Ecosystem manipulation for increasing biological N2 fixation by blue-green algae (CYANOBACTERIA) in lowland rice fields

Abstract

An introduction to the soil/floodwater ecosystem of lowland rice fields is given. Two primary consumers are particularly important in limiting the growth and N2-fixing activities of blue-green algae in irrigated rice ; the OSTRACODA (Class CRUSTACEA) and the PULMONATA (MULUSCA). Control of grazing by neem seeds AZADIRACHTA INDICA A. Juss and cultural practices enhanced BGA biomass and increased N2-fixation ten fold. Significant increases in rice grain protein occur if heterocystous algae bloom early in the rice cultivation cycle and grazing control is maintained over 40 days. A large positive N balance was obtained over 3 rice crops by using neem seeds to control grazing of BGA. Algal inoculants used in conjunction with grazer control failed to establish themselves, and factors other than grazing were considered responsible. Plant-derived pesticides showed great promise for sustainable agriculture. (Résumé d'auteur