Changes in Selected Chemical Properties of Karbala and Jalawla Sands during Cultivation under a Sandponics System

Abstract

This plant-house experiment compared temporal changes in selected chemical properties of Karbala and Jalawla sands cultivated under a Sandponics system. Six independent growing basins were used, with three replicate basins for each sand type. Each basin contained 15 red cabbage, 15 chard, and 15 lettuce plants, and sand samples were collected separately from every basin before and after cultivation. The measured properties were pH, electrical conductivity (EC), alkali-extractable silica (SiO₂), and KCl-extractable mineral nitrogen. Karbala sand showed a decrease of 1.067 pH units, from 6.360 to 5.293 [t(2) = 160.000, p < 0.001], whereas Jalawla sand decreased by 0.763 pH units, from 6.000 to 5.237 [t(2) = 22.564, p = 0.002]. EC decreased by 80.349% in Karbala sand and 87.919% in Jalawla sand. Alkali-extractable SiO₂ decreased by 20.557% and 20.690%, respectively. KCl-extractable mineral nitrogen decreased by 11.992% in Karbala sand [t(2) = 13.536, p = 0.005] and by 5.515% in Jalawla sand; however, the paired t-value for Jalawla was not estimable because the paired differences were identical across the three basins. The large EC decrease may indicate salt leaching, whereas decreases in pH, mineral nitrogen, and alkali-extractable silica require cautious interpretation as possible consequences of acidification, plant uptake, leaching, or mineral transformation. Because no untreated control was included, the observed changes cannot be attributed exclusively to the Sandponics system.