Laboratory incubation and field experiments were conducted to evaluate thiourea, ATC (4-amino-1, 2, 4 triazole hydrochloride) and N-Serve 24 E (2-chloro-6-trichloromethyl-pyridine) as inhibitors of nitrification of fertilizer N. In the incubation experiment, most of the added aqueous NH3 or urea was nitrified at 14 days on both soils, but addition of the inhibitors to fertilizer N decreased the conversion of NH4−N to NO3−N markedly. There was less nitrification for ATC and thiourea but not for N-Serve 24 E when the fertilizers and the inhibitors were placed at a point as opposed to when mixed into soil. After 28 days, ATC and N-Serve 24 E were more effective in inhibiting nitrification than thiourea. ATC and N-Serve 24 E also inhibited release of mineral N (NH4−N+NO3−N) from native soil N. In the uncropped field experiment, which received N fertilizers in the fall, nitrification of fall-applied N placed in the 15-cm bands was almost complete by early May in the Malmo soil, but not in the Breton soil. When ATC or thiourea had been applied with urea, nitrification of fall-applied N was depressed by May and the recovery of applied N as NH4−N was greater with increasing band spacing to 60 cm or placing N fertilizer in nests (a method of application where urea prills were placed at a point in the soil in the center of 60×60 cm area). In late June, the percentage recovery of fall-applied N in soil as NH4−N or mineral N increased with wide band spacing, or nest placement, or by adding ATC to fertilizer N on both soils. These results indicate that placing ammonium-based N fertilizers in widely-spaced bands or in nests with low rates of inhibitors slows nitrification enough to prevent much of the losses from fall-applied N.
aqua ammoniaATCbandingfall-applied Ninhibitorsmineral N lossesnestingnitrificationN-Serve 24 Epoint placementthioureaurea