Retention of ions by vocanit sand used in hydroponic cultures

Abstract

Volcanic sands were treated with nutrient solutions for a period of six weeks and were washed with deionized water (until constant conductivity) for several weeks. These basaltic materials had been used in commercial hydroponic cultures for 6-, 5-, 4-, and 1 year, while another, as control, had not been used before. The activity of the materials on the NH+4-, NO-3-, H2PO-4-, K+-, Ca++-, Mg++, and Na+ contents of the nutrient solution was examined. All material had retention of NH+4 and H2PO-4, and released K+, Ca++, Mg++ and Na+. The non used material is the one which had the lowest activity in the nutrient solution composition. The pH of the material decreased about 1 unit (from 8 to 7). The NH4-Acetate extractable Ca++, Mg++, and Na+ and the NaHCO3 extractable P increased after treatments. There was also a nitrification of the NH+4 retained, increasing the NO-3 in the nutrient solutions except in the non-used material.