Effect of land use on hydraulic properties of a nitisol and a lixisol

Abstract

Infiltration rates, saturated hydraulic conductivity (Ksat) and antecedent water content (w) were investigated in Kabete Nitisol and Kibwezi Lixisol under Forest, Grass, Cultivated Bare and Compacted Bare Landuse as treatments. Comparison of soil water release and retention of the same soils was made under Grass (virgin) treatment. Infiltration tests were done in the dry and wet soil moisture status referred to as dryrun (DR) and Wetrun (WR) infiltration rates respectively using the double ring infiltrometer. The soil physical variables (thought) to influence the above hydraulic properties were also investigated. These included organic carbon (OC) , bulk density (Pb) and texture. The Pb, OC and Ksat showed significant differences at 5% level with respect to site conditions and the two soil types. Treatment textural variations were insignificant but for soil types Kabete was predominantly clayey and Kibwezi predominantly sandy. The Ksat for both areas revealed significant differences only in the Forest, due to its high OC and lower Pb. There was no overall difference between Ksat of Kabete and Kibwezi. The DR antecedent water in order of decreasing magnitude for Kabete was Forest, Grass, Cultivated and Compacted Bare site, but the results were somehow distorted for Kibwezi due to irrigation. These observations were significant at 5% level. In Kabete, the (newly) cultivated site had the highest water intake rates, followed by Forest tben Grass and lastly compacted site. In Kibwezi, the rates in decreasing order of magnitudes were: Forest, Grass, Cultivated (and compacted by machinery) and compacted site. Significant correlations (r) between infiltration rates and OC, Pb and Ksat at selected times were obtained for Kabete and Kibwezi. In the Virgin site, significant differences (P<0.05) in soil water retention and release were obtained. soil water retention in the 0 - 1500 KPa range was significantly higt ':"(P<O. 05) under Kabete Nitisol than under Kibwezi Lixisol. The opposite trend was