Manure: Waste Turned to Benefit

Peter Wright
Animal Waste Specialist, Cornell University

As we drive around the farmlands of our state and particularly that of the Cayuga Lake watershed, we see and certainly smell freshly manured fields.

The farmer needs the by-product of his dairy herd, manure, to restore the fertility of his fields. It is these fields that provide the dairy cows with the feed that produces milk, the farm's product. And because dairy farming is a low margin business, that is, the cost of producing the product comes close to the income the farmer receives for the product, it is essential that the farmer use this fertilizer wisely to grow the crops that the cows eat that gives the milk that the farmer sells.

It is these crops of alfalfa, corn and grass that give us the open spaces, beautiful views, and wildlife that we all enjoy. Along with these crops there is an important need for lots of clean, fresh water. A dairy cow can easily consume 30 gallons of water a day during the summer. So farmers are vitally concerned about the soil and water that they use to grow their crops and produce their product of milk. Which translates to the fact that farmers are also vitally interested in the environment.

But as each cow will produce about 2.5 gallons of manure for every gallon of milk it produces, the farmer must control how this manure is stored and used to reduce the potential for pollution.

To reduce surface and ground water pollution, and to eliminate soil compaction that drastically cuts crop yields, more and more farms are avoiding spreading manure on rain-saturated ground. Manure nutrients are soluble and may move off the fields if saturated water leaves the field as surface water runoff, which flows into the lake, or by leaching into the ground water where most of us eventually get the water we drink.

By storing manure, farms can avoid spreading during wet conditions and spread more manure closer to when crops will take up the nutrients. Stored manure reacts biologically as it ages and decomposes. When this stored manure is emptied and applied to the fields as organic fertilizer, it creates the smell most of us find objectionable. The nutrient value of the manure doesn't cover the cost of transporting it very far. Trucking or pumping costs of a few miles can exceed the nutrient value of the manure. Farms then may apply the manure to nearby fields at higher rates than can safely be incorporated or than the plants can use. In those cases, farmers need to allow the nitrogen in the manure to escape into the air to avoid contaminating the ground water.

At lower spreading rates, farms can quickly mix the manure into the soil to reduce the time the manure gives off its odor. Doing this doesn't allow very much of the nitrogen to escape into the air, a good thing if you need the extra nitrogen for plant growth; but a bad thing if you are concerned that the extra nitrogen will convert biologically to nitrate and leach down into the ground water before the plants can use it.

Storing manure and leaving it on the surface after spreading can create odor problems but ultimately, this practice reduces the risk of water pollution and helps farmland remain in our watershed. The best solution environmentally is to use the manure over a larger area at rates that can safely be incorporated, with the added advantage of reducing dependence on purchased fertilizers.