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Effect of Planting Date on Water-Use and Its Efficiency in Dryland Grain Sorghum¹

It has been postulated that water regime was the major operative factor responsible for different yield response of dryland grain sorghum [Sorghum bicolor (L.) Moench] to different planting dates. Our research was done in order to appraise this postulation.

For four consecutive years, four grain sorghum hybrids were planted on two planting dates (March 20–24 and April 12–16) in Israel under conditions of limited water supply as determined by the amount of stored soil moisture prior to planting. Vegetative development, grain yield, and soil water extraction profiles were determined.

Early planting, as compared with late planting, increased grain yield through increased tillering and greater weight per grain. During the period from emergence to 51 days, early planted sorghum used about halt as much water as late-planted sorghum. Early planted sorghum was less water stressed, as evidenced by lower leaf diffusive resistance prior to heading and smaller reduction in LAI (leaf desiccation) after heading, as compared with late-planted sorghum. Lower water use in early planted sorghum, during the period prior to heading, was ascribed to lower potential evapotranspiration, smaller LAI, and possibly slower root development, as compared with the respective period in late-planted sorghum. Total amount of water used at maturity did not differ between planting dates, apparently due to the longer period of growth and the larger amount of stover dry matter per plant in early planted sorghum, which served to offset the decreased water use during the earlier phase of growth.

No appreciable differences were found between hybrids tested in terms of adaption to early planting or water use.

Key Words: Soil moisture stress • Water stress • Evapotranspiration • Grain yield • Leaf area index • Leaf diffusive resistance • Roots • Sorghum hybrids

² Research Agronomist, Division of Field Crops.

Received for publication March 13, 1972.