Details about the study

Using the National Soil Resources Institute’s soil bin at Cranfield’s Silsoe campus, the research work conducted by Ansorge, who is studying for a Ph.D. doctorate in Agricultural Engineering, found that with tracks, soil movement between depths of 100mm (4in) and 600mm (23in) was reduced by an average of 65%. Overall, he found that whilst the initial soil loading from tracks was greater but contained within cultivation depth, after 400mm (15in) there was statistically little difference with an uncompacted soil.

Measurements on the test installation with LEXION 580 TERRA TRAC

Using a test rig that can reproduce the weight loading on the front axle of a fully loaded CLAAS LEXION 580, his research work compared the CLAAS TERRA TRAC system with commonly used front and rear combine tyre sizes. He then went on to consider the implications of his findings for subsequent cultivations and the cost implications.

Sandy loam soils were placed in layers with talcum powder markers between each layer, and then by digging a section across the bin it was possible to see how far each layer had moved after each pass of the track or tyre. A cone penetrometer was also used to calculate soil loading levels at different depths.

Tracks and Tyres Compared

Comparing TERRA TRACs loaded to 12t to allow for their extra weight, with a 900/60 tyre loaded to 10.5 tonnes, the research found that the tracks resulted in a shallower initial rut with, on average, a 65% reduction in soil movement below that.    

As expected, the wider the tyre, the less the loading, and the results clearly showed that a 900/60 tyre created the least damage of all the tyres tested. However the trial also showed that there was little difference between a 800/65 tyre and the larger rolling radius 680/85 tyre, making this the best option where road width is an issue.  

Dirk Ansorge’s research went on to consider the optimum rear tyre options for both TERRA TRACs and the best front tyre option.

For TERRA TRACs because the higher initial soil loading creates a ‘roadway’ for the rear tyre to run on, comparing 500/70, 500/85 and 700/55 sized tyres he found there was little difference between the three sizes. Therefore in order to maintain the transport width advantage 500/70 or ideally 500/85 tyres are the best option.

However, with the 900/60 front tyres, again it was a case of the wider the better as when comparing 700/55 and 500/70 rear tyres, the wider option resulted in considerably less additional soil movement.

Whole machine ground pressure

By comparison, the tracks (green line) show a higher initial soil compaction down to a depth of approximately 120 mm, but afterwards it decreases drastically. Then at about 400 mm hardly any difference is evident with an uncompacted soil.

For those who plough, whilst at a typical ploughing depth of 220mm (9in) the majority of the loading from the TERRA TRACs is removed, it only just touches the damage done by even the best front/rear wheel combination. This leaves significant soil loading left untouched that will require additional deep, and expensive, cultivations.

Even where subsoiling at a typical depth of 460mm (18in), whilst all the soil loading from the tracks has been removed, deeper compaction from tyres does still remain untouched.

For those in a minimal cultivation based system with a disc/tine cultivator capable of working down to 300mm (12in), this will eliminate the vast majority of the soil loading from tracks, although deeper loading from wheels will still remain.

Ultimately, the research shows that whilst subsoiling will always be required after a wheeled combine, ploughing or cultivations will remove virtually all the soil loading from tracks.

Taking his research work one stage further, Dirk Ansorge has also looked at the power needed to subsoil and the cost implications of this.

As expected, at 450mm it was found that the power needed to subsoil after tracks was 36% less than the power needed to remove the loading from tyres.

However, due to the shallower loading caused by tracks, there is the opportunity to raise the working depth with a resulting reduction in draft force required.

By subsoiling at just 350mm (14in), the draft force required drops from 240hp, costing about £6/ha, to just 88hp at a cost of just £2/ha - a reduction of 63%.

With TERRA TRACs costing around £2.50/ha (£1/acre), this is more than recouped compared to the cost of subsoiling after tyres at £6.00/ha (£2.50/ac), in addition to the crop yield and timeliness benefits of tracks.