Effects of Agri-Silvopastoral Practices on Soil Physical and Chemical Properties in Machakos County, Kenya

Background and Objective: Although agroforestry is known to enhance soil quality, the specific impacts of various agri-silvopastoral systems on the physical and chemical properties of soils, particularly in the tropical regions of Sub-Saharan Africa, remain insufficiently understood. This study investigated the influence of agri-silvopastoral practices on soil physical and chemical parameters. Materials and Methods: Soil was sampled from 73 different farmers with different agri-silvopastoral practices using a soil auger. Soil physical properties measured were sand, clay, and bulk density. The soil chemical properties included pH, total nitrogen, total phosphorus, total organic carbon, as well as carbon-to-nitrogen ratio (C/N). In addition, exchangeable bases such as potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na), as well as micronutrients including manganese (Mn), copper (Cu), iron (Fe), and zinc (Zn), were also analyzed. Differences in time among agri-silvopastoral practices were evaluated using One-way Analysis of Variance (ANOVA). Statistical significance was set at p<0.05. Results: Agroforestry practices such as boundary cropping and scattered tree planting significantly increased the sand content in soils, while alley cropping, followed by woodlots, increased silt content. Adjacent to boundary planting, as well as scattered tree planting, was higher bulk density in soils. The TN was highest in alley cropping and woodlots, while elevated TOC and C/N ratios occurred in soils where alley cropping was practiced. The concentration of Ca occurred in soils where alley cropping and scattered tree planting were practiced, Mg and Na were highest in soils practicing alley cropping and woodlots. The highest concentration of Mn, Cu, and Zn occurred in soils practicing hedgerow and alley cropping, and was lowest in soils practicing scattered tree planting and boundary. Conclusion: The physical and chemical attributes in the soil appeared to be affected by the type of agri-silvicultural practice. The study recommends adoption of silvopastoral activities in most of the dryland regions to improve soil parameters.