Masters Degrees (Soil Science)

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Browsing Masters Degrees (Soil Science) by Author "Daiber, Rocco"

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    Role of soil carbon in crop yields and quality in crop rotational system
    (2023-03) Daiber, Rocco; Hardie-Pieters, Ailsa G.; Strauss, J. A.; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.
    ENGLISH ABSTRACT: Conservation agriculture (CA), which includes no-till (NT) and crop rotation, can be implemented for a positive effect on soil organic matter (SOM) accumulation and carbon sequestration. This can lead to greater soil health and resilience, with subsequently increased yields. Previous research has shown soil organic carbon (SOC) accumulation is site-specific, with the climate, crops, and the soil properties to be considered. Studies about the role that SOC plays in wheat yield are lacking in the Western Cape. In this study, soil (0-15 cm) and yield data from long- term field trials under CA conducted at Langgewens Research Farm (24ᵗʰ year) and Tygerhoek Experimental Farm (20ᵗʰ year) in the Western Cape were analyzed. The rotational systems implemented during the trials included wheat monoculture, 100% crop, 50% crop/50% pasture, and 33% crop/67% pasture. The objectives of this research project were i) to look at the long-term effect of the no-till crop rotations systems on SOC and wheat yield, ii) explore the relationship between the SOC content and the yield and protein content of wheat, and iii) obtaining optimum values and sufficiency ranges for the factors affecting wheat yield, protein content, and SOC content using boundary Line Analysis (BLA). Over the entire trial period, a significant increase in SOC content was only found at Langgewens (0.4%) attributed to it its substantially lower starting SOC (0.91%). The average SOC content being higher at Tygerhoek (1.68%) compared to Langgewens (1.17%) attributed to differences in soil properties and climate. It was observed that the SOC had likely reached a ‘saturation point’ at both sites. At both sites, the wheat monoculture had a significantly lower yield, and the incorporation of natural vegetation (pastures and saltbush) had a benefit on the SOC content, wheat yield, and protein content. The rainfall showed a significant linear correlation with wheat yields. While soil pH, lime, gypsum, N fertilizer, soil nutrients, and the clay:C ratio did not show a significant correlation. No linear correlation was found between wheat yield and the SOC content, while some seasons showed a significant partial correlation. A panel regression showed significant correlations of some variables to wheat yield. Wheat monoculture and 100% crops had a significantly lower protein content at Langgewens and Tygerhoek respectively. The BLA for wheat yield showed that above and below a certain SOC point wheat yield will decrease at each site. Protein content decreased above 20 mg kg⁻¹ soil Sulphur. The BLA showed a decreased protein content above and below a certain SOC point. A significant negative correlation between average minimum temperatures and SOC content was found. The focus of this study was the long-term dynamics of SOC and yields, and their relationship. There was SOC accumulation with the implementation of CA but is dependent on the soil and climate, along with a ‘saturation point’. The SOC did not directly correlate with yield as it is likely not directly addressing the main yield limiting factors in this production area, which are mainly climate and soil related.