Variable Rate P & K

vf949

Well-Known Member
A few years back there was some chat on here about variable rate P & K spreading. The general feeling amongst a few was that yes maybe do variable rate lime alright but variable rate P &K wasn't worth the cost and extra work involved.

Now that we are a few years on, technology has moved on and TAMS has come along maybe a few more people have upgraded Spreaders/GPS systems and started doing variable rate P & K?

What are peoples thoughts on it now?
 
A few years back there was some chat on here about variable rate P & K spreading. The general feeling amongst a few was that yes maybe do variable rate lime alright but variable rate P &K wasn't worth the cost and extra work involved.

Now that we are a few years on, technology has moved on and TAMS has come along maybe a few more people have upgraded Spreaders/GPS systems and started doing variable rate P & K?

What are peoples thoughts on it now?
I variable rate spread P and to a lesser degree K, but no fancy GPS or spreader.
I go around the areas that are low in P and spread approx 200kg/ha 0/10/20 or TSP in the Autumn, the whole field then gets maintenance P&K in the form of 12/5/25 or similar in the spring and the areas that low in K get an extra approx. 100kg/ha of MOP in early summer.
I just give a copy of the soil test maps to the man on the spreader with the instructions written on them.
 
I suspect the biggest issue with GPS variable rate P & K application is the need to Purchase and apply both P and K separately (unless you have a front and rear mounted spreader) which complicates a relatively simple job.
 
I variable rate spread P and to a lesser degree K, but no fancy GPS or spreader.
I go around the areas that are low in P and spread approx 200kg/ha 0/10/20 or TSP in the Autumn, the whole field then gets maintenance P&K in the form of 12/5/25 or similar in the spring and the areas that low in K get an extra approx. 100kg/ha of MOP in early summer.
I just give a copy of the soil test maps to the man on the spreader with the instructions written on them.

That sounds a good way of doing it without complicated technology! Also the way you do the spreading throughout the season lowers the number of trips through wet tramlines in Feb/March. Have you found that the P & K has evened up a lot not when you test the soils? How often are you getting the soils tested?
 
That sounds a good way of doing it without complicated technology! Also the way you do the spreading throughout the season lowers the number of trips through wet tramlines in Feb/March. Have you found that the P & K has evened up a lot not when you test the soils? How often are you getting the soils tested?
Will only be starting to retest this Autumn and will only be doing problem areas first, but have seen yields evening up.
 
Did I see a trailer spreader somewhere with a split hopper?? Vague memory of it. P in one section k in the other? Blended before they drop onto the discs? Basically two weigh cell machines with one set of discs. If not then I’ve just invented it. I suppose a front and back spinner would do the same.
 
Did I see a trailer spreader somewhere with a split hopper?? Vague memory of it. P in one section k in the other? Blended before they drop onto the discs? Basically two weigh cell machines with one set of discs. If not then I’ve just invented it. I suppose a front and back spinner would do the same.
Dam it I had just invented that idea during the week because the one problem when I was doing it was all the extra traveling when conditions were poor.
 
Variable rate P means using TSP which gets locked up in soil after 8-10 weeks
While it will raise P index it might not be available
We have tons of P locked up in soil
My interest is unlocking this P using various methods
Index of P doesn’t really bother me as long as you feed crops it’s needs
Variable rate lime interests me alright
 
Variable rate P means using TSP which gets locked up in soil after 8-10 weeks
While it will raise P index it might not be available
We have tons of P locked up in soil
My interest is unlocking this P using various methods
Index of P doesn’t really bother me as long as you feed crops it’s needs
Variable rate lime interests me alright
Lime is cheap, does the cost of testing every ha and the technology needed for variable rate justify it, does the over application in places cause enough of issues to justify it also?
 
In my humble opinion , A daft idea ,

The cost of the technology to implement it , would cost far far more than having your whole farm in index 5 ?

I could be very wrong though .


PS , it appears @Blackwater boy was a bit quicker on the key board.
 
A lot of the spreaders that are around now should be able to do it with very little upgrade from what I can see. They already have the GPS for guidance, GPS on off for section control and headland on/off. It's the testing and mapping that would probably be the expensive part I would think. The spreading will only be as accurate as the testing that you do I guess.
 
We have been spot spreading lime for years . We used test the field with a W pattern but go back with litmus paper kits or one of those probes you get in the garden centers .
I put up some pictures of the SOYL tests that we got done a few years ago and the cost was easily covered by the saving we made on the lime . We just marked out the field and got the friendly lime spreader to do certain areas .
I have proved that chopping the straw raised our K levels that were traditionally low .
I might look into rigging the GPS up to the Bogballe .
 
I'm inclined to think variable rate pk is a sexy metal solution to a more simple chemistry problem. Build om. Provide more capacity to retain and cycle major nutrients and use less bag. The generated maps are interesting for all kinds of reasons. Mg and ca among them. I've done it on the place here and was trying to spread more compost and chicken shite on the spots with lower pk indices. But I had a thought then.....lightest sandiest spots seemed to correlate with lower indices. My new unscientific theory is that building organic matter with cc and shite and not letting these sandy spots leach will be the best tac.
 
How do you calculate the correct amount of fert if I was to use 0-10-20 and a second run of 50 %K.
Do I multiply the ETSB *.1.6 to give me tonnes of 0-10-20 / field.
And multiply MOP *2.5 to give me tonnes. /field . And deduct the K in the 0-10-20 to give me the tonnes 50%K
7E3A6A0A-6E54-4713-B72E-F3223121E73C.png
 
How do you calculate the correct amount of fert if I was to use 0-10-20 and a second run of 50 %K.
Do I multiply the ETSB *.1.6 to give me tonnes of 0-10-20 / field.
And multiply MOP *2.5 to give me tonnes. /field . And deduct the K in the 0-10-20 to give me the tonnes 50%K
View attachment 60907
Your P levels must be low enough?
My reading of it you need 34.02 tons of 16% P and 13.79 tons of 50% K
Or 54.43 tons of 0/10/20 and that would over supply your K requirement significantly.
TSP or DAP look more suitable to your needs, if I am reading it, for example is the big field in Kellistown lowish in P (between 3 and 5) and high in K (above 150) ?
 
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Your P levels must be low enough?
My reading of it you need 34.02 tons of 16% P and 13.79 tons of 50% K
Or 54.43 tons of 0/10/20 and that would over supply your K requirement significantly.

There is a big difference between the IAS tests and the SOYL tests as the Soyl test goes down to 15cm and we may have layering due to min tillage .
 
TSP or
There is a big difference between the IAS tests and the SOYL tests as the Soyl test goes down to 15cm and we may have layering due to min tillage .
If it was mine I would use 0/10/20 or 10/10/20 as suits across the whole lot, if you are thinking of selling straw.
 
The lines with the blue are 2017 results of IAS soil test in the same field. The SOYL tests are done to 15 cm where as we would test about 10 cm and have up to recently being chopping and have a huge amount of Biological activity in the top layers .
There is consistent difference between SOYL and IAS or FBA .
33171FBD-24AE-4414-91C7-853CC2037124.png
 
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