Evaluating the soil health status of conservation and regenerative agricultural systems across multiple ecotopes in South Africa

Abstract

Conventional agriculture negatively impacts soil health in South Africa due to an over-reliance on synthetic fertilisers, intensive tillage, no or limited crop rotations, as well as heavy irrigation. In response to these challenges, conservation and regenerative agriculture offer more resource-efficient alternatives with the potential to mitigate soil health degradation. However, further research is needed to quantify and validate the impact of conservation and regenerative agriculture under varying South African environmental contexts. Therefore, this study aimed to assess the impact of conservation and regenerative agriculture on soil health across multiple ecotopes in maize production regions of South Africa and to identify cost-effective indicators of soil health status. On-farm trial sites included Nicol de Vos (Kinross, Mpumalanga), Hendrik Odendaal (Standerton, Mpumalanga), and Nant Yzel (Marquard, Maluti). The trial design included implementation of conventional, conservation, and regenerative agriculture. Each according to their unique implementation principles. The effect of these implementations was monitored across three consecutive cropping seasons (2020/2021 - 2021/2022 - 2022/2023). Soil samples were collected during the summer growing seasons of each cropping season. Whereafter soil for soil texture (a physical parameter) and permanganate-oxidisable carbon (POXC) (a biological parameter) were analysed at the North-West University (NWU). Additional parameters were analysed using the Haney Analysis at Ward Laboratories Inc. in the United States of America. This study utilised Permutational Multivariate Analyses of Variance (PERMANOVAs) and Principal Component Analyses (PCAs) to assess the effects of ecotopes, farming systems, and cropping season on soil health. Pairwise comparisons were conducted to identify significant differences (p < 0.05) in soil health parameters, while distance-based linear models were used to determine the best subset of proxy indicators for soil health. The results revealed that soil texture and volumetric aggregate stability were the physical parameters most affected by farming systems across all three cropping seasons. Chemical parameters most affected by farming systems during the first cropping season included copper, magnesium, iron, and pH. During the second cropping season sulphur, manganese, and pH were most affected by the farming systems. Whereas sodium, iron, and inorganic nitrogen were most affected by farming systems during the final cropping season. Results further revealed that organic matter was consistently identified to be the most affected by farming systems across all three cropping seasons. However, the soil health status remained largely unchanged in the short term (<5 years). Only the final cropping season (2022/2023) indicated an improvement in soil health at Nant Yzel, the ecotope that exhibited the poorest soil health at the start of the study. Furthermore, this study identified magnesium, organic matter, pH, sodium, potassium, microbial active carbon, and nitrogen (total and inorganic) as key indicators that can serve as proxies of soil health status. The improvement in soil health at Nant Yzel were attributed to the slight increase in organic matter. However, due to the time it takes for organic matter to accumulate, it is anticipated that a longer study duration would have revealed more conclusive results. Due to the strong correlation between organic matter accumulation and the effects of conservation and regenerative agriculture on soil health, along with its identification as a key proxy indicator, it was recommended that organic matter be measured as a single proxy for soil health status.