EFFECTS OF SALINITY AND VARYING BORON CONCENTRATIONS ON BORON UPTAKE AND GROWTH OF WHEAT

Two sandculture experiments were conducted with wheat (Triticum aestivum) to determine the effects of (1) osmotic potential (.PSI..pi.) and (2) fluctuating boron (B) concentrations on B availability (toxicity), shoot growth and leaf concentrations of B of wheat. The first experiment consisted of growing wheat to the spike emergence stage in sandcultures irrigated with a complete nutrient solution containing 1.0, 7.5, and 15.0 mg Bl-1 and having .PSI..pi. values of -0.02, -.0.07, -0.12, and -0.17 MPa produced by CaCl2-NaCl additions. Statistically, shoot weight was independently influenced by the B and .PSI..pi. treatments but not by their interaction. Only the B treatment had a significant effect on leaf boron concentrations; the B .times. .PSI..pi. interaction was nonsignificant with respect to leaf B concentrations. The second experiment was designed to determine if growth and B uptake of wheat responds to the time integrated mean (TIM) concentration of B. This experiment consisted of four fixed-B concentrations and four fluctuating-B concentrations designed to produce two TIM concentrations (3.9 and 7.4 mg Bl-1) approached low to high and vice versa. With respect to shoot weight, there was no statistical difference among treatments having the same TIM concentration during the 10 week experiment. However, shoot B concentrations differed greatly; they were higher when the B concentration was progressively increased over the 10 week period. Leaf B concentrations (Y leaf at flowering), while not as high as the shoot B concentrations, were also higher under the treatment of increasing B concentration, indicating B uptake rates are higher for mature plants than for seedlings.