Effects of land use change on soil qualities in Sasumua catchment

Sustainability of natural resource base is dependent on good land management. Land use change
from forest to agricultural land can endanger sustainability of soil productivity if not well
managed. Effects of land use change from forest to annual crop cultivation and grazing on soil
qualities were investigated in Sasumua catchment with the aim of (a) determining the changes in
selected physical and chemical qualities (b) establishing how various soil quality indicators vary
with different land management practices and (c) developing the minimum data set for
determination of soil health. A survey of farms and forest was carried out by collecting soil and
water samples from randomly selected sites. Measurement of CEC, exchangeable Ca, Mg, K and
Na, pH, EC, base saturation, total N, soil carbon and texture, bulk density and hydraulic
conductivity was done on soil samples while water samples were analyzed for quality. Effects of
land management practices were determined using structured questionnaire. The long term
effects of cultivation of land after land use change from forest was determined by comparing the
levels of selected soil qualities over a 30 years period. These results were then subjected to
factor analysis using principal component analysis to determine the appropriate indicators by
developing the minimum data set. The results shows significant change of soil pH and silt
content when land is converted from forest to grazing land and annual crops cultivation. In
grazing land ; CEC , exchangeable Ca2+ and Mg2+, base saturation and sac decreased by 8%,
42%, 52%, 32% and 8% respectively while Total N increased by 6 % . In annual crop cultivated
land; exchangeable Ca2+and Mg2+, base saturation and sac decreased by 31% ,40% ,32% and
8% respectively, while CEC, Total N, and bulk density increased by 14%, 23% and 10%
respectively. Land management practices such as intensive cultivation of horticultural crops,
overgrazing of pastureland and farming on steep areas were contributing to soil chemical and
physical degradation while addition of farmyard manure and agro forestry were contributing to
sustainability of soil organic carbon and bulk density. Tillage in cultivated fields influenced
increase in CEC. Water quality results indicated that land use management affected quality as it
flows from forest to areas with human settlements. It was found that there is a decline of soil
quality over the 30 year period. This soil quality decline from 1977 to 2007 is related to the
increase in the area population from 9 to 260 persons per square kilometer over the same period.
Soil pH, texture, sac and CEC were found to be the best indicators of soil health In the
catchment.