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Nitrification of Ammonium Nitrogen in Soils Treated with XDE-474

Dep. of Agric. Sciences, Milbank Hall, Tuskegee Univ., Tuskegee, AL 36088

Randy Killorn^*

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

*Corresponding author (rkillorn{at}iastate.edu).

ABSTRACT

Retardation 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 (K_max), duration of lag period (t'), period of maximum nitrification (t), and duration of lag plus maximum nitrification period (t_s). 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 K_max on OC, pH, and clay showed that only OC and pH were significant in accounting for the variation in K_max. The resulting three-dimensional response surface indicated that XDE-474 was less affected than nitrapyrin by changes in OC and pH.

This study was funded, in part, by a grant from DowElanco. Journal Paper no. J-16077 of the Iowa Agric. and Home Economics Exp. Stn. Project no. 2217.

Received for publication November 7, 1994.