Farmyard Manure


Animal manures are an excellent source of plant nutrients. Approximately 70-80% of the nitrogen, 60-85% of the phosphorus and 80-90% of the potassium in feeds is excreted in the manure. The amount of nutrients available for recycling to plants varies widely being dependent upon the composition of the feed ration, the amount of bedding and water added or lost, the method of manure collection and storage, the method of land application, and characteristics of the soil, crop and climate. Manure contains all the plant nutrients needed for crop growth including trace elements.  The availability or efficiency of manure utilization by a crop is determined by the method of application, time to incorporation and the rate of manure decomposition by microorganisms in soil.

 Manure contains stable and unstable forms of nitrogen.  Unstable N occurs in urine as urea and may account for more than 50% of the total N in manure.  Urea changes rapidly to ammonium ions then quickly to ammonia as pH increases and manure begins to dry. Ammonia is extremely volatile resulting in N loss.  Nearly all the ammonium N can be lost from surface applied manure if it is not incorporated within a few days (Table 1). As for example, 25 tons/acre of dairy manure containing 8 lbs N/ton (from analysis) applied, and incorporated the same day, will give approximately 120 lbs N/acre available the year of application. Even though 200 lbs of N would be added to the soil, only 60% of that N is available the first year with the remainder becoming available in subsequent years from the more stable organic N fraction. However, if  manure incorporation  is delayed 7 or more days  only 40 lbs  N/acre  will  be  available;

80 lbs N/acre will have been loss to the atmosphere.

Table 1. Nitrogen availability as influenced by time of incorporation.



                                                        % nitrogen available

  Manure application                         Poultry            Other      


  Applied in spring (current year)

        incorporated same day                       75                    60

        incorporated 2-4 days                         45                    40

        incorporated 5-6 days                         30                    30

        incorporated > 7 days                         15                    20


  Applied in fall, no cover crop                   15                    20

  Applied in fall, with cover crop                50                    40


* adapted from the University of Minnesota and Pennsylvania State University



The more stable organic N occurs in the feces and is slowly released. Approximately 40-50% of the stable organic N will be available the first year, 12-15% of the N remaining the year after, 5-6% in the third year and lessor amounts in each subsequent year.  These figures are approximations and could  vary   in   different   Massachusetts locations due to variations in the rate of microorganism breakdown and climate.  The decay series is only for the stable organic N and does not include the urea or ammonium N which is 100% available the first year if not lost as ammonia.

When manure is applied at a rate to supply the N need of a corn crop, the P and K will likely be in excess of the crop requirement. Essentially all of the K is available for plant growth the year manure is applied.  However, some of the P may be in the form of insoluble inorganic compounds or as organic  P and, like stable organic N must be mineralized before it is available.  

Timing and method of manure application determine the efficiency of nutrient recycling. Incorporating manure immediately minimizes odors and ammonia loss. If manure supplies more N than needed then some ammonia loss is unimportant. However, it is better to apply manure to more acres than to apply an excess to fewer acres. 

Manure must be spread uniformly to get consistent results. Applying and incorporating manure too early for the crop, and in the fall or early winter in high rainfall areas, could result in N loss and groundwater contamination.  Likewise surface runoff and soil erosion must be controlled to protect surface waters.  A cover crop planted early (late August to mid September) can be effective in reducing nitrogen leaching through plant uptake (Table 1), and in controlling surface erosion. To save money and to protect the environment avoid over applications.


Stephen J. Herbert

Dept. of Plant and Soil Sciences

University of Massachusetts Amherst

Crops, Dairy, Livestock News. Vol. 3:1 Spring 1998

Adapted from various Northeast Publications


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Last updated: 11/11/02.