Do your math! Manure smells more like money

I’m often asked the value of organic fertilizers, such as manure or biosolids.

While it can be difficult to quantify the true value of an organic nutrient source, we can put a value on the nitrogen (N), phosphorus (P2O5) and potassium (K2O) relatively easy.

When purchasing or being given an organic nutrient source insist on having the product analyzed. This analysis provides us with the best means of determining the product’s true value.

Consider for example, poultry litter I recently had analyzed. The analysis read:

      TKN:      (as is)

      Nitrogen (N)       52.91 lbs/ton

      Ammonia -N (NH2-N)       3.36 lbs/ton

      Nitrate -N (NO3-N)       0 lbs/ton

      Phosphorous as (P2O5)      91.3 lbs/ton

      Potassium as (K2O)       60.49 lbs/ton

The actual analysis of manure or biosolids will vary based on storage, digestion method, diet of the animals, etc. This is why it is a good idea to have the analysis.

Let’s look at nitrogen first. We have to determine plant available nitrogen (PAN) to put a value on nitrogen.

To get started you have to set a value for K2O, P2O5 and N.

Your prices will vary but for educational purposes we’ll use:

* K2O = $ .153/lb

* P2O5 = $ .25/lb

* N = $ .23/lb

The value of the nitrogen in this source depends on when we apply and how we apply this manure. For instance, we can lose up to 75 percent of the ammonia nitrogen if we surface apply this product in July or August.

The plant available nitrogen = the organic nitrogen x (efficiency factor) + ammonium N x (efficiency factor) + nitrate nitrogen.

We’ll surface apply in March and use the following efficiency factors (from OSU Bulletin 879):

* Organic nitrogen = (TKN) 52.91 – (ammonia N) 3.36 = 49.55 lbs/ton

* Organic nitrogen = 49.55 x (efficiency factor .30) x ammonia nitrogen 3.36 x (efficiency factor .50) + (nitrate nitrogen 0) = 16.55 lbs/ton of Plant Available Nitrogen.

We only have 16.55 pounds per ton of nitrogen available to our growing plants in the initial year of application.

Yes, organic nitrogen sources break down and some nitrogen will be available next year.

Ammonium nitrogen, if not incorporated, can be lost to the atmosphere very quickly in dry, hot weather.

      Nitrogen       16.55 lbs/ton       x       $.23/lb       =       $ 3.81

      Phosphorus       91.3 lbs/ton       x       $.25/lb       =       $ 22.83

      Potassium       60.49 lbs/ton       x      $.153/lb       =       $ 9.26

      Total value                               $ 35.90/ton as is

From this total value we can subtract our trucking and spreading costs. Trucking cost may exceed $10 a ton and spreading costs vary from $4-$6 a ton. Use the above formulas to see what kind of deal you are getting.

Continued application of manure or biosolids will result in a build up of soil phosphorus levels.

For more information on the application of these products, contact your local extension office.

(The author is an OSU Extension Agriculture and Natural Resources Agent in Guernsey County. Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem OH 44460.)