Dynamics of Inorganic Nitrogen in Nitrate and Glucose-amended Alkaline–saline Soil

Induction of assimilatory NO3− reduction through the application of an easily decomposable substrate in alkaline–saline soils of the former lake Texcoco (Mexico) resulted in a fast immobilization of NO3− in excess of N required for metabolic activity and the release of large concentrations of NO2− and smaller amounts of NH4+. We postulated that this was regulated by the amounts of NO3− and glucose added, and affected by the specific characteristics of soil from the former lake Texcoco. This was investigated by spiking soils of different electrolytic conductivity (EC) 56.0 dS  m−1 (soil A of Texcoco) and 11.6 dS  m−1 (soil B of Texcoco) with different concentrations of NO3− and glucose while dynamics of CO2, NH4+, NO2− and NO3− were monitored in an aerobic incubation for 7 days. For comparison reasons (control) an agricultural soil with low EC (0.3 dS  m−1) was included as well. In the agricultural soil, 67% of the added glucose mineralized within 7 days, but only 15% in soil A of Texcoco and 20% in soil B of Texcoco. The application of NO3− to the agricultural soil added with glucose increased cumulative production of CO2 1.2 times, 1.5 times in soil A of Texcoco and 1.8 times in soil B of Texcoco. Concentration of NO2− increased to > 100 mg NO2−-N kg−1 when 1000 mg glucose-C kg−1 and 500 mg NO3−-N kg−1 were added to soil A and B of Texcoco, but remained < 3 mg NO2−-N kg−1 in the agricultural soil. The ratio between the cumulative production of CO2 and the decrease in concentration of NO3− was approximately one in soil A and B of Texcoco, but 10 in the agricultural soil after 3 days. It was found that micro-organisms in the alkaline–saline soil of the former lake Texcoco were capable of immobilizing large quantities of NO3− when an easy decomposable substrate was available in excess of what might be required for metabolic activity while producing large concentrations of NO2−, but these phenomena were absent in an agricultural soil. In soil of Texcoco, concentrations of NO2− and NH4+ increased with increased salinity and availability of NO3−. This ability to remove large quantities of NO3− under these conditions and then utilize it at a later time might benefit micro-organisms of the N limited alkaline–saline soils of Texcoco.