Understanding the Value of Animal Manure- Don’t Waste a Valuable Waste
Have your manure tested to know its value. Whether you are buying, selling, or using manure generated on your farm, you need to analyze samples that represent what you will spread. This allows the manure to be applied at the appropriate rate for the field.
One way to do this is collect the sample as you are spreading, but you would want to know ahead of time if you buying or selling the manure. The sample should represent what will be applied to the field. Sampling a lagoon is more difficult than a dry manure because many of the nutrients settle out with the solids. It takes many small subsamples thoroughly mixed together to make one good sample to send off to the lab. For ex-ample, with a liquid you might want to grab 10 or 15 sub- samples of about 1 pint in size and thoroughly mix them in a bucket. Dry manure should include multiple samples from different parts of the pile excluding the crust if stockpiled.
The University of Kentucky Agricultural Economics Department provides several useful spreadsheets (link provided). The Fertilizer Price Calculator allows you to input your price for various types of fertilizer and returns the value per unit of P2O5, K2O, or N. For example, if urea costs $900/ton, potash costs $810/ton, and DAP costs $860/ton then you’re paying $0.98/lb of N, $0.55/lb of P2O5 , and $0.68/lb of K2O.
If your manure test returns 42 lb of total N, 21 lb of P2O5, and 33 lb of K2O per 1000 gallons, then based on fertilizer replacement the manure is worth about $75 per 1000 gallons. If your soil test report does not call for any phosphorus (P) or potassium (K) then that manure is only worth $40 to you. Remember that you might lose nitro-gen (N) value as ammonia gas volatilizing off the soil surface. In addition, you can lose significant amounts of N from Kentucky soils when you apply manure in the fall or winter when crops aren’t present or have little need for N.
If your soil tests do not call for phosphorus or potassium, you might be able to sell your manure to a neighbor who has fields that need those nutrients. With current fertilizer prices many farmers are very interested in manure nutrients.
Determine if you need additional nitrogen fertilizer
If you have repeatedly applied manure to a field over the years, or have grown a legume recently (like alfalfa), you might not need additional inorganic N fertilizer. That would be a big money saver with current N prices!!
To find out if you need extra N for your corn use the Pre-sidedress Soil Nitrate Test (PSNT). Collect a representa-tive soil sample for each field. Unlike normal soil samples, PSNT samples need to be 12 inches deep and collected when corn plants are about 12 inches tall. To get a representative sample collect 20 soil cores and mix thoroughly in a clean plastic bucket. Then grab about a pint of soil from bucket. You want to air-dry that soil before sending to the lab. Nitrogen in field moist soil will change a lot on the way to the lab. To dry the soil, do not heat the soil, just spread it in a thin layer on a paper plate in front of a fan – set on low, you don’t want it all to blow away!
Many labs (including the University of Kentucky) provide PSNT analysis. You can even test the sample yourself with a high-quality testing kit (like the “Nitrachek” kit – beware most home soil test kits aren’t very good). We have a lot of confidence that if your PSNT comes back higher than 25 ppm nitrate-N (NO3-N) you don’t need to add additional fertilizer N. Talk to your County Agent about the PSNT if you’re interested!
High fertilizer prices provide risk and opportunity
Know what you need! Soil test for phosphorus (P), potassium (K) and pH. Apply just what you need. Now is not the time to apply “maintenance” rates or “build” for the future. Stay on top of your lime program though – soil pH is the most important variable in a good crop fertility program.
Know what you are applying! Test your manure and check your spreader to know how much you are putting out. Spending $25 on a manure analysis will usually repay that investment many times over. Now is not the time to skip soil testing either, it is one of the best investments a person can make in their soil fertility program.
If you generate manure and don’t need it, use this time of high fertilizer prices to generate extra income by selling manure N, P, K, and organic matter to neighbors. They might even be willing to pay you to apply the product if they don’t have a manure spreader.
Additional Resources
AEN-91: Managing Liquid Dairy Manure (uky.edu)
