Yield water relationships of summer fallowed winter wheat triticum aestivum cultivar tascosa a precision study in the texas panhandle usa

Johnson, W.C.; Davis, R.G.

U S Department of Agriculture Science and Education Administration Agricultural Research Results ARR-S 5: 1-43


Accession: 006925079

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In a 10 yr study (1968-1977), special techniques, including minor land leveling and the use of a rolling platform while taking neutron readings, were used to increase the reliability of soil water determinations. The maximum amount of stored soil water that 'Tascosa' wheat, T. aestivum L., used from Pullman clay loam, the premier soil of the Texas High Plains was 7 in. and the maximum depth of extraction from the soil was 6 ft. A close relationship (r = 0.97) occurred between total water use (soil water plus growing season precipitation) and wheat yield. The average yield increase was 2.41 bu/acre per extra inch of total water used. The average yield increase was 2.70 bu/acre per extra inch of soil water extracted and 2.22 bu/acre per extra inch of growing season precipitation. Statistical analyses showed that growing season precipitation was of the greatest overall importance in determining yield. Total water use by individual crops ranged 4.1-21.9 in. for yields ranging 10.5-51.4 bu/acre. Tillage frequency ranging from infrequent (once before and once after simulated chemical fallow) to 1.4 times normal or conventional tillage frequency had a negligible effect on grain yield and protein content. Favorable water conditions in the fall were highly important in enabling some crops to develop an efficient root system and endure long periods of winter and spring drought. Under favorable conditions, some crops extracted water to depth of 6 ft in the soil and left no available soil water at harvest. Following a dry fall, other crops extracted soil water to a depth of only 3 ft and left unused as much as 4.25 in. of available soil water at harvest. Little water was conserved by fallowing during the summer months. Most water was stored when there was accumulation from fairly heavy rains in late spring or early fall.