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. http://www.gardenmyths.com/tag/compost-too-much/

Monday, 26 December 2016

Still learning new things after 50+ years of gardening.

Just read James Wong's article on
https://www.theguardian.com/lifeandstyle/2016/oct/23/coffee-grounds-are-not-good-for-plants-its-a-myth.
So this seems to have come from an auto toxicity of coffee plants and a resultant degradation of the soil for coffee growing in places like Latin America. This has occurred due to tens of years of monoculture. It seems that some of the aromatic herbs like sage will help to ameliorate this problem.
I think that this is a classic example of why monoculture is a bad way of cultivating plants.  Not only do we get depletion of specific nutrients and an increase in pests and diseases but also a build up of potentially growth retarding chemicals. 

It is also an example of the danger of extrapolating scientific results without carefully considering whether this is appropriate. 

In Coffea arabica growing regions of Brazil, coffee fruit peel is composted and used on vegetables, fruit trees and for coffee culture itself not only as an organic fertiliser but also as a weed suppressant.  It seems to slow the growth of fine roots.

There are relatively high concentrations of phenols, flavonoids and caffeine found in extracts.  It is amazing what we find good to drink! One or more of these compounds may have allelopathic properties.  It has been found that coffee bean water extracts and dry powder decrease germination in certain plants.  So needs to be pretty concentrated then?  In other plants there is less germination but stronger seedlings than controls.  This has been interpreted as coffee water extracts and lower dose dry powder have allelopathic effects on some seedlings.  Higher doses of incorporated coffee powder has a depressing allelopathic effect on some  plant's growth. 

I would not really worry about putting coffee grounds on growing beds for at least two reasons. You have just put them through a procedure that removes lots of the chemicals from the bean when it has been percolated. The research papers that I have read use quite concentrated coffee extracts to get an effect.    Secondly, you have not been putting coffee on growing areas for tens of years and finally you are not growing a monoculture of coffee. 

I put my coffee grounds on the compost heap. They are relatively rich in nitrogen even after percolation and this means they will help to accelerate decomposition.

I have used comfrey in the same way as James Wong did coffee grounds in the newspaper article and got similar results. I think that his results could have something to do with too much nitrogen rather than the allelopathic effects of coffee grounds. I would not repeatedly put any chemical on growing areas like this because plants only need tiny amounts of nutrients from the soil.

Are celery plants perennial?  There are lots of vegetable plants that are grown as annuals that are biennials or perennials.  It seems that celery is one of them.  It dies after it has flowered so if you can stop it from flowering, you can keep if for several years.  I find it difficult to stop it flowering in the first year and am delighted when I can pick some for Christmas dinner as I did this year. 

Friday, 23 December 2016

December photographs of the allotment.

December and the weather is getting much colder.  The allotment needed tidying and some woody material needed burying.  There were some very rotten logs about 15cm in diameter under the chippings that no one would want so they could be used for a Hugelkultur.  I wanted to take down the Victoria Plum and bury it somewhere too.   The most appropriate place to dig some trenches was the new potato bed.  The tops of the pumpkins, courgettes, sweet corn and French beans had been dug in after the first frosts and had already rotted away.  Just a few of the French bean vines could be seen in the soil.    A four foot trench was taken out three spits deep. The bottom spit was dug out and put into the wheel barrow so that the path concrete slabs could be levelled.  The bottom of the trench was forked over, which means that I went down four spits.  I have just been reading in "The Manual of Gardening" by L.H. Bailey (1910) that potatoes grow well if they have a deep root run and I tend to agree.  Well they will certainly have an unrestricted root run here. 

Filling the trench with organic matter.
I put the logs, branches and brash at the bottom of the trench and tried to mix it in with the subsoil.  On top of the woody material went the organic matter from tidying up the allotment. 
Soil taken out of the trench.  The canes are indicating where the rhubarb is. 


