Response of different soybean varieties to phosphorus fertilizer microdosing and rhizobium inoculation in the sub-humid zone of Northern Benin

Abstract

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.