Animal Manures and Biosolids on Forages
Considering the high cost of commercial fertilizers, applying animal manures, poultry litter and biosolids in pastures may be a valuable alternative for forage production. These waste products not only provide essential nutrients, but can also add organic matter to improve structure, aeration and water-holding capacity of soil. Research in Oklahoma has shown that poultry litter is comparable to commercial fertilizers in increasing bermudagrass forage yields and crude protein.
Before considering these products, we need to understand some basic management issues. The following guidelines need to be followed for application and development of a proper nutrient management plan for animal waste products in pasture production.
- Nitrogen (N) is mostly in its organic form in litter or manures. The rate it mineralizes into an inorganic form depends on the prevailing environmental conditions. We normally estimate about 50 percent, 15 percent and 6 percent of N in manure is available during the first, second and third years, respectively. When applying manure to the same field year after year, credit for nitrogen should be given for the previous year's application. About 90 percent of phosphorus (P) and potassium are available during the first year of application. Excess application can result in phosphorus buildup in the soils and may contaminate water through leaching and runoff.
- Representative soil and waste product samples are needed for accurate nutrient analysis. The soil and waste product analyses along with realistic yield goals are necessary to calculate required rate of application for the waste product. Moisture content of manure or litter should be taken into consideration when calculating the application rate since the analysis is usually on a dry matter basis.
- Nutrient application should be based on soil P test recommendations. Even though litter or manure N:P ratio is almost 1:1, bermudagrass uses N and P in an approximate 4:1 ratio. Supplementation with commercial N fertilizers is a safe and effective method for supplying the required amount of nitrogen to meet yield goals without over-applying phosphorus.
- Application should coincide with the growing season for the target forage crop. Typically, for warm- season forages, it is best to apply in spring or summer as mineralization of the nitrogen will take place more readily if temperatures are above 50°F.
- Better results can be expected from soil incorporation of waste products immediately after application. Unless it is incorporated or washed into the soil through irrigation or rain within a few days, approximately 25 percent of the total N applied can be lost through volatilization, or evaporation, into the atmosphere.
- Nutrient content of waste products varies with type of material, how and how long it is stored, and this should be reflected in price. Proper storage is essential to maintain fertilizer value, minimize health hazards and prevent pollution of surface and ground waters.
- Transportation costs associated with procurement and applying waste products can be prohibitive if the forages are located far from the source. Compare the cost of waste products as delivered and spread against commercial fertilizers supplying the same quantity of nutrients.
- Calibrate the application equipment to obtain the correct rate and distribution of the waste product.
- Avoid application of manure or litter to slopes greater than 15 percent and before heavy rain to avoid runoff.
- Be courteous to neighbors who might be disturbed by a manure or litter application. Notify them in advance, and do not apply on windy days. Inform them that the odor is not harmful and should not last long.
- Utilize grass buffer strips between the application sites and water sources. Do not apply manures or litter within 150 feet of water wells, streams, rivers or lakes.