Sc. Rao et Tw. Popham, Urea placement and nitrification inhibitor effects on growth and nitrogen accumulation by no-till winter wheat, CROP SCI, 39(4), 1999, pp. 1115-1119
Reduced forage production, grain yield, and visual N deficiency symptoms in
no-till winter wheat (Triticum aestivum L.) prompted this study. Our objec
tives were to determine the effect of urea placement and two nitrification
inhibitors-nitrapyrin [2-chloro-6 (trichloromethyl) pyridine] (NP) and dicy
andiamide? (DCD)-on aerial dry matter and N accumulation. A 4-yr field stud
y,vas conducted on a Renfrow silt loam soil (fine-silty, mixed, thermic Ude
rtic Paleustoll) silt loam near El Reno, OK. The seven treatments included
urea fertilizer (60 kg N ha(-1)) with and without the two inhibitors, surfa
ce broadcast or bended 3 to 4 cm below the seed row, and an unfertilized co
ntrol. Aerial dry matter accumulation during autumn was higher for banded u
rea plus DCD (22%) and broadcast urea plus DCD (25%), than for broadcast ur
ea without an inhibitor. Whole plant N content during autumn also was highe
r For banded urea plus DCD (28%) than for broadcast urea without an inhibit
or. Neither inhibitor nor placement affected total dry matter accumulation
measured at tillering, but differences were noted at spike emergence, grain
fill, and final harvest. At spike emergence in 1991, when climatic conditio
ns were favorable for early season wheat growth, N content was greater for
broadcast urea plus nitrapyrin than for broadcast urea or banded urea witho
ut inhibitor. At final harvest, both DCD treatments exhibited greater N con
tent than all other N treatments. In 1993, when climatic conditions were fa
vorable for leaching, DCD was effective in slowing nitrification and increa
sing N uptake, regardless of fertilizer placement. Our results suggest that
fall application of DCD with urea can potentially increase autumn forage p
roduction and N content, thus prolonging the sating season or accommodating
increased stocking rates.