Residue and fertility effects on yield of no-till wheat

High levels of crop residue can adversely affect wheal (Triticum aestivum L.) yield, thereby slowing adoption of conservation tillage practices that effectively control soil erosion. This study was conducted to determine the influence of standing wheat residue and fertilizer application on the yield of no-till wheat. Winter wheat was grown in even years and spring wheat in odd years on the same site from 1984 through 1988. The soil (a Walla Walla silt loam; coarse silty, mixed mesic Typic Haploxeroll) is considered highly deficient in N and marginally deficient in P and S for annual cereal production. Crop residue was finely chopped in 1984 and burned in 1985 to 1988, to compare with stubble left standing. Fertility treatments consisted of increasing rates of N, P, and S [none (0-0-0 kg N-P-S ha(-1)), low (56-6-9), moderate (112-11-18), and high (168-17-27)], banded 5 cm below the seed. Grain yield, straw yield, grain protein, head density, kernels per head, and kernel weight were determined at harvest. Standing stubble decreased grain yield of winter wheat 13% and straw yield 15%, compared with chopping or burning; it decreased spring wheat grain and straw yields <5%. Standing residue affected straw and grain yields similarly, but had little effect on grain protein. Fertilizer increased grain and straw yield every year, and more so in winter than in spring wheat. Average grain yields for none, low, mod(:rate, and high fertility were 1.12, 3.02, 4.75, and 5.08 t ha(-1), respectively, for winter wheat and 1.17, 2.64, 3.18, and 3.20 t ha(-1) for spring wheat. Increasing fertilization increased head numbers, had variable effect on head size, and generally decreased kernel weight. Most of the yield reduction in winter wheat due to standing residue was attributed to lower head numbers, not compensated by increased head site or kernel weight. Fertility x residue interaction did not occur in yield or grain protein responses, but was found in kernel yield and kernel weight. Lack of such interaction suggests that inadequate nutrition was not the cause of reduced yield in no-till wheat with residue left standing.