What minerals does soil lose when overgrazed with sheep?

Hi everyone,

I've got a sheep-related question but it's not about keeping sheep. It's about forestry.

Does anyone know what kind of mineral deficiencies are most likely in a soil when it is consistenly grazed (and overgrazed) by sheep?

I am asking because I own a small patch of forest that was established on an overgrazed hilltop. It's likely that the grazing had been happening there for several centuries (this is in Europe: the Netherlands) before the forest was planted around 1900.

Many tree species don't do well on the soil, and in part that may be because it is high in sand and low in clay or silt. But I also believe it has something to do with the fact that it's been exploited for sheep grazing. The sheep were generally taken back downhill at the end of the day, so that their dung could be collected near the farm.

The problems I see in the trees are primarily crooked growth. Black cherry (imported from the US, now something of a pest) in particular will grow almost everywhere, but it never has straight stems as seen on better soils. Only one individual, which has had garden waste heaped onto the soil below it, grows nice and straight. It also has a much shinier bark.

Serious leaf problems are rare, except on native (European/English) oak, which is always susceptible to mildew, but particularly so on the driest parts of our soil.

I'm thinking of testing if it would help to add certain minerals to the soil. But it would be great to get some pointers to the most likely deficient minerals.

Thanks for any tips!

Wytze

Wytze Schouten wrote:
I am asking because I own a small patch of forest that was established on an overgrazed hilltop. ...

Many tree species don't do well on the soil, and in part that may be because it is high in sand and low in clay or silt. But I also believe it has something to do with the fact that it's been exploited for sheep grazing. ...

The problems I see in the trees are primarily crooked growth.

Could the crooked growth be the result of windy conditions due to the hill top?

The overgrazing could cause compaction & erosion but I think minerals come from deep underground and can't be depleted. If the soil is compacted the pH could be too acidic and be "locking out" some minerals but they are still there. I think this is generally a problem for annuals, not deep rooted trees.

What are you trying to grow?

How about a pic?

Hi Cj,

Thanks for your reply. I'm not sure I agree with all of your beliefs though.

And I remain interested in anyone who can answer my original question: what minerals tend to get depleted first when sheep overgraze a particular patch of land?

First off, a photo as requested:

Photo 1 Black cherry (the crooked one) under a canopy of pine. Most of the thinner trunks in the background are crooked cherries, most of the thicker trunks are pine from circa 1960. The cherry looks dead but all its foliage is at the top, outside the picture. The green haze against the sky is the foliage of the cherries farther back.

In answer to your questions:

I am trying to grow trees with straight trunks, for timber. The section I'm talking about is part of 50 hectares of forest that we own. This particular section has been a pine monoculture since around 1900, with periodic invasions of black cherry that we have fought back with lots of labor and glyfosate.

Our problem with black cherry is its unhappy combination of crooked growth (meaning no hardwood value) and its tendency to shade out other tree species. The only value they have is that they are willing to grow on this poor soil and that their leaf litter improves the quality of the soil over the course of several decades.

The crooked growth is not a wind thing. The 'hill' we're on is extremely shallow and fully forested, so it's not a windy place, certainly not below the canopy. The black cherry grows crooked everywhere, regardless of wind or light conditions, and the crookedness goes in all directions, and differently so in each individual plant.

In part that could be because these trees are descended from a shrub variety that was planted on purpose in the mid-20th century to improve the soil. They turned out not to stay quite as shrubby as expected (they grow to about 15 meters), so that was a big bummer for my great-grandparents and for foresters all across Western Europe who tried the same cheat.

Getting the cherries to be more tree-like is most certainly dependent on the quality of the soil: they can't grow straight unless it is moist and rich in minerals. That's why the one individual with garden waste heaped below it is growing so nice and straight, while all the others are higgledy-piggledy. So this is why I ask my question: what soil minerals get depleted when sheep overgraze the soil and their manure is taken away?

You suggest compaction: that could certainly be a good explanation, but it doesn't apply here. It's been forest for over a hundred years, which is well over the threshold that soils need to recover from any compaction (80 years). Besides, when it was first planted, the soil was plowed down to 50cm, which would have taken care of any compaction by sheep trampling right at the start. Harvesters may compact some soil, but certainly not all of it. Being mostly sand, the soil there is not prone to much compaction at all.

I disagree with your belief that minerals can't be depleted. Check out Australia: it's got some of the oldest surface on the planet, and most of its soils are dirt poor, because all the minerals have been leached out over millions of years. It's not a matter of acidic conditions locking out the minerals: they've simply been removed. Though to be fair to Australia's soil, large parts of it could be a lot less dry and shrubby if it were better managed by sheep-herding humans.

Minerals needed by trees don't ususally come from deep underground. Trees prefer to get them in the easiest place they can: the topsoil, where most of their roots and most of their fungal support system sit. If the topsoil doesn't have the minerals, some trees may grow deeper roots. This is why our forest was originally mostly pine: they root deeper, they need less calcium, and they don't need good topsoil.

