Modeling Dry Matter Accumulation in Dryland Winter Wheat
1975
Rickman, R. W. | Ramig, R. E. | Allmaras, R. R.
A deterministic model of dryland winter wheat [Triticum aestivum ssp. vulgare (Vill., Host) ‘Nugaines’) growth in the Pacific Northwest was developed and field tested to more adequately quantify the influences of tillage induced microclimatic changes on wheat production. Daily dry matter accumulation of winter wheat is described by a modification of the Blackman compound interest formula. Daily environmental variables (soil water supply, N supply, soil and air temperature, relative humidity, wind, rainfall, and solar radiation) are used in the two-component model. For inputs, initial conditions are needed which describe the field location (soil depth, water supply, fertilizer added, crop dry matter present, growth constants for the wheat variety, maximum rooting depth, and average temperature for the last 3 days). Dry matter production and the water budget are determined daily, until the water supply is exhausted or the crop is mature. Field tests of the model indicated accurate prediction of the effects of water and N supply and surface mulch for the first half of the growing season. After flowering, the observed dry matter accumulation was greater than projected by the water response function of the model. Much greater water use efficiency (daily increase in dry matter/ daily water transpired) occurred after flowering. This may be partially attributable to upward water flow from below 240 cm, which was not included in the measured available water. To improve growth prediction by the model, accurate measurement of the available water supply and alteration of the late season water response function are needed.
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