Effects of zeolite-amended peat substrates on water retention and physiological-biochemical responses of Swiss chard and radish grown under greenhouse conditions

Zeolite has been increasingly investigated as a substrate amendment due to its capacity to improve water retention and nutrient availability in horticultural systems. However, its influence on plant physiological responses may vary depending the plant species and the application rate. Therefore, this study evaluated the effect of natural and commercial zeolite incorporated into peat moss on water retention and physiological–biochemical parameters in Swiss chard (Beta vulgaris var. ‘Cicla’) and radish (Raphanus sativus L.) cultivated under greenhouse conditions. The experiment was conducted at the Universidad Autónoma de Chihuahua using a completely randomized design with five treatments: T1 (peat moss control), T2 and T3 (peat moss + 200 and 400 g natural zeolite), and T4 and T5 (peat moss + 200 and 400 g commercial zeolite). The highest substrate moisture retention 63% was observed in Swiss chard under T5, whereas radish showed no significant differences among treatments. SPAD values remained statistically unchanged in Swiss chard but were significantly higher in the control treatment of radish. However, total chlorophyll increased by 13.5% under T5 in radish. Nitrate reductase activity was highest in T4, increasing by 18% in Swiss chard and 40.3% in radish relative to the control. Proline concentrations decreased in treatments with zeolite, suggesting a reduction in physiological stress, while soluble carbohydrates increased in T2 for Swiss chard and T4 for radish. These results indicate that zeolite amendments can modify water retention and nitrogen assimilation processes in peat-based substrates, although the physiological responses depend strongly on both species and application rate.