Once the rhubarb had lost its leaves in the second frost, I decided to move it a small distance.  This will make the two beds either side of it a little more equal in area.  I had to break a few of the larger roots but not too many.  It is just like moving a herbaceous perennial in the flower garden.  The roots can be divided like herbaceous perennials too.  They got a good dose of sieved compost  in the planting holes to give them a boost next spring. 


I wanted to reduce the Victoria plum tree and cut out all the canker in its trunk.  This meant virtually cutting it down completely.  There was a water shoot growing low down and I thought that this might develop into a tree again given some time.  The trunk and branches that were cut off could be put at the bottom of the trench. 
Totally the wrong time of year to cut a plum but if the trunk and branches were to be
buried it would have to be done now.  If I am lucky it wont get silver leaf disease.
I thought that, if I cut the trunk at quite a sharp angle, water would run off cleaning the surface of fungal spores.  I don't really think that it works like that but there is no harm in trying it out.  One of the gooseberries that I planted under the plum has grown into a thicket.  It has thorns and small black, blackcurrant looking berries.  It only produces one or two berries every year so it is not worth bothering with.  However, it is good to have another interesting plant growing on the allotment and I think that this might be an American gooseberry. 
The American gooseberries.  One of the mints growing through the gooseberry.
Now that I have cut the plum hard back, I can use this ground for vegetables so the gooseberries are going to have to go somewhere else.  I might put them in the border around the carpark just so they are not thrown away.  I took off all the top growth and put it into the trench.  This means that it is easier to take out the gooseberry roots.  The soil here is very good but not very deep.  It has a layer of hard core about 20cm down.  I will have to break this up if I am going to grow runner beans here next season. 
Subsoil dug from the bottom of the trench. 
I didn't take all the third spit of subsoil out of the trench but I did take this.  I have left the subsoil in the composting area and I will use it to mix into the compost.  The soil will not add anything to the compost but the compost might add something to the subsoil while it is being turned every two days.  The trench is deeper and can be filled with more organic matter from around the allotment and I get more top soil like material from the compost bins. 
I am emptying the compost bins and putting the compost in the trenches.  It wasn't rotting down very quickly even though I was turning it every two days.  I want to empty the compost bins and tidy them away before I get some more farmyard manure from the farm. 
I am putting this into the Hugelkultur trench on top of the
branches and trunk pieces.
Any other organic matter that I want cleared off the allotment is being put into the trench.  The old chard, perpetual spinach, prunings from the fruit trees, and a few weeds are all grist to the mill.  I am then capping this material with a layer of woody chippings from the pile on the car park and the old mulching from the peach greenhouse. 

 

Taking out the woody chippings from the peach greenhouse means that any disease in the mulch is removed. I will be planting the tomatoes in the same place again next season and will need a base that has not had contact with tomatoes before.  I am only going to put a couple of tomatoes here because the peach has got quite large and needs the space.  The tomatoes shaded the peach quite a lot this year and I don't want that to happen again. 

 I am also taking out all the peach leaves and any disease on them.  I removed and replaced about 20-30cm of chippings.  It is a bit of a chore but much easier than changing top soil each year.  The peach got its final winter pruning and I tried very hard to keep all the small side shoots that grew last year.  These are the shoots that will have the fruit on them next season. 
Fan trained peach in the small greenhouse.  I don't know how long I will be able to keep it in
the greenhouse but I will probably have to move the greenhouse rather than the peach. 

Some of the subsoil from the trench was used to straighten the path.  I was trying to do it fairly quickly so it is not perfect but it is much better than it was.  I don't think that I am going to do any more to the path unless I can find some more slabs to finish it off. 
I ran out of slabs half way down the path so I finished it off with woody chippings.
My allotment on the left and Sue's on the right. 
The leeks got rust on them so the outer leaves have died right back but they are fine underneath.  There does not seem to be much damage from leek miner fly.  I will be eating these during the rest of the winter.  All the cuttings that I just stuck in have taken.  About five redcurrants and four buddleias.  As the Cox's Orange Pippin budding didn't grow, I took out the rootstock and potted it up.  I replaced the Cox with a May Queen graft that I did this year.  Hopefully that will be more successful. 

