Harper L A, Denmead O T, Freney J R, Byers F M
Southern Piedmont Conservation Research Unit, JPCSNRCC-USDA-Agricultural Research Service, Watkinsville, GA 30677, USA.
J Anim Sci. 1999 Jun;77(6):1392-401. doi: 10.2527/1999.7761392x.
Methane (CH4) emissions from animals represent a significant contribution to anthropogenically produced radiatively active trace gases. Global and national CH4 budgets currently use predictive models based on emission data from laboratory experiments to estimate the magnitude of the animal source. This paper presents a method for measuring CH4 from animals under undisturbed field conditions and examines the performance of common models used to simulate field conditions. A micrometeorological mass difference technique was developed to measure CH4 production by cattle in pasture and feedlot conditions. Measurements were made continuously under field conditions, semiautomatically for several days, and the technique was virtually nonintrusive. The method permits a relatively large number of cattle to be sampled. Limitations include light winds (less than approximately 2 m/s), rapid wind direction changes, and high-precision CH4 gas concentration measurement. Methane production showed a marked periodicity, with greater emissions during periods of rumination as opposed to grazing. When the cattle were grazed on pasture, they produced .23 kg CH4 x animal(-1) x d(-1), which corresponded to the conversion of 7.7 to 8.4% of gross energy into CH4. When the same cattle were fed a highly digestible, high-grain diet, they produced .07 kg CH4 x animal(-1) x d(-1), corresponding to a conversion of only 1.9 to 2.2% of the feed energy to CH4. These measurements clearly document higher CH4 production (about four times) for cattle receiving low-quality, high-fiber diets than for cattle fed high-grain diets. The mass difference method provides a useful tool for "undisturbed" measurements on the influence of feedstuffs and nutritional management practices on CH4 production from animals and for developing improved management practice for enhanced environmental quality.
动物排放的甲烷（CH₄）是人为产生的辐射活性微量气体的重要组成部分。全球和国家的CH₄预算目前使用基于实验室实验排放数据的预测模型来估算动物源的排放量。本文介绍了一种在未受干扰的田间条件下测量动物CH₄排放的方法，并检验了用于模拟田间条件的常用模型的性能。开发了一种微气象质量差技术来测量牧场和饲养场条件下牛的CH₄排放量。在田间条件下连续进行测量，半自动测量数天，该技术几乎不具有侵入性。该方法允许对相对大量的牛进行采样。其局限性包括微风（小于约2米/秒）、风向快速变化以及高精度的CH₄气体浓度测量。甲烷排放呈现出明显的周期性，反刍期间的排放量高于放牧期间。当牛在牧场放牧时，它们产生0.23千克CH₄×动物⁻¹×天⁻¹，这相当于将7.7%至8.4%的总能转化为CH₄。当给同一批牛喂食易消化的高谷物日粮时，它们产生0.07千克CH₄×动物⁻¹×天⁻¹，仅相当于将1.9%至2.2%的饲料能量转化为CH₄。这些测量清楚地表明，食用低质量、高纤维日粮的牛产生的CH₄量（约为四倍）高于食用高谷物日粮的牛。质量差法为“不受干扰”地测量饲料和营养管理措施对动物CH₄产生的影响以及制定改善环境质量的管理措施提供了一个有用的工具。
