Gravel Culture of <i>Nopalea cochenillifera</i>, the Edible Cactus: Effect of Cultivation Method, Fertilizer Concentration and Irrigation Amount on Daughter Cladodes Growth, Zinc and Iron Content

We examined the effects of fertilizer concentration and irrigation amount on the growth of Nopalea cochenillifera (L.) Salm-Dyck, the edible cactus, under soil and gravel culture conditions. Although fertilizer supplementation was effective in promoting daughter cladode growth, high concentration led to growth inhibition in gravel culture. In gravel culture experiments, plants were watered at different frequencies: once a week (1/w), once every two weeks (1/2w) and once every four weeks (1/4w). Cladode growth was promoted at 1/w and 1/2w leading to increased harvest of daughter cladodes compared with 1/4w treatment when electrical conductivity of fertilizer was 2.6 dS m-1 (gravel ×1). Under “gravel ×1”treatments, growth of daughter cladodes was significantly higher in gravel culture (gravel ×1, 1/w) compared with soil culture (soil ×2, 1/w), resulting in about 185% increase in fresh weight. We evaluated the effect of zinc (Zn) and iron (Fe) on cladodes growth and checked the metal accumulation in cladodes by exposing them to 100 ppm Zn and Fe under gravel culture. Subsequently, large amount of Zn and Fe accumulated in cladodes compared with those untreated with Zn and Fe as well as those in soil culture. These results suggested that gravel culture is effective in growth promotion and biofortification of N. cochenillifera.