Integration of azolla, fish and herbicides for rice weed management

Integrated fish farming has received considerable attention in recent years in many developing countries. Rice and fish are not only compatible but also mutually beneficial when grown together. Herbivorous fish serve the purpose of biological weed control in lowland rice. Dual culturing of azolla in rice fields besides fixing atmospheric nitrogen has the added benefit of weed suppression. Considering the multiple benefits of integrating these two component farming enterprises in lowland rice, laboratory and field experiments were conducted at the Department of Agronomy, Annamalai University, India to optimize the size of fish fingerlings and their time of release in lowland rice treated with herbicides, to study the weed control effect of azolla, fish and herbicides independently and in combination. The results of laboratory studies revealed that fish fingerlings of length 4 to 5 cm were observed to be safe with survival if released 12 days after herbicide application. From the field experiments, it was observed that azolla independently contributed for 34 per cent weed control index, fish independently contributed for 21 per cent weed control index whereas their combination contributed for 40 per cent (mean values from two seasons). Based on these results, another field study over two consecutive seasons were conducted to compare the performance of three different herbicides in rice + fish + azolla system. Integration of azolla and fish culture with oxyfluorfen 0.25 kg/ha offered higher weed control indices (75%) and rice grain yields (6.0 t/ha). However, the histopathological studies revealed that fishes suffered tissue deformation in gills, muscle and liver.