Summary
This split-plot field trial examined how intercropping sunn hemp with maize at different timings and densities affects soil properties and yields under in-field rainwater harvesting in semi-arid South Africa. Early sunn hemp planting significantly increased soil organic matter by 32.4% compared to late planting at low stand density, whilst two-season cumulative effects showed marked enhancements in organic matter (+39.7%), nitrogen (+19.0%), potassium (+21%), and manganese (+60.6%), alongside reductions in calcium, sodium, and iron. Maize yields in medium and high sunn hemp stand densities were substantially higher in the first season (15.3%–34.3% increases) than the second season.
UK applicability
The findings have limited direct applicability to UK farming given the distinct semi-arid climate, rainfall patterns, and soil types of South Africa. However, the intercropping principles and soil organic matter accumulation strategies may inform UK regenerative arable systems, particularly in drier regions, though site-adapted legume covers and management timing would be required.
Key measures
Soil organic matter (%), nitrogen (%), potassium (%), manganese (%), calcium (%), sodium (%), iron (%), soil moisture content, maize grain yield, intercropping timing (three stages), sunn hemp stand density (16, 32, 48 plants m⁻²)
Outcomes reported
The study measured effects of intercropping timing and stand density on soil chemical properties (organic matter, nitrogen, potassium, manganese, calcium, sodium, iron), soil moisture content, and maize grain yield over two growing seasons.
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