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Calculating the fertilizer value of manure from livestock operations EC 1094 Reprinted November 1993 J.A. Moore and M.J. Gamroth Do you want to print a copy? We recommend downloading the print version (803 K). First download the free Adobe Reader, if you don't already have it. Contents Benefits Hazards Plant nutrient content of manure Table 1--Total poduction and nutrient content Nutrient losses during collection and storage Table 2--Percentage of nutrient content retained Nutrients removed in solids Nutrient losses during field application Table 3--Percentage of nutrient content delivered Denitrification losses in the field Table 4--Percentage of nitrogen available to plants Availability of nutrients for crops Table 5--Rates of nutrients used Table 6--Application rates Calculating land application rates Livestock producers know that manure can be applied to croplands as a soil amendment as well as a fertilizer. This publication outlines a method for calculating appropriate manure application rates for particular crops and soil conditions. It also identifies losses of nutrients that can occur at different stages in the management and application system--from collection, through storage, to land application. The values represent the best available knowledge that we can suggest over a statewide area. Where you have specific values, such as from manure or soil analyses, you're encouraged to use them. A worksheet and example are included for your use (Calculating land application rates). Benefits Increased crop production can result when you add the nutrients contained in manure. A manure slurry will also provide some water to the soil. Adding manure to soil can lessen wind and water erosion, improve soil aeration and tilth, increase soil organic matter, and promote the growth of microorganisms that are beneficial to crops. Hazards On the other hand, excess applications of manure can be harmful to crops, soil, surface and ground water quality. In some cases (most commonly with fresh poultry manure) manure with high nitrogen content can burn crops. Heavy applications of manure also can cause excess accumulation of soluble salts in the soil, especially in some of eastern Oregon's arid regions, where little or no leaching occurs. High salt content in soil can decrease water availability, which inhibits plant growth. In addition, a large volume of manure in one application can cause temporary soil sealing, particularly in low spots. Soil sealing increases the potential hazard of manure runoff with any subsequent rainfall. top Plant nutrient content of manure A laboratory analysis of a representative manure sample will determine its nitrogen, phosphorus, and potassium (N-P-K) content. You can then calculate the economic value of the manure according to its plant nutrient content. Although other nutrients and trace elements in the manure are beneficial to crops, it's difficult to determine the value of that benefit. Sample the manure to determine the concentration of nutrients in storage. In liquid tanks, mix thoroughly before sampling or sample at different places in the storage unit to get a representative value. Mix these together and put a sample in a plastic jug or jar with a screw lid. Keep the sample in a cool location to prevent gas buildup and rupture of the container. A local feed store, county health department, or your county Extension agent can help you locate a laboratory that will analyze the sample. Some studies have been conducted on the production and nutrient content of fresh manures from farm animals (table 1). To find the total weight originally available, multiply the nutrient value from table 1 times the number of animals times the number of days the manure has been collected and stored. For a portion of the year, the animals may spend part of a day in an area where the manure will be collected, and the rest of the day out on pasture. When this applies, adjust the production values accordingly. For that period when the animals are pastured, use the grazing option to account for the nutrients handled in that way. Be sure to account for the manure produced for 365 days. top top Nutrient losses during collection and storage Nutrient losses from manure occur in collection, during storage, while spreading, and after land application. These losses vary widely--under some conditions, up to 70 or 80% of the initial concentration will be lost. Table 2 lists the percentage of original nutrient concentrations retained by various collection and storage methods. These values represent a range of values, and yours could be higher or lower, depending on several factors. In addition to the frequency and method of manure collection, the type of animal housing and handling system affects the final nutrient composition by influencing the addition of bedding, wastewater, and other materials. The duration, type, and location of storage also affect the final concentrations of nutrients in manure. Covered storage units generally are cooler and have less biological activity than open units. This usually means smaller losses from these units. Open storage units are subjected to precipitation, resulting in leaching and runoff. Less nitrogen, for example, is lost from deep pits and roofed areas that are protected from high temperatures and rainfall. From the animal source through field application, nitrogen is subject to the greatest losses of all the plant nutrients contained in manure. About 50% of the nitrogen in fresh manure is in the organic form and appears as partially digested feed and microorganisms. The other 50% is inorganic, usually as ammonia, and it's subject to significant losses during collection, storage, and application. In most manure management systems, 5 to 15% of the original phosphorus and potassium is lost in handling. In open lots, however, as much as 50% of the phosphorus and 40% of the potassium can be lost through runoff, leaching, and mixing with the soil on the lot surface. In lagoon systems, up to 80% of the phosphorus and nitrogen can be lost. Much of the phosphorus is in the sludge along the bottom--and very difficult to remove in normal emptying operations. You'll notice that earthen storage losses of nitrogen are much less than those from a lagoon. The basic reason is that a treatment lagoon is never emptied and is constantly undergoing biological breakdown, but an earthen storage unit will be emptied several times a year and applied to land. top Nutrients removed in solids Some operators use a liquid-solid separator to remove solids from the manure/wastewater slurry. If you remove the solids (or any other part of the manure) off farm, subtract that fraction from the amount of nutrients left to be applied to your crop land. A separator is capable of removing solids containing about 22% of the nitrogen, and 20% of both phosphorus and potassium. Don't use this calculation if you field-apply the solids to your land. top Nutrient losses during field application Nitrogen can volatilize when manure is spread on cropland (fresh manure odor is mostly volatilized ammonia). Essentially all the phosphorus and potassium applied will be available for the crop. Runoff can remove a portion of all three nutrients; however, this type of loss is very site-specific