Responses of soybean–maize succession to increasing phosphate fertilization rates under phosphate-solubilizing microorganism inoculation

Low phosphorus (P) availability constrains crop productivity in weathered tropical soils, particularly within soybean–maize succession systems. Combined application of phosphate fertilization and phosphate-solubilizing microorganisms has been proposed, but its field performance in soybean-maize succession systems remains poorly documented. This study evaluated the response of a soybean–maize succession to increasing rates of monoammonium phosphate (MAP) under seed inoculation with phosphate-solubilizing microorganisms (PSM), Bacillus subtilis (CNPMS B2084) and Priestia megaterium (CNPMS B119) in a Cerrado Oxisol, assessing soil P availability, plant nutritional status, physiological traits, yield, and soil biochemical attributes (glomalin, β -glucosidase, arylsulfatase, and acid and alkaline phosphatases).The field experiment followed a randomized complete block design with P 2 O 5 rates of 0, 19.5, 39.0, 59.5, and 78.0 kg ha⁻ 1 (all inoculated with PSM), plus an absolute control without P fertilizer and without PSM inoculation. In maize, grain yield increased linearly with P₂O₅ rate under PSM inoculation. Yield values in fertilized treatments under PSM inoculation were higher than those observed in the absolute control. In soybean, grain yield was not affected, whereas grain P concentration increased linearly with P 2 O 5 rate. Soil β -glucosidase activity also increased with P 2 O 5 rates under PSM inoculation, suggesting stimulated microbial C-cycling activity, while photosystem II photochemical parameters and arylsulfatase activity remained unaffected. The results indicate that increasing MAP rates under PSM inoculation were associated with higher maize grain yield, soybean grain P accumulation, and soil β -glucosidase activity. Because all fertilized treatments received PSM inoculation, the independent contribution of PSM could not be determined.