Sorghum productivity, organic carbon and selected soil quality parameters under sorghum-based climate smart agriculture on sandy soils under semiarid and sub-humid rainfed conditions in South Africa.

Abstract

The negative effects of intensive conventional tillage on infertile, sandy soils with low organic carbon (SOC), coupled with low water content and climate change, present significant challenges to smallholder agriculture, particularly under rainfed conditions. Conservation agriculture, which combines no-tillage (NT), residue retention and crop rotation, can improve soil quality. This study determined the effects of planting date (early and late), tillage (conventional tillage (CT) and NT, sorghum cultivar (Pan8816 and Macia), and crop rotation (with cowpea or continuous sorghum) on sorghum yield, soil water content, SOC and its fractions and microbial functional diversity on sandy soils within rainfed grain sorghum production systems, under semi-arid and sub-humid conditions. The study was conducted on sandy soils (<10% clay; <1.0% SOC) at Mphanama village (Limpopo Province) and at Clau-Clau village (Mpumalanga Province), South Africa. The experimental set up was a randomized complete block design (RCBD) with a strip-split-split-plot treatment structure, replicated three times. At Mphanama, early planting promoted greater plant height and thousand seed weight (TSW), while the interaction between early planting and NT increased sorghum yield in season three. Planting sorghum early significantly improved crop growth and yield in the second growing season, whereas late planting and planting under NT significantly increased TSW during the third growing season at Cla-Clau. No-tillage significantly improved soil water content at Mphanama and increased available phosphorus (P), potassium (K), and SOC in bulk soil and in all measured fractions at Clau-Clau, while CT significantly increased soil water content. Late planted sorghum significantly increased SOC, calcium (Ca), magnesium (Mg) during season two and increased fine particulate organic carbon (POC), acid phosphomonoesterase, microbial richness (R) and average well colour development (AWCD) index during season three at Mphanama. The NT treatment increased the microbial evenness (E) and decreased AWCD index in season three at Mphanama. Late planting and NT improved AWCD index in season three at Clau-Clau. The findings of this study suggest that the effects of planting time, tillage and crop rotation on soil properties in sandy soils are site specific possibly due to differences in climatic conditions and soil types. The findings will be useful in the selection of conservation agriculture systems, depending on the site properties and the objectives.