It's fairly widely assumed that geologists, like gardeners, can't wait to get their hands dirty. Well, it's true. So it was no surprise that when we returned to Foxcombe Hall for our second visit, that Tom and I would be given the job of digging the soil pit and testing the soil. Armed with spade, we chose a spot in the old oak woodland and commenced digging. The aim of a soil pit is to get a good look at the stratigraphy or layers in the soil and see what its composition is and what kind of condition it is in. It's a square pit which should have a least one 'clean' vertical face. The idea is to dig down to bed-rock (or at least as far as is humanly possible).
We started by cutting out a square and peeling back the turf, this exposes the upper-most layer of soil. It is a this point that you do the soil testing - as this is the part of the soil that the plants grow in, dig down too deep before testing and you won't get an appropriate sample.

Soil testing:
Most DIY stores sell soil testing kits or probes. Many of these are simply a means to determine whether the soil is acid or alkali (others also test how much water the soil holds and nutrient levels). They can be in the form of a powder that you add to a soil and water mix, or a strip of litmus paper that you dip into the mix - in either case a colour change occurs which indicates the composition of the soil. If it's acidic the colour change is usually towards the yellow or red end of the spectrum, if it's alkali the colour change is towards green.

You can watch Tom and Janet doing the soil testing.



So there you have it - the soil at Foxcombe is acidic (see photo).
This is useful to know because if we do decide to clear out some of the invasive species and plant or seed native species - we will be able to chose the right mix i.e. those that grow well on acidic soil. Actually, we were rather expecting this result as Tom and I already had a good idea of what the bedrock was (see below), and several plants in the woodland (e.g. bracken, foxglove and rhododendron) prefer acid soils. Usually only soils on rocks like chalk or limestone have alkali soils.
After more vigorous digging and Tom and I eventually had our soil pit constructed.



The top 2cm or so is leaf litter and peat, below that is a dark brownish layer, which is rich in dark organic matter which helps to give it the colour. This is the part of the soil profile where all the biological activity takes place. It contains plant roots, burrows, worms and other invertebrates. Below that is a gradual colour change to pale yellowish-brown, this is known as the subsoil, and is rich in mineral matter - in this case lots of quartz. This is to be expected because when Tom and I hit bedrock we discovered it is a very rotten sandstone called 'Greensand' (go to Tom's blog for more about the geology). This is quite a hard rock, capping ridges round Oxford, but weathers to a soft, 'rotten' material that crumbles easily. The subsoil has a lot less organic matter and biological activity, although there are a few tree roots working their way down looking for water.

Janet will talk you through the soil profile at Foxcombe


In the afternoon Tom went off with Alan to map some of the springs on the site and I was detailed to 'weeding duty'.


Invasive Small Balsam is starting to to get a grip all over the site, so we had decided to take positive action and clear a few patches immediately. The Small Balsam is still in flower at the moment, spring is really the best time to clear it, as it has not yet had chance to flower and seed - but hey, every little helps! For such an invasive and prolific plant it is surprisingly easy to clear, especially in the dry loose soil of Foxcombe. You can simply pull it up with your hands - in just half an hour I cleared quite a large area and had bundles of the stuff ready to be disposed.
Picture
Important safety tip - it's probably not a good idea to just chuck this on your compost heap - better to burn it or use an appropriate weed killer. Well we had a busy and achieved all kinds of things. Most importantly, we now have an accurate idea of what is on the site and can, together with the site manager Alan, make some informed descisions about the positive action we can take when we return in October.