Abstract:In order to verify the optimum nitrogen application rate and planting density for higher yield、quality and nitrogen use efficiency of watermelon in gravel mulched field, and to provide basis for the development of rational cultivation measures, Longkang 9 representing late variety was used in this study. Under field condition, three planting densities (9525, 12120, 16680 plant/ha) and four nitrogen rates (0, 100, 200, 300 kg/ha) were applied to study the interaction between nitrogen and density on yield、quality and nitrogen use efficiency of watermelon in Gravelmulched field. The results show that planting density and nitrogen rate have significant effects on yield and quality of watermelon, but the interactive effect between them was not significant. Compared with the nitrogen rates planting density is a key factor for increasing the yield, with increased planting density, the yield of watermelon has improved, the yield of high density increased by 23.46% and 45.58% respectively compared to middle density and low density. The nitrogen rate have significant regulating effect for quality of watermelon, when nitrogen application rate increased from 0 up to 200 kg/ha, the yield and quality were also increased with nitrogen application rate, and lowered while continue to increase amount of nitrogen fertilizer, the N200 treatment increased sugar content of watermelon by 1.43% and 1.92%, and of the Vc content by 13.09% and 8.42% compared to N0 and N300.The partial factor productivity and recovery efficiency of applied N were improved for increasing yield of watermelon. In this study, taking yield、quality and nitrogen use efficiency into consideration, the appropriate plant density and nitrogen rate of watermelon in sandy field are 16680 plant/ha and N 200 kg/ha respectively, the yield、sugar content and nitrogen recovery efficiency of which were 61754 kg/ha, 10.59% and 22.29%.