Verified FBN Member (MN)

Fertilizer Prescriptions

Wondering if any of you guys create your own fert prescriptions for your operation?

Verified FBN Member (NE)

Yes for starter fertilizer, I use the program JD Apex. I think it is absolutele now! Lol I used it since 2011.

Verified FBN Member (SD)

I do not just 5 gallons of 10-34-0 plus 1 qrt. of zinc in furrow on everthing. Variable rate is done in the fall via strip till using 3 different products through air cart, and variable rate topdress in early june via spreader or bar.

Verified FBN Member (MN)


Actually I've been gathering data on such for the last 25 years. Just this week I organized it all. I've gained this data from magazine and newspaper articles as well as farm supplier meetings.

Several reccomendations have changed over the years, especially for K. Hope this helps.

Soil Test Analysis

Things to consider:

One acre of soil 6” deep weighs about two million pounds

Pounds per acre on a 6” deep soil test = ppm X 2

Soil has a negative charge

MAP 11-52-0 has a pH of 4.5

DAP 18-46-0 has a pH of 7.5 and should not be used in soils with a pH of = or > 7.5

Urea 46-0-0 is less effective in dry years

28% weighs 10.67 pounds

32% weighs 11.06 pounds

6-24-6 weighs 11.1 pounds

10-34-0 weighs 11.2-11.8 pounds

The most leachable nutrients (in order): Nitrate, Sulfate, Boron, Chloride, Salt

These are nutrients to best manage

The least leachable nutrients (in order): Phosphorus, Zink (?), Copper, Potassium

These are nutrients that could be “banked”

N,P,&K are all more than twice as effective if properly banded

Nutrients needed for: (given as grain + plant material above ground = total) (from IPNI)

250 bushel Corn 100 bushel beans

Nitrogen 167.50+112.50= 280.00 325.00+110.00=435.00

Phosphate 87.50+ 40.00= 127.50 73.00+ 24.00= 97.00

Potassium(K2O) 62.50+275.00= 337.50 120.00+100.00=220.00

Magnesium 8.33+ 51.25= 59.58 15.00+ 35.00= 50.00

Calcium 3.38+ 32.50= 35.88 15.00+ 80.00= 95.00

Sulfur 20.00+ 17.50= 37.50 18.00+ 80.00= 35.00

Zink .27+ .38= .64 .10+ .52= .62

Manganese .18+ 1.88= 2.06 .12+ .88= 1.00

Iron .38+ .63= 1.01 1.00+ 2.00= 3.00

Copper .12+ .06= .18 .10+ .05= .15

Boron .60+ .06= .66 .12+ .58= .70

1. SOIL pH

Ideally 6.3-6.8 for corn & soybeans (6.4 per Pat)

Acidity higher amounts of hydrogen ions

Alkalinity higher amounts of hydroxide ions

Lowering pH can be done by:

adding tile

plant crops with lots of roots, healthy plants release organic acids

add manure

add biologicals

use cover crops reduce tillage

use AMS, especially elemental sulfur

Raising pH can be done by:

adding calcitic lime if Mg is ok

adding dolomitic lime if Mg is low

*smaller lime particles enhance availability greatly

*too much lime ties up micronutrients

*test lime source for heavy metals

2. Cation Exchange Capacity

CEC X 10 = The capacity of soil to hold N (in pounds)

3. Organic Matter

for each 1% the soil can hold about 4% more water

raising O.M. can be done by:

plant crops with lots of roots

add manure

add biologicals

use cover crops reduce tillage

Each 1% of O.M. will release about:

N 20 30 pounds when warm, otherwise figure 4 7 pounds

P 4 7 pounds

S 2 3 pounds

4. Base Saturation

It is the balance of five major positively charged elements in %. Ideally in the following ranges

Na <1

Higher Na raises pH

Na should be = or <.5% (per Pat)

Tile is the best method to reduce Na

If test show high Ca and some lime try adding elemental sulfur

If test show no lime try adding gypsum

If test show low Ca and no lime try adding both elemental sulfur and lime

H 2-10

Add lime (calcium carbonate) to lower H

Ca 65-80

Ca below 60% will reduce N, P, Zn, Fe, Mn, and Cu up take

Adding Ca will loosen soil (i.e. Ca to Mg of 7:1)

Higher Ca will give heavier test weight and quicker dry down

Adding lime will raise Ca

Ca should be >70% (per Pat)

Ca should be at least 25 times greater than Mg

Mg 12-20 (10-15% as per Pat)

Mg over 20% likely needs tile

Higher Mg raises pH

Adding Ca and S (if needed) will lower Mg

Mg should be <13% (per Pat)

Mg is needed for photosynthesis and protein formation

K 4-8 (7-10 per Pat)

