EVALUATION OF SELECTED CROP YIELD WATER USE MODELS FOR A WHEAT CROP.

EVALUATION OF SELECTED CROP YIELD WATER USE MODELS FOR A WHEAT CROP.

Abstract:

Relationships between crop yields (dry matter and grain yields) and seasonal evapotranspiration for wheat in Samaru- Zaria, Nigeria, under conditions of moisture stress caused by evapotranspiration deficits at four growth stages of the wheat crop are presented. Wheat, (Triticum aestivum L.CV. sete ceros) was planted in the Institute for Agricultural Research (I..R.) farm during the 1995/96 cool harmattan season, under irrigation. Evapotranspiration deficits were created by withholding irrigation for some days in excess of the regular 7 day irrigation interval at each of the four growth stages considered. The resultant moisture stress affected grain and dry matter yields. Crop water use was monitored throughout the season for each treatment and grain and dry matter yields were recorded at harvest. Two multiplicative crop yield models: Jensen(1968) and Minnas et al (1974); and two additive models: Stewart et al (1977) and Bras and Cordova (1981) were evaluated using the experimental data, and their stress sensitivity factors estimated for the four growth stages considered. Their accuracy and predictability of crop yields were also tested. The results indicated that strong linear relationships exist between grain and dry matter yields and seasonal evapotranspiration within the limits tested. An evapotranspiration (ET) threshold of 69.3mm is required for dry matter yield initiation, while an ET threshold of 145mm is required for grain yield. Thereafter, an increment of 10.2 kg/ha in grain yield and 22.5kg/ha in dry matter yield is expected for every mm of crop water use. The four models, using the estimated stress sensitivity factors, were found to adequately predict crop yield. However, the Jensen (1968) and Bras and Cordova(198l) models predicted closer results than the others. The grain yield losses due to the moisture stress caused by the evapotranspiration deficits were relatively equal to the dry matter yield losses at booting to heading stage, and at soft dough to hard dough development, while moisture stress at flowering to milkdough development had greater yield reduction effect on the grain yield than dry matter yield.

EVALUATION OF SELECTED CROP YIELD WATER USE MODELS FOR A WHEAT CROP.

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