MELON FRUIT QUALITY AS AFFECTED BY TIMING, DURATION, AND CONCENTRATION OF PHOSPHATE AND NITROGEN SOURCES IN RECYCLED HYDROPONIC SYSTEM

ABSTRACT

Fruit load in melon plants may cause a reduction in fruit quality especially when several fruits are ripening simultaneously on a single plant. Three experiments using Galia F₁ hybrid (Cucumis melo L.) were conducted in an insect proof net house during the autumn (August–October) growing season in Israel. The plants were grown on silica pumice in a recycled hydroponic system. The influence of the duration of P application at four concentrations (0.3, 0.5, 0.75, and 1 mM P) in the nutrient solution (NS) on the number and quality of simultaneously ripening fruits were measured (Experiment 1). In a second experiment three levels of P in the NS (0.5, 0.75, and 1 mM) were tested on two concentrations of nitrate (2.6 and 5.2 mM). In a third experiment, two ratios of ammonium (10 and 20%) were tested each with two levels of N:P ratios (5.2 : 0.5 and 7.2 : 0.8 mM). Withholding phosphorus (P) at 10–26 or 10–33 days after germination (DAG) or delay in P (25–60 DAG) at concentration of 0.3 or 0.5 mM resulted in lower yield as compared to 0.75 or 1 mM P in the NS. The highest yield of 4.6 kg fruits per plant was obtained with solution containing 0.5 mM P applied throughout growing period (10–60 DAG). Applying 0.5 or 0.75 mM P throughout growing period (10–60 DAG) minimized harvest period to six days as compared to 15 days with P applied during 10–26 or 10–33 DAG. During each period of P presence in the NS, TSS was increased with increasing concentration of P in the NS. The stem is used as storage for P, which is later translocated to the leaves and serves to move sugars to the fruit as it measured by TSS. A linear correlation between P concentration in the NS or in the leaves and fruit TSS was found in each timing and duration of P. In Experiment 2, with 5.2 mM nitrate and 0.75 mM P in the NS, 87% of the total yield (5.3 kg plant⁻¹) ripened within five days from first picking. Simultaneous fruit ripening shortened the period of soluble solids accumulation in the fruit and decreased its quality. In Experiment 3, ammonium level in the NS did not have any effect on fruit TSS regardless of yield load. The harvesting period lasted 12 days when ammonium was present in the NS, but only nine days when nitrate at 5.2 mM was used.

Keywords:

• Phosphate
• Nitrate
• Ammonium
• TSS

ACKNOWLEDGMENTS

The valuable comments by Dr. H. Nerson and Dr. Z. Karchi of the Neve Ya'ar Experimental Station, P.O. 1021, Haifa 30095, Israel and Dr. S. Kant of the Department of Agronomy, CCS, Haryana Agricultural University, Hisar, India, 125004, are highly appreciated.