In line with the weatherman’s predictions, the rains continue to pound various parts of the country. Besides loss of lives, the other major problem the floods are causing is soil erosion. We have seen in the media farms being wiped away. How can farmers cope with this situation to avoid soil erosion on their farms?
Now, soil erosion is the movement of soil from one place to another. This can be caused by force of high wind velocity especially in dry lands or surface runoff where there is much rainfall.
Soil erosion by rain water is regarded as most critical because of the damage caused on the affected land within a short time. Soil erosion will occur mostly on slopping land that has been cleared for cultivation.
Accelerated soil erosion will occur where land tillage is done up and down slope that creates channels for runoff water flow. The eroded soil takes away plant nutrients leaving the eroded land infertile. This drastically reduces crop yields and the land productivity will not be sustained for long. Soil erosion control is therefore essential for sustainability.
Establish soil type
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There are different methods of soil erosion control depending on local factors like rainfall amount, soil type, steepness of the land and slope length.
The first measures of soil erosion control involves good agronomic practices that include contour ploughing, surface mulching with crop residue which will protect the soil against rain drops impact and also slow down surface runoff, planting grass strips that will hold eroded soil and slow down the surface runoff.
Second, is using conservation structures where surface runoff is very high and would cause serious damage to the land. The recommended structures include terraces, cutoff drains and waterways. Terraces will protect soil from being eroded.
Terraces will also retain soil water which is critical for crop production in the drylands. Cutoff drains and waterways have to be designed and constructed for safe disposal of excess runoff during heavy rains without causing further erosion. Third, are gully erosion control structures where there has been severe erosion due to high volumes of surface runoff.
Gully erosion control
The aim of gully control structures is to reduce the velocity of surface runoff in the gully channel to control further channel erosion and enlargement of the gully, cause deposition of the eroded soil in the gully which will finally fill up and vegetation established.
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Gully control structures are referred to as check dams which can be constructed using locally available vegetation and woody material or stones. They are designed and constructed starting from the top end of the gully and working downwards to the whole length. They have to be properly spaced for effective control of runoff velocity in the gully. There are cases where gullies can be effectively controlled and be put back into production again.
Measures should be put in place to allow more rainwater infiltration into the soil profile and minimise surface runoff accumulation. Every gully has a catchment from where surface runoff accumulates and flows into defined channels which enlarge to form big gullies. Maintaining vegetation cover and applying good agronomic practices as described above will reduce the volume of surface runoff into the gully.
There are places where use of gabions is inevitable. For example gullies may cause destruction of a section of a road affecting many people or encroaching public utility like school buildings. In such cases the community can be mobilised to participate in gabion construction and this will be made easy by shared responsibility.
[The writer is the Dean, Faculty of Agriculture, JKUAT and an expert in soil and water management. [email protected]]