K should be kept less than half of Mg

5. Nitrogen

Given as Nitrate on soil test

Adding N will change pH, do not soil test after adding N

Organic Matter X 20 could be added to show Total N available

Following a dry year residual N is much higher, perhaps use 2’ deep soil test

Adding more than 155 pounds of N is a waste! (As per U of M in 3 S MN plots)

Nitrate (available) is leachable. Ammonium (most available) is not.

nitrification inhibitors don’t last long when soil temperatures are above 60 degrees

Any minor incorporation or rain does a lot to stabilize N

Anhydrous is available in about 3 8 weeks

UAN is available in about 25%ammonium-0 weeks,25% nitrate- 1-2 weeks,50% urea-1.5-3 weeks

Urea is available in about 1.5 3 weeks, using urea in high pH soil results in higher N loss

Ammonium Sulfate (10-34-0, MAP, DAP) is available in about 1-2 weeks

Ammonium nitrate is available in about 50% 0 weeks, 50% 1-2 weeks

N deficiencies show up as leaf yellowing at the tip & goes down the mid rib, bottom leaves first

Soybeans can produce a maximum of about 260 pounds of N, high bean yields need more

6. Phosphorus (two test methods) Potash - Potassium

Use P1 if pH is under 7. P1 is available P now. P2 is the total P available possibly by year end

Use Olsen if pH is over 7

Take this number X 2.3 (2?), then add Organic Matter X 4 to show Total P available

Soil tilth helps P availability

Much of the total P is unavailable because it is fixed to Fe, Al, and Ca

P is consumed in the breakdown of O.M.

If P1 is over 20 ppm crop response is minimal

P is needed for photosynthesis

P deficiencies show up as purple leaves, this symptom is usually temporary

Too much P limits Zn and Cu uptake

If pH is over 7.5 P availability is governed by calcium

If pH is under 5.5 P is governed by iron and aluminum

Without erosion P does not move in soil

7. Potassium

K helps with good stalks, photosynthesis, disease resistance, sugar (flavor) & starch production

K helps transport water, nutrients, and sugars within the plant

To calculate how much K to apply (current ppm X % goal (7) / current % - current ppm) X 2 = actual K. Potash is 50% K (don’t use the 60% K2O), so then double the calculated actual K amount

Higher CEC requires higher K amounts

Only about 50 pounds of K leave a corn field in grain. It takes near 300 Pounds to grow it though it is the highest amount of nutrient needed in corn.

I bet your under applying this important nutrient (Per Pat). Check your early July tissue samples!

If pH is far from 7.0, split applications of K may be beneficial

If pH is over 7.5 proper K levels are more important

K deficiencies show up as yellowing on the outer edges of leaves

If K and Na add up to>10% it could cause germination issues

If K test show 200 ppm crop response is minimal

K shortage increases aphid reproduction

Adding K when over 200 ppm will likely not add more yield

8. Sulfur

Ideally between 20 80 ppm

Organic Matter X 2 could be added to show Total S available

Sulfur = Sulfate/3

Converting sulfur to sulfate requires warm temperatures

Sulfate is the form plants actually use

P levels over 90 ppm ties up plant uptake

Sulfate is an anion and is quite leachable, (elemental) sulfur is not leachable

Adding S may slow N release

Higher S lowers pH

To lower pH try adding 15# S for every .1 pH desired change, retest in 3 years, use 2.5 acre grids

S applications are more likely to pay off in lighter soils low in O.M..

S is an important part of building proteins

S is not mobile in plants

S deficiencies show up as stunting and shortened internodes

Don’t apply S in the fall if you have low CEC, use elemental sulfur + sulfate in the spring

If pH is over 7.5, S becomes more important

*Micronutrients use DPTA test rather than the Mehlich 3 test

Micronutrients in order of importance: Zink, Manganese, and Boron (as per Pat)

9. Zink

Should be 1.8 3.5 ppm

If P1/10 is higher use this instead for Total Zn available

Zn is important for germination, plant vigor, starch production, protein synthesis, root development, growth hormones, enzyme systems, flower formation and frost protection

Microbial life love Zn, N, and carbon

Higher responses if P is high (more than 10 X Zn to P)

Without erosion Zn does not move in soil

Zn deficiencies are more likely in high P or high pH conditions

10. Manganese

Should be 20 40 ppm

If pH is under 6.7 available Mn is higher

Mn is most available in the sulfate form, chelated ok, oxide worst

Mn shortages are often related to Ca, Mg, and Fe

Mn helps stalk strength, aids chlorophyll and pollen production, photo synthesis, nitrate assimilation, iron metabolism, and adds kernel weight

Mn reduces white mold, lodging and disease

Mn is not mobile in the plant

Mn deficiencies show up as lighter strips running the entire length of a corn leaf, veins are dark

Mn is not very available in cold soil

In high O.M. soils foliar treatments may be more effective than soil applied.

