Agronomy

Soil compaction

In an agronomic approach of soil protection, the compaction is a serious concern. Today it’s a major obstacle to the productivity of the agricultural grounds because it affects directly the root system and the soil quality. At a world level it affects 68 000 000 hectares, the equivalent of Brazil agricultural surface! (Flowers et Al.1998)

A well structured soil consists of 25 % of air, 25 % of water, 45 % of mineral matter and 5 % of organic matter. By causing a loss of porosity, compaction engenders an increase of soil density and makes the root system development difficult.

The spring cultivations such as corn are the most sensitive to compaction. Their life cycle being very short (just like that of the legumes which need an aereted soil). Pivoting root plants are also sensitive because they possess few roots (colza, sunflower, beets).

There is two compaction type:

  • Surface compaction: less than 20cm depth
  • Depth compaction: beyond 20cm depth

Surface compaction is caused by an excessive pressure of tyres on the surface of the soil. It is the most harmful for the yield but the remedy is easy.

Deep compaction is caused by a load by axle too high. It has less immediate effect on the yield but is more difficult to notice and solutions are more difficult to implement. Ideally you should not exceed 10Tons/axle, but on trucks or tanks with large capacity this threshold is quickly crossed, as well as on the self-propelled harvester (self-propelled beet harvester typically).

The solution to fight against compaction of surface is to increase the footprint of machines. On average power tractors, low pressure tyres of last generation are a viable solution but when the need for grip is important, as for powerfull tractors, then caterpillars are the ideal way to optimise tractor preformances. They are also an interesting option for harvest equipments, which are bigger and bigger, and whose weight by axles is important.

CTF : Controlled Traffic Farming

What is CTF?

The controlled traffic is a simple technique which consists in localizing the traffic in fixed paths year after year to limit the collapse to precise zones and never affect the rest of the plot. Controlled Traffic Farming has been developed since the 1990s in Australia.

It allows a reduction of 20 % of the running surface, against more than 80 % in a classic system. Over a year, with different working widths and different tracks machines takes, the diversity of the cultivation, angle overlap which we sometimes take to work the soil, the compacted area can affect almost 100 % of the surface!

It is better to ride always on the same track without offset day-in and day-out , especially for heavy loads. As a matter of fact 75 % of the compaction occurs during the first passage!

If you practice the strip-till and if you use a RTK guiding system then you already experimenting a sort of controlled traffic. At best your combine harvester already use the same tracks as your tractors which are strip-tilling and drilling?

What are controlled traffic farming advantages?

The main benefits of controlled traffic farming are:

  • Improvement of the soil structure
  • Better water circulation (in case of excess or lack)
  • Improvement of the efficiency of inputs (better punctuality of treatments and fertilizer spreading thanks to the improvement of grip)
  • Easier Management of adventitious
  • Better quality of the harvests (better oil production for rapeseed)
  • Reduced cost of setting-up (deep tillage opération becomes useless, traction power decrease)
  • Increase of the yields

The advantages of CTF are visible in various situations. At first used in Australia to create tracks favorable to groundwater flow in humid regions, this technique has been becoming increasingly established in the drier regions today where the improvement of soil structure shows rises of yield from 15 to 30 %. In England, the results of long-term experiments also show an increase of yield from 10 to 20 % (Harper Adams University). According to European studies, spring cultivations show generally a gain of yield larger than autumn cereal. As they are taking root in wet soil, them have generally less problem to explore the soil and to take benefit of the improvemed structure of the soil (as we can see it with strip-till for short cycle cultivations).

How do we set up the controlled traffic farming?

In large farming operation, the width of the CTF “system” is determined by the width of the combine harvester’s cut or the sprayer boom. In this case the easiest solution is to divide the width of the sprayer into multiple, for example:

  • 36m sprayeur
  • 12m or 9m Drill and mulch disc tillers

In such a system the surfaces affected by trafic are 15%.

In this case tractors have to roll as much as possible in the combine harvester’s tracks:

  • 3m track width to run exactly in the same tracks but it is then difficult to circulate on the road
  • 2m track width, and thanks to the tyres width they will partially overlap the tracks of the combine harvester

compaction-01

For widths lower than 9m it is also possible to use the CTF! Here is an example with a 4 meter drill:

The combine harvester has a 2m track width and 6m of cutting width

The tractor with a 4m drill has a 1.80m track width

Track width are not exactly the same but it builds a model which repeats every 12m. The running surface is from 30 to 40 % according to the tyres width

compaction-02

Conclusion

The controlled trafic farming start from a simple principle: organize the passages to decrease and localize the compaction. It is a complementary approach of conservation agriculture, or the strip-till to improve the soil structure. In some situations it is the controlled traffic that will improve the results in no-till. Once the passages defined, the CTF opens new opportunities thanks to the guidance precision used, as the sowing between rows of the previous cultivation, the location of fertilizer, or inter-row treatments.

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