Problematic soil management in soil science
- 1. Lecture 7 Eroded soil – Genesis, types and characteristics: water erosion- sheet, rill, gully, ravines; wind erosion- Aeolian, loess, saltation, suspension and soil creep; USLE and erosion control measures SAC 202 Problematic Soils and their Management (2+0)
- 2. Eroded soil – Genesis Soil erosion is defined as the detachment of soil particles, their transportation from one place to another and deposition elsewhere through water, wind, coastal waves, snow, gravity and other forces. Soil erosion involves three steps, viz. I. Detachment of soil particles from the main soil body, II. Their transportation by splashing, floating, rolling, dragging, and III. Their deposition at another place. The major factors which encourage detachment of soil particles are; Rainfall impact, vegetation destruction, freezing and thawing, flowing water, and wind velocity .
- 3. Erosion Natural or Geological Erosion Accelerated Erosion Wind Erosion Water Erosion Raindrop splash Rill Sheet Gully Stream channel Saltation Surface creep Suspension
- 4. Eroded soil – types Geological erosion It refers to natural or normal erosion. It represents the erosion when the land is in natural equilibrium under the cover of vegetation. Geological erosion takes place as a result of the action of water, wind, gravity, and glaciers and its rate is so slow that the loss of soil is compensated by the formation of new soil under natural weathering processes. Geological erosion may be considered a part of the natural soil forming processes which results in the existing form and distribution of soils. This kind of erosion does not pose any problem.
- 5. Accelerated soil erosion When soil erosion exceeds the normal rate and becomes unusually destructive and unproductive ,it is called accelerated erosion. When man or animal interferes with the existing balance in nature, by way of removal of vegetative cover, indiscriminate cutting of trees, over grazing, faulty agricultural practices, etc. There is deterioration and loss of soil. This signifies accelerated erosion. Accelerated soil erosion has been a major process in degradation of land resources and has destroyed about 430 million hectares (Mha) of area in different countries or about 30% of the cultivated land of the world or 50% of the geographical area of India. This erosion often results in vast deposits from sedimentary rocks.
- 6. Eroded soil – characteristics
- 7. Water erosion- sheet, rill, gully, ravines Water erosion It is the removal of soil from land surface by water, including runoff from melted snow and ice and is one of the major causes of soil degradation . Water erosion has been sub-divided into various types in relation to progressive concentration of surface runoff . Different types of water erosion are described below:
- 8. Splash erosion A falling rain drop is capable of generating a force equals to almost 14-times of its weight. A rain drop produces three important effects during splash erosion: a. Its beating action breaks down the soil aggregates, b. It detaches soil particles and, c. Its splash after touching the ground causes displacement of soil. Under low intensity and low rainfall conditions , if the dispersed material is not removed by the runoff , it forms a hard crust after drying. Under such condition , germination of seeds is hampered and sometimes, if this condition develops just after sowing, the crop stand remains poor due to very low germination. The rain drops beat the soil with force and splash may take away soil even up to 2 meters
- 9. Sheet erosion The erosion in which soil matrix is lost but remains undetected for a long period and a thin layer of soil is removed from large areas uniformly during every rain, even producing a runoff, is called sheet erosion. The eroding and transporting power of sheet flow is a function of the depth and velocity of runoff for a given size, shape and quantity of soil particles or aggregates. Sheet erosion can result from: a. Surface creeping of the soil in uniform layers and its deposition at another place or washing away along with runoff in the drainage system, b. Saltation, which results when water causes soil particles to hop or slip during their downward movement, and c. Suspension of the soil particles in runoff as they do not touch the soil surface.
- 10. Severe sheet erosion in Sangadevarkoppa series, SIP Area, Kalaghatgi, Dharwad
- 11. Sheet erosion continuously makes the soil shallower with a progressive decline in crop yields. It is generally neglected , although the soil deteriorates slowly and imperceptibly. Its existence however , can be detected by the muddy colour of the runoff arising from the fields/areas. The most serious sheet erosion occurs in red and black soils, occupying 69 Mha and 67 Mha of land , respectively in the country.
