Azolla as a green manure: use and management in crop production.
Azolla, a tiny aquatic fern, is used in China and Vietnam as a green manure in flooded rice cultivation. The azolla plants harbour blue-green algae that live symbiotically with the fern, fixing atmospheric nitrogen; Chinese rice farmers have exploited this nitrogen fixation potential for centuries. This book draws on Chinese, Vietnamese, and Western literature to provide a scientific and management framework for the use of azolla in agriculture, especially in the developing world. Of particular economic interest are a chapter on the use of azolla in labour-intensive farming systems (pp.109-140), and one by S.N. Talley and D.W. Rains on the potential for mechanizing azolla cultivation on rice fields. Azolla stands the greatest chance of success in irrigated rice farming systems. The economics are marginal at best, even in China and Vietnam where labour costs are lower than in most developing countries. Special tools, transport systems, varietal selection, advanced nursery and multiplication techniques, combined with economic analyses will be essential to realize its full potential. An appropriate economic evaluation method might be to grow azolla as a green manure for rice for several years, and then compare costs with a nitrogen based system giving the same yields.