The Effects of Swine Manure Application Timing and Nitrapyrin On Corn Production and N Availability.

Manure can provide essential nutrients for row crops like corn (Zea mays L.). In the northern Corn Belt swine manure is typically applied in the fall after harvest. Delaying the application of manure until soil temperatures have cooled or adding a nitrification inhibitor can slow nitrification of nitrogen (N) in the manure, thereby reducing the potential for N loss. The objective of this study was to determine the effects of manure application timing and nitrapyrin [2-chloro-6-(trichloromethyl) pyridine] rate on corn production and N availability. Field experiments were conducted from 2010 through 2013 on Webster (Typic Endoaquolls) and Nicollet (Aquic Hapludolls) clay loam soils. Treatments consisted of a factorial combination of two application timings (October and November) and three rates (0, 0.57, and 1.13 kg ai ha^-1) of nitrapyrin as Instinct™ (Dow AgroSciences). Manure was sweep-injected about 10 cm deep at 134 kg of available N ha^-1 (based on 80% availability of the total N in manure). Additional treatments, a zero N control and 134 kg ha^-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 averaged 1:1, 2.5:1 and 3:1 with the 0, 0.57 and 1.13 kg ai ha^-1 rates of nitrapyrin, respectively. These data clearly showed adding nitrapyrin to manure slowed nitrification of the N in fall-applied swine manure. In 2011 (a wet year), corn grain yields were 0.7 Mg ha^-1 greater with November manure application compared with October application and 0.7 Mg ha^-1 greater with nitrapyrin than without nitrapyrin. In 2012 (a dry year), no significant yield differences were found.