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The temporal and spatial variation of soil respiration of farmland has great influence on regional and global carbon cycle. Irrigation is an important factor to soil respiration in farmland. Existing study on the effect of irrigation on farmland soil respiration mainly focused on the dry farmland, but less research focused on paddy fields. Relationships between soil respiration and water depth and short-term drying of paddy fields with flooding irrigation were analyzed in existing studies. In order to reveal the difference of soil respiration in paddy fields with water-saving irrigation and traditional irrigation, the diurnal variation of soil respiration, the impact of alternation of wetting and drying on soil respiration, and the influencing factors of soil respiration for paddy fields were analyzed based on lysimeter experiment. The results showed that diurnal variations of soil respiration of paddy fields with water-saving irrigation and normal irrigation were similar at the period when the status difference of soil moisture was small between the two irrigation modes. Diurnal variations of soil respiration of paddy field with water-saving irrigation showed wider range, and the fluxes and rangeability of soil respiration of paddy field with water-saving irrigation were larger than those for traditional irrigation when the status difference of soil moisture was large. The mean value of soil respiration of diurnal variation during the whole growth period for water-saving irrigation was 1.47 times that for traditional irrigation. But during early tillering stage, jointing-booting stage and milk stage in which water managements were obviously different, the mean values of soil respiration diurnal variations for water-saving irrigation were 3.85, 1.42 and 3.74 times those for traditional irrigation. This results could contribute to frequent alternation of wetting and drying of paddy fields with controlled irrigation. The processes of soil rewatering and soil moisture depletion both had a certain effect on soil respiration of paddy fields. Peaks of soil respiration appeared at the critical point of soil moisture depletion. In the critical point of soil rewatering, the increase of soil respiration rate was not obvious if the rewatering depth was thicker, and the increase was significant if the rewatering depth was thinner. And small peaks of soil respiration appeared when soil water content decreased close to the lower limit of soil water content of paddy field with controlled irrigation during the irrigation interval. Soil temperature and soil moisture had great impact on soil respiration of paddy field with water-saving irrigation. Good exponential dependence was showed between soil respiration flux and soil temperature in the depth of 5 cm in paddy fields, and the correlation reached significant level for paddy field with water-saving irrigation (P<0.05). Management mode without water layer for controlled irrigation led the soil moisture conditions to be similar to dry farmland, so the relationship between soil respiration and soil temperature of paddy fields with controlled irrigation was more consistent with the existing results in dry farmland and forest. Water layer was kept in field surface for a long time under traditional irrigation, which led the soil into strict anaerobic conditions, and the effects of soil temperature on soil respiration was relatively weaken. The soil volumetric moisture content of 43% was the critical point for soil respiration of paddy field with water-saving irrigation when the soil volumetric moisture content ranged from 35% to 55%. Soil respiration flux in paddy field with water-saving irrigation increased with the enhancement of soil moisture content when the soil volumetric water content was lower than the critical value (P<0.05). And soil respiration flux in paddy field with water-saving irrigation decreased with the increase of soil moisture content when the soil volumetric water content was larger than the critical value (P<0.05). This conclusion was consistent with the existing research results. The appropriate soil volumetric moisture content was about 43%, which could create a suitable environment for respirations of rice roots, soil microbes and so on, and increase soil respiration rate. The results of this paper can support for more comprehensively evaluating the ecological environment effect of rice water-saving irrigation. At the same time, it can be helpful to accurately evaluate the carbon source/sink features of paddy field ecosystem. [ABSTRACT FROM AUTHOR]

Continuous emissions of greenhouse gases (GHGs) will cause further warming and changes of the climate system. Nitrous oxide (N2O) is an important GHG. Irrigation mode is an important factor in regulating N2O emissions from croplands. Controlled irrigation (CI) is one of the major water-saving irrigation practices, and has been widely applied. Compared with traditional irrigation (TI), CI leads to remarkable changes in soil properties and soil biochemical processes, which consequently induces changes in N2O emissions. Whether CI practiced during the rice season has subsequent effects on N2O emission during the following winter wheat season is worthy of further study. Thus, a field experiment was designed to study the effects of CI during the rice season on N2O emissions from the rice-winter wheat rotation systems, with TI as the control. The gas samples were collected by the static chamber technique. The chamber, consisting of 2 separate layers with the same size (0.5 m × 0.5 m × 0.6 m), was made of polyvinyl chloride. Samples were collected by 50 mL syringes, which were connected to chambers and sealed airbags through 3 stopcocks. Irrigation mode during the rice growing season had obvious subsequent effects on N2O emission from the following winter wheat growing season. Compared to TI, CI significantly increased the N2O emission during the rice growing season (P<0.05), but significantly