| Methane (CH4) and nitrous oxide (N20) are two important trace gases, which are considered to have 15-30 and 150-200 times more radiatively active than C02, respectively. It is well known that agricultural soils are the major sources of atmospheric CR4 and N20. Several studies have identified some parameters that affect the rates of Cl-it and N20 emission, including soil properties, climate, agricultural practices, such as water regime and management and organic matter amendment, and plant physiology. IPCC(1996) reported that global wanning potentials (GWP) of CR4 and N20 are different. More recent results from fieldwork showed that mitigation strategies for CR4 flux, such as mid-season drainage, might have the opposite effect on N20 emission. In addition, organic matter applied such as winter wheat straw can greatly enhance CR4 emission, but the effect of organic matter amendment on N20 emission is unclear. So the quantitative dependence of Cl-it and N20 emission from paddy soils on different agricultural managements is still far from being understood. The main objectives of this fieldwork are to validate the feasibility of drainage during rice growing seasons as a mitigation strategy, to compare the effect of organic matter application on CR4 and N20 emissions from rice field under different water regimes, and to quantify the impact of planting density on N20 emission from winter wheat field. Field experiments were performed in a rice-wheat rotation system during 1999-2000 seasons. The experimental field was selected in the county of Jinagning near Nanjing of Jiangsu province, China, located at latitude 31~ 52扤, longitude 11 8 50扙. The average air temperature in June through October was 24.40(2 during 1999 rice-growing season and 25.70Cduring 2000 rice-growing season. The total rainfall was 696.5mm in 1999 and 428.7mm in 2000 nce-growing season. The soil was classified as Hydromonohic with clay percentage of 49%. Amounts of soil organic carbon, total nitrogen, phosphorous and potassium in the cultivation layer are 19.4gkg? 1 .9gkg? 1 .3gP2O5kg?and lO2mgK2Okg? respectively. Soil pH (H20) is 6.7. 3 Ajaponica cultivar named #9516 was planted on May 14th, 1999 and on May 30th, 2000. The cross treatments were given to compare the effect of organic application on CH4 and N20 emission under the conditions of normal irrigation and permanent flooding. Two plots received previous crop (winter wheat) straw at the rates of approximately 2.25 and 4.Stlha before transplanting and one plot in the same field had no additional organic matter incorporated under the two water regimes. The transplanting date was June 21St during 1999 rice-growing season and June 29th during 2000 rice-growing season, and heading occurred on September 5th, 1999 and September 3rd, 2000. The plants were harvested on October 20th, 1999 and October 22nd, 2000. Permanent flooding was initiated 3 days in 1999 and 36days in 2000 before transplanting, and field remained flooded until 10 days before harvest. Chemical fertilizer (total of 300kgNIha) was applied at transplanting (55%), elongation (28%) and booting (17%) during the 1999 flee-growing season. For the 2000 rice-growing season, 44%, 25%, 19% and 12% of nitrogen fertilizer (total of 277 kgN/ha) were applied at transplanting, tillering, jointing and panicle differentiation, respectively. During the two-year rice field experiments, the emissions of CH4 and N20 we...
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