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

Abstract

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 ,N H 4 + , 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.