decreased it during the wheat season (P<0.05). During the rice growing season, the mean of N2O emissions from the CI plots was 229.25 μg/(m2.h), which was 1.66 times higher than that from the TI plots. During the winter wheat season, N2O emissions from the CI plots were generally lower than those from the TI plots. High N2O emissions from the CI plots were mainly observed after the regreening fertilizer application. Two or three peaks were observed from the CI plots in the middle and late stage of wheat growth, and the peak values were less than those from the TI plots. In the TI plots, N2O emissions were always high in the early stage of wheat growth and after the regreening fertilizer application, and were low during the overwintering period of wheat growth. Four peaks of N2O emissions were observed from the TI plots. During the winter wheat season, N2O emissions were closely related to rainfall. High N2O emissions were observed from 7 to 10 days after rainfall. Compared to TI, CI significantly increased the cumulative N2O emission in rice growing season by 136.9% (P<0.05), but decreased it in wheat growing season by 47.1% (P<0.05). Over the whole annual cycle, the cumulative N2O emission from the plots under the CI was 761.50 mg/m2, 1.0% lower than that under TI (P>0.05). During the 2009-2010 and 2010-2011 wheat growing season, the cumulative N2O emissions from the CI fields were reduced by 46.7% and 47.6% respectively, compared with those from the TI fields. The cumulative N2O emissions from the rotation systems under CI were 6.88 and 8.35 kg/ha in 2009-2010 and 2010-2011, respectively, reduced by 5.7% and increased by 3.2% respectively, compared with those from the TI fields. The N2O-N loss was used to measure the amount of N2O emissions from the croplands. During the rice growing season in 2009 and 2010, the mean N2O-N losses under CI were 0.97% and 1.13%, respectively, while the mean N2O-N losses under TI were 0.40% and 0.49%, respectively. During the 2009-2010 and 2010-2011 wheat season, the mean N2O-N losses in the CI plots were both 0.86%, while N2O-N losses in TI plots were 1.62% and 1.63%, respectively. Over the whole annual cycle, the mean N2O-N losses were 1.01% and 0.98% in CI and TI plots, respectively. These results suggest that controlled irrigation dose not increase the cumulative N2O emission from the rice-winter wheat rotation systems, compared to traditional irrigation. [ABSTRACT FROM AUTHOR]

In order to reveal the difference of evapotranspiration of paddy fields under water-saving irrigation on different scales, the differences of evapotranspiration between field scale and plot scale of paddy field under water-saving irrigation was analyzed based on the field experiment. In addition, the reasons for the difference between evapotranspiration of paddy fields under water-saving irrigation on different scales were investigated in this paper. The evapotranspiration on field scale and plot scale of paddy fields under water-saving irrigation was measured by eddy covariance system and lysimeter, respectively. The results showed that there were significant (p < 0.05) differences between the evapotranspiration of paddy fields under water-saving irrigation on filed scale and plot scale in the whole and early, middle and late growth stages. The variation trend of evapotranspiration of paddy fields under water-saving irrigation on field scale was similar to that on plot scale. But the difference existed on value of evapotranspiration of paddy fields under water-saving irrigation. The evapotranspiration on field scale of paddy fields under water-saving irrigation in the whole growth stages was 18.7% smaller than that on plot scale. The evapotranspiration on field scale of paddy fields under water-saving irrigation in the early, middle and late growth stages was 15.5%-20.5% smaller than those on plot scale. The significant differences (p < 0.05) were also showed between the evapotranspiration of paddy fields under water-saving irrigation on field scale and plot scale in the different growth stages. High significant differences (p < 0.01) were showed between the evapotranspiration of paddy fields under water-saving irrigation on field scale and plot scale in different times (ten days, five days). The evapotranspiration of paddy fields under water-saving irrigation on field scale in ripening stage increased by 7.9% compared to that on plot scale. The evapotranspiration of paddy fields under water-saving irrigation on field scale in other growth stage decreased by 10.2%-29.5% compared to that on plot scale. As the day time shortened, the decreased amplitude of evapotranspiration on field scale of paddy fields under water-saving irrigation increased compared to that on plot scale. Differences between different time steps of evapotranspiration of paddy fields under water-saving irrigation on different scales was caused by underlying surface, atmospheric turbulence conditions, meteorological factors, soil moisture condition, irrigation process and so on. Underlying surface conditions, atmospheric turbulence, the process of water replenishment, the soil water status and meteorological factors were the main reasons for the differences between evapotranspiration of paddy fields under water-saving irrigation on filed scale and plot scale. Relative air humidity and air temperature can lead to the differences of evapotranspiration of paddy fields under water-saving irrigation on different scales. They were the main factors affecting the difference of evapotranspiration of paddy fields under water-saving irrigation on different scales. The effect of meteorological factors on evapotranspiration of paddy fields under water-saving irrigation was mainly related to soil moisture and marginal effect. The reveal of the evapotranspiration differences of paddy fields under water-saving irrigation on different scales can be used for the transformation of evapotranspiration of paddy field under water-saving irrigation on different scales. [ABSTRACT FROM AUTHOR]