Saturday, 18 February 2017

Starting off a new Hugelkultur in the potato bed.

Bloke came down with the shredded woody material and had some logs on the back as well.  He gave me the logs so I decided to make another trench Hugelkultur in the potato bed.  I wanted to raise the soil at the north end of the bed in order to create a surface water calming bank alongside the espaliered fruit trees.  The Hugelkultur trench will be a subsurface water calming structure until it decomposes in the future. 
I dug down one spit today and left the soil on the side of the trench.

I always use garden lines because I can't keep a straight line without them.  There are lots of reasons for not digging but there is no other way of introducing large quantities of organic matter and deepening the top soil.  I will take another spit out of the bottom of the trench and then fork over the bottom which will give me three spits of turned over soil.  Loads of waste material from around the allotment will be used to put into the trench. 

The old vegetables from last season.  A few celery and celeriac together with carrots and beetroot. 

Old bits of wood that I have collected from under the hedge and in the woody chippings piles.  I will probably get some more before I fill in the trench.  I will certainly clean the bottom of the hedge a little more. 
The logs off the lorry.  These will go at the bottom of the trench.  I think they are mostly cherry laurel. 
I will move the frames off the hot bed, which has not been that hot during the winter.  The woody chippings have rotted down now and will go at the bottom of the trench.  I will put the frames on top soil now and just rely on the glass to heat the soil.   If that is not enough shreddings, I will resort to the woody chippings pile to add more woody material.
Mostly X Cupressocyparis laylandii and holly but it is all grist to the mill.  I will also be putting the cuttings from my daughter's garden in the trench too.  It will all be two spits down and can moulder there for a year under the potatoes and whichever green manure I plant after them. 

The top soil is deepening and now is more than a spit deep.  The subsoil is darkening with organic matter too.  Deeper topsoil means more organic matter, more nutrients, more microbes, more water and more air for vegetable roots to delve into. 

Now I am going to try and explain why I think that it is a good idea to introduce organic matter into the subsoil as deep as I can.  In normal conditions plants can get water and dissolved nutrients easily from the top soil.  There is usually decomposition going on and nutrients being released.  As drought conditions start to appear the roots start to forage for water lower and lower in the soil profile.  The dry top soil means that they cannot obtain nutrients from here because there is no water to dissolve them in.  Nutrients can only enter the root as dissolved ions.   As the roots pass out of the dry topsoil they pass into the moist but infertile subsoil where nutrients are much more scarce.  Little is dissolved in this water and although the plants have adequate water they begin to get nutrient shortages.  Bottom old leaves start to yellow as nitrogen is transported away to the growing tips, though the plant is not wilting.  If we can deepen the soil, adding lots of organic matter, it will make plants more able to withstand drought conditions and the shortage of nutrients that it might bring.

So that's what I have been doing today - that and turning one of the compost bins.  I will use the compost to mix in with the top soil as I rake it back into the trench. 

Wednesday, 8 February 2017

The possibilities of using slope to benefit the allotment.

My allotment slopes to the south east.  What advantages does that give to the allotment crops?  The aspect of the allotment can give quite an advantage.  Being south facing means that the sun's heat and light is a little more concentrated and will warm up the soil earlier in the year and allow crops to be grown later in the autumn. 

Path alongside the allotments looking down the south facing slope.

Although I grow crops in north south rows,  I have put in paths from east to west at right angles to the slope.  The paths have been made as mini ditches and soil has been taken out and put onto the growing areas to raise them.  The mini ditches are aligned more or less with the contours across the allotment.  Water will flow at right angles to the contours soaking in as it does.  Some surface water will flow into the ditches and spread out.   I have filled the  ditches  with woody shreddings which will soak up some of the water and prevent it from evaporating creating a reservoir of stored water. 

Espaliers planted on the top of the raised bank.

This allows surface rain water to be spread out evenly along the path, slowed down and soaked into the soil.  Although irrigation is not a particular priority in the UK climate, we still have to consider the effects of leaching and soil erosion. 

Raising the level of the soil, creating banks on the downside of the slope and planting espaliered fruit trees or soft fruit along the east west raised soil aids in the slowing down of water (mass flow) through the soil.  As the water is slowed, it allows dissolved nutrients to be taken up by plants before it is lost though leaching. 

