The Difference Of Organic Nitrogen In Long-term Different Tillage Soils And The Effect Of Straw Returning On Organic Nitrogen Mineralization

Reaseach of the long-term effect of conservation and concentional tillage on soil organicnitrogen, and the short-term effect of straw returning on soil organic nitrogen mineralizationcan provide theoretical basis for the determination of reasonable fertilizer nitrogen rate underconservation tillage.We measured different forms of organic nitrogen in long-termconservation tillage and conventional tillage soil. Then the nitrogen mineralization rate weredetermined under the laboratory conditions (constant temperature and humidity) and the fieldconditions.By using15N isotope tracer technique the straw nitrogen mineralization and thepriming effect induced by straw returning was studied.The research results are showed asbelow.（1）Different forms of organic nitrogen content in different tillage soilsCompared to conventional tillage soil, the improvement of nitrogen mineralization rateunder conservation tillage soil without staw returning in contributed to the increase ofdifferent soil organic content.In our experiment, the total nitrogen, MBN, PON, hydrolysisammonium nitrogen and amino acid nitrogen is enhanced at0-10cm layer of conservationtillage soil. At0-5cm soil layer, compared to conventional tillage soil, the total nitrogencontent in conservation tillage soil was enhanced by72.86%, the microbe biomass nitrogenwas enhanced by205.26%, the particle organic nitrogen was enhanced by117.26%,hydrolysable amino acid nitrogen was enhanced by24.79%, hydrolysable ammonia nitrogenwas enhanced by92.75%. At0-5cm soil layer, the total nitrogen content in conservationtillage soil was enhanced by76.03%, the particle organic nitrogen was enhanced by107.74%, hydrolysable amino acid nitrogen was enhanced by31.43%,hydrolysable ammonianitrogen was enhanced by51.52%.The effect of conservation at10-60cm was smaller,totalnitrogen and hydrolysable ammonia nitrogen contents had a tendency to reduce.（2）The result of effect of straw returning on soil organic nitrogen mineralizationStraw retuning promote the organic nitrogen mineralization in conservation tillage soiland restrain it in conventional tillage soil at0-60cm soil layer.In conservation tillage soil, theorganic nitrogen mineralization was promoted by147.27%,51.40%and25.00%at0-10cm, 10-30cm and30-60cm layers. In conventional tillage soil,the organic nitrogen mineralizationwas promoted by70.64%,20.00%and7.92%at0-10cm,10-30cm and30-60cm layers.（3）The mechanism of effect of straw returning on soil organic nitrogen mineralizationWith15N isotope tracer technique,we found the effect of straw nitrogen mineralizationwas very small,and the priming effect was the determining factor.According to the differentresults under field conditions(with different straw returned ways)and laboratory simulatedconditions(with same straw returned ways),the different results in field conditions in causedby straw returned ways.In addition, our reasach also clarified the difference of soil and straw organic nitrogenmineralization varying with time between field production conditions and laboratorysimulation conditions.