Effect of zeolite application on soil enzyme activity of potted sandy soil cultivated with Swiss chard and cabbage

Abstract

A zeolite pot experiment was conducted at the Agricultural Research Council Infruitec-Nietvoorbij in Stellenbosch, South Africa, under greenhouse conditions. The experiment aimed to investigate the impact of zeolite application on soil enzyme activities in sandy soils cultivated with Swiss chard (Beta vulgaris Var. cicla) and cabbage (Brassica oleracea Var. capitata L.) over two years (2018-2019). Different zeolite-to-soil ratios (0:1, 1:9, 2:8, and 3:7 w/w) were used, with each pot containing 12 kg of soil. The experiment involved 72 pots for each vegetable, arranged in a randomized complete block design (RCBD). Soil enzyme activities, including acid phosphatase, β-glucosidase, and urease, as well as soil chemical properties (pH, total plant-available nitrogen, organic carbon, and phosphorus), were analyzed. Key findings indicate that the effect of zeolite application on enzyme activities varied between the vegetable species. Zeolite application significantly increased (P<0.05) soil pH across all treatments. However, higher zeolite levels decreased (P<0.05) soil phosphorus availability, likely due to phosphorus adsorption by zeolite. Acid phosphatase activity decreased with rising zeolite levels, possibly due to increased soil pH. Additionally, zeolite application reduced (P<0.05) soil organic carbon, which may explain some of the enzyme activity responses. Alteration Index Three (AI3) scores suggested improved soil biological activity with zeolite application, although responses varied between crops. Cabbage soils showed improvement in all treatments, while Swiss chard soils exhibited mixed responses. In conclusion, while zeolite application can enhance soil pH and nutrient retention, it may also reduce phosphorus availability and organic carbon. The enzyme activity responses observed are complex and crop-specific, highlighting the need for tailored soil management practices. Further research is recommended to explore the long-term impacts and optimal integration of zeolite with organic amendments for sustainable soil fertility management.