Food &
ResourC!S
Course:
Advanced Plant & Soil Science '
Lesson:
Determine Fertilizer Application Rates
TEKS:
130.21 (c) (5) (C), (D)
Developed By:
Erynne Treptow Graduate Assistant Department of Agricultural Leadership, Education, and Communications Texas A&M University Complimentary materials developed through the Texas Education Agency Educational Excellence project Additional teaching materials may be found at the Educational Excellence project web site
http://tea.im. tamu.edu
Fertilizer Application Rates Fertilizer Numbers Which bag has the highest percentage of phosphorous? _ Bag A with 16-16-16 or _ ~ag B with 16-20-0-15? Which bag has the highest percentage of nitrogen? _ Bag A with 16-16-16 or _ Bag B with 16-20-0-15? Which bag has the highest percentage of potassium? _ Bag A with 16-16-16 or _ Bag B 16-20-0-15? Which bag contains sulfur? _ Bag A 16-16-16 or _ Bag ~ 16-20-0-15? What do these numbers represent? What does the fourth number indicates?
If you have a 100-pound bag ofIJ6-15-11
fertilizer how many pounds of nitrogen do you have?
I!
How many pounds of phosphorous?
How many pounds of potassium?
Calculating Application Rates
Your irrigated pasture has been tested and it is suggested that you fertilize at a rate of 140 pounds
of nitrogen per acre. You are using Ammonium Sulfate, a 16-20-0-15 fertilizer. A 1~O-pound
bag of this fertilizer will contain 16 pounds of nitrogen. How many pounds ofthis type of
fertilizer should you apply, per acre?
What does this cost, per acre, if Ammonium Sulfate sells for $12 per 100 pound bag?
Date:- - - - - -
Fertilizer Application Rates
Fertilizer Numbers Which bag has the highest percentage ofphosphorous? _ Bag A with 16-16-16 or
Bag B with 16-20-0-15? Which bag has the highest percentage of nitrogen? Bag A with 16-16-16 or _ Bag B with 16-20-0-15?
Which bag has the highest percentage ofpotassium?
_ Bag A with 16-16-16 or
Bag B 16-20-0-15?
Which bag contains sulfur?
_ Bag A 16-16-16 or
Bag B 16-20-0-15?
What do these numbers represent?
What does the fourth number indicates?
If you have a 100-pound bag of 16-15-11 fertilizer how many pounds of nitrogen do you have?
How many pounds of phosphorous?
How many pounds of potassium?
Calculating Application Rates Your irrigated pasture has been tested and it is suggested that you fertilize at a rate of 140 pounds
of nitrogen per acre. You are using Ammonium Sulfate, a 16-20-0-15 fertilizer. A 100-pound
bag of this fertilizer will contain 16 pounds of nitrogen. How many pounds ofthis type of
fertilizer should you apply, per acre?
What does this cost, per acre, if Ammonium Sulfate sells for $12 per 100 pound bag?
What if you needed to add 57 pounds of phosphorous per acre instead of nitrogen, still
using Ammonium Sulfate? How many pounds of this type of fertilizer should you apply,
per acre?
What does this cost, per acre, if Ammonium Sulfate sells for $12 per 100 pound bag?
What if you needed to add 95 pounds of sulfur per acre instead of nitrogen or phosphorous,
still using Ammonium Sulfate? How many pounds of this type of fertilizer should you
apply, per acre?
What does this cost, per acre, if Ammonium Sulfate sells for $12 per 100 pound bag?
Your dry land pasture has been soil tested and the recommendation from the testing lab is
to add 40 pounds of nitrogen per acre. You would like to do this as cheaply as possible. You
have access to two (2) different fertilizers:
Ammonium Sulfate 16-20-0-15 cost
$12.00 per 100 pounds
Ammonium Nitrate 28-14-0 cost = $17.50 per 100 pounds
Which is cheaper to use?
Your dry land pasture has been soil tested and the recommendation from the testing lab is
to add 70 pounds of phosphorous per acre. You would like to do this as cheaply as possible.
You have access to two (2) different fertilizers:
Ammonium Sulfate 16-20-0-15 cost
$12.00 per 100 pounds
Ammonium Nitrate 28-14-0 cost = $17.50 per 100 pounds
Which is cheaper to use?
Fertilizer Application Rates Warm-up
Which bag has the highest percentage of phosphorous?
_ Bag A with 16-16-16 or
Bag B with 16-20-0-15?
Which bag has the highest percentage of nitrogen?
Bag A with 16-16-16 or _ Bag B with 16-20-0-15?
Same amount
Which bag has the highest percentage ofpotassium?
~
Bag A with 16-16-16 or _ Bag B 16-20-0-15?
Which bag contains sulfur?
_BagA 16-16-16 or ~BagB 16-20-0-15?
Remember that the numbers on the fertilizer bag indicate the percentage of elements in a specific
order: N - P - K (Nitrogen, Phosphorous, Potassium). If there is a fourth number, it indicates the
amount of sulfur.
Intro
How do you calculate the amount of fertilizer to add to soil? Soil test results will recommend a
certain number of pounds of a certain element to add to your soil, generally on a per acre basis.
