Effect of zeolite-amended sandy soils on growth & yield of Copenhagen cabbage

A greenhouse pot experiment was conducted at the Agricultural Research Council, Infruitec-Nietvoorbij, Stellenbosch, South Africa, to assess the effect of zeolite on the fresh head yield & growth characteristics of cabbage cv. Copenhagen. Zeolite was applied at 0:10, 1:9, 2:8, & 3:7 zeolite to sandy soil (w/w). Cabbage growth parameters, plant height, & number of loose leaves showed significant improvements (p < 0.05) under zeolite-amended treatments in the second growing season. Maximum chlorophyll content index (CCI) values ranged from 70.03 to 78.04 in the first season & 52.37 to 61.59 in the second growing season. While leaf area showed no significant differences (p > 0.05) in the first growing season. Additionally, marketable cabbage head traits (head diameter, head circumference, & fresh weight) exhibited no significant differences (p > 0.05) among treatments in the first season. Still, significant improvements were observed in the second season. Zeolite applications at 30% reduced cabbage yields by 15.12% (without loose outer leaves) & by 11.64% (with outer leaves) compared to a 20% zeolite application. Furthermore, the findings highlight a practical implication: a 20% zeolite amendment appears to be the optimal level for improving cabbage yield without the negative effects observed at higher application rates. Overall, this study revealed that zeolite could enhance certain cabbage growth parameters & yield, particularly in the second season. This indicates that zeolite might require a fallowing period within the soil to fully benefit plant growth. Additionally, the results also indicate that zeolite soil amendment may have a limit to its beneficial effects. To support broader adoption, the study recommends applying zeolite at 20% prior to planting, integrated with conventional fertilisers, and guided by soil testing in follow-up seasons.