Effects of Agroforestry Practices on Soil Properties in the Drylands of Eastern Kenya

Drylands, which are home to about 2 billion people face a myriad of problems among them low land productivity. Agroforestry is one of the land use practices that is perceived to be sustainable with beneficial effects on soil properties. However, the effects of agroforestry practices on soils especially in the drylands have rarely been quantified and studied in details. The study determined the effects of selected agroforestry practices on soil properties in Makueni County of Kenya where agroforestry has been promoted by various organizations. Four soil samples were collected at 0-15cm, 15-30cm, 30-45cm and 45-60cm depths in a zigzag pattern at each 10 x 10m plots established along line transects laid in woodlots established in 2007, 2010 and 2013 and their adjacent parkland and grazing land. Seven randomly selected farms were sampled. The samples were analyzed using laboratory methods for soil nutrients and physical properties. Density of tree species in these established plots were also determined using quadrat technique. Tree density was higher in woodlots followed by grazing area and parkland .Soil samples showed that Soil Organic Carbon and Total Nitrogen were significantly higher in the woodlots than in the parkland and grazing lands ((p≤0.05). Soil Organic Carbon was significantly higher in woodlots established in 2007 than those established in 2013. Phosphorus was significantly higher in cropland compared to woodlots and grazing land. Phosphorus and Potassium were significantly higher at 0-15 cm depth compared to other soil depths. Bulky density was significantly higher with a corresponding lower total porosity in grazing lands than in the woodlots and parklands. The results suggest that different agroforestry practices contribute differently to soil properties. Mixed tree woodlots contributed significantly to improving soil properties and could be considered as a strategy to sustainably restore degraded and infertile soils in the drylands