Analysis of soil water and water stress for pearl millet in an Indian arid region using the SPAW Model

The profile soil water and crop water stress index (WSI) under pearl millet cropgrown in sandy loam soils were computed using the daily soil water SPAW (Soil-Plant-Air-Water) model to provide a computational model in order to estimate soil water status and millet grain yields from the crop reporting district of Jodhpur in the Indian arid region. The simulated soil water conditions for the calibration years 1989, 1990 and 1991 were very close to the observed data with calibration within 3% by volume. The estimated actual evapo-transpiration of the crop was within 10% of the measured values from a gravimetric lysimeter. The relationship between WSI and pearl millet grain yields of the Jodhpur district was Y = −45•38 WSI + 526•18 (r = −0•9427). The soil water budget components and resulting WSI values explained 89% of the variation in yields during the 1971 to 1989 study period.