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Publication Date
1981
Description
Nitrogen-balance studies have shown losses of applied nitrogen (N) from grazed pastures in southeastern Queensland. Losses as high as 80% have been observed from urea N broadcast at 376 kg N/ha/yr over 8 years on a Setaria sp1uu:elata cv. Nandi pasture. Management techniques aimed at reducing this loss and thereby increasing the efficiency of use of N by pastures cannot be devised until the pathways of loss are known. The objective of this research was to estimate the annual ammonia (NH3) loss by convective transport from a urea-fertilized pasture at Samford Pasture Research Station in southeastern Queensland. Urea was broadcast onto a grazed pasture at 94 kg N/ha in February, May, August, and November 1978 and February 1979. Ammonia fluxes above the pasture were estimated by the momentum balance method, which uses micrometeorological measurements, and the NH3 concentration profiles in the air above the pasture. Fluxes were measured fo:r 24-hour periods on the day before urea application, on the day of application, and then on the second, fourth, seventh, tenth, fourteenth, and fiftieth days. Supporting soil data, including temperature, pH, water, and mineral N contents, were also obtained. The annual net loss was estimated to be 90. 7 kg N /ha, equivalent to 24 % of the applied N. Of that loss, 82 % occurred within 2 weeks of application. The greatest loss was from the May fertilizer application, when in 2 weeks losses were 42 % of the applied N, while on the other occasions lo&1es ranged from 9 % to 13 % . Days when there was a net gain of NH3 -N by the pasture from the atmosphere were common. This fact demonstrates that the pasture is both a source and a sink for atmospheric NH3• The estimated loss of 24% of applied N does not fully explain losses observed in previous work. Other loss pathways, including denitrification and leaching, now need to be assessed.
DOI
Ammonia volatilization, Setaria sphacelata, urea, cattle, nitrogen loss.
Citation
Catchpoole, V R.; Harper, L A.; and Keyers, R J.K, "Annual Losses of Ammonia from a Grazed Pasture Fertilized with Urea" (1981). IGC Proceedings (1981-2023). 7.
(URL: https://uknowledge.uky.edu/igc/1981/seection4/7)
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Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Annual Losses of Ammonia from a Grazed Pasture Fertilized with Urea
Nitrogen-balance studies have shown losses of applied nitrogen (N) from grazed pastures in southeastern Queensland. Losses as high as 80% have been observed from urea N broadcast at 376 kg N/ha/yr over 8 years on a Setaria sp1uu:elata cv. Nandi pasture. Management techniques aimed at reducing this loss and thereby increasing the efficiency of use of N by pastures cannot be devised until the pathways of loss are known. The objective of this research was to estimate the annual ammonia (NH3) loss by convective transport from a urea-fertilized pasture at Samford Pasture Research Station in southeastern Queensland. Urea was broadcast onto a grazed pasture at 94 kg N/ha in February, May, August, and November 1978 and February 1979. Ammonia fluxes above the pasture were estimated by the momentum balance method, which uses micrometeorological measurements, and the NH3 concentration profiles in the air above the pasture. Fluxes were measured fo:r 24-hour periods on the day before urea application, on the day of application, and then on the second, fourth, seventh, tenth, fourteenth, and fiftieth days. Supporting soil data, including temperature, pH, water, and mineral N contents, were also obtained. The annual net loss was estimated to be 90. 7 kg N /ha, equivalent to 24 % of the applied N. Of that loss, 82 % occurred within 2 weeks of application. The greatest loss was from the May fertilizer application, when in 2 weeks losses were 42 % of the applied N, while on the other occasions lo&1es ranged from 9 % to 13 % . Days when there was a net gain of NH3 -N by the pasture from the atmosphere were common. This fact demonstrates that the pasture is both a source and a sink for atmospheric NH3• The estimated loss of 24% of applied N does not fully explain losses observed in previous work. Other loss pathways, including denitrification and leaching, now need to be assessed.
