Nitrogen and Water Effects on Yield, Quality and Tissue Nitrate Concentration in Subsurface Trickle Irrigated Melons

Rising water costs and concern for groundwater contamination are encouraging growers to improve irrigation and fertilization efficiency. The objectives of this study were to determine water and fertilizer nitrogen (N) rates leading to optimum yield and harvest quality and to develop a plant tissue test to aid in melon nitrogen fertilization. In 1990, a field experiment consisting of a complete 3x3 factorial arrangement of optimum, sub- and super-optimum rates of urea ammonium- nitrate and water applied through a subsurface trickle irrigation system to cantaloupe, honeyloupe and watermelon was conducted at the Maricopa Agricultural Center. Petioles were sampled from the youngest mature leaf beginning at the early runner stage and then weekly until first harvest. Petiole nitrate concentrations were determined using a high pressure liquid ion chromatograph. Harvested melons were weighed and graded for marketability and soluble solids were determined. Petiole nitrate levels were highly responsive to N fertilizer treatments and accurately quantified visual observations of crop N status. Petiole nitrate results also indicated that later fertilizer split applications occurred after the point of maximum plant uptake. Tensiometer readings suggested that the highest rate of water application led to deep percolation and nitrate leaching where nitrogen fertilizer was excessive. Watermelon showed the clearest yield response to the water and nitrogen treatments. Honeyloupe responded well to high water but poorly to higher nitrogen application rates. Cantaloupe yields responded best to higher nitrogen and medium water levels