The use of biochar as a soil ameliorant has recently gained momentum. However, its application has been reported to have some adverse effects soon after the pyrolysis process. This study aimed to determine the effect of different biochar ageing methods and fertiliser applications on selected soil properties, growth, and yield of red radish (Raphanus sativus L.). A 2 x 3 factorial arrangement was used in a complete randomised design (CRD) with three replications. The factors were (1) biochar ageing at three levels, i.e., naturally aged biochar (NB), artificially aged biochar (AB), and fresh biochar (FB), and (2) fertiliser at two levels viz fertilised (F) and non-fertilised (NF). A control treatment (without biochar) was also included. Irrespective of the ageing method used, biochar application significantly increased soil pH, while fertiliser application significantly reduced soil pH throughout the experiment. Similarly, biochar application significantly increased soil hydraulic conductivity compared to the control. However, after ten weeks, significantly higher soil hydraulic conductivity was reported in treatments with AB biochar compared to both NB and FB. The application of fertiliser in biochar-amended soils improves the soil's hydraulic properties and increases radish growth. The study concludes that AB biochar + fertiliser application improves soil properties and growth of radish.

Agricultural food production in Africa is low and cannot sustain its ever-growing population. Climate change-induced high rainfall variability and temperature fluctuations are blamed for the low agricultural productivity amongst African smallholder farmers. Additionally, land degradation is causing shrinkages in the cultivated land and abandonment of crop fields in most African countries. Land degradation is worsened by the anthropogenic activities that lead to the depletion of soil organic carbon, a vital constituent of soil quality. Most farmers in the continent are resource-poor and therefore practise low input agriculture, continuous crop monoculture and use heavy soil tilling methods that enhance the decomposition of the already low soil organic carbon. Researchers devised several interventions like conservation agriculture, but adoption remains poor owing to various associated issues like trade-offs. In addition, the response of soil to these interventions requires several years in most cases, and most smallholder farmers are not patient for that long. Researchers have recently been calling for other supplementary and climate-smart strategies that increase soil organic matter, nutrients and reduce greenhouse gas emissions. This chapter aims to review the potential benefits of biochar-vermicompost on crop and soil productivity with a specific focus on Africa. Despite the limited information on the effect of biochar-vermicompost mixture, adding biochar, especially to sewage sludge, can reduce the amount of hazardous contaminants like heavy metals, E. coli and reduce the moisture content in vermicompost. With the benefits of both biochar and vermicompost in agriculture well recorded, the critical question is if biochar and vermicompost mixture will synergistically benefit soil quality and crop yield.

Sustainable food security is important for social and economic development, particularly in sub-Saharan Africa (SSA), where population growth is at the highest rate and most lands are degraded. Sustainable agricultural intensification techniques such as integrated use of manure and inorganic fertilizer are therefore required as they result in higher crop yields at a minimal negative impact on the environment while improving restoring marginal lands. Integrated use of manure and inorganic fertilizer can potentially enhance yields whilst conserving soils in the marginal lands of SSA. The collected data show that the application of manure treatments enhances soil quality indices. However, before massive implementation of integrated use of manure and inorganic fertilizer practices, further investigation of local level in SSA is required. We conclude that integrated use of manure and inorganic fertilizer remains a promising option to optimize sustainable agricultural intensification in marginal lands, resulting in both improved yields and soil restoration.

Soil aggregation is regarded as a key indicator of soil quality and behaviour that is mainly influenced by land use and management. There is lack of information on the effects of conservation agriculture (CA) on soil aggregation in low soil organic carbon (SOC) soils of South Africa. This study therefore aimed to quantify the effect of tillage, crop rotation and crop residue management on aggregate stability, binding agents and the resulting aggregate microstructure in a sweet sorghum-based cropping system in a low organic carbon soil. Two tillage levels; no-till (NT) and conventional tillage (CT), two crop rotations, i.e., sweet sorghum-grazing vetch-sweet sorghum (S-V-S) and sweet sorghum-fallow-sweet sorghum (S-F-S) and three crop residue retention levels, i.e., 0%, 15 % and 30 % were tested. The aggregate microstructure was quantified on aggregates of similar to 5 mm diameter with micro-focus Xray computed tomography (mu XCT) and image analysis was done using VGstudio MAX 3.2. Aggregate stability, soil organic carbon and glomalin related soil protein content (GRSP) were statistically higher under NT than in CT. GRSP was also enhanced by 30 % residue retention compared to other residue management practices. NT and CT accompanied by 30 % residue retention had the highest total porosity. NT + S-V-S + 30 % treatment combination generally had higher observed total porosity, higher frequency of pores within each pore class and denser microstructure visualisation. This study showed that tillage is the main factor that influences soil aggregation followed by residue management. Thus, application of NT + S-V-S+ 30 % enhanced soil quality in low SOC soils after three years. The study also demonstrated that aggregate stability is linked to aggregate microstructure and regular pores are dominated in degraded soils with low SOC.

