Dynamics of inorganic nitrogen in nitrate and glucose-amended alkaline-saline soil

Induction of assimilatory NO ₃ - 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 NO ₃ - in excess of N required for metabolic activity and the release of large concentrations of NO ₂ - and smaller amounts of NH ₄ ⁺ . We postulated that this was regulated by the amounts of NO ₃ - 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 NO ₃ - and glucose while dynamics of CO₂, NH ₄ ⁺ , NO ₂ - and NO ₃ - 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 NO ₃ - 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 NO ₂ - increased to > 100 mg NO ₂ - -N kg-¹ when 1000 mg glucose-C kg-¹ and 500 mg NO ₃ - -N kg-¹ were added to soil A and B of Texcoco, but remained < 3 mg NO ₂ - -N kg-¹ in the agricultural soil. The ratio between the cumulative production of CO₂ and the decrease in concentration of NO ₃ - 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 NO ₃ - when an easy decomposable substrate was available in excess of what might be required for metabolic activity while producing large concentrations of NO ₂ - , but these phenomena were absent in an agricultural soil. In soil of Texcoco, concentrations of NO ₂ - and NH ₄ ⁺ increased with increased salinity and availability of NO ₃ - . This ability to remove large quantities of NO ₃ - under these conditions and then utilize it at a later time might benefit micro-organisms of the N limited alkaline-saline soils of Texcoco.