SP FAQ - The Importance of Soil Carbon
In two main respects. Firstly, they simply do not utilize the surface residues to advantage. Residues are treated as being something of a nuisance rather than an asset. And secondly, they continue to at least partly-pulverise the soil, which destroys soil structure, soil organisms, and oxidizes soil carbon.
Not using the residues is the most important mistake. Residue from the previous crop is the single biggest asset that true no-tillage possesses, which is why no-tillage openers should focus on utilizing, rather than avoiding residues through partially burying them, removing them or pushing them aside.
The worst practice of all is to burn the residues. Yet there are still consultants who recommend burning residue-loads greater than 4 tonnes/hectare (4,000lb/acre). This simply reflects ignorance on their part of technologies like Cross Slot that can happily handle 15 tonne/hectare residue loads.
Decomposition of surface residues is nature's way of re-stocking the soil with carbon that has otherwise found its way into the atmosphere. Re-stocking the soil with carbon is the single most important thing that can be done to make world food production truly sustainable.
The products of the decomposition of crop residues (organic matter) are largely carbon-based (often referred to as humus). The Western Australian Department of Agriculture has found that 1 kg (or pound) of humus holds as much water in the soil as 9 kg (or pounds) of clay. So the first effect is simply to increase the water holding capacity of soils, which usually translates directly into crop yield.
The second effect is that this humus feeds the millions of soil microbes that hold the soil together and make it into a living entity rather than the sterile 'dirt beneath our feet' . Some microbes (such as abuscular mycorrhizal fungi - AMF) form symbiotic relationships with plant roots that helps them take up nutrients. Soil biologists now claim that the presence of AMF can raise crop yields by as much as 15%. Other microbes seek out plant pathogens and destroy them. And the exudates of most microbes help hold the soil together.
Scientists now claim that one teaspoon of a healthy soil can contain about 6 billion microbes many of them are so small that they can only be identified by their DNA.
It is drastically reduced in tilled soils, which is why tillage is such a destructive practice, especially repetitive tillage! When the soil is tilled it becomes aerated and this aeration oxidizes much of the labile (readily available) soil carbon into carbon dioxide, which escapes into the atmosphere (scientists now estimate that up to 15% of the atmospheric CO2 comes from the world's annual tillage of its soils). There are other forms of less-available carbon that are not easily oxidized, such as are found in so-called 'Biochar' (a form of charcoal).
But that is not the most important issue. If any one soil is tilled annually for long enough the soil organic matter level will gradually ramp downwards, starving the all-important soil microbes until they die and the soil becomes almost inert like talcum powder. The dust storms of the USA Midwest in the 1930s attested to this occurrence. It is now know that the dust storms were largely a result of repeat tillage of the prairie soils, which had stripped them of their natural (pre-ploughing) organic matter.
Unfortunately no. The soil disturbance caused by the very act of ploughing usually oxidizes as much (or more) existing soil carbon into CO2 than is gained from the buried straw. And it kills invertebrates like earthworms, which are otherwise the most obvious indicators of soil health. The only way to get a net increase in soil carbon is either to cart in humus from elsewhere (e.g. compost) or to adopt true no-tillage that allows the residues and straw to decompose on the surface of the ground and become incorporated into the soil by the earthworms and soil microbes. This is why minimum soil disturbance and maximum residue retention are the cornerstones of true no-tillage.
Sadly, no. True no-tillage is a more organic process than so-called 'organic farming' ; at least as it applies to the growing of annual crops (90% of the world's food comes from annual crops). Because 'organic farming' of annual crops does not allow the use of synthesised herbicides to kill weeds, it usually relies on tillage to do this and (as described above) tillage is about the most inorganic thing that can be done to any soil.
Therefore, regardless of whether or not organic food is better for human consumption, where 'organic farming' of annual crops depends on tillage for weed control it is certainly not a sustainable or environmentally responsible practice at the farm level. On the other hand, where weeds can be controlled by non-herbicide methods (other than tillage) organic farming is every bit as environmentally sustainable and responsible as true no-tillage.
The three photographs below show three spade-slices of the same soil in Ukraine. The left hand photo shows the soil in its natural state that has not been disturbed in any way for the past 50 years. The soil (of glacial origin) is very healthy with a lot of buried organic. A healthy crumb structure has formed that in turn has created pore spaces between the individual (crumbs). This soil is as healthy as you will see anywhere in the world.
The centre photo shows the same soil after 50 years of continuous tillage, which has oxidized much of the organic matter, resulting in loss of structure and development of compaction with little porosity. The visible cracks have resulted from digging the soil up and would not have been present in the undisturbed soil. Crop yields would have declined cumulatively.
The right hand photo shows the same previously-tilled soil after 9 years of minimum tillage. There is a clear horizontal break about half way down the profile (shown by the arrow). Deeper than this break-line the soil has not been tilled for 9 years and its recovery towards its natural state is well advanced. Crumb structure has re-formed. But at depths shallower than the break line the soil is still being tilled and is no better that in the poorly-structured soil in the central photograph.
The message is clear and simple:
9 years of minimum (shallow) tillage has done wonders for half of the soil, but not all of it. Total recovery of this soil will not be achieved until genuine low-disturbance no-tillage is applied to the full soil profile. Minimum tillage has improved the situation, but has only gone half way.
a. For all crops, learn how important soil carbon and organic matter are to crop yield and sustainability.
b. For all crops, aim for maximum residue retention and minimum soil disturbance.
c. Remember that lying straw decomposes faster than standing stubble.
d. For annual crops, leave short rather than long standing stubble (standing stubble takes longer to decompose but may be helpful for short periods as a wind protection for seedlings and for trellising of subsequent legume crops).
e. Row spacing should primarily reflect the available soil water and this will likely increase as soil organic matter increases. With Cross Slot openers, it is not necessary to have wide rows for residue handling purposes, but of course they keep the machinery costs down.
Absolutely! It is not only suitable, it is highly desirable! The purpose of fallowing such land has been to rebuild its organic matter content by interrupting the destructive tillage cycle for 10 years or more. As a result, the soil will likely be as healthy as it has ever been. The worst thing that could then happen to it is to disturb it more than absolutely necessary. Any form of tillage (or even minimum tillage) would be a disaster and most other no-tillage options will simply not cope with the amount of residues present nor their tangled nature.
Cross Slot no-tillage openers will handle the tangled residues with ease as well as preserve all of the good soil biology and structure that has accumulated.
Firstly, make sure that any lingering pests and weeds are dealt with.
Then just spray it and drill it. It is as simple and fail-safe as that.