Nitrification of Ammonium Nitrogen in Soils Treated with XDE‐474

Abstract

AbstractRetardation of NH+4 nitrification constitutes one means to conserve fertilizers applied to soils. A new nitrification inhibitor, XDE‐474, has been developed by DowElanco Chemical Company (Indianapolis, IN) and needs to be evaluated. Laboratory studies evaluated the effect of nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine] and XDE‐474 on nitrification rates in five Iowa soils varying markedly in organic C (OC), pH, and texture. A 10‐g sample of surface soil treated with 1 mL of solution containing 2 mg N as either NH4OH or (NH4)2SO4 and 4 µg a.i. g−1 soil of nitrapyrin or XDE‐474 was incubated at 20 ± 1°C for 0, 7, 15, 30, 45, and 60 d. First‐order equations were used to calculate the maximum nitrification rate (Kmax), duration of lag period (t′), period of maximum nitrification (Δt), and duration of lag plus maximum nitrification period (ts). Nitrification rates were significantly affected by N sources and inhibitors used. In the Okoboji soil (43.0 g kg−1 OC), nitrification of NH4OH was 19.5 mg kg−1 d−1 NO−3‐N in the control soil but reduced to 15.2 or 4.43 mg kg−1 d−1 NO−3‐N when nitrapyrin or XDE‐474 were added, respectively. Extension of the lag period due to the inhibitors varied from 0.73 d in the Okoboji soil to 18.8 d in the Storden soil (11.0 g kg−1 OC). Multiple regression equations expressing the dependence of Kmax on OC, pH, and clay showed that only OC and pH were significant in accounting for the variation in Kmax. The resulting three‐dimensional response surface indicated that XDE‐474 was less affected than nitrapyrin by changes in OC and pH.