EFFECTS OF OZONE, SULFUR-DIOXIDE, SOIL-WATER DEFICIT, AND CULTIVAR ON YIELDS OF SOYBEAN

The effects of ozone (O3) stress on bean yields and seed size of four soybean cultivars [Glycine max (L.) Merr.] grown in open-top chambers in 1981, 1982, and 1983 are presented. The O3 treatments included charcoal filtered (CF) and nonfiltered (NF) air, and 0.03, 0.06, and 0.09 μL L-1 O3 added 7 h d-1 to NF air. The effects of SO2 in concentrations from 0.005 to 0.224 μL L-1 (4 h d-1, 5 d wk-1) from the seedling stage to maturity were studied in 1981 and 1982. In 1982 and 1983 the effects of soil moisture stress (SMS) and well-watered (WW) soil conditions on the response of soybean to O3 stress were determined. The primary objective was the evaluation of 3 yr of soybean data from our site using the nonlinear Weibull and the polynomial dose-response models to relate yield responses to O3 exposure doses. The variables also included SO2, soil moisture, and cultivar. The homogeneity of the response equations were compared to permit development of the smallest set of homogeneous equations over years. Both O3 and SO2 negatively impacted bean yields and seed size. No interactions between O3 and SO2 were indicated. With the Weibull model, interactions between O3 and soil moisture were observed with 'Forrest' in 1982 and 'Williams' in 1983. With an O3 level considered typical in soybean production areas (seasonal 7 h d-1, 0.055 μL L-1) compared to background O3 (0.025 μL L-1) and using all data from 3 yr of experiments, the Weibull model predicted the same (15%) mean yield loss under both SMS and WW regimes.