- 12. Severe sheet erosion in Illuppakudi series, S.No.186, Kayankulam village
- 13. Sheet Erosion -water Rill Erosion -water Gully Erosion -water Sheet Erosion -water
- 14. Rill erosion It is the removal of soil by water to form small channels which develop due to concentration of surface flow along the slope. It generally develops on bare and unprotected land where soil conservation measures are not adopted. In advanced stage , it may take the shape of gullies. The rill erosion is an intermediary stage between sheet erosion and gully erosion. The rill can be removed by normal tillage operations. Generally , these rills vanish after cultivation , but may reappear with ensuing rains.
- 15. Gully erosion It is the advanced stage of rill erosion which cannot be removed by normal tillage operations. Rills with more than 30 cm depth are generally called gullies. Gullies obstruct the operation of farm machinery and tends to deepen and widen with every heavy rainfall. They cutup large fields into small fragments and in course of time make them unfit for cultivation. The rate of gully erosion depends on several factors, viz. Runoff producing characteristics , channel alignment, slope and vegetative cover on the ground, etc. Gully erosion indicates misuse, neglect and mismanagement of land over a long period of time.
- 16. Severe sheet and rill erosion in black soil areas- Bijapur dist.
- 17. Rill and gully formation in black soils
- 18. Result of Gully erosion in black soils.
- 19. Gully erosion in red soils Rajangunte, Bengaluru
- 20. Sheet Rill Rill - Gully Gully Mass EROSION BY WATER
- 21. Estimation of soil and water erosion Universal soil loss equation (USLE) has been designed to predict soil loss from agricultural lands under various agro-climatic and topographical situations. The essence of the USLE is to isolate each variable and reduce its effect to a number so that when the numbers are multiplied together, the answer is the amount of soil loss
- 22. The universal soil equation is presented by expression A = R x K x L x S x C x P A = Computed soil loss per unit area, R = Rainfall factor, is the number of erosion-index units in a normal year’s rain. The erosion index is a measure of the erosive force of specific rainfall. K =Soil-erodibility factor, is the erosion rate per unit of erosion index for a specific soil in cultivated continuous fallow , on a 9% slope , 22m long. L= Slope-length factor is the ratio of soil loss from the field slope length to that from a 22-m length on the same soil type and gradient, S = Slope-gradient factor, is the ratio of soil loss from the field gradient to that from a 9% slope, C =Cropping management factor, is the ratio of soil loss from a field with specified cropping and management to that fallow condition on which the factor K is evaluated, P =Erosion-control practice factor, is the ratio of soil loss with contouring, strip cropping or terracing to that with straight-row farming, up and down slope.
- 23. wind erosion- Aeolian, loess, saltation, suspension and soil creep Wind erosion The south-western desertic zone of India covers about 28.6 Mha of area (about 8.7% of the geographical area of the country). The annual rainfall in the area ranges from 100 to 500mm against the annual potential evapotranspiration of 1600 to 2000 mm. Wind erosion is mainly due to a strong wind regime, low atmospheric humidity, high solar radiation and single grain structure of sandy soil. About 14% and 28% of the area of the arid zone of Rajasthan suffers from severe and moderately sever form of wind erosion, respectively. It occurs in arid and semi-arid areas which are devoid of vegetation , and where wind velocity is high. The single-grained sandy soil particles on the land surface are lifted and blown off as dust- storms. When the velocity of dust-bearing wind retards, the coarser soil particles are deposited in the form of dunes, sometimes rendering fertile lands unfit for cultivation. The finer particles are carried away to farther distances. The fertile soil is blown away by winds and the sub soil is considerably reduced.
- 24. Suspension The movement of very fine soil particles of less than 0.1mm in diameter into the air remaining suspended there is called suspension. The particles are kicked up into the air by the action of particles in saltation. The movement of fine dust in suspension is completely governed by the characteristics movement of the wind. The suspended material is carried to long distances from its original location and thus there is a considerable loss to the eroded area, accounting for about 40% of soil movement. Aeolian Sand dunes and depositions from the materials transported by wind are called ‘Aeolian deposits’ Loess These wind-blown materials, comprised primarily silt or silt with some fine sand and clay are called ‘loess’.
- 26. Saltation The movement of soil by wind in a series of short bounces along the surface of land carrying fine particles of 0.1 to 0.5 mm diameter is called saltation. It is caused by the direct pressure of wind on soil particles and their collisions with other particles. After being pushed along the ground surface by the wind, the particles leap almost vertically in the first stage of saltation. Some grains rise only to small heights and, others leap upto 30cm or even higher, depending directly on the wind velocity and the rise from the ground. In this process the particles drop down within the eroded area or its immediate vicinity. Depending on the nature of the soil, Wind speed and vegetative cover, saltation accounts for 50 to 75% of the total soil movement through wind erosion.
