Positive interactions between legume intensification technologies and agronomic management: Evidence from participatory on-farm experiments

Smallholder farming in Tanzania centres predominantly on maize as the staple crop, integrated with grain legumes. Technologies like mineral fertilisers and rhizobial inoculants can enhance legume yields and overall farm production, yet their adoption remains limited. This study explores the performance of these technologies across diverse field conditions and assesses their relevance for smallholders. In the 2022/2023 seasons, 40 on-farm experiments were conducted on diverse farmers’ fields in the Songwe region, Tanzania. We assessed the effects of phosphorus (P) fertilisers and Rhizobium inoculation on soybean ( Glycine max ) and common bean ( Phaseolus vulgaris ) yields with improved varieties, and farmer perceptions of these technologies. Grain yields in unamended control plots varied widely: from 0.2 t ha −1 to 2.3 t ha −1 for soybean and from 0.1 t ha −1 to 1.2 t ha −1 for common bean, influenced by soil properties such as soil pH, soil P, and agronomic practices such as timing of weeding. On average, Rhizobium inoculation increased soybean yields by 46 % but did not affect common bean yields; On average phosphorus application increased soybean and common bean by 52 % and 50 %, respectively. Combining P and inoculation raised mean soybean yields by 66 % and common bean by 75 %. Mean return on investment exceeds 2 for all technologies, with soybean inoculation favoured by farmers for its cost-effectiveness. Delayed weeding caused a 75 % reduction in soybean yield in controls. However, delayed weeding with P fertilisers and/or Rhizobium inoculation had no significant negative yield effect, indicating a positive interaction between these technologies and management practices. Our findings show the potential of legume intensification technologies, yet with availability, cost, and market challenges. Treatments: P = P-fertiliser (20 kg ha⁻¹), I = Rhizobium inoculants. A-B = Soybean (Glycine max (L.) Merr.); C-D = Common bean (Phaseolus vulgaris L.) • For soybean, mean yields increased 46 % with inoculation (I), 52 % with P application and 66 % with P + I. • For common beans, mean yields increased with P (50 %), and with P + I (75 %) but not with only I. • Application of P and/or I mitigated weed pressure (with 75 % reduction compared to control yields of soybean). • The mean return on investment (ROI) was above 2 for all legume technologies • Farmers preferred rhizobial inoculation on soybean.