Rice cultivation requires large amounts of fertilizers and also emits greenhouse gases. The use of nitrogen-fixing cyanobacteria (microalgae) has been used in traditional low-yield rice culture in some countries (Vietnam, India, etc.) but not yet developed for the intensive rice agriculture practiced in Japan and other countries. One concept is to integrate microalgae culture with rice cultivation, but this suffers from the problem of limited time available for the algae to grow before canopy closure. An alternative is to utilize a part of the rice field to cultivate nitrogen-fixing cyanobacteria such as Anabaena or Nostic in raceway type paddle wheel mixed ponds that are then used to irrigate and fertilize rice fields.
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