Rooting, water use and yield relations in wheat on loamy sand and sandy loam soils

Abstract

Abstract The effect on wheat of the timing of small amounts of irrigation, in relation to the water retentivity of soils has been studied in field experiments over four years on loamy sand and three years on sandy loam soils. Irrigation 30 days after sowing stimulated root growth. Root growth at heading was linearly related to the soil water content in the surface 30 cm soil layer during the 30–60 day period. The capacity of the plant to absorb water when the supply was limited was closely related to the size of the root system. Root weight index (RWI = mg root cm−2 soil surface in the entire root zone) and available soil water fraction (ASWF) both influenced water uptake by the crop. With high RWI, a higher rate of water uptake could be sustained even at relatively low ASWF. Also higher leaf water potentials at higher RWI irrespective of ASWF showed the overriding importance of the root system for water uptake by the crop. Although grain yield was a linear function of total water use (r2 = 0.81) during the crop season, the coefficient of determination markedly improved when relative yield was regressed over relative evapotranspiration (ET) during different time periods after sowing (R2 = 0.90). Interrelations among root growth, water use and grain yield are ascribed to positive effects of rooting on plant water status during the growing season of the crop.