Soil and Water Conservation

What to remember

• Soil erosion is the detachment and carrying away of soil by water or wind. Water erosion is the main type in India; it passes through splash, sheet, rill and gully stages.
• Conservation means protecting soil cover, reducing slope length and runoff, and raising infiltration. Agronomic measures suit gentle slopes; mechanical (engineering) measures suit steeper slopes.
• Water conservation covers saving rain water and using irrigation water efficiently (drip, sprinkler, mulching, scheduling), as water is the scarcest input of rainfed farming.

Soil erosion: kinds and causes

Erosion has two stages: detachment and transport. Agents are water, wind, ice and gravity. Natural (geological) erosion is slow; accelerated erosion is caused by human activity such as clearing trees, overgrazing and up-and-down ploughing.

Stages of water erosion:

Gully classes by depth: small gully up to about 3 m deep, medium 3 to 9 m, and large (deep) gullies more than 9 m (guideline values).

Wind erosion occurs in dry, bare, loose soils with little vegetation. Soil particles move by three modes: saltation (jumping, about 50 to 75 percent of movement), surface creep (rolling, about 5 to 25 percent) and suspension (fine dust carried high, about 3 to 40 percent).

Factors affecting erosion: rainfall intensity and amount, slope degree and length, soil type and structure, vegetation cover, land use and management. Soil texture influences erodibility: silt and fine sand erode easily; clay with strong aggregates and gravel resist erosion.

The Universal Soil Loss Equation (USLE)

A = R x K x LS x C x P

• A = average annual soil loss per unit area (tonnes per hectare per year).
• R = rainfall erosivity factor.
• K = soil erodibility factor.
• LS = slope length and slope steepness factor.
• C = cover and management factor (crop).
• P = support practice factor (contour, strip, terrace).

Worked example: R = 300, K = 0.2, LS = 1.5, C = 0.4, P = 0.5. A = 300 x 0.2 x 1.5 x 0.4 x 0.5 = 18 tonnes per hectare per year.

Another: if contouring halves P from 1.0 to 0.5, soil loss is halved, when other factors stay constant.

Permissible (tolerable) soil loss is the highest rate at which soil formation can balance loss; it is often taken near 5 to 12 tonnes per hectare per year depending on soil depth. Treat that range as a guideline.

Soil conservation measures

1. Agronomic (biological) measures.

• Contour farming: ploughing and sowing across the slope.
• Strip cropping: alternate strips of close-growing and erosion-permitting crops along contours.
• Cover crops and intercrops, mulching, mixed cropping, crop rotation.
• Conservation tillage and zero or minimum tillage; stubble mulching.
• Grass and legume cover, vegetative barriers (vetiver, Cenchrus, Dichanthium).
• Afforestation, agro-forestry, shelterbelts and windbreaks for wind erosion.

2. Mechanical (engineering) measures.

• Contour bunds: for slopes up to about 6 percent and in low rainfall tracts.
• Graded bunds (channel terraces): for heavier rainfall and soils of low permeability to drain excess water.
• Bench terraces: for slopes about 6 to 30 percent (guideline). Types include level, inward sloping and outward sloping bench terraces.
• Contour trenches, staggered trenches and half-moon terraces for tree planting.
• Gully control: gully plugs, check dams, drop spillways, chute spillways, diversion drains and grassed waterways.
• Land levelling and land shaping.

3. Wind erosion control.

• Windbreaks and shelterbelts at right angles to the wind direction.
• Keeping the soil under cover, rough tillage to form clods, mulches, stubble retention, and strip cropping across the wind.

Agronomic versus mechanical measures

Water conservation in agriculture

In-situ rain water conservation (rainfed farming).

• Field bunding and levelling, broad-bed and furrow system, ridges and furrows, tied ridges, compartmental bunds.
• Mulching with crop residue or polythene to reduce evaporation.
• Conservation furrows, deep summer ploughing, opening of furrows after every few rows, and weed control.
• Anti-transpirants for short periods and drought-tolerant crops.

Harvesting for supplemental use.

• Farm ponds, tanks and recharge of open wells and bore wells by channelling runoff into them.
• Protective (life-saving) irrigation at critical stages.

Efficient irrigation.

Drip irrigation saves water, reduces weeds and allows fertigation (fertilizer through the system). Pressure and filter care are essential.

Irrigation scheduling: irrigate when the soil moisture depletion reaches a set fraction of available water, or by climatological approach (IW/CPE ratio), or at critical growth stages.

