TRACTORS that are wider than tennis courts may be set to loom large in the
rural landscape. The Dowler 鈥済antry鈥� tractor鈥檚 developers say it could raise
crop yields by as much as 25 per cent, halve farmers鈥� fuel use, lower
fertiliser bills and reduce applications of herbicide by up to 70 per
cent.
The machine consists of two 鈥渉alf-tractors鈥� connected by an 11-metre
gantry. Tools such as sprayers, drilling rigs, ploughs and harvesters hang
down from the gantry and can be operated from cabs on either of the half-
tractors.
Traditional tractors ruin soil by crushing it beneath their wheels. 鈥淭his
impedes movement of air, water, microorganisms and nutrients in the soil, and
hampers root development,鈥� says the gantry tractor鈥檚 inventor, David Dowler, a
farmer in Chipping Norton, Oxfordshire. Instead, the wheels on his tractor run
in narrow alleys on each side of the plot spanned by the gantry.
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Farmers usually restore the structure of compacted soil by ploughing, but
ploughing is seldom necessary with the Dowler tractor because the soil
structure remains intact. 鈥淵ou don鈥檛 have to undo the damage you鈥檝e just done
with the tractor,鈥� says Tim Chamen, a soil scientist at the government鈥檚
Silsoe Research Institute in Silsoe, Bedfordshire.
In tests at Silsoe, Chamen discovered that doing away with the need to
plough halved the energy required to keep soil in shape. And because the soil
is in such good condition, Chamen found, yields of cereals rise by 15 per
cent. 鈥淭he gains are pretty substantial,鈥� he says. He believes that even
bigger gains are possible for root crops such as potatoes and sugar beet
because they are more dependent than cereals on soil condition.
Dowler says that the two fields in which he has been testing prototype
gantry tractors have not needed ploughing for 20 years. Although crop waste
and weeds still need to be removed, farmers can shift them with lighter, rake-
like machinery, rather than ploughing them in. According to Chamen, the soil
dug up from the Dowler鈥檚 unploughed fields 鈥渋s in perfect condition鈥�.
Because the gantry is so wide, it can cover a given area more quickly than
a traditional tractor. And according to Dowler, the tractor is simple to
manoeuvre because each wheel can turn through a complete circle. The machine
can rotate about its centre or about any of its four wheels. After completing
a strip in a field, the machine can either turn, or the driver can swivel the
wheels through 90 degrees and drive into position for the next strip. The
swivelling wheels also enable the farmer to drive the tractor along the road
with one cab in front of the other.
In trials in the Netherlands, researchers found that the gantry tractor
could apply chemicals more precisely than traditional booms and sprayers. By
targeting the chemicals more carefully among the rows of crops, they achieved
the same yield with 40 per cent less fertiliser and a 70 per cent reduction in
the use of herbicides. The key to this precision is the subframe on which the
sprayers are mounted. The subframe鈥檚 position is constantly adjusted to lock
onto a laser beam shone from the end of the field. Hydraulic devices keep the
subframe locked onto the beam, even when the supporting gantry wobbles.
Dowler spent 20 years developing his tractor. 鈥淲e really are on the verge
of making it all happen,鈥� he says. A major manufacturer of agricultural
machinery is negotiating with Dowler鈥檚 agents for a licence to build a
commercial version.
The only cloud on the horizon is that the gantry tractor could cost as much
as 30 per cent more than the most powerful traditional models, although the
price could come down with mass production. And Peter Limb, chairman of the
cereals committee of the National Farmers鈥� Union, believes that farmers would
resent having to completely replace their existing machinery. 鈥淭he concept is
right, but farmers are already geared up with conventional machinery,鈥� he
says.
鈥淚t won鈥檛 catch on tomorrow, but you might well see some take-up in more
specialised applications where farmers grow high-value crops,鈥� says Limb.
鈥淭hey are the most likely to recoup their investment.鈥�
