The Effect Of Different C Sources On Microbe Immobilization By Supplemental N

The foundation of the effective utilization of fertilizer nitrogen is to adjust its microbial transformation in soil matrics. The activity of carbon was the key factor to improve the utilization efficiency of the fertilizer nitrogen In our experiment glucose and other two kinds of organic matter with different nitrogen form were incorporated into soils and the soil samples were incubated in laboratory. The concentration of NH4+-N, NO3--N, microbial biomass carbon and nitrogen, soil pH and soil respiration CO2 were determined to study the effect of carbon source on the nitrogen transformation.The results showed that microbial immobilization of nitrogen was effected significantly by the existence and amount of the liable carbon. The addition of carbon supplied adequate energy for microorganisms, so the metabolism rate of the microorganisms was increased. Besides the microorganisms can use the addition nitrogen quickly and produce microbial biomass nitrogen. The supply of carbon increased the activity of soil microorganism significantly, while at the same time the accumulation of inorganic nitrogen was decreased remarkably. Thus, we can manipulate the process of nitrogen transportation by the manipulation of the carbon addition. As for different nitrogen source, the microorganisms preferred to utilize NH4+-N than NO3-. Soil microorganisms not only need enough carbon for energy but also nitrogen for self-contribution, which means that only when carbon and nitrogen are both adequate, microorganisms can have high activity and use the nitrogen quickly. So, the balance between carbon and nitrogen supply is guarantee for the high activity of soil microorganisms. Organic matter effected microbial immobilization of the addition nitrogen significantly. In the high C/N organic matter treatment, microorganisms can immobilize more nitrogen than that under low C/N organic matter input. Compared with the glucose addition, microbial biomass nitrogen under organic matter treatment decreased significantly, indicating the availability of carbon is the key factor which affected the synthesis of microbial biomass nitrogen.The crop residue input into soils applied the dominant carbon source in agro-ecosystems, which had significant effect on the nitrogen transformation. According to our results, we can conclude that appropriate proportion between crop residue and fertilizer nitrogen was essential to increase the utilization efficiency of nitrogen.