Masters Degrees (Conservation Ecology and Entomology)

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Browsing Masters Degrees (Conservation Ecology and Entomology) by Author "Andrews, Jade"

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    Evaluating the short-term effects of conservation agriculture on soil health and crop production
    (Stellenbosch : Stellenbosch University, 2023-03) Andrews, Jade; Swanepoel, Pieter Andreas ; Roets, Francois; Crous, Casper; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Conservation agriculture (CA) – broadly defined as the implementation of three management principles – permanent soil cover, diverse crop rotations, and reduced soil disturbance – has increased steadily over the years and now accounts for 12.5% of global croplands. The implementation of these principles has improved soil health and crop yields, reduced production costs, and increased the profitability of agricultural systems. However, the application of CA in vegetable production systems is limited. As vegetable production is constrained by its high nutrient and water requirements, and crops are plagued by pests and diseases, the implementation of sustainable farming practices in these intensive systems is essential for sustained food production. This study aimed to evaluate the short-term effects of CA adoption in an irrigated vegetable production system located in Lutzville, South Africa. This area is known for wine and table grape production; vegetable production is also a major contributor towards the agricultural economy in the region. The effects of three treatments – control (“business-as-usual”), mulch (wheat straw mulch), and cover crop (a mixture of two cereals and a legume) – was determined on (i) soil fertility and biological activity; and (ii) crop yield (cauliflower seed, watermelon, tomato, and sweet melon). Soil fertility indicators included pHKCl, electrical resistance, organic C, and macronutrients, while biological activity indicators, such as enzyme activity, active C, and microbial activity, were measured. These treatments were applied to three crop rotation systems: (1) cauliflower- watermelon-soil cover; (2) soil cover-tomato-cauliflower; and (3) soil cover-sweet melon-soil cover. Clear site and crop effects were observed on soil biochemical properties. While soil biological indicators did not differ between treatments, the effects of treatments on soil fertility varied between crop rotations. Sodium content and pHKCl were higher on mulch plots, resistance lower on control plots, and P lowest on cover crop plots on rotation 2, while no treatment differences were found on rotation 1. However, soil potassium content was higher on mulch plots and phosphorus was lowest on cover crop treatments on crop rotation 3. Treatment effects on summer crop yield were varied between crops species. Mulch treatments increased cauliflower seed yield, but not watermelon yield on rotation 1. This increase in cauliflower yield was likely due to the higher application rate of compost on mulch plots (30 m³ ha⁻¹) in comparison to control and cover crop plots (15 m³ ha⁻¹), rather than soil cover treatment as it was only applied towards the end of the study period. While tomato yield was highest on control plots, no treatment effects were observed for sweet melon yield. The findings of this study suggest that the effects of treatments on both soil biochemical properties and crop yield may differ with rotation systems. Although this was a short-term study – and differences are usually only seen after at least 2 years of CA adoption – these results are promising for CA adoption and provides a good starting point for further studies in irrigated vegetable production systems in semi-arid regions.