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Compost Barns: What We Learned From Sampling Cleanout Material

Wayne Schoper

Published in Dairy Star December 9, 2005

Compost dairy barns, otherwise known as bedded pack barns, have been a fairly recent concept for dairy cattle housing. Since the first barn went up in the fall of 2001, there has been a lot of interest in these types of facilities because of the positive effect on cow comfort, and consequently on milk production. At the same time, dairy producers who have gone to this type housing for their milking herd have generally seen lower Somatic Cell Counts (SCC) due in no small part to increased cow comfort. We must remember comfortable, well-nourished cows are generally healthier and thus able to handle the stress of lactation better. As a result, they may be around for a few more years of production, an additional benefit to the dairy producer.

With the increased popularity of these barns being constructed, where do we go from here? Will there be enough sawdust available for everyone or without an unreasonable cost in the future? What other potential bedding materials are available? Can we re-compost this material and use it again? To get a better handle on these issues, the University of Minnesota will be conducting research to take a look at alternatives to sawdust. A bedding option perhaps would be mixing chopped cornstalks with sawdust or using soybean residue. Or, maybe some other organic material might work that has not been tried yet.

What we do know so far is that these barns do work well. But, there are two very important keys that make them work: 1) they require management; and 2) maintaining a dry surface for the cows to lie on. The surface of the pack must be stirred twice per day to incorporate the accumulation of manure into the pack. Also, sawdust must be added on a regular basis to maintain good cow cleanliness. Once the manure is incorporated into the pack, the presence of bacteria combined with heat and moisture begin to work together to break the sawdust down and render it into a mulch-like product that is an excellent fertilizer.

This fall, I sampled six south central Minnesota area barns at clean-out to see what kind of material was being applied to farmers' fields. Here are the results of that sampling:

Nutrients - Nitrogen, Phosphorous and Potassium (NPK) are the main crop nutrients that were analyzed. The following are the averages:


Actual Analysis

Total Nutrients (lbs/ton)


63 %



1.02 %



0.31 %



0.58 %


As can be seen, these results show an average NPK analysis of 21-8-15. According to this analysis, and allowing for application losses, there would be a need of about 15 ton per acre of this material to support a yield goal of 180 bushel corn, allowing for a 30% availability of the nitrogen in the manure.

Another advantage of these compost dairy barns is they can be cleaned out and the manure hauled with conventional dry manure hauling equipment. One cautionary note - if there is a need to haul a somewhat long distance, say over a couple of miles, then it might be economically more feasible to consider hiring a commercial manure hauler, as there is quite a bit of material that comes out of these barns.

 Carbon/Nitrogen Ratio - We have been wondering about the carbon/nitrogen (C/N) ratio of the material coming out of these barns. Raw sawdust has a C/N ratio of 400/1. If enough of this was spread on a field that was planted to corn, the sawdust then would tie up much of the nitrogen during its breakdown in the soil, causing a potential shortage of nitrogen to the growing corn crop. However, through our fall testing, we found that the C/N ratio had fallen to an average of around 15/1. That is very good news. It is important that ratio be under 30/1 to be assured that very little, if any, nitrogen would be unavailable to the growing crop.

Another one of the benefits of this type of dairy barn is that the manure storage is built right into the facility. This also aids in the breakdown of the sawdust as it holds all of the manure and sawdust together. This means that it heats up and, together with the oxygen and manure incorporated during the stirring process, helps break the sawdust down into a good, organic fertilizer.

pH - This is a measure of the acidity or alkalinity of a substance. One of the interesting phenomena that we have observed while reading the nutrient test results is the alkalinity of this material. Neutral pH is 7.0. Anything over that is considered alkaline. The average pH of our samples this fall averaged around 8.6. We will be looking at this during our continuing research to see what effect, if any, it has on cow and udder health.

In summary, sampling the manure at clean-out time from the compost dairy barns on these six dairy farms has helped answer a few questions many people have had. This sampling project has also shown that the sawdust bedding/manure material at clean-out had the same characteristics of well-rotted manure and it is a material ready to be utilized by the next year's corn crop.

Find more Compost Dairy Barn resources on the University of Minnesota Extension Dairy website.

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