Agronomic evaluation of WonderGro soil conditioner on maize productivity in Kenya
Despite maize being a staple food crop in Kenya, its productivity remains low, mainly due to inappropriate soil fertility management. The use of balanced and adequate fertilizers, while improving other soil conditions, is a prerequisite for increasing fertilizer use efficiency and maize production. This study assessed the performance of two WonderGro soil conditioner formulations (WG3 and WG21) in combination with the commonly applied DAP fertilizer on maize yield and economic returns under different soil pH conditions. On-farm trials were conducted during the 2023 and 2024 long rains (LR) and the 2023 short rains (SR). A total of 16 study sites located in two agroecological zones (AEZs) a medium-potential zone (western Kenya) and a high-potential zone (Rift Valley) were selected for the experiments. Each AEZ comprised eight sites equally distributed across two counties. The study evaluated fertilizer performance under suboptimal (pH < 5.5) and optimal (pH ≥ 5.5) soil pH conditions for maize production. Treatments included an absolute control (0 kg DAP ha −1 ) and four fertilizer treatments: 133 kg DAP ha −1 , 67 kg DAP ha −1 , 67 kg DAP + 67 kg WG3 ha −1 , and 67 kg DAP + 67 kg WG21 ha −1 , each replicated four times. Maize grain yield response to WonderGro application was greatest when 67 kg DAP + 67 kg WG21 ha −1 was applied in soils with pH < 5.5 in the medium-potential zone, where grain yield reached 4.4 t ha⁻¹ during the 2023 LR season. In contrast, fertilizer treatments showed no significant differences in yield in soils with pH ≥ 5.5 in the high-potential zone, where average maize grain yields were 7.3 t ha −1 and 6.1 t ha −1 during the 2023 and 2024 LR seasons, respectively. From an economic perspective, the application of 67 kg DAP + 67 kg WG21 ha −1 produced the highest value-cost ratios (VCRs) of 7.54 and 8.24 during the 2023 and 2024 LR seasons, respectively, under suboptimal pH conditions in the high-potential zone. These results indicate that the WonderGro formulations have the potential to partially substitute for 133 kg DAP ha −1 without yield losses, thereby improving economic returns to farmers. The findings further suggest that the benefits of WonderGro are more pronounced under suboptimal soil pH conditions, where improvements in maize productivity and profitability can be achieved.