Liquid manure is preferred to solid manure as a handling form large swine and dairy cattle operations. Liquid manure is cheaper to store and manipulate, it offers a great level of mineralized nutrients readily absorbed by the plants, when applied as a soil fertilizer, and it nitrogen conservation potential is improved through its higher water content. But, liquid manure produces obnoxious odours. Much work has been conducted over the past ten years to understand how manure odours are produced and how they can be controlled.
Liquid manure produces obnoxious odours when exposed to both an aerobic and anaerobic phase. The aerobic phase produces oxidized S (sulphur) compounds which feed the S reducing reactions occurring in the anaerobic phase. The human nose is especially sensitive to low molecular weight compounds containing reduced S, being able to detect them even diluted by a factor of 1010. Thus, aerating or maintaining complete anaerobic conditions will minimize the production of odorous gases from liquid manure.
Solutions to the manure odour emission problem are therefore: in the feed management, improve protein digestibility, because the S compounds are found in proteins; once the manure are produced, either use an aerobic or anaerobic treatment. Improving feed management is profitable while treating the manure always costs while bringing very little gain. Half of the odour problems are caused during manure spreading because of the intensity of the odour, while 30% come from the storage facility and 20% from the shelter. The general rule to odour control are: move the waste out of the livestock shelter as soon as it is produced; treat before storage, either under aerobic or anaerobic conditions; and spread as low to the soil as possible or better still, inject into the soil when applying to cropped land. To reduce manure treatment cost, in storage systems are being developed and anaerobic treatment is particularly well suited for this.
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