Pentrometer

[Tony Croft aka hamadryad]

With some organic composts you will be adding a large amount of freely available N (not good for trees, and you could be polluting local aquafers) also there are regulations on total N applications. Also you can taylor the application to the nutrient ballance. Also 5% of what? What is actually needed for most trees is to establish an 'O' horizon to reflect what would be seen in a forest soil. On a % basis this would be more than 5% of the vadose layer but would be less than 5% of the total occupied soil depth. This is why mulches work, they reduce competition for water and nutrients but they also reflect the natural delivery of nutients to trees (and perhaps water as well). The problem is that to establish a 'natualised' 'O' horizon you can't put all the organic matter on in one go and also you need to know when you can reapply. Also I am not convinced by the 5% figure the references trace back to what is seen as optimal for grassland/ agronomic situations and don't tie in with trees.

 

When you say SOME organic composts do yo have any idea of the N content of mature deciduos woodchip, say 6 week maturation cycle (without turning or additional amonia)

 

with regards to poluuting aquafers, this would have to be on a very industrial scale, and tree chip origins too would be a factor, say wide scale application of Chestnut (hippocastinum) which exudes a blue substance ive forgotten the name of! aesculin?

Edited June 21, 2010 by Tony Croft aka hamadryad

[Marcus B-T]

The main pollutant is nitrogen, you are only allowed to apply 250 kg h/a in any one year, even if it is a localised appliction. If your compost is from an urban area you may also fall fowl of limits on heavy metal applications.

 

This might seem a bit harsh for mulching trees, and at the moment probably is, but if we start mulching trees in larger amounts then collectively it would have a significant impact on soil and water quality. It all has to go somewhere and invariably it goes down.

 

In terms of the nutrient content in a wood chip pile this is a 'how long is a piece of string' question. The N output would be determined by the source material, the size of the composting heap, the degree of aeration and the outside temperature. For full stabilisation would would need longer than 6 weeks for a ststic pile and even so turning would be recommended or at least removing the top layer and recomposting it, only using the lower layers that have been allowed to compost.

 

The best thing is to send off a sample for analysis, it used to work out at about £30 . This will then give you the definative answers you need.

[Tony Croft aka hamadryad]

I think this is where science tends to be a little mmmmm, OTT.

 

Mulching a root plate to a depth of 75-100mm is always going to be a good thing, as for heavy metals, well if were going to worry about these in pur domestic woodchip mulch applications i would have to say behave, go away and bug somone more deserving of polution control!

 

there are SOOOO many things we can "worry about" why concern ourselves with this?

 

Have you got some research to give me good cause to pay any atention whatsoever to such a completle waste of my time? As right now, I wouldnt bat an eyelid at the potential for heavy metals, so enlighten.

[Marcus B-T]

I'm sure in the Alpine air of the home counties that heavy metals are not a problem but there have been a number of cases in london where repeat applications of compost have led to high levels of heavy metals. This due to interception of heavy metals from the air by leaves. You do need repeat applications over a number of years to get to this stage though. Problem is that once the heavy metals are in the soil they tend to stay there and accumulate over time.

 

Re the nitrogen levels there are two issues here. First is what is good for the trees. If you have green material in your chip heap, then after 6 weeks you will still have at least 2Kg per dry tonne of free nitrogen, you could have a great deal more. On a 100 mm application with is equivalent to around a 400 kg per ha N fertiliser application. This is more that you would apply to wheat fields or arrable grass land (in some cases that would be 2 years worth of N application), even young trees wouldn't need this much. This level of free nitrogen will favour N-bacteria in the soil at the expense of fungi and other bacteria, so you upset the soil microflora balance.

 

About half this rate is closer to the mark, better still find out what the free N content is there are cheap self analysis kits out there. Then you can adjust the application rate, 50-80 Kg per ha is a good target.

 

The other point is this. If it becomes widespread practice to apply organic matter to trees as a mulch, then all sorts of other waste streams will come out of the woodwork as mulches. This is basically because it is cheaper to spread than to landfill. So if we don't appreciate the limits and why they are in place then we will be open to exploitation by the cowboys. This has already happened in agriculture, horticulture and landscaping on a number of occasions.

