Effects of different biochar application rates on soil fertility and soil water retention in on-farm experiments on smallholder farms in Kenya

University essay from SLU/Dept. of Soil and Environment

Abstract: Biochar is produced through pyrolysis, the thermo-chemical degradation of biomass under anaerobic or oxygen-limited conditions. Due to its properties related to surface area and porosity, bulk density, nutrient content, stability, cation exchange capacity (CEC), pH value, and carbon content, biochar has the potential to improve physical as well as chemical soil properties and thus improve crop productivity and contribute to carbon sequestration. This study determined the effects of four different biochar rates on retention of plant available soil water, soil bulk density and availability of macronutrients. The research was conducted on smallholder farms in two counties in Kenya, namely Siaya and Embu. Maize cobs and stover biochar was applied in Siaya and coffee husk biochar was applied in Embu. Spectra of soil samples and maize leaves were taken with a visible near infrared (VNIR) spectroradiom-eter in order to determine soil moisture and available macronutrients. Also, bulk density and soil moisture at different suction pressures were determined. Regarding plant available water, a trend of increasing soil moisture with biochar rate and significance for the two highest biochar rates compared to control was found in Siaya. For soil moisture at different water tensions, a notable difference between presence and absence of biochar was observed at the two lower water tensions (pF of 1.7 and 3) in Siaya, but not on a significant level. No significant differences or trends in plant available water were observed in Embu. For bulk density, no trend for decreasing bulk density with biochar rate was found and significant differences found were not conclusive for both Siaya and Embu. As to availability of macronutrients, no conclusive significant differences and trends for increasing nutrient content of maize leaves with biochar rate were found in either Siaya or Embu.

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