As plant nutrients are soluble minerals they will be leached slowly as the water flows to the bottom of the slope.  I have planted comfrey at the bottom of the slope to catch as much leached nutrient as I can.  Their deep roots will absorb much of the available nitrogen and any potassium and phosphorus that is available.  The leaves and stems of the comfrey can then be composted, made into comfrey liquid or put into the worm bin to recycle the nutrients. 
It is all about slowing the mass flow of water through the soil.  This will slow leaching, allow more time for uptake of soluble minerals; capture eroded soil particles, enhance water filtration  and provide more opportunity for upward water capillary action for plant growth.

My compost heaps are at the top of the slope so that any leachate that they produce will flow down the slope and into the allotment soil.  In a similar way, I have planted perennial nitrogen fixing legumes along the top of the slope so that any nitrogen they fix will flow naturally into the allotment top soil.  I will be planting perennial legumes alongside the fruit trees and bushes on the banks alongside the paths so that nitrogen will flow with the water into the growing areas. 

Compost bins at the top of the slope so that leachate will flow into the allotment.

Laburnum and lupins planted at the top of the slope so that nitrogen they fix will
flow into the allotment growing areas.

In the UK there is often too much water flowing through the allotment.  It is necessary to put in some kind of drainage to prevent waterlogging.  I have dug out a trench at the bottom of the allotment and filled it with stone sieved from the top soil.  The stone was covered with paving slabs to make a path alongside the hedge. 
Drainage ditch under the slabs.  Path is at the bottom of the slope.   

During the driest months in summer, the soil is covered by mulches to reduce evaporation and the trench Hugelkultur further slows the soil water and retains it as a reservoir that is accessible to plant crop roots. 

So slopes can be very useful. 

Wednesday, 18 January 2017

Is mulch made from conifer wood chip or bark acidic?

I have seen it often suggested that organic mulches such as wood chip and bark from conifers is acidic.  The pH is a measure of the amount (the negative log of the concentration)of hydrogen ions and this measurement must be done in a liquid.  You cannot measure the pH of a solid unless you dissolve it in water.  As most of the solid from wood chip and bark  is insoluble in water, it is virtually impossible to measure the pH of these materials.

The woody chippings or bark could be giving off substances that acidify the soil solution as they decompose.  However, neither pine bark nor pine chippings have been found to have any effect on soil pH.  (Tahboub, Lendemann and Murray 2008) There is no significant change in soil pH for wood chip incorporated into soil measured over a three year period.   Bare soil is more likely to have a low pH (be acidic) than organic mulches.  Shredded bark and woodchip have been found to be the least acidifying of the organic mulches.

Regardless, wood chip could be shaken up in water and the resultant solution tested.  This should be done with distilled water or deionised water to make sure that you are testing the pH of the dissolved substance not the pH of the water.  Tap water contains a lot of substances although it usually has a neutral pH of around 7. 

Now, I haven't tested the pH of  woodchip solution, however I would conjecture that it would be fairly neutral or possibly slightly alkaline.  There are some that suggest that the phenolic substances secreted by the above ground structures of a plant may be acidic. I don't know. 

What I am going to do is test the soil beneath an estimated 2000 year old yew tree.  The tree is in my local nature reserve.  There is nothing growing under the tree within about a 50 food diameter. 

I would suggest that the pH of the soil is no different from the rest of the wood so I will take samples from outside the yew trees influence as well as under its canopy.  After 2000 years of falling litter surely it would have affected the soil underneath it. 

My suggestion is that there will be no difference between the soil pH from beneath the canopy of the yew tree and the soil from outside the canopy.   

The fact that there is no build up of litter under the tree would suggest to me that some invertebrates, such as worms, are feeding on the organic matter from the tree.  Worm's preferred habitat is one with a neutral or alkaline pH.

Usually scientific consensus is pretty solid, however sometimes explanations that purport to be scientific are merely based on hearsay and anecdote and need to be challenged by experiment. 

Sunday, 15 January 2017

Too much mulch?

It is self evident that if you cover a plant completely with mulch you will kill it through lack of light.  This is one of the benefits of mulching - weed control.  However, what is the correct amount of mulch to apply to crop plants? 

There is a lot of advice to suggest that heaping relatively large amounts of compost around fruit tree trunks could cause the trees to die.
There is a reduction of oxygen diffusing through to lenticels and reaching respiring cells below bark in the trunk.

Now I went along with this until I though, hang on a minute.  When I put woody cuttings into soil or compost, there is a similar reduction of the free flow of oxygen to growing cells in the woody stem of the cutting.  Lenticels are covered in the same way.  So how do cuttings survive this treatment? 

