2.1.3.4. Ridge tillage.The practice of planting crops on ridges is
widespread in both tropical and temperate climates. The crop row
may be planted on ridge top, along both ridge sides or in the
furrow. Ridge tillage facilitate mixed cropping system in which
more than one crop can be grown simultaneously in the same plot
of land, a common practice throughout the tropics and subtropics
(Bradfield, 1970). Ridges may be made on contour with graded
furrows draining into grassed waterways or the ridges may have
short cross-ties to create a series of basins to store water. The later
system is called tied-ridge system. However, this system increases
soil vulnerable to both wind and water erosion, especially when
working against wind and water flow directions. The system is also
mostly suitable for annual row crops, and wheel spacing and other
machinery modifications may be needed.
2.1.4. Conservation tillage for cassava
The traditional methods of farming have in most cases resulted
in soil deterioration without considering the soil improvement and
continuous cultivation at constant depth creates zone of high
compaction in the surface soil. The depth of the zone of compaction
will depend on the farmer practices (Spoor, 2000). Thus, soil
management will be responsible for important changes in soil
quality parameters, particularly those related to soil structure and
water movement. Most of cassava plantations in Thailand are
grown in loose textured soils where the soils are easily eroded. In
most cases, cassava farmers prepare their land by ploughing with a
3-disc plough followed by a 7-disc harrow and ridger. This causes a
very loose soil which is free of weeds and easy to plant. It also
causes the soil to be highly susceptible to erosion, while the direct
exposure of the soil to sun and rain causes rapid decomposition of
organic matter, leaving many soils almost devoid of organic matter
and with very poor structure. A minimum tillage or no tillage
system often referred to as conservation tillage is thought to be the
appropriate technique for these soils.
A broad range of the minimum tillage systems is used to
conserve soil and water, and sustain agricultural productivity. Notill is one type of this system, in which the crop is sown directly
into an untilled seedbed without any primary or secondary tillage.
Previous crop residue is left on the surface and weeds are generally
controlled by herbicides. This system is also called zero-tillage or
no-tillage system (Lal, 1995). In a Brazilian Oxisol, Roth et al.
(1998) reported that bulk density at 20–30 cm depth was
significantly lower in no-tillage and minimum tillage systems
compared with the conventional tillage system. Accordingly, the
total porosity was significantly higher in minimum tillage and notillage compared with conventional tillage systems.Jongruaysup
et al. (2003) reported that there were certain improved soil
structural parameters, with an increase in air porosity under no-till
comparatively with conventional tillage. He also found out that soil
bulk density under no-till agriculture is lower when compared to
the conventional tillage. He attributed these findings to, firstly, the
in situ mulching of the plant biomass residues in NT plot.
Numerous studies have also indicated that crop residues decrease
Stubble mulch tillageor stubble mulch farming (sub-tillage) is a
crop production system that involve leaving the soil with surface
residues cover for controlling water erosion, wind erosion and
reduce surface runoff (Unger et al., 1988).