Originally Posted by growingcrazy
It is assumed that field soil weighs 2,000,000 lbs per acre to the depth of a furrow slice. This is where the parts per million come into play...
Most Farmer's will use that number and assume 40,000 sqft per acre to make math easier.
This is for field soil...aka real soil.
To be 100% accurate with a soil less mix you would need to know what a cubic foot of it weighs. Then from there you can determine the weight of an acre of that soil and get your amendments very close.
Now... I don't do all of that... If I am in field soil and we are fertilizing to a depth of 6" I use the normal method, If your fertilizing to 12", double your numbers.
In soil-less mixes I have always just halved the 6" number to account for the light weight medium...I have always been very close to my numbers..whether that is luck or not... I have been using the k3 from spectrum and see very little difference in the tests coming from MSU that are not weighed.
Someone that actually weighs there mix and does the calculations that way should chime in and let us know how they do it.
Well for starters we use 43560 square feet per acre.
But other than that you're spot on. I guess the only thing about the bulk density is you convert it into lbs per acre. We just weigh it to grams per cup than convert.
In n field soil, this math is important but where you sample and what other assumptions you make are more important cause you use those numbers in you final calculations