Chapter

Soils and Rice-Fields

DOI: 10.1007/0-306-46855-7_8

ABSTRACT Cyanobacteria are an important component of many soils. including the surface crusts that sometimes cover extensive areas
in semiarid regions and mine spoil wastes. They are also abundant in many areas which are wet or submerged for part of the
year. especially rice-fields. Most soils forms have sheaths or mucilage and this polysaccharide has important effects onthe
soil. mostly beneficial. such as improved soil structure. but sometimes adverse where a dense surface layer impedes drainage.
Nitrogen-fixing species often constitute half or more of the species present in soils not enriched with nitrogenous fertilizer
and these can contribute combined nitrogen in several ways to adjacent vascular plants.

Attempts to enhance crop yield by adding cyanobacteria to soils have mostly focussed on paddy rice. Although many studies
have reported positive effects of such ‘algalization’. the number of locations where it has been adopted as routine practice
appear to be few. in contrast to the relatively widespread use of Azolla with rice culture. Algalization is most successful where local species are used to prepare the inoculum. but there is considerable
scope for other improvements. It is important to obtain a much more detailed understanding of cyanobacterial population dynamics
over the whole annual cycle in agricultural systems where rice is grown for only part of the year.

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