Soil acidification is a serious challenge and a major cause of declining soil and crop productivity in the Eastern parts of South Africa (SA). An incubation experiment investigated effects of different maize residue biochar rates on selected soil properties and soil loss in acidic Hutton soils. Biochar amendment rates were 0%, 2.5%, 5%, 7.5%, and 10% (soil weight) laid as a completely randomized design. Soil sampling was done on a 20-day interval for 140 days to give a 5 × 7 factorial experiment. Rainfall simulation was conducted at 60, 100 and 140 days after incubation to quantify soil loss. Relative to the control biochar amendments significantly improved soil physicochemical properties. After 140 days, biochar increased soil pH by between 0.34 to 1.51 points, soil organic carbon (SOC) by 2.2% to 2.34%, and microbial activity (MBC) by 496 to 1615 mg kg⁻¹ compared to control. Soil aggregation (MWD) changes varied from 0.58 mm to 0.70 mm for the duration of the trial. Soil loss significantly decreased by 27% to 70% under biochar amendment compared to control. This indicates that maize residue biochar application has the potential to improve the soil properties and reduce soil loss in the degraded acidic Hutton soil.

Questions on sustainable and appropriate cropping systems for bioenergy sweet sorghum in the smallholder farming sector still exist. Therefore, a short-term experiment was carried out to study the influence of management on microbial biomass carbon (MBC), β-glucosidase, acid phosphatase, and urease activities in a sweet sorghum cropping system in South Africa. Tillage [no-till (NT) and conventional tillage (CT)], rotation [sorghum-vetch-sorghum (S-V-S) and sorghum-fallow-sorghum (S-F-S)] and residue retention [0%, 15% and 30%] were evaluated. Tillage× rotation× residue management interaction influenced (P < 0.05) MBC whilst crop rotation residue influenced (P < 0.05) β-glucosidase. Tillage affected β-glucosidase (P < 0.05), acid phosphatase (P < 0.001), and urease enzyme (P < 0.01) while crop rotation only influenced acid phosphatase (P < 0.01). Residue retention affected acid phosphatase (P < 0.001) and urease enzyme (P < 0.001). NT + S-V-S+30% interaction resulted in the highest MBC content compared to CT + S-F-S+0%. NT+30% enhanced β-glucosidase activity, S-V-S enhanced acid phosphatase compared to S-F-S. MBC and enzyme activities were positively correlated with each other. Tillage and residue management were the main factors influencing soil biological indicators under bioenergy sweet sorghum in South African marginal soils in the short-term. Soil biological indicators were higher under NT and 30% residue retention respectively. NT + S-V-S+30% was a better treatment combination to enhance soil quality under bioenergy sweet sorghum in South African marginal soils.

Conservation agriculture (CA) as a system is still evolving on many of the smallholder farms in sub-Saharan Africa (SSA) and questions on the impact of individual components and pathways toward adoption still require answers. A short-term study was conducted to investigate the effect of tillage, crop rotation, and crop residue management, including maize residue biochar on above ground biomass, cumulative carbon (C) input, soil organic carbon (SOC), and maize grain yield. A split–split plot design was used to evaluate two tillage operations (conventional tillage (CT) and no-till (NT)), three crop rotations (maize–fallow–maize (MFM), maize–oat–maize (MOM), and maize–vetch–maize (MVM)), and three-crop residue management (retention (R+), removal (R−), and biochar (B)). The cumulative above ground biomass produced in the MOM rotation was significantly higher by 78.9% and 88.7% relative to MVM and MFM rotations, respectively. The cumulative C input under residue management treatments ranged from 10.65 to 12.16 Mg ha⁻¹. The highest SOC was observed under R+ (1.10%) followed by B (1.0%) and the lowest was in R− (0.96%). Crop residue management significantly affected grain yields in 2015/2016 (p < 0.05) and 2016/2017 (p < 0.01) summer seasons. Biochar did not result in an obvious improvement in both C input and crop yield. Smallholder farmers can potentially switch from CT to NT without any significant yield penalty, as well as adopt MOM and R+ practices for increased biomass and C input.

Conservation agriculture (CA) is believed to contribute to sustainable crop production. However, there are contrasting reports on its short-term effects on soil properties. An experiment was conducted to determine the effects of CA on bulk density (BD), porosity, mean weight diameter (MWD) and penetration resistance (PR) in a semiarid province of South Africa (SA). A split–split–plot design was used; the main treatment factor was allocated to tillage [(Conventional Tillage (CT) and No-Till (NT)], sub-factor of crop rotation [(Maize-Fallow- Maize (MFM), Maize–Oat–Maize (MOM and Maize–Vetch–Maize (MVM))] and sub-sub factor of residue management [(retention (R+); removal (R-) and biochar (B)]. No-tillage, significantly increased soil organic carbon (SOC) compared to CT at the 0–5 cm depth. Tillage, crop rotation and residue management significantly (P < 0.01) affected MWD at the 0–5 cm depth, but not (p > 0.05) on BD, porosity and PR. The lack of significant differences, in both NT and CT plots, between biochar applications and residue retention with respect to BD, MWD across seasons and PR, also show that biochar can potentially be used as a crop residue strategy in a CA system. However, there is a need to further tests and also explore the biochar crop residue retention combinations.

Invasive alien plant species are a problem to global biodiversity, ecosystem dynamics, and human livelihood. The risks and potential effects of invasive alien species on local vegetation are growing, particularly the potential loss of ecological services. Thus, this study aimed to synthesise the impacts of acacia 'species' on soil physicochemical properties in South Africa. A Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework for conducting a systematic review was followed. A total of 16 studies that met the study selection criteria were used. Data were extracted and evaluated by checking if any soil physicochemical parameters increased (+) or decreased (−) the impacts on invaded and cleared soils. The results showed increased quantities of soil organic carbon, total nitrogen, and gravimetric water content in invaded soil than in cleared soil. Acacia species generally positively improved the soil's physical and chemical properties during their invasion, and some minor changes may occur after their clearance, such as a decrease in cations. The results of this study only explain how acacias affect soil physical and chemical properties in three provinces; therefore, there need to be more studies from other provinces which could have further given insights into a particular region.