Poultry litter (or poultry manure) is an excellent source of nutrients that can be incorporated into many cropping systems in North Carolina. Producers using poultry litter must practice sound soil fertility management to prevent nutrient imbalances as well as surface water and groundwater contamination. The key to successful management is to match the nutrient requirements of the crop with nutrients available in the litter. Determining the economic value of poultry litter varies not only by its nutrient composition and availability, but also with management and handling costs.

Nutrient Composition and Sampling Procedure

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The nutrient composition of poultry litter varies, depending on the type and life stage of bird, feed ration, proportion of bedding to droppings, manure handling system, and type of litter (cake versus whole house). Consequently, all litters should be sampled and analyzed to determine the actual nutrient content before you apply them to the land. Waste samples can be analyzed for $8 through the North Carolina Department of Agriculture & Consumer Services (NCDA&CS) Agronomic Division, Plant and Waste Analysis Lab. For more information, call 919-733-2655 or visit the NCDA&CS Agronomic Services—Waste/Compost Analysis web page. Other qualified private laboratories can also perform the analysis (fees vary).

Collecting a representative litter sample is essential to reliable nutrient analysis. The nutrient value of litter varies greatly by its location in the poultry house. To reduce sample variability, collect subsamples of litter from 10 to 12 areas of the house. Samples taken around waterers, feeders, and brooders should be proportionate to the space these areas occupy in the house. At each location, collect litter from the surface down to the soil, assuming all of the litter will be removed and land-applied (whole-house cleanout). Be careful, however, not to include soil. Place the subsamples in a clean plastic bucket, mix thoroughly, and transfer approximately 1 pint of the mixture to a sample container. Take samples of stockpiled litter from 10 to 12 locations around the pile, sampling to a depth of at least 18 inches. Mix subsamples thoroughly and submit them for analysis.

To increase sample uniformity in poultry manure slurries and lagoon sludges, stir them before sampling. Within an anaerobic lagoon, liquids are relatively uniform above the sludge zone; nevertheless, take several subsamples and combine them, making sure to collect subsamples at least 6 feet from the lagoon bank to a depth of about 1 foot.

For new operations requiring a nutrient management plan, use the mean nutrient values for your specific type of poultry manure found on the Nutrient Management in North Carolina website to estimate acreage required to utilize all of the litter produced by the facility. While these averages can be used for initial nutrient management planning, actual waste analyses should determine the application rates.

Be careful to avoid overfertilization or underfertilization based on average values for manure nutrient composition, as these averages may not accurately represent the litter produced by your operation. Also keep in mind that in fields with long-term repeated manure application, elements such as copper or zinc may accumulate and reach very high levels, which can cause severe plant toxicity. To avoid problems, use a current waste analysis and soil test report to monitor nutrient levels and make application decisions. Avoid planting peanuts in fields with a zinc-index above 300, and never plant peanuts when the zinc-index is above 500. When the zinc or copper indices hit 2000, start considering alternative application areas; when the index exceeds 3000, you will need to discontinue applying manure or any other amendments containing zinc or copper. Average values for micronutrients in poultry litters, poultry lagoon sludge, poultry lagoon liquid, and poultry composts can be found in Table 1.

Table 1. Average secondary and micronutrient content of poultry manures.

Nutrient Availabilities

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Nitrogen takes several forms in poultry litters, each of which can be lost when subjected to different environmental conditions or management practices. Nitrogen in poultry wastes comes from uric acid, ammonia salts, and organic (fecal) matter. The predominant form is uric acid, which readily transforms to ammonia (NH₃), a gaseous form of nitrogen that can volatilize to the atmosphere if not mixed into the soil. When poultry litter is incorporated into the soil, the ammonia changes to ammonium (NH₄⁺), which can be temporarily held on clay particles and organic matter. Thus, soil mixing or manure injection can reduce gaseous nitrogen losses and increase the amount of available nitrogen for plants.

Not all manure nutrients are immediately available for plant uptake. Determine the available nutrients by multiplying the availability coefficient (found at Nutrient Management in North Carolina’s Plant Availability Coefficient web page) for various poultry manures by the nutrient content listed on the waste analysis report or on the Nutrient Management in North Carolina’s Manure Nutrient Content web page. As stated, broiler litter contains 57.8 pounds of total nitrogen, and the availability coefficient is 0.5 for broadcast application. If a producer applies 1 ton of litter per acre using a broadcast spinner spreader, the litter will provide 28.9 pounds of plant available nitrogen per acre for the receiving crop.

