MYCORRHIZATION STIMULANT IN SOYBEAN ASSOCIATED WITH PHOSPHATE FERTILIZATION IN OXISOLS

The use of stimulants in the establishment of arbuscular mycorrhizal fungi has great potential in contributing to P uptake by plants. This study aimed to evaluate the effect of isoflavonoid formononetin as mycorrhization stimulant on soybean associated with phosphate fertilizer in Oxisols with intermediate (OPi) and low (OP1) phosphorus availability, in the Cerrado region of Piaui. The experiment in each soil consisted of randomized blocks design in a 4 x4 factorial scheme, with four replications. The treatments comprised of four phosphorus doses (0, 26.66, 40 and 80 kg ha(-1 )P(2)O(5)), and four isoflavonoid formononetin doses (0, 0.5, 0.9 and 1.8 g kg(-1) soybean seeds). The variables evaluated were soybean growth, yield, nodulation and mycorrhizal colonization rate. With the exception of mycorrhizal colonization rate in OPi, plant height and number of pods per plant in OP1, the other variables were not affected by the application of isoflavonoid formononetin, in both soils. Yield linearly increased with increase in the phosphorus doses in OP1, and presented agronomic efficiency of similar to 15 kg ha(-1) grain for each kg ha(-1) P2O5 applied to the soil.