Some willow herb weeds growing in the decayed woody chippings mulch. 


The Phacelia tanacetifolia has not been killed off by the frost as I was expecting.  So the ground will be covered throughout the winter with this and trefoil.  I will dig the green manure in during February or the beginning of March when I start to plant the sweet peas. 
Blackcurrant bushes.
The black currant bushes have been thinned out and the older wood removed.  I have left as much new wood as I can to fruit next year.  They have had a good mulch of woody chippings.  If I have any farmyard manure left over, I will scrape off the chippings and put manure around the bottoms of these bushes replacing the chippings afterwards. 
Daphnia in the pots are still surviving.

 I have cut back the gooseberry fan trained on the shed so that there are no stems growing out. 

 I did the same with the red currant. 
This is a white scented clematis grown from a cutting. 
Red clover, crimson clover and broad beans
green manure.
The broad beans got cut back by the frosts but the crimson and red clover has thrived.  This will overwinter and be dug in during March next year.  It is where the onions, leeks, garlic and celery are going next season. 
Path between my allotments
I cut the lavender, rosemary and mint hard back and put the tops in the trench.  The oca has died right back now but I am leaving the tubers in the soil.  I am gambling that the frost will not kill them and I can use them for soups and stews during the winter.  King of the Pippins on the left and Royal Reinette apple on the right.  Maybe I need to level this path off a little too.  It shows that even in our climate there is significant erosion of top soil through surface run off.  The eroded soil is collecting where the puddles have dried up. 
More leeks and Phacelia tanacetifolia

Queen Cox apple.
I have started to plant this year's grafts.  I have not put up the supports for them yet and I am very prone to treading on and breaking the grafts so I will have to put some protection around them soon.  The green manure is just starting to germinate even at this time of the year.  I have already dug in some clover.  It was becoming very weedy so digging in seemed expedient.  Reseeded with whatever I had at hand. 
Roots bed before I tidied it up.
Still got carrots, beetroot and parsnips in the ground.  I gave the espaliers one more  going over to remove any stems growing out.  They are fairly well pruned now.  Hopefully I will get some pears this season.  I only know the Ribstone Pippin espalier in the middle.  The one on the left is a pear and the one on the right is probably a James Grieves apple.  I've also planted a Orleans Reinette on the other side of this bed. 
Pruned the loganberry and blackberries hard so that they could be trained to the supports. 
Top bed with mostly red clover green manure
The grape has been cut hard back and will have to be kept much more in order this season.  It has been allowed to run up long stems and these become very unkempt.  So they will be pruned off straight away this season.  I have planted May Queen, Claygate Pearman and Elis Bitter alongside the trackway.  I have left the laburnums in to act as nursery trees and provide the apples with a little nutrient because they are nitrogen fixing legumes.  Not all legumes are nitrogen fixing.  Alongside the path on this side I have a Court of Wick and Christmas Pearman family tree.  This was not planned and I grafted them together because I had run out of rootstock and didn't want to waste a sion.  I have a Winter density and a Mosses seedling on the other side. 
This espalier is a Newton Wonder - I think with Ben Sarek black currant this end and
Gooseberry 'Hinnonmaki Yellow' at the far end near the metal watering pots.

Top bed the other side covered with green manure. 
Fan trained currant bushes behind the peach greenhouse. 


Path up to the greenhouse.

 I have planted the Norfolk Royal apple tree between the two supports and will espalier it like the other apples. 
 My not very successful attempt at making a hot bed using woody chippings.  The chippings do heat up but the heat does not last very long. 

The green manure didn't germinate very well on this bed so I have begun to cover it with sieved compost.  It will have some farmyard manure dug into it during the winter. 
I have got some good salad out of the frames but the heat came more because of the glass than the heap of woody chippings.  The mound of woody chippings will be removed in the spring and either composted or put onto the paths. 

Bay trees alongside the greenhouse for protection.  I am pruning these to standard trees with
ball heads.  The Egremont Russet espalier is in the background. 

