Department of Agricultural Resources and Economics
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Item Integrating Cordia Africana Trees on Farms Differentially Improves Soil Properties in Small Holder Farms in Kirinyaga County, Kenya(2023-08-08) Kamau, Miriam; Kinyanjui, Mwangi; Kamiri, HellenTree-based solutions are more efficient in nutrient cycling in farming systems and hence ideally suited for impoverished farmers experiencing food insecurity. Agroforestry trees have a positive effect on soil fertility through litter fall by the canopies compared to that of the adjacent open fields. Field sampling involved selecting mature Cordia africana trees from ten farms and collecting soil samples at varying distances from the tree trunks and at two depths (0-15 and 15-30cm). For each selected farm, soil samples were collected at three sampling points defined by distance from the tree base thus: - 5M (under the tree canopy), 11M (at the edge of the crown), and 30M (from the tree's influence. Laboratory analyses measured concentrations of nitrogen, phosphorus, potassium, calcium, magnesium, and organic carbon. The soil parameters investigated (Nitrogen, Phosphorus, Soil organic carbon, Potassium, and Calcium) were significantly higher in the topsoil than in the subsoil. The horizontal effect of trees with increasing distance from the tree on soil nitrogen, organic carbon, and phosphorus is minimal, the effect being more on vertical distribution (across depth). Differences in nutrient contents in soil nutrient variables between agroforestry and cropped land showed that soil nutrients within the Cordia africana system were higher than those under cultivated land implying that Cordia africana has a positive effect on soil quality. Thus, the study emphasizes the adoption of Cordia africana in agroforestry practices with a view to increase soil fertility and improve crop yields in sustainable farming. There is therefore need for the formulation of appropriate measures of soil management based on the characteristics of the sites.Item Influence of Vegetation Cover and Topographic Position on Water Infiltration, Organic Matter Content and Aggregate Stability of Grassland Soils in Semi-Arid Kenya(Advances in Agricultural Science, 2019) Mutuku, Daisy; Kamiri, Hellen; Ndufa, James; Kiama, Stephen; Mware, MugoA study was conducted in Mpala and Ilmotiok ranches in Laikipia County, Kenya, to investigate the influence of vegetation cover and topographic position on soil organic matter, bulk density, aggregate stability and water infiltration rate. Three vegetation cover types; (Tree, Grass and Bare) and four topographic positions (Hillslope, Headwater, Riparian, and Plateau) were evaluated. Soil samples were collected along the topographic positions and within the vegetation cover types at five levels of depth; 0-10, 10-20, 20-30, 30-40, 40-50 cm during the dry season May to August 2016. The samples were analyzed for soil organic matter, bulk density and soil aggregate stability. Water infiltration rate was measured in situ on the soil surface using a mini-disk Infiltrometer. Soil aggregate stability varied significantly between topographic zones (p=0.0124) but not between the vegetation cover types and soil depth in Ilmotiok site. Mpala site showed a significant difference in aggregate stability between the topographic zones (p=0.0152). However, no significant difference was observed in variation of aggregate stability between the vegetation cover types and soil depth (p=0.8998; p=0.8284) respectively. In Ilmotiok site, the highest infiltration rate was recorded in the Tree covered fields (73.3 mm/hr) and decreased in Grass fields and Bare grounds at 25 and 17 mm/hr, respectively. The Headwater zones had the highest infiltration rates (73.3 mm/hr) while the lowest infiltration rates were (0 mm/hr) in the Hillslope zones. The infiltration rates in Mpala site were highest in Bare grounds (37.8 mm/hr) and lowest in Tree fields with 5.7 mm/hr. The Headwater zones had the highest infiltration rates followed by Hillslope zones with (8.9 mm/hr) while the Riparian zones had the lowest infiltration rates (0.00 mm/hr). Soil organic matter (SOM) differed significantly at P (<0.0001) among the vegetation cover types, topographic zones and soil depth for both sites. In Ilmotiok site, the mean soil organic matter was highest (1.96%) in Hillslopes zones and lowest in Grass covered fields (0.30%). In Mpala, SOM content was highest in Tree covered fields at 2.28%, and lowest in Grass covered fields at 0.38%, for RIP and PLA zones respectively. Topographic positions and grazing management influenced soil properties in the semi-arid grasslands, hence the need for strategies in grazing management that will promote restoration of these degraded areas.