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 artificiall y drained and irrigated with sewage effluents since the late 1980s. Undrain ed soil and soil drained for 1, 5 and 8 years were sampled, characterized a nd 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 ino rganic C and Ca2+ concentrations more than 5-fold while total P was not aff ected. Microbial biomass C decreased with increased length of drainage but bacteria, actinomycetes, denitrifiers and cellulose-utilizing bacteria tend ed to show opposite trends. CO2 production was less in soils drained greate r 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 N H4+ remained constant over time in each soil. Nitrification, as witnessed b y increases in NO3- concentrations, occurred in soil drained for 8 years. N O2- concentrations decreased in soils drained less than or equal to1 year i n the first 7 days of the incubation and remained constant thereafter. It w as found that artificial drainage of soils from the former Lake Texcoco pro foundly affected soil characteristics. Decreases in pH and Na+, (+), Cl- an d SO42- concentrations made conditions more favourable for giant growth, al though low concentrations of inorganic N and available P might be limiting factors.