I think calcium is quite abundant in soil, all we need is the right pH. Similarly wood ash will certainly have these micronutrients like zinc and manganese. Again we need the right pH to bring them into soluble form. Wood ash is very alkaline like a laundry soap (you must have noticed that our villagers often use wood ash for cleaning cooking pots). This table might be helpful, taken from here. Note that ash pH is 12 similar to laundry detergent.
Thank you Farooq sahib for the information.
Below are some details about an environmentally friendly approach known as "NO DIG GARDENING" which increases soil fertility and has proven to be very successful in particular Brazil where it's has been implemented in more than 50% of the irrigated land.
1. NO DIG GARDENING
The presence of air in top 15-30 cm of soil is why most soil organisms are concentrated there. This layer is known as the topsoil and if we dig a hole its clearly more visible as its much darker than the subsoil layer below, its colour comes from humus-rich organic matter that has been broken down by worms, fungi and other micro-organisms into a soft black material.
Subsoil beneath the topsoil contains a diminishing proportion of micro-organism life the deeper we dig. It’s basically just a collection of compacted and inert clay, sand and silt and is a very poor growing medium in comparison to the good stuff above. This is precisely the reason why the subsoil must never be mixed with the topsoil.
Digging or tilling is bad for the soil. When the top soil is removed it contributes to soil erosion as important nutrients are leached out apart from destroying the beneficial micro-organisms mentioned above. In addition more watering is also required as the soil is now more disturbed and has less ability to conserve water.
Most people think that ploughing is essential for soil. Yet in some places some people do not plough at all. After harvesting a crop farmer leave what’s left of last year’s crop to rot in the soil. The next year’s crop is planted directly on this decomposed mat. It’s called ‘no dig or no till’ approach.
More 50% of Brazil’s soil is not ploughed and practices the ‘no till’ approach which in 1990, was merely 2.2%. This partly has been one of the reasons which have transformed Brazil into a breadbasket within a decade. Details about the Brazilian miracle has been discussed in a post titled “Brazilian Agriculture:Miracle of Cerrado” at the url mentioned below.
‘No till’ has also become popular in water scarce places like Australia and some parts of USA. In certain parts of India farmers save so much time by using no till that they are able to squeeze in an extra crop.
This approach can ideally also be used in our gardens in plain areas around end of April till August. Around end of April when the flowering of spring annuals is over and the choice selection of summer annuals is very limited. Additionally even if we choose to go ahead with plantation of summer annuals like Zinnia for instance the display time span of these annuals lasts for a month or maximum 2 months which is cut short by monsoon onset in July. Thus we may as well allow the soil replenish its nutrients. The bed area can be left in this condition for 4 months (May, June, July & August).
Below are steps to steps outlining the ‘No Dig’ approach.
First we need to remove large obtrusive weeds from a leveled area. Removing the small weeds is not essential as they eventually will be suffocated by the much layer which will added later on.
Next adding opened out pieces of cardboard or layers of newspapers on the leveled area and then watering it.. If using newspaper put down layers at least of 6 pages of papers. Wet the paper with as hose after spreading it and ensuring that the layers of newspapers are interlaced so no soil is showing. This layer works as a natural weed matting to kill any grass or weeds Cardboard and newspapers are broken down easily by earthworms and micro-organism activity in the soil. Just avoid using glossy magazines and waxed boxes-they don’t rot easy and contain harmful chemicals. These wet layers are eaten up by earthworms, bacteria and fungi within a few months-long enough for any grass or weed to be killed.
Then add at least 10 cm layer of mulch (dried leaves, composted leaf mold, grass cuttings, straw, paper, wood scraps, untreated sawdust etc) on top of the damp layers of newspapers or cardboard. Any organic material if fine but its important to include grass clippings or animal manure like cow manure as these are high in nitrogen and start the composting and breakdown of all these materials into soil. However a note of caution it’s difficult to get hold of weed free manure here in Pakistan and may better to avoid cow manure as it inevitably would lead to weeds later.
As each layer of mulch is placed it should be wet (wet no soggy) thoroughly with a hose.
The mulching material spread over should not touch the plant stems which would suffer adversely from the heat generated by new mulch, but not, under any circumstances, dug in to the soil.
Hopefully in another 2-3 months this newly constructed layer will turn into rich compost.
Note: Also included are some articles on No-Dig from some magazines which give another perspective.