Iowa State University researchers concluded from a long-term field study that poultry manure, when applied at a rate to meet crop nitrogen (N) requirements, can reduce nitrate loss and achieve equal or better yields in corn-soybean production systems. This research effort, Long-term Effects of Poultry Manure Application on Nitrate Leaching in Tile Drain Waters, evaluated tile drained field plots over 12 cropping seasons. While this research focused on nitrate (NO­3-N) loss by field-tile drains (typically placed 3 to 6 feet deep), similar trends would be anticipated in Nebraska for nitrate leaching below the crop root zone and the eventual impacts on ground and, possibly, surface water quality.

The research team evaluated four N treatments, including poultry manure application rates of 150 lbs N/acre (PM150) and 300 lbs N/acre (PM300), urea ammonium nitrate (UAN) at 150 lbs N/acre (UAN150), and a control at 0 lbs N/acre (Control) on a tile-drained field near Ames, Iowa from 1998 to 2009. Manure and UAN were typically applied on the same day, typically between mid-April and mid-May. The research was conducted in loam soils with organic matter averaging 3.4% in the top 12 inches. Nitrate-N loss was measured from mid-March to October.

Read more of this article to find out which treatments showed the least nitrate loss to water and which treatments offered the highest corn and soybean yields.