The Reserch Of Soil Nitrogen Mineralization Charactreistics And Influencing Factors Of Main Tobacco Soil In Liangshan And Panzhihua Province

Nitrogen is the important essential nutrients for tobacco and soil is a major source for avaliable nitrogen.Liangshang and Panzhihua have special features of the climate and geography where soil nitrogen mineralization has effected by ecotope,soil type,planting system and planting years.The research of soil nitrogen mineralization characteristic in this region has a guiding significance to tobacco product.This research had choosen tobacco soil in Liangshan and Pazhihua be the object of study, and modified the local weather in production season,two treatments had be set:CW for water content below 25%in cubation and FW for 1-2cm waterflooding under soil sample.during the experiment regularly sampled for soil inorganic nitrogen mineralization morphology and composition of nitrogen mineralization associated drive activity variation.The results as follows:(1) Under different water conditions, the mineralized nitrogen accumulation quantity of the planting tobacco soil was significant difference.During cubation period (0-64 days),the accumulation quantity of soil mineralized nitrogen were 254.6 mg/kg (FW) and 397.69 mg/kg (CW),among them, the accumulation release quantity of the ammonium nitrogen were 42.95 mg/kg (FW) and 11.05 mg/kg (CW), respectively, accumulation release quantity of nitrate nitrogen were 155.36 mg/kg (FW) and 531.99 mg/kg (CW), respectively.The mineralized nitrogen accumulation of the planting tobacco wasgiven priority to with nitrate nitrogen, Cumulative mineralization rate of soil conversion fast early, the late change rate decrease and remain flat under different water conditions.Under the condition of constant wet, soil net nitrification rate in 2-64 days was less than 0,soil nitrate nitrogen consumption was greater than the accumulation,under the condition of wet,soil net mineralization rate was greater than 0, soil nitrate nitrogen gave priority to in order to accumulate.In LiangPan region,the soil nitrogen mineralization characteristic that was "the fast before and the slow after"matchs the law of nitrogen requirement in early stage of the tobacco leaf growth (transplanting to prosperous long-term),but the soil is too wet (constant wet) may result soil nitrogen supply capacity is weak, is not conducive to the growth of tobacco plant.(2) With altitude rised, the tobacco soil nitrogen mineralization content reduced.the mineralized nitrogen accumulation under 1500m was significantly higher than 1500m above, the cumulative mineralized rate performance:1500m below>1500-2000m>2000-2500m, the difference in CW was more significant. Under different water conditions, the higher altitude,the lower cumulative of soil ammounium and nitrate.(3) The previous crop and the years of planting tobacco had significant effects on soil nitrogen transformation. Within the range of altitude 1500-2000m,the highest mineralization of soil nitrogen accumulation and the cumulative mineralization of the humid condition, leisure and wheat stubble soil were 468.2lmg/kg and 462.66mg/kg.It was significantly higher than sugarcane before crop and green manure crops (P< 0.05). Within the range of altitude 1500-2000m, the inorganic nitrogen mineralization of planting tobacco soil, during the period of the culture.the highest cumulative mineralization were 461.50mg/kg(CW)and297.79mg/kg(FW).The rate of cumulative mineralization was higher than that soil of 1-5 and 6-10 years planted tobacco. It indicated that the productions of flue-cured tobacco(planting tobacco 1-10 years) had inhibitory effect on the soil nitrogen mineralization,in the whole. The soil nitrogen mineralization and mineralization rates was relatively higher which was to the cropping continued of flue-cured tobacco within five years or the humid condition, leisure and wheat stubble soil. It guaranteed the supply of planting tobacco soil nitrogen to some extent.(4) The results of activities of soil enzyme which has relation with nitrogen mineralization showed thetrend of urease activity had the consistency with niteate content under CW.That indicated that soil ammonia content increased because of urease transformation,and the ammonia oxidated to nitrate.Activity in paddy soil significant higher than red soil and purple soil.Protease activity and soil ammonium nitrogen content in the same trend,and protease catalyzed the organic nitrogen into ammina. Within 1500-2000m the protease activity was higher than other altitude,there was not significant difference between diffrernt soil types.The activity of nitrite reductase was higher in low elevation(< 1500m) under FW than other height. And lower in red soil than other soil types. Nitrite reductase activity had correlation with soil aeration,therefore, drain away water was necessary in agricultural production to avoid the accumulation of hazardous substance.(5) Correlation analysis results show that the ammonium nitrogen mineralization and soil inorganic nitrogen accumulation amount was positively related under the constant humidity condition,which mainly activated by protease activation,and soil nitrogen mineralization rate mainly limited by ammonification rate,urease activity and nitrite reductase activity. Under humid conditions,content of nitrate nitrogen is the main source of the total change of soil inorganic nitrogen,which directly determining the soil nitrogen mineralization rate; soil mineralization rates is influenced by the positive effectsof urease and protease’sactivities,and nitrite reductase activity become a major limiting factortomoist soil nitrogen mineralization.