Dumb question about fertilizer

[Smelly buck]

I'm trying to figure out exactly how the fertilizer works and I can't seem to figure out why all three #s don't equal 100% is there more of all three ingredience in a 50 lb bag of 18-18-18 than in a 50 lb bag of say 10-10-10. For instance is there twice as much nitrogen, phosphate and potash in a 50 lb bag of 20-20-20 as compared to a 50 lb bag of 10-10-10 and if so is there some kind of fillers in there?

 

[Telemark]

is there twice as much nitrogen, phosphate and potash in a 50 lb bag of 20-20-20 as compared to a 50 lb bag of 10-10-10 and if so is there some kind of fillers in there?

Yes and yes.

 

[swat1018]

The numbers signify how many pounds of N-P-K are in a hundred pounds of the product.

 

[Smallplot]

The numbers represent the percentage of actual fertilizer in the bag and given as N-P- K. So 13-13-13 contains 13% by weight of each N, P, and K. Hope this helps.


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[Smelly buck]

As confusing as this seems, both answers #3 and #4 seem radically different however if you do the math with a 50 lbs bag of 10-10-10 I think with both answers you end up with 5lbs of N, 5 lbs. of P and 5lbs of K. If that is correct why do you have to handle a 50 lbs bag of something to get the 15 pounds of product you desire; is it just that there's always going to be a byproduct that you have to deal with?

 

[MickT]

It’s because you don’t have raw elements in the sack- you are spreading salts. The remaining % is the other ions in the salts.


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[Smallplot]

And having more material makes it easier to spread evenly rather than trying to spread 5 pounds.

You have to look at the numbers. Some of the available commercial fertilizer available to me is not loaded with as many fillers such as the 60% 60-0-0 urea I can get.

Always have to look at the tags and do some math to make sure how much of something you have to apply to reach your specific goals.


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[Telemark]

why do you have to handle a 50 lbs bag of something to get the 15 pounds of product you desire; is it just that there's always going to be a byproduct that you have to deal with?

It's just an industry standard. You can calibrate a machine to spread so many pounds of fettilizer per acre, and you can vary the amount of nutrients you apply based on what percentage of the product is N, P, and K. Plus it would be very difficult (i.e. expensive) to separate out the pure N, P, and K.

They're 50 lb bags, so the numbers on the front is just pounds of the nutrients per two bags.

 

[yoderjac]

As confusing as this seems, both answers #3 and #4 seem radically different however if you do the math with a 50 lbs bag of 10-10-10 I think with both answers you end up with 5lbs of N, 5 lbs. of P and 5lbs of K. If that is correct why do you have to handle a 50 lbs bag of something to get the 15 pounds of product you desire; is it just that there's always going to be a byproduct that you have to deal with?

Answer #4 is the correct one. They are percentages by weight. Typically, soil tests recommend fertilizer by the number of pounds of each element. One thing that confuses most folks is that it is almost impossible to buy bags of fertilizer and get a match to your soil test. Unless you happen to be unusually lucky, you will end of with more of one element and less of another than your test calls for. If you are working in bulk, most coops that sell bulk fertilizer will mix it for you giving you a better ratio than you will get from bags, but still approximate.

The good news is that it doesn't matter that much. The soil tests we use that provide fertilizer recommendations are as much art as science and they are generally targeted at farmers planting and harvesting monocultures trying to maximize yield. As deer managers, we have far different goals than farmers. I've given the soil test results without the fertilizer recommendation to several soil science guys, told them what I planed to plant and asked for fertilizer recommendations. They were all a bit different and all different from the recommendation from the lab.

You do need to understand the difference between pound of element and percentage of product to get in the right ballpark, but from there, close is good enough.

If you read and follow some of Crimson N Camo's throw and grow threads and avoid or minimize tillage, you will find in the long run you will need much less fertilizer than soil test recommend.

Thanks,

jack

 

[j-bird]

As confusing as this seems, both answers #3 and #4 seem radically different however if you do the math with a 50 lbs bag of 10-10-10 I think with both answers you end up with 5lbs of N, 5 lbs. of P and 5lbs of K. If that is correct why do you have to handle a 50 lbs bag of something to get the 15 pounds of product you desire; is it just that there's always going to be a byproduct that you have to deal with?

