Soil organic carbon, weed suppression and fruit yield in response to cover crop species and termination method in citrus orchard (eureka lemon)

Abstract

Cover crops are increasingly used in citrus production systems to improve soil health, reduce weed pressure and enhance fruit yield and quality. While the benefits of integrating cover crops into orchard management have been widely reported in several countries, information on their use under South African citrus-growing conditions remains limited. Therefore, this study was undertaken to investigate the influence of different cover crop species on soil organic carbon, weed biomass and citrus fruit yield under two cover crop termination practices, namely slashing and non-slashing. The cover crop treatments consisted of vetch, medics, oats and an untreated control without cover crops. The experiment was established as a split-plot arrangement within a randomized complete block design with six replications. Cover crop species constituted the main plot factor, while termination method was assigned to sub-plots. Soil was sampled before planting cover crops and one year after planting cover crops. Cover crop and weed dry weight samples were collected during the termination stage and fruit weight measurements were taken at harvest. Legume cover crops significantly increased Soil Organic Carbon (SOC) in the 0–30 cm soil depth, with vetch recording the highest SOC (0.6–0.8%), representing an increase of approximately 0.14% compared with oats. No significant SOC differences were observed at the 30–60 cm depth. Weed biomass declined markedly over time, from more than 1.4 t ha−1 in 2021/22 to less than 0.6 t ha−1 in 2022/23. Oats provided the greatest weed suppression, reducing weed dry weight to approximately 0.10 t ha−1 in 2022/23, whereas the control treatment consistently recorded the highest weed biomass. Cover crop biomass was highest under oats in 2021/22 (1.50 t ha−1), while excessive rainfall in 2022/23 reduced biomass production across treatments. Termination methods did not significantly influence weed biomass or cover crop biomass. Citrus fruit yield was not significantly affected by either cover crop species or termination method during the short-term study period. The findings indicate that legume cover crops improve SOC, while oats are more effective for weed suppression in lemon orchards. However, longer-term studies are needed to determine whether these soil and weed management benefits translate into increased citrus productivity.