Effects of wood ash on soil fertility and plant performance in southwestern Kenya

Sammanfattning: A field experiment was conducted in Kisii county, southwestern Kenya from February to May 2017. The purpose of the study was to examine the effect of wood ash on soil pH, soil nutrient content and productivity of common bean (Phaseolus vulgaris L.) and compare it to effects from mineral fertilizer (Diammonium phosphate, DAP) application and liming using calcium carbonate, CaCO3. Two weeding approaches with different timings were also included in the study. The experiment was two-factorial with six fertilizer/lime treatments (recommended dose of mineral fertilizer, mineral fertilizer dose used by farmers, mineral fertilizer dose used by farmers with lime, lime only, wood ash and a control where no amendments were made) and two weeding treatments (early and farmers practice) replicated four times. Soil samples were collected before experiment establishment and four weeks after the experiment was established. Data was taken on soil pH, available P, exchangeable base cation content, CEC and BS. Parameters for plant growth and development recorded were emergence, days to developmental stage V4 and R1, number of flowers and pods, bean yield and plant biomass. This was collected throughout the growing season. Data were analysed using ANOVA and Spearman’s correlation coefficient. The soil pH after treatments was found to be significantly higher in the ash treatment compared to the control and the treatments where only mineral fertilizer and no lime was applied. Lime application had no significant effect on the soil pH. However, base saturation was higher in the treatments where lime was applied than in the other treatments. No significant effects by the different treatments were recorded on available P or exchangeable base cations. The number of flowers and pods per plant was higher in plots treated with ash than in those treated with lime. The harvested plant biomass was lower in the lime treatment than in the other treatments. No significant differences were found in bean yield. Plant performance did not differ between weeding treatments, nor were there any significant interactions between fertilizer/lime treatment and weeding approach. Based on these results ash successfully increased soil pH. There are also indications that wood ash can provide other nutrients to meet the requirement of beans when grown under these conditions. Studies performed over a longer period of time would be required to see long term effects on soil pH, nutrient status and plant performance.