for Increasing Organic Matter and
Supplying Nutrients
The quickest way to rebuild a poor soil is to practice
dairy farming, growing forage crops, buying . . .
grain rich in protein, handling the manure properly,
and returning it to the soil promptly.
— J. L. HILLS, C. H. JONES, AND C. CUTLER, 1908
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.
The value of the nutrients in manure from a 70- cow dairy farm may exceed $7,000 per year; manure from a 50-sow farrow-to-finish operation is worth about $4,000; and manure from a 20,000- bird broiler operation is worth about $3,000. The other benefits to soil organic matter build-up, 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, 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 organ 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 deal mainly with dairy cow manure, because there’s more information about its use on cropland. We’ll also offer general information about the characteristics and uses of some other animal manures.
MANURE HANDLING SYSTEMS
Solid versus Liquid
The type of barn on the farmstead frequently determines how manure is handled on a dairy farm. Dairy-cow manure containing a fair amount of bedding, usually around 13 to 20 percent dry matter, is spread as a solid. This is most common on farms where cows are kept in individual stanchions. Liquid manure-handling systems are common where animals are kept in a “free stall” barn with little bedding. Liquid manure is usually in the range of from 2 to 10 percent dry matter (90 percent or more water). Manures with characteristics between solid and liquid are usually referred to as semi-solid or slurry, depending on the method of handling.
Composting manures is becoming an increasingly popular option for farmers. By composting manure you help stabilize nutrients, have a smaller amount of material to spread, and have a more pleasant material to spread (and if neighbors have complained about manure odors, that might be a big plus). Although it’s easier to compost manure that has been handled as a solid, some farmers are separating the solids from liquid manure and then irrigating with the liquid and composting the solids.
Storage of Manure
Researchers have been investigating how best to store manure to reduce the problems that come with year-round manure spreading. Storage allows the farmer to apply manure when it’s best for the crop and during appropriate weather conditions. This reduces nutrient loss from the manure caused by water runoff from the field. However, significant losses of nutrients from stored manure also may occur. One study found that, during the year, dairy manure stored in uncovered piles lost 3 percent of the solids, 10 percent of the nitrogen, 3 percent of the phosphorus, and 20 percent of the potassium. Covered piles or well-contained liquid systems, which tend to form a crust on the surface, do a better job of conserving the nutrients and solids than unprotected piles. Poultry manure, with its high amount of ammonium, may lose 50 percent of its nitrogen during storage as ammonia gas volatilizes, unless precautions are taken to conserve nitrogen.
CHEMICAL CHARACTERISTICS
OF MANURES
A high percentage of the nutrients in feeds passes right through animals and ends up in their manure. Over 70 percent of the nitrogen, 60 percent of the phosphorus, and 80 percent of the potassium in feeds may be available in manures for use on cropland. In addition to the nitrogen, phosphorus, and potassium contributions given in table 9.1, manures also contain significant amounts of other nutrients, such as calcium, magnesium, and sulfur. In regions where the micronutrient zinc tends to be deficient, there is rarely any deficiency on soils receiving regular manure applications.
Differences in feeds, mineral supplements, bedding materials, and storage systems make manure analysis quite variable. Yet, as long as feeding, bedding, and storage practices remain unchanged on a given farm, manure characteristics will be similar from year to year. The major difference among all the manures is that poultry manure is significantly higher in nitrogen and phosphorus than the other manure types. This is partially due to the difference in feeds given poultry versus other farm animals.
The relatively high percentage of dry matter in poultry manure is also partially responsible for the higher analyses of certain nutrients, when expressed on a wet ton basis.
It is possible to take the guesswork out of estimating manure characteristics; most soil-testing laboratories will now analyze manure. Manure analysis should become a routine part of the soil fertility management program on animal- based farms.
( Building Soil For Better Crops - Fred Magdoff and Harold van Es)
