The Influences Of Phenolic Acids To Soil Nitrification In Continuous Cropping Poplar Plantation

This study revealed the mechanism of nitrification, which is the central part of nitrogen cycling, by quantitative research migration and transformation of nitrogen, taking poplar plantation forest soils in Shandong Ningyang as the research object, using the combining method of applying fertilizermarking with 15 N isotope to forest soils and indoor training by adding phenolic. Studying the soil nitrogen of poplar plantations, improve the soil fertility decline on continuous cropping plantation.1 The results of positioning experimental poplar plantation forest by applying NH4-N show that:(1) The phenolic content of poplar plantation soils presented the II generation rhizosphere > I generation rhizosphere > II generation non-rhizosphere > I generation non-rhizosphere.(2) In the same piece of forestland of poplar, the change rate of ammonium nitrogen and nitrate nitrogen and the nitrification activity in rhizosphere soil were significantly higher than non-rhizosphere soil. The Hydroxylamine reductase and nitrite reductase associating with nitrogen losses were no significant differences,while nitrate reductase activity was significantly differentbetween rhizosphere and non-rhizosphere soil.(3) In different stands, the successive generations of poplar plantationincreases thesoil phenolic acid cause microbial activity decreased, the rate and amount of transformation from ammonium to nitrate decreased by the results of ammonium’s remaining amount, the nitrate’s accumulated amount, the rate of transform and the activity of microbial which inhibits the nutrient cycling in soil microenvironment. It can be said, continuous cropping inhibited nitrification. Meanwhile in the nitrification process, continuous cropping had almost no effect on hydroxylamine reductase, nitrate reductase and nitrite reductase, and almost no effect on the nitrogen loss, but there is a tendency to accelerate the loss of nitrogen.2 The laboratory study results about adding a gradient of exogenous phenolicacids to the I-generation non-rhizosphere soil of poplar plantation showed:As the concentration of phenolic acids increased, accumulate asymptotic values of NO3-N and consume asymptotic values of NH4-N both decreased gradually, and the nitrification activity of nitrobacteria gradually decreased. All of the results showed that: the phenolic acid inhibit the nitrification. Besides, with the increasing concentration of the phenolic acid, the activity of nitrate reductaseaccording to denitrification became increased, and thus the loss of nitrogen in the soilincreased.3 Conclusions were found by researching the continuous cropping poplar plantation and the nitrification process under the action of gradient acid. On the one hand, by inhibiting nitrification microbial activity, phenolic acid affected the conversion of ammonium to nitrate. Nitrification process was inhibited. On the other hand, phenolic acid promoted the nitrate reductase activity associated with denitrification. For the reason that gaseous nitrogen losses increased and the "Library" source of nitrogen in the soil decreased. Both poplar stand productivity and soil fertility declined due to nitrogen that poplar could absorb and utilize reduced.