Crop Residue, Soil Water, and Soil Fertility Related to Spring Wheat Production and Quality After Fallow

Abstract Over an 8‐year period, wheat straw mulch rates of 0, 1,680, 3,360, and 6,730 kg/ha were established each spring of the fallow year in alternate crop‐fallow blocks in three replications on a Dooley sandy loam. Fertilizer subplot treatments applied before seeding spring wheat ( Triticum aestivum L.) were as follows: Check, N, P, and N plus P. Both elements were applied at a rate of 34 kg/ha; N was applied each crop year, and P was applied initially and every other crop year thereafter. After 14 and 21 months of fallow, average available soil water stored to a depth of 1.5 m increased significantly and was positively correlated with increasing residue levels. Each metric ton of surface residue increased average available soil water supplies 0.5 cm. Mean grain yields were positively correlated with stored soil water at seeding only when both N and P were applied. N‐P fertilization increased mean grain yields 410, 580, 690, and 760 kg/ha per year for corresponding residue levels of 0, 1,680, 3,360, and 6,730 kg/ha, respectively. A significant decrease in grain protein level associated with increasing residue level was caused by N dilution and was proportionate to the yield increases obtained with increasing residue levels within each fertilizer treatment. Residue treatments did not significantly influence total N uptake by grain plus straw at maturity. Grain protein levels could be increased and maintained near 15% with N or N‐P fertilization even though grain yield increased considerably.