Characterization of Naturally Separated Dairy Manure Fractions.

The traditional recommendation for land application of liquid manure has included prior agitation of stored manure to provide a uniform source of crop nutrients.  However, research has shown that different crops have different nutrient requirements, and these nutrient requirements can often be better met by applying different separated manure fractions (eg. Bittman et al).  There have been significant advancements in creating separated manure fractions, but many technologies, such as mechanical separation, are often cost prohibitive.  Natural separation of manure fractions occurs in most liquid manure storages, through settling of solids.  There is also potential for coarse solids to rise to the surface to form crusts.  Under this scenario a certain amount of the thinner supernatant liquid below the crust can be pumped and land applied, followed by agitation and land application of thicker slurry.  Thicker slurry generally contains more nutrients than thin supernatant and the phosphorus (P) / nitrogen (N) ratio is also greater, meaning that a higher percentage of P compared to N is in the solid fraction.

The purpose of this project was to characterize the nutrient content of naturally separated dairy manure fractions in dairy farm liquid storages.  A second objective was to determine how these fractions varied depending on management practices such as bedding and water inputs, and manure treatment/handling before entering storage.  Results from 2014 sampling at various depths from 18 storages showed negligible, some, and considerable separation of fractions at 7, 4, and 7 storages, respectively.   For storages with considerable separation average dry matter content ranged from 1.5% for the shallowest depths (below crust) to 7.7% for the deepest depths.  For these same depth positions average total nitrogen increased from 0.090% to 0.193%, and average total phosphorus from 0.015% to 0.041%.  Settling of solids and nutrient stratification was minimal when coarse solids were mechanically separated from liquid manure prior to entering storage, and/or there was considerable disturbance of manure when transferring it from the barn into the manure storage.  For example, manure pumping involves more disturbance than scraping.

These results suggest that availability of naturally separated dairy manure fractions will depend on various management practices impacting manure before it enters the storage.  Results from 2015 will be incorporated into this presentation, and findings will be adjusted accordingly.