Value of manure as a fertilizer

Ray Massey, Economist, Commercial Ag Program,
University of Missouri

An oft-asked question is, “What is the value of manure?” This question is difficult to answer because value is determined by markets. In the absence of markets for manure, its value is unknown. The best that can be done is to estimate the potential value of manure for a specific purpose.

The estimation process is called hedonic pricing. In the absence of a market, the sum of the value of various manure components determines a value for the manure itself. Hedonic pricing is heavily dependent on the many assumptions imposed on the use of manure. Any change in assumptions will result in a change in the value of manure.

Because this type of estimation of the value of manure is dependent on its many assumptions rather than on market supply and demand, it is only as a starting point for negotiations in a developing market. A person with an estimate of potential manure value can use it to interest another in buying the manure, thus creating a market that begins to reveal the actual value of manure.

The potential value of manure is affected by:
• the fertilizer value of its components (nitrogen, phosphorus, potassium, minor nutrients, organic matter)

• the crop or cropping system

• soil fertility needs

• the yield of the crop receiving the manure

• manure source

• manure application method

• legal application limits

• total quantity of manure nutrients applied

Components that decrease the value of manure include:

• negative components (weed seed, foreign matter – wire, concrete, etc., undesirable chemicals – antibiotics, hormones, heavy metals, etc.)

• timing of application

• legal constraints

The remainder of this [article] will present information on how each of the components affects the potential value of manure.

Units of value
In order for price to be meaningful, an explicit or implied unit is necessary. When farmers sell corn, they sell it by the bushel. When livestock feeders feed corn they consider it by the pound or hundredweight. To say that corn is worth $2.50 without mentioning the unit bushels, is potentially confusing to the feeder wondering what the cost per hundredweight of his feed will be.

The same phenomenon exists for manure. Different actors in the market will be considering different units. While growing, marketing and feeding corn is so commonplace that the unit is understood from the context of the discussion, the units of manure implied in a particular conversation will not be so easily discerned.
Three units are useful for discussing value:

1. dollars per 1,000 gallons (or ton)

2. dollars per acre

3. total dollars of annual manure production

All three have different uses. (Note: For the remainder of this discussion, I will use 1,000 gallons and ignore tons. This is for brevity and clarity. Persons using dry manure will need to translate “1,000 gallons” into “tons.”)

Because manure is seen as a fertilizer substitute, the dollars per acre puts it in a unit that can be compared to other fertilizers. Valuing manure in dollars per acre differs from the method of application which is usually 1,000-gallon units. The person interested in possibly buying the manure is the crop producer who is going to compare manure to his current per-acre fertility expense. Assuming that all the fertilizer needs of the crop are going to be met, the value per acre will be constant between different types of manure – only the application rates will differ.

Value per 1,000 gallons is useful when comparing the value of different manure types. By determining the value per 1,000 gallons, comparisons can be made between dairy and swine manure or between slurry and lagoon effluent. This type of information is useful when deciding what type of manure storage to use and how it will impact your manure value.

Total value of annual production is useful in understanding the system impact of any manure management decisions. Applying manure according to a phosphorus limit may reduce the value per 1,000 gallons or value per acre but actually increase the total value of annual production because more acres will receive the manure. The positive impact of more acres can be greater than the negative impact of less value per acre.

Fertilizer form and manure nutrient value
The easiest way to value a pound of N, P2O5 and K2O in manure is to use the value of common commercial fertilizers. The correlation is not complete because form is important in determining value. Even with commercial fertilizers, the form of the fertilizer impacts the cost per pound of nutrient.

•Nitrogen (N)
Recognizing the nitrogen in the form of anhydrous ammonia is valued at half that of nitrogen in the form of ammonium nitrate, it is a logical step to assume that nitrogen in the form of manure will be valued differently than either one. Manure-supplied nitrogen would logically be less valuable than commercial fertilizer because manure is bulky and the nutrient content is not guaranteed, as in commercial fertilizers. On the other hand, organic producers would ascribe more value to manure-supplied nitrogen than to inorganic sources of fertilizer.

The expected availability of manure-supplied nitrogen is dependent on the form of the nitrogen and the application method. Organic N becomes available over time to the plants so not all is available during the season it is applied. Nitrogen in the ammonia form if applied too early (i.e., in the fall for use by spring-planted crops) may not be available for crop use because of its volatile nature.

Most manure management plans use nutrient retention values that consider the impact of application method on plant availability. More nitrogen is volatilized when applied on the surface than when injected. Therefore, effluent that is land-applied via an irrigation system may have only 10 or 20 percent of the nitrogen in the effluent available to the plant when the plant needs it. The nitrogen value of the manure therefore is not the nitrogen content in the manure but the amount of nitrogen that is actually useful to the plant.

For ease, the value of the fertilizer that would have been used if manure had not supplied the nutrient is probably the best value to use. This value gives a reasonable estimate of the value of the fertilizer used by growing crops. Fertilizer value of nitrogen probably does not represent the price that neighbors are willing to pay for the manure-supplied nutrients.

