Soybean cultivation has expanded among farmers in Benin, yet yields remain below potential, mainly due to declining soil fertility and poor seed quality. This study evaluated the effects of organo-mineral microdose fertilization and rhizobium inoculation on the agronomic performance of three soybean varieties in the sub-humid zone of Northern Benin over two consecutive growing seasons. A split-plot design with three replications was used. The main factor was soybean variety, consisting of one traditional variety and two improved varieties (TGX1910-14F and TGX1830-20E). The sub-factor was fertilization, with nine treatments: i) control (no fertilizer, manure or inoculum), ii) phosphorus microdosing (MD; 10 kg P/ha), iii) recommended phosphorus rate (RR; 33 kg P/ha), iv) rhizobium inoculation (I), v) MD+I, vi) farmyard manure (F; 3 t/ha), vii) MD+F, viii) F+I, and ix) MD+I+F. The results showed that variety, fertilization and their interaction significantly affected soybean yield parameters. The improved variety TGX1910-14F produced the highest grain yield (2492 kg/ha), outperforming both the traditional variety and TGX1830-20E. The RR, MD+I+F and MD+F treatments resulted in the greatest yield improvements, with increases of approximately 95%, 100% and 103% compared to the control, respectively. Economic analysis indicated that these same treatments also generated the highest gross margins, with increases of 140%, 142% and 149% compared to the unfertilized control. Overall, the combined application of microdose phosphorus with inoculum, manure or both, particularly when applied to the TGX1910-14F variety, appears to be an effective strategy for improving soybean productivity and farmer income in Northern Benin.
