Integrated rice-fish production for enhancing yield of the system while conserving environment

Description

Introduction

Integrated rice-fish culture has a high potential for increasing agricultural productivity in rice-producing countries through complementary resource utilization. In view of today’s need to feed rapidly growing populations in developing countries, rice-fish culture can contribute substantially to the supply of  protein, and is thus a promising approach for combating malnutrition. This project aimed to investigate productivity and the environmental effects of integrated rice-fish culture.

Objectives

-To improve the productivity of both rice and fish through optimized management, using two fish species of world-wide importance, i.e. common carp, Cyprinus carpio L., and Nile tilapia, Oreochromis nilotius (L.) in single and mixed culture and with different inputs.

–To synergies nutrient utilization between rice and fish by establishing nutrient budgets.

- To assess the effect of rice-fish culture on the environment and on the rice field ecology. An important and novel aspect studied was the effect of fish on methane emissions from rice fields.

Progress made

The potential of fish as part of an integrated pest management strategy was explored by monitoring the rice field arthropod population, the benthic fauna, and the weed abundance. A two-stepped approach was adopted, including a greenhouse study in a controlled environment, followed by field experiments at the Bangladesh Agricultural University in Mymensingh (Bangladesh).

Both the greenhouse and field studies yielded quite comparable results. It was shown that rice plants and fish utilize nutrient input in a synergetic way. The environmental studies revealed both negative and positive effects of fish. The presence of fish was shown to boost methane emissions. Various explanation were found for this phenomenon. First, the presence of fish led to a drop in the floodwater dissolved oxygen concentration, thus reducing the amount of oxygen available in the soil/water interface. By grazing on the aquatic flora and by increasing the water turbidity, fish limited the aquatic photosynthesis and thus oxygen release. In addition, fish consumed oxygen for their metabolism. Floodwater oxygen levels showed significant negative correlations with the level of methane emissions, indicating that this was an important cause of the increase in emissions observed. A second explanation was that fish released methane entrapped in the soil through bioturbation while searching for feed. These activities lead to dissipation of methane to the water column, as reflected in higher levels of dissolved methane.

Fish were found to have some potential as biological control agents. However, most rice insect pests do not have any aquatic phase during their life cycle, and are thus difficult to control by fish. A significant effect was detected only on species of the order Diptera, which are mostly considered as indifferent in rice production. Significant effects of fish were found on the benthic fauna, i.e. molluscs, oligochaete worms, and chironomid larvae. The abundance of aquatic weeds was controlled very efficiently by fish.

In conclusion, the production of O niloticus and C. carpio in rice fields can contribute substantially to the supply of high quality protein in developing countries. Rice-fish culture has the major benefit of using scarce resources such as land, water, and nutrients, in a complementary way. The environmental drawback of a moderate increase in methane emissions might be compensated by economic and ecological benefits for the farmers.