A permanent vegetative cover is the best protection for soil. The moment vegetation is destroy the condition becomes favorable for soil erosion. Studies at Phewa Tal watershed has indicated that bare ground allows four times more soil erosion compared to permanent plant covered ground. In this method we try to plant such species, which are capable of holding soil strongly and can survive in very adverse soil condition. Beside this the farming system should also be considered. Improper cultivation leads to severe soil erosion. So land use system should be properly implemented. The main principle of biological control is to prevent high speed of water and conserve water within the soil. In biological control following method can be adopted.

  1. Mulching: mulching is the covering of the soil with crop residues such as straw, maize, stalks etc. these cover protects the soil from the rain drop impact and reduces the velocity of run off and wind. It is also useful as an alternative to cover crop in dry areas where a cover crop should complete for moisture with the main crop.
  2. Cover crop: they are grown as a conservation measure either during off-season or as ground protection under trees. They are grown as winter annuals and, after harvest, are ploughed to form a green manure.
  3. Multiple cropping: the aim of multiple cropping is to increase the production from the land whilst providing protection of the soil against erosion. It includes:
    1. Rotation: growing different crops consequently in rotation reduces erosion as high rate of soil loss under row crop is counteracted by low rates under other crops.
    2. Strip cropping: row crops and protection effective crops (legumes and grasses) are grown in alternate strips aligned on the contour or perpendicular to the wind. It is suitable for the slope of 30o.
  4. High density cropping: it is used to try to obtain the same effects for a monoculture that multiple cropping achieves for two or more crops.
  5. Agro forestry: Trees can be incorporated within a farming system by planting them on terraces, contour bounds and as ornamental around the homestead. This reduces soil erosion and provides additional needs to the farmers.
  6. Shifting cultivation: an areas forest is cleared by slash and burn, and cultivated with crops for a second year before being allowed to revert to scrub and secondary forest. This practice will maintain soil fertility and reduce soil erosion as long as the low ratio population to land areas is maintained.
  7. Rotational grazing: for controlling erosion on grasslands, rotational grazing is practiced.i.e. The stock is moved from one pasture to other, to give time for the grass to recover.
  8. Proper forest management: though erosion under forest cover is less, sever erosion may result when the hill forest area is subjected to clear felling, selection or shelter wood system should be adopted.
  9. Reforestation / afforestation: vegetations play the major role in erosion control on gullies areas and landslides. So forestation programs should be prioritized.
  10. Soil management: it maintains and improves fertility and structure of soils. High fertile soil results in high crop yield, good plant cover and therefore in conditions, which minimize the affect of erosive agent nevertheless extensive soil, management is not viable for land use other than agriculture. It includes;
    1. Increasing organic matter content: organic matter improves the cohesiveness, water retention capacity and structure of soil. Green manure, straw etc should be added as organic substance in agriculture lands, though tree litters maintain adequate organic content in forest soil.
    2. Using soil stabilizers:Â it consists of organic by products, synthetic polymers and polyvalent salts. The former two bind the soil particles into aggregates and latter bring about flocculation of the clay particles. However soil stabilizers are expensive for general forestry use.
  11. Continued covering: - Once the land is naked there is high possibility of soil erosion. Hence the land should be kept covered all round the year.
  12. Inter cropping: - In this method, the spaces among the tree species are covered with agriculture crops, which help in soil and water conservation.
  13. Mixed cropping: - In this system two or more than two crops are raised in the same land and in the same time. The benefit is that due to different kind of roots, soil is protected more perfectly.
  14. Wind breaks: - Windbreaks are usually used in plain areas where the wind moves rapidly and forcely which detaches soil particles causing soil erosion. In this method tree species of streng trunk, deep rooted and large crown are preferred which are raised around the agricultural land
  15. Rotational cropping: - Raising only one species every year may turn the soil infertile and may lead to erosion. So rotational cropping is necessary. In this system one crop is followed by next crop usually legume which makes the soil fertile.
  16. Terracing: - In hilly areas, the farming should be done only when the land is terraced properly because without terracing the run-off is increased and soil is easily eroded.

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