Other Nutrients in Manure
Potassium (K) and other nutrients essential for plant growth are supplied in manure. Some nutrients and heavy metals may reach toxic levels with repeated high rates of application. Heavy metals could be of greater concern when manure from animals that have consumed feeds containing heavy metals is applied directly to grazing land. However, heavy metals normally are not in animal manures unless the animals have been fed supplemental feeds that include zinc, copper, or selenium. Feedlot manure often contains significant amounts of calcium carbonate and can have a liming effect on acidic soils.
Calcium carbonate (lime) is a common additive to livestock diets. Manure can contain between one and four percent calcium carbonate, depending on the diet formulation. One way to account for the liming effect of manure is to monitor the pH of the soil over time. The pH of manured soils should increase, or become more basic. Used in conjunction with a good liming plan, the amount of agricultural lime needed can be reduced on manured fields.
A more direct way to determine the amount of calcium carbonate in manure is to test it for effective calcium carbonate (ECC), which is a commercial fertilizer test. Request an ECC test which will report the amount of calcium carbonate equivalent in the manure.
Potassium or Potash?
Potassium content in soil, plants, and animal rations is expressed as potassium (K) content but potassium in fertilizers and manure intended for land application is expressed as potash, or more correctly, potassium oxide (K2O).
- To convert K to K2O concentration, multiply by 1.2.
- To convert K2O to K, multiply by 0.83.
Liming effect of manure: Assume a feedlot manure sample test returns two percent calcium carbonate. If the manure was applied at 25 tons/acre and the manure was 20 percent moisture, the equivalent lime application would be 800 pounds (20 tons of dry manure/acre). In this example, one ton of dry manure contained 40 pounds of available lime. Therefore, if the producer's soil test showed a 2,500- pound lime requirement, he would only need a 1,700-pound application after the manure application.