CONTOUR RIDGES and NARROW & BROAD CONTOUR RIDGES and NARROW & BROAD BASED TERRACESBASED TERRACES

Ridge & furrowRidge & furrow

• Slope on which possible is limited by soil type Slope on which possible is limited by soil type (strength / infiltration) & by tractor stability if (strength / infiltration) & by tractor stability if mechanisedmechanised

• Construct on grade (0.25 - 0.5%) on less Construct on grade (0.25 - 0.5%) on less permeable soil or steeper land, otherwise if permeable soil or steeper land, otherwise if medium to high infiltration soil and/or high medium to high infiltration soil and/or high ridges, construct on the contourridges, construct on the contour

• Maximum slope depends on soil type Maximum slope depends on soil type (perhaps up to 10 or 20% from calculations - (perhaps up to 10 or 20% from calculations - but in practice often limited to slopes less but in practice often limited to slopes less than 2%)than 2%)

• Larger ridges may be semi-permanent Larger ridges may be semi-permanent ("splitting" the ridge every other year or so); ("splitting" the ridge every other year or so); common technique is to place residues into common technique is to place residues into lines, then ridges constructed over them (2 lines, then ridges constructed over them (2 to 4 rows /ridge)to 4 rows /ridge)

• plant drought resistant crop on sideplant drought resistant crop on side• It is good practice to provide open field It is good practice to provide open field

drains at intervals down field as insurance drains at intervals down field as insurance against breakagesagainst breakages

• Can use plough to construct - disk plough Can use plough to construct - disk plough bestbest

• Survey "contours" every 10 to 20 m then fill Survey "contours" every 10 to 20 m then fill in between (by pacing or using tractor in between (by pacing or using tractor settings); ridges will then run more-or-less settings); ridges will then run more-or-less parallel; fill in the irregular spaces (with parallel; fill in the irregular spaces (with crop or fodder grasses or fodder legumes)crop or fodder grasses or fodder legumes)

• Breakages will occur:Breakages will occur:• if ridges are not on the "contour"if ridges are not on the "contour"• if soil not consolidatedif soil not consolidated

• Danger of breakage have led some soil Danger of breakage have led some soil conservationists to prefer not to use conservationists to prefer not to use

Tied ridgesTied ridges

• Ties recommended at 2 to 5 m spacing along Ties recommended at 2 to 5 m spacing along furrows (not as high as ridge tops) to prevent furrows (not as high as ridge tops) to prevent breakage and improve storagebreakage and improve storage

• Special cultivators are available for tractors, Special cultivators are available for tractors, e.g. Chinene & Pauwelyn (1991) e.g. Chinene & Pauwelyn (1991)

Tied ridges in Zimbabwe with crops planted in Tied ridges in Zimbabwe with crops planted in furrow: vertisol soil, 1.5 m spacing, 0.3 m high, furrow: vertisol soil, 1.5 m spacing, 0.3 m high, parallel to contour, ties at 5 to 7 m, fertiliser parallel to contour, ties at 5 to 7 m, fertiliser next to furrownext to furrow

Broad Broad bedsbeds

• Broad-bed & furrow mainly for impermeable Broad-bed & furrow mainly for impermeable soils, especially vertisolssoils, especially vertisols

Broadbed-makers sometimes used, e.g. those Broadbed-makers sometimes used, e.g. those developed by the old International Livestock developed by the old International Livestock Centre for Africa (now ILRI) Centre for Africa (now ILRI)

consists of two traditional wooden frame ploughs consists of two traditional wooden frame ploughs & two winged, metal ploughshares made to & two winged, metal ploughshares made to throw soil in opposite directions, scoop soil throw soil in opposite directions, scoop soil towards middle, creating a mound which are towards middle, creating a mound which are manually formed into beds 15 cm high x 80 cm manually formed into beds 15 cm high x 80 cm wide separated by 40 cm wide furrowwide separated by 40 cm wide furrow

Beds normally made by hand so 40% of labour Beds normally made by hand so 40% of labour requirement is conserved. Earlier planting is requirement is conserved. Earlier planting is possible because soil dries out easier. Longer possible because soil dries out easier. Longer duration varieties or 2 short duration crops are duration varieties or 2 short duration crops are possible.possible.

Ridge and furrow used as water harvesting Ridge and furrow used as water harvesting structuresstructures

Cultivated terracesCultivated terraces • Like contour ridges but on a larger scale (4 to Like contour ridges but on a larger scale (4 to

7 m?)7 m?)• Usually considered as terraces in the books Usually considered as terraces in the books

more like large ridgesmore like large ridges• On mechanised farms, blade on tractor or On mechanised farms, blade on tractor or

bulldozer can be used. Possibly oxen could be bulldozer can be used. Possibly oxen could be used.used.

• Use graded furrows on more impermeable Use graded furrows on more impermeable soilssoils

• Plant lower sides of furrows with more drought Plant lower sides of furrows with more drought sensitive crops (behaves rather like water sensitive crops (behaves rather like water harvesting system)harvesting system)

Crops grown in channel and on bank but channel Crops grown in channel and on bank but channel slopes to drain water into waterwayslopes to drain water into waterway

Constructed on the contourConstructed on the contour