But there are some things to remember about the calculation. The soil test will tell you how
many pounds of a certain element to add to your soil. It is up to you to calculate the actual
pounds of fertilizer to apply to achieve that concentration of a specific element. You must also
remember to calculate your actual fertilizer needs based on your acreage.
• Remember that a 100-pound bag of 16-16-16 fertilizer actually contains only 16 pounds
of nitrogen, 16 pounds of phosphorous and 16 pounds ofpotassium; the rest is inert
ingredients.
• If your soil test suggests adding 40 pounds of nitrogen per acre, you will actually have to
apply 250 lbs of the 16-16-16 fertilizer per acre to get to the desired level of nitrogen.
Calculating Application Rates
Your irrigated pasture has been tested and it is suggested that you fertilize at a rate of 140
pounds of nitrogen per acre. You are using Ammonium Sulfate, a 16-20-0-15 fertilizer. A
100-pound bag of this fertilizer will contain 16 pounds of nitrogen. How many pounds of
this type of fertilizer should you apply, per acre?
140 pounds divided by 16 = 8.75 bags. Each bag is 100 pounds, so the grand total is 875 pounds
of 16-20-0-15 fertilizer per acre to actually apply 140 pounds of nitrogen per acre.
(140/16
8.75
8.75 x 100
875 pounds of 16-20-0-15 fertilizer per acre)
What does this cost, per acre, if Ammonium Sulfate sells for $12 per 100 pound bag?
8.75 bags times $12 per 100-pound bag of fertilizer would cost $105.00 per acre.
(8.75 x $12
$105 per acre)
What if you needed to add 57 pounds of phosphorous per acre instead of nitrogen, still
using Ammonium Sulfate? How many pounds of this type of fertilizer should you apply,
per acre?
57 pounds divided by 20 2.85 bags. Each bag is 100 pounds, so the grand total is 285 pounds
of 16-20-0-15 fertilizer per acre to actually apply 57 pounds of phosphorous per acre.
(57/20
2.85
2.85 x 100 = 285 pounds of 16-20-0-15 fertilizer per acre)
What does this cost, per acre,.if Ammonium Sulfate sells for $12 per 100 pound bag?
2.85 bags times $12 per 100-pound bag of fertilizer would cost $34.20 per acre.
(2.85 x $12 = $34.20 per acre)
What if you needed to add 95.pounds of sulfur per acre instead of nitrogen or phosphorous,
still using Ammonium Sulfate? How many pounds of this type of fertilizer should you
apply, per acre?
95 pounds divided by 15 = 6.33 bags. Each bag is 100 pounds, so the grand total is 633 pounds of 16-20-0-15 fertilizer per acre to actually apply 95 pounds of sulfur per acre. (95/15 = 6.33
6.33 x 100
633 pounds of 16-20-0-15 fertilizer per acre) What does this cost, per acre, if Ammonium Sulfate sells for $12 per 100 pound bag?
6.33 bags times $12 per 100-pound bag of fertilizer would cost $75.96 per acre.
(6.33 x $12
$75.96 per acre)
Your dry land pasture has been soil tested and the recommendation from the testing lab is
to add 40 pounds of nitrogen per acre. You would like to do this as cheaply as possible. You
have access to two (2) different fertilizers:
Ammonium Sulfate 16-20-0-15 cost = $12.00 per 100 pounds
Ammonium Nitrate 28-14-0 cost = $17.50 per 100 pounds
Which is cheaper to use?
Ammonium Sulfate: 40 pounds nitrogen required divided by 16 pounds of nitrogen per 100­
pound bag = 2.5 bags per acre or 250 pounds of Ammonium Sulfate per acre. 2.5 bags at $12.00
per bag = $30 per acre
(40/16 = 2.5
2.5 x $12
$30 per acre) Ammonium Nitrate: 40 pounds of nitrogen required divided by 28 pounds of nitrogen per 100 pound bag = 1.4 bags per acre or 140 pounds per acre. 1.4 bags at $17.50 per bag $24.50 per acre (40/28
= 1.4
1.4 x $17.50
$24.50 per acre) Ifthere is no need to add sulfur to your soil, the Ammonium Nitrate would be a cheaper
fertilizer.
Your dry land pasture has been soil tested and the recommendation from the testing lab is
to add 70 pounds of phosphorous per acre. You would like to do this as cheaply as possible.
You have access to two (2) different fertilizers:
Ammonium Sulfate 16-20-0-15 cost = $12.00 per 100 pounds
Ammonium Nitrate 28-14-0 cost
$17.50 per 100 pounds
Which is cheaper to use?
Ammonium Sulfate: 70 pounds nitrogen required divided by 20 pounds of phosphorous per 100­
pound bag = 3.5 bags per acre or 350 pounds of Ammonium Sulfate per acre. 3.5 bags at $12.00
per bag $42 per acre
(70/20 = 3.5
3.5 x $12 = $42 per acre) Ammonium Nitrate: 70 pounds of phosphorous required divided by 14 pounds of nitrogen per 100 pound bag 5 bags per acre or 500 pounds per acre. 5 bags at $17.50 per bag = $87.50 per acre (70114 = 5
5 x $17.50 = $87.50 per acre) The Ammonium Sulfate would be a cheaper fertilizer.