This is probably the best of the bays at the moment.  The trunks look a little wobbly but
when they get a little bigger they straighten out. 



Pond
I have started clearing out the pond.  I like to empty the water out and replace it with rainwater from the butts.  The pond water is full of nutrients and weed which makes a very good compost starter.  The pond plants will be thinned down and replanted in their baskets and put back into the pond.  A lot of the oxygenating plants will be kept because they are full of pond creatures.  The lavender has died right back and I don't know whether it will regenerate next spring.  If it doesn't, I will take it out and plant something a little more suitable there. 
Not very good photograph of the brassica bed
I've put about four barrow loads of sieved compost onto the bed but it does not look like very much.  It is pretty rich because I have been adding comfrey liquid to this compost so I probably don't need to put any more nutrients  on this ground.  If I don't dig it in, I could just rake the compost over the surface.  So why do I keep thinking that I need to put more manure or compost on here.  Particularly when I dug in lots of farmyard manure last year? Regardless,  I probably will put more farmyard manure on it but it doesn't need any. 
Cropping Brussel sprouts, kale, cabbage and kohl rabbi from this bed. 


The Pear 'Doyenne du Comice' Espalier.  . 
 I have had to expand the supports to accommodate the growth of the branches.  I am going to allow them to grow to full length until they fill up the available space.


Greenhouse with the sweet peas and lupins.  A few of the pumpkins have not been used yet.
One of the new apple grafts that I will prune to espalier.
The two previous grafts of Norfolk Royal I have stepped on and broken.  This one I was treating very carefully and put the supports around it to protect it.  Somehow or other I endeavoured to damage it by knocking off one of the grafts.  I think that this graft will grow on now and it means that I do not have to decide which of the grafts is the strongest to grow on.  This is a good photograph of the woody chippings mulch that I have used over the whole allotment this year.  Most of the mulch has rotted away now but I replenished this when I planted the apple.  There is a piece of charcoal I added last year in the chippings.  I didn't break this up like I usually do.  I might find it and hit it with a bull hammer so that the smaller pieces can be incorporated into the soil a little more efficiently than this big piece is doing. 


So still getting a lot of vegetables from the allotment even at this time of the year and I have not mentioned the vegetables in the store shed.

Tuesday, 13 December 2016

Total compaction. Repairing the concrete slab path.

The path between Sue's and my allotment was not laid very well and I promised both myself and Sue that I would take it up and do it again.  As I was digging a deep trench across the new potato bed to bury some logs and hedge trimmings, I dug out some sub soil to put under the slabs to level them out. 

The subsoil was pretty dire being a mixture of old red sandstone and boulder clay.  However, it does make an effective levelling base for the concrete slabs.  The clay is especially good at squishing itself level under the weight of the slabs. 

I was putting off this job because I do not relish the opportunity to go one to one with three foot by two foot, two inch thick concrete slabs.  They just ooze malevolence.  I had begged these monoliths from people around the allotment and struggled them back to the path.  I had promised myself that once they were down they would never ever be moved again - by me.  As far as I was concerned they could stay there until the next ice age when the glaciers could take their turn. 

So, of course, yesterday I decide to move them.

They were very old, pock marked, scarred and covered in immovable donuts of cement.  I used the chisel and bull hammer on the cement and a few meagre scraps were knocked off.  I then made the executive decision that the donuts had not really made a significant dent on our health and safety and promptly gave up. 

I had to lift the slabs out of the way to level the soil underneath them.  I do it with the fork and this faithful tool seems to rise to the challenge, raising each one of them with alacrity.  That, however, is only the beginning.  After the fork has levered the concrete high enough to get a grip on, I have to lift it up.  And every time I hear my son saying in my head, if he is not physically standing behind me, "Use your legs". I always, always use my legs. I do not need to be told every time; especially by the little voice in my head. 

But this time I didn't use my legs, I used my arms.  Not sensible but if you can do it quite quickly and safely, balancing it on end at the finale then it is effective.  Unless of course it decides to slide about and aim for you foot.  Luckily this time all the slabs were very well behaved.