One pound actual Mn in 30 gallon of water can be effective, in severe shortages use 1.5-2 #

Do not use chelated Mn for foliar treatments, Manganese sulfate is preferred

Wait at least 2 days (7-8 preferably days) after any glyphosate applications to apply Mn

Deficiencies show up as yellowing between the veins on new leaves of bean plants

Mn ppm should be lower than Fe ppm

Lime can reduce Mn uptake

11. Iron

Should be 20 40 ppm

Fe helps with respiration, photosynthesis, enzyme systems, energy transfer

Fe shortages are related to high pH, Cu, Mn, P, as well as cold temperatures

Excess Ca will limit Fe, especially when pH is >7.7

Excess liming will limit Fe

12. Copper

Should be 1.4 2.0 ppm (2 is best per Pat)

Cu helps stalk strength, enzyme systems, photosynthesis, nitrogen metabolism, test weight, diseases, and reduces lodging

13. Boron

Should be 1.2 3.0

B is important for moving sugars, starch, and hormones within plants

B is important for cell structure, protein formation, pollination, seed production, N, P, & K metabolism, pod retention, and developing flowers and pods

B helps corn ear tip fill, if you have adequate K and don’t have good tip fill, it’s likely a B shortage

Annual B applications are needed because leaching loss generally exceeds crop removal

Too much K and Ca reduce B uptake

Placing B directly on seed is risky

B deficiencies are common in low O.M. soils

B is not mobile in plants

Typical applications range .5 1.5 pounds per acre

Typical foliar applications range .1-.3 pounds per acre

14. Cobalt

Typically Co is deficient in low CEC soils

Co is important for coleoptile, bud, flower and stem growth

Co helps CO2 absorption, frost protection, and plant vigor

15. Molybdenum

Mo is essential for converting nitrate into amino acids

Mo is important for converting P, protein synthesis, enzyme systems, N metabolism

Mo is mobile in plants, both the xylem and the phloem

P applications may increase Mo levels in plants

Low pH has major effects on Mo deficiencies

Excess sulfate, Fe, and aluminum oxides may decrease Mo levels in plants

Mo is leachable

16. Selenium

Se can act as a PGR

Se protects against pathogens in plants

Se at higher levels is toxic to plants

17. Chloride

Cl by itself is not toxic

Cl is essential for photosynthesis, water efficiency, sugar translocation, and disease suppression

Cl helps reduce lodging

Potash is 45% Cl

Soluble salts (do not confuse this with Na in base saturation)

If you have high saline soil add tile

Or if test show >75% Ca and low S use elemental sulfur

Or if test show <75% Ca and low S use gypsum

Gypsum is calcium sulfate, it has a neutral pH and about 22% Ca and 17% S)

AMS is acidic

Generally Sulfur and micro nutrients (other than B, Mo, & Mn) are not mobile in plants. Deficiencies show up at the top of plant.

N, P, and K are mobile in the plant. Deficiencies show up at the bottom of plant.

There are five major hormone groups in plants: auxins, gibberellins, cytokinin, ethylene, and abscisic

Verified FBN Member (SD)

And if it doesnt rain or you get to much rain, or if it is to cold or to hot you get what you get?

Verified FBN Member (SD)

Yes I have for quite a few years, have GPS yield and moisture data back to 1996. I used JD office (now Apex) at first and used "normalized" yield maps to create variable rate prescription maps and then used the same map for variable rate fertilizer application through our strip tiller and air cart. It only worked ok and was hard, JD software never good at working with others. But now I have used SMS basic software for 15 years and love it, talks to all brands!!! I am able to create variable rate maps for my striptilling using soils maps, yield maps and grid samples taken. I am able to make prescriptions for topdressing urea and give to custom applicator. It works very well, I think if you spend the money and by SMS pro it is even easier. RTK is a must for strip till, variable rate fertilizer in the fall, and variable rate planting in the spring!

Verified FBN Member (ND)

I use Agleader SMS to make variable rate fertilizer and planting maps along with all our data management. It works good once you know what your doing but if I was doing a lot of it there are other programs I would use. There is a learning curve but Agleader has a lot of good training on their site and puts on classes across the country which I have taken several of. I have kept all our planting, harvest, fertilizing and spraying data for about 15 years.

If your using harvest data as input data make sure you proof it. I have certain years that I have excluded because I know they are not good examples of a normal year either a drought, hail, cattle damage, a bad variety, etc.. Also make sure your combines are calibrated well or the yield data is worthless. I will combine the years of good data to make my maps along with soil sampling. Planting maps I make off the variable rate fertilizer map. There are a lot of option of what you can use for input data though, soil type maps, grid sampling, LIDAR elevation maps, MZB soil maps.

