Microorganisms in sewage sludge added to an extreme alkaline saline soil affect carbon and nitrogen dynamics

There are plans to vegetate soil of the former lake Texcoco and use wastewater sludge to provide nutrients. However, the Texcoco soil is N depleted, so the amount of N available to the vegetation might be limited and the dynamics of C and N affected. We investigated how emissions of CO2, N2O and N-2, and dynamics of mineral N were affected when different types of N fertilizer, i.e. NH4+, NO3-, or unsterilized or sterilized wastewater sludge, were added to the Texcoco soil. An agricultural soil served as control. Sewage sludge added to an alkaline saline soil (Texcoco soil) induced a decrease in concentrations of NH4+ and NO3-. Addition of sewage sludge increased the CO2 emission rate > two times compared to soil amended with sterilized sludge. The NH4+ concentration was lower when sludge was added to an agricultural soil for the first 28 days and in the Texcoco soil for 56 days compared to soil amended with sterilized sludge. Production of N2O in the agricultural soil was mainly clue to nitrification, even when sludge was added, but denitrification was the main source of N2O in the Texcoco soil. Microorganisms in the sludge reduced N2O to N-2, but not the soil microorganisms. It was found that microorganisms added with the sludge accelerated organic material decomposition, increased NH4+ immobilization, and induced immobilization of NO3- (in Texcoco soil). These results suggest that wastewater sludge improves soil fertility at Otumba (an agricultural soil) and would favour the vegetation of the Texcoco soil (alkaline saline). (C) 2010 Elsevier B.V. All rights reserved.