MICROBIAL ACTIVITY SOIL-STRUCTURE - RESPONSE TO SALINE WATER IRRIGATION

Our study was made to determine the influence that saline water of agr icultural quality has on microbial processes that contribute to soil s tructure formation. Pots with Yolo fine sandy loam soil were watered f or 6 weeks with saline water (SW) of EC = 5 ds m-1 and with regular wa ter (RW) of EC = 1 ds m-1. Every 14 days the pots were sampled and the following measurements were made: C and N mineralization rate; microb ial biomass-C and -N content, carbohydrate production and soil aggrega tion and stability. Irrigation with saline water increased the accumul ation of C and N in microbial biomass, but decreased the rate of C and N mineralization, carbohydrate content and aggregate stability. The p roportion of macroaggregates (0.2-3.0 mm) in the soil was reduced due to the effect of dry soil wetting, regardless of water type. It seems that structure deterioration of soil under saline water irrigation, is not solely due to chemical and physical interactions between the soil particles and the solution salts, but also to the fact that saline wa ter irrigation causes a reduction in carbohydrates produced by microor ganisms, and thus a reduction in aggregate stability.