Grain Yields, Soil Water Storage, and Weed Growth in a Winter Wheat‐Corn‐Fallow Rotation1

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Abstract
This research involves factors affecting crop production in a no‐till crop rotation of winter wheat (Triticum aestivum L.)−corn (Zea mays L.)−fallow. Experiments were conducted in the field at North Platte, Nebr. during 1974 to 1977 on a Holdrege silt loam (fine−silty, mixed, mesic Typic Argiustolls) to determine the effect of weed control in growing winter wheat and stubble after harvest on annual weed growth, soil water storage, and winter wheat and corn yields. Winter wheat was an excellent competitor to weeds. Winter wheat allowed to grow until harvest (10 July) reduced weed weight taken 7 weeks after harvest (1 September) 56% as compared with plots where winter wheat and weeds were removed on 22 May. Weed competition reduced winter wheat yields by 15% in 1975 but not in 1976 when weeds succumbed to drought and competition from winter wheat. Glyphosate [N−(phosphonomethyl)glycine] applied after winter wheat harvest did not immediately kill weeds which resulted in unnecessary soil water loss when compared to plots receiving tillage. Volunteer wheat and weeds emerged after an application of glyphosate or one tillage after harvest. A residual herbicide should be applied to prevent these weeds from using soil water. Weeds in plots that were allowed to produce viable seed in the winter wheat or in the stubble after harvest significantly reduced weed control in corn planted the following spring as compared with plots in which weeds were not allowed to produce viable seed. Escaped weeds that produce seed during any period of a crop rotation will provide competition to subsequent crops. Standing stubble trapped snow which increased corn yields as compared to plots where tillage had knocked stubble down. Removal of winter wheat stubble after corn planting caused less brace root penetration, more lodging. and reduced corn yields 15% as compared to plots where stubble was left undisturbed.