High magnesium soils

[Wobblebox]

Just had my first Soyl samples back and I'm surprised that a lot of our area is high in Mg, we normally apply FYM, urea, MOP and TSP, would any of these problems be exacerbating the situation?
Any products we should use/avoid?
What nutrients will the Mg be locking up?

 

[snipe]

Fym will have a little bit of mg. calcium is needed to combat mg I think.. gypsum would be a cheap product. Mg sticks soil particles together. Not good it you have heavy clay soils.

 

[Wobblebox]

They are heavy clay soils

 

[Old Spot]

High mag locks up most things, I had loads of the horrible stuff!
Put on as much sulphur as you can afford every year for the rest of your life, it's amazing what difference you will start to see after 5 years gets much better after 10!

 

[Wobblebox]

 

[franklin]

are they at the bottom corner of the field where the water runs down to?

 

[ih1455xl]

Cake it in gypsum mostly free if you can take it winter tipped

 

[warksfarmer]

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Wish ours were your levels! We are dealing with 800ppm figures and as mentioned with clay soils they virtually never dry out. We’ve tried gypsum over a few years and the levels didn’t alter when retested. @Tom H has the same problems.

I must admit the sulphur thing is intriguing as I think we’ve been low only going around 60-70kg in the past. This year we are trying nearly 100kg.

 

[Brisel]

Adding calcium is going to help high mag soils.

Gypsum, compost, sewage cake, Fibrophos, Kalfos

 

[Princess Pooper]

I was told by a leading soil scientist once on a local farm walk that it would not be worth us putting gypsum on our high Mg Ragdale clays. High Mg soils are always very 'tight' and hard to work, organic matter the best 'solution' but if they are potash releasing as well (ours are) make sure you don't overdo the K.

 

[Tom H]

Wish ours were your levels! We are dealing with 800ppm figures and as mentioned with clay soils they virtually never dry out. We’ve tried gypsum over a few years and the levels didn’t alter when retested. @Tom H has the same problems.

I must admit the sulphur thing is intriguing as I think we’ve been low only going around 60-70kg in the past. This year we are trying nearly 100kg.

As Lee mentions we have a considerable area that ranges from 500-900 ppm, we ran a split field where we applied gypsum for a good few years with no real result. The ironically our area is where the best quality gypsum is mined, with big areas of the farm underling in the stuff. I guess it's at too much depth to be useful. Fladbury series clays are the worst suffer for us. Manure will help you far more - even though these soils have SOM% of 6-12%

 

[ollie989898]

You have clay? You will have high Mg. Keep land in good heart, it is all you can do, high Mag tends to lock up stuff but the trick is to have plenty of organic matter and manures at various stages of breakdown, so the crop is drip fed. As it warms in spring the breakdown is accelerated and crops will flourish. Any transient or seasonal effects you can combat in crop with timely use of foliar products if you think it is serious or prolonged enough.

 

[PSQ]

Any products we should use/avoid?

To state the bleeding' obvious, try to avoid Mag Lime, and if the haulage isn't too prohibitive use the finest *ground* Calcium lime you can find.
But then again your pH maps look OK, and the lowest pH areas are lower in Mg, possibly lighter corners of the field?

 

[Warnesworth]

Time to add a little detail to some of the comments on this thread. Yes, high mag can be reduced with applications of gypsum or straight sulphur in SOME (but not all) circumstances, but before liberally applying whatever you can lay your hands own in the vain belief it will help, you need to have a CEC analysis of your soil to establish the cation saturations. This will then allow you to make the most cost effective and correct application. Applying gypsum to a high mag soil with sufficient calcium will only prove expensive because its unlikely you will see a response, which is what I suspect @Tom H has experienced, in his post above.
Similarly @warksfarmer is considering applying higher levels of sulphur ('nearly 100kg/ha'). I suspect @warksfarmer will be applying this sulphur with his nitrogen in the growing season, therefore the sulphur will be used by the plants and the soil biology before it does anything for the magnesium levels. Also you need water movement through the soil for the sulphur to 'move' the magnesium so spring applied sulphur is never going to achieve this. Also 100kg of sulphur will make very little difference to the mg level.