 

The regulations are there to protect the environment from over application of N in particular. We are after all trying to help the trees, not make this good in the short term and then worse?

 

I have published some papers in the arb journal on the use of mulches, also on the WRAP web site and in other publications and there are some other things kicking around the net.

[Tony Croft aka hamadryad]

David, are you o.k with this conversation diverting for a mo?

 

marcus, the nitrogen balance may deter fungi? but seriously?

 

when we talk about adding a mulch layer to trees it is often for the first time, often to relieve compaction and to retain moisture. In the conditions (rhizosphere) MOST trees are found in where treatment is going to be proposed there is VERY little if any soil fauna, that is the whole point.

 

Sure there will be a lag between the exhuastion of N from the mulch and the moving in or re colonisation of soil fauna (that where missing from the start) but once this lag period is passed natural soil ecology will slowly year on year begin to build up again, and thats when the real benifits and health differences will be seen.

 

your point is a good one, but more relevent to secondary or third applications of mulch in an established program of renewal and maintenence.

 

To apply strict criteria to an initial application would put some off doing it in the first place, and i do not care what anyone says, a tree is better mulched than not, period.

[Will Hinchliffe]

Really interesting stuff Marcus.

 

I would like to see alot more research on this sort of stuff, especialy the effects of soil additives and mulchs on the microbial fauna in the soil. It is well known that fungi - plant associations are formed over a long time and are sensitive to nutrient levels in the soil enviroment. This seems to be often over looked in research suporting the benefits of soil additives.

 

Fungal comunities in the soil are built up over hundreds of years, these comunities once damaged could easily be lost forever on the damaged site.

 

I think the approach being taken by Monkeyd to first investigate before prescribing treatment is fantastic. Keep up the good work.

 

I would realy like to be involved in this sort of work but most of the job oppertunities in these areas are never quite right.

[Tony Croft aka hamadryad]

If the fungi are there we need do nothing!

 

but if they are not there, because of compaction etc, then what is the use in worrying about them being there!

 

Establish the environment and they will come

 

This is NOT rocket science.

 

Mulch is good, even BAD mulch is better than the current regime MOST trees live in, and I mean even at Hatfield forest, where some really great examples are living in bare well trodden earth.

[Will Hinchliffe]

If a fungal comunitie has existed in a low nutrient soil for a long time then you add a load of mulch you change the soil enviroment. Other fungal species may then become more competetive and the make up of the community changes irreversably.

 

Its not rocket science. Its Ecology which is probably a more complex science as there are so many influences and interactions going on.

 

Soil additives and mulches are great on made up land and industrial sites but its much more complex messing round with the soil under a veteran tree or in an Ancient woodland. I hold my hands up to not being fully read up on the subject but I do think arborists need to proceed with caution so as not to cause irreversable damage to ancient soil communitys.

 

We really need to think about the complex interactions going on in ancient soils before messing with them.

[Tony Croft aka hamadryad]

If a fungal comunitie has existed in a low nutrient soil for a long time then you add a load of mulch you change the soil enviroment. Other fungal species may then become more competetive and the make up of the community changes irreversably.

 

Its not rocket science. Its Ecology which is probably a more complex science as there are so many influences and interactions going on.

 

Soil additives and mulches are great on made up land and industrial sites but its much more complex messing round with the soil under a veteran tree or in an Ancient woodland. I hold my hands up to not being fully read up on the subject but I do think arborists need to proceed with caution so as not to cause irreversable damage to ancient soil communitys.

 

We really need to think about the complex interactions going on in ancient soils before messing with them.

 

and while your all debating the relationships etc millions of people will continue to compact the soil, errode the soil and generaly have a party at the trees expense!

[Will Hinchliffe]

We have completly derailed this thread. We will have to start a propper ancient soils thread where we can rip apart those that dare to pulverise them with air spades and polute them with inoculations of foreign fungi !!! (Please excuse the spellings)