| Rice paddy field is the main source of agricultural greenhouse gas emissions and plays a significant role in global greenhouse effect. Compared to southern area’s rice paddy field, rice paddy field of cold region in northeastern area has a relatively colder and longer winter, higher soil organic matters and difference in water and fertilizer management modes. Therefore, it is necessary to carry out experimental study on the emissions of CO2, CH4 and N2 O in northeastern cold region rice paddy field, in order to provide scientific basis for the accurate calculation of rice paddy field soil total emissions of CO2, CH4 and N2 O in China. The research method combining field experiment and laboratory analysis was adopted during the experiment. Three treatments of moisture management mode（control irrigation、wet irrigation、intermittent irrigation and flood irrigation.） and four nitrogen supply levels（0、75、105、135 kg'hm-2）were implemented in this experiment. Based upon the practical monitoring data of greenhouse gas collected under different water and nitrogen management modes, the experiment aimed at discussing the law of emissions of CO2, CH4 and N2 O, illuminating the relationship between environmental factors in rice paddy field and greenhouse gas emission, analyzing the influence mechanism of rice growth’s variation on greenhouse gas emissions of CO2, CH4 and N2 O, defining the environmentally friendly water saving irrigation and fertilizing mode which will improve the utilization ratio of water and hydrogen on rice and reduce the total warming potentiality. Main research results are shown as below:（1）Under all water and nitrogen management modes, the peak value of CH4 emission flux always showed in three stages, including tillering period, incubation period and break-up period. Both variations of CH4 emission flux under control irrigation and intermittent irrigation was less than the variation under basin irrigation mode. CH4 emission flux during early and late rice growing periods remained at low level and no CH4 emission was detected after seeding period and harvesting period. Under control irrigation and intermittent irrigation modes, accumulated CH4 emission had a very small variation. Accumulated CH4 emission under basin irrigation showed a notable variation（p<0.05） by the range of 284.34419.27 kg'hm-2. With a same level of fertilizer, accumulated CH4 emission under basin irrigation mode is higher than emission under control irrigation and intermittent irrigation modes. Seasonally accumulated CH4 emission had less relative relationship with soil p H value. Under basin irrigation mode, CH4 emission flux had less relative relationship with soil p H value, except for the CH4 emission of unfertilized treatment. CH4 emission flux under treatments C1N1, C1N3 and C1N4 has less notable relative relationship with soil nitrate nitrogen concentration. CH4 emission flux of other treatment all had notably relative relationship with soil’s nitrate nitrogen concentration. CH4 emission in rice paddy has a close relationship with environmental factors and will be obviously influenced by meteorological factors. Most concentrated period of CH4 emission occurred at when the average daily temperature is relatively high. CH4 emission has a negatively relationship with soil Eh and a notably positively relationship with 5 cm soil temperature and irrigation water depth.（2）During rice growing season, the peak value of N2 O emission showed in both tilleringsunning and elongation-incubation periods. However, N2 O emission showed a lower level during seeding-tillering and post field sunning periods. During earlier growth period, N2 O emission under all treatment conditions remained a lower level. There is barely any N2 O emission during field soaking period. N2 O emission increased slightly after the tillering period. N2 O emission had a slightly rising and showed the peak value during the rehydration period coming after the field sunning period. Seasonal accumulated N2 O emission under control irrigation and intermittent irrigation were obviously higher than treatments under basin irrigation mode. Accumulated N2 O emission of the whole growing period has the highest level under C2N1 treatment, reaching 0.41 kg'hm-2 and the lowest level under C3N2 and C3N4 treatments, reaching 0.14 kg'hm-2. Rice paddy field’s N2 O emission was increased under the intermittent irrigation mode. Water control and nitrogen fertilizer respectively has a close relationship with average N2 O emission flux during growing period and seasonal accumulated N2 O emission. N2 O emission will be increased as the temperature become higher. N2 O emission flux under different water and fertilizer treatments has no relationship with soil’s content of NH4+-N. N2 O emission flux under C1N2 treatment has a negatively relationship with soil p H valve. N2 O emission flux under C3N1 treatment has a positively relationship with soil p H value. There is no relationship between the N2 O emission flux and soil p H value under other treatments. N2 O emission has a negatively relationship with soil EH and has no notably relationship with 5cm soil temperature and irrigation water depth.