Chemical and biological characteristics of alkaline saline soils from the former Lake Texcoco as affected by artificial drainage

Soils from the former Lake Texcoco are alkaline saline and were artificially drained and irrigated with sewage effluents since the late 1980s. Undrained soil and soil drained for 1, 5 and 8 years were sampled, characterized and incubated aerobically for 90 days at 22 +/- 1 degreesC while production of CO2, available P and concentrations of NH4+, NO2 and NO3- were monitored. Artificial drainage decreased pH(H2O), water holding capacity, organic C, total N, and Na+, K+, Mg2+, B, Cl- and SO42- concentrations, increased inorganic C and Ca2+ concentrations more than 5-fold while total P was not affected. Microbial biomass C decreased with increased length of drainage but bacteria, actinomycetes, denitrifiers and cellulose-utilizing bacteria tended to show opposite trends. CO2 production was less in soils drained greater than or equal to5 years compared to undrained soil but more than in soils drained for 1 year. Emission of NH3 was negligible and concentrations of NH4+ remained constant over time in each soil. Nitrification, as witnessed by increases in NO3- concentrations, occurred in soil drained for 8 years. NO2- concentrations decreased in soils drained less than or equal to1 year in the first 7 days of the incubation and remained constant thereafter. It was found that artificial drainage of soils from the former Lake Texcoco profoundly affected soil characteristics. Decreases in pH and Na+, (+), Cl- and SO42- concentrations made conditions more favourable for giant growth, although low concentrations of inorganic N and available P might be limiting factors.