There are three reasons for doing this:
1. contamination:
The first was already assumed, for growing flowerbulbs they want to change soil every year: the full layer of soil is buried 2 feet deep before planting, so all diseases die during the next growing season.
2. prior to grading a field:
on high spots, the topsoil is buried under subsoil. Then tractor drawn scrapers move that subsoil to lower areas. when scraping is done, they use the plough again, to put the subsoil back down where it belongs, and get the topsoil from under the fill. This way you can level a field without disturbing the soil profile: It prevents that you remove all topsoil from the high parts, and make the layer of topsoil even thicker on the low muddy patches.
It may sound odd, but its the only way to keep an even layer of topsoil when levelling a field with more than a foot of level differences.
3. To mix various soil types
Some soil mixtures are better than the individual layers: the Dutch soil is partly washed in from the sea, partly washed in from the rivers from the Alps, partly rotten plant material (peat) and partly virgin clay soil by damming a part of the sea and pumping out 5 meters (16 feet) of water.
Because our country is river delta mostly, soils occur in all fashions: peat on top of a clay layer, (a pool with lots of plants that rotted away over the years) sand on clay, (foreign sand washed over the clay by natural water flows) sand on peat (sand washed over peat soil)
Pure peat on its own isnt fertile at all: thats why they mix it with a clay or sand subsoil, this way it will have a better Ph, and be less prone to compaction and water pooling.
What is seen in the video, is on a former seabottom: the clay soil is very fertile but very hard on equipment, prone to slump, and there is a lot of soil tarr on root crops like potatoes and sugar beet.
Then it pays to mix some sand subsoil through the layer of clay.
I worked a short while for the company that runs the Cameco and Fendt with that deep plough.
Or actually ploughS because they dont just have one, but have them in steps of 30 cm working depth:2 and 3 foot working depth 2 furrow ploughs, 4 / 5 and 6 1/2 foot 1 furrow ploughs.
They are specialists and can pick the right plough for the job, like an artist picks the right brush for the painting
Their fleet of extreme ploughs is partially "home" made (well, they are a very big company with a professional workshop) and some are made by Panter special ploughs:
Panter Ploegen
The Cameco was purpose built for this operation, and weighs 23 ton. Therefor, it isnt used on peat soils, they are afraid that the soil will swallow it some day.
Then they run 3 Fendts, of 180, 230 and 260 hp. Individual tractors are easier to extract from the bog, if the soil decides to swallow one of them.
the 3pt hitch of the Fendt carrying the plough is reinforced: It doesnt have the quick tach lower links because the hooks bend open: It doesnt have a normal toplink, but a solid bar of steel. The short arms to which the 3pt lift cylinders attach, is connected outside the lift cover by a U shaped arm, torched out of solid steel of 4 inch thick: when tipping the 2 way plough, the momentum is so high that the original torsion shaft of the Fendt linkage snaps.
the link arm connection to the rear axle has been modified: not only reinforced, but it also has a tow eye: In the 80's Van Werven has ripped 1 or 2 Fendts in two with the Cameco: Since then, they attach the chain not to the tractor, but to this modified lower link arm attachment bar. (also torched out of solid steel)
What you see on the front of the tractor, is only a large hoop, to guide the cable from underneath the tractor.
The old truck tire which is inbetween the chains that attach Fendt and Cameco to absorb the shocks, lasts only a couple of days. Next to Ag work, Van Werven has a big trucking and container fleet, so pulling the tire apart is the least worry
They told me they ran a 570 hp Challenger tracked. Because of the big side incline of the deep furrow, the (any) tractor tends to pull into the furrow into the ploughed land. The challenger could easily pull the plough alone, but the steering hydraulics ran hot because they constantly had to adjust.
This company is the only specialist in the world, because it is mostly done in Holland because of our funny soil that was washed in from sea and rivers, or built up from rotten plants in wetlands.
Panter incidentially also exports ploughs for forests, planting new forests as well as reclaiming existing forests.
They have also sold one to africa for a pine apple farm, because the pines didnt root deep enough on the hard dry african soil.
