Land Degradation in Mixed Farming Systems on the Southern

margins of the Kalahari: Soil chemical processes and farmer

perceptions

Andrew Dougill, Chasca Twyman and David Thomas

Methodological Context: Key Research Questions

• How best to provide simple, reliable and applicable assessments of land degradation in mixed farming systems?

• How to integrate simple environmental indicators (e.g. crop yields and growth characteristics, erosion and deposition features) into Participatory Learning and Action (PLA) approaches?

• What extra information can partial nutrient budget approaches (and basic soil chemical analysis) provide for assessments of soil chemical processes (and degradation)?

Study Site : Molopo Basin, South Africa and Botswana

Mixed farming region classed by international (e.g. GLASOD) and national surveys (e.g. NBI, 2000 below) as affected by severe degradation

Study Site : Molopo Basin, South Africa and Botswana

Traditional system involves transfer of organic nutrients (as kraal manure) from rangeland to arable fields, complementing fertiliser additions

Communally owned rangeland, but with individual farmer kraals (manure supply) and privately owned (or leased) arable lands

Study Site : Molopo Basin, South Africa and Botswana

Low and variable crop growth recognised by increasing no. of farmers

Fencelines and nebkha dunes around arable fields indicate wind erosion occurrence (but limited extent)

Research MethodsAim - combine different information sources for simple and applicable

land degradation assessment at a field scale1. Inventory of conventional environmental indicators of soil degradation

(fencelines, nebkha dunes, rills) and livelihoods survey identifying farmers concerns

2. Participatory nutrient budget studies - farmer interviews aimed at quantifying nutrient fluxes at field and farm scales (15 farmers at 3 cross-border villages)

3. Soil chemical analysis (N, P, K, pH and OM)from study fields chosen by farmer

4. Soil degradation discussions - two-way discussion of soil degradation constraints on farming practices and crop yields

Research Results - Key Findings

• Field-scale nutrient budget analysis highlight that for 1998 / 99 growing season nutrient inputs exceeded outputs when farmers were able to afford compound fertiliser inputs - excess nutrients will increase risk of soil acidification

• Manure inputs alone lead to soil nutrient depletion (even for low rainfall study year)

• Perception of need for no fertiliseraddition to groundnuts leading tosoil nutrient depletion

• Integrated nutrient management as used by 2 of 15 study farmerscapable of avoiding most soil degradation processes

Opportunities Provided by Combining Information Sources

• Simultaneous collection of several indicators of land degradation (and processes causing it) leads to more applicable assessment of land degradation and its practical relevance to land users

• Improved shared understanding of land degradation pressures (including less visible threats of soil nutrient depletion and acidification) provides the basis for PLA (ie. Learning and Action)

• Improved extension advice can involve farmers in experimentation, monitoring and evaluation of adaptations to farming systems

• Lack of farmer interest in integrated nutrient management decisions (due to non-farming livelihood options, or due to lack of manure caused by decline in herd size) will lead to difficulties in ensuring long-term environmental sustainability

Conclusions

• Soil fertility assessments in combination with farmer interviews suggest acidification (due to fertiliser inputs) or nutrient depletion (due to reduced manure inputs) are the main processes of land degradation

• Participatory studies highlight key constraints as a decline in flow of nutrients from rangeland to arable and need to facilitate changes in livelihood systems to encourage integrated nutrient management

• Institutional frameworks need to enable increased availability and use of organic manure inputs as key factor affecting sustainability of arable production on sandy soils