Optimizing mineral fertilizer rates with biochar and compost: a slow-release fertilizer for nutrient use efficiency and cotton yield improvement in northern Benin

In Benin, the sustainability of cotton (Gossypium hirsutum L.) production is threatened by the dependency on mineral fertilizers (MFs). Although MFs are effective in increasing cotton yields, they are often misused by farmers, leading to soil degradation and detrimental environmental impacts. This study optimizes nutrient use efficiency by activating biochar with two nutrient sources, MF (NPKSB+urea) and Compost (C), which was tested on cotton. The design was an RCBD with four replicates and eighteen (18) treatment combinations:three proportions of biochar (0%, 15%, and 25%, named B0, B15, and B25, respectively) and six fertilizer rates (combinations of MF and compost: 25% C+50% MF; 50% C+50% MF; 25% C+75% MF; 0% C+100% MF; 0% C+75% MF; and 0% C+50% MF, named C25N50; C50N50; C25N75; C0N100; C0N75; and C0N50, respectively). Variables measured included yield (YLD: 180 days after planting (DAP)), plant height (HT: 45, 60, 90, and 120 DAP), number of fruiting branches per plant (NFB: 120 DAP), and number of capsules per branch (NCF: 120 DAP). Analysis of variance (ANOVA) was performed using standard procedure in R version 4.4.2. The results show that yield was strongly influenced by the application of NPK fertilizer with or without compost compensation, while biochar does not show a significant effect (p = 0.912). But MF has a significant effect on all response variables, particularly on HT (p < 0.001) and NFB (p = 0.001). Application of 25% biochar combined with 75% fertilizer exhibited higher performance, with an average of 141.2 cm. NFB increased with B15C50N50 (30.65 compared to 21,4 per plant on control plot). Regarding the cottonseed yield, an average highest yield of 3,41 t/ha was determined with B15C25N75 compared to 2.25 t/ha in B0C0N0. These results highlight the potential of biochar as a sustainable amendment to improve nutrient use efficiency. Combining MF application with biochar and compost maximizes cotton performance while reducing environmental impacts.