Transcript Land Degradation in Mixed Farming Systems on the Southern

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 Methods
Aim - combine different information sources for simple and
applicable land degradation assessment at a field scale
1. 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 fertiliser
addition to groundnuts leading to
soil nutrient depletion
• Integrated nutrient management
as used by 2 of 15 study farmers
capable 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