A field-by-field nutrient management program requires multiple components to maintain adequate fertility for crop growth and development. A well-designed soil sampling plan, including proper soil test interpretations along with manure sampling, manure nutrient analysis, equipment calibration, appropriate application rates and application methods are all necessary components of a nutrient management plan. Implementing these components allows manure to be recognized and used as a credible nutrient resource, potentially reducing input costs and the potential of environmental impacts.
Animal manure has long been used as a source of nutrients for crop growth. Standard nutrient values are guides to determine the amount of nutrients that animal manure will supply as a fertilizer source. Iowa State University Extension publication, Managing Manure Nutrients for Crop Production (PM 1811), recommends manure nutrient content and credits by type of animal, handling system and application methods.
While “book values” like those in PM-1811 are reasonable average values, an individual farm’s manure analyses can vary from those averages by 50% or more. Species, age of animal, feed rations, water use, bedding type, management, and other factors make every farm’s manure different. Two key factors affecting the nutrient content of manure are manure handling and type of storage structures used. Each handling system results in different types of nutrient losses — some unavoidable and others that can be controlled to a certain degree. Because every livestock production and manure management system is unique, the best way to assess manure nutrients is by sampling and analyzing the manure at a laboratory.
This article describes how to sample solid, semi-solid, and liquid manure. Manure with greater than 20% solids (by weight) is classified as dry manure and is handled as a solid, usually with box-type spreaders. Manure with 10% to 20% solids is classified as semi-solid manure and can usually be handled as a liquid. Semi-solid manure usually requires the use of chopper pumps to provide thorough agitation before pumping. Manure with less than 10% solids is classified as liquid manure and is handled with pumps, pipes, tank wagons, and irrigation equipment.
A representative manure sample is needed to provide an accurate reflection of the nutrient content. Unfortunately, manure nutrient content is not uniform within storage structures, so obtaining a representative sample can be challenging. Mixing and sampling strategies should therefore ensure that samples simulate as closely as possible the type of manure that will be applied.