| Nitrous oxide(N2O) and methane(CH4) originated from animal production in agriculture are major contributors to the global greenhouse gas budget and the emitted ammonia(NH3) from animal production is also major pollutants to atmospheric, water and soils. N2 O, CH4 and NH3 emissions from China’s beef industry ranked in the very front at the respective global scale. However, the lack of integrative researches on the emission patterns, emission factors and driving forces of N2 O, CH4 and NH3 emissions for China’s beef industry have caused large difficulty when identifying potential mitigation practices and evaluating their respective mitigation potentials. Consequently, characterizing diurnal emission patterns of N2 O, CH4 and NH3 at beef operation scale as well as estimating their emission intensities are not only necessary to provide useful techniques and recommendations for the sustainability of China beef production, and is also very helpful for the other animal production in China.In this study, a self-designed automatic sampling device, open-path tunable diode laser and an inverse dispersion technique were used to quantify N2 O, CH4 and NH3 emissions of two intensive beef feedlots in the North China Plain either with restricted feeding strategy or ad libitum feeding strategy. Field measurements were carried out from September 3rd to 28 th 2013 and from May 16 th to June 12 th 2014 in restricted feeding strategy beef feedlot and from October 21 th to November 19 th 2013 and from March 15 th to April 11 th 2014 in ad libitum feeding strategy beef feedlot. The impact of feeding strategies and manure collection frequence on diurnal emission patterns of N2 O, CH4 and NH3, their emission intensities and conversion factors were calculated accordingly. Meanwhile, soil samples(0-100 cm) within the experimental beef feedlots as well as their adjancet arable lands were collected to examaine the difference of vertical N distribution under different agricultural sites and to investigate the risk of N leaching underneath beef feedlot. The main results are in below:1. The N2 O emissions from beef feedlot vary largely and are characterized with a certain diurnal pattern. The N2 O emissions peak value occurs at 10:30am from September 3rd to 28 th 2013, and peaked at 8:30 am-16:30 pm from May 16 th to June 12 th 2014 and their respective daily N2 O emission rates were 7.5 g/head/d and 10.9 g/head/d, and their conversion factors were estimated to be 2.5% and 3.7%, respectively. While for the feedlot with ad libitum feeding strategy, the nitrous oxide emission peaks occurred during 08:00 am to 17:30 pm in October 21 th to November 19 th 2013 and March 15 th to April 11 th in 2014. The daily N2 O emission rate was 12.99 g/head/d and 29.42 g/head/d, respectively, and their conversion factors were estimated to be approximately 5.2% and 11.7%, respectively.2. The CH4 emissions of beef feedlots under different feeding strategies were observed with large variations and different diunal patterns. Results showed that for the feedlot with restricted feeding strategy, the hourly CH4 emission rates varied from 6.2 g/head/h to 12.4 g/head/h in September 2013 and 7.0 g/head/h to 13.6 g/head/h in May 2014, and the daily emission rate of CH4 was 219 g/head/d and 240 g/head/d, respectively, during two measurement periods. Diurnal pattern characterized with two emission peaks occurring at 9:30 am and 17:30 pm during a day were obtained, and such diurnal patterns of CH4 emissions generally corresponded with the feeding schedule. The conversion factor Ym for enteric CH4 was estimated to be approximately 6.5% and 7.1%, respectively. While for the feedlot with ad libitum strategy, the hourly CH4 emission rates varied from 2.6 g/head/h to 15.5 g/head/h and from 5.3 g/head/h to 10.8 g/head/h during two measurement priods. A diurnal pattern characterized with only one emission peak during a day from 8:00 to 18:00 was found. The daily emission rate of CH4 was 204 g/head/d and 192 g/head/d, and their respective conversion factors Ym for enteric CH4 was estimated to be approximately 6.9% and 6.5%, respectively.3. Apparent diurnal pattern of NH3 emissions from beef feedlots were also identified. There was only one NH3 emission peak at 10:00 am to 14:00 pm. The daily emission rate of NH3 were estimated to be 172 g/head/d and 157 g/head/d, respectively, during two measurement periods, and the corresponding conversion factors of emitted NH3 to feed N were estimated to be 75.3% and 68.8%, respectively.4. Comparison of N distribution between feedlot and adjancent arable lands indicated that, in general, total N and NO3-N of all layers in the beef feedlots are significantly greater than their adjancent lands and the order is: feeding zone>excersing zone>arable lands, which were reusted from the large raising dencity and long-term stacking of feedlot manure. Such might hint a risk that the accumulated NO3-N might penetrate to subground water through leaching caused by heavy precipitations. |
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