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David Humphries

Root zone amelioration

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David, under the general heading of the thread I was interested in whether you had any awareness of the use of green manures for root zone amelioration?

 

It's a growing subject of interest (if you'll forgive the pun) in arable agriculture - various voices are beginning to suggest that simply churning the top nine inches of soil over each year by ploughing may not be the best, or cheapest option and building up the soil structure is a better move. There is a move towards specific planting to do this, depending on the aim, using either catch-cropping between main crops and mown/harrowed off, or as an under-planting. This includes a range of different species, with different functions such as nitrogen fixing, smothering out invasive species or sowing deep rooting species to break up soil compaction.

 

Compared with an airspade or a dose of fertilizer it is obviously very slow, and you would need the right site for it where the visual impact was acceptable for the species selected, although some nitrogen fixers such as red or white clover also make a good cover planting which may be generally aesthetically acceptable. The main advantages would seem to be that it is non-invasive, very quick and cheap (things I am looking at are around £30-60/hectare which would do a lot of drip zones!).

 

Has it been tried, and if so any known results?

 

Alec

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Im not an advocate of using the air spade for large areas of soil decompaction and tbh I'd be very cautious of using large amounts of mulch as an earlier post says mulch can potentially contain to much nitrogen and shock the tree

 

Great read David, with the benefit of hindsight etc in your case I would of decompacted using the root zone using my decompactor or an air spade (decompacter being first choice) and simply filled the holes 1 per metre with sharp sand with maybe 10% organic matter. This is what I reccomened for a large job in a Cambridge Jesus park, a large avenue of planes

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Thanks for updating on the progress of this tree. Did you notice any differences in the crown that varied from other parts, eg shoot extension, colour etc... ? Just curious if the response is even or if you can see any correlation to decompacted sections and sections in the crown?

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...........It would be interesting to take samples of the 'ameolirated' soils vs the untouched, to ascertain moisture and nutrient levels. Do you ever perform bulk density tests?

 

So overall would you say the condition of the tree is better now or back then?

 

We haven't taken any soil samples from around this tree, mainly because we hadn't thought to do that and it's just a single amenity tree. Where as we have had samples analysed for nutrient levels where there is a wider health issue over a larger population of trees across this set of open spaces.

 

............Did you notice any differences in the crown that varied from other parts, eg shoot extension, colour etc... ? Just curious if the response is even or if you can see any correlation to decompacted sections and sections in the crown?

 

I would say that the condition of the canopy in terms of epicormics, level of shoot extension and chlorosis is pretty even across the canopy Tobias. (taken from a ground perspective that is)

 

We have thought/talked about getting hold of a Fluorometer and getting up into a couple of different levels of the cardinal points of the canopy to have a look at the Chlorophyl fluorescence potential of the leaves.

 

Over all (based only on anecdotal images taken before, during and after) I think there is a small but maintained increase in its vitality which could I guess be debated that its is a sign that the tree has (or is trying to) arrest it's decline. Although looking at the peripheral canopy shoot die back, I'm of a mind to program in a further reduction to lower the stress on the individual branches by reducing the length that the assimilates need to travel up and down from tip to root.

 

It's a all a big interesting learning curve.

 

.

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Im not an advocate of using the air spade for large areas of soil decompaction and tbh I'd be very cautious of using large amounts of mulch as an earlier post says mulch can potentially contain to much nitrogen and shock the tree

 

Great read David, with the benefit of hindsight etc in your case I would of decompacted using the root zone using my decompactor or an air spade (decompacter being first choice) and simply filled the holes 1 per metre with sharp sand with maybe 10% organic matter. This is what I reccomened for a large job in a Cambridge Jesus park, a large avenue of planes

 

 

Ideally Lee, I would have liked to just have mulched the entire surface of this tree (much like the Pear in the 'to mulch or not to mulch' thread) but the local management were in opposition to the idea due to concerns that the mulch wouldn't stay put because of the slope it's on and being next to a path. I'm sure if I'd tried harder I could have persuaded them to allow a containment barrier to hold the mulch but it wasn't getting through at the time.

 

Did you mean Jesus 'green' in Cambridge, the bit next to midsummer common ?

Did you do the work or was it just the recommendation?

 

If so I might nip down and have a look-see.

 

 

Any scope for amelioration down under?

 

.

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I will add regarding mulching with wood chippings. bacteria (who are first on to the breakdown process) cannot deal with excessive amounts and as a result take nutrients from the soil to assist them in the breakdown process, adding over 4" will cause this.

 

using wood chip around a tree such as in this thread - clearly under stress I would be cautious and use less than 4" and partly decomposed as is the case here

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David, under the general heading of the thread I was interested in whether you had any awareness of the use of green manures for root zone amelioration?

