The present investigation was carried out at Thirumaraiyur village, Sattankulam taluk, Thoothukudi district to study the effect of organic amendments with recommended dose of fertilizers on growth and yield of watermelon and physic-chemical properties of Theri soil (red sand dunes) during the year 2018 and 2019. The experiment was laid out in Randomized Block Design with Factorial concept (FRBD). In all there were three factors as organic amendments with 6 treatment combinations for each factor, which were assigned at random in each plots with three replications. The recommended dose of fertilizers in treatments were two levels as 75 and 100 per cent. Among the treatment combinations, the tank silt application @ 100 t ha-1 with 100 per cent recommended fertilizer as 200:100:100 kg of NPK ha-1 through fertigation at 7 days interval (A1N5) produced maximum number of branches (10.67), longest vine (362.0 cm), number of fruits plant-1 (2.57), weight of fruit (5.27 kg), fruit yield (68.77 t ha-1), gross return ( 4,09,320/ha), B:C ratio (2.45) and improved the physic-chemical properties viz., particle density (2.45 Mg m-3), bulk density (1.31 Mg m-3), per cent pore space (48.33%), pH (6.58), EC (0.35 dSm-1) and organic carbon content (0.52%).