Short-term effects of sunn hemp intercropping management in a maize-based system on the soil fertility of a Plinthic Cambisol in Free State, South Africa

Abstract Intercropping is a promising strategy of improving soil fertility in no-till rainwater harvesting practices. However, the effect of intercropping forage legumes at various planting times and densities on soil fertility response under the in-field rainwater harvesting (IRWH) technique remains unknown in South Africa. The objective of this study was to determine the seasonal effect of sunn hemp (Crotalaria juncea L.) intercropping at different planting periods and densities into maize (Zea mays L.) after two growing seasons on selected soil fertility of a Plinthic Cambisol in Free State, South Africa. The experiment was a randomized complete block design with a factorial combination replicated thrice. The factorial combination consisted of three sunn hemp plantings dates viz., at maize planting, planting at V15 maize growth stage, and R1 maize growth stage, and three sunn hemp planting densities viz., 16.1 plants m− 2, 32.1 plants m− 2, and 48.1 plants m− 2. The results showed that the interaction of sunn hemp planting date and density was significant (p < 0.05) on soil organic matter (SOM) and Zinc (Zn). The growing season had a significant impact on changes in SOM, nitrogen (N), potassium (K), calcium (Ca), sodium (Na), manganese (Mn), and iron (Fe). Due to the intercropping periods and planting densities, the retention of sunn hemp residues with varying quantities and qualities may have influenced the soil nutrient dynamics in the short-term. Significant changes in soil fertility may take longer, and future research should be carried out in agricultural regions with different soil mineral matrices.