Soil Nitrate, Soil Water, and Grain Yields in a Wheat‐Fallow Rotation in the Great Plains as Influenced by Straw Mulch1

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Abstract
Wheat straw mulch rates greater than 3,360 kg/ha were needed to significantly reduce soil NO3−N during fallow at three Great Plains locations. Smaller amounts of NO3−N in the soil at the end of fallow with stubble mulch did not limit grain production. Grain yields of wheat (Triticum aestivum L.) were positively correlated with stored soil water at seeding all years at Akron, 2 out of 5 years at North Platte and 2 out of 3 years at Sidney, but there was no relation between grain yields and soil NO3−N at seeding at any of the locations. Mulched soils contained more water and less NO3−N at seeding than bare soils. In 7 out of a total of 11 crop years from all locations when grain yields were higher from mulched soil than from bare soil, soil NO3−N was available in sufficient quantity under both treatments so that final grain yields were not limited. In those years when grain yields were reduced by the presence of a straw mulch, no evidence was obtained that indicated this reduction was due to an inadequate supply of N. Grain yield responses to added N were greater on bare soil than on mulched soil.

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