Another point is that sulphur should be applied in a 1:2 ratio with N so 100kg of sul[phur onto a wheat crop is just about enough if you are applying over 200kg of N.

 

[Warnesworth]

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A basic bit of of nutritional advice, some areas of these fields look terrible (sorry to be so blunt). You have magnesium levels well in excess of the potash so you are probably experiencing some poor yields. I suspect the crops are probably magnesium deficient as well (I know how crazy that sounds in a soil stuffed full of magnesium but bare with me). Some areas are certainly also calcium deficient and the pH is elevated due to the high magnesium.

 

[Brisel]

Interesting. Sorry to hijack your thread @Wobblebox

What would you do with a field like this @Warnesworth ? It's nearly the opposite of the OP's situation.

Soil type is pretty chalky, with slighlty increasing clay content as you go NE.

 

[Warnesworth]

@Brisel Interesting. Has this received sewage cake?

 

[scholland]

@Warnesworth what products do you like for helping with calcium?
Can only get mag lime here, trying to address that, do use beach sand at times but not always an option.

 

[warksfarmer]

Time to add a little detail to some of the comments on this thread. Yes, high mag can be reduced with applications of gypsum or straight sulphur in SOME (but not all) circumstances, but before liberally applying whatever you can lay your hands own in the vain belief it will help, you need to have a CEC analysis of your soil to establish the cation saturations. This will then allow you to make the most cost effective and correct application. Applying gypsum to a high mag soil with sufficient calcium will only prove expensive because its unlikely you will see a response, which is what I suspect @Tom H has experienced, in his post above.
Similarly @warksfarmer is considering applying higher levels of sulphur ('nearly 100kg/ha'). I suspect @warksfarmer will be applying this sulphur with his nitrogen in the growing season, therefore the sulphur will be used by the plants and the soil biology before it does anything for the magnesium levels. Also you need water movement through the soil for the sulphur to 'move' the magnesium so spring applied sulphur is never going to achieve this. Also 100kg of sulphur will make very little difference to the mg level.

Another point is that sulphur should be applied in a 1:2 ratio with N so 100kg of sul[phur onto a wheat crop is just about enough if you are applying over 200kg of N.

We aren’t applying sulphur to the soils ...... given up on that years ago. The sulphur is for the growing crop.

 

[Warnesworth]

@scholland Prilled calcium lime.

I know all the nay-sayers will be along to tell you that's its exactly the same as aglime and they are absolutely right, but ag-lime in my experience is a big con. I bought a set of very expensive laboratory sieves last autumn and tested ground limestone as delivered on-farm from at least 5 different quarries. Not one reached the claimed specification of 40% passing a 150 micron sieve. This is the important bit as it is the portion that reacts with the hydrogen in the soil and brings the pH up. Some of the samples only made 1-2% passing the 150 micron sieve, the best was about 24%. That is criminal.

So with prilled lime you get the nice fine dust in a prilled form, (the glue that holds the prill is water dispersible, I have done some of my own trials with it and it disperses within a couple of months if left on the surface). That you can spread yourself, accurately, saving cost, reducing potential soil damage and at a time that is better agronomically. Whenever I see an ag-lime spreader working it's usually followed by a cloud of dust as the nice fine reactible dust blows over the hedge. So you've paid for 40% finely ground, what's delivered is half that amount, and then the rest blows away, that's good value! Prills are less susceptible to wind blow so you get a much more even spread.

I don't advocate large amounts in one go, the recommendation generally works out at a cost of ~£25-35/ha/yr BUT you know what you are getting. Consistency in spread and product. What's not to like?

I usually do calcium recommendations based on a accurate CEC test, not the usual 'finger in the air' pH test.