 

It's a growing subject of interest (if you'll forgive the pun) in arable agriculture - various voices are beginning to suggest that simply churning the top nine inches of soil over each year by ploughing may not be the best, or cheapest option and building up the soil structure is a better move. There is a move towards specific planting to do this, depending on the aim, using either catch-cropping between main crops and mown/harrowed off, or as an under-planting. This includes a range of different species, with different functions such as nitrogen fixing, smothering out invasive species or sowing deep rooting species to break up soil compaction.

 

Compared with an airspade or a dose of fertilizer it is obviously very slow, and you would need the right site for it where the visual impact was acceptable for the species selected, although some nitrogen fixers such as red or white clover also make a good cover planting which may be generally aesthetically acceptable. The main advantages would seem to be that it is non-invasive, very quick and cheap (things I am looking at are around £30-60/hectare which would do a lot of drip zones!).

 

Has it been tried, and if so any known results?

 

Alec

 

 

The first issue that springs to mind with the use of "green manures" is that the use as you describe is dependant on the plants not completing their lifecycles but being ploughed in, sprayed off or crimped and oversown etc.

 

Clover for example is only beneficial when it gets damaged through grazing, mowing etc and more so still when the whole plant is damaged by shallow non-inverting cultivation.

Most other green manures I am aware of would require similar treatment to be of most benefit to soil life but this would not necessarily be beneficial to the tree?

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The first issue that springs to mind with the use of "green manures" is that the use as you describe is dependant on the plants not completing their lifecycles but being ploughed in, sprayed off or crimped and oversown etc.

 

Clover for example is only beneficial when it gets damaged through grazing, mowing etc and more so still when the whole plant is damaged by shallow non-inverting cultivation.

Most other green manures I am aware of would require similar treatment to be of most benefit to soil life but this would not necessarily be beneficial to the tree?

 

In an arable setting, the plants are deliberately killed off, mainly because you are then re-sowing and it reduces the need for a pre-emergent weedkiller (preferable on cost grounds but also because the type of farmer who is using green manures is usually trying to reduce reliance on chemical intervention.

 

Plants which fix nitrogen through their roots on nodules will do so whether they are killed off at the end of a cycle or not - you can use clover for gradual nitrogen enrichment of a permanent sward, which may be beneficial in some circumstances, or use a nitrogen-fixing annual such as yellow trefoil. Similarly, deep-rooting annuals or biennials will break up soil compaction and then die, leaving roots which will break down leaving organic matter and air pathways through the soil, and organic matter on the top which will form a mulch, regardless of whether they are tilled in. If they set seed first then the cycle will repeat, which is what arable farming is seeking to avoid, but may not matter in the context of trees?

 

There is definitely faster breakdown if the growth is cut before it hardens (important for annual crops, maybe not so for trees).

 

Some species, such as buckwheat, can be killed simply by cutting once, or by frost, so if sown later in the year - August onwards really, will shade out aggressive weed growth.

 

I agree that 'turning in' may defeat the point, but anything which can be killed by mowing, or dies out naturally, or is suitable for treating as a long-term underplanting may add value? The biggest disadvantage I can see potentially arising is the water uptake - in a year like this that wouldn't be a problem but in a drought year it could make a difference - I suppose a lot depends on location, soil type and whether the tree in question is deep rooting.

 

It would be interesting to see if, correctly selected, you could get beneficial results.

 

Alec

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Ideally Lee, I would have liked to just have mulched the entire surface of this tree (much like the Pear in the 'to mulch or not to mulch' thread) but the local management were in opposition to the idea due to concerns that the mulch wouldn't stay put because of the slope it's on and being next to a path. I'm sure if I'd tried harder I could have persuaded them to allow a containment barrier to hold the mulch but it wasn't getting through at the time.

 

Did you mean Jesus 'green' in Cambridge, the bit next to midsummer common ?

Did you do the work or was it just the recommendation?

 

If so I might nip down and have a look-see.

 

 

Any scope for amelioration down under?

 

.

 

 

Hi David I put in a quote and my recommendations as you correctly pointed out Jesus Green, but I never heard back from them even after a couple of follow up calls. So I don't know what happened, I wouldn't be surprised if they went OTT with decompaction , mycchor,and fert etc, if the work ever got done.

 

If you don't want mulch to migrate verticle mulching imo is the way to go imo

 

As for downunder fingers crossed mate, but again I'll refrain from mulch etc keep it simple I think is the best policy, if mulch is used I think introducing small amounts over time is the way to go

Edited by Lee Winger

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