Soil Conservation Point Wise Notes for Competitive exam

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• Agents causing erosion are wind and water.

Sheet erosion is uniform removal of top soil in thin layer from the field.

• Sheet erosion is least conspicuous and is the first stage of erosion.

• In rill erosion due to runoff, channelisation begins and erosion is no longer uniform.

• In rill erosion incisions are formed on the ground and erosion is more apparent than sheet erosion.

• Rill erosion is the second stage of erosion.

Gullies are formed when channelised runoff from vast sloping land is sufficient in volume and velocity to cut deep and wide channels.

• Gullies are the most spectacular symptoms of erosion.

Gullies if unchecked cultivation becomes difficult.

• Ravines are the manifestation of a prolonged process of gully erosion.

Ravines are typically found in the large expanses of deep alluvial soils.

• Ravines are deep and wide gullies and their formation indicates very advanced stage of gully erosion.

• Sliding down of large chunk of soil due to steep slopes is called land slides.

Landslides occur in mountain slopes when the slope exceeds 20 percent and width 6m.

• Along with runoff, soil is carried away as fine particles of less than 0.5 mm in diameter are suspended in water.

• Rill erosion starts only when the amount of runoff exceeds 0.3 to 0.7 mm/s.

• Majority of rain drops are between 1 and 4 mm in diameter though the size may vary from tiny droplets to a maximum diameter of 7 mm.

• The rainfall intensity of more than 5 cm/hr is considered as severe.

Erosivity is the capacity of agents causing erosion.

Erodibility is the susceptibility of soil to erosion.

• Universal soil loss equation was developed by Wischmeir and Smith.

• Soil loss equation due to water erosion

A = RKLSCP

A = predicted soil loss (t/ac/year)

R = Rainfall and runoff factor

K = soil erodibility

L = Slope length

S = Slope gradient or steepness

C = Soil cover and management

P = erosion control practice

Soil erodibility factor (K) gives an indication of the soil loss from a unit plot of 22 m long with a 9 percent slope under continuous fallow.

• K value varies from 0 to 0.6.

• K value is low for soils into which water readily infiltrates.

• Soils with intermediate infiltration capacity and moderate soil structural ability have a K factor of 0.2 to 0.3.

• More easily eroded soils with low infiltration capacities have a K value of 0.3 or higher.

Topographic factor (L.S) reflects influence of length and steepness of slope.

• Topographic factor is the ratio of soil loss from the field in question to that of a unit plot with 9% slope, 22 m long and continuously followed.

• Soil cover and management factor (C) indicates influence of cropping systems and management on soil loss.

Forests and grass are the best natural soil protective agencies known and are about equal in their effectiveness.

Forage crops, both legumes and grasses are next in effectiveness because of their relatively dense cover.

• C is the ratio of soil loss under the conditions found in the field in question to that which would occur under clean tilled continuous fallow conditions.

C =1 for bare soil before crop canopy develops

C < 0.1 when large amounts of crop residues are on the land or in areas of dense forests

Support Practice factor (P) reflects the benefits of contouring, strip cropping and other supporting factors.

• Support practice factor (P) is the ratio of soil loss with a given support practice to the corresponding loss when crop culture is along the slope.

• Annual soil loss in India is 16.35 t/ha.

• Permissible limit of soil loss is 11 t/ha.

29% of the total eroded soil is lost permanently to the sea and 10% is deposited in reservoirs.

• About 175 mha constituting 53.3% of India’s geographical area of 328 mha is subject to some kind of degradation.

• Active soil erosion by water and wind is prevalent over 140 mha resulting in the loss of 6000 mt of fertile soil containing 5.53 mt of NPK.

• Based on the capability or limitations, the lands are grouped into eight classes by the U.S. SOIL CONSERVATION SERVICE.

First four classes are used for agriculture or cultivation of crops.

• Classes from five to eight are not capable of supporting cultivation of crops.

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