Contours are lines of the same height on ground and represented on a map. Contour farming includes all the various farm operations that are done along the contour lines including ploughing, tilling, planting and any other farm activities.
In areas that are hilly and have undulating terrains, run-off can be high from the upstream downwards. Contour tilling or ploughing creates furrows across the hills and slopes.Other structures done along the contour lines include stone and grass bunds.
Contour bunds called fanya juu and fanya chini have been practiced in the Eastern Africa region hence bearing the Kiswahili names. Fanya juus are canals dug along contours with 0.5m to 0.6m width and 0.45 to 1m depth. They are constructed either at the lowest or in the mid part of the field byscooping the soil and placing it on the upper side of the trench to form the bund.
The bund is then stabilised by compacting or planting grass preferably Paspalum or similar species along the bund embankment. A tie bund (undisturbed soil) of width 0.45m to 0.6m placed about every 10m apart is usually left apart to trap more water and enhance uniform water infiltration into the soil.
Fanya chini are constructed at the top most boundary of the field. They are of the same size with fanya juus. They involve scooping the soil from the dug trench and placing it on the lower part of the trench forming a bund. Tie bunds are also constructed just like the case with fanya juus.
Benefits of contour farming
1.Contour farming traps run-off from the upstream to downstream, hence minimising damages.
2.It increases soil water infiltration since the retention times are increased.
3.Contour ploughing creates furrows across the field slope eventually reducing soil erosion.
4.Contour ploughing also increases moisture conservation in the soil which is vital for sustained plant growth in the dry season.
5.Contour ploughing reduces occurrence of eutrophication downstream since it reduces downstream transfer of eroded agricultural chemicals to the water bodies downstream.
6.The loss of farm soil fertility is greatly minimised since water loss is reduced.
7.Land conflicts arising from uncontrollable washing away of top soil and resizing agricultural fields among neighbouring gardens are avoided.
8.Contour farming brings into productive use land with marginal, sloping and hilly lands where the soil productivity would otherwise be very poor.
9.Where live grass bunds are used in contour tillage operations, there is increased livestock productivity through better fodder availability.
10.Sedimentation and silting of the water bodies downstream reduces. Hence reduced flooding of the banks and surrounding areas near the water bodieswhile enhancing water quality and aquatic life.
11.Contour farming is done at a low-cost. It is simple to implement and uses locally available materials.
12.Environmental degradation is greatly reduced since vegetation cover and fauna are maintained.
For maximum and desirable output from contour cultivation, the following could be considered:
Contour plough may not be favourable for very steep slopes which require bigger water collection ditches across the field to collect and reduce the excess run-off. Also the contours may be closely spaced for steep slopes; 10m for 20 to 30 percent slope, 20m for 12 to 20 percent slope and 30m for gently sloping lands with less than 12 percent.
For soils that are water saturated at particular times of the year, especially during the rainy seasons, contour ploughing, planting and other operations may not withstand the high volumes of water since the soil water retention capacity is easily exceeded.
To further strengthen the operations of the contour ploughing operations, row cropping should be practiced as they are known to also reduce run-off and increase infiltration.
Long slopes should be avoided since they are great catalyst for run-off speed build-up. These should have periodic slope breaks or drops so as to regain gently sloping fields.
Erodible soils that are easily eroded require amalgamation of other soil and water conservation measures including fertiliser application, organic manure addition and mulching among others.
The writer is a practicing agricultural engineer.