EFFECTS OF NITROGEN, PHOSPHORUS AND POTASSIUM TREATMENTS ON PHOSPHORUS FRACTIONS IN MELON PLANTS

The effects of nitrogen (N), phosphorus (P), and potassium (K) treatme nts on the P fractions in muskmelon plants (Cucumis melo L. cv. Galia) are presented. Plants were grown under greenhouse conditions with dif ferent NPK treatments. Leaves were sampled every two weeks from the mi ddle third of each plant. After washing in nonionic soap and distilled water, the leaves were dried in an oven at 70 degrees C and then grou nd. The foliar contents of several P fractions [inorganic P (Pinorg), organic P, lipid P, RNA-P, DNA-P, and proteic P] were determined. Inor ganic and organic P were found to be the major fractions. For both N a nd K treatments, the Pinorg content increased, although at high doses (N24 and K30), there was a reduction in leaf content. With the P treat ments, the contents of the fractions increased steadily, but with the highest doses (P15 and P20), the leaf content of the fractions was ver y similar, indicating a saturation phenomenon. Evolution of the fracti ons over time showed similar behavior. Constant export occurred in all the fractions, with the only difference between them being in the ins tensity of the export effect. The data presented highlight the need to consider the effects of NPK treatments when P fractions are being use d as tools for nutritional diagnostics.