Calculating Fertilizer Value of Compost Bedding Pack
Now you can figure out the fertilizer value of compost bedding pack when doing nutrient management plans.
Compost bedding pack barns have become an interesting alternative to traditional loose housing systems for several Ontario dairy producers. They like the increased comfort and freedom this housing gives their cows.
The increased interest in compost bedding pack has led to the need for information in many areas, including the fertilizer value of the compost pack. If you have adopted this type of bedding, recent Minnesota research has addressed this and other questions that come up when you do nutrient management planning.
One study, by A.E. Barberg, quantified parameters used in 12 compost bedding pack barns in the state. These included barn dimensions, pack size and ventilation, as well as the characteristics of the pack itself, such as moisture content, temperature and nutrient content. Another study, by K.A. Janni, conducted on six Minnesota CBP barns dealt with recommendations for layout and management, but also included pack parameters. More recent work by Michael Russelle was intended to improve some of the data collection methods used in the earlier studies.
Russelle's study collected samples from eight compost bedding pack barns in late September 2006. A soil auger designed to sample wet soils was used to remove the samples from the pack. At least six locations were sampled in each pack, including near the outside and interior retaining walls, and the pack centre. A certified commercial laboratory analysed the samples.
Herd sizes in the Russelle study ranged from 38 to more than 200 milking cows. Pack space varied from 60 to 90 square feet per cow. Cows were confined in six of the barns, while animals in the other two had access to pasture.
All the producers used wood chips or sawdust for bedding, with sources varying from ground particle board to fine hardwoods sawdust. Some producers tried other bedding, including sunflower hulls, wheat and barley middings, small grain straw and waste hay. Bedding was added as needed, but the definition varied among producers.
The producers stirred packs twice daily with a skid steer or small tractor equipped with a front or rearmounted cultivator. The stirring resulted in a pack with two layers of different consistency. Manure content and density in the loose surface layer, ranging from about three to eight inches thick, gradually increased. The compacted layer below increased in thickness as old surface layers were incorporated. This layer was partially composted.
The pack's moisture content varied with depth, at 61 per cent in the surface layer and 64 per cent in the compacted layer, Russelle found. Moisture contents were lower closer to the outside wall. Barberg's study measured an average of 53 per cent in the surface layer and 57 per cent in the compacted layer, while Janni's research did not distinguish between the two layers, measuring average pack moisture content at 63 per cent.
Russelle measured total nitrogen concentration of 1.09 per cent, and noted it did not change with depth or location in the pack. Phosphate concentration averaged 0.28 per cent, and again did not change with depth or sampling location. The potash concentration averaged 0.70 per cent and did not change with sampling location, but was higher in the surface layer than in the compacted layer. All the studies got similar results.
Russelle measured carbon-to-nitrogen ratios of 11.2 to 20.9, similar to Janni's at 12.2 to 20.2. Russelle recorded a pH of 7.5 compared to 8.5 recorded by both Barberg and Janni. Barberg was the only one to record an average temperature-42.5 degrees Celsius.
Table 1 compares the preferred conditions for composting to the actual conditions measured in the CBP barn studies. Numbers used are from Russelle's study where available.
Collected data compared to preferred conditions for proper composting suggested pack material was not composting in the traditional sense. However, the researchers concluded heat and biological activity of the pack was sufficient to control environmental mastitis organisms, fly larvae and other potential problems.
Russelle also determined the average bulk density of composted bedding pack was 55.3 pounds per cubic foot. The density was similar throughout the barns sampled. You can use this number to calculate the amount of pack by weight, if the volume is known.
The three studies also provided other useful information. For example, producers estimated 25 to 30 per cent of the manure was deposited on the scrape alleys, Janni found. Although amount of bedding used varied widely, he noted one producer was using 19 pounds per cow per day.
Russelle made several recommendations for taking samples in CBP barn packs:
Table 2 summarizes characteristics of the compost bedding pack collected by the three researchers. This information provides a guide for doing nutrient management planning for new barns. Once your barn is in operation, it is advisable to take samples to determine the characteristics of your own operation based on the bedding material used, moisture content and other variables.
1 SL - surface layer top 3 to 8"
2 CL - compacted layer >8"
3 Information for one barn only
Barberg, A.E., M.I. Endres, and K.A. Janni. 2007. Compost dairy barns in Minnesota: A descriptive study. Appl. Eng. Agric. 23:231-238.
Janni, K.A., M.I. Endres, J.K. Reneau, and W.W. Schoper, 2007. Compost dairy barn layout and management recommendations. Appl. Eng. Agric. 23:97 - 102.
Russelle, M.,K. Blanchet, and L. Everett. 2007 Characteristics and Fertilizer Value of Compost Dairy Barn Manure. Proc. Of the National Compost Dairy Barn Confernece. June 21 & 22, 2007. Burnsville, NM.
This article appeared in the December 2008 Ruminations column of the Milk Producer magazine.
For more information:
Toll Free: 1-877-424-1300