Availability of Magnesium in FYM?

[flyonthewall]

Updating an RB209 here, section 3, P18 states if Mg is an indices 0 or 1 to top up with 50-100 kg/Ha MgO, referring back to p17 of section 2 it does not give the availability in FYM like it does p and k, does anybody know a commonly accepted/agreed percentage figure?

 

[Cowabunga]

I've no idea but years ago this area was known for Mg deficiency. Back about 40 years ago I had Mag Lime spread at about 1.5 tons an acre over most of the farm and that was the only time I ever spread it or anything with Mg.

However, I did a soil analysis of several fields this year and found that Mg levels were very high in all of them. Too high if anything. Could it be that high mag cow minerals were mostly excreted by the cows and the few tons [less than 10 in those 40 years I hazard a guess] raised the soil index? It's just something that I thought about last Spring and forgot until I read the above question.

 

[Sonoftheheir]

Our Mg levels are 5-6 this year, they were mucked with cattle manure that was just cultivated in for now. My agronomist is saying put some gypsum on to try and bring the levels down??

 

[Brisel]

Updating an RB209 here, section 3, P18 states if Mg is an indices 0 or 1 to top up with 50-100 kg/Ha MgO, referring back to p17 of section 2 it does not give the availability in FYM like it does p and k, does anybody know a commonly accepted/agreed percentage figure?

I wouldn't worry about it too much. Magnesium may be a macronutrient but not to the same extent as P or K. The quantities required are much smaller. Without looking at RB209, the older version of this only suggested a top up every few years.

 

[Luke Cropwalker]

Updating an RB209 here, section 3, P18 states if Mg is an indices 0 or 1 to top up with 50-100 kg/Ha MgO, referring back to p17 of section 2 it does not give the availability in FYM like it does p and k, does anybody know a commonly accepted/agreed percentage figure?

If you are seeing Mg deficiency or growing a responsive crop then I wouldn't rely on the Mg from any type of manure. The FYM will help to supply the crop with some Mg but the availability will be very variable, a bit of Kieserite or foliar MgSo4 is cheap enough.

 

[Bogweevil]

Good observation - I had missed that.

University of Nebraska* speaks thus:

Potassium (K) availability from manure is nearly 100%; therefore, manure can be used similar to K fertilizer. When manure was analyzed for plant available nutrients, greater than 55% of calcium (Ca) and magnesium (Mg) and less than 40% of zinc (Zn), iron (Fe), manganese (Mn), copper (Cu), sulfur (5), and boron (B) were plant-available. To effectively utilize the nutrients in manure, their mineralization potential should be considered when determining application rates.

Therefore if you wish to address the measured lack of magnesium you can assume about half the content of whatever the analysis of your manure (or book values if no analysis has been done) says will be available to resolve the immediate deficiency and the remainder will become available to add to soil reserves in time.

Of course Nebraska is bustard cold in winter and devilish hot in summer so mineralisation will vary from that in our balmy climate, but it gives an idea of sorts. And also in Nebraska it is feedlot manure not our sturdy British FYM with much well trodden straw, but straw contains little magnesium; it is mostly silica and calcium, so I am reasonably confident the two are comparable.

*https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1138&context=biosysengfacpub

 

[flyonthewall]

Thanks for the input - I'll work on 55% then, appreciate that Mg in FYM is minimal. I'm filling out a "tried and tested nutrient management plan" for each field to submit and finalize a planning application. Seemingly the planners feel us farmers must go around spreading N like orangutans, the amount of local authority paperwork for 6 calving bays is unreal. The good news is that all of the fields are at indices 2, bar one which is at 1, interestingly this doesn't have any much on as part of it is used as football pitch. It looks like once you've got Mg to where it needs to be it stays there, unlike P and K which are at indices 1 on some fields. Going to address this with Fibrophos in the spring at 500-750kg/Ha. I blame my ex-fert rep as he advised just to use straight AN and make the rest up with FYM, whereas my late father only ever used 20:10:10.