Water-use formulas and worked problems

• Water application efficiency = (water stored in the root zone / water applied) x 100.
• Water requirement of crop = consumptive use + application losses + special needs.
• Depth of irrigation (cm) = (field capacity − present moisture, as a fraction) x bulk density factor x root depth. A simple form: depth = (FC − PWP) x allowed depletion x root zone depth, with FC and PWP as fractions of volume.
• Volume of water (m3) = area (m2) x depth (m). 1 ha-cm = 100 m3. 1 ha-mm = 10 m3.

Examples:

• Worked 1: Irrigate 2 ha with 6 cm depth. Volume = 2 x 6 = 12 ha-cm = 1,200 m3.
• Worked 2: If 800 m3 is applied and 600 m3 is stored in the root zone, efficiency = 600 / 800 x 100 = 75 percent.
• Worked 3: FC = 30 percent, PWP = 12 percent (both by volume), root zone depth = 60 cm, allowed depletion 50 percent. Depth = (0.30 − 0.12) x 60 x 0.5 = 5.4 cm.
• Worked 4: A drip system emitter gives 4 litres per hour for 5 hours daily to 200 plants. Daily water = 4 x 5 x 200 = 4,000 litres (assuming one emitter per plant).

Land capability and use

Land is grouped into capability classes I to VIII. Classes I to IV are suited to regular cultivation, with limits increasing from I to IV. Classes V to VII are not suited to regular cultivation and are kept under pasture, forest or other permanent cover. Class VIII is best left to wildlife, recreation or water supply. The general rule: use land according to its capability and treat it according to its needs. Steeper, shallower and more eroded land gets more permanent vegetative cover and fewer ploughed crops.

Soil and water conservation programmes

• The National Watershed Development Project for Rainfed Areas, the Integrated Watershed Management Programme and PMKSY (with a "per drop more crop" micro-irrigation component) support these works.
• Rural wage-employment works (MGNREGS, replaced from 1 July 2026 by VB-G RAM G under the 2025 Act, 125 days) provide wage work for bunds, trenches, ponds and plantations.
• The soil conservation work is guided by Soil Conservation units of the agriculture department; AP also runs state programmes for micro-irrigation (drip and sprinkler) with subsidy to farmers. Check the latest scheme names before quoting any.
• Soil Health Card scheme advises nutrient use and supports sustainable soil management.

Exam traps

• Splash is the first stage of water erosion; sheet erosion is the removal of a thin layer.
• Rill can be removed by ploughing; gully cannot.
• Saltation is the main mode of wind erosion movement (not suspension).
• LS factor covers slope length and slope steepness, not soil loss itself.
• In USLE, P is the support practice factor, C is the crop cover factor.
• Contour bunds suit gentle slopes; bench terraces suit steeper slopes.
• Graded bunds drain excess water; level contour bunds retain it.
• Drip has the highest efficiency among common irrigation methods.

One-liners

• Splash erosion starts the erosion process.
• USLE: A = R x K x LS x C x P.
• Contour farming runs across the slope.
• 1 ha-cm of water = 100 m3.
• Windbreaks are placed at right angles to the wind.
• Strip cropping uses alternate close-growing crop strips.
• Drip irrigation allows fertigation.
• Gullies cannot be removed by normal tillage.
• Mulch cuts evaporation and protects against raindrop impact.
• Vetiver is a vegetative barrier grass.
• Sheet erosion removes a uniform thin soil layer.
• Check dams and gully plugs control gullies.

Practice questions

1. The first stage of water erosion is

   1. gully erosion
   2. sheet erosion
   3. splash erosion
   4. stream bank erosion
   Answer

   C. splash erosion

   Raindrop impact detaches soil particles first.

2. Removal of a thin uniform layer of soil from the whole surface is

   1. landslide
   2. rill erosion
   3. gully erosion
   4. sheet erosion
   Answer

   D. sheet erosion

   It is hard to notice but removes fertile topsoil.

3. Small finger-like channels that ordinary tillage can remove are called

   1. bunds
   2. rills
   3. gullies
   4. terraces
   Answer

   B. rills

   Rills are shallow; gullies cannot be removed by normal tillage.

4. The main mode of soil particle movement in wind erosion is

   1. surface creep
   2. saltation
   3. solution
   4. suspension
   Answer

   B. saltation

   Jumping movement accounts for the largest share.

5. Which of the following is the main factor causing accelerated erosion?

   1. Slow weathering of rock
   2. Rise of the water table
   3. Formation of soil horizons
   4. Human activities such as deforestation and overgrazing
   Answer

   D. Human activities such as deforestation and overgrazing

   Geological erosion is slow; accelerated erosion is human-driven.

6. In USLE, the letter R stands for

   1. rooting depth
   2. residue
   3. rainfall erosivity
   4. runoff
   Answer

   C. rainfall erosivity

   R is the rainfall erosivity factor.