and is not included in these calculations. Table 3 outlines the percentage of original nutrient content delivered and available for plant use by various application methods. These figures represent both application and field losses before plant use (preutilization). top Denitrification losses in the field Nitrogen may also be lost by denitrification (loss of inorganic nitrogen by biological conversion to nitrogen gas). Anaerobic bacteria, which work in the absence of oxygen, break down nitrate nitrogen to release nitrogen gas; thus the more oxygen in the soil, the less nitrogen that is lost. This loss is related to the soil type and the rainfall pattern. Heavy, wet soils provide the ideal condition for maximum nitrogen loss through denitrification. Soil drainage rate is one of the factors used to calculate denitrification losses. For denitrification to occur, the nitrogen must first be oxidized to nitrate and then reduced to nitrogen gas or nitrous oxide gas. The rather complex processes that govern these transform- ations depend on the cycle of aeration and saturated (anaerobic) conditions. Denitrification coefficients range from 5% loss in well-drained soils to 50% loss in poor drainage conditions. The wide rainfall patterns and diverse soil types make a complex set of values for Oregon. The values shown in table 4 indicate average expected nitrogen available to plants after denitrification losses. top Leaching loss of nitrate nitrogen is caused by percolating water moving below the root zone. Once below the root zone, this nitrate is a potential ground water pollutant. Again, soil type and rainfall are the major influencing factors. Soil permeability can range from less than 0.06 inch per hour for clay soils to greater than 20 inches per hour for gravelly sandy soils. The amount of nutrients (nitrogen, primarily) that are lost to deep leaching depends on physical conditions and on the rate and season of manure application. top Availability of nutrients for crops Nitrogen is a vital nutrient, and its availability influences both microbial activity and plant growth. The carbon-nitrogen ratio (C/N) of applied wastes affects this availability and, therefore, affects plant growth. If a material with a high C/N ratio, such as manure with a lot of bedding, is added to a soil, organisms that decompose the organic matter grow until limited by available minerals and nitrogen. All the immediately available nitrogen may be bound by the microorganisms; for the short run, you may have to add more commercial fertilizer to the soil than before you applied the manure. The nitrogen bound by the microorganisms will become available to the plant, but it will take a longer time. Inorganic nitrogen is the form that is taken up by the plant root system and used for growth. The organically bound nitrogen in the soil breaks down with time to form inorganic nitrogen. With enough time, the organic nitrogen present in manure will be converted to plant-usable inorganic nitrogen. The exact percentage will vary, but researchers agree that from 4 to 25% of the nitrogen in manure will contribute to the organic matter of the soil. This means that a fraction of the added manure won't be available for plant uptake. This nonavailable fraction is sometimes referred to as the recalcitrant fraction. For the calculations in this publication, we've classified a value of 10% of the manure nitrogen as recalcitrant. This means you can add 10% more nutrients than your crop will use, and we've included this value in the suggested application rates in tables 5 and 6. This fraction won't add to surface or ground water pollution problems. The breakdown process of manure is called mineralization. Since livestock feeds have various particle sizes and compositions, manures have different mineralization rates, and some of the manure may be in the soil 2 years before all the organic nitrogen is converted to plant-usable inorganic nitrogen. Therefore, not all the nitrogen contained in manure that has been incorporated into the soil can be used by the plants during the first year after manure application. top   The rate of mineralization depends on the soil moisture content, organic matter level, and temperature. However, most animal manure is spread on the same fields year after year. Therefore, except for the recalcitrant component, the exact mineralization rate is unimportant because the plant will receive the same amount of nutrients each year after the first year-some from the current year's application, some from last year, and so on. This will be exactly the same amount next year. For efficient use of nutrients, apply manure so nutrients added do not greatly exceed those removed by crops on an annual basis. Table 5 lists nutrient application rates for crops common on livestock operations in Oregon. Table 6 lists two levels of fertilization for pastures. For example, if a beef operator grazes the animals full time on the pasture and cuts no hay, all the nutrients that leave this field must go in the beef produced. A lower fertilization rate is recom- mended for this type of operation. Harvesting by cutting of hay (green chopping) is the most efficient harvest and removes all of the grass. The amount of applied fertilizer should be reflected in the nutrients that are removed from the field. Management of the animals and crop is very important in determining proper application and use values. It's impossible to place a numerical value on the management factor, but tables 5 and 6 reflect the values suggested under a good management program. There are also different values for four different regions in the State. Table 6 includes these to represent differences in growing degree days and general soil types. Because moisture availability is critical to grass production, the irrigated and nonirrigated choices reflect these levels of production. Manure nutrients, especially nitrogen, are used more efficiently by grasses and cereals than by legumes. Inoculated legumes can get most of their nitrogen from the air, so additional nitrogen is not normally needed. Get your soil tested to determine specific fertilizer requirements for your land. See EC 628 for the procedure, and ask if your county Extension office has the OSU Extension videotape, How to Take a Soil Sample. Adjust manure application rates for your soil conditions to balance crop nutrient needs with the soil test results. In most cases, if you apply manure at a rate to satisfy the nitrogen requirements, you'll overapply phosphorus or potassium. Apply manure to satisfy the requirements of the least-needed nutrient and supplement the other two. The worksheet and example (Calculating land application rates) will let you follow the process and insert the values for your livestock operation. A computer program called NCALC has been developed using these same values and procedures. See your county Extension agent about access to this program. top top Prepared by James A. Moore, Extension agricultural engineer, and Michael J. Gamroth, Extension dairy specialist, Oregon State University, prepared this revision from a version written by Moore and the late Ted L. Willrich, professor emeritus of agricultural engineering, Oregon State University. Reprinted November 1993.

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