The low soil fertility status of South African marginal soils threatens sustainable production of biofuel feedstock in smallholder farmers. It is therefore imperative to development sustainable and optimal management practices that improve soil fertility. The objective of this study was to determine the effect of tillage, rotation and crop residue management on nutrient availability in a bioenergy sweet sorghum-based cropping system in marginal soils. Two tillage levels, no-till (NT) and conventional tillage (CT); two crop rotations, sweet sorghum–grazing vetch–sweet sorghum (SVS) and sweet sorghum–fallow–sweet sorghum (SFS); and three crop residue retention levels, 0%, 15% and 30%, were tested. No-till enhanced total nitrogen, total organic nitrogen (TON), magnesium (Mg) and sodium (Na) by 3.19% to 45% compared to CT. SVS rotation increased ammonium (NH4+-N) and nitrate (NO3−-N) by 3.42% to 5.98% compared to SFS. A 30% crop residue retention increased NH4+-N, NO3−-N, available phosphorus (Available P), cation exchange capacity (CEC), calcium (Ca), Mg and potassium (K) by 3.58% to 31.94% compared to crop residue removal. In the short term, a 30% crop residue retention was the main treatment that enhanced soil fertility. The application of NT−30% was a better practice to enhance soil fertility. However, research on inclusion of crop diversity/intercropping can add more value to the NT–30% practice in enhancing soil fertility.

Labile organic carbon (LOC) fractions are considered as sensitive indicators of change in soil quality and can serve as proxies for soil organic carbon (SOC). Although the impact of tillage, crop rotation and crop residue management on soil quality is well known, less is known about LOC and SOC dynamics in the sweet sorghum production systems in South Africa. This short-term study tested two tillage levels: no-till and conventional-tillage, two crop rotations: sweet-sorghum/winter grazing vetch/sweet sorghum and sweet-sorghum/winter fallow/sweet sorghum rotations and three crop residue retention levels: 30%, 15% and 0%. Tillage was the main factor to influence SOC and LOC fractions under the sweet sorghum cropping system in South Africa. NT increased SOC and all LOC fractions compared to CT, which concurs with previous findings. Cold water extractable organic carbon (CWEOC) and hot water extractable organic carbon (HWEOC) were found to be more sensitive to tillage and strongly positively correlated to SOC. An increase in residue retention led to an increase in microbial biomass carbon (MBC). This study concludes that CWEOC and HWEOC can serve as sensitive early indicators of change in soil quality and are an ideal proxy for SOC in the sweet-sorghum cropping system in South Africa.

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.

Soil use and management effect on soil microstructure was quantified. Soil aggregates ∼10 mm diameter were collected from two fields: a five-year-old No-till natural fallow management (NTNF) and continuous cultivation (CC). The aggregate microstructure was determined with X-ray micro-focus computed tomography (X-ray μCT) and image analysis was done using VGstudio MAX 3.0. Aggregate stability was higher in NTNF by ≈ 5.7%. Micro-aggregates constituted ≥80% of the aggregates in both treatments. Total porosity, microstructural pore properties (pore distribution, pore shape proportion) and visualization were similar in NTNF and CC. Despite the similarities, aggregates under NTNF had higher total number of pores. Therefore, managing soil through NTNF improve porosity even when the effect on the overall soil aggregation is not obvious. The study showed that aggregate stability is significantly linked to aggregate microstructure.

The increase in greenhouse gases (GHG) emissions in the world has significantly contributed to climate change, prompting an active search for renewable and sustainable biofuels. Sweet sorghum (Sorghum bicolor (L.) Moench) is a leading biofuel feedstock that is produced with minimum inputs and does well even in semi-arid areas with soils of low fertility. However, a sustainable production system for sweet sorghum is not yet established in South Africa. Lately, conservation agriculture (CA) has gained research focus because of its benefits as a sustainable crop production system. Therefore, CA may offset the negative impacts of intensive agronomic practices during biofuel crop production. This paper reviewed CA as a possible sustainable crop production system for sweet sorghum as a biofuel feedstock. CA enhanced soil quality, reduced carbon dioxide emissions, and increased yield of sorghum and related cereals. It was concluded that CA has potential to enhance sweet sorghum production as a biofuel feedstock under semi-arid conditions in South Africa. Therefore, local field experiments on sweet sorghum production under CA are desirable in South Africa.