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Old 04-07-2018, 11:41 PM #11
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Quote:
Originally Posted by bsgospel View Post
I can dig it- lemme see if I got this right

Desired PPM- Double it to get PPA

Desired PPA = Usable lbs/acre
% of element

Usable lbs/acre = Amount/ft of soil (adjust for cu. yd.)
furrow cu. ft./acre

Does that jive?
Doubling it is a huge assumption. You would have to use the bulk density of the soil in the correct units. Although for all intensive purposes doubling is adequate.
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Old 04-08-2018, 12:33 AM #12
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Got it- so to get to bulk density we take the dry weight of the soil and divide by total volume- and then... multiply that by the desired PPM?
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Old 04-08-2018, 06:13 AM #13
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No you by use the bulk density and you use it to get the weight of the soil per acre than use that to get the factor that you would use to get parts per mil to lbs per acre.
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Old 04-08-2018, 05:16 PM #14
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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.
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Old 04-08-2018, 08:58 PM #15
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Quote:
Originally Posted by growingcrazy View Post
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
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Old 04-09-2018, 03:35 AM #16
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I agree, I always use 43,560.

Lots of old timers still don't around here...maybe it is something about calculators...
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Old 04-10-2018, 04:17 PM #17
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Quote:
Originally Posted by growingcrazy View Post
I agree, I always use 43,560.

Lots of old timers still don't around here...maybe it is something about calculators...

I mean it kinda makes sense. 3500 is a very little percentage of 40000 so it appears negligible. But it's not that negligible really. Especially at larger scales.
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Old 04-11-2018, 05:17 PM #18
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It looks like We are alone here ...

Which route are we taking here? Are more people interested in soil-less mediums or real soil?
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Old 04-11-2018, 05:45 PM #19
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Soilless this year
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Old 04-12-2018, 04:33 AM #20
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I would love to see some ideas for soiless peat and coco mixes - specifically some recommendations for gypsum and borax amendment amounts for these mixes.

I blindly played with gypsum and borax all year on a multitude of strains in a peat/perlite mix in 5 and 7 gallon containers. I saw the good, the bad and the ugly, but saw enough good to know that this is something I have to figure out.

Ideally I'd love to see ideas specific enough to be input into a spreadsheet so one could enter the details of the mix they wanted to use and the spreadsheet would calculate the amounts of amendments to add for a decent balance.

Maybe that's a pipe dream, but I'd like to see us work toward that end.
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