The smells of spring in Vermont can be magical, but there are days when they can be downright disgusting. Those days are when the local dairy farm is spreading liquid manure.

In the old days, and on some small farms today, manure was spread as a solid, and solid manure has an entirely different smell from the modern stench of ammonia and sulfides emanating from an agitating manure pit. Solid manure has the chance to breathe as it accumulates in a pile. Gases escape into the air from manure piles, but they are in small quantities and blend with other smells. While we wax wistfully of the wafting fragrance of old time manure, it is useful to reflect on why that bucolic nasal image is no longer a reality.

The story is complicated beginning with the evolution of barns along with the changing diet of cows over the last 50 years. In the 1960s almost all cows in Vermont were still housed in barns with either stanchions (where cows are kept in place with a loose-fitting vice mechanism around their necks that allows limited motion) or tie stalls (where a chain is hooked to a collar around the cow’s neck, allowing more freedom of motion than a stanchion). Everything the cows ate was carried to them. For example, on the farm where I worked as a teenager, we pulled baled hay out of the central hay mow (rhymes with now), broke up the bale in the feed alley in front of the stanchions, and distributed the hay to the cows. At milking time we pushed a wheeled cart full of grain around the barn, ladling out portions to each cow. The farm had two upright silos where corn silage was stored, so we also filled a cart with silage and doled that out. That was it. The bulk of their diet through the winter was the dry hay.

The drier a cow’s diet, the drier is their manure. Cows were liberally bedded with sawdust, which in those days was a cheap and plentiful waste product of Vermont’s many sawmills and wood processing businesses. The combination of fairly dry manure and plenty of sawdust yielded an easily stackable mixture that stayed aerobic in the pile.

The vision of a red Vermont barn where the cows are nice and comfy in their warm barn is a false vision. In reality, most of those barns were too warm for cow comfort and poorly ventilated which led to respiratory diseases. The cows stayed locked up and were milked in place, which led to other problems. As farms increased in size, the old style barns required too much labor to be tenable.

In about 1970, the Routhiers in Bloomfield built what I think was the first open “free-stall” barn in the Northeast Kingdom. Bloomfield (on the Connecticut River south of Colebrook, N.H.) is the coldest town in Vermont, and fellow farmers thought they were crazy. The design of the barn allowed cold air to circulate through the barn and it turned out that the cows thrived in the colder environment. The cows were also allowed to roam around the open barn, and had access to stalls where they could lie down for a nap or a good chew on their cud. At feeding time they strolled over to a long concrete trough where their food was distributed and they could eat at their leisure. Their feed was delivered not by a hand cart, but by a tractor pulling a mechanical cart that unloaded itself as the tractor drove down the alley. Today most cows live in this type of barn.

Dairy nutritionists have refined the bovine diet continuously over the years, striving for a healthier and more productive balance of ingredients that would support ever increasing milk production. Most cows now eat a TMR, or total mixed ration, which consists of the various feeds produced on the farm, blended with supplements such as grain, which are purchased off the farm. The ration is mostly silage, either corn or grass, which is much wetter than dry hay. Silage is more easily digestible than dry hay, lacking the coarse fiber, resulting in manure that is much wetter. Less bedding is needed in free stall barns, and most now bed with sand instead of sawdust, which has become a rare and expensive commodity. All of this means that modern dairy manure will not stack and must be contained somehow when it is pushed out of the barn.

Until the 1980s the majority of Vermont farmers spread manure into the winter, as long as their tractors could navigate the snow. In the spring a good portion of that manure ran off the fields as the snow melted. Lake Champlain was in trouble and regulations were needed. In 1995, the State banned the spreading of manure from December 15 to April 1. It became imperative that dairy farms build manure pits to store all that unstackable manure through the winter. The heavy initial investment to build the pits was shared by taxpayers through programs offered first by USDA and later supplemented by the State of Vermont. Today, almost every dairy farm in Vermont has a liquid manure pit.


Last year a set of Required Agricultural Practices (RAPs) was adopted in Vermont. With regard to manure, they ban the spreading of manure on frozen, snow covered, or saturated ground, no matter the date. On March 31st, The Vermont Agency of Agriculture sent out an email to all dairy farmers, reminding them that there was still snow on the ground and more in the air, and the new RAPs do not allow the spreading of manure on snow, period. The idea is that precipitation needs a chance to infiltrate the ground, carrying the nutrients in the manure down into the soil rather than off the field into the nearest stream, lake, or well. No manure is to be spread within 100 feet of a private water supply or 200 feet from a public water supply, nor within 25 feet of the top of bank of surface water. Manure is not to be stacked within 200 feet of the top of bank of surface water, nor within 200 feet of a public or private water supply, nor within 100 feet of a property line. The next step is enforcement of the RAPs, which will rely on regular inspections by the State and on citizen complaints.

By May spring is here and all those pits must be emptied. The first step is agitation because in a manure pit, some separation takes place over the several months of storage. Often, a crust forms on top where sun and wind dry out the top layer. Where sand is used for bedding, the sand settles to the bottom of the pit. So when it is time to spread manure, the pit must be mixed up, or agitated. Modern dairy manure is over 90% liquid, and most of the volume of a manure pit stays anaerobic until agitated. As the farmer backs the long shaft of the agitator pump into the pit and starts it up, a suite of gases begins to be released and our noses begin to wrinkle.

The four main gases produced from decomposing manure are hydrogen sulfide, methane, ammonia, and carbon dioxide. Methane is the only one that is lighter than air, and is also odorless, so it floats up into the atmosphere, unnoticed except by climate scientists. Hydrogen sulfide produces the rotten egg smell and hangs close to the ground until a good breeze can mix it with clean air and dilute the smell. Ammonia is the sharp, penetrating component of the smell. Carbon dioxide displaces oxygen but is hard to detect and not really a factor in the smell of manure.

The release of all that gas is the subject of much debate and research, and I expect our noses will detect an evolution over the next twenty years as the emphasis shifts from water pollution to air pollution. For instance, a number of large farms in Vermont have installed (at great expense) manure digesters to utilize the gases to generate heat and electricity, in the process separating the solids from the liquids. The final product spread on the fields has little odor. Other lower tech possibilities are also in the pipeline. Sniffing through my crystal nose, I won’t be surprised to see regulations someday requiring the capture of gases from manure pits. For now, we are stuck with the smell for a few days each year and must take consolation from the fact that the manure is being recycled into the soil to fertilize the corn and hay that will feed the cows that produce the milk we consume.

Tim McKay is a conservationist, tree farmer, furniture maker, and writer who has lived in Peacham since 1977. Tim retired in 2010 from a career with the USDA Natural Resources Conservation Service field office in St Johnsbury.