INTERACTIVE EFFECTS OF SALINITY AND AMMONIUM-NITRATE RATIO ON GROWTH AND CHEMICAL-COMPOSITION OF MELON PLANTS

The response of melon plants (Cucumis melo L. cv Galia) to different ratios of NH4-N/(NH4+NO3)-N (0, 0.15, 0.3 and 0.6) in saline (9 dS/m) and nonsaline (1.5 dS/m) nutrient solutions (in which the total N level was 5 mmol l-1) was studied using an aerohydroponic system in a greenhouse. The total production of dry matter and the concentration of macronutrients and other elements in plant shoot and root tissue were determined 68 days after transplanting. Dry matter production was not significantly affected by the NH4/NO3 ratio but the following general trend of NH4 effect on crop yield cannot be ignored. In nonsaline solutions the presence of a relatively low proportion (0.15) of NH4-N enhanced the yield of shoot dry matter, whereas under saline conditions the presence of NH4 exerted a negative effect on plant growth. Ammonium nutrition tended to increase the level of total N in plant tissue. Increasing NH4/NO3 ratio (decreasing NO3 level) resulted in higher Na and Cl and lower Ca, K and NO3 levels in plant tissue. The concentration of Mg in plant tissue was the result of the interactions between the NH4/NO3 ratio and salt effects.