A topsoil poor in minerals will support little micro life, which means it won't have much water-retaining capacity. Which means trees will have a harder time too. Now black cherry is a kind of zombie in this respect: its seeds will germinate anywhere, and some individuals will survive even in thin and poor and dry soil. But though they will survive, they won't thrive. They will stay shrubby and crooked, and part of the blame is with the soil.

So this is why I'm into the soil mineral thing.

If grasses and shrubs keep extracting new minerals from the soil for their own growth, and sheep keep eating that growth and pooping elsewhere, then eventually the part of the soil that's accessible to roots will run out of certain minerals. I'm sure fungal activity and weathering can unleash new minerals from stone and bedrock over the long run, but that's going to take millennia, and those fungi need a moist soil to live in while they do their work.

So forgive me for rudely re-asking my question: what minerals do sheep deplete first when a soil is overgrazed?

Best regards,
Wytze

Wytze Schouten wrote: what minerals do sheep deplete first when a soil is overgrazed?

It's a really complicated question. Have you done a soil pH test?

If grasses and shrubs keep extracting new minerals from the soil for their own growth, and sheep keep eating that growth and pooping elsewhere, then eventually the part of the soil that's accessible to roots will run out of certain minerals. I'm sure fungal activity and weathering can unleash new minerals from stone and bedrock over the long run, but that's going to take millennia, and those fungi need a moist soil to live in while they do their work.

So, what grasses and shrubs were there?

Basics are the obvious N,P,K and probably calcium--but past that needs more research. Phosporous and potassium were my big ones.

I gave up on soil tests--they vary too much every ten feet. I went to feeding free choice mineral to my grazers in intensive rotational grazing. They crave what the plant is missing, then poop it back out close to where it was needed. Lock your grazers at the hilltops overnight and the nutrient will leach INTO your soil.

Hi R Scott,

Thanks for your suggestions!

What grew there before was: heather. Calluna vulgaris. The soil was probably podzol, i.e. a hardpan of iron and aliminium at 50cm depth, and bare sand above that which would periodically be waterlogged and whose nutrients would mostly have been leached out. The hardpan, if it was indeed there, would have been broken by the plowing.

I guess one way to go about it is to add some of the nutrients you mention to different specimens, and see which nutrient begets the best response.

Regards,
Wytze

R Scott wrote:I went to feeding free choice mineral to my grazers in intensive rotational grazing. They crave what the plant is missing, then poop it back out close to where it was needed. Lock your grazers at the hilltops overnight and the nutrient will leach INTO your soil.

Yeah, Geoff Lawton really promotes this - remineralizing the soil thru livestock. My impression is that sheep are not grazing there, and haven't been for a long time.

I asked about the soil test because pH lockout seems more likely to me than the soil being depleted from overgrazing done 100 years ago.

This chart shows what gets locked out at various pH levels:

Compaction causes acid soil which locks out many minerals.
I guess better than a pH test is to see what indicator weeds are growing.

Wytze Schouten wrote:What grew there before was: heather. Calluna vulgaris

Heathers like things pretty seriously acidic, so I think we can assume a rather low ph.

Cj Verde wrote:I guess better than a pH test is to see what indicator weeds are growing.

Wytze, is the heather common/dominant in that area?

Wytze Schouten wrote:they can't grow straight unless it is moist and rich in minerals. That's why the one individual with garden waste heaped below it is growing so nice and straight(...)
A topsoil poor in minerals will support little micro life, which means it won't have much water-retaining capacity. Which means trees will have a harder time too

My first thought here was to replace the word 'minerals' with 'organic matter'-
could the longterm overgrazing and manure removal still be having an impact?
I kind of doubt it, but...
If it was me, I'd get a detailed lab test as it should give a pretty good picture of the mineral profile, and any major mineral deficiency should stand out
(especially if the lab has a technician who will explain the results )

Hi Leila and CJ,

Thanks for these awesome tips!

The overgrazing has been pretty intense and certainly long-term: the place has most likely been heather since the Middle Ages. Many similar parts of the Netherlands (usually the parts that are between 10-30m above sea level, and higher than their immediate surroundings) were so overgrazed that they had become full-blown deserts by the 1900s. Photos from our area around that time show small areas that were essentially sand dunes.

Over a century of forestry has left a decent amount of organic matter on the forest floor, but in this one section it's mostly pine detritus, which is highly aerated (dries out), resists decomposition and lets most of its minerals leach out over time. So in this sense, at least, some of the stuff that a plant needs is indeed present but locked up.

The indicator weeds would under normal circumstances be heather. Because of consistently high atmospheric nitrogen deposition over the last few decades, heather now tends to lose out to brambles and Wavy Hairgrass, which are both nitrogen lovers.

So: an acidic soil with lots of atmospheric nitrogen.

As far as I understand it, some extra nitrogen is rarely a problem for a forest, but lots of extra nitrogen (more than plants and soil can absorb) will actually cause acidification. The nitrogen will be stored in the form of ammonium, which acidifies the soil. Some of the ammonium will be converted to nitrates, which binds to positively charged minerals like calcium and magnesium and get washed out of the soil by rain. Acidification somehow also causes aluminium (which is likely to be present in this soil) to become 'mobilized' and reach toxic levels.