The other big thing I've learned is know the equipment that will be applying it. We originally hired maps made and out of 3 services that did it for us 2 of them caused lots of issues. If the zones have hard edges were a rate changes a lot going into the next zone we had a lot of issues. The NH3 applicator couldn't adjust that fast, also a JD air cart can't spin the meter adjustment fast enough being its a gear box system. The way around this is instead of 3 or 4 rates in the field do more and make them inbetween so your edges are more feathered. The downfall to this is some monitors have a limitation as to how many polygons they can support. Also know what the max and min your machine is capable of on each product. When we used a JD air cart our meter for Potash had a bottom range of about 25lbs per acre so that was my min. Some machines are far more forgiving then others. PWM controlled hydraulic drives on dry meter systems are very forgiving from my experience.

The other thing we learned is on our soil type and location variable rate can hurt us. We have a decent amount of elevation soil type change along with the fact that we are not drained. It bit us twice on what we thought was going to be a dry year. After everything was planted and up the weather changed on us and we got wet. Our hills all the sudden became the areas we should have pushed fertilizer and population to and our low areas drowned out. If you have a way to go in and supplement ferilizer it will help but you still dont have as much potential because of the population.

My last thought and something that was drummed into me from one of the classes I took was proof everything. There is a lot of science involved in mapping but it is also part art and needs to be proofed by the farmer that knows the land. Make sure it makes sense you know the land.

Verified FBN Member (ND)

Also using SMS. Totally agree with everything in this post.

As the farmer, you have first hand knowledge of where good/bad ares of your fields are and can use that to verify a prescription, where a 2nd party can't say if something in a map is unnecessarily added or missing. I also adjust prescriptions based on how much variability there is in a field. Some fields have a huge range, other fields that don't still get scripts, but the rate changes are much less. If i'm not confident in a specific prescription, I don't vary the rate as much either.

I was told once that writing prescriptions is as much art as it is science.

Verified FBN Member (AB, CAN)

Try Swat maps ,I would say they have got a pretty good Platform for variable rate!

Verified FBN Member (ND)

I'd say yes. We've been doing variable rate and zoning mapping for about 7 years now. Started with JD Apex, was pretty crude but it work and now have everything moved in to the JD operation center which work very well. Every aspect has to be used when building maps. We can overlay every years harvest data to put a good average together on helping build zones, but I would have to agree with another comment on here that not every year can be used do to weather/disease etc. We've been using the same soil test points all these years. If you don't it's a waste of time. Usually use 3-4 zones per field/farm. Saw another comment on here that equipment can limit the amount of zones in a field which is true with us. Some of our land has 5-6 different soil types in a 50 acre field and yield tends to follow that so electric variable rate motors on Deere seed carts really get a work out. The one thing that I've noticed is that over all the years of doing mapping and variable rate is that our field have tended to "flatten out" when it comes to the big changes to zones. When we first started we could have a 50-70 lb swing from one zone to the next, but now that has dropped to 10-20 lbs from zone to zone. We're making the ground more efficient and putting the fertilizer where it needs to be, along with our seed. All that being said we still work side by side with our agronomist. And we've got a great group of people precision ag with our local Deere dealership if I have any questions or issues with anything. I know a lot of people that have private companies or agronomists that take all the information and build prescriptions for their customers, which is great and I don't have problem with that, but after seeing some of the prices that are charged, and sometimes I think that they must work for fertilizer companies, the rates that they had come up with on some of our fields was CRAZY. I decided to take some time during the winters and figure it out myself with the help of RDO and John Deere. Also, nobody knows your field better than you do, so you understand why the yield are the way they are or if something changes from year to year.

Verified FBN Member (AB, CAN)

What would you say is a fair price for that service

Verified FBN Member (ND)

Since I basically build all the maps, there not too much of a charge there. I do have to pay for the soil testing and having everything analysed usually around 25.00/field. I also do a $900.00 yearly subscription with RDO Equipment JD for Precision Ag help. So if I've got a question on anything, they are right there to assist. In the grand scheme of things it's pretty cheap. I don't charge for my time lol. But it did take me a good amount of time to train myself to make the maps myself, but it's definetely a benefit in the long run.

Verified FBN Member (AB, CAN)

*** Swat maps charges around $10/acre for the first year and around $3.40 /acre in the second and however many years you stick with you think thats reasonable ?

Verified FBN Member (ND)

$10.00 per acre the first year is steep. But I think it's in the ball park. First year is the biggest investment and the hardest work. Starting from scratch and inputting so much information. Lot's of time for the agronomist. $3.40 for the the years to follow doesn't sound bad at all. It's been probably 6 years since I got a quote from an agronomy center and I want to say it was around 5-6 per acre back then. I would hope that it's come down since then. I guess service is everything and if you can get that at $3.40/acre that'd be a good rate.

Verified FBN Member (OH)

Yes. We use ArcGIS Pro software. It is the most affordable solution on a per acre basis and gives you a ton of flexibility in writing your own prescriptions.

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