NCDA&CS’s Agronomic Division includes the plant available nutrients for the first crop on its waste report. Therefore, there is no need to make this adjustment if your sample has been analyzed by NCDA&CS. Be aware that other laboratories may list total nitrogen and require adjustment using the availability coefficient. If you are unsure whether the lab has listed available nitrogen, contact your county Cooperative Extension center for assistance.

Application Rates

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Land application rates of manure are determined by matching the available nitrogen or phosphorus content of the wastes to the nutrient requirements of the crop to be planted. In most cases, nitrogen determines the application rate. Nitrogen recommendations for various crops are determined using the soil type and crop rotation. Use the Realistic Yield Expectation (RYE) website. To determine the RYE, select your county and the dominant soil type found in your field. Next, use the resulting table to find the RYE and Realistic Nitrogen Rate for your crop. Use the Realistic Nitrogen Rate and your waste analysis to identify allowable nitrogen-based manure application rates. In feed and forage crops, excessive manure application can produce high nutrient concentrations (phosphorus, potassium, zinc, copper) in soils and plants, which can reduce the yield and quality of crops or result in water quality impairment.

If a facility is required to run the Phosphorus Loss Assessment Tool (PLAT), a rating of “high” would require phosphorus-based management, and a rating of “very high” would allow for no further application. More information on facilities required to run PLAT can be found in the NC State Extension’s SoilFacts publication The North Carolina Phosphorus Loss Assessment Tool (PLAT). When running the PLAT analysis, conservation practices implemented on your farm will affect the calculated risk of phosphorus loss to the environment. These conservation practices include, but are not limited to, buffer strips, contour planting, controlled drainage, and reduced tillage. Leaching of phosphorus is limited in the piedmont and mountain regions of the state and therefore should not contribute to groundwater contamination, though leaching has been known to occur in sandy soils. Deep soil sampling may be required, depending on the soil series and soil-test phosphorus level. NC State Extension’s SoilFacts publication Deep Soil Sampling for Nutrient Management describes protocols for deep soil sampling. For nonlegume crops, phosphorus-based manure application will not supply adequate nitrogen to meet the RYE; supplemental commercial fertilizer will be required.

In feed and forage crops, excessive manure application can produce high nitrate concentrations, which can harm livestock (through nitrate poisoning) and promote nutrient imbalances. If application rates are based on phosphorus, apply the amount suggested by soil test recommendations or the rate at which phosphorus will be removed by the crop. Because manure may not supply adequate amounts of all other nutrients required by the crop, be sure to take a soil test and, if necessary, supplement with commercial fertilizer for nutrients other than nitrogen. The maximum allowable nitrogen rate is determined using the RYE nitrogen rate or yield records.

Besides the correct application of nutrients, proper soil pH is required to improve crop yields and ensure nutrient availability. The biological conversion of ammonium to nitrate is an acid-forming process that will continue to reduce soil pH unless you follow an adequate sampling and liming program, although often manures can increase the pH of soil.

A worksheet is provided to help you determine land application rates.

Timing and Uniformity of Manure Applications

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Besides carefully calculating the application rate, you must also minimize the delay between applying the manure and planting the crop. Precise timing increases the amount of nitrogen the crop uses and can reduce the risk of nitrogen loss via leaching. Apply manure only to an actively growing crop—within 30 days of planting or within 30 days of breaking dormancy. On sandy-textured soils, apply manures at low rates throughout the growing season, wherever possible, to reduce nitrogen leaching.

Use caution when applying lagoon liquid through irrigation onto standing crops that are undergoing stresses, as the salt concentration can cause additional problems.

Whether poultry waste is applied by manure spreaders or irrigation systems, you must apply it uniformly. A lack of uniformity leads to nutrient imbalances within the field, which can result in reduced yields or quality. It is vital to calibrate spreading equipment to maintain uniformity within the spreading pattern and to pay special attention to maintaining the appropriate swath spacing during application. Spreader calibration can also help you identify any mechanical problems with spreader equipment. If you have any questions about how to calibrate your spreader, contact your county Cooperative Extension Center or regional Area Specialized Agent in Poultry.

Manure Processing

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There are several options for poultry manure processing. The processing goals are to improve manure characteristics (density, nutrient availability, nutrient profile, and energy content) to make its utilization easier or to create value-added products from manure. These products include compost, biogas, thermal energy (heat), biochar, and acidified poultry manure. The choice of processing method depends on resources available on the farm (such as space, labor, capital, equipment, and fields to utilize the manure) and also market demand for these products.

