Transcript No Slide Title

CONTOUR RIDGES and NARROW & BROAD
BASED TERRACES
Ridge & furrow
• Slope on which possible is limited by soil type
(strength / infiltration) & by tractor stability if
mechanised
• Construct on grade (0.25 - 0.5%) on less
permeable soil or steeper land, otherwise if
medium to high infiltration soil and/or high
ridges, construct on the contour
• Maximum slope depends on soil type (perhaps up
to 10 or 20% from calculations - but in practice
often limited to slopes less than 2%)
• Larger ridges may be semi-permanent ("splitting"
the ridge every other year or so); common
technique is to place residues into lines, then
ridges constructed over them (2 to 4 rows
/ridge)
• plant drought resistant crop on side
• It is good practice to provide open field drains
at intervals down field as insurance against
breakages
• Can use plough to construct - disk plough best
• Survey "contours" every 10 to 20 m then fill in
between (by pacing or using tractor settings);
ridges will then run more-or-less parallel; fill in
the irregular spaces (with crop or fodder
grasses or fodder legumes)
• Breakages will occur:
• if ridges are not on the "contour"
• if soil not consolidated
• Danger of breakage have led some soil
conservationists to prefer not to use
Tied ridges
• Ties recommended at 2 to 5 m spacing along
furrows (not as high as ridge tops) to prevent
breakage and improve storage
• Special cultivators are available for tractors, e.g.
Chinene & Pauwelyn (1991)
Tied ridges in Zimbabwe with crops planted in
furrow: vertisol soil, 1.5 m spacing, 0.3 m high,
parallel to contour, ties at 5 to 7 m, fertiliser next
to furrow
Year 1 (416 mm)
Year 2 (247 mm)
Crop
Yield with
treatment
(t/acre)
Flat planted
(t/acre)
Sorghum
1.2
0.9
Maize
1.4
1.0
Cotton
0.6
0.6
Sorghum
0.6
0.2
Maize
0.04
0
Cotton
0.4
0.2
Note: proportional benefit is much greater in the dry year
Broad
beds
• Broad-bed & furrow mainly for impermeable soils,
especially vertisols
Broadbed-makers sometimes used, e.g. those
developed by the old International Livestock Centre
for Africa (now ILRI)
consists of two traditional wooden frame ploughs &
two winged, metal ploughshares made to throw soil in
opposite directions, scoop soil towards middle,
creating a mound which are manually formed into
beds 15 cm high x 80 cm wide separated by 40 cm
wide furrow
Beds normally made by hand so 40% of labour
requirement is conserved. Earlier planting is
possible because soil dries out easier. Longer
duration varieties or 2 short duration crops are
possible.
Ridge and furrow used as water harvesting
structures
Cultivated terraces
• Like contour ridges but on a larger scale (4 to 7
m?)
• Usually considered as terraces in the books more
like large ridges
• On mechanised farms, blade on tractor or
bulldozer can be used. Possibly oxen could be
used.
• Use graded furrows on more impermeable soils
• Plant lower sides of furrows with more drought
sensitive crops (behaves rather like water
harvesting system)
Crops grown in channel and on bank but channel slopes
to drain water into waterway
Constructed on the contour