 

[Wombat]

Thanks for the input - I'll work on 55% then, appreciate that Mg in FYM is minimal. I'm filling out a "tried and tested nutrient management plan" for each field to submit and finalize a planning application. Seemingly the planners feel us farmers must go around spreading N like orangutans, the amount of local authority paperwork for 6 calving bays is unreal. The good news is that all of the fields are at indices 2, bar one which is at 1, interestingly this doesn't have any much on as part of it is used as football pitch. It looks like once you've got Mg to where it needs to be it stays there, unlike P and K which are at indices 1 on some fields. Going to address this with Fibrophos in the spring at 500-750kg/Ha. I blame my ex-fert rep as he advised just to use straight AN and make the rest up with FYM, whereas my late father only ever used 20:10:10.

Index 1, [emoji33]

 

[Cowabunga]

Fertiliser needs vary from one year to the next dependant on the indices and crops grown. After years of using 20-10-10 it is quite possible that you had high enough indices to use just N for a couple or three years, but certainly not in the long term with FYM unless you were/are very extensive as far as grazing and especially forage harvesting on the land is concerned, with very low applications of N.

 

[Brisel]

Index 1 is ok for Mg

 

[Wombat]

Index 1 is ok for Mg

Haha yeah I wondered what index 1 looked like [emoji3]

 

[Flat 10]

Index 1 is ok for Mg

Is that right? I didn’t know that. Routinely use kieserite here which I think benefits crops on our high Ca soils. Indices vary between 1-2.

 

[deleted user 837354]

Somerset farmers be like: 'my Mg indices are 4 or 5, does this mean I can't apply any muck to them at all....?'

RB209 is ridiculously out of date. I'm here filling in the tried and tested nutrient plan for someone, the recommendations for grass are suspect.

EDIT: just noticed there is a later version of RB209 lol.

Grass and sulphur is also another 'we don't know' question. It suggests 40kg per cut. Then says the critical ratio is 13:1 for N:S.

 

[deleted user 837354]

Thanks for the input - I'll work on 55% then, appreciate that Mg in FYM is minimal. I'm filling out a "tried and tested nutrient management plan" for each field to submit and finalize a planning application. Seemingly the planners feel us farmers must go around spreading N like orangutans, the amount of local authority paperwork for 6 calving bays is unreal. The good news is that all of the fields are at indices 2, bar one which is at 1, interestingly this doesn't have any much on as part of it is used as football pitch. It looks like once you've got Mg to where it needs to be it stays there, unlike P and K which are at indices 1 on some fields. Going to address this with Fibrophos in the spring at 500-750kg/Ha. I blame my ex-fert rep as he advised just to use straight AN and make the rest up with FYM, whereas my late father only ever used 20:10:10.

No one should be advising straight N and FYM for everything else- that is just lazy. The amounts and availability of some nutrients in manures is actually very modest. I always aimed to be a lot more sensible than that.

 

[Wombat]

Somerset farmers be like: 'my Mg indices are 4 or 5, does this mean I can't apply any muck to them at all....?'

RB209 is ridiculously out of date. I'm here filling in the tried and tested nutrient plan for someone, the recommendations for grass are suspect.

EDIT: just noticed there is a later version of RB209 lol.

Grass and sulphur is also another 'we don't know' question. It suggests 40kg per cut. Then says the critical ratio is 13:1 for N:S.

We are buggered then at index 8 and 9

 

[Brisel]

We are buggered then at index 8 and 9

Do you buy much calcium?

 

[Brisel]

Is that right? I didn’t know that. Routinely use kieserite here which I think benefits crops on our high Ca soils. Indices vary between 1-2.

I don’t think that you are doing anything wrong by being at a higher index than 1 other than being a lower priority to spend your cash, unless your source of other nutrients is rich in Mag. A few tissue tests in the growing season will tell you what is missing.

 

[teslacoils]

We are buggered then at index 8 and 9

Yup. I've a couple of lighter fields at index 5!

 

[N.Yorks.]

Our Mg levels are 5-6 this year, they were mucked with cattle manure that was just cultivated in for now. My agronomist is saying put some gypsum on to try and bring the levels down??

If the agronomist is talking about gypsum does that mean you're experiencing poor soil structure in a clay soil?

 

[Sonoftheheir]

If the agronomist is talking about gypsum does that mean you're experiencing poor soil structure in a clay soil?

Yes, spot on.