RESUMO
BACKGROUND: The changes in land use and land cover have a strong effect on the total soil organic carbon, its fractions and its overall soil health. This study carried out in Olesharo Catchment, Kenya, was to quantify the differences in total organic carbon (TOC), particulate organic carbon (POC), mineral organic carbon (MOC) and carbon management index (CMI) among four land use types: grasslands, shrublands, agricultural lands and barelands. It was also purported to evaluate the use of CMI as an indicator for soil degradation or improvement in response to land use and land cover changes. RESULTS: The results of the study show that the mean values of TOC, POC and MOC are significantly different between land use types. Thus, shrublands have significantly higher TOC (22.26 g kg-1) than grasslands (10.29 g kg-1) and bare lands (7.56 g kg-1). They also have significantly higher POC (7.79 g kg-1) and MOC (10.04 g kg-1) than all the other land use types. The agricultural lands have higher CMI than grasslands (53% vs 41% relative to shrublands) suggesting that grasslands face serious degradation through overgrazing. CONCLUSIONS: This study shows that different land use types have an influence on soil organic carbon pools, and consequently on the CMI, the CMI could be used as an indicator for soil degradation or improvement in response to land use and land cover changes.
RESUMO
A field study was carried out to evaluate the effects of tillage practices on soil physical properties in Mwala district, Eastern Kenya, during the long rains (LR) and short rains (SR) of 2012/13. The treatments were disc ploughing (DP), disc ploughing and harrowing (DPH), ox-ploughing (OX), subsoiling-ripping (SSR), hand hoeing with tied ridges (HTR), hand hoeing only (H). These were investigated under three cropping systems of sole maize, sole bean, and maize-bean intercrop in a split-plot design with four replications. Soil physical properties were monitored at different weeks after planting (WAP) throughout the growing seasons. A four-season average shows that soil moisture content was significantly (P < 0.05) higher in OX > SSR > DPH > H > HTR > DP with values ranging from 13.1 to 14.1%. Soil surface roughness and crust strength varied significantly (P < 0.05) over time within the growing seasons, between the tillage practices, and across the different seasons with values ranging from 26 to 66% and 1.21 to 1.31 MPa, respectively. Tillage practices and cropping systems did not significantly affect bulk density, porosity, or K sat values. It is apparent that long term tillage experiment (>4 seasons) would be required to detect changes in soil physical properties as a result of the soil management practices.
