Short-term Emissions of Ammonia and Carbon Dioxide from Cattle Urine Contaminated Tropical Grassland Microcosm

The study was designed to understand the emissions of ammonia (NH₃) and carbon dioxide (CO₂) from a single cattle urination event on a tropical grassland and underline the significance of the emissions in the context of huge animal population grazing on large pasture areas in some countries. Emissions of ammonia (NH₃) and carbon dioxide (CO₂) were monitored for three weeks from a tropical grassland (dominated by Cynodon dactylon Pers.) microcosm contaminated with cow and buffalo urine. The grassland microcosms were treated with urine (50 and 100 ml of each) only once and irrigated with water once every week. Ammonia was sampled by an automatic sampling system comprising of a vacuum pump, three-way stopcocks and rubber tubing and an impinger containing suitable absorbing solution (H₂SO₄), connected to the tubing suitably. The sampled gas, after sucked by the vacuum pump and absorbed in H₂SO₄, was allowed to enter the closed microcosm again maintaining internal pressure of the microcosm. Carbon dioxide was sampled by absorption in an alkali (NaOH) trap inside the microcosm. Both NH₃ and CO₂ emissions were highly variable temporally and there was no continuous increasing or decreasing emission trend with time. Respectively, 45 and 46% of total NH₃-N were emitted within first 48 h from 50 and 100 ml cow urine application while the corresponding values for buffalo urine were 34 and 32%. Total NH₃-N emissions, integrated for sampling days (i.e. 1, 2, 3, 4, 6, 15, 18 and 21st) were 11 and 6% in cow and 8 and 5% in buffalo urine, of the total-N added through 50 and 100 ml urine samples. Carbon dioxide emissions were standardized at 25 ^∘C by using a suitable formula which were lower than actual emissions at actual soil temperature (> 25 ^∘C). Carbon dioxide emission rates were classified on the basis of soil repiratory classification and classes ranged from moderately low soil activity up to unusually high soil activity, the latter observed only on very few sampling days. Grasses in the microcosm had shown appreciable growth after urine application. Although variable and somewhat unpredictable, emissions were appreciable and that too only from a patch of single urination, indicating to the huge magnitude of total emissions under the scenario of thousands of cattle grazing on hundreds of acres of grasslands in a tropical country.