Nutrient losses in subsurface drainage water from dairy manure and urea applied for corn

Land application of dairy (Bos taurus) manure has generated concern regarding the downward movement of nutrients and pathogens from the manure through the soil profile into subsurface drainage water and ultimately to surface waters. The objective of this study was to determine the effect of dairy manure and urea applied at equivalent rates of 'available' N on (i) NO₃-N, total phosphorus (TP), ortho. P, NH₃-N, and Escherichia coli losses to subsurface tile drainage; (ii) corn (Zea mays L.) production; and (iii) changes in soil test phosphorus (STP) and soil test potassium (STK). Liquid dairy manure and urea fertilizer were broadcast applied at equivalent total 'available' N rates ranging from 154 to 224 kg ha^-1 yr^{- 1} each fall during 1993-1996. The soil was a poorly drained Webster clay loam (fine loamy, mixed, superactive, Typic Endoaquoll). Nitrate N, TP, and ortho-P concentrations and NO₃-N losses in the subsurface drainage water were not different between the two N sources. Total P exceeded the minimum detection limit in 40 and 52% of the drainage samples from the urea and manured plots, respectively, while only 22 and 35% of the samples had detectable levels of ortho-P. Losses of TP and ortho-P were very small and averaged 31 and 10 g ha^-1 yr^-1, respectively, from the manured plots or <:0.02% of the manure-P applied. Four- year average corn yields were 0.7 Mg ha^-1 greater for the urea treatment compared with dairy manure. Soil test P and STK in the top 20 cm were increased 1 mg kg^-1 for every 12 kg P ha^-1 and 10 kg K ha^-1 applied as manure. We conclude that dairy manure, when applied at optimal rates and incorporated immediately, does not lead to greater losses of N and P in subsurface drainage water on this fine-textured soil compared with urea.