Are soil indices and variable rate spreading completely flawed?

[ajd132]

ive though this for years now for a number of reasons and thought it would be interesting to see others views, especially after some of the comments on the power harrow thread. A few thoughts below.

Low p fields performing better than they should.
Different results from the same soil sample to different companies.
Are the tests really showing up available nutrients or locked up stuff?
Variable rate p and k just evening out reserves of locked up nutrients.
Massive reserves of soil nutrients are there just the soil is not performing properly to unlock it.
Soil degradation by removing straw to then go and spend money on granular product to replace it.

Is the science behind this whole thing completely flawed? Is variable rate p and k utterly worthless (I think it is)? Is the system a road to nowhere?

 

[SilliamWhale]

Maybe.

But indices do tell you something.

 

[PSQ]

Is the science behind this whole thing completely flawed? Is variable rate p and k utterly worthless (I think it is)? Is the system a road to nowhere?

Back up a step. If VR is flawed, then so is flat rate application across an entire field. Its the same science and soil test for both, the only difference is the resolution of the results: per field, or per Ha.
In fact, if your sceptical of established science then ignore all soil test results for 25 years, and see if you're still in business.

 

[Simon C]

Back up a step. If VR is flawed, then so is flat rate application across an entire field. Its the same science and soil test for both, the only difference is the resolution of the results: per field, or per Ha.
In fact, if your sceptical of established science then ignore all soil test results for 25 years, and see if you're still in business.

Plenty of us not applied any P or K for twenty years, and yup, still in business.

That reminds me, must pay that tax bill by the end of the week!

Yes, @ajd132 , the tests are flawed.

 

[ajd132]

Back up a step. If VR is flawed, then so is flat rate application across an entire field. Its the same science and soil test for both, the only difference is the resolution of the results: per field, or per Ha.
In fact, if your sceptical of established science then ignore all soil test results for 25 years, and see if you're still in business.

I would say applying flat rate bagged p and k religiously to mostly add to a bank of locked up nutrients is probably completely flawed also.

 

[Feldspar]

Back up a step. If VR is flawed, then so is flat rate application across an entire field. Its the same science and soil test for both, the only difference is the resolution of the results: per field, or per Ha.
In fact, if your sceptical of established science then ignore all soil test results for 25 years, and see if you're still in business.

This is what one of our indepedent agronomists has said who I respect a lot. He's still revising his thinking, but based on the results he has seen over the last years, he comment was that the current system is "broken".

 

[PSQ]

This is what one of our indepedent agronomists has said who I respect a lot. He's still revising his thinking, but based on the results he has seen over the last years, he comment was that the current system is "broken".

Agreed, it would appear to be flawed. But until anyone comes up with some cast iron theory to replace it, it's the best we've got.

5 years ago everyone raved about Kinsey and treated 'Hands on agronomy' like the gospel. Funnily enough I haven't heard his name mentioned by his former evangelists for quite some time, but isn't that always the way with fads.

 

[farmerfred86]

We have known for a while the results are flawed or unreliable... as a result we use the offtake figures from the previous crop and apply that. It has the advantage that I don’t have to wait for sample results post harvest and can crack. Accurate to work with and we maintain what we have that way.

As for doing nothing that is frankly rediculous. I’ve heard of people doing this and eventually crops producing no ears/heads is the result. The samples might not be good but we all know basic plant science. (That is not to say you won’t get away with it for several years and some do when they know they are in it short term!)

 

[ajd132]

We have known for a while the results are flawed or unreliable... as a result we use the offtake figures from the previous crop and apply that. It has the advantage that I don’t have to wait for sample results post harvest and can crack. Accurate to work with and we maintain what we have that way.

As for doing nothing that is frankly rediculous. I’ve heard of people doing this and eventually crops producing no ears/heads is the result. The samples might not be good but we all know basic plant science. (That is not to say you won’t get away with it for several years and some do when they know they are in it short term!)

Oh I agree, we use chicken muck, fibrophos, starter ferts etc.
What I’m getting is how much can we ‘mine’ that has been locked up for years and years by getting the biological side of stuff correct which has been completely overlooked.
And how much time has been wasted lining the pockets of these companies having maps made and variable rate stuff put on an has this actually been a negative?
I agree on the basic science and there was no way I was suggesting don’t do anything.

 

[7800]

worth a look at the Broadbalk experiment at Rothamsted, over 100 years of fertiliser trials
But I agree soil testing is only a guide, I've had results that differ by a whole index out of the same bucket to the same lab
'mapping' is seen as the professional way forward but I've not done any!
I think some low P soils are yielding well & the big crop is taking the P in offtake, the P level is not the reason for the high yield

 

[farmerfred86]

the latest “in thing” of organic matter sampling is just as bad. There is no standard depth or type of test and so results can be wildly different and not really telling you anything useful.

 

[ajd132]

the latest “in thing” of organic matter sampling is just as bad. There is no standard depth or type of test and so results can be wildly different and not really telling you anything useful.

