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Nutrient Availability In Poultry Manure

Dec 22, 2017
By Peter Tomlinson
Environmental Quality Specialist
 
Poultry litter can provide a significant and important supply of nutrients for crop production in areas of Kansas where a supply of litter is available. Although Kansas is not a major producer of poultry, there is an abundant supply of litter from the nearby states of Arkansas, Missouri, and Oklahoma, which rank among the largest producers of poultry in the U.S. The acreage available to receive poultry litter has been declining in Arkansas, Missouri, and Oklahoma in recent years because of environmental concerns and nutrient management regulations. That trend, coupled with high fertilizer prices, has meant the availability of litter to areas such as southeast Kansas has been on the rise.
 
Poultry litter should serve as an excellent complement to commercial nitrogen (N) fertilizers. Phosphorus (P) content in poultry litter is usually high, and applications rates should be based on P levels to avoid potential surface water contamination.
 
Table 1. Types and properties of poultry litter

Source

Typical moisture
content

Typical nutrient content
(lb per ton)

  

N

P2O5

K2O

Layer

High

35

40

20

Pullet

Low

40

45

40

Breeder

High

40

60

40

Turkey

Low

60

60

55

Broiler

Low

60

60

55

 
Moisture content and nutrient concentration in poultry litter can be highly variable and depends mainly upon production conditions, storage, and handling methods. Therefore, laboratory analysis is the best way to determine the level of N and P in the material to be applied. Table 1 presents average values of moisture and nutrient content for the different types of poultry manure collected over a period of time. The graph (Figure 1) presents the actual laboratory analysis of 213 poultry manure samples from southeast Kansas. There is a large range in nutrient values, likely due to the source of the litter. However, a good sample average to expect would be a 56-53-46.
 
Figure 1. Results of analysis of 213 samples of poultry manure from southeast Kansas. 
 
For maximum efficiency of manure use, it is essential to know the nutrient content of the manure. Using a manure lab analysis will help in determining the actual nutrient rates applied. A laboratory analysis should be done on the poultry litter before applying it to land. A laboratory analyses provides information regarding nutrient levels, as well as the chemical forms of these nutrients. This information is necessary for an adequate estimation of nutrient availability and application rates. For more information, see K State Extension publication MF-2562, “Estimating Manure Nutrient Availability,” at: http://www.ksre.ksu.edu/bookstore/pubs/MF2562.pdf
 
Nitrogen availability
 
A common question with poultry litter application is how much N and P will be available to the crop shortly after application. In the case of N, it is important to consider that this nutrient is primarily in the organic form in poultry litter (up to 75-80% organic N). Organic N needs to mineralize into inorganic forms before becoming available to crops. A fraction of this organic N may become part of the soil organic matter pool and unavailable to crops in the short term.
 
Field and laboratory studies suggest the fraction of total nitrogen that becomes plant available the first year of application is approximately 45-55%, which includes both the inorganic N in the manure and a percentage of the organic N. This value varies depending upon components in the litter, and the method of handling and application. For example, poultry litter that contains a large fraction of bedding material will tend to have lower N availability the year of application. Reduction in N availability may also occur when litter is aged and has undergone some level of composting. Nitrogen lost from the volatile ammonium fraction at the time of application to the soil surface can also reduce plant available N. Ammonium volatilization is typically higher during windy and warm days. Incorporation of litter immediately after application will reduce volatilization and potential nutrient loss by water runoff in case of a rainfall event, in addition to reducing the odor of the litter.
 
If the manure is applied to pastures, the percentage of N utilized by the forage the first year will depend on whether the pasture consists of cool-season or warm-season grasses. For cool-season grasses, such as fescue pasture, N utilization will likely be less than 50% the first year. Most of the growth in cool-season pasture occurs early in the year. The microbial community will not mineralize as much N early in the spring as they will later in the summer. Fall applications may result in better N utilization for fescue than winter or spring applications. For warm-season grasses, such as bermudagrass pasture, nitrogen utilization from manure will likely be close to 50%. In both cases, producers should base application rates on the P and potassium (K) needs of the grass, and supplement additional N fertilizer to meet the N needs of the grass.
 
Phosphorus and potassium availability
 
When manure is applied to the soil, what percentage of this P and K is available to the crop during the first year?
 
A large fraction of the P in manure is considered to be plant available immediately after application. The fraction that is not plant available shortly after application will become available over time.
 
Estimated values of P availability are from 50 to 100%. This range accounts for variation in sampling and analysis, and for P requirements with different soil test levels. Use the lower end of the range of P availability values (50%) for soils testing “Very Low” and “Low” (below 20 ppm) in phosphorus. In these situations, large yield loss could occur if insufficient P is applied and soil P buildup is desirable.
 
On the other hand, use 100% availability when manure is applied to maintain soil test P in the “Optimum” soil test category, and when the probability of a yield response is small.
 
Several studies have shown that manure P is a valuable resource, comparable to inorganic fertilizer P for crop production. These two P sources are similarly effective when the manure P concentration is known and the manure is applied properly.
 
Nevertheless, excessive application of manure P (for example, applying manure at rates sufficient to meet the crop’s nitrogen needs) often results in excessive soil P buildup over time, resulting in higher risk of surface water contamination. This problem of excessive P buildup in the long-term can be minimized by:
  • Applying manure to meet the 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 potential impact of phosphorus buildup on water quality.
Producers should think in terms of actual phosphorus application rates and not just tons per acre of manure being applied. Uniform application of manure at precise rates can also be difficult. Careful calibration of manure applicators is needed. If these aspects are not considered, the efficiency of manure P compared with inorganic fertilizer P may be reduced. Careful management pays off.
 
Availability of potassium is usually near 100% with proper application. Poultry litter can also provide significant amounts of secondary and micronutrients.