Fall 2006

BMPs for Manure Management


By Angela Rieck-Hinz, Department of Agronomy

Weighing manure tank wagon for calibrationBest management practices, or BMPs can mean a myriad of different things to different people.  Traditionally, in agriculture, a best management practice has been a series of practices, standards or implementation of  physical structures based on the best possible science to address environmental, production and economic issues all at the same time. By definition BMPs can and should change over time.  Unfortunately, perhaps, we have become so obsessed on what the regulations require that we forget there are BMPs, tools or resources that can help us make sound management decisions without the need to require that these practices be mandated by state or federal law.  Some of these practices require an investment of time, resources and money, but overall, these investments may be quite small compared to the cost of regulatory compliance.

Manure Sampling.  Taking a manure sample and having it analyzed for nutrient content is the single best practice to help you fully know and use your manure as a fertilizer source for crop production.  While book values for manure nutrient analysis can provide a reasonable starting place for new facilities that do not have access to existing manure analyses, actual nutrient concentrations can vary significantly from book values.  Manure nutrient content is affected by many things, age of animal, feed sources, management, manure storage type, length manure is stored, land application methods, weather conditions and so forth.  Also because of the time involved in collecting a database of  manure samples, book values are often dated and do not reflect current feeding or management strategies. 

For example, with the increased use of distiller’s grain in animal diets in Iowa, there are no book values for manure from animals being fed these diets. Manure sampling for nutrient analysis is not without its challenges, so be prepared to collect samples over several years to see if they change yearly, why they change yearly and how to manage and use your nutrient analysis. For a list of laboratories that offer manure analysis please see: http://extension.agron.iastate.edu/immag/splabssma.html Remember. if you choose to use a manure analysis in your state-required manure management plan for the Iowa Department of Natural Resources, you must use actual documented manure production volumes from your farm.

Equipment Calibration.  Now that we know what is in the manure by taking manure samples, we need to know how much we are land-applying for crop production.  Unless you own a liquid manure tank wagon with a flow-meter, most producers still calculate application rates in terms of loads of manure applied per acre, and then back-calculate to determine actual tons or gallons per acres and subsequent nutrient rates.  Flow meters are very expensive so they are primarily used in the commercial manure application business.  Generally speaking, if you are land applying liquid manure, you should calibrate your tank wagon once per year.  After several seasons with the same equipment, you should have a general idea of tractor speeds and application rates.  Solid manure calibration can be a little more difficult depending on if bedding is used and how this affects how the manure is stacked in the spreader and how the manure is distributed from the back of the spreader.  

Specific details on how to collect manure samples or to calibrate equipment can be found in fact sheets developed by Iowa State University Extension.  Please see the article titled “Using Your Resources” for additional information on how to obtain copies of these publications. 


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