Then the slab has to be walked a safe distance away from the work area and laid down in such a way as to make it "easier" to lift up again to put back. 

The ground underneath the slab was very consolidated probably because of the weight of the concrete slab but I expect that having lots of people and laden wheel barrows trundling across didn't help much either.  So compaction was the order of the day.

If compaction is the evil that most books would have us believe, then why was there so much life under the slab?  Woodlice, slugs, snails, centipedes, millipedes, spiders, ground beetles and various other scuttling creatures abounded under each of the slabs.  Not to mention worms.  They do it just to spite me.  Oh no we aren't going to burrow in Tony's lovely friable growing beds we would rather burrow in the really difficult compacted subsoil under the slabs. 

The compaction was no defence against horse tail and bind weed and in each crack between the slabs were the inevitable dock, couch grass and dandelion.  All grist to the mill for the worm bin but not defeated by compaction. 

Now I know that real compaction is totally destructive to soil fertility and health but it is a lot harder to achieve than just walking over the soil.  You need a multi tonne dumper truck to get some really good soil destroying compaction.    Do not misunderstand me.  I am not encouraging you. 

Walking on the lawn does not compact the soil to the extent that grass will no longer grow.  It really irritates me that the worst treated lawns always seem to grow much better than molly coddled ones like mine. 

I have always been taught that you should consolidate the ground by treading it before you sow or plant.  A fine tilth can be made using the rake and the friable soil created will form close contact with the roots or the seeds, particularly if the ground is watered afterwards. 

I do not needlessly walk on the growing beds but I will not submit to the gardening gestapo who say never walk on the growing beds.  Life is far, far too short and I can't be doing with going all the way round each time. 

Monday, 5 December 2016

You can't sterilise soil by digging.

Soil cannot be sterilised by digging.  If this was the case, the danger of such things as onion white rot, club root and parasitic nematodes could be removed by simply turning over the soil.  Even after several years of digging and trenching, these diseases and pests remain in the soil and can only be diminished by strict rotation and removal of infected plants.

Unfortunately slugs cannot be discouraged merely by digging over the garden. 

They couldn't decontaminate Gruinard Island from anthrax just by ploughing the soil.

What irritates me is that I was beginning to be convinced by the statements that digging killed life in the soil.  I was also taken in when Geoff Lawton said that the heat of a compost heap came from dead organisms killed off by the turning process.   Experience and thought experiments must at least give pause for thought.

The compost in the bins in the photograph below has been turned every other day for two weeks, following the Berkley method of composting.  It could be suggested that the mixing of the compost is similar to digging and trenching allotment soil.  The population of worms in the compost does not diminish, in fact there is evidence that it actually increases. 

The species of worm, probably Eisenia fetida,  may be adapted to living in a habitat that is constantly being disturbed by the compost turning process but that is unlikely.  However, it is remarkable that Eisenia fetida seem to prosper in an environment of disturbance in a compost that is regularly turned whilst, it is often said, soil living worms, like Lumbricus terrestris,  have their population drastically reduced by a similar activity when allotment beds are dug over. It is very hard to accept. 

This is the rough compost sieved and returned to the bins.  The black berry and black
currant stems prunings can still be identified but they are very easy to break apart now.
Oh, and lots of worms. 

The evidence of the survey on earthwormwatch.org/science results, found that vegetable beds had the highest density of total earthworms.  They suggest that this was against their expectations and probably due to the beds being regularly turned over and organic matter added.  However, with the data that they have at the moment there is no significant correlation between the amount of organic matter and the number of worms. 

Previously it was reported that there were far more worms in pasture than in cultivated land.  For example Satchell in 1967 showed that at Rothamsted  there were more worms in Park Grass, a permanent mowing meadow, than of Broadbalk which was under a continuous cultivation of wheat.  I think that Darwin said something similar too.  So it is a surprising result from the earthworm watch experiment.  This may just be due to habitat preference or some other factor.

