Pentrometer

[David Humphries]

So, we got hold of one & had a play today.

 

Measured out increments of length out on compass points from trunk, then recorded multiples of drops - down to 300mm.

 

Will return in 6 months to replicate, & will measure pre & post access change around Vets.

 

 

Early days, but appears simplistically useful.

 

 

Tom the apprentice dropping the weight........

 

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[Tony Croft aka hamadryad]

Is marcus going to elaborate on better techniques for bulk density calcs?

[Will Hinchliffe]

I think you can measure bulk density by taking a known volume of soil and then divide it by its dry weight. I think you can dry it in a oven set at 70 with the door open for 8 hours. My girlfriend would definatly frown on this so I have never tried it.

[Will Hinchliffe]

Really interesting tool David, would be interesting to play with.

[David Humphries]

Really interesting tool David, would be interesting to play with.

 

Yeah, it certainly seems to be Will.

 

Really nicely engineered.

 

Though not sure exactly how long the point at the base will last, as I'm sure stone will dull it's edge.

I'd imagine (without looking at sorbus's site,) that we could probably replace if neccessary.

 

I can see us using the simple results, to show various comittees how & why we occassionally will need to alter public access around vets at the site.

 

Bearing in mind that our little 600 acre site has in excess of 7 million annual visits

 

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[Bundle 2]

Really interesting tool David, would be interesting to play with.

 

Very simply made and as a tool to measure directly comparative values on a site, one way to evidence improvements to soil density and so porosity.

I made this point to a consultant @ mattheck seminar but as he looked at me rather blankly, I suspect he failed entirely to understand the limitations Once you get that, its useful.

As a matter of management procedures, it would make sense to keep records of measurements gained and so be able to expand the horizons of its usefulness too....

[Marcus B-T]

I didn't g to the Mattheck seminar so I don't know how much of this was discussed or how much people already know about this. I will only be able to give an intro at this time, just too busy with other things today, and it is Sunday, but I will get round to a longer answer at some point.

 

The penetrometer is not a measure of bulk density, it is a measure of penetration resistance (this in itself is useful info), the realtionship between compaction, bulk density and mechanical resistance is complex but you can estimate bulk density from mechanical resistance, the main problem is the realtionship between resistance and soil water content, this relationship varies with soil texture and to a lesser extent structure. Also pororsity can have an effect and also varies with the type of compaction force applied.

 

This is all before you consider the errors form hitting stone or tree roots.

 

The direct measurement is to use bulk density tins as described above, but this is time consuming and also you usually need at least 12 hours dying time and it can be up to 36 hrs.

 

There are soil coring apparatus as well. Form what I understand from David he is just trying to do a demonstartion of change so as long as he measures like with like, i.e. the same area with the same moisture content, then this is OK, however with some soil types you may not see the changes in penetrometer resisitance until there has been big change is soil conditions.

 

Regards

 

M B-T

[Marcus B-T]

One more thing, I have been comissioned to produce an application rate calculator for organic waste but it could equaly be used to calculate application rates for composts to trees.

[Tony Croft aka hamadryad]

One more thing, I have been comissioned to produce an application rate calculator for organic waste but it could equaly be used to calculate application rates for composts to trees.

 

surely this isnt rocket science marcus, i mean 5% organic content is considere optimal, and being a little over or under is no big deal so whats the point exactly?

[Marcus B-T]

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.