•Phosphorus (P) and potassium (K)
The value of commercial P and K fertilizer will likely approximate the value of manure-supplied P and K because manure-supplied P and K are stable. The value of P and K fertilizer is an acceptable value to use in estimating the value of manure.

•Minor nutrients
Any minor nutrients that are supplied by manure have potential value. In order to consider that value, the presence of them would need to be established by manure testing and the need would require establishing by a soil test. While not the same as commercial fertilizer’s guaranteed analysis, a manure test showing the concentrations of nutrients helps establish manure’s potential value as a source of minor nutrients.

•Organic matter
Many people believe that the organic matter in manure should be given a value. In order to justify this estimation of value for organic matter two things need to exist:

1. the organic matter must contribute to production

2. a market price for the organic matter needs to be obtained

Organic matter can contribute to production by increasing the quantity or quality of the crop being harvested or by providing an environmental benefit. In soils that are worn or low in organic matter, the organic matter may have value. Certain manures (poultry litter) are going to supply more organic matter than others (swine lagoon effluent). Those which supply little organic matter may contribute nothing while those that contribute significant amounts of organic matter may contribute enough to be valued.

Once it is determined that the organic matter is contributing to production, it needs to be valued. This is difficult because organic matter does not typically have a market. Estimating the impact of the additional organic matter on yield or quality is one way to estimate the value of organic matter. Organic matter that provides an environmental benefit is more difficult to value because a person cannot isolate its contribution to the profit of the farm.

Cropping system
Often livestock producers assume that all of the plant nutrients supplied by manure have value. Actually, a manure-supplied nutrient has fertilizer value only if it enhances the yield or quality of the crop harvested. The assumption of value to all nutrients is limited by the following considerations:

•Nitrogen applied to legumes such as soybeans and alfalfa is not valued because those crops could have been grown without nitrogen fertilizer.

•Nutrients in excess of crop need are not valued unless there is some peculiarity of the cropping system that merits valuing the over-supplied nutrient.

When manure is applied at a rate that approximates the crop removal of nitrogen by corn, frequently excess P and K are applied. If the manure is applied to the same ground each year and corn is grown on that ground each year, the excess P and K will never have value. In fact, the excess P and K has the potential to reduce the value of that particular parcel of ground by making it unsuitable to receive manure in the future and increasing the cost of manure application as the animal feeding operation seeks suitable land farther away.

However, if the manure is applied every other year to land in a corn-soybean rotation, the excess P and K in the corn year is useful to the soybeans in the subsequent year and thus has value. By altering the cropping system and the manure application schedule the value of the manure can possibly be increased.

By growing crops that have value and that remove a substantial amount of nutrients, the value of the manure can be increased. Cropping systems such as corn silage can increase the value of manure over a corn-grain cropping system. The P and K in the stover removed increase the demand for those nutrients, fewer pounds of P and K are in excess and thus a larger percent of the P and K supplied by the manure have value.

In some areas of the country, manure is applied to crops that may remove a lot of nutrients but then have very little value themselves. In these situations, crop production is not a profit center but rather a part of the manure-environmental management system of the animal feeding operation. Manure applied to low-value crops will not have much, if any, value.

Soil fertility
Soils testing low in P and K are frequently improved by adding P and K in excess of crop removal until the soil test levels meet a predefined agronomic optimum. The period of time when excess P and K are added is referred to as a soil build-up period.

During a soil build-up period, all manure-supplied nutrients have value. The principle is that manure-supplied nutrients have value when they increase crop yield or quality. During build-up, the supplied nutrients are expected to increase crop value in the year of application and in subsequent years because the quality of the soil has been enhanced. Once the soil nutrient levels have been built to agronomic optimums, the value of the manure reverts back to just the crop removal value of the nutrients.

In fields that have very high soil test levels of P and K, additional P and K will not enhance crop value; any manure-supplied P and K is not valued. Manure-supplied nutrients have no value on soils testing very high in P and K. Indeed, they can have negative value because they are perceived as an environmental hazard. Manure value can be enhanced by seeking land with low fertility to receive the manure.
Crop yield

Because manure-supplied nutrients are generally valued on their crop removal basis, the higher the crop yield, the greater the value of the manure. Manure will have more value on productive soils than on poor soils because more crop is removed and sold. Manure value can be enhanced by applying it to land that is high yielding.

Manure source
The manure from different species of animals has different total and relative concentrations of nutrients. Manures that have been stored in different structures have different total and relative concentrations of nutrients.

Manures with more total nutrients have potentially higher value because more nutrients exist to provide value. However, the nutrients have value only if the animal feeding operation can receive their value. While lagoons tend to dissipate N so that it is not available to crops, this can be a reasonable form of manure storage if the business does not need the nitrogen. When an animal feeding operation is integrated with a crop farm of sufficient size to use all the excreted nutrients or can sell the manure, storage that preserves the nutrients would increase the value of the manure.

Manures whose relative concentration of nutrients is closely aligned with the crop removal rate of those nutrients will have greater value. When manure’s relative nutrient concentrations are not well aligned with crop removal, the potential exists for many of the applied nutrients to be in excess of crop need and therefore have no value.

