K. Kpomblekoua et R. Killorn, NITRIFICATION OF AMMONIUM NITROGEN IN SOILS TREATED WITH XDE-474, Soil Science Society of America journal, 60(5), 1996, pp. 1482-1489
Retardation of NH4+ nitrification constitutes one means to conserve fe
rtilizers applied to soils. A new nitrification inhibitor, XDE-474, ha
s been developed by DowElanco Chemical Company (Indianapolis, IN) and
needs to be evaluated. Laboratory studies evaluated the effect of nitr
apyrin [2-chloro-6-(trichloromethyl)pyridine] and XDE-474 on nitrifica
tion 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 soluti
on containing 2 mg N as either NH4OH or (NH4)(2)SO4 and 4 mu g a.i. g(
-1) soil of nitrapyrin or XDE-474 was incubated at 20 +/- 1 degrees C
for 0, 7, 15, 30, 45, and 60 d. First-order equations were used to cal
culate the maximum nitrification rate (K-max), duration of lag period
(t'), period of maximum nitrification (Delta t), and duration of lag p
lus maximum nitrification period (t(s)). Nitrification rates were sign
ificantly affected by N sources and inhibitors used. In the Okoboji so
il (43.0 g kg(-1) OC), nitrification of NH4OH was 19.5 mg kg(-1) d(-1)
NO3--N in the control soil but reduced to 15.2 or 4.43 mg kg(-1) d(-1
) NO3--N when nitrapyrin or XDE-474 were added, respectively, Extensio
n of the lag period due to the inhibitors varied from 0.73 d in the Ok
oboji 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 th
e variation in K-max. The resulting three-dimensional response surface
indicated that XDE-474 was less affected than nitrapyrin by changes i
n OC and pH.