Abstract
【Objectives】 A field experiment was conducted at Jiangjin District of Chongqing City, the differences and characteristics of methane(CH4) emissions as influenced by nitrogen fertilization were examined and evaluated under differentcropping systems which were originally derived from single rice system. 【Methods】 The main factor was three cropping systems: maize-wheat (MW), rice-wheat (RW) and rice-winter flooded fallow (RF) system. The subtreatments were N application levels: N0 (no N application), Nopt(96 kg/hm2 in wheat, 150 kg/hm2 in maize or rice) and Ncon (180 kg/hm2 in wheat, 225 kg/hm2 in maize or rice), respectively. in situ static chamber-gas chromatography system was used to collect and measure the emmision of CH4 in frequency of one to three times a week during the whole year’s experimental period.【Results】 The highest CH4 emissions was found in RF system while the lowest in MW cropping system. The annual average CH4 emissions from MW, RW and RF systems were CH4-C 13.5, 26.7, 89.8 kg/hm2 in the first experimetal year (2013/2014), and 0.8, 22.7, 236.3 kg/hm2 in the second year (2014/2015), respectively. N fertilization did not affect CH4 emissions significantly across three cropping systems except for treatment Nopt in RW and RF systems. In the first year, the CH4 fluxes of N0 treatemnts in the MW, RW, RF systems were respectively 17.7, 30.5, 85.7 kg/hm2, and those in Nopt treatments were 87.5%, 111.3%, 119.4%, and in Ncon treatments were 41.5%, 51.1%, 94.8% of corresponding N0 treatments, respectively. In the second year, the CH4 fluxes in N0 treatemnts of MW, RW, RF rotation systems were CH4-C 0.4, 26.0, 227.4 kg/hm2, respectively, and those in Nopt treatments were 240.4%, 103.9%, 104.9%, and in Ncon treatments were 229.6%, 58.6%, 100.1% of the corresponding N0 treatments, respectively. The net CH4 emissions were all occured from MW, RW and RF systems on average for two years’s period. In MW system, the highest emissions was measured in the maize season, averaged accounting for 87.7%, 87.2%, 76.2% of the system for the N0, Nopt and Ncon treatment, respectively; In RW system, the highest was in rice season, averagedly accounted for 91.4%, 95.7%, 94.9% of the system in the N0, Nopt and Ncon treatments, respectively; Similarly in the RF system, the highest emissions were in the rice season, accounted for 84.2%, 84.9%, 84.8% of those from the system for the N0, Nopt and Ncon treatments, respectively. CH4 emissions durning fertilizing periods accounted for 9%-32% of wheat growing seasons; CH4 emissions during fertilizing periods accounted for 6%-11% of maize growing seasons in the first year but 30%-45% of maize seasons in the second year; CH4 emissions during fertilizing periods accounted for 37%-50% of rice seasons in RW systems; CH4 emissions during fertilizing periods accounted for 21%-28% of rice growing seasons in RF systems. Flooded fallow seasons also contributed about 16% of annual CH4 emissions for RF system.【Conclusions】Total net emission of CH4 was highest in rice-flooding fallow system, followed by rice-wheat rotation system and the lowest in maize-wheat rotation system. In the first year after the single rice system was changed to maize-wheat rotation, there was an emission peak in the maize season, but not in the second year, and the total emission was similar in the two year’s time. In the second year of the rice-flooding fallowe system, the CH4 emissions increased significantly. The net CH4 emissions occured in all the three systems, and mianly in the maize or rice season. Nitrogen fertilization inhibited the CH4 fluxes in maize-wheat and rice-wheat rotation systems, but not in rice-flooding fallow system.
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