Page 68 - Soil Degradation, Conservation and Remediation

54 2 Physical Deterioration of Soil

Fig. 2.2 Heavy farm machineries that can seriously compact soil

The major cause of soil compaction is the traffic over the fields and that too with

heavy farm machineries. Farm tractors, combines, and other equipment are large
and heavy. Tractors weigh up to 20 t and liquid manure spreaders can weigh as
much as 15 t when fully loaded.

Heavy Farm Machineries and Soil Compaction
Farm operations in industrial countries are completely mechanized. Tillage,
seeding, planting, harvesting, and processing are done with heavy machiner-
ies. Agricultural tractors and other implements such as combines are used for
tilling, planting, and harvesting. These 20–200 HP gasoline and diesel 2-wheel
drive and 4 × 4 machines usually have power steering, dual-range transmis-
sions, and two- speed live power take off (Fig. 2.2 ). Other farm implements
include disks, plows, tillers, scrapers, and diggers. Tractors alone have weights
of about 20 t. These heavy agricultural machineries result in much irreversible

damage to the soil. Soil compaction, induced by wheel traffic from large agri-
cultural equipment, has been shown to extend well below the depth of plow-
ing, reducing crop growth and yield in many situations. Estimates suggest that
the area of soil degradation due to compaction in Europe may exceed 33 M ha.

Higher tire inflation pressures are used to support such heavyweights. This
heavyweight gives higher pressures on the soil surface. Soil pressure is approxi-

mately equal to inflation pressure with radial tires, while with bias-ply tires there is
increased soil pressure at the tire’s edge because the sidewall carries part of the load.
Both radial and bias-ply tires are used on tractors, combines, and implements. Dual
tractor tires, compared to single tires, decrease pressure on soil, but increase the
affected area. As little as 4 psi pressure can cause soil compaction, duals or even
high-flotation tires do not prevent compaction; they merely change the distribution.

A pickup truck will impose about 50 psi pressure on the soil, a liquid manure
spreader 70–90 psi, and a 500 kg cow approximately 40 psi. Number of passes of

equipments over the field is important regarding soil compaction. Even one pass

over a field under poor conditions can cause significant damage. The first pass of a