The impacts of inorganic nitrogen application on mineralization of 14C-labelled maize and glucose, and on priming effect in saline alkaline soil

Organic matter dynamics and nutrient availability in saline alkaline soil of the former lake Texcoco will determine the success of a planned reforestation program. Uniformly labelled 14C-maize (MAI-treatment) and glucose (GLU-treatment) with or without 200 mg NH4+−N kg−1 soil (MAI-N treatment and GLU-N treatment, respectively) were added to soils with electrolytic conductivity (EC) 56 dS m−1 (soil A) and 12 dS m−1 (soil B) to investigate the importance of N availability on decomposition of organic material. Production of CO2 and CO214 and inorganic N dynamics were monitored. The amount of 14C-glucose mineralized increased 1.8-times in the soil A, but had no effect in the soil B when 200 mg NH4+−N kg−1 soil was added, while the amount of 14C-maize mineralized increased 1.7 and 1.3-times when 200 NH4+−N kg−1 soil was added in the soils A and B, respectively. Application of NH4+ increased priming effect 3.7-times in the MAI-treatment of the soil A and 3.4-times in the GLU-treatment, while in the soil B the increase of priming effect was 4.1-times in the MAI-treatment and 3.7-times in the GLU-treatment. Of the 200 mg NH4+−N kg−1 added to both soils less than 10 mg NH3-N kg−1 was volatilized within one day, while 22 and 44 mg NH4+−N kg−1 soil was fixed on the soil matrix in the soil A and the soil B, respectively. Therefore more than 100 mg NH4+−N kg−1 was immobilized into the microbial biomass within the first day. Concentration of nitrite (NO2−) increased sharply in all the treatments of soil A at the onset of the incubation followed by a decrease. A similar pattern was observed in the GLU-N and MAI-N treatments of the soil B, but not in the other treatments. A decrease in concentration of NO3− was observed in both soils followed by an increase in the MAI-N and GLU-N treatments of the soil B. It was found that application of NH4+ had a stimulating effect on the decomposition of maize and glucose, and on the priming effect, while assimilatory reduction of NO3− resulted in an increase of NO2− in the soil A, and nitrification in the soil B.