My rooted willow cuttings from stems just pushed into the soil. I put quite a bit of woody
mulch on these too.
I have just been turning the composts today and found some woody stems I threw in  from the willow.  They were right in the middle of the compost and merrily throwing out new growth. 
Layering woody shrubs would not work if this were correct and we would never get Irishmen's cuttings. 
For an explanation to have credibility it must be consistent with all the data collected. Inconsistencies must lead you to question sloppy explanations. 

So here is another piece of data that does not really fit in to the " not too much mulch" hypothesis.  I tend to heap compost, manure and woody chippings around my soft fruit bushes.  They do not die throwing out lots of adventitious roots into the compost.  A little irritating because this means that the roots need to be covered again when the mulch decomposes and they are exposed. 

Blackcurrants and rhubarb with a thick woody shredding mulch.

Blackcurrants with a thick horse manure mulch.

I think that much more tree and shrub death occurs from poor planting practices than the addition of too much mulch. 

Brussel sprouts with a thick woody mulch to stop them from falling over.
Mulching brassicas with compost or hoeing them up does not kill them.  I do this to stop them from flopping over.  The Brussel sprouts produce adventitious roots that root into the mulch or soil. 

Having said all that, I have found that it is unnecessary to add more than a couple of centimeters of woody shreddings to get all the benefits associated with mulching.  Adding more does risk substantial nitrogen drawdown.  This immobilisation of nutrient does have an affect if excessive woody shredding material is used for mulching.

Friday, 30 December 2016

So, why do I still use mycorrhizal fungi?

I know the mycologists think that gardeners are stupid for using mycorrhizal spores but there are some circumstances where it might be appropriate to use them. I am no particular fan of RHS but they still promote the use of mycorrhizal spores when planting trees and shrubs. 

Most plants seem to be naturally infected by some kind of fungi and these seem to give plants advantages. The amount of research into the mutualistic symbiosis of plants and fungi is remarkable and ongoing.  It may well lead us to understand the world of plants as that of vast organisms encompassing whole forests and acres of soil.  Infection happens naturally. The biochemistry is fascinating and involves exudates from both roots and fungi.  Both fungi and plants are fundamentally changed; unique genes are switched on and new structures are formed both by roots and fungi. 

While this description seems to paint a very cosy relationship just between the fungi and the plant, this hides the interaction of the rest of the soil organisms.  Bacteria, both pathogenic and benign, are trying to gain entry to the root.  Fungal spores are being transported by nematodes and earthworms; hyphae and spores are being eaten by herbivorous nematodes,  arthropods and fungivourous collembola  and the whole lot is reliant on the constant addition of dead organic matter.

What is more there seems to be an incredible chemical communication between plants, fungi and animals living in the soil.  I don't know why I am amazed at this because it has long been known that plants produce exudates in their aerial structures.  Flowers produce scents and nectar to communicate their presence to pollenating organisms.  Resins and exudates are often produced by stems and trunks.

So if this all happens naturally why bother with adding mycorrhizal fungi spores to planting holes or growing medium?

I would suggest that if you left wood chippings in a plastic bag they would eventually become infected with fungi. The likelihood of them being oyster mushrooms is not that great, so using spores to impregnate the wood seems to be appropriate.  There are many species of fungi all inhabiting different niches.  Some are saprophytic heterotrophs, others are parasitic and many are mycorrhizal.  There are slimy ones, microscopic ones and enormous ones.  Most reproduce using tiny spores that are ubiquitous.  I would conjecture that there are oyster mushroom spores floating around my allotment in both air and the soil solution just as there are mycorrhizal fungi.  Their fitness will depend upon finding an appropriate habitat.    If I, as a gardener, alter the environment to favour these fungi then I am likely to accelerate their success. 

So, when we add mycorrhizal fungal spores to planting holes, we are just speeding up the process and making sure the appropriate fungi are in the growing medium.  Lots of commercial growing mediums are relatively sterile.  Organic gardening uses the understanding we have of the natural world and turns it to our advantage. 

In cultivated land hyphae may be broken up and killed so adding spores to planting holes seems to be a reasonable thing to do. Also if you are trying to reclaim degraded soil where there may be a lack of diversity, adding spores and improving the fungal environment by adding compost and woody shreddings as mulch seems to be a valuable thing to do. Gardening is an intervention and to some extent gardeners degrade the soil. We must attempt at every opportunity to increase diversity and improve the habitat of soil living organisms by adding lots of organic matter - something that Robert Pavlis questions too.