Manure composting is a low-cost, aerobic biological process that reduces manure volume, pathogens, and odor and creates a soil amendment for crop fields, pastures, and lawns. Depending on poultry manure composition, adding a carbon-rich material (for example, straw or wood chips) might be necessary to ensure favorable carbon-to-nitrogen (C/N) ratio, between 20 and 30, to initiate the process. Alternatively, poultry manure can be treated in a digester using anaerobic digestion (AD) to generate a gaseous fuel (biogas). The biogas can be combusted to generate heat or electricity for local use, or it can be cleaned and injected into a natural gas pipeline as a transportation fuel. Note that digesting manure also generates a biologically degraded manure fraction (digestate) that requires nutrient analysis and planning before the digestate can be used in crop production. The high ammonia (NH₃) content in poultry manure can inhibit anaerobic digestion and either must be blended with low-NH₃ feedstocks or a treatment step must be included to reduce the ammonia content.

In addition to biological processes, poultry manure is a suitable feedstock for thermal processing such as pyrolysis, gasification, and combustion. Poultry litter has a low moisture content (<30%) and medium energy content (4,500 to 7,000 Btu/lb), which improves the process energy balance. These processes use high temperature and controlled air levels to generate thermal energy (heat) or gaseous fuels (syngas), depending on the process conditions. Thermal processing technologies significantly reduce the manure volume by converting it to char or ash that can be shipped and incorporated with mineral fertilizer for wider distribution. Key considerations with these technologies are (1) equipment cost and maintenance, which can be significant, and (2) gas cleanup after conversion due to the high nitrogen (N) and chlorine (Cl), which create harmful air emissions if left untreated. Depending on the choice of processing technology, operators need to consult specialists and regulatory agencies such as the N.C. Department of Environmental Quality (DEQ) to learn about regulations relevant to this process (if they exist) and whether any testing is required for the byproducts (compost, biochar, ash) prior to implementation and byproduct distribution.

Acreage Requirements for New Facilities

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Whenever litter samples are available for analysis, they should be used to determine application rates and acreage requirements. When you are planning new facilities, however, the average values can help determine approximate acreage requirements for a poultry operation of a given size. Based on the soil types found within the application areas, RYE and nutrient requirements can be determined, providing an estimate of how many acres are required for the flock size.

Suppose that a producer located in Wilkes County is interested in building two broiler houses with a combined 50,000 bird capacity/growout. The producer is planning to spread this litter on fescue hay fields with a Braddock clay loam soil type, which produces 5.7 tons/ac (RYE). The fescue will require 239 pounds plant available nitrogen (PAN) per acre. How many acres of fescue would be needed for the entire year’s waste? For every 1,000 broilers, 7.2 tons of litter is produced annually from whole-house cleanout. For a 50,000-bird growout operation, the producer would need to acquire enough acreage to apply 360 tons per year. Therefore, the producer would need 39.2 acres for a year’s worth of litter (360 tons of litter produced annually × 52 lb N/ton × 0.5 availability for surface application ÷ 239 lb PAN/ac).

Value of Manure

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To compare the value of manure to commercial fertilizer, convert total manure nutrients to available nutrients by using the availability coefficients. Consider the following example: analysis of the available nitrogen, phosphorus (P₂O₅), and potassium (K₂O) content in a broiler litter sample that will be incorporated shows that it contains 43 pounds of nitrogen per ton, 62 pounds of phosphate per ton, and 37 pounds of potash per ton. The current fertilizer prices for nitrogen, phosphate, and potash are: $0.45 per pound of nitrogen; $0.60 per pound of phosphate; and $0.22 per pound of potash as potassium chloride. One ton of broiler litter would be worth the following: (43 × $0.45) + (62 × $0.60) + (37 × $0.22) = $64.69 per ton.

The previous estimated value of the poultry litter does not include labor, hauling, handling, or application costs, nor does it include the value of other essential nutrients available in the manure. The estimate also assumes that the soil test has recommended each nutrient, though many of them may not be needed, such as the ratio of nitrogen to phosphorus in this example. Using total nutrient value will generally result in overestimating the dollar value of the manure. Consider only necessary nutrients when assessing the financial value of the manure.

Acknowledgments

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This publication is a revision of an earlier version. The authors would like to thank D. A. Crouse, J. C. Barker, T. A. Carter, and J. P. Zublena for their earlier contributions. The authors wish to acknowledge the assistance and cooperation of the North Carolina Department of Agriculture and Consumer Services Agronomic Division in analyzing samples and developing data used in this publication.

Authors

Steph Kulesza Assistant Professor & Extension Specialist – Nutrient Management & Animal Waste
Crop & Soil Sciences

Mahmoud Sharara Waste Management Extension Specialist and Assistant Professor
Biological & Agricultural Engineering