| This study focuses on a subwatershed in the Middle Mountains and addresses four research questions: What is the current soil fertility status? How is it changing? Why is it changing? and What are the implications for production, sustainability and management? Soil surveys, plot studies, nutrient balance modelling, household questionnaires and GIS mapping techniques are used to address these questions.; The overall soil fertility conditions of the study area are poor and appear to be declining under most land uses. Soil pH averages 4.8 {dollar}pm{dollar} 0.4 and is below desirable levels for crop production. Soil carbon (0.99 {dollar}pm{dollar} 0.5%) and cation exchange capacity (10.8 {dollar}pm{dollar} 4.1 cmol kg{dollar}sp{lcub}-1{rcub}{dollar}) are low, and available phosphorus (16.6 {dollar}pm{dollar} 18.9 mg kg{dollar}sp{lcub}-1{rcub}{dollar}) is a concern given the low pH. Land use is the most important factor influencing soil fertility. Soil type is the second most important factor influencing soil fertility, with red soils displaying significantly lower available P than non-red soils (9.8 versus 22.1 mg kg{dollar}sp{lcub}-1{rcub}{dollar}).; Nutrient balance modelling provides estimates of nutrient depletion from the soil pool and raises concerns about the sustainability of upland farming, intensive vegetable crop production and forest nutrient cycling. Dryland maize production results in deficits of 188 kg N, 38 kg {dollar}rm Psb2Osb5{dollar} and 21 kg Ca per ha furrow slice. Rice-wheat cultivation on irrigated land appears to have limited impact on the soil nutrient pool, but the addition of premonsoon maize to the rotation results in deficits of 106kg N and 12kg {dollar}rm Psb2Osb5{dollar} per ha furrow slice. Rates of soil fertility depletion estimated from differences in soil fertility between land uses indicate substantial N and Ca losses from forest land (94 and 57 kg ha per furrow slice respectively).; Land use change, the impact on nutrient flows and relationships between nutrient inputs, crop uptake, nutrient balances and soil fertility provide an understanding of why soil fertility is changing. Expansion and marginalization of dryland agriculture were noted from 1972-1990, as former grazing, shrub and abandoned lands were terraced and cultivated. Nutrient fluxes indicate that inputs are insufficient to maintain the soil nutrient pool under dryland cultivation due to the high nutrient requirements of maize and nutrient losses through erosion.; Population growth, land tenure, culture and poverty are the underlying socio-economic factors which influence farming system dynamics, directly impact nutrient inputs, and indirectly drive soil fertility degradation. Population growth rates of 2.6% have contributed to agricultural intensification and marginalization, and pressure on forest resources. The distribution of land is highly skewed with 15% of the surveyed households owning 46% of the land. Women play a central role in soil fertility management through their responsibilities for livestock care, litter collection and compost application, but increasing workloads related to commercial milk production, cash cropping and the off-farm employment of males are a major concern. (Abstract shortened by UMI.)... |
