Impacts Of Management Regimes On Soil CO₂Emission From Croplands

Management regimes of croplands are to exclude the adverse factors for crop growth by altering crop environment on farmland ecosystem, and eventually to get a high yield. Changes in the environment of crop growth generally have important impacts on soil CO2emission from croplands, and further on atmosphere-soil C cycling and C budget. In this study, the black soils of croplands were selected as the object, we studied the impacts of different management regimes (including fertilization, tillage, cropping, and land use) on soil CO2emission, in order to reveal the variations of soil organic carbon and soil CO2emission patterns, and to clarify the factors to affect soil CO2emission and its influence mechanisms, and finally to provide some information on the manipulation of C cycling.The NPK+OM2fertilization treatment improved the SOC concentration by12%compared with the control. However, the SOC concentrations in other treatments were not significantly different from that in the control. During the growth season of maize, the soil CO2emission rate with different fertilization treatments had the same regulation trend with time. Soil CO2fluxes, regardless of organic or chemical fertilizer application, increased gradually from the experiment beginning in May and reached a maximum on August6. Both the soil CO2emission rate and cumulative CO2emission were significantly increased by the applications of organic straw and manure. The order of soil cumulative CO2emission is:NPK+OM2>NPK+OM1>NPK+MS2>NPK+MS1>CK>NPK. The relationships between soil CO2flux and soil temperature (5and10cm) could well be expressed as an exponential equation when we restricted to the period from the elongation stage to the harvest time. Soil moisture (water-filled pore space, WFPS) also significantly affected soil CO2flux when the influence of soil temperature was excluded. A log-transformed multiple regression model log (f)=a+b Tlog (W) including soil temperature and soil moisture was established, which could account for50-88%of the season variation in soil CO2flux.Soil organic carbon content of rotation system was higher than continuous system, but there was no difference between them in statistics. The soil CO2flux of continuous maize monoculture was higher than other treatments and reached a maximum on August6(596mg CO2m-2h-1).however, the soil in continuous soybean monoculture emitted the least CO2(396mg CO2m-2h-1). The relationships between soil CO2flux and soil temperature at5cm depth and soil WFPS in the5cm layer could well be expressed as an exponential equation when we restricted to the period from the elongation stage to the harvest time. The temperature sensitivity (Q10) of soil CO2fluxes during the growing season, ranged between1.63and2.31, and Q10in10cm layer was higher than that in5cm layer.There was no significant differences in soil organic carbon between no-tillage and conventional tillage. When we compared with no-tillage treatment, the soil CO2flux and cumulative CO2emission of conventional tillage was higher in the treatment conventional tillage by39%and42%, respectively. Cumulative CO2emission was significantly correlated with soil microbial biomass carbon. The relationships between soil CO2flux and soil temperature and soil WFPS could well be expressed as an exponential equation under conventional tillage and no-tillage. Soil temperature and soil WFPS together could account for49-64%of the season variation in soil CO2flux.Soil organic carbon in grassland is the highest (40g kg-1) among the different land use. The maximums of soil CO2fluxes in grassland and cropland were774mg CO2m-2h-1and404mg CO2m-2h"1on August6, respectively; whereas the maximum in bare land was393mg CO2m-2h-1on July23. Grassland and cropland have improved the cumulative CO2emission by176%and46%compared with bare land, and there were significantly difference between the three treatments (P<0.05). Cumulative CO2emission was significantly correlated with soil microbial biomass carbon (r2=0.9062). Relationship between soil temperature in10cm depth and soil CO2flux is better than that in5cm depth. The joint effect of soil temperature and soil moisture could account for41-81%of the season variation in soil CO2flux.In conclusion, management regimes of croplands had significant influences on soil CO2emissions. Both Soil temperature and moisture can mostly explain the seasonal changes of soil CO2emissions. Compared with5cm underground temperature,10cm underground temperature had more contributions and higher sensitivity(Q10).Under different conditions, we should combined the data of this paper with different ecological systems of black, soil in order to choose right management measure that could reduce soil CO2emissions and mitigate the greenhouse effect.