（3）The CO2 emission flux showed peak value during tillering period and elongationincubation period, had a relatively low level of emission in other growing periods and rise slightly in harvest period. Water control mode has no regular influence on rice average CO2 emission flux during growing period and accumulated emission. Under same level of fertilizer treatment, compared to basin irrigation mode, the accumulated CO2 emission of control irrigation and intermittent irrigation modes are declined. Water control and nitrogen fertilizer have an interactive relationship with average seasonally growing CO2 emission and season accumulated emission. Meteorology is also an important factor having influence on field’s CO2 emission. Soil content of ammonium nitrogen has no relative relationship with CO2 emission flux. C1N2 treatment is the only one which has a significantly different relationship with soil content of ammonium nitrogen（p<0.05）. Soil content of nitrate nitrogen under different treatment modes has on relative relationship with CO2 emission flux. Soil content of nitrate nitrogen under control irrigation mode has a positive relationship with CO2 emission flux. Soil content of nitrate nitrogen under intermittent irrigation and basin irrigation modes has a slightly negative relationship with CO2 emission flux. Under control irrigation mode, CO2 emission flux of different treatments has a negative relationship with soil p H value. C1N1 reached extremely notable level and C1N2 reached notable level. CO2 emission has notably relationship with 5cm soil temperature and no relationship with irrigation water depth. CO2 emission was strongly influenced by rice biological factor and has a positive relationship with the quantity of biomass above the rice paddy field.（4）Rice yield will be notably increased by utilizing water-saving irrigation combined with nitrogenous fertilizer. Single irrigation mode has no obvious influence on rice yield. Under control irrigation mode, compared to treatment without nitrogen fertilizer, average yield of high application of nitrogen treatment（C1N1） will be increased by 62.9%. Average yield of medium application of nitrogen treatment（C1N2） will be increased by 64.7%. Under High application of nitrogen fertilizer will also greatly help to increase the rice yield. Interactive treatment between water and fertilizer will mainly affect the number of productive ears. Under same irrigation mode, the increasing of nitrogen fertilizer will promote growing of rice seed and increase the yield of rice straw which will help to improve the overall gain in yield.（5）Under different water and nitrogen treatment, the variation of CO2 emission per unit output has no regular characteristics. Under same irrigation mode, the increasing of fertilizer will decrease the CH4 emission per unit output. Compared to control irrigation and intermittent irrigation, CH4 emission per unit output under basin irrigation mode has a higher level and reached a peak value 48.66 g·kg-1under C3N4 treatment. CO2 emission per unit under different water and nitrogen treatment has no obvious variation, but irrigation mode has a slight influence on the N2 O emission.（6）Rotation treatment between water and nitrogen has a slight effect on the water and nitrogen efficiencies. Under same utilization rate of nitrogen fertilizer, the utilization rate of water follows the sequence as below, from high to low, control irrigation, intermittent irrigation and basin irrigation. Under same level of water treatment, rice’s utilization rate of water will be increased by the increasing of fertilizer. The utilization rate of water will be increased with the growing of nitrogen fertilizer within limits, but the yield rate and the utilization rate of water wont’ be continuously increased when the nitrogen utilization reached the specific level. Under same irrigation mode, the variation of fertilizer will greatly influence the utilization rate of rice nitrogen fertilizer. Water and nitrogen treatment has no obviously regular characteristics on rice physiological utilization rate of nitrogen fertilizer. Variation of agricultural utilization rate has similar characteristics with the utilization rate of nitrogen. Under same irrigation mode, the increasing of nitrogen fertilizer will cause the downtrend of rice partial productive force on nitrogen fertilizer. Water control and the quantity of nitrogen fertilizer has an interactive relationship with all indicators of the nitrogen use efficiency which reached a significance level（p<0.01）.（7）Compared to greenhouse effect caused by CO2 and N2 O emission, greenhouse effect caused by CH4 emission has a higher level. Greenhouse effect caused by CO2 has a range within 1824.222187.7 kg CO2·hm-2, but greenhouse effect caused by CH2 has a higher range within 4545.968804.75 kg CO2·hm-2. Greenhouse effect caused by CH4 emission contributes over 71% of over warming potential. Greenhouse effect caused by CH4 is 3.28 times of the values caused by CO2 and 76.4 times of the value caused by NO2. By analyzing the overall warming potential, the variation of different water and nitrogen treatment ranged from 5850.91 to 10581.95 kg CO2·hm-2. Under same irrigation mode, different nitrogen treatment’s variation of overall greenhouse effect is almost negligible. Irrigation mode has a slight effect on overall warming potential. Compared to control irrigation and intermittent irrigation, the GWP under basin irrigation mode has a higher level.（8）Aiming at climate characteristics of cold paddy in Heilongjiang province, the model of CH4 and N2 O emission in rice growing season was established under control irrigation, intermittent irrigation and flood irrigation mode. After establish models, the N2 O and CH4 emission flux of season can be simulated and prediction according to the content of NO3—N in soil and single factor or double factor of temperature. The parameters of models are few, so models are convenient application and practical. Application of models can provide decision support for management control of greenhouse gas emissions in Heilongjiang cold rice production.Combined with appropriate utilization of nitrogen fertilizer, water saving irrigation mode will increase rice yield, improve the utilization rate of water and nitrogen, and effectively reduce the overall greenhouse effect caused by CO2, CH4 and N2 O. In Heilongjiang cold rice cropping region, rice yield and greenhouse effect shall be comprehensively taken into consideration and irrigation modes also need to be focused. |
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