7. In USLE, the factor K represents

   1. crop cover
   2. slope length
   3. soil erodibility
   4. support practice
   Answer

   C. soil erodibility

   K measures how easily a soil is eroded.

8. In USLE, the factor P represents

   1. precipitation
   2. percolation
   3. plant height
   4. support practice such as contouring
   Answer

   D. support practice such as contouring

   P covers contour, strip and terrace practices.

9. The USLE gives soil loss as

   1. percent of slope
   2. tonnes per hectare per year
   3. litres per second
   4. millimetres per hour
   Answer

   B. tonnes per hectare per year

   A is average annual soil loss per unit area.

10. Using USLE with R = 200, K = 0.3, LS = 2, C = 0.5, P = 0.5, soil loss in t per ha per year is

    1. 3
    2. 60
    3. 15
    4. 30
    Answer

    D. 30

    200 x 0.3 x 2 x 0.5 x 0.5 = 30.

11. With R = 400, K = 0.25, LS = 1, C = 0.2, P = 1, soil loss is

    1. 20 t per ha per year
    2. 2 t per ha per year
    3. 40 t per ha per year
    4. 80 t per ha per year
    Answer

    A. 20 t per ha per year

    400 x 0.25 x 1 x 0.2 x 1 = 20.

12. If contouring changes P from 1.0 to 0.6 and all other factors stay equal, soil loss becomes

    1. 40 percent of the earlier loss
    2. the same
    3. 60 percent of the earlier loss
    4. 160 percent of the earlier loss
    Answer

    C. 60 percent of the earlier loss

    Loss is proportional to P.

13. Contour farming means

    1. ploughing up and down the slope
    2. ploughing and sowing across the slope
    3. leaving land fallow on slopes
    4. burning the stubble
    Answer

    B. ploughing and sowing across the slope

    It reduces runoff velocity.

14. Strip cropping is

    1. growing one crop in a very large block
    2. growing different crops in alternate strips along the contour
    3. cutting crops into strips for fodder
    4. planting trees in a straight row only
    Answer

    B. growing different crops in alternate strips along the contour

    Close-growing strips check runoff from erosion-permitting strips.

15. Contour bunds are most suitable for

    1. very steep hills
    2. flooded rice lands only
    3. gentle slopes in low rainfall areas
    4. salt marshes
    Answer

    C. gentle slopes in low rainfall areas

    They hold water along the contour.

16. Graded bunds (channel terraces) are designed mainly to

    1. drain excess water safely to a waterway
    2. hold all water in the field
    3. trap wind-blown dust
    4. raise the water table only
    Answer

    A. drain excess water safely to a waterway

    They are used in heavier rain and slowly permeable soils.

17. Bench terraces are used on

    1. flat land
    2. steeper arable slopes
    3. desert dunes only
    4. river beds
    Answer

    B. steeper arable slopes

    Terraces convert slope into level steps.

18. Windbreaks and shelterbelts should be planted

    1. parallel to the wind
    2. only along the road
    3. without regard to wind
    4. at right angles to the prevailing wind
    Answer

    D. at right angles to the prevailing wind

    That position gives maximum protection.

19. Which is a vegetative barrier grass?

    1. Vetiver
    2. Groundnut
    3. Cotton
    4. Paddy
    Answer

    A. Vetiver

    Vetiver forms dense, deep-rooted hedges.

20. Mulching helps conserve water mainly by

    1. raising soil temperature
    2. removing weeds from the root zone
    3. increasing wind speed
    4. reducing evaporation and runoff
    Answer

    D. reducing evaporation and runoff

    Cover protects soil from sun and raindrops.

21. A tied ridge system is used to

    1. spread fertilizer
    2. store grain
    3. hold rain water in furrows in rainfed fields
    4. drain water from fields
    Answer

    C. hold rain water in furrows in rainfed fields

    Cross-ties in furrows trap rain water.

22. Which irrigation method generally has the highest application efficiency?

    1. Drip
    2. Border strip
    3. Furrow
    4. Surface flood
    Answer

    A. Drip

    Drip applies water near roots with little loss.

23. Fertigation means

    1. applying lime by hand
    2. growing crops without soil
    3. draining salts
    4. applying fertilizer through the irrigation water
    Answer

    D. applying fertilizer through the irrigation water

    It is commonly done with drip systems.

24. Which irrigation method suits undulating land and avoids land levelling?

    1. Flood
    2. Sprinkler
    3. Basin
    4. Border
    Answer

    B. Sprinkler

    Sprinklers can irrigate uneven fields.

