mikep
Member
- Location
- Arse end of Surrey, UK
Add material that once lived to the soil, it then starts to be broken down by living organisms such as fungi, bacteria, actinomycetes, algae, protozoa and larger organisms like earthworms down to nematodes. In a cubic meter of topsoil it is estimated there are around 7 trillion individual organisms. I mention just this one figure to put into context the enormity of the living mass within the soil, and I am sure that the actual figure in any given area of soil will be highly variable. Put this another way, in a grassland soil the approx. weight of bacteria is in the range of 1-2 t/ha and fungi 2-5 t/ha.
In your minds visualise two groups of soil matter: the first used to be alive, the second is still alive.
The matter that used to be alive (crop residues, FYM, compost, destroyed cover crops, dead microbes etc) will not just remain they will be 'dismantled' from their whole into smaller fractions i.e. they are broken down by the living matter within the soil. Basically it's a massive food chain
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Plant matter/ crop residues can be split into:
Some of these crop residues can be broken down quickly by a relatively few number of organisms and others will be broken down gradually by a diverse range of organisms. I'll avoid attempting a detailed description of which organisms do what, as we'd probably be here all night and I'd probably not get it totally correct either.
- rapidly decomposed: sugars, starches, proteins
- less rapidly decomposed: cellulose, hemicellulose
- slowly decomposed: waxes, resins, lignin
Basically it's a massive food chain.
The value of all this to farmers are huge.
The breakdown by-products will partly be plant nutrients that can be used by growing crops to satisfy their nutritional requirements. This is why FYM use provides N, P, K, Mg, Ca. The type of matter that is being broken down will determine how quickly these plant nutrients can be re-cycled.
There are also a number of compounds excreted by the organisms that are responsible for maintaining soil structure which in turn is critical to maintaining pores within the soil through which water can drain and air can diffuse.
If you take away the organic matter from the soil these beneficial characteristics start to reduce.
By now hopefully you envisage the soil as having a number of inter related mechanisms, a bit like an engine and gear box. If you stop the supply of fuel into an engine you know what happens. If you stop/restrict the feeding of once living matter (OM) then that restricts the ability of the complex array of living organisms to exist and that in turn restricts the benefits that we need in order to maintain soil fertility and crop production.
Another dimension to appreciate is that the array of organisms present in the soil will be larger when more diverse types of organic matter are available. So a soil that just gets a stubble ploughed back every year will have a narrower range of living organisms than a soil that gets stubble, FYM/compost, cover crops etc. The current thinking is that a soil that has a greater diversity of organisms will be more likely to recover from a system shock such as prolonged water logging or a drought or perhaps even a change in cultivation policy.
Basically, there isn't one cost effective way that should be favoured, you'll get more resilient soils that are able to maintain long term function if you 'treat them' to as wide a range of once living material.
And finally the humus is a "chemical junkyard" as it is the accumulation of resistant plant material and microbial waste products. Humus is stable and very slowly broken down.
It's all about re-cycling.......... be it FYM, dead roots already in the soil or compost!
I've tried to condense what could easily be written down on hundreds of pages into a few paragraphs, I hope you get the gist.
All true but you dont mention the controlling factor which by and large is oxygen supply. All the soil living elements require a supply of oxygen in some form mostly free form but regulated supply. This is the driving force and where the analogy to fire comes from, increase the supply and the rate of breakdown increases as the aerobic elements are in control, reduce the supply and it slows down.
A compost heap may steam but turn it at the wrong time and it can burn.
The slower the reaction the more thorough and more efficient and this is where no till has an advantage by keeping a steadier level of oxygen going into the soil.
I always was amazed that in the ploughing days you would plough up last years straw discoloured and brittle but more or less intact and it would disappear within weeks when it hit the air.