NITROGEN–PHOSPHORUS–POTASSIUM EFFECTS ON FORMS OF SULFUR IN LEAVES AND FRUITS OF CUCUMBER

Abstract

ABSTRACT The impact that nitrogen (N), phosphorus (P), and potassium (K) application rates on the sulfur (S) fractions in leaves and fruits of greenhouse-grown cucumbers plants (Cucumis sativus L. cv. Brunex) are presented. The treatments were as follows: N (N1=5 g NO3NH4/m2, N2=10 g NO3NH4/m2, N3=20 g NO3NH4/m2, N4=40 g NO3NH4/m2), two levels of P (P1=8 g H3PO4/m2 and P2=16 g H3PO4/m2), and two levels of K (K1=20 g K2SO4/m2 and K2=40 g K2SO4/m2). The foliar and fruit contents were determined for total S, organic S and sulfate. The influence of the N treatments on the total S (St: organic S +sulfate) concentration, proved significant, showing a progressive increase in the leaf and fruit concentrations. In the leaves, the P slightly diminished the St concentration but values in the fruits did not appreciably differ from control. The K dosage did not cause the St concentration to differ from that of P, although in the fruit a slightly lower St concentration appeared in the K2 treatment. The response of the organic-S concentration in the leaves resembled that of St, and thus organic S should not be used as a diagnostic method for S status. In the relationship SO4 2-/St, the SO4 2- concentration proved more influential than did the St form, providing a more accurate representation of the potential status of this nutrient in the plant.