Plant Spacing, Density, And Yield Of Wheat Subjected To Postanthesis Water Deficits

The optimum planting density for Gutha wheat (Triticum aestivum L. emend. Thell.) grown in mediterranean-type environments varies with site and season. This study investigated the influence of postanthesis water deficits on the water relations and yield of wheat sown at different plant densities with even and uneven plant densities along the row. Unevenness of machine planting resulted in a yield reduction of 20% compared with evenly spaced plants in plants subjected to postanthesis water deficits, but no yield reduction was observed in irrigated wheat. Wheat at high densities (100 and 200 plants m(-2)) developed lower leaf and ear water potentials than plants at low densities (25 and 50 plants m(-2)) during postanthesis water deficits. The greater deficits, however, did not reduce yields. Grain yields were generally lower at densities of 25 and 50 plants per square meter than at 200 plants per square meter when postanthesis water deficits developed, but not when irrigated. The later-formed tillers (Tillers 2, 3 and 4), which were only produced at low densities, had smaller thousand-grain weights compared to those of the mainstem and the first tiller when water deficits were induced during the postanthesis period. The delay in anthesis in the later-formed tillers was up to 20 d and this resulted in grain fill occurring at low leaf and ear water potentials. We conclude that reducing the density of plants to reduce water use may decrease rather than increase wheat yield under water-limited conditions.