Soil Respiration In Arid Upland Fields During Summer Fallow Season On The Losses Plateau

Soil respiration from farmland is the most active part in the soil carbon cycle. Arableland in Losses Plateau area is15%of the nationwide. Fallow season (July to September) afterwheat harvest is an important period in this region, during which high temperature andhumidity is ubiquitous. Environment like this combined with tillage during this period wouldcause severe microbial activities. Thus, research on soil respiration during fallow season hasimportant significance on understanding relationship between soil respiration, temperatureand moisture and regulating farmland organic carbon.An infrared gas analyzer was employed to investigate the soil CO2efflux during fallowseason in2012in a bare land and a conventional wheat field of the Losses Plateau, China.Soil respiration, soil temperature, soil moisture, soil physical and chemical properties weremeasures from July to September. We fitted the equation between soil respiration and soiltemperature and soil moisture, respectively. The double factor models including both soiltemperature and soil moisture were also derived in both plots. The results showed that:(1) Soil respiration in fallow land and bare land showed unimodal curve, similar with thetrend of air temperature. The maximum values appeared in15:00~17:00. Soil respiration infallow land varied drastically within the range from13.40to1.93μmol·m-2·s-1with avariation coefficient of74.80%and a mean of4.99μmol·m-2·s-1. Compare with fallow land,Soil respiration in bare land varied gently within the range from2.49to0.65μmol·m-2·s-1with a variation coefficient of40.36%and a mean of1.41μmol·m-2·s-1.(2) Correlation analysis between soil respiration and its influencing factors showed that,there was extremely significantly negative correlation relationship (P<0.01) between soilrespiration and soil temperature in different soil depth under the influence of soil tillage,correlation between soil respiration and soil moisture was extremely significantly positiverelationships (P<0.01). However, correlation in bare land was much lower. In bare land,correlation relationship between soil respiration and soil temperature was positive, with extremely significantly relationships only in10cm and20cm soil depths (P<0.01). There wasno significance between soil respiration and soil moisture except in50cm soil depth. Therewere no significance (P>0.05) between soil respiration and soil physical and chemicalproperties including soil organic matter, total nitrogen, urease activity, CAT activity and pHvalue in both plots.(3) In fallow land, the functional relationship between soil respiration and temperaturecould be described well by exponential and the coefficients of determination r2varied from0.531to0.707in different soil depth. The functional relationship between soil respiration andmoisture could be described well by quadratic. The coefficients of determination r2variedfrom0.490to0.813in different soil depth. In bare land, there was significant exponentialrelationships between soil respiration and temperature in four soil depth except50cm, and thecoefficients of determination r2varied from0.306to0.532. Relationship between soilrespiration and soil moisture could be well described by exponential function in50cm soildepth only.(4) Bivariate model including both temperature and moisture was recommended formodeling soil respiration in fallow land, and models fitted by temperature and moisture in30cm soil depth with the r2of0.828. However, univariate model including temperature only hada better fitting than the bivariate model in bare land. The current research results could beused to model the dynamics of soil respiration during fallow season in semi-arid regionswithin the ranges of soil temperature and soil moisture accordingly.(5)There was significance between CO2-C efflux in the two plots, total CO2-C effluxduring fallow season was3.96and1.06Mg/ha in the fallow land and bare land, respectively.