Tillstar buries stone as it tills potato land
Is it a bed tiller or a stone separator? Actually, the implement that has everyone in the potato industry talking is both – because the Tillerstar buries stone as it tills the bed.
George Moate, the Yorkshire potato grower behind the machine, readily admits he has not invented some new technology; but he has used existing technology in a unique way.
“It struck me that fitting star rollers behind a contra-rotating tiller could separate stone and big clods at the same time as preparing the bed for planting,” he says. “That way, you cut out an expensive operation with a dedicated separator and save both costs and manpower.”
After two years experimenting with the now-patented combination, a fully fledged commercial version has been developed in single-, double- and triple-bed sizes. It uses a proprietary tiller built in Italy as the basis of the machine, but with a lot of bespoke parts manufactured in Britain.
The key to the Tillerstar’s ability to bury stone is that its rotor turns in the opposite direction to that of a regular potato bed tiller, so the blades cultivate with an upward cutting action.
That is of little consequence in itself; the important thing is that this action throws soil and stones over the top of the rotor. Since there is no tight-fitting hood, the material can continue its journey out of the back of the machine until it lands on four finger star rollers.
Friable soil is sieved through the rollers to form the bed, but stones and large clods that cannot pass through are transported forwards – not to the rear of the machine as on a conventional separator. This places them into a void just behind the contra-rotating rotor.
“The angle of the star rollers is adjustable to fine-tune the sieving effect,” explains Mr Moate. “The rollers can also be adjusted up and down, and forward and back, to change their position relative to the rotor.”
On very cloddy soils, adjusting the star wheels close to the rotor gives the blades a chance to break them down so they contribute to the finished bed. But on very stony ground, a more generous spacing allows the stones to fall to the base of the bed, where they are covered by soil passing through the star rollers as the machine moves forward.
“In other words, the stone is buried across the full width of the implement, not heaped up between the beds,” Mr Moate points out. “That means they remain evenly distributed for subsequent cropping, which a lot of growers who let their land for potato production will prefer.”
Experience has shown that the implement will not only work effectively on ploughed or bed-formed ground, but also direct into stubble – ideally after subsoiling to remove any compaction caused during field operations for the preceding crop.
While the Tillerstar appears a panacea, particularly for growers on low to medium stone content land, Matt Smallwood, head of potato agronomy at SAC, sounds a word of caution.
“The impact on crop of burying large quantities of stone under the ridge is still unknown,” he points out. “It may increase free drainage, which would be positive for powdery scab and water logging, but negative for drought tolerance and possibly common scab.
“It is likely that roots will find their way through gaps between stones, but their growth may slow during this process,” he adds. “In addition to these considerations, it will be the physical capability of this machine to produce a deep enough stone-free tilth without causing compaction, particularly in wet conditions, when the optimum for ware crops is 30cm that will determine its success.”
As with any potato cultivation system, it will doubtless be a case of horses for courses, with the approach modified as necessary according to soil type, prevailing conditions and crop requirements.
