Performance evaluation of concurrent rice–fish–prawn culture with and without cull harvesting

摘要

This study was carried out in farmers' fields for three experimental culture cycles to evaluate the performance of rice–fish–prawn culture. The treatments carried out were deepwater rice mono-cropping (R), and rice–fish–prawn culture with cull harvesting (R–FC) and without cull harvesting (R–F). Water pH and total alkalinity were significantly higher (P0.05) in R–FC than in R–F, while the concentrations of total suspended solids, plankton and chlorophyll a were higher in R–F. Cull harvesting in R–FC had no marked influence on the concentrations of dissolved oxygen, NH₄+, nitrite, nitrate and phosphate compared with the R–F treatment. The significantly higher fish and prawn yields (P0.05) and species-wise faster individual growth performance in R–FC than in R–F were probably due to periodic cull harvesting, which minimized the competition for food and space as well as physiological stress at reduced density. The paddy yield and percentage increase in paddy yield over rice mono-crop was significantly higher (P0.05) in R–FC (25%), followed by R–F (16.9%), probably due to lower chlorophyll a (36.7 mg m−3) and plankton density (1.4 × 104 L−1), which minimized the competition for nutrients with rice plants. The highest rice equivalent yield (38.5), output value–cultivation cost ratio (1.56) and enhanced net return (28%) in deepwater rice–fish culture were recorded when cull harvesting was practiced.