AGRI-BRIEFS   AGRONOMIC NEWS ITEMS

From Agronomists of the Potash & Phosphate Institute 655 Engineering Drive, Suite 110 Norcross, Georgia 30092-2837 Phone (770) 447-0335

Winter 2002, No. 3

Animal manures have been applied to soil since ancient times. Although many important chemical, physical, and biological benefits accrue from manure additions to soil, a number of factors combine to make the use of animal manures economically and environmentally inefficient.

Although their use as a nutrient source and soil amendment is well documented, there are many unresolved questions regarding their most appropriate use. The perceived value of animal manure has changed in many parts of the country from a valuable product to a waste material that requires disposal.

To assist growers in utilizing animal manure as part of a fertility program, consider three essential components:

Total manure	-------------->	Manure nutrients	-------------->	Crop-available
nutrients produced		after storage losses		manure nutrients

Returning manures to crop fields can be a valuable part of the cropping system if the nutrient content of the manure is known, an estimate of the plant availability is made, and soil testing is performed to keep nutrients in balance.

• Nitrogen has generally received the most attention of the nutrients found in manure. This organic material can function as an excellent slow-release source of nitrogen when it decomposes. However, it is difficult to accurately predict the speed with which the microorganisms will carry out this process. When errors are made with estimating the nutrient content or the rate of breakdown, poor crop growth and serious environmental problems may result.

• Manure can be an excellent source of phosphorus when applied properly. Special attention should be made to avoid over-application of phosphorus in nutrient-sensitive watersheds. Much of the manure phosphorus may be present in organic compounds that require breakdown before the plants can utilize it.

• Potassium in manure is typically available immediately for plant uptake and does not pose any environmental concerns.

Production of high quality forages and feed are an essential component to fuel the rapidly expanding animal industry. Forages remove large amounts of nutrients from soil—nutrients that must be returned in order to achieve sustainability and high levels of productivity. Animal manures are generally more difficult to manage than traditional fertilizers, but they are an important part of every animal production system, and require careful attention. A major goal of everyone in agriculture is to produce abundant, healthy food on productive farms that make minimal environmental impacts. Proper manure management can play an important role in achieving this goal.