Soil Erosion And Runoff Effect On Soil Moisture Conservation

Detachment and transport of soil and soil material caused by water and wind are widely prevalent in dry farming regions. Erosion takes place in both red soils and black soils. Soil and water are the most critical basic resources, which must be conserved as effectively as possible. No phenomenon is more destructive than soil erosion through which fertile topsoil and rainwater are lost. Soil and water conservation is the only known way to protect the lands from degradation and conserving rainwater for improving the productivity of dry land crops. Runoff leads to wastage of rainfall. Under unchecked conditions, even up to 40% of rainfall may be lost as runoff. Even when moisture conservation practices are adopted, about 10-20% of rainfall may be lost as runoff because of high intensity rainfall. Erosion removes topsoil and exposes hard impermeable sub soil, increasing the chances of more run off. Erosion adversely affects soil physical properties such as loss of structure, reduced infiltration, soil depth and soil moisture storage capacity. Loss of topsoil through erosion leads to loss of plant nutrients and poor soil fertility.

Soil erosion: Soil erosion is the process of detachment of soil particles from the topsoil and transportation of the detached soil particles by wind and/or water. The detaching agents are falling raindrop, channel flow and wind. The transporting agents are flowing water, rain splash and wind. Out of 328 m.ha. of India’s geographical area, 175 m.ha. (53.3%) subject to soil erosion and all kind of land degradation. Out of which 104.6 m.ha. are cultivable. Recent estimates indicate that about 5,333 mt. (16.35 t/ha) of soil is detached annually (29% carried away by rivers to the sea, 10% deposited in reservoirs resulting 1–2% loss of storage capacity).

Types of erosion

(a) Geological erosion: It is said to be in equilibrium with the soil forming process. It takes place under natural vegetative cover completely undisturbed by biotic factors. This long time slow process has developed the present topographic features like stream channels, valleys, etc., through weather abnormalities such as intensive rainfall and biotic interference.

(b) Accelerated erosion: It is due to disturbance in natural equilibrium by the activities of man and animals through land mismanagement, destruction of forests, overgrazing, etc. Soil loss through erosion is more than the soil formed due to soil forming process.

(c) Water erosion: Water and wind are the main agencies responsible for soil erosion. Loss of soil from land surface by water, including runoff from melted snow and ice is usually referred to as water erosion. The major erosive agents in water erosion are impacting raindrops and runoff water flowing over the soil surface. Erosion and sedimentation embody the processes of detachment, transportation and deposition of soil particles. Detachment is dislodging of soil particles from soil mass by the erosive agents. Transportation is movement of detached soil particles (sediment) from their original location. The sediment moves along the stream and part of it may eventually reach the ocean.

Some sediment is usually deposited at the base of the slopes, reservoirs and flood plains along the way.

(i) Forms of water erosion: Sheet, Rill, gully, ravine, landslide and stream bank erosion.

(ii) Factors affecting water erosion:

• Rainfall – amount, intensity, duration and distribution

• Soils – primary particle size, distribution, organic matter, structure, Fe and Al oxides, initial moisture content

• Topography – nature and length of slope

• Soil surface cover – plant canopy or mulches

• Biotic interference – disturbance of natural balance

(iii) Losses due to erosion: The losses due to erosion are loss of fertile top soil, loss of rain water, nutrient losses, silting up of reservoirs, damage to forests, reduced ground water potential, damage to reservoirs and irrigation channels and adverse effect on public health.

(iv) Water erosion control: Water erosion can be minimized by preventing the detachment of soil particles and their transportation.

Principles of water erosion control are:

• Maintenance of soil infiltration capacity

• Soil protection from rainfall

• Control of surface runoff

• Safe disposal of surface runoff Control measures are grouped in to agronomic, mechanical and forestry measures

Agronomic: Choice of crops, land preparation, contour cultivation, strip cropping, mulching, application of manures and fertilizers and appropriate cropping systems.

Mechanical: Contour bunding, graded bunding, bench terracing, contour trenching, gully control and vegetative barriers.

Forestry: Perennial trees and grasses.

(d) Wind erosion – Erosion of soil by the action of wind is known as wind erosion. It is a serious problem on lands devoid of vegetation. It is more common in arid and semiarid region. It is essentially a dry weather phenomenon stimulated by soil moisture deficiency. The process of wind erosion consists of three phases: initiation of movement, transportation and deposition. About 33 m.ha in India is affected by wind erosion. It includes 23.9 m.ha of desert and about 6.5 m.ha of coastal sands.

(i) Forms of wind erosion: Transportation of soil particles by wind takes place in three ways.

Saltation: Movement of soil particles by a short series of bounces along the ground surface.

Suspension: Movement of fine dust particles, smaller than 0.1mm dia floating in the air.

Surface creep: Rolling and sliding of soil particles along the ground surface due to impact of particles descending and hitting during saltation is called surface creep.

(ii) Factors affecting wind erosion: The factors are soil clodiness, surface roughness, water stable aggregates and surface crust (Mechanical stability), wind and soil moisture (surface is dry or slightly moist), field length, vegetative cover, organic matter (cementing), topography and soil type (sand erodes easily).

(iii) Losses due to wind erosion: Fertile topsoil is lost. Fertile soils are converted into unproductive sandy soils drifting sand. Yield losses due to abrasive action of wind driven soil particles, especially on broad leaved crops.

(iv) Wind erosion control: Greatest damage by wind erosion occurs during summer months in dry regions, where soil surface is bare and wind velocity is at its peak.

Basic principles of wind erosion control are:

• Reducing wind velocity at ground surface, sufficient to prevent it being able to pickup soil particles.

• Increasing the size of soil aggregates or covering the soil with a non-erodable surface.

• Trapping the saltating soil particles.

• Keeping the soil moist so that soil particles moving by saltation loose their momentum at the surface.

Practices such as stubble mulching and minimum tillage, cover crops, strip-cropping, crop rotation, wind barriers and shelterbelts and mulches can be practiced to minimize wind erosion.