Microalgal polysaccharide production for the conditioning of agricultural soils

Two species of mucilaginous green algae, Chlamydomonas mexicana and C. sajao, were evaluated for in situ production of polysaccharides in untilled samples of selected agricultural soils. Greenhouse experiments indicated that the moisture content of the soils must be maintained near 100% of field capacity to permit growth of the algae. The algae increased the polysaccharide content of the uppermost 2 mm of soil by 20% to 129%, but in only 3 treatments out of 12 was there any significant increase in soil polysaccharide content at the 3-8 millimeter depth. More than 99% of the algal cells and most of the polysaccharide produced by the algae remained in the top 2 millimeters of soil. The results suggest that although these algae can increase the polysaccharide content of the uppermost strata, where soil crust formation may present problems in agriculture, frequent irrigation is necessary to maintain algal growth. Tillage would be necessary to incorporate the algal polymers for soil conditioning at depths greater than 2 millimeters.