Effect of Etridiazol and Nitrapyrin Treated N Fertilizers on Soil Mineral N Status and Wheat Yields

Etridiazol[5-ethoxy-3-(trichloromethyl)-1,2,4-thiadiazole] and nitrapyrin [2-chloro-6-(trichloromethyl)pyridine] are two nitrification inhibitors that offer potential for reducing N losses in soils from denitrification and leaching, thereby improving N utilization by crops. The objective of this study was to evaluate the ability of these two compounds to reduce nitrification of applied N fertilizers in soils and influence wheat (Triticum aestivum L.) yields. Experiments were conducted in 1977, 1979, and 1980 on Weir (fine, montmorillonitic, mesic Typic Ochraqualfs) and Stoy (fine-silty, mixed, mesic Aquic Hapludalfs) silt loam soils, typical for wheat production in southern Illinois. Anhydrous ammonia, urea, and urea-ammonium nitrate (UAN) solutions were applied without and with the two inhibitors at 0.56 and 1.12 kg/ha. Nitrogen rates varied incrementally from 0 to 150 kg/ha. Fertilizers with the inhibitors were applied in the fall prior to wheat seeding. Mineral N forms in soils were determined periodically after application. Etridiazol and nitrapyrin were equally effective in reducing nitrification of ammonium N in soils up to 160 days following application when compared to nontreated fertilizers. Above normal precipitation and temperature tended to reduce inhibitor effectiveness. Both inhibitors at the higher rate generally had greater amounts of -N present in soils on any date following application than the lower rate. Treating N fertilizers increased wheat yields from zero up to 32% above nontreated comparisons applied in the fall. Greatest responses were always associated with climatic and soil conditions that favored N losses by denitrification. No yield benefits accrued from the use of inhibitors when the applied N was not subject to loss conditions. Nitrification inhibitors added to fallapplied N resulted in wheat yields that were similar to and occasionally greater than those obtained from spring N topdressings.