INFLUENCES OF SOIL-PH AND CLIMATE ON THE TOLERANCES OF BARLEY AND WHEAT TO CHLORSULFURON

The effects of soil pH and seasonal conditions on the responses of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) to chlorsulfuron were investigated at 3 sites in southern New South Wales in 1986, 1987 and 1988. The sites varied in soil pH (4.3-6.2) and annual rainfall (360-560 mm). In addition to the variation in soil pH between sites, 2 surface pH levels were obtained at each site by the addition of lime. The effect of post-emergence applications of 7.5, 15.0, 22.5, 30.0 and 37.5 g a.i./ha chlorsulfuron on the yield of weed-free barley and wheat varied with season, site and the addition of lime. The yield reduction was greatest in 1986, and the extent of the reduction was always greater in barley than wheat. In 1986, a recommended rate of chlorsulfuron (15 g a.i./ha) significantly (P < 0.05) reduced the grain yield of barley at all sites by up to 18% and of wheat by up to 13%. Therefore, the reduced tolerance of barley and wheat to chlorsulfuron in some seasons was not restricted to the acid soils. Significant lime x chlorsulfuron interactions occurred with barley in 3 of the 9 trials, but the interactions were not consistent. At Ariah Park in 1986, grain yield reductions were greatest in unamended soils, while at both Ariah Park and Goolgowi in 1987, grain yield reductions were greatest with the limed plots. There were no significant interactions for wheat. In pot trials the effect of chlorsulfuron on the shoot dry weight of barley varied with soil type. However, there was no direct relationship between soil pH and dry weight reduction. When the pH of an acid soil was amended by liming to give soils with pH of 4.1-7.3, there was a trend to more damage at pH values of 5-6. With 4 soils of different pH and texture, there was less damage in the barley grown in soils of pH 7.3 and 7.4 than in soils of pH 4.1 and 6.0. While these results suggest that soil pH affects the tolerance of barley to chlorsulfuron, it is likely that soil pH is of less importance than other edaphic or climatic factors.