Studies Of Soil Respiration And Influencing Factors In Oasis Cotton Field Of The Arid Area

The study sites, in this paper, are located in the north of Tianshan mountain—Shihezi city.Taking oasis cotton field,abandoned farmland as investigative object.The subject has been carried out by combining field observation with experiment treatment and using LI-8100 Automated Soil CO₂ Flux System for 2 years.The method is applied to analyze the change of the soil respiration in cotton filed and influencing factors,moreover, the model of soil respiration has been established in this paper.So as to provide some reference for the study of the carbon cycle in arid zone.Thus we make some studies and draw conclusions as following:1) The monthly variation of soil respiration is significant from May to October.Soil respiration changes in singlet way. soil respiration is higher in June and July than other months. The rate of soil respiration in cotton filed is far higher than that of deserted farmland.The average rate of soil respiration per month: drip irrigation field 3.41μmol·m^-2·s^-1; flooding field: 3.22μmol·m^-2·s^-1;abandoned farmland: 1.43μmol·m^-2·s^-1; moreover,the monthly variation range of soil respiration is: flooding filed> weeping field> abandoned farmland.2) The daily variation of soil respiration is characterized by single-peaked curve for the farmland in sunny day.The average rate of soil respiration per month: drip irrigation field 3.45μmol·m^-2·s^-1; flooding field: 3.37μmol·m^-2·s^-1;abandoned farmland: 1.63μmol·m^-2·s^-1.In addition, the peak of rate of soil respiration appear at about 15:00 to 20:00 (BeiJing time),and the valley value occurr at about 4:00 to 6:00.Different land has different appearing time.The changes of three kinds of land are similar in different weather. however, The change of soil respiration in diurnally is acuter than that in nighttime;but variation range of soil is low in cloudy day.3) There appear exponential relationship(0cm,5cm,10cm) among the rate of soil respiration,temperature and ground temperature in different field. Temperature, 5cm ground temperature and the rate of soil respiration show positive correlation (P<0.01) The tmperature sensitivity to soil respiration(Q₁₀) exhibite that:air temperature>5cm soil temperature>0cm soil temperature. The soil respiration of cotton field represent a significantly negative correlation with air humidity,but positive correlation with soil humidity at 5cm depth.(R₂=0.835,P<0.005)and the correlation with soil temperature weakene with soil depth at 10cm,20cm. Furthermore, rate of soil respirationat sites tend to increase rapidly after typical wetting events (rainfall and irrigation ), These results indicated that the rate of soil respirationat is increased by 2 times after irrigation and the range of change increase.The rate of soil respiration is influenced highly by rainfall.4) The results show that CO₂ cumulate release in cotton ecosystem exhibite a significantly linear correlation with NPP and underground biomass. The result that microorganism respiration and roots respiration contributes to full respiration is up to 40.8%,36.7%. Furthermore,the rate of soil respiration in cotton field is upper than hungriness,desert,abandoned farmland. And the rate of soil respiration become lower from oasis to desert.5) The method of spatial statistic is applied to establish model of soil respiration with experiential model. R_m=1.633 e^0.026T+5.443(W²+W)-1.618. and the estimate of annualrate of soil respiration by model in cotton field show that soil release more carbon to air,up to 681.6gC/m²,469.2gC/m², on condition that reclaiming framland from desert and abandoned farmland is cultivated again,so reclaiming framland with reason is beneficial to restrain the loss of soil carbon.