This says more about monocultures and soil degradation than it does about worms.  If the suggestion that we get more worms with more organic matter is correct,  then maybe the amount or quality of the organic matter in the Broadbalk field may have some bearing on the population of worms. 

There is some support for the idea that compost made from a variety of plant and animal material is better than that made from one source. The hypothesis is that the types of organic matter, their associated ecology and how these are mixed within the compost heap will affect how beneficial it will be for vegetable crops. 

Continuous secretion of the same exudates from a monoculture year after year will lead to a modification of the populations of soil organisms.  

Apart from the concentration of organic matter, other factors may influence the quantity of worms in the soil.  This is already quite evident that worms like Eisenia fetida prefer to live in habitats that are almost entirely decaying plants and animals, whilst others will live in soil which has a much lower percentage of organic matter. 

There is some suggestion that putting lawn mowings into the compost will produce a thick mush of wet, smelly, anaerobic decomposition.  Although turning the grass mowings and mixing them thoroughly with other ingredients usually prevents this from happening,  the number of compost worms associated with matted compost is noticeably greater than the rest of the compost. 

Turning the compost every two days makes it particularly friable.  The low bulk density of this material must allow ease of movement into and through the compost.   Also the introduction of copious amounts of air will allow access of many different invertebrates to populate the heap and this is what is found. 

The comparison with turning the soil over cannot be ignored particularly if copious amounts of organic matter, that is well mixed and from a variety of sources, is added at the same time. 

There are many reasons for not digging the soil but the often stated "It reduces the populations of invertebrates" is not necessarily a valid one.

I would suggest that the reduction in the population of all soil organisms in seriously degraded soil has little to do with cultivation by digging or ploughing but much more to do with the lack of compost, manure or other good quality organic matter being added. 

Soil organisms need a source of carbon to consume.  Without it they will starve and populations will fall.  Digging adds air to the soil and this will increase the speed of decomposition of organic matter leading to its depletion unless it is constantly replenished. 

The production of heat in a compost heap comes from the exothermic reactions of metabolism.  Food (carbon) is burnt (in a very controlled way) to produce energy.  One type of energy that is produced is heat.  To get heat in the compost heap there must be life.  So much life that the compost heats up quite a bit.  The carbon used up to form this exothermic reaction produces energy and is lost as carbon dioxide to the atmosphere.  The amount of carbon in the compost heap is reduced and the concentration of other nutrients is concentrated in what is left.  The nutrients are already there they are not made by the composting process they are just concentrated. 

If the life in the compost were to die, due to turning every two days, there would be no increase in temperature.  The temperature increase is brought about by the life in the compost thriving and multiplying.  If these organisms had been killed off by the turning/digging of the compost there would be no increase in temperature. It would remain cold. 

The heat of a compost heap does not come from nowhere.  Turning or digging the compost adds air to the compost heap and this enables more aerobic decomposition to occur.  Now there are obligate anaerobic bacteria that are poisoned by oxygen and there are obligate aerobic bacteria that need oxygen but there are a significant number of facultative anaerobic bacteria that can live both anaerobically and aerobically.  In fact there is a confusing number of different methods of metabolism in bacteria. Believe me bacteria are ubiquitous and, as we are now finding, they are quite difficult to kill off.  Bacteria are so minute  turning/ digging the compost would be extremely unlikely to affect their populations significantly.

While I can accept that the heat generated by the compost heap will tend to kill off weed seeds, I find it difficult to accept that disease organisms will be overly affected.  Best not to put diseased material on the compost heap. 

Fungi are obligate aerobic heterotrophs.  They are also throughout the compost.

To say that anaerobic bacteria are bad and aerobic bacteria are good is totally meaningless.   Both types of bacteria decompose dead material and mineralise forming plant available nutrients. 

The thing about an aerobic metabolism is that it produces much more energy, due to the citric acid cycle and electron transfer chain,  decomposing and assimilating much more quickly.  This means that mineralisation, producing plant available nutrients, occurs much more speedily. 

So you don't sterilise compost heaps when they are turned and you don't sterilise soil when you dig it.  Use better reasons for not digging.