- 27. Surface creep The soil particles varying between 0.5 mm and 1.0 mm in diameter, are too heavy and move along the surface resulting in the formation of surface creep. The movement through surface creep is the kinetic energy derived from the impact of particles moved in saltation. The particles raised from the ground move by rolling and sliding along the surface of soil drop down within the eroded area of its immediate vicinity. It accounts for about 5% to 25%of soil erosion through wind.
- 28. Factors affecting wind erosion The major factors affecting wind erosion are: Climate, Soil and Vegetation. The climatic parameters influencing wind erosion are: rainfall, temperature, wind, humidity, viscosity and intensity of the air. The amount and distribution of rainfall and its effect on soil moisture regime are the most important factors. The principal characteristics of wind affecting erosion are : velocity, direction, duration, and turbulence. Soil characteristics affecting wind erosion are: texture, structure, density of soil particles organic matter, and surface roughness. The vegetative factors that affect wind erosion are :kind of vegetation, height, density, etc. Living plant roots and tops are more effective in retarding wind erosion.
- 29. Control of wind erosion The basic principles in the control of wind erosion are breaking of wind velocity at the soil-atmosphere interface and the reduction in soil erodibility. This can be achieved through vegetation or cultural practices. Wind erosion control measures include: I. Creation of permanent grass strips across the prevailing wind direction, II. Roughening of the soil surface to trap some of the moving particles, III. Provision of stubble mulch, IV. Tillage to provide cloddy surface condition which is at right angles to the wind direction, V. Strip cropping which can prove useful in reducing the effect of wind , and VI. Wind-breaks with tree linings which are effective in reducing wind velocity for short distances.
- 30. Estimation of wind erosion Wind erosion can be estimated by using equation given by Chepil and Woodruff (1963), which predicts the relationship between annual soil loss by wind erosion from a given field and the five factors influencing wind erosion: E = f ( I x K x C x L x V ) Where, E = Average annual soil loss in tones/acre, I = Soil erodibility index indicated by soil aggregates greater than 0.84 mm in diameter and percentage of land slope, C = Climatic factor indicated by wind velocity and surface soil moisture, L = Unsheltered field width measured along the direction of the prevailing wind, and V = vegetative cover. Equation is useful in determining I. Potential wind erosion on any field under existing conditions, and II. Conditions or surface roughness, soil cloddiness, vegetative cover, sheltering or width and orientation of field necessary to reduce wind erosion to tolerable level.
- 31. Soil conservation measures The following soil conservation measures may be adopted for controlling soil erosion, depending on the degree and length of the slope and physical configuration of the land Mechanical measures I. Contour bunds II. Graded bunds III. Bench terraces IV. Half moon terraces V. Grassed waterways VI. Water harvesting ponds VII. Conservation bench terraces VIII.Gully control structures IX. Contour trenches X. Stream bank and torrents control Agronomical measures I. Cropping system II. Crop geometry III. Contour cultivation IV. Tillage V. Grasses
- 32. Agronomical-cum-mechanical measures Depending upon the needs of land and intensity of erosion, bio-engineering measures are sometimes preferred as compared to either mechanical or agronomical measures in isolation. In black soils with 45-50% clay, both agronomical and mechanical measures have been found to reduce runoff and soil losses. This conserve soil moisture and thereby increase crop yield. The treatment of vertical mulch and surface mulch has been found to be most effective in controlling runoff and soil losses, and consequently, could produce maximum sorghum grain yield. Under mechanical measures, the graded bunding has been found to be superior to conservation ditch and contour bunds.
- 33. Contour Bunding vs Graded Bunding • Contour Bunding entails constructing earthen dams across the slope of the land, as closely as possible following the Contour. Contour Bunding aids in the capture and retention of rainfall before it becomes runoff. • The area is divided into strips by a series of bunds, reducing the water runoff velocity. • Graded bunds, graded terraces, or channel balconies are laid along a pre- determined longitudinal incline near the Contour but not precisely along the shape. Graded bunding creates obstacles across the path to retain water flowing through the watershed and thus help control soil erosion. • These terraces act as drainage canals to control and conduct runoff at non- erosive velocity.