How to convert exchangeable K value to lbs/acre...?

Question

here's the question,

a corn crop requires about 120 lbs K/acre for a high yield, while a pine stand might need 25 lbs K/acre/year to make good growth. Convert your exchangeable K value to lbs/acre and compare this to these two crop requirements for your soil.

I don't expect anyone to work the problem out for me, I just would like alittle bit of help getting it started.

thanks

Answer 1

What are the units of your exchangeable K?

If we have mcg/kg, we then have to convert an acre at some agreed depth into kg of soil

Then we have to  take that number of kg times number of mcg /kg

mcg being one millionth of a gram, we divide by one billion (USA term billion) to get to kg. and then multiply by 2.2 to get to pounds.

If you were in France, billions are 1000 USA billions.

Answer 2

It's been a long time since my CCA training, but isn't ppm (parts per million) the same as pounds per acre at 6 inchs of depth?

ADDITIONAL

I was wrong, 1ppm is 2 lbs/acre at 6 inches of soil depth and 1 lb/acre at 12 inches soil depth.

I'm looking at a soil test right now and K shows 173ppm.  If the soil for the test was taken at a 6 inch depth, that means there's 346 lbs of available K per acre.  If the soil was takeen down to a 12 inch depth, that means there's 173lbs/acre of available K.

You might keep in mind that for sure most of the corn's feeder roots will be in the top 6 inches of soil.  I'm not sure, but in Missouri, most feeder roots on oak trees are found in the top 8-10 inches of soil.  You might see if you can find the feeder root depth of pine trees before you answer your question.  Check on the soil test for the soil sampling depth, 6 inches is standard but for orchards, I've had to go 10-12 inches, which is something you want to specify on the test or else the results will be skewed.

Answer 3

Try using this site. I think it will help you out. Good Luck

http://www.solu-cal.com/soil.html

Answer 4

Basics of this problem...

120 lbs of K is what your maintenance is for the crop.

the 25 lbs of K is your buildup of the soil.

120 + 25= 155 lbs of K.

A typical K fertilizer is Red Potash 0-0-60

155 lbs of K divided by .60

That will get you actual fertilizer lbs for Red Potash.

In Illinois, we use different figures

Maintenance: .28 X the previous year in corn yield

Buildup: typical soil needs to be around 300 lbs an acre 4lbs of K2O will raise the soil test 1 lbs.

It may sound really difficult, but once you do it enough it just comes natural.