Spring Wheat Yield Model for Limited Moisture Conditions
1978
Rasmussen, V. P. | Hanks, R. J.
Models are useful to predict the effect of one or more of the complex climatic soil, water, or crop variables on yield. Such predictions can be used to make economic evaluation of, for example, the cost and benefit of irrigation or date of planting on yield. The objective of this study was to develop a model for spring wheat (Triticum aestivum L.) which could be used for such purposes and which required only readily available data. The model, a modified form of that developed by Hanks (1974) for corn (Zea mays L.), is based on a water balance of irrigation, precipitation, soil water, evapotranspiration, and drainage. Relative dry matter yield is assumed to be directly related to relative seasonal transpiration. Relative grain yield is assumed to be related to the multiple of relative transpiration for each of four growth stages raised to the 0.25 power. The validity of the model was tested in 1975 using field experimental data collected especially for this purpose. Two soft white spring wheat and three hard red spring wheat cultivars were grown under several levels of irrigation. Predicted yields agreed closely with measured yields. An additional test of the validity of the model for other irrigated cultivar trials in 1975, 1974, 1973, and 1972 at the same location, and a dryland trial in 1975 at another location, was made. Good agreement with measured results was found for the 1973, 1974, and 1975 irrigated and the 1975 dryland trial. However, the predicted results for the 1972 irrigated trials were about 20% lower than the measured yields.
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