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Based on the results of continuous flux measurements in the Taihu Lake Region of China, the carbon dioxide (CO 2 ) exchange of paddy fields under water-saving irrigation and its influence factors were analyzed. The net ecosystem exchange of CO 2 ( NEE ) were negative during the daytime and positive at night, and the minimum value appeared around noon. The peak CO 2 uptake in the flourishing period was approximately 1.5 times the values observed in the tillering and ripening stages. Frequent alternation of wetting and drying in paddy fields with water-saving irrigation resulted in larger NEE for the typical day before soil rewatering than that for the day after soil rewatering in the early growth stage. These alterations had a minimal effect on diurnal variation of NEE in the late rice growth stage. The average NEE for the typical days after soil rewatering in July and August were 2.30 and 1.38 times that before soil rewatering, respectively. CO 2 exchange in paddy field ecosystem under water-saving irrigation displayed seasonal variation with the change of rice plant growth. The total ecosystem respiration ( R eco ), NEE and gross primary productivity ( GPP ) were 1996.88, −1284.15 and 3281.03 g m −2 , respectively, throughout the growth stage. These results showed that the paddy field ecosystem under water-saving irrigation was a sink for atmospheric CO 2 . Frequent alternation of wetting and drying processes increased the ecosystem reparation of paddy fields under water-saving irrigation and produced smaller net CO 2 absorption compared to that of flooding irrigation. The net CO 2 absorption because of plant photosynthesis during the daytime and the net CO 2 release at night measured by static transparent chamber method were larger than those measured by eddy covariance method ( P < 0.05). The nighttime respiration of paddy field ecosystem under water-saving irrigation increased exponentially with temperature. Additionally, a larger temperature sensitivity coefficient ( Q 10 ) was observed for paddy fields under water-saving irrigation compared to that under flooding irrigation. The photosynthetic photon flux density ( PPFD ) was the most important factor for regulating daytime GPP . And the light saturation point during the heading-flowering and milk stages of paddy field ecosystem with water-saving irrigation (1500 μmol m −2 s −1 ) was higher than that of fields with flooding irrigation in previous studies. A significant positive correlation was found between the leaf area index ( LAI ) and the daily GPP . [ABSTRACT FROM AUTHOR]

The effect of controlled drainage on methane (CH4) and nitrous oxide (N2O) emissions from a paddy field under controlled irrigation (CI) was investigated by controlling the sub-surface drainage percolation rate with a lysimeter. CI technology is one of the major water-saving irrigation methods for rice growing in China. Water percolation rates were adjusted to three values (2, 5, and 8 mm d−1) in the study. On the one hand, the CH4emission flux and total CH4emission from paddy fields under CI decreased with the increase of percolation rates. Total CH4emissions during the growth stage of rice were 1.83, 1.16, and 1.05 g m−2in the 2, 5, and 8 mm d−1plots, respectively. On the other hand, the N2O emission flux and total N2O emissions from paddy fields under CI increased with the increase of percolation rates. Total N2O emissions during the growth stage of rice were 0.304, 0.367, and 0.480 g m−2in the 2, 5, and 8 mm d−1plots, respectively. The seasonal carbon dioxide (CO2) equivalent of CH4and N2O emissions from paddy fields under CI was lowest in the 2 mm d−1plot (1364 kg CO2ha−1). This value was 1.4% and 19.4% lower compared with that in the 5 and 8 mm d−1plots, respectively. The joint application of CI and controlled drainage may be an effective mitigation strategy for reducing the carbon dioxide equivalents of CH4and N2O emissions from paddy fields. [ABSTRACT FROM AUTHOR]

High rates of nitrogen (N) fertilizer were applied to a paddy field in the Taihu Lake region of China to maximize crop production. Excessive N input has resulted in serious agricultural nonpoint pollution. Water and N management are two important approaches to regulating N loss from paddy fields. This study aimed to determine N losses through ammonia volatilization, runoff, and leaching from a paddy field during the rice-growing season in Taihu Lake region. Field experiments with two water and two N managements were conducted. The N exported to the environment through ammonia volatilization, runoff, and leaching from the paddy field was 37.2 kg N ha−1to 102 kg N ha−1, with ammonia volatilization accounting for 69.6% to 83.5% of N loss. Ammonium and dissolved organic N significantly contributed to N loss through runoff and leaching. Controlled irrigation and site-specific N management (CS) significantly decreased N losses through ammonia volatilization, runoff, and leaching. Compared with the N and irrigation water inputs in traditional water and N management, those generated by controlled irrigation and site-specific N management were reduced by 34.6% to 43.0% and 59.2% to 63.3%, respectively. Moreover, the reduction in N and water input in the CS paddy field enabled the maintenance of high rice yield; it significantly increased N use efficiency by 15.1% to 34.9% and decreased the N exported to the environment by ammonia volatilization, runoff, and leaching by 53.1% to 56.1%. Therefore, the joint application of controlled irrigation and site-specific N management efficiently reduces agricultural nonpoint pollution through N loss from paddy fields. [ABSTRACT FROM AUTHOR]