Manure application method
Manure that is surface-applied will have more N volatilized than manure that is injected or incorporated into the soil. Farmers wanting to conserve the nitrogen value of manure can increase the manure value by injection or incorporation.

Legal application limits
Manure value is affected by whether manure is limited to the crop nitrogen removal rate or crop phosphorus removal rate. Manure applied to meet the nitrogen needs of the crop will probably meet all of the N, P and K needs of the crop. Since all of the nutrient needs of the crop are met, the per-acre value of the manure will be equal to the commercial fertilizer expense of growing the crop. Not all of the nutrients applied will be valued because excess P and K have no value. Overapplied, unvalued nutrients decrease the manure’s value per 1,000 gallons.

Manure applied to meet the P needs of the crop will probably undersupply the nitrogen needs of the crop (assuming that it is not a legume). In this situation, the manure value per acre is decreased by the amount of N fertility that needs to be supplemented by commercial fertilizer. Since all of the N and P and more of the K are valued when the application is limited to P removal, the value per 1,000 gallons increases.

Some crop producers do not like to depend on manure to supply all of their nitrogen needs because the quantity and availability of the N is less certain with manure than with commercial fertilizers. When manure is applied to crops to meet all of the nitrogen needs, environmental regulations frequently forbid the addition of other nitrogen fertilizers. However, when manure is applied at a rate less than the N removal rate of the crop, commercial fertilization is permitted.

Some farmers may request that manure be applied at the P removal rate rather than an N removal rate because it gives them the flexibility to supplement with commercial fertilizer. Though the farmer desires the lower application rate, they will still recognize that their total fertilizer expense has not been met with the manure. The maximum value they will ascribe to manure is the normal fertilizer expense per acres less the cost of necessary supplemental N and commercial fertilizer application. Willingness to sell manure at this lower value per acre, may translate into increased farmer willingness to use manure as a fertilizer.

Total quantity of manure nutrients applied
During the planning stages of designing an animal feeding operation, the type of storage is a major decision. The choice of manure storage structures will influence the total value of manure by influencing the amount of nutrients retained and available for use as a fertilizer.

Lagoons volatilize N and precipitate P and K so that the effluent pumped onto cropland has few nutrients. Lagoons may fit well with particular systems, such as when the animal feeding operation has little cropland to use the manure or must apply the effluent to growing crops. But it decreases its total potential value of the manure.

Storing manures in slurry pits conserves more nutrients and therefore increases the total value of the manure applied. Animal feeding operations with adequate need or market potential for manure-supplied nutrients could increase the total potential value of manure by using slurry storage systems.

Negative components
The impact of any negative components on the value of manure will be difficult to quantify. Frequently their presence is used as justification for not accepting manure, regardless of the price of manure.

Foreign material
Farmers tend to value manure as an inferior fertilizer when it contains material that interferes with their cropping activities. If manures contain viable weed seed or foreign materials such as wire or concrete, it will interfere with profitable crop production. The more likely a manure source is to have weed seed or foreign materials, the lower its value will become. Animal feeding operations can increase the value of their manure by managing their operation in such a way that these negative components do not make it to the field.

Chemicals within manure that are not necessary for crop production can also reduce the value of manure. Salt build-up, heavy metals (more common with municipal waste), hormones or antibiotics are considered potential negative impacts of manure use. While these will probably never decrease the quantity or quality of crop removed, farmers will tend to discount manure because of their potential presence.

Timing of application
Due to its bulky form, supplying crop nutrients in the form of manure takes more time than the use of commercial fertilizers. If the application window available for fertilizing activities is limited, farmers will tend to value commercial fertilizers over manure.

Compaction
Driving heavy equipment over fields, particularly in the spring, causes soil compaction that reduces productivity. Manure application can cause more compaction than commercial fertilizer application because manure application equipment tends to be heavy and occurs under less-than-ideal conditions if the animal feeding operation needs to empty its manure storage structures during wet seasons. Farmers are wise to discount manure use if compaction occurs.

Legal constraints
Various states require that manure application be accompanied by increased nutrient management planning and record keeping. Farmers who can apply commercial fertilizer without regulatory hassle will discount manure that requires that they maintain and provide records for environmental agencies.

Summary
Until a local market develops for manure, its value will remain unknown. The sum of the value of the nutrients in manure is not going to be the price that animal feeders will be able to sell manure. The maximum potential value of the manure will depend on nutrient composition and the customary cropping activities of the locale.

Animal feeders can foster the development of a manure market by understanding what crop producers value and discount in receiving crop nutrients in the form of manure. Efforts to increase the value of manure to crop producers will increase their acceptance of it and increase its eventual market price.

Flexibility in application rates, timing of application and choice of application method will all improve the opportunity for developing a market for manure. As the market develops the price of manure will fluctuate as the supply of manure and the demand for it changes from year to year. Manure price, like that of livestock and crops, will fluctuate from year to year.

Other potential markets, such as feeds or energy production, exist for manure. Many of the same principles apply but the list of positive and negative characteristics of manure would be different. ANM

References omitted but are available upon request at editor@progressivedairy.com

—Excerpts from the National Livestock and Poultry Environmental Learning Center website