Swiss chard (Beta vulgaris var. cicla) growth and yield response to solid winery waste compost and NPK fertiliser application in sandy soil

Vegetable producers struggle with soil fertility challenges and ever-increasing inorganic fertiliser prices. Solid winery waste compost provides a promising solution to these problems and mitigates the environmental consequences of discarded winery waste. The use of organic soil amendments improves crop growth and yield; however, there is limited information on the responses of Swiss chard (Beta vulgaris var. cicla) to solid winery waste compost. This study assessed the effect of NPK fertiliser and two rates of solid winery waste compost on Swiss chard growth and yield. The experiment was conducted at the Agricultural Research Council, Bien Donné Farm, Paarl, South Africa, from April to June and was laid out in a randomised complete block design with four treatments: control, NPK fertiliser, and two solid winery waste compost rates. All plant growth parameters, the number of leaves, leaf length, and leaf width improved significantly with the solid winery waste compost treatments compared to the control. This was linked to the compost’s ability to act as a sponge, retaining water and slowly releasing nutrients throughout the growth cycle. The fresh yield of Swiss chard did not show a statistically significant difference (p>0.05) among the amended treatments. The lower compost rate resulted in a slightly larger, but not significantly different, yield (12.95 t/ha) compared to the high compost rate (11.78 t/ha) and NPK treatment (11.39 t/ha). This was attributed to a potential optimal application rate at the lower compost rate, in which conditions were optimal for nutrient absorption and soil pH. The high compost rate may have resulted in an antagonistic relationship with nutrients due to its higher pH and sodium content, leading to osmotic stress. These findings suggest that although solid winery waste compost is an effective soil amendment for improving Swiss chard growth, further research is needed to determine the optimal application rate necessary for significant yield improvement.