This is where putting too much emphasis on tests is pointless. We can tell a good soil from a bad one easily.

 

[david]

So the lab is telling you the nutrient contents of say 50-100 grams of soil that has been collected from say a 10 acre block of how many thousands of tons of soil ?

 

[Macsky]

Viva la revolucion!

 

[Kiwi Pete]

Agree with the above, it has some usefulness, but I think we all know fields that constantly "overperform" and ones that underperform, I certainly don't follow whatever logic keeps people spending on what their soils don't actually lack.

There's obviously so much that the biology does, that the tests don't show; our real knowledge of soil biology is WAY behind our knowledge of soil chemistry.

I won't begin to explain why that may be.... because I think it's very apparent?

 

[yellow belly]

i have had my highest yield from a filed with the lowest index

often from 1950 onwards basic slag plus some 20 10 10 at drilling in the spring or 0 23 23 in the autumn field near to muck heap have higher indices

my theory is that over the years with flat rate applications of p and k the highest yielding field have the lowest levels the lowest yielding fields have the highest index .lower yields are often due to poor drainage pests lime status or low water reserves depending on the soil type

feeding the soil based on the yield oftake is most likely the most accurate way to maintain the soil

the latest guidelines from rescent trial do show that maintaining index 2 is the most cost effective system although some soils see no profitable gain from trying to raise the level if the soil is index 1

I have had fields that on one test gave index 5 then 5 year later gave index 1 so I now treat with caution indexes on new land that are very high
I have some land that has regular tested index 2 for 30 years or more with no variation

there is no cost effective alternative system than current index
variable rate application is not cost effective the saving may pay for the system but not if soil are relatively uniform
if the soil is variable it can be identified with a soil map and normal soil sampling based on soil type

 

[jonnyjon]

ive though this for years now for a number of reasons and thought it would be interesting to see others views, especially after some of the comments on the power harrow thread. A few thoughts below.

Low p fields performing better than they should.
Different results from the same soil sample to different companies.
Are the tests really showing up available nutrients or locked up stuff?
Variable rate p and k just evening out reserves of locked up nutrients.
Massive reserves of soil nutrients are there just the soil is not performing properly to unlock it.
Soil degradation by removing straw to then go and spend money on granular product to replace it.

Is the science behind this whole thing completely flawed? Is variable rate p and k utterly worthless (I think it is)? Is the system a road to nowhere?

My suggestion would be to listen to some of Gabe Brown's presentation's, above average yields with no inputs. It's all about having the biology working in the soil, probably explain why some fields yield different to what the soil sample result would suggest

 

[Simon C]

I have soil tests showing 1.7 tonnes of TOTAL P per ha in the top 4 inches, never mind the other 20 inches that roots go down to below. What is the point of putting a few kgs of fert on when there is all that to go at. All you need to do is get the biology working and it will be made available as and when needed.

Of course you do have to stop adding P fertiliser, otherwise the biology will think it doesn't need to work.

 

[Brisel]

Yes, the tests are flawed, but until you've got a seriously lively soil with extensive mychorrizal systems the lab tests are the best you have available. There are more detailed tests looking at base saturations etc but these cost more obviously so you've got the reasonably cheap ones that your clients' agents will understand too.

NIAB TAG did a study on low P index soils a while ago. The basic conclusion was that you could certainly run "available" reserves down but ran the risk that one day you'd lose a crop for the sake of a few kg of P. One of my best fields had a P index of 0 and boosting that to 2 made no difference to yield.

The photo I unashamedly stole from a Joel Williams presentation in Baldock in 2016 illustrates what the potential can be. Accessing what is there is what you need decent soil biology for.

 

[SilliamWhale]

The problem is....

The only way we feed the plant via the soil is biological (ignoring some foliar feed). Every bit of plant food (artificial, fibrophos, fym, lime, co2) has to be transported to the plant via root hairs, liquids, acids, microbes and other stuff too late to go into detail on now.

But our analysis of soil is purely chemical. So we can only test the chemical components of the soil (which isn't un-useful by any stretch, its just limited) on its own merits and not by the biological factors.

My own take on it is the chemistry can tell you if something is or is not there and it does have a place, but the biology is the thing that helps us use the chemistry efficiently. And we are only really now trying to figure out how to analyse the efficiency of system.

We don't know well enough for example if old plant roots are capable of storing more P for us than if they were tilled away (my feeling is yes). All the secretions from the soil biota will definitely be contributing to a better plant utilisation efficiency. If this wasn't the case then soil fertility would never have developed in the first place - we see soil fertility as a process which we need to add amendments too (and sometimes we do) but don't forget in the geological perspective its always been a succession of plant types to get there - lichen on rock, to moss, to annuals, to perennials, to woodland etc. All constantly being knocked down and pushed up again - even stones contain chemical elements of fertility!

Read Jeff Lowenfels Books