Estimation Of N₂O Emissions From Cropland In Sichuan And Chongqing

In recent years, as one of the micro conponents in atmosphere, N₂O is given attentions to in all of the world. N₂O absorbs the thermal radiation comes from the land, and reduces the thermal radiation that goes out of the troposphere, consequently it produces the greenhouse effect. The temperature increasing effect of N₂O is 280～310 times as many as CO₂. Not only chemical processes and biochemical processes in natural ecosystems, but also human activities including the use of inorganic nitrogenous fertilizer, croplands irrigation and cultivation, organism conbustion, the production of nitric acid and adipic acid, and mineral conbustion that cause N₂G emissions to the air, especially the fertilized cropland who approximately account for 18% of the total contrived direct N₂O emission, is considered as the principal part of contrived direct N₂O emission source, the ratio in China is much higher. Human activity made the concetration of N₂O in atmosphere rise fast from approximately 275ppbv before industrial revolution to 317ppbv. And In the past half century, the rising is especially rapid. Agricultural soil produce approximately 4.2TgN/aN₂O, about half of which is generate from direct emission. As the need of grain caused by the growing population increasing, the use of inorganic nitrogenous fertilizer will rise each year. N₂O emission amount also has a tendency to increase. From a long-term point of view, the research of N₂O is much more pressing.At present, in the estimating of N₂O emission from cropland, the activity datas of N₂O is the provincial level. In order to get the datas of N₂O emissions amount and flux from the cropland, and the informations of N₂O emission in different area and different type of croplands in Sichuan province and Chongqing, with the correction of rainfall average and temperature average to the N₂O activity datas, the IAP-N model which is based on IPCC is used to estimate the N₂O emissions from croplands in Sichuan and Chongqing and from the year 1990 to 2004, The conclusions as follows:The total emissions of N₂O and N₂O flux are on the rise in the fifteen years. In The total emissions of N₂O in each year from the year 1990 to 2004 are: 39255.45, 40011.74, 40670.95, 43382.38, 42087.77, 43850.34, 43566.87, 39929.23, 61130.81, 54081.34, 50667.93, 48636.66, 57497.75, 55711.65, 58696.46(tN/a).The high N₂O emission area is around the boundary of Sichuan and Chongqing, and this is accord with the high multiple-cropping index in the Sichuan Basin. Panzhihua, Ganzi and Aba which are located in western Sichuan province are the lowest cropland N₂O emission area.The highest N₂O emission cropland type is upland crop planting(paddy-upland crop rotation), while the lowest is single-paddy+winter water flooding. The general N₂O emission amount of different cropland types are arranged as follow:Non-vegetable field > paddy-upland crop rotation (the whole period) > vegetable field > all types of paddy field(the whole period). The N₂O emission amount in upland crop planting(paddy-upland crop rotation) is much more than paddy crop planting(paddy-upland crop rotation). The gradation of three different types of paddy fields' N₂O emission amount is single-paddy+fallow > double-paddys+fallow > single-paddy+winter water flooding. In paddy field, the N₂O direct emission was restrained by water. Compared the year 2004 to the year 1990, the biggest space-time change of N₂O emissions is in non-vegetable field and upland crop planting(paddy-upland crop rotation), while the smallest is in single-paddy+winter water flooding.The result of the estimating method(IAP-N model) which take cropland type into consideration is lower than the method which not.In order to get better control of cropland N₂O emissions, the measures were suggested such as study the appropriate nitrogenous fertilizer amount of the soil and crops in agricultural area with high multiple-cropping index, advance the fertilizer use ratio of soil by ploughingless, and improve the cropland eco-system N₂O estimating modeis.