Optimizing Soil and Fertilizer Nitrogen Use by Intensively Managed Winter Wheat. I. Crop Nitrogen Uptake

Information is lacking on the N uptake pattern of intensively managed soft red winter wheat (Triticum aesrivum L.) in the mid-Atlantic region of the United States. Such information would facilitate decision making for N fertilizer management, increase the precision of simulation models used in research, and delineate crop growth stages for use as indicators of plant N needs. Field experiments were conducted in the Atlantic Coastal Plain region of Virginia during the 1981–1982 through 1984–1985 winter wheat growing seasons to describe the winter wheat N uptake pattern and measure responses to N fertilization. The treatments in these experiments consisted of single or split spring N applications at Zadoks growth stages 25 (GS 25) and 30 (GS 30) totaling 0, 90, or 135 kg N/ha. Total dry matter production and total N concentration were measured in the aboveground plant material and in leaves, stems, and heads. These measurements were made shortly after dormancy, at GS 30,45, and 58, and at harvest to assess the effects of the N fertilizer rates and climatic conditions on crop N uptake. Maximum daily N uptake rates were obtained in the period immediately after GS 30, suggesting that this is when the highest efficiency of N fertilizer use could be expected. Crop N uptake at GS 30 also appeared as a potentially good indicator of the plant N requirement. Total amounts of N found in leaves and stems decreased with time during the spring, while spike N increased from the early stages of head development until harvest. Climatic conditions in the different growing seasons affected plant N uptake. Variations in residual soil N and temperatures in early spring probably determined the differences in amounts and patterns of N uptake by whole plants and by the various plant fractions. Contribution 24061. Contnbution of the Agronomy Dep., Virginia Polytechnic Inst. and State Univ. Research was supported by grants from. the Potash and Phosphate Inst. and the Foundation for Agronomic Research.