Effects of tillage and mulching on selected soil properties, growth and yield of sunflower (Helianthus annuus L.)

Abstract

Excessive and unnecessary tillage without residue retention can degrade the soil’s physical quality, decrease soil organic carbon contents and crop yields. Although the benefits of improved tillage methods and mulching have been reported in literature, little information is available on South Africa and more so on highly weathered soils of the Limpopo province. A study was conducted under dryland conditions at the University of Venda experimental farm, Limpopo province, South Africa. The aim of the study was to determine the effects of tillage and mulching on selected soil properties, growth and yield of sunflower (Helianthus annuus L.). The experiment was laid out in a split plot design with three replications. The experiment was conducted during the 2018/19 and 2019/20 cropping seasons. Treatments consisted of two (2) tillage methods (conventional and minimum tillage) and three (3) levels of avocado leaf mulch (0, 6 and 12 t/ha). The following soil properties were determined: soil organic carbon (SOC), soil water content (SWC), bulk density (BD), infiltration rate (IR), cumulative infiltration (CI) and aggregate stability (AS). Sunflower plant parameters including plant height, leaf area index, dry matter at flowering stage (FS), total biomass at harvest maturity stage (HMS), head diameter, head dry weight, seed weight and grain yield were determined. Minimum tillage resulted in significantly higher SOC, final IR and AS than conventional tillage. Conventional tillage outperformed the minimum tillage with respect to SWC and CI in both seasons. Minimum tillage recorded significantly higher plant height, LAI, head diameter, head dry weight, seed weight and grain yield than conventional tillage. Tillage had no effect on BD, dry matter at FS and total biomass at HMS in both seasons. Avocado leaf mulch application influenced SWC, CI and AS, but had no effect on SOC, BD, final IR, sunflower growth and grain yields. The 6 t/ha and 12 t/ha mulch treatments had significantly higher SWC, CI and AS than no-mulch treatment. Significant interactions between tillage and mulch rate observed on SOC at 42 days after planting (DAP), final IR, CI and AS indicated that the differences in SOC, final IR, CI and AS in the two tillage practices can be explained, in part, by the differences in how the two tillage practices react to different levels of avocado leaf mulch. The results suggested that tillage and mulching could improve sunflower crop yields, soil organic carbon, soil water content, infiltration rate and aggregate stability under the experimental conditions.