Chemical characteristics of degraded soils in Uzbekistan and remediation by cyanobacteria

Abstract

Precipitation in Uzbekistan is limited, so irrigation must be used widely in local agriculture. However, irrigation is carried out with inadequate drainage systems that result in salt damage, as the re-accumulation of salt from irrigation water on the soil surface; thus, soil salinization becomes severe in irrigated agricultural areas. To address this problem, leaching has been recommended locally. Nevertheless, local farmers input excessive irrigation water, and inadequate drainage systems are attributed to salt damage. Cyanobacteria are salt-tolerant microorganisms with photosynthetic and N2-fixing abilities, so inoculation of cyanobacteria into salt-affected soil would be effective for its bioremediation. In this study, we isolated cyanobacteria from several local soils in Uzbekistan and evaluated their salt tolerance. The soil electrical conductivity (EC) ranged from 19 to 1970 mS m−1, and most of the soil had a high EC. Cyanobacteria isolated from Navoi in north-western Uzbekistan grew better under NaCl conditions than under conditions without NaCl. This result indicated that Navoi strains were able to grow under high EC conditions and could be used for salt-affected soil remediation. A pot experiment using the cyanobacterium Navoi strain was conducted to evaluate its restoration abilities in degraded salt-affected soil. Inoculating with the Navoi strain reduced salt stress to the same extent as leaching by decreasing soil Na+ and EC, which increased inorganic soil nitrogen by increasing soluble organic nitrogen from decomposed cyanobacteria in soil and fixing atmospheric nitrogen by cyanobacteria. These results suggested that cyanobacterial application might be effective for salt-affected soil remediation in Uzbekistan.