in nutrient pollution of surface and subsurface waters. Dairy wastewater is a low nutrient, high volume effluent composed of water from milking barns, consisting of waste milk, hoof dirt, silage pad runoff and small quantities of manure. Current practices typically involve direct application of these waste products to land, often as irrigation water since nutrient content is relatively low, but the high volume of water can result in preferential flow into waterways. Alternative methods for dairy wastewater treatment are necessary for long term environmental, social and economical sustainability as well as cost and labor reduction. A subirrigation system was designed to handle and utilize dairy wastewater in an environmentally friendly fashion, at a farm near Hudson, Michigan. The system was chosen as both irrigation and a wastewater disposal tool and was installed underneath an area of approximately 20 acres, split into two separate fields. Wastewater was treated in a collection pond followed by flow through a constructed wetland prior to being supplied to the crops. Maize was planted on the site for three years, soybeans for only two. Plant uptake of nutrients was measured at least 3 times during the growing season for each of the three years. Dairy wastewater subirrigation resulted in increased crop yields for maize, especially in dry years, but had minimal effect on soybean yields. Tissue and grain were analyzed for P, K, Mg, Ca, S, Na, Fe, Al, Mn, B, Cu, Zn and total nitrogen. Of these, only magnesium and calcium showed a consistent correlation with distance away from tile lines.