Nitrogen Form Ratio Influence on Muskmelon Growth, Composition, and Manganese Toxicity

Abstract

Muskmelon ( Cucumis melo L.) ‘Harvest Queen’ was grown in sand culture to investigate the effects of NH 4 :NO 3 ratios on melon growth and elemental composition. Plants grown at NH 4 :NO 3 ratios of 98:14, 84:28, and 56:56 developed NH 4 toxicity symptoms, whereas plants grown with 20 ppm Mn and NH 4 :NO 3 ratios of 0:112, 14:98, 28:84, and 56:56 developed Mn toxicity symptoms. Increasing the proportion of NH 4 in nutrient solution up to 1:1 with NO 3 decreased Mn concentrations in plant tissues and alleviated Mn toxicity symptoms, whereas at NH 4 :NO 3 ratios of 84:28 and 98:14 uptake of Mn was inhibited and never reached a concentration in the tissue that developed toxicity symptoms. Shoot and root growth was greatest when grown at the 14:98 NH 4 :NO 3 ratio. Increasing NH 4 in the solution beyond 14 ppm in the 112-ppm N mixture resulted in increasing limitation of growth. Increasing Mn concentration in the nutrient solution to 20 ppm restricted growth at NH 4 :NO 3 ratios ≤1. However, Mn treatment did not influence the growth of plants grown at NH 4 :NO 3 ratios >1 at 84:28 and 98:14.