# Compost on Bermudagrass Hayfields



## terraceridge (Jul 21, 2011)

There is a company about 25 miles from me that produces large quantities of compost for use as a soil amendment. At least one farmer in this area has used the compost on his pastures and seems to have had good success with the product. The company is charging $9/yard for the compost (delivered, but not spread). They say that a yard weighs about 1250 lbs, putting the per ton price around $14.40. The company recommends an initial application of 10 tons per acre, but the local farmer who is using the compost has applied a total of about 35 tons per acre over the past 3 years, so I know that larger applications may be necessary. I have attached the nutrient analysis of the compost, and I wanted to run it by everyone here to see if it looks like a reasonable buy.

Another large benefit of using the compost would be the increase in soil organic matter. My sandy soil only holds approximately 1/2 inch of water (13,577 gallons per acre) in the top 12 inches of the soil profile under normal conditions. The compost company claims, though, that by increasing the organic matter component of the soil by 1% (40,000+/- lbs/acre by my figuring), the soil can hold an additional 17,000 gallons of water in the top 12 inches, more than doubling my current water holding capacity. I came up with 40,000 lbs/acre by using the bulk density listed on my soil test, 1.35 g/cm3, and figuring that there are 1,336,271,983 cubic centimeters per acre foot of soil depth, giving me a little more than 40,000 lbs/acre as being 1% of the total soil mass in the top 12 inches. I'm sure there is some sketchy math in there somewhere, so I don't know if my numbers are actually relevant in the real world. I believe that the dry matter content of the compost would also have to be considered when determining how much to apply to actually give the desired 1% increase in organic matter content.

I would really appreciate some feedback from everyone (especially Dr. Haby!) on this idea. It seems to be a fair buy, but I am not sure if there is something I am overlooking. Thanks again!


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## deadmoose (Oct 30, 2011)

What is the source?


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## terraceridge (Jul 21, 2011)

Do you mean the name of the company or what the compost is made from? The company is Brooks Contractor in Goldston, NC. The compost is made out of food residue, leaves, eggshells, animal bedding, and I am sure lots of other things.

Here is a link to their website: http://www.brookscontractor.com/?page_id=30


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## vhaby (Dec 30, 2009)

I have not rechecked your calculations, but with only 63.3% DM, you would need to apply 2,734 lb of this compost per acre to get one ton of DM. With that you would be applying about 34 lb total N/acre, 17 lb P2O5, 6 lb K2O, 328 lb Ca, 5.8 lb Mg, and 5.8 lb of S per acre. To apply 40,000 lb of DM/ac you would need to apply 27.34 tons of compost at a cost nearing $395 per acre. Since it is your checkbook, only you can decide the value of attempting to raise the organic matter level by 1% in your coarse sandy soil. To determine how much N, P2O5, K2O, etc you would be putting on your soil, multiply the amounts listed above by 27.34. The total N applied would be valued at near 42 cents per pound, etc.


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## terraceridge (Jul 21, 2011)

vhaby said:


> I have not rechecked your calculations, but with only 63.3% DM, you would need to apply 2,734 lb of this compost per acre to get one ton of DM. With that you would be applying about 34 lb total N/acre, 17 lb P2O5, 6 lb K2O, 328 lb Ca, 5.8 lb Mg, and 5.8 lb of S per acre. To apply 40,000 lb of DM/ac you would need to apply 27.34 tons of compost at a cost nearing $395 per acre. Since it is your checkbook, only you can decide the value of attempting to raise the organic matter level by 1% in your coarse sandy soil. To determine how much N, P2O5, K2O, etc you would be putting on your soil, multiply the amounts listed above by 27.34. The total N applied would be valued at near 42 cents per pound, etc.


Thanks for your input! I do have a question, though. How did you come up with valuing nitrogen at 42 cents/lb? In my area, 34-0-0 is about $600/ton, or 88 cents/lb. What am I missing with this calculation? Thanks!


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## vhaby (Dec 30, 2009)

One ton of DM contains 33.8 lb of N and costs $14.40. $14.40 divided by 33.8 = $0.426 per lb of N, unless I have made a mistake in calculation. Since you need to apply 2734 lb of material to obtain 2000 lb of DM, your cost becomes $19.71 per ton of DM. (2734 divided by 2000 = 1.367) 1.367 x $14.40 = $19.68/ton of DM. Therefore, $19.68 divided by 33.8 = $0.582 per lb of N.

As stated, not all of the N is going to be available the first year, and some of it may never be available for plants. The calculation reflects the pounds of N per ton of DM, not what is available to the plant, so you cannot compare apples (ammonium nitrate) to oranges (compost).


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