High magnesium levels

[AKA]

Hi, I've recently rented my first farm from last summer, it is mainly arable crops I've sown. As part of the tenancy my landlord had to provide soil tests of each field at the start of the tenancy. I have only recently received these and nearly every field is high in magnesium. Is this a problem? And how do I reduce it to normal?

 

[Wombat]

What do you call high?

 

[BigBarl]

magnesium in high levels can make soil 'hard' to work. best thing is to put some calcium (gypsum etc...) this will hopefully make the ground easier to work as the bigger calcium particle size opens the soil up slightly. magnesium particles are very small and so pack tightly together from my understanding.

 

[dannewhouse]

its common in Yorkshire I have been advised there's not much you can do about it just that whenever lime is required always use calcium lime have you found your P and K indices to be high as well ? I was also advised that the high mag "locks them up" most of my land is index 5 mag and index 4/5 for P and K. never had a nitrogen test done as I know the land has been well under fertilised forever. I was advised to just put straight N on as P and K wouldn't do anything. I always put N and S on first application the top up with N.
There's still people round here putting 20:10:10 on cereals and there land must be similar to mine with high P and K levels so their either throwing money away or they know something I don't.

 

[marco]

You want to find out your mg % compared to ca% in an Albrecht test. You can plot a coarse of action when you have the facts.

 

[Casemx120]

Used Calcifert S last year for this reason. Supplied S in one early hit and believe the Ca locked up some Mg. Did a test by telling fertiliser man to only do half a field but not tell me which half! was able to tell the difference on the combine, no yield monitor, NH8060, but could see it when combining. Only prob was the half that was def lower yielding did not receive any S. So jury still out. Had good crops last year but it was a good year

 

[SoilMan]

as marco said, albrecht test to look at base saturation of Ca and Mg in your soils and also look at your soils CEC cation exchange capacity. This effectively measures the negative charge of your soil which will predominently be your clay colloids and some humus. Which will allow you to judge the type of soil remedial to use (most likely gypsum) and at what rate as lighter soils can benefit from slightly higher Mg levels to hold them together whereas heavier soils will want higher Ca levels to open up the soil (but not too much as this can lock up P, the more you look into these things the more confusing but fun it gets!)

 

[franklin]

1) Check how long tenancy is for.
2) If you have done soil tests at the beginning, are you going to be a) penalised or b) rewarded for increasing / decreasing soil nutrients? If so, who is responsible for doing the soil tests? If you then good. If the landlords agent then bad.

I'd base what I did regards high mg on the answers to these questions.

 

[Tom H]

I have a lot of soils with a CEC of 35 and a Ca:Mg ratio of 18:1 and indices of Mg getting well over 6-7 I'm afraid gypsum doesn't really touch it!

 

[SoilMan]

Agreed in the short term, but over a long period of time using gypsum and compost you would expect to see improvements surely? On a short term tenancy would you see the benefit? Probably not!

But as with all things related to the soil, just looking at one dimesion (say applying gypsum) and expecting that one thing to change everything is a naive view point. If you genuinely want to improve your soil and yields (and keep them consistently higher and not just a one trick wonder) then you need to look at your whole system e.g. rotation, type of cultivations, amount of nitrogen used, chemicals used, FYM, composts, cover cropping etc, and see how each element will benefit and compliment the other.

 

[Tom H]

60 years since its seen a plough. Gypsum application for 10 years (stopped now) Gypsum is also removed from the ground next door, all of this soil type is underlying the stuff. SOM of 6%. Sludge has been applied in rotation along with chicken muck. Good rotation now. Cover crops , 4th year if CTF. Some soils are just what they are. You can't polish a turd! Fladbury series clay.

 

[AKA]

Most of the land is heavyish with the mg indexes of between 5 and 6.

 

[Wombat]

Ok if it's 5 to 6 I wouldn't be too worried by it, as other have said you can try some gypsum. How long have you got the tenancy? What part of the soil tests are they going to hold u to?

 

[AKA]

It's a 5 year term to start with, I don't think they'll hold me too anything as some fields needed liming at my cost and phosphate indices were down in most fields too. What sort of money would i expect to pay for gypsum and how many t/ha?

 

[franklin]

I have 800+ ppm mag and in reality there is very little that can be done to reduce it. Certainly not very economically, and certainly not with wheat at £100/t. Best to get a proper soil test done to see what other imbalances there are and address them.

You may find your crops will be happier by spending the money that gypsum will cost on having a look at the drainage plans and giving it a good mole ploughing which will last you five years.

 

[SoilMan]

60 years since its seen a plough. Gypsum application for 10 years (stopped now) Gypsum is also removed from the ground next door, all of this soil type is underlying the stuff. SOM of 6%. Sludge has been applied in rotation along with chicken muck. Good rotation now. Cover crops , 4th year if CTF. Some soils are just what they are. You can't polish a turd! Fladbury series clay.

that'll do the trick, it seems you have done the correct thing and rather than look at one element or 'quick fix' have changed the management and system to benefit and improve your soil.

are you noticing improvement in soils structure or any other imrpovements with ctf and cover cropping?

 

[ajd132]

In reference to organic matter testing, I have been reliably informed by numerous people the loss on ignition is pretty much useless on clay soils because of the water content. Apparently dry combustion is the way forward? (Is that joe?!

 

[SoilMan]

cheers adam, yes LOI (loss on ignition) can also count water moelecules bound tightly by clay collieds and in carbonates found in calcaerous soils which will count to the LOI test and be assumed as OM.

But with all things it is a case of using these tests along with visual inspections of the soil and using logic to interpret what all these things say. We cant judge all our decisions as a matter of fact by blindly following soil tests, they should be used as an aid to assist in decision making.

the other option is the Walkley Black test, this is expensive and uses Dichromate as one of the reagents which is highly toxic and carcinogenic (I'll assume we can guess why people arent keen on doing this test!)

 

[ajd132]

Have emailed you.
The reason I want OM tests done is basically to quantify what we are doing to land owners and agents

 

[warksfarmer]

Hi, I've recently rented my first farm from last summer, it is mainly arable crops I've sown. As part of the tenancy my landlord had to provide soil tests of each field at the start of the tenancy. I have only recently received these and nearly every field is high in magnesium. Is this a problem? And how do I reduce it to normal?

Welcome to the club ....... If it's clay then it will be sticky and very slow to dry out. It locks N up a bit so putting another 20-30kg/ha on will be of benefit.

Shallow tillage to create till and allow quicker drying works but deep work isn't required and it will crack itself in the summer.