Abstract: Water-saving practices for rice production has become one of the major agricultural policies in China due to the severe water scarcity. However, greenhouse gases emissions from paddy field may be changed with water-saving practices. In the two-year field experiment at Thaihu Lake Basin of China, CH4 and N2O fluxes from paddy field under controlled irrigation and continuous flooding irrigation were monitored using closed chambers. Total CH4 emission from paddy field under controlled irrigation during the rice-growing period were 2.47 and 1.88gm−2 in 2006 and 2007, respectively, reduced by 79.1% on average compared with continuous flooding irrigation. The CH4 emission from paddy field was further concentrated in the initial and middle tillering stages of rice growth under controlled irrigation for 2years. The N2O emission from paddy field under controlled irrigation was mostly larger than those from flooding irrigation during the rice-growing period. Total N2O emission from paddy field under controlled irrigation during the rice-growing period was 106mgm−2, increased by 10.6% compared with those from flooding irrigation. Carbon dioxide equivalents of CH4 and N2O emissions from paddy field during the rice-growing period under controlled irrigation were 788kg CO2 ha−1, reduced by 61.4% compared with those from flooding irrigation. It can be concluded that controlled irrigation is an effective technique for mitigating the carbon dioxide equivalents of CH4 and N2O emissions from paddy field. [Copyright &y& Elsevier]

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]

Surface energy distribution in paddy fields and the ratio of latent heat flux (LE) to available energy, termed as the evaporative fraction (EF), are essential for an understanding of water and energy processes. They are expected to vary in different ways in response to changes in the soil moisture condition under water-saving irrigation practice. In this study, the diurnal and seasonal variations in energy distribution were examined based on the data measured by the eddy covariance system and corrected with enforcing energy balance closure by the EF method in water-saving irrigated rice paddies in 2015 and 2016. Soil heat flux (G) values were similar in magnitude to sensible heat flux (Hs) values, with both accounting for approximately 5% of the energy input. Both magnitudes of G and Hs were significantly lower than that of LE. Generally, EF in water-saving irrigated rice paddies was larger than that of other ecosystems, and varied within a narrow range from 0.7 to 1.0. Diurnally, EF decreased till noon and then increased slowly in the afternoon till sunset. It was found be less varied between 10:00 and 14:00. Seasonally, the alternative drying-wetting soil water conditions in water-saving irrigated rice paddies resulted in a change in the variation of the EF. The LE flux is the largest component of available energy, with EF being mostly higher than 0.9. EF, increasing consistently till the tillering stage, remaining high from the late tillering to milk stage, and then following a declining trend. The maximum EF (approaching 1.0) was found in the milk stage. The results of EF in water-saving irrigated rice paddies will be helpful for estimating daily or long temporal scale evapotranspiration (ET) by the EF method based on satellite-derived ET. [ABSTRACT FROM AUTHOR]

Abstract: Water management is one of the most important practices that affect methane (CH4) and nitrous oxide (N2O) emissions from paddy fields. A field experiment was designed to study the effects of controlled irrigation (CI) on CH4 and N2O emissions from paddy fields, with traditional irrigation (TI) as the control. The effects of CI on CH4 and N2O emissions from paddy fields were very clear. The peaks of CH4 emissions from the CI paddies were observed 1–2d after the water layer disappeared. Afterward, the emissions reduced rapidly and remained low until the soil was re-flooded. A slight increase of CH4 emission was observed in a short period after re-flooding. N2O emissions peaks from CI paddies were all observed 8–10d after the fertilization at the WFPS ranging from 78.1% to 85.3%. Soil drying caused substantial N2O emissions, whereas no substantial N2O emissions were observed when the soil was re-wetted after the dry phase. Compared with TI, the cumulative CH4 emissions from the CI fields were reduced by 81.8% on the average, whereas the cumulative N2O emissions were increased by 135.4% on the average. The integrative global warming potential of CH4 and N2O on a 100-year horizon decreased by 27.3% in the CI paddy fields, whereas no significant difference in the rice yield was observed between the CI and TI fields. These results suggest that CI can effectively mitigate the integrative greenhouse effect caused by CH4 and N2O emissions from paddy fields while ensuring the rice yield. [Copyright &y& Elsevier]