Kinetics of denitrification in soil and the effect of perennial ryegrass on nitrate concentration in soil.

摘要

Nitrogen transformation through denitrification in soil can have a significant impact on the environmental quality. The kinetics of soil denitrification, however, is still not well understood. The available information on kinetics of denitrification in soil has been mostly obtained under strictly anaerobic conditions with inadequate consideration of the facultative nature of the process. In this study, experiments were conducted to investigate denitrification kinetics under varying soil temperature, organic C content, nitrate concentration and soil water content using a sandy clay loam soil. The acetylene inhibition method was used to measure the denitrification product. A kinetics model was developed and calibrated with the experimental data. The experimental results showed that (1) at 20°C soil water content had a more significant effect on the denitrification process than at 10 and 30°C. The average total denitrification at 20 and 30°C was 2.7 and 3.7 times of that at 10°C. (2) The addition of glucose (92.3 mg C/kg soil) increased the denitrification rate from 0.13 to 0.27 mg N/kg soil/h when soil water content was within a range between field capacity and saturation. (3) Maximum total denitrification at the nitrate levels of 11.7, 42.5 and 73.2 mg N/kg soil occurred at 90%, 95% and 100% saturation, respectively. The stepwise first-order dynamic denitrification model developed could simulate the change in NO₃−, NO₂− concentrations and the production of N₂O during the denitrification process over the wide soil water content range, thus describe facultative feature of denitrification. The model also described the competition for organic C as well as the interactions between the transformations of NO₃ − to NO₂− and NO₂ − to N₂O.; A greenhouse experiment was conducted to investigate effective ways to reduce NO₃− leaching using perennial ryegrass (Lolium perenne L.). The results indicated that when total inorganic N input and uptake were balanced, the ryegrass increased the ratio of soil NH₄+-N to NO₃−-N from 4.8 to 12.1 and resulted in a very low nitrate concentration. When total inorganic N input was 26–57% higher than the uptake, the ryegrass maintained a 2.5–3.0 NH₄+-N to NO₃ −-N ratio in soil. Therefore, the potential of nitrate leaching can be reduced significantly by the existence of ryegrass.