10 years ago, researchers at Harper Adams University in Shropshire in the UK set out on a long-term project to question the effects of machinery traffic and cultivation techniques, such as a plough, on the soil.
A decade later, some concrete results are emerging and these were discussed at a recent conference entitled 'Carbon, Traffic and Tillage' held by the Soil and Water Management Centre, based at the university.
Plough and other techniques
Three different traffic regimes were incorporated into the trial along with three different tillage depths to produce nine plots overall.
The three traffic regimes were tractors with standard tyres, tractors with tyres running at a reduced pressure, and controlled traffic farming (CTF), in which the same field routes are followed every season.
The three tillage depths were to plough, shallow cultivation and zero depth (minimum tillage).
Soil quality was assessed in various ways; these included the soil organic matter, porosity and water penetration properties, biodiversity and worm populations.
The results were set out in detail on the day and it is fair to say that the overall trend was for CTF to come out on top in all categories measured, except for the worm count where it fell behind that of the reduced tyre pressure plots.
Somewhat surprisingly, given the attention that has been devoted to the relationship between tyres and soil damage, the difference between the two tyre pressures was rarely of any great significance, although running softer tyres tended to have a beneficial effect in all cases.
Unfortunately, what was not clear was the effect of tyre type on the soil as modern high-flexion tyres are designed to provide a larger ground contact area than a simple standard tyre with some air let out.
Quite whether the latest carcass designs produce a more profound effect was not clear, but the message that some benefit was derived from running at lower pressures was certainly apparent.
A question of bio-activity
Earthworm populations was another factor considered and the results were not always what might have been predicted.
The biggest surprise was that the CTF plots came second to reduced tyre pressure when counting the worm population.
These numbers were derived from the abundance of worms in a given area rather than their total mass. Yet, there is so little we know about the subterranean ecosphere and these are only tantalising glimpses of what might be going on.
Interestingly, the method for tempting them to the surface was by the application of a solution of mustard powder which, apparently, acts as an irritant to worms and they head for the surface. All were returned to the soil unharmed.
One result that was expected was that the depth of tillage does significantly affect earthworm numbers, with a negative correlation to greater depth of penetration.
Yield results
As much as we may pay attention to the various effects on the soil, the most pressing question is the total yield and the following table was presented to show the interaction of the methods for winter wheat over the years.
| Standard pressure | Low pressure | CTF | |
|---|---|---|---|
| Deep tillage/ plough | 97.5 | 101.9 | 102.4 |
| Shallow tillage | 101.1 | 100.6 | 106.8 |
| No tillage | 96.7 | 97 | 96.3 |
The overriding message here is that it is not entirely necessary to throw the plough over the hedge in a bid to get better results. It is more the need to reduce stress on the soil.
It was mentioned that it is better to think of the soil as a living organism rather than an inert matrix that needs knocking into shape.
It must also be borne in mind that these plots have been micromanaged over the years, and although the intention is to replicate field conditions, the results can only act as a guide rather than a definite proof.
Despite this caveat, there is a clear indication that shallow tillage combined with CTF led to the best yields, and no tillage performed consistently below average in all traffic regimes.
However, the yield is only one side of the coin, the other is the cost of field operations and inputs. An economic analysis of the trial showed that the financial margin was not entirely dependent on the amount of produce harvested.
It was also shown that moving towards CTF, or even low ground pressure tyres, with the required investment in technology could be justified in as little as one year for tillage farms as small 100ha.
The carbon content of soil
The first 10 years of this trial had demonstrated that systems geared to reducing the exposure of the soil to the atmosphere had tended to increase soil organic matter.
It would then appear a simple matter to build up the carbon content by encouraging practices that increase the amount of organic matter in the soil.
Unfortunately, the closer the carbon cycle is studied, the more complex it becomes, and the development of a single index by which it can be measured, and compared, is looking ever more remote.
One key feature that is starting to emerge is that soils are subject to saturation and they may not retain any extra that may be added beyond their natural equilibrium.
This obviously places a huge obstacle to the idea of a simple reward scheme for farmers sequestrating carbon.
Everyone agrees that retaining more carbon to stay in the soil is a good thing, but when moving beyond that laudable aim to look at the how and why, it very soon starts to get messy.
It was noted that there are major limitations to how much extra carbon can be sequestrated and various claims that have been made about absolute quantities should be treated with caution.
This may not be what some environmental activists would wish to hear, blaming farmers for all the ills of the world has long been a popular pastime for some, yet their zeal will need to be countered before aspirational targets that simply cannot be achieved are set out in legislation.
Soil management and future for the plough?
As more becomes known about how the natural world works, strategies which embrace the new knowledge will need to be constantly developed and revised.
The increasing appreciation that soil is an asset that needs to be nurtured as an entity in its own right is growing, if only because agriculture is being called upon to ensure it acts as a larger carbon sink, and therefore greater attention is being paid to the way in which it functions.
The realisation that tractors are best kept off it altogether, if and where possible, is also growing and it may be this which forces a fundamental rethink of machinery design.
It may indeed have a greater effect than the onward march of digital technology.
Nexat's gantry system, which represents a substantial investment in one alternative approach, may turn out to be more of a harbinger of things to come than the ever increasing cascade of digital technology.
