Manure: An opportunity, Part II
March 13, 2008 by Trevor Wallace
In the previous column in Manure
Manager, we identified several similarities as well as differences
between manure and fertilizer.
In the previous column in Manure Manager, we identified several similarities as well as differences between manure and fertilizer.
The key to maintaining the value of manure is preventing nutrient loss before, during and after application. The amount of ammonia-nitrogen (N) lost from manure depends on the type of storage, length of the storage period, environmental conditions during application and the selected method of application.
The longer manure is stored, the greater the potential for N to be lost as ammonia-N. Incorporating and injecting manure, especially liquid manure, reduces ammonia-N losses dramatically, since exposure to air is minimized. Ammonia-N losses are greater when manure is surface applied during warm, dry conditions compared to wet, cool conditions. Ground cover (e.g., cover crops, stubble) protects the soil, keeps the surface temperature cooler and reduces wind movement, thereby reducing volatilization as compared to broadcasting on bare ground.
If you are able to reduce input costs with manure, it must have a dollar value. The question is how to go about estimating what it is worth.
Since manure is not presently traded as a commodity and there is no formal marketing system in place, assigning a dollar value is somewhat challenging.
A simple method for determining the dollar value of manure requires two key pieces of information: the current value of each of the major nutrients (based on fertilizer costs) and the nutrient composition of your manure, ideally from a laboratory manure analysis. Multiplying the value of each nutrient by its concentration in the manure, and then adding the values of each nutrient will give you a fertilizer equivalent value of the manure per ton (or per acre if you have determined your application rate).
Two approaches can be taken when calculating the value using this method.
The first approach uses the total nitrogen, phosphorus, potassium and sulphur content of a sample of manure, making no adjustment to nutrient content based on nutrient availability or due to nutrient loss through management. This approach would be similar to fertilizer, where the price is for the total nutrient content and does not factor in losses that may result from application.
The second, and more conservative approach, adjusts the manure sample’s nutrient content to account for nutrient availability and attempts to account for nutrient losses likely to result on application. This approach assigns a value to manure that accounts for only the nutrients that will be available for crop production.
A more complex method calculates the value of manure by assigning a value to only those nutrients applied in the manure which offset recommended fertilizer requirements. This method factors in the manure nutrient composition, application rate (tons/acre), the fertilizer recommendation (pounds/acre of nutrient) and the cost of fertilizer nutrients to arrive at a value for the manure. These methods only value the nutrients actually used by the crop. Nutrients applied in excess of fertilizer recommendations are not valued.
Residual nutrients, as long as they are not lost from the soil system, will only have an economic benefit if subsequent fertility applications are adjusted to account for these nutrients, and subsequent crops use these nutrients. Management practices can therefore significantly affect the economic value of the manure. If manure is applied annually to the same soil and subsequent crops do not use the nutrients, then these nutrients do not provide an economic benefit.
Aside from manure’s value as a nutrient source, manure also has beneficial impacts on soil quality that are more difficult to quantify. Manure makes valuable contributions to building soil organic matter and to overall soil quality. The soil conditioning benefits of solid manure can be assumed to add an additional 25 to 75 percent over and above its nutrient value, while for liquid manure the additional benefit is 10 to 30 percent. These are conservative estimates – and some would argue the economic importance of the soil building properties of manure are equal to, if not greater than, the value of the nutrients.
The difference in soil building value between solid and liquid manures relates to their difference in solids content, and therefore the organic matter contribution to soil. The ranges for each manure type result from the influence of soil quality. Poor quality soils generally benefit more from manure application compared to soils with higher organic matter content.
The discussion of manure value underscores two important points. First, knowing the nutrient content of manure is extremely important in assigning an accurate value to manure. While average or ‘book’ values of manure content are readily available, the actual manure nutrient profile is highly dependent on a number of factors, including livestock species, diet, animal management, performance level, feed intake, manure storage conditions and climate. The most reliable estimate can only be obtained through laboratory analysis of a representative sample. The other key point is that sloppy manure management leads to increased nutrient losses, in particular N, stripping manure of part of its value.
In summary, the economic value of manure is a product of two components: the value of manure nutrients, and the value of manure’s soil building properties. The estimated economic value of manure nutrients may or may not factor in nutrient availability, expected nutrient losses during application or application of nutrients in excess of crop removal. Soil conditioning benefits of manure add an additional 10 to 75 percent to the estimated economic value of manure nutrients, depending on the type of manure and soil quality.
Trevor Wallace is a Nutrient Management Specialist with Environmental Practices and Livestock Welfare, Alberta Agriculture, Food and Rural Development.
Detailed information on the methods described is available at the department’s web site at www1.agric.gov.ab.ca
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