Using manure as a nutrient source
By David G. Hallauer
Meadowlark District Extension Agent, Crops and Soils/Horticulture
For some producers, manure can be a vital nutrient source for crop land or forages. Fully understanding its value as a phosphorus source does take some effort, however. What do you need to know?
Nutrient Value: The total phosphorus content in manure varies depending on the animal species, age, diet, and how stored. Phosphorous levels in some manures (poultry, for example) may be up to 80 to 90 pounds P2O5 per ton. Others may be as low as 4 pounds P2O5 per ton. Either way, a laboratory analysis is the best way to determine exactly what you are working with. When applying, think in terms of actual P rates, not gallons or tons per acre.
Availability: A large fraction of the P in manure is considered plant available during the first year after application. The fraction not plant available will become potentially available over time. Estimated availability differs based on soil test. When applied properly, P manure is comparable to inorganic fertilizer P for crop production.
Losses: Excessive application of manure P can result in excessive soil P buildup and potential surface water contamination. You can minimize this potential by applying manure to cover P needs of the crop and using inorganic sources of fertilizer to complement nitrogen needs, constantly monitoring soil test P levels, and using the P- index to assess the potential impact of P buildup on water quality. Avoid storage where runoff to surface water sources is an issue and avoid application on snow-covered or frozen soils. Manure incorporation where possible is advised.
Application: Uniform application at precise rates can be difficult. Calibration of manure applicators is a necessity so that P application rates are accurate. If applied properly, manure is a great P, AND micro/macronutrient source.
For more information, see K-State Research and Extension publication MF-2562, "Estimating Manure Nutrient Availability," at www.ksre.ksu.edu/library/crpsl2/mf2562.pdf.