Response of Spring Wheat to N Fertilizer Placement, Row Spacing, and Wild Oat Herbicides in a No‐Till System1

Abstract

AbstractA 2‐year study was conducted on a north facing Thatuna silt loam (fine‐silty, mixed, mesic Xeric Argialbolls) to evaluate the influence of N fertilizer placement, crop row spacing, and wild oat (Avena fatuaL.) herbicides on wild oat populations and wheat (Triticum aestivumL.) yield in no‐till spring wheat. The treatments were factorial arrangements of ammonium nitrate either surface applied preplant or banded 50 mm below the crop seed at planting; wild oat control using triallate [S‐(2,3,3‐trichloroallyl)diisopropylthiocarbamate]pre‐emergence, difenzoquat [1,2‐dimethyl‐3,5‐diphenyl‐1H‐pyrazolium] post‐emergence, or no herbicide (check); and crop row spacings of either 200,300, or 400 mm. Surface‐applied fertilizer N significantly increased wild oat populations compared with banding the N fertilizer below the seed, but had no effect on dry weight or N uptake. Banded N increased total dry weight N uptake, and grain yields of wheat. These responses indicate that banded fertilizer N was positionally more available to wheat than was broadcast N, but banding N did not reduce availability of N to wild oat. However, surface‐applied N stimulated wild oat emergence. Triallate decreased wild oat populations compared to difenzoquat or no herbicide, but was no more effective than difenzoquat in reducing wild oat dry weight and total Kjeldahl N uptake. Both herbicides reduced wild oat dry weight as compared to the no herbicide check and significantly increased wheat yields. Row spacing did not affect wild oat dry weight or total N uptake, but the 200 m row increased wheat dry weight, total Kjeldahl N uptake, and grain yields compared to the 300 and 400 cm rows. There were no significant interactions.