Animal Manures for Increasing Organic Matter and Supplying Nutrients

Once cheap fertilizers became widely available after World War II, many farmers, extension agents, and scientists looked down their noses at manure. People thought more about how to get rid of manure than how to put it to good use. In fact, some scientists tried to find out the absolute maximum amount of manure that could be applied to an acre without reducing crop yields. Some farmers who didn’t want to spread manure actually piled it next to a stream and hoped that next spring’s flood waters would wash it away. We now know that manure, like money, is better spread around than concentrated in a few places. The economic contribution of farm manures can be considerable. On a national basis, the manure from 100 million cattle, 60 million hogs, and 9 billion chickens contains about 23 million tons of nitrogen. At a value of 50 cents per pound, that works out to a value of about $25 billion for just the N contained in animal manures. The value of the nutrients in manure from a 100-cow dairy farm may exceed $20,000 per year; manure from a 100-sow farrow-to-finish operation is worth about $16,000; and manure from a 20,000bird broiler operation is worth about $6,000. The other benefits to soil organic matter buildup, such as enhanced soil structure and better diversity and activity of soil organisms, may double the value of the manure. If you’re not getting the full fertility benefit from manures on your farm, you may be wasting money.

Animal manures can have very different properties, depending on the animal species, feed, bedding, handling, and manure-storage practices. The amounts of nutrients in the manure that become available to crops also depend on what time of year the manure is applied and how quickly it is worked into the soil. In addition, the influence of manure on soil organic matter and plant growth is influenced by soil type. In other words, it’s impossible to give blanket manure application recommendations. They need to be tailored for every situation.

We’ll start the discussion with dairy cow manure but will also offer information about the handling, characteristics, and uses of some other animal manures.