INCREASING PLANT-DENSITY IN SPRING WHEAT TO AMELIORATE THE EFFECTS OFSALINITY ON GRAIN-YIELD

Root-zone salinity reduces the grain yield of spring wheat mainly by p reventing the initiation and growth of plant tillers. A counter practi ce might be to multiply the number of plants grown per unit area, ther eby increasing the number of more resistant mainstems. A spring wheat cultivar (Katepwa) was seeded in large greenhouse sand tanks and water ed with hydroponic solutions containing Na and Ca solutes in treatment s of 2, 4, 6, 9, 12, and 16 dS/m. Seeding densities equalled 100, 232 and 344 seeds/m(2), the numbers necessary to achieve below, at, and ab ove normal plant densities for dryland wheat production. The average n umber of plants harvested per m(2) across all salinities equalled 97.6 , 225.8, and 331.3/m(2), respectively, resulting in a mean correlation coefficient of 0.998. Grain yields averaged for all salinity levels e xcept one increased significantly with all increasing seeding densitie s at p = 0.10, but were only significant between the below-re-normal s eedings at p = 0.05. Progressively greater salinity significantly redu ced biomass, grain yield, and spikes per m(2), but not the number of p lants/m(2). The number of spikes and the grain yield per plant also de creased significantly, but not the grain per spike; the harvest index even grew slightly as salinity increased. The results showed that the increases above the normal Katepwa wheat population that would be nece ssary in order to offset reductions in grain yield caused by salinity could be logarithmically governed. Consequently, to be effective, plan t densities would have to increase to such numbers that water requirem ents in non-irrigated, semiarid climates will still likely limit produ ction during most years. Crowding multi-tillering Katepwa wheat planes appear to offer only limited hope for compensating grain losses cause d by salinity.