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A 3-yr study was conducted to determine the effects of inhibiting nitrification and addition of anhydrous ammonia on the fertilizer value of swine manure. Nitrapyrin (0.56, 1.12, 1.68 kg/ha), etradiazol (0.6, 1.2 kg/ha) and sodium methyl dithiocarbamate (1.2 kg/ha) were added to swine manure enriched with either 3.59 kg NH3/IOOO L for finishing, nursery and gestation house manure or 4.79 kg NH3/1000 L for farrowing house manure. All manures were injected in an Odell silt loam soil cropped to corn (Zea Mays L.) during fall or spring seasons at the rate of 28,062 to 30,868 L/ha for finishing, nursery and gestation house manure and 42,093 to 46,770 L/ha for farrowing house manure. Total nitrogen application rates on the manure plots ranged from 133 to 295 kg N/ha based on the corn plant requirement of 207 kg N/ha with a 7493 kg/ha grain yield. At above optimal nitrogen application levels, average corn yields were increased over 6% by addition of nitrification inhibitors. The beneficial effects of nitrification inhibitors on corn yields were greater when manure was applied in the fall compared to spring application. Over the entire study, adding 1.12 kg/ha of nitraprin or etradiazol to manure increased corn yields the most compared to other inhibitor levels or sodium methyl dithiocarbamate. Addition of 0.56 kg/ha of nitrapyrin in the fall also increased corn yields compared to manure applications without the inhibitor. Soil nutrient levels did not increase from the manure applications. Ammonia enrichment of the manure increased the proportion of the manure N in the NH4-N form. Lower stalk rot incidence and a trend towards increased N in grain and corn leaves were observed with the use of nitrification inhibitors.