What are Erosion Preventive Measures?
Measures to prevent erosion may be broadly grouped as agronomic, chemical, mechanical, forestry, agrostological and other measures:
(1) Agronomic measures:
Agronomic measures include contour cultivation, tillage, mulching, crop rotation, strip cropping, trash farming, cover crops and dry farming practices. Soil erosion can be controlled by these methods when the slope is gentle i.e. less than 2 %. When these methods are used in combination, erosion can be reduced even if the slope is more than 2%.
(i) Contour cultivation : Contour cultivation includes contour ploughing, contour sowing and other intercultural operations. By ploughing and sowing across the slope, each ridge of plough furrow and each row of the crop act as an obstruction to runoff, providing more opportunity for water to enter into the soil and reduce soil loss. Contour cultivation is a very simple practice and can easily be practiced.
(ii) Tillage : Tillage is opening of soil for seed bed preparation. The tillage is distinguished into conventional tillage and conservational tillage. Conventional tillage includes ploughing twice or thrice by harrowing and planking. It leaves no residues on the soil surface. Conservation tillage is disturbing the soil to the minimum extent necessary and leaving crop residues on the soil. Conservation tillage practices which include zero tillage and minimum tillage can reduce soil loss up to 99% over conventional tillage. In most cases, conservation tillage reduces soil loss by 50% over conventional tillage.
(iii) Mulching :It refers to covering the soil with plant residues. It is effective against wind as well as water erosion. Mulches reduce soil moisture evaporation and increase amount of soil moisture by addition of organic matter to soil.
(iv) Crop rotation :It refers to alternate growing of crops. It decreases soil loss and preserves the productivity of land. The growing of same crop year after year depletes the soil minerals. Use of legumes in crop rotation maintains the fertility of the soil.
(v) Strip cropping :It is a system of crop production in which long and narrow strips of erosion resisting crops (close-growing crops) are alternated with strips of erosion permitting crops (erect-growing crops). The strips are laid across the slope. Strips of close-growing crops reduce the transporting and eroding power of water by forming obstruction to run off and filter out the soil from the runoff and retain it in the field.
(vi) Trash farming : It is a technique of soil conservation where chopped crop residues are spread and ploughed in order to produce a better tilth in the soil.
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(vii) Cover crops : Cover crops are the crops grown to cover the soil during off-season. Certain cash crops like peanuts cotton, soyabean etc. do not produce enough residue to provide adequate ground cover. Cover crops usually legumes are used to provide the needed protection against erosion and also add nitrogen to soil.
(viii) Dry farming : This practice is useful for croplands grown in low and moderate rainfall areas, where ordinary farming is at risk. Crop production, animal husbandry and growing grazing fields are the only possibilities of checking erosion. Some of them are land fallowing, strip-cropping, crop rotation etc.
(2) Chemical measures :
Breakdown of aggregate by the falling rain drops is the main cause of detachment of soil particles. Soils with stable aggregates resist break down and thus resist erosion. Aggregate stability can be increased by spraying chemicals like polyvinyl alcohol at 480 kg ha-1, the rate, however, depends on the type of soil. Soils treated with bitumin increase water stable aggregates and infiltration capacity of soil.
(3) Mechanical measures :
The mechanical measures are adopted to supplement the agronomical measures when the later alone are not adequate. These measures include Basin listing, Sub-soiling and Contour terracing.
(I) Basin listing :It is constructing of small basin along the contours to retain water which also reduces its velocity. It is especially effective on retentive soils having mild slopes.
(II) Sub-soiling:This method consists in breaking with a subsoiler the hard and impermeable subsoil to conserve more rain-water by improving the physical condition of a soil. This operation promotes greater moisture penetration into the soil, reduces both run-off and soil erosion.
(III) Contour terracing :It is constructing a channel along the slope to intercept or direct the run off water. This may be :
(a) Channel terrace : to dig channels at suitable intervals and the excavated soil deposited as a wide, low ridge along the lower edge of the channel.
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(b) Broad based ridge terrace : to construct ridge along both the sides of the channel; and
(c) Bench terrace : to construct a number of platforms along contours or suitable graded lines across the slope.
(4) Forestry measures:
Afforestation of eroded lands is best method of erosion control. The standing vegetation and dried leaves on the floor intercept the rain and reduce the impact of rain drops. Thus averting the erosion process. Moreover, the decomposition of fallen dead plant parts i.e. leaves and twigs not only increase the fertility of the soil but also improve the soil structure, which resist the soil erosion.
(5) Agrostological measures :
Grasses are helpful in control of soil erosion, hence they are used as erosion-resisting plants. Grasses are grown in strips between the crops. Agrostological measures include :
(i) Lay farming : This aim to grow grasses in rotation with field crops, which helps in building up the structure of soil and improving its fertility and
(ii) Retiring lands to grasses : It involves to grow grasses on such lands where major proportion of the top soil has been eroded. Generally grasses are allowed to grazing under suitable climate conditions.
(6) Other measures :These include:
(i) Gully control: To check the formation or widening of gullies by constructing bunds, dams, drains or diversions through which excess run off water is channelled.
(ii) Stream bank protection: To grow vegetation alongside the river bank, to construct drains, concrete or stone pitching etc. For checking the cutting and caving of river banks.
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