So: based on the general chemistry, calcium and magnesium are likely to be scarce, and aluminium is likely to be overabundant.

I realize now that I'm not just interested in which minerals are deficient. I want to know how to get them back, on a forest scale, preferably in a permacultural kind of way. Enclosing cattle and giving them the minerals they lack sounds like a good idea (though hard in practice, as we don't live on-site).

Perhaps I could do a small-scale experiment where I try adding calcium, magnesium or both to an few plants or to a selected small area. Trouble is, even if I found that one mineral did the trick, I wouldn't know how to expand to a larger scale.

Thanks again!

Wytze

Pine forests cause acidification of soils too.

Firstly, the pine detritus is creating a lot of acidification, combine that with aluminum salts being formed in the soil and you have a serious problem. It can be remedied though, as mentioned already the use of animal manures will, over time, correct the defects in mineral quantities. The addition of lime and trace minerals could speed up the process a little but would be fairly cost prohibitive I would think. Bringing in compost, particularly good worm casing enriched compost would be the preferred method after grazing animals. Since you do not live on this land, and therefore would have problems with bringing in grazers for manure resurrection. It would most likely be the compost introduction that would currently be of the most help to this forest.

Was there a forest a long long time ago, before over grazing?
What type of forest?

Hi everyone,

Thanks for those last responses from Bryant and Aljaz and Sue. An amazing thing happened: in my parents' documentation, I found a report from a government-subsidized project that actually tested the mineral content of the trees. Pine trees were tested in three areas for six major minerals (N, Ca, P, K, Mg and one more) and it turns out the trees contain too little K and Mg. All the other elements are within normal range.

K deficits often occur in light sandy soils where lots of rain falls because it is easily dissolved in water. That applies to our forests.

Mg deficits can be caused by too much K (so that's conveniently ruled out) or by a plain lack of the mineral in the soil. It doens't leach particularly easily.

Bryant, thanks to you in particular for your thoughtful suggestions. Grazing would be hard to organize but it certainly seems the preferred natural solution. Perhaps we could electro-fence sections and have some pigs or sheep or goats root around. Then again I've looked into grazing and it seems like most animal species would only be useful in very low numbers - which in turn makes me wonder how much manure they might ever add.

The role of pine: I agree. Plus their long needles ventilate the soil much more than other tree species, so it dries out faster. We do need to have some spruce and fir for economic reasons, but in general my goal is to have a much more broadleaved forest. Nature is taking care of that all by herself. I just wish there was a cheap and easy way to help it through the stage in which the broadleaf that does all the broadleaf colonizing is that shrubby black cherry.

As for previous forestation: it's uncertain what grew here before the heath. Historical sources don't go back far enough. Judging by the histories of similar landscapes and soils, it's likely to have been a strip pattern of oak and pine (on sandy soil) and richer broadleaf forest (on richer soil: this area used to have strips of clay/loam that were mined in the nineteenth century) and perhaps peat bog on the flatter sections with poor soil.

Thanks again!

Wytze

Wytze, if you have not researched mob grazing, and your comments suggest you have not, I strongly recommend you look into it. Also, since you know that the primary vegetation growing in the area when it was being heavily grazed was heather, research into what minerals heather uses would tell you what was being removed from the system. After all, it isn't the sheep that pull the minerals out of the soil, but the plants. The sheep are just a vector for removing the plants from the area

The general description of the soil tells me that it was not the sheep that were the problem. Sandy soil does not hold anything well. Not water, not minerals, everything washes through it and away. Rain almost certainly took more minerals from that soil than the sheep ever could.

Do a soil test. In Netherlander you guys have some good labs. If not send a soil sample to Logan Labs in USA. It cost 30$ (plus shipping), but you will know exactly what your soil needs.

In general you need to lime your soil. I would use marble rock dust (if available in your area) or coarsely grounded limestone, so it will release Ca for few years. As your soil has probably low Cation Exchange Capacity that's the way you need to work with it.

To change pine needles into humus, your soil will need sulfur (you definitely have deficit of sulfur) - you can add sulfur by using gypsum (it will provide you with calcium as well).

For phosphorus (and calcium) you can use bone meal. I bet you have plenty of it in your country as your meat producing industry is well developed.

How big area are we talking about? Few hectares or more? If it's up to few hectares you can do it by hand - it's very tiring, but you can do it in few days.

I know nothing, but some obvious things come to mind.

Trees pull up nutrients from deep in the ground every year and shed all those nutrients all over the grass. Perhaps some deciduous trees could help out your soil. like someone else said, you may have to alter the existing soil to get it going a little faster than waiting for acorns to climb up a hill. lime, remove a few coniferous trees, plant some nitrogen fixing perennials that work in the area, etc...wait a few years. voila, better soil for better plant health for better animal health.