25. The volume of water for 3 ha at a depth of 5 cm is

    1. 300 m3
    2. 150 m3
    3. 1,500 m3
    4. 15,000 m3
    Answer

    C. 1,500 m3

    3 x 5 = 15 ha-cm and 1 ha-cm = 100 m3.

26. 1 ha-cm of water equals

    1. 10 m3
    2. 1 m3
    3. 100 m3
    4. 1,000 m3
    Answer

    C. 100 m3

    10,000 m2 x 0.01 m = 100 m3.

27. If 500 m3 of water is applied and 400 m3 is stored in the root zone, application efficiency is

    1. 20 percent
    2. 80 percent
    3. 40 percent
    4. 125 percent
    Answer

    B. 80 percent

    400 / 500 x 100 = 80.

28. Field capacity is 28 percent, wilting point 10 percent (both by volume), root depth 50 cm and allowed depletion 50 percent. The irrigation depth is

    1. 2.25 cm
    2. 18 cm
    3. 9 cm
    4. 4.5 cm
    Answer

    D. 4.5 cm

    (0.28 - 0.10) x 50 x 0.5 = 4.5 cm.

29. A drip emitter gives 2 litres per hour. For 5 emitters running for 4 hours the water used is

    1. 40 litres
    2. 80 litres
    3. 10 litres
    4. 20 litres
    Answer

    A. 40 litres

    2 x 5 x 4 = 40.

30. A farm pond holds 120 m3. This is how many litres?

    1. 1,200,000
    2. 12,000
    3. 1,200
    4. 120,000
    Answer

    D. 120,000

    1 m3 = 1,000 litres.

31. Total water to be given to 0.5 ha at 8 cm depth is

    1. 4,000 m3
    2. 400 m3
    3. 40 m3
    4. 80 m3
    Answer

    B. 400 m3

    0.5 x 8 = 4 ha-cm = 400 m3.

32. Consider the statements. 1. Splash erosion is the first stage of water erosion. 2. Gully erosion can be removed by ordinary ploughing. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Gullies are too deep for ordinary tillage.

33. Consider the statements. 1. Contour bunds retain water on gentle slopes. 2. Graded bunds are meant to drain extra water. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

34. Consider the statements. 1. Saltation is jumping movement of soil grains in wind. 2. Suspension is the main mode of movement of coarse sand. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Suspension carries fine dust, not coarse sand.

35. Consider the statements. 1. Agronomic measures are costlier than mechanical measures. 2. Mulching is an agronomic measure. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Agronomic measures are low cost.

36. Consider the statements. 1. In USLE, C is the cover and management factor. 2. In USLE, LS accounts for slope length and steepness. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both match the standard definitions.

37. Consider the statements. 1. Drip irrigation allows fertigation. 2. Surface flood irrigation is more efficient than drip. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Drip is far more efficient than flood.

38. Consider the statements. 1. Windbreaks reduce wind speed. 2. Windbreaks are planted parallel to the wind. Which is/are correct?

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    They are planted across the wind direction.

39. Match the pair: Bench terrace

    1. a pond lining
    2. a drip emitter
    3. a wind-protecting tree row
    4. level steps cut on a steep slope
    Answer

    D. level steps cut on a steep slope

    It shortens slope length and holds water.

40. Which practice is NOT good for soil conservation on a slope?

    1. Contour cultivation
    2. Mulching
    3. Ploughing up and down the slope
    4. Strip cropping
    Answer

    C. Ploughing up and down the slope

    Up-and-down ploughing creates channels for runoff.

41. Soil erosion removes mostly the

    1. parent rock
    2. bedrock
    3. deep subsoil only
    4. fertile topsoil
    Answer

    D. fertile topsoil

    Nutrient-rich topsoil is lost first.

42. Which soil particles are most easily eroded?

    1. Well-aggregated clay
    2. Silt and fine sand
    3. Coarse gravel
    4. Stones
    Answer

    B. Silt and fine sand

    They are light and weakly bound.

43. Which is an in-situ moisture conservation practice in rainfed farming?

    1. Building a canal
    2. Laying a pipeline
    3. Broad-bed and furrow system
    4. Installing a pump house
    Answer

    C. Broad-bed and furrow system

    Rain water is retained where it falls.

44. Which scheme has a 'per drop more crop' micro-irrigation component?

    1. PMAY
    2. PMKSY
    3. PM-KISAN
    4. PMFBY
    Answer

    B. PMKSY

    Pradhan Mantri Krishi Sinchayee Yojana promotes micro-irrigation.

45. The Soil Health Card scheme gives farmers

    1. crop insurance
    2. free seeds
    3. cheap loans
    4. soil test based nutrient advice
    Answer

    D. soil test based nutrient advice

    It supports balanced fertilizer use.