The Effects of Swine Manure Application Timing and Nitrapyrin On Corn Yield and Nitrogen Availability.

Manure is an excellent source of nitrogen (N) for corn. In the northern Corn Belt swine manure is typically applied in the fall after soybean harvest. Delaying the application of manure until soil temperatures have cooled or adding a nitrification inhibitor can slow nitrification of the N in manure, thereby reducing the potential for N loss. The objective of this study was to determine the effects of manure application timing and Instinct (Dow AgroSciences) on corn grain yield and N availability. Field experiments were initiated in the fall of 2010 on Nicollet–Webster clay loam soils in southern Minnesota. Treatments consisted of a factorial combination of two application timings (October and November) and three rates (0, 35, and 70 oz ac^-1) of Instinct. Manure was sweep-injected about 4 inches deep at 120 lb of available N ac^-1 (based on 80% availability of the total N in manure). Additional treatments, a zero N control and 120 lb ac^-1 of fertilizer N as anhydrous ammonia were included for comparison. Treatments were arranged in a randomized-complete block design with four replicates. Soil samples were taken from manure bands about five weeks after the October manure application and analyzed for nitrate- and ammonium-N concentration. Ammonium to nitrate ratios in soil samples averaged 1:1, 2.5:1 and 3:1 with the 0, 35 and 70 oz ac^-1 rates of Instinct, respectively. These data clearly showed adding Instinct to manure slowed nitrification of the N in fall-applied swine manure. In 2011 (wet spring), corn grain yields were 11 bu ac^-1 greater with November manure application compared with October application and averaged 11 bu ac^-1 greater with Instinct than without Instinct. In 2012 (dry spring), no significant yield differences were found.