If you drove around Iowa at all this spring you may have noticed an aroma. And not a pleasant aroma. An odorous aroma. Why does it smell so bad?
What you are smelling is possibly swine manure that has been spread out on fields. Luckily the smell is short lived and soon dissipates after farmers finish spreading the manure on their fields. But, why do they do that? What benefit is there from spreading manure on fields?
Plants need a series of nutrients to grow well and three of the most important nutrients that plants need are nitrogen, phosphorus and potassium or N-P-K. Manure is an excellent natural source of nitrogen. When spread on a field, it decomposes and acts as a fertilizer for the growing corn and soybean plants. These plants are able to put the nitrogen to good use. Using manure also saves farmers money. By using this natural form of fertilizer they don’t have to apply commercially produced nitrogen to their crops. Corn especially has positive increases in bushels per acre when manure is applied.
So how does that swine manure get from the hog barn to the field? It all starts with a farmer developing a Manure Management Plan that works best for their operation. A good plan will take into consideration soil tests, crop rotations, manure collection, manure storage, and manure transportation. Many hog barns are now built with slotted floors that allow manure to fall through the floor to collection points underneath. Some barns might scrape the floors regularly to keep the barns clean and collect the manure. Outdoor swine lots are scraped every week or two to control odor and ensure rainfall runoff stays mostly free of manure.
Once collected, manure is transported to a storage facility until it can be spread on cropland. Some manure is handled as a solid and can be transported by front end loader to truck. But a lot of swine manure is handled as a liquid and once collected is mixed with water that can be pumped through pipes to the storage facility. In liquid form it can also be more easily spread onto fields.
Many new swine facilities manage manure in underground pits or in sealed watertight structures rather than open pits or lagoons. This enclosed system obviously helps reduce the smell, but it also helps retain the nutrients. Open systems can lose up to half or three-quarters of the nitrogen in the manure. Closed systems might only lose a quarter of the nitrogen value.
Many farmers spread manure on fields in the spring. The manure has been collected throughout the winter. Spring application ensures that the nitrogen is readily available for those newly growing plants.
Solid waste is put on fields with a manure spreader. A conveyor belt carries the manure to beaters which flail the manure onto the field trying to evenly distribute it. Liquid manure can be pumped into trucks of up to 10,000 gallons. These tank wagons can spray the manure onto the field or inject the slurry directly into the ground. Injection helps reduce the odor, but it can only be done when the soil is not frozen or too rocky. Ultimately the goal is to get the manure onto the fields in an efficient and effective way.
So the next time you are driving around Iowa and crinkle your nose to the smell, think about the complex system that farmers manage to recycle manure and keep plants healthy with a great source of nitrogen.