Actually 3 and 4 (if you get into the math) are the same....just worded differently. The number on the bag is the percentage of that bag that is that particular element. Percentages are based on 100%..... 15-15-15 - means that 15% of the contents of that bag is actual N, P & K each......so really only 45% of that bag is the elements you want - the rest is just carrier material. Now - not all fertilizer comes in 50 pound bags.....especially in retail stores. Also keep in mind you can get fertilizers that have higher aspects of one element vs the others. Urea for example is all nitrogen (with its associated carrier material) 46-0-0.....meaning 46% of the bag is N, but there is no P or K in it. So you can mix and match to try to get you in the ballpark.

 

[swat1018]

Actually 3 and 4 (if you get into the math) are the same....just worded differently. The number on the bag is the percentage of that bag that is that particular element. Percentages are based on 100%..... 15-15-15 - means that 15% of the contents of that bag is actual N, P & K each......so really only 45% of that bag is the elements you want - the rest is just carrier material. Now - not all fertilizer comes in 50 pound bags.....especially in retail stores. Also keep in mind you can get fertilizers that have higher aspects of one element vs the others. Urea for example is all nitrogen (with its associated carrier material) 46-0-0.....meaning 46% of the bag is N, but there is no P or K in it. So you can mix and match to try to get you in the ballpark.

Yea. Let him explain that one in 15 paragraphs or less...

 

[FarmerDan]

Oh boy! The numbers on the bag are the guaranteed percentage of actual plant food in the bag. If you buy a 50 lb bag of 10-10-10 you (or your plants) are guaranteed to receive 5 lbs each of elemental N, P, & K. So, that same 50 lb bag of 10 -10 -10 has 35 lbs of inert material. Why? There's no way to deliver the actual elemental forms of plant material. Its the chemical reactions that occur in the soil that breaks down the basic fertilizer compounds (compounds) into elemental form.

Let's use three compounds to make or blend our 10 - 10 - 10. We will need potassium oxide (K2O); phosphate, to keep it simple (P205): and some nitrogen compound. Let's pick urea (CH4N20), Never mind the chemical compound formula. It just illustrates that there are other elements associated with the compounds we blend to get to a guaranteed analysis.

Potash and phosphate are mined. Both go through processes to remove some of the inert material. Urea is manufactured. The basic compounds are delivered to a fertilizer manufacture to blend or -- prill and ammoniate.

Potassium Oxide, or potash, is 60% elemental potassium (K). Phosphate, and I've bastardized the name for sake of explanation - its really triple super phosphaste - is 45% phosphorous. Urea is 46% nitrogen.

To blend a ton of 10 - 10 -10 we shovel 333 lbs of potash (K20), 444 lbs of triple super phosphate, and 435 lbs of urea into a blender. But, but we still don't have a ton of material although we have 200 lbs of N, P, and K. That's what a ton of 10 - 10 -10 should contain, right? Ten percent of 2,000 lbs is 200 lbs.

What to do? Add filler, about 788 lbs of filler, inert stuff - like chunks of limestone - or gravel. Whatever's cheapest and spreadable.

If we don't add the filler and stop at 1,212 lbs, our guaranteed plant food will be 19% N, 19% P, and 19% K. The proof? 200 lbs of plant food divided by a total of 1,212 pounds of material should equal 19%. Somebody check my math!

There are many more materials the industry uses and figuring percentages gets a little more involved, but it isn't rocket science. In my experience people get confused by the guaranteed analysis and the actual plant food supplied. I'll just stop there, but if you ever want a clinic, let me know.

 

[FarmerDan]

Ah heck, let's keep going. You get back your soil test and it tells you to apply 80 lbs of nitrogen, 40 lbs of phosphorous, and 120 lbs of potassium. You tell this to your fertilizer dealer. You tell him you need enough to fertilizer for one acre\s. He needs to mix something to get you 80 - 40 - 120, in shorthand form. He fires up the loader and goes to the urea bin and throws 174 lbs of urea into the blender. Next, he heads to the phosphate bin where we fills the bucket with 89 lbs of triple super phosphate. On the last trip he scoops up 200 lbs of potash. In the blender there is now a total of 463 lbs of material that will deliver 80 lbs of elemental nitrogen, 40 lbs of elemental phosphorous, and 120 lbs of potassium.

What's the guaranteed analysis? Nitrogen - 80/463 = 17%. Phosphorous - 40/463 = 8%. Potassium - 25%.

The pile that gets dumped into your truck or spreader will supply 80 lbs N - 40 lbs P - 120 lbs of K.........80-40-120.
The guaranteed (percentage) analysis is 17-8-25.

Why do we care about percentages? Regulations. It's s throw back to the days of the horse and buggy which we continue to admire, for some unknown reason.