Bastard Digging or True digging. 

There are methods of bastard digging that the Victorians developed that allowed you to dig continuously without having to stop.  I do not use these methods but dig out trenches.  The trenches are usually about three spits deep.  Bastard digging mixes 'subsoil' with topsoil or replaces the top soil with 'subsoil'.  This begs the question, "What is subsoil."  In the past, I could have easily described subsoil.  It is that part of the soil that is below the topsoil and is usually a different lighter colour to that of the topsoil.  The dark colour of the topsoil is due to the presence of organic matter.  The lack of dark colour in the subsoil is probably due to the lack of organic matter.  The subsoil usually has a different structure to that of topsoil and feels different.  However, after bastard trenching for several years the 'subsoil' has become more and more like topsoil and there is little difference throughout the profile until you get below the third spit deep.  

It has been said that the subsoil is less fertile than that of the tops soil and should never be brought to the top of the soil.  It usually has a greater number of stones in it than the topsoil.  The lack of fertility and the abundance of stones would make the germination of seeds difficult and the growth of transplants slow.  

So why did the Victorians develop bastard digging husbandry where topsoil was buried below 'subsoil' and the subsoil was placed on the top?  

The main method of transport in Victorian and earlier times was the horse.  Horses produce prodigious amounts of manure.  Manure was seen as a waste material that needed to be disposed of.   The stables of  the super rich were bulging with horses which produced lots of manure.  One way of disposing of this waste material was to bury it deep within the subsoil.  Large trenches were dug and manure laid at the bottom, covered with subsoil and the topsoil replaced.  The exceptional gardeners of the Victorian era and earlier noticed that horse manure helped vegetables grow.  However, they had just buried the manure deep in the soil.  Here horse manure decomposed and formed a very friable fertile layer that mixed with the subsoil.  They dug this fertile soil from the bottom of their trenches and placed it on the top of the soil.  Stale topsoil full of weed seeds and disease was put at the bottom of the trenches and covered with copious amounts of horse manure together with any other organic matter they could find.  The trench was filled to the top with 'subsoil' infused with horse manure and vegetable mould.  Eventually they achieved a very deep topsoil.  A spit of topsoil could cheerfully be buried because the subsoil had become organically rich and could be brought to the surface increasing the fertility of the soil to at least one metre deep.  

If very poor subsoil from deep in the soil is composted with organic matter it changes very quickly into a topsoil like soil.

I am bastard trenching at the moment but I am not necessarily bothering to separate top spit soil from that of the lower spits.  There is a difference.  The top spit has noticeable amounts of vegetable mould mixed within it and the lower spits have the remnants of previous year's hügelkultur.  

One of the reasons I dig is to add organic matter.  The larger and deeper the trench the more organic matter I can bury.   I have buried the remnants of two goat willows and a small oak tree from my neighbours allotment.  Also the brushwood from a branch that fell from an ancient oak tree further down the allotment site and some sycamore brushwood have been buried in the most recent hügelkultur trenches.

As I removed soil from the trench, I passed it through my bread tray sieve. 

The vegetable mould mulches and the old hügelkultur wood that had rotted down to a friable, spongy mass are being mixed thoroughly with the soil removed from the trench making it a very homogeneous mixture.  Whether mixing topsoil like this makes an iota of difference to the growth of crops is debatable.  But I think that it does; on the anecdotal evidence that I have accumulated over 60 seasons.  Why would commercial compost makers mix their concoctions if it did not make any difference to the growth of plants.  

So why do I dig?  I dig - particularly bastard dig - to add copious amounts of organic matter to the soil.  What some would call compost trenching nowadays.  Logs and brushwood can be added to the bottom of the trenches and dug into the true subsoil at the bottom.  I dig to mix vegetable mould and the decomposed remnants of hügelkultur with the top soil.  I dig deeply to remove the rhizomes of bindweed and the rhizoids horse tail.  I dig deeply to bury topsoil wildflower and grass seeds deep within the soil.  I bastard dig to bury stale and disease ridden top soil well away from from next year's crops.  I don't necessarily dig to add air to the soil.  Air and the oxygen within it will infuse the topsoil whether I dig or not.  I add more air when digging and sieving the soil and this removes organic matter by encouraging aerobic microbes to mineralise it to carbon dioxide, water and micronutrients.  This is what I want to happen.  My vegetable crops need the micronutrients.  However, at this time of year few of the nutrients would be used. So I sow  a good cover crop like rye grass to mop up the nutrients and lock them up until next spring when they can be dug into the soil to release them again for the new crops. 

I bastard dig to deepen the soil.  Adding big pieces of organic matter like branches and brushwood raises the level of the soil and breaks down adding to the volume of soil.  

I do not raise beds.  I raise allotments.