RESUMEN
The current study examined whether soil pH could influence the toxicity of herbicides to soybean-rhizobium symbiosis. This can be useful for farmers to minimize the toxicity of them to crop-rhizobium symbiosis via applying their reduced doses. The toxicity of bentazon, metribuzin, and trifluralin to soybean-rhizobium symbiosis was investigated in pH 6.4, 7.2, and 8 soils. Seed inoculation decreased shoot:root (S:R) ratio but increased height, shoot dry weight (SDW), root dry weight (RDW), shoot nitrogen content (SNC), root nitrogen content (RNC), and nitrogen fixation effectiveness (NFE) in the pH 7.2 soil without herbicide application. All herbicides decreased NFE in all soil pH regimes except metribuzin in the pH 6.4 soil. Unlike trifluralin, the toxicity of bentazon and metribuzin to soybean-rhizobium symbiosis was influenced by the soil pH. It can be concluded that soil acidification and alkalization, which can rapidly occur in agroecosystems, can decrease and increase the toxicity of bentazon and metribuzin to soybean-rhizobium symbiosis, respectively.