There is no surer sign of spring in the countryside than the evidence from our noses of manure application in full swing.
Odour complaints occur every year, especially where urban settlements border livestock farms. Although manure odour is inconvenient, most farms do consider wind direction and make an effort to apply and incorporate manure as quickly as possible to minimize odours. Some farms are also looking at manure additives to help control odours.
The combination of livestock species, feed ration and manure storages result in hundreds of complex compounds that can produce odorous gases. Some of these gases are dangerous, while others are just unpleasant. The control of manure odours is a complex issue that requires a combination of control strategies at the barn, in storage and during field application. Manure additives represent one practice that can be useful in a comprehensive strategy for avoiding or reducing odour.
Innovative treatment strategies such as anaerobic digestion and solids separation can help manage odour, and while effective, these treatments are expensive. Manure additives are popular because they are relatively easy to use. Many commercial additives are advertised to reduce manure odours, however, no product will control all odours. A variety of products, such as pH modifiers, acidifiers, oxidizers, digestive additives, oxidizing agents, disinfectants, adsorbents, enzyme inhibitors, and combinations of these, will impact some, but not all compounds in the manure. Additives can result in the reduction of hydrogen sulphide, and/or ammonium nitrogen, or oxidizing organic compounds, or change the microbial composition of manure, but none of these changes will eliminate all odours.
While there are many testimonials claiming odour reduction, few additives have been evaluated under controlled, unbiased conditions or tested for cost effectiveness. Cost of additives can range from 30 cents to 62 dollars per 100 gallons of fresh waste. Testing is difficult, and where studies have been done, results show that odor reduction is inconsistent, temporary, or sometimes nonexistent.
Practices that can reduce the unpleasantness for neighbours include incorporation soon after application, or application when wind direction is away from residences and neighbourhoods. The best way to reduce phosphorous and nitrogen losses to the environment is to apply manure during the growing season and onto standing crops. Unfortunately, summer application is more odorous than winter applications. Manure stinks, but if we want clean snow and clean rivers and lakes, we may just have to learn to live with the smell of the fresh country air during the growing season.