CONTOUR RIDGES and NARROW & BROAD BASED TERRACES Ridge & furrow Slope on which possible is limited by soil type (strength / infiltration) & by tractor stability if mechanisedSlope on which possible is limited by soil type (strength / infiltration) & by tractor stability if mechanised Construct on grade ( %) on less permeable soil or steeper land, otherwise if medium to high infiltration soil and/or high ridges, construct on the contourConstruct on grade ( %) 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%)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)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 sideplant drought resistant crop on side It is good practice to provide open field drains at intervals down field as insurance against breakagesIt is good practice to provide open field drains at intervals down field as insurance against breakages Can use plough to construct - disk plough bestCan 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)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: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 conservationists to prefer not to useDanger 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 storageTies 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)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

Broadbeds

Broad-bed & furrow mainly for impermeable soils, especially vertisolsBroad-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?)Like contour ridges but on a larger scale (4 to 7 m?) Usually considered as terraces in the books more like large ridgesUsually 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.On mechanised farms, blade on tractor or bulldozer can be used. Possibly oxen could be used. Use graded furrows on more impermeable soilsUse graded furrows on more impermeable soils Plant lower sides of furrows with more drought sensitive crops (behaves rather like water harvesting system)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