Secondary salinity effects on soil microbial biomass

Secondary soil salinilization is a big problem in irrigated agriculture. We have studied the effects of irrigation-induced salinity on microbial biomass of soil under traditional cotton (Gossypium hirsutum L.) monoculture in Sayhunobod district of the Syr-Darya province of northwest Uzbekistan. Composite samples were randomly collected at 0-30 cm depth from weakly saline (2.3 +/- 0.3 dS m(-1)), moderately saline (5.6 +/- 0.6 dS m(-1)), and strongly saline (7.1 +/- 0.6 dS m(-1)) replicated fields, 2-mm sieved, and analyzed for pH, electrical conductivity, total C, organic C (C-Org), and extractable C, total N and P, and exchangeable ions (Ca2+, Mg2+, K+, Na+, Cl-, and CO (3) (2-) ), microbial biomass (C-mic). The Na+ and Cl- concentrations were 36-80% higher in strongly saline compared to weakly saline soil. The C-Org concentration was decreased by 10% and C-Ext by 40% by increasing soil salinity, whereas decrease in C-mic ranged from 18-42% and the percentage of C-Org present as C-mic from 8% to 26%. We conclude that irrigation-induced secondary salinity significantly affects soil chemical properties and the size of soil microflora.