• Measures to prevent erosion grouped as agronomic, mechanical, forestry and agrostological measures.
• When these are used in combination, erosion can be reduced even if the slope is more than 2 per cent.
• Soil erosion can be controlled by agronomic methods when the slope is gentle i.e., less than 2 %.
• Agronomic measures include contour cultivation, tillage, mulching, strip cropping and other improved dryland practices.
• Guatemala grass (Tripsacum laxum) can be used for mulching.
• Strip-cropping 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).
• Erosion resistant crops are groundnut, mothbean, horsegram (pulses).
• Erosion permitting crops are sorghum, maize and millet.
• Aggregate stability can be increased by spraying chemicals like polyvinyl alcohol at 480 kg/ha.
• Soils treated with bitumen increase water stable aggregates and infiltration capacity of the soil.
• Dead furrows (with closed ends) formed at 3.6 m interval after emergence of the crop sown across slope, reduce the length of the run of rain water, hold water and increase opportune time for infiltration.
• Mechanical measures to control soil erosion include contour bunding, graded bunding, bench terracing, gully control etc.
• Contour bunding = upto 6%
slope Graded bunds = 6 – 10%
slope Graded trenches = 10 – 16%
slope Bench terracing = 16 – 33% slope
• VI = S/2+3
S = percent slope
VI = vertical interval between bunds
• Height of contour bund depends on the spacing between bunds, soil conditions and maximum intensity of rainfall.
• D = FR/6
D = Depth of water to be impounded in feet Or Theoretical height of the bund to be put up
R = Total runoff in inches
F = vertical fall between bunds in feet
• Contour bunds are usually laid in areas with less than 1500 mm rainfall and up to 6 per cent slope of land.
• Graded bunding is recommended in situations where the rain water is not readily absorbed due to high rainfall or low intake of the soil.
• In graded bunds soil from the excavation of the channel is formed into a bund on the downstream to guide the water into a grassed waterway.
• In deep black soils with high clay content develop deep cracks in summer and bunds in these soils breach extensively during rainy season, especially where rains are of high intensity.
• In deep black soils broad based terraces are constructed.
• A terrace is a combination of ridge and channel built across the slope on a controlled grade.
• In broad base terrace excess rain water is led at non-erosive velocity into grassed water ways.
• On steeply sloping and undulated land, intensive farming is possible only with bench terracing.
• Bench terracing consists of principally transforming relatively steep land into a series of level strips or platforms across the slope of the land.
• Bench terracing reduces the slope length and consequently erosion.
Type of terraces for different soil and rainfall conditions
Type : Suitability
Level and table top: Area receiving medium rainfall (750 mm) of even distribution with highly permeable deep soils
Sloping outwards: Low rainfall (< 750 mm) area with permeable soil of medium depth
Sloping inwards: Heavy rainfall areas (> 750mm) with soil of poor infiltration rate
• Zing terracing is adopted in lands with 3 – 10% slope.
• Zing terraces are constructed in medium to deep soils in moderate to high rainfall areas.
• In zing terracing length of the field is divided into donor area and receiving area in the ratio of 2:1 to 5:1, but usually 2:1.
• Vegetative barrier = Khus khus grass (Vetivaria zeylanica).
• Check dams are constructed across gullies to reduce the velocity of runoff, heal the gully, store water for use by livestock and recharge groundwater in wells lower down.
• Grasses are used for stabilizing the surfaces of waterways, contour bunds and front faces of bench-terraces.
• Cenchrus ciliaris + Clitoria ternate is the best mixture for eroded soils of UP.
• Cenchrus ciliaris + Stylosanthes hamata combination is the best for Andhra Pradesh
. • Growing a mixture of grasses instead of any single grass proved to be better to stabilize newly formed bunds or terraces.
• Wind erosion is a natural phenomenon in arid and semi-arid zones.
• Minimum wind velocity necessary for initiating the movement of most erodible soil particles is about 16 km hr-1 at a height of 30.5 cm.
• Movement of soil particles through wind erosion takes place in three stages i.e., saltation, surface creep and suspension.
• Saltation is the first stage of movement of soil particles in series of jumps.
• Soil particles moved by saltation are between 0.1 to 0.5 mm in diameter (fine sand).
• In saltation soil particles jump up vertically into air and rise to a height of 30 to 60 cm.
• 50 to 75% of the weight of soil lost by wind erosion is carried in saltation.
• Rolling of coarse grains, larger than 0.5 to 3 mm in diameter and too heavy to be lifted, by wind along the surface of the ground is called surface creep.
• 5 to 25 % weight of the soil lost by wind erosion is carried in surface creep.
• Floating of fine dust particles smaller than 0.1 mm diameter through the air is known as suspension.
• 3 to 4 % of the weight of soil lost by wind erosion is carried in suspension.
• Equation to predict soil loss due to wind erosion
E = I.R.K.F.C.W.D.B
E = soil loss by wind erosion
I = Soil cloddiness factor
R = Surface cover factor
K = Surface roughness factor
C = local wind factor
W = Field width factor
D = Wind direction factor
B = Wind barrier factor
• Trees selected for agroforestry should have quick growth and less crown.
• Casuarina, cashew and coconut are useful for coastal sands and date palms are suitable for deserts.
• Among the pasture grasses Cenchrus ciliaris is drought resistant and persistent grass.
• Among the fodder trees, subabul is best suited because of its fast growth, adaptability and multiplicity of uses.
• For establishment of pastures in wastelands, it is better to grow leguminous plants initially.
• During subsequent years i.e., after improvement of soil fertility, grasses can be included to increase fodder production.