At manure applicator certification meetings in Iowa this winter, one point that's been emphasized is the importance of having manure tested to find out its true fertilizer nutrient value before applying it to fields. Getting a representative sample of the manure your livestock operation produces and sending it to a lab for analysis is much more accurate than using so-called book values.
Farmers used to be able to rely on book values or thumb rules for various types of animal manure to determine how much to apply per acre to cropland. Angela Rieck-Hinz, the Iowa State University Extension specialist who coordinates the manure applicator training program in Iowa, says that has changed because of the changes in livestock feed inputs being used today.
It pays to have manure tested instead of using "book values" to decide how much to apply
"It is very important to take manure samples get them tested instead of using book values because feed inputs are changing constantly," she emphasizes. Test results will tell how much nitrogen, phosphorus and potassium are in the manure, providing a more accurate guide on whether or not you need to apply commercial fertilizer in addition to manure, or how much fertilizer to apply per acre.
Timing of application is also important to get the full value of manure nutrients. Manure nutrients can be in the organic or inorganic forms, or both. In the inorganic form they are readily available for plant uptake—for example, in liquid swine manure. That's one of the reasons to apply liquid swine manure as late as possible in the fall. With the nitrogen mostly in the ammonium form, it can quickly convert to nitrate and potentially be lost due to leaching. However, if you delay application and wait until soil temperatures are cooler, you can delay the conversion process and reduce the risk of nitrogen loss. That increases the chance the N will be available in spring when corn can get it.
Solid manure and manure with bedding usually have a higher proportion of nitrogen in the organic form and must first mineralize in the soil before plants can take up the N. If you apply solid manure or manure with bedding, it's probably better to apply it in the fall, says Rieck-Hinz. As it decomposes and mineralizes, the nutrients become available by the time stops begin growing in the spring.
Source: ISU Extension
For more information, visit the Iowa Manure Management Action Group (IMMAG) website at www.agronext.iastate.edu/immag/.