Abatement of nitrogen-based greenhouse gas emissions from beef feedlots

Summary

​One of the major issues facing the Australian feedlot industry into the future is the issue of rations supplying N contents greater than those required by the animal to maintain high levels of productivity. This practice can lead to increase emissions of ammonia and nitrous oxide from manures. Feeding elevated levels of crude protein in the ration did not alter the N efficiency of the animal but did lead to manures with higher labile N content. Direct ammonia emissions from feed pads may not differ between manures from animals offered contrasting N contents, but losses from the stockpile are greater from manures of animals offered elevated levels of crude protein in the feed. Lignite can be considered as a cost effective mitigation technology that can be applied to feedlot systems. The emissions of ammonia can be reduced substantially from the feed pad by using a rate of between 3 to 4 kg/m2 (based on economic analysis of a range of addition of lignite from 3 to 6 kg/m2 over a period of 56 day manure harvesting periods). In contrast to the manure harvested from pens managed under differing crude protein contents, lignite retained N in the stockpile and its subsequent use in cropping systems achieved good yield increases (approximately 63% physiological N response in relation to urea controls). This retention of N inevitably reduces overall ration costs as increased yields of forages grown on land receiving lignite amended manure can be recycled into the feed formulation at a lower cost than purchased-in feeds.