Fffects Of Straw Returing And Irrigation Condition On Yield Formation Of Super Japonica Rice And Emission Of Greenhouse Gases From Paddy Field

The research was conducted in the experimental farms of Yangzhou University from2012to2013.Wheat was used as the test material in the past, and this research set three factors:types、straw returning and irrigation modes. Nanjing44and Wuyunjing24were the two types of rice. The research used two kinds of straw returning methods: the full amount of straw to field and no straw returning, the amount of straw returning is calculated as hectare yield of6.75t hm-1of wheat. Irrigation modes were divided into routine irrigation mode and switching from wet and dry mode. Straw returning and irrigation modes formulate four combinations: routine irrigation straw not to field, routine irrigation with full amount of straw to field, alternating wet and dry not return to field and alternating wet and dry with full amount of straw to field.Under the routine irrigation mode, rice should be kept in shallow layer after transplanting, and was rested in fields (until soil has cracks) again in enough seedling (seedling is about240000),then rebuild shallow layer after it until10days before maturity. Under the alternating wet and dry mode, rice should be irrigated in shallow water after transplanting, and was exposed at night in the field for7-10days(still in the shallow layer in day).When tillers reach about80%of the expected amounts(about20000),rice should be rested in field for1-3times. After that, irrigation mode ought to be kept as alternating wet and dry, but put wet as the first priority until filling stage (about20days after heading).After filling stage, the research kept alternating wet and dry mode but it gave preference to dry till maturity. The main research findings are as follows:1、Obvious differences exist between the theoretical yields and actual outputs of different field processing rice:Wet straw> No straw dry> Straw-General>No straw General; As far as different panicle numbers in each processing unit area is concerned, Wet straw was the largest, followed by No straw dry and No straw General, while the Straw-General was the lowest; Grain number per spike and1000-grain weight have the same law as Wet straw came first, followed by No straw dry and Straw-General, while No straw General came last. And there is no obvious difference exists in different processed seed setting rates.2、Different dry weights of processed single stems have the following law during the whole fertility cycle:Wet straw is the largest, while No straw General is the smallest. Group dry weight has no obvious differences before jointing. However, after jointing, Wet straw came the first place, followed by No straw dry and straw-General, while No straw General came last. And the differences between them become larger as the advancement of growth process. The law of rice leaf area and photosynthetic potential with different processes before jointing is under the order of decreasing: Wet straw、No straw dry、straw-General and No straw general. The photosynthetic potential also decreases from jointing to heading stage, but population growth rate and net assimilation rate vary a little. The effective rice leas areas of distinct processed rice during their heading stages shows no obvious difference, while high-efficient leaf area show especially obvious differences:Wet straw is extremely higher than No straw dry and straw-General, and the latter two are extremely higher than No straw general. After heading stage, the leaf area index、photosynthetic potential、population growth rate and net assimilation rate are all the same: Wet straw is the largest and No straw general is the smallest.3、With different planting methods in rice growing season, the emission of CH4and CO2firstly increase but then reduce as a result, while emission of N2O has three emission peaks during growth season. The emission of CH4focused on transplanting period to critical stage of tillering, with its accumulated emission accounts for 45.06-58.55%of its total emission during the whole growth period. The emission of CO2focused on heading stage to maturity stage, and the accumulated emission accounts for34.81-37.36%of its total emission during the whole growth period. The emission of N2O focused on transplanting period to critical stage of tillering, critical stage of tillering to jointing stage. And from heading stage to maturity stage, the accumulated emission is relatively high, and there is little variation between each stage.Under the straw returning condition, wet and dry irrigation reduced CH4emission, but it increased the emission of CO2and N2O.And in the early stage, the increased use of N Fertilizer significantly increased N2O emission. In the growth period, there was a significant negative correlation between the seasonal changes of CH4emission and soil Eh, but there was a significant positive correlation between N2O emission and soil Eh. However, there was no significant correlation between the seasonal changes of CO2emission and soil Eh. Straw returning and increased use of N Fertilizer increased green gas emission in the early stage, but100on an annual basis, compared with common irrigation, wet and dry irrigation reduced Global Warming Potential (GWP) and GWP per unit of production. In a word, under the condition of straw returning and increased use of N Fertilizer, wet and dry irrigation not only guarantee high productivity but also significantly reduced the green gas emission.