Impacts of Irrigated Legume-Based Cropping on Rhizobia Diversity, Insect Pollinators, and Soil Seed Bank in a Rangeland Ecosystem, Isinya District, Kenya: Using the Sustainable Preferred-Stable-State Model in a Narrative
22 Pages Posted: 20 Oct 2010
Date Written: October 18, 2010
Range assessment in the past involved the monitoring of the growing condition of natural vegetation, and thus prospect for yield of animal products. The assumptions were: (1) that land will be managed to maintain range ecology vegetation to the exclusion of annual food crops, (2) that land carrying capacity assessment will provide adequate information on range trend and condition, and (3) that flux in community is merely produced through grazing, burning, and clearing, and climax is expected to re-establish through natural sequence of regenerations. This approach in range management came under scrutiny in Africa in the 1980s due to a better appreciation of the multifunctional use of the range.
Practically, the past approach could only produce a partial picture of what is happening in the tropical rangelands. The present reality is that population pressure is causing people to migrate from the humid regions and settling in rangelands, bringing with them non-traditional range agricultural practices; and some pastoralists are forced by circumstances to also acquire and incorporate these new forms of land use in order to subsist on the range. In East Africa this social adjustment has been helped by better access to technology such as groundwater irrigation and improved cultivars developed for drylands. Crop production – alone or accompanied by livestock keeping – has become viable, profitable and in practice on the range. Grain outputs are supplementing if not replacing milk and meat as sources of nutrition and income for range households. Carrying capacity based on number of livestock or forage production is no longer adequate for range assessment. What is needed now is a total assessment of range conditions using approaches that reflect the current rangeland uses. Where mixed farming is practiced, an overall range assessment must look at the total sustainable yield of grains and animal products. Clearing and cultivation together with the biodiversity implications must now be put on the same level as burning and grazing as factors of range assessment. The biodiversity implications of irrigated farming and the multifuntionality of the East African rangelands must now come under increasing focus.
The present reality in the East African rangelands calls for a deviation from the normal management that depends too highly on the Clementsian theory of vegetation succession to maintain one operational state. The outcome of the old approach will not meet utilitarian and economic needs of the land own today. Moreover, the approach seems over determined by natural environmental conditions, and has not fully factored in the human ability to change the fortunes of the dryland through innovation and progress in technology. The rangeland inhabitants of East Africa are re-inventing and redefining the range land use potential by embracing appropriate and increasingly affordable agricultural technology, such as simple irrigation systems and biotechnology of improved cultivar for dryland farming. Under the changing demographic structure the system is more complex than ever; so rather than working to maintain one operational stable state, range management that leans towards non-equilibrium concepts such as the state-and transition model or the self-organizing holarchic open system theory will provide a better assessment of condition and trends in the rangelands of East Africa. Drawing from these theories, this study proposes the sustainable preferred-stable-state model as an approach for regional range monitoring and assessment.
Keywords: African Rangelands, Rhizobia Assessment, Climatic Limitations, Vegetation, Irrigation, Sustainable Preferred-Stable-State
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