How to Control Soil Erosion?

In this article we will discuss about how to control soil erosion.

Contents:

1. Introduction to Soil Erosion
2. Planning for Erosion Control 
3. Principles of Erosion Control 
4. Approaches to Erosion Control 
5. Technological Interventions for Soil and Moisture Conservation 
6. Principles of Water and Wind Erosion Control 

Introduction to Soil Erosion:

Erosion is derived from the Latin word erodere; that is, the steady eating away and removal of soil material. Detachment of soil from its original location and transportation to a new location through the action of wind, water in motion or by the beating action of rain drops is known as soil erosion. The natural erosion under a balanced condition of forest and vegetative cover is responsible for creation of earth’s crust over a million of years.

Weathered and disintegrated rocks mixed with decomposed organic matter got deposited on the surface during this slow process of soil formation. This top soil surface (30 cm soil depth) supports all plant life and consequently animal and human life also.

This top layer of the soil is continuously exposed to the actions of water and wind, which dislodge the top layer and transport them from one place to another. It takes centuries to form one inch layer of soil but does not take long to lose it by erosion. In India, about 60 to 70 per cent of the cultivated land has been affected by erosion in varying degrees.

Erosion forms many kinds of soil from rock and is controlled by rock properties, topography, vegetation, and climate. Some forms of erosion result in topsoil removal, rock failures, landslides, slumps, and riverbank cutting. Soil loss is affected by composition of soil, type of vegetative cover, soil management practices, and microclimate conditions. With highly fertile soils, erosion has little adverse effect on productivity but increases cost of production.

In soils with medium rooting depth and surface thickness, the effects of erosion can be hidden by the use of technological interventions that work these potentially fragile soils. Erosion of marginal soils with shallow rooting depth, results in continued decline of crop yields.

Mismanagement of marginal soils can lead to permanent loss of soil fertility. Loss of a few centimeters of topsoil can reduce the productivity of good soils by 40 per cent and poor soils by 60 per cent. Land use planning should aim for an acceptable income and a minimal soil loss.

Planning for Erosion Control:

The under mentioned factors should be considered during the process of planning for controlling erosion which will help to protect the soil:

i. Soil type

ii. Extent of erosion

iii. Topography

iv. Tillage

v. Cropping system

vi. Location of waterways

vii. Drainage

viii. Runoff diversions, and

ix. Size and arrangements of fields.

Hence, soil and water conservation is the only way to protect the lands from degradation and conserving rainwater for improving the productivity of dryland crops.

Principles of Erosion Control:

i. Dissipate the power of the rain, by intercepting with vegetation, mulch or other materials.

ii. Minimize the rate of runoff by increasing infiltration of the soil and by maximizing the use of water by plants.

iii. Prevent runoff generating excessive power by controlling slope, and stopping the accumulation and concentration of flows.

iv. Increase the resistance of the soil by increasing its structural strength by improving fertility (via organic cycling) and incorporating sound tillage practices.

Approaches to Erosion Control:

i. Infiltrate and transmit rain through the soil where it falls

ii. Use as much water as possible on site

iii. Maximize soil cover by controlling the total grazing pressure or tillage and weed management practices

iv. Improve organic matter content of soil

v. Use cultivation sparingly, and

vi. Match land use with the capability of the land type to support that use.

Technological Interventions for Soil and Moisture Conservation:

Land use planning aims for the maximum retention of rainwater by allowing more percolation, controlled removal of excess rainfall and protection of soil. It is to be emphasized that conservation and optimization of the use of rainwater so that it stays in the soil for longer periods and is released slowly for the use of crops, become important steps for improved dryland farming. Such utilization of rainfall is accomplished through appropriate agronomic practices and certain engineering structures.

Principles of Water and Wind Erosion Control:

A. Water Erosion:

i. Soil protection from rainfall.

ii. Maintenance of soil infiltration capacity.

iii. Control of surface runoff.

iv. Safe disposal of surface runoff.

B. Wind Erosion:

i. Increasing the size of soil aggregates.

ii. Reducing wind velocity at ground surface.

iii. Trapping the saltating soil particles.

iv. The loss of soil particles through saltation can be minimized by keeping the soil moist.

Soil and moisture conservation measures for agricultural lands depend upon the soil, land slope and rainfall characteristics of the area.

These measures are broadly classified as:

(1) Agronomic measures, and

(2) Mechanical measures.

The agronomic measures are adopted when the land slopes are small and erosion problems are not severe. When the land slopes are more than 2 per cent, engineering measures may become necessary. Agronomic measures are also adopted in conjunction with engineering measures.

(1) Agronomic Measures:

i. Tillage:

Tillage operations help to keep the upper soil layers porous for a short time especially in compact soils that restrict root development and infiltration. Ploughing helps to minimize runoff by assisting infiltration. A wide range of special tillage operations involving soil inversion, chiselling, subsoiling or deep tillage have been found to be beneficial in improving surface detention, storage, infiltration, root development and by minimizing soil hardening.

The effectiveness of ploughing in soil and water conservation also depends on the conditions under which it is carried out and its frequency. Recent studies have emphasized the importance of cultivating only when soil conditions, particularly the soil moisture content are right to avoid structural breakdown and smearing.

The pulverizing effect of conventional tillage can be minimized by reducing the number of operations on the land. This can be achieved by cultivating only the small strips of land required for seed beds thus leaving wide unfilled zones (strip zone tillage); by carrying out tillage with a mulch retained on the ground (mulch tillage) or completing as many activities as possible in one pass (minimum tillage) as with plough-plant operations.

To achieve best results for soil conservation, the following points should be considered for tillage operations:

a. Till no more than necessary.

b. Till only, when soil moisture is in the favourable limit.

c. Vary the depth of ploughing.

ii. Mulch Tillage/Mulch Farming:

Mulching covers the soil with materials that reduce soil moisture evaporation and inhibit weed growth. Mulching slows rainfall infiltration and protects the soil from direct impact of rain. Mulch tillage or stubble mulching is a crop and soil management practice that utilizes the residual mulches of the preceding crop leaving a large percentage of vegetative residues on or near the surface of the ground. The system is particularly valuable where a satisfactory plant cover cannot be established at the time of year when erosion risk is the greatest.

Application of organic wastes as mulch increased the soil moisture content by preventing runoff and soil loss. It also enhances burrowing activity of some species of earthworms (e.g. Hyperiodrilus spp. and Eudrilus spp. Through proper mulching, soil moisture can be improved to a greater extent and that can be utilized for production of crops. The best mulching materials have high humus content, along with good infiltration rates and water storage capacity.

The mulching materials should have the under mentioned properties:

(a) Withstand the forces of runoff.

(b) Should decompose slowly.

(c) Should allow percolation of water.

(d) Ease of application.

(e) Inexpensive.

Types of Mulches:

a. Natural Mulch:

Straw, wood chips, cut grasses, saw dust, papers and sand stones.

b. Synthetic Mulch:

Plastic, PVC, bitumen and asphalt.

Advantages of Mulching:

i. Mulch breaks the fall of the rain drops and dissipates their energy.

ii. Leaves, stems and roots with in the mulch impede surface flow which controls sheet erosion.

iii. Promotes infiltration rate of soil.

iv. Preserves physical structure of soil.

v. Reduction in velocity of wind.

vi. Conserves moisture effectively leading proper growth and development of crops.

vii. Protects soil against blasting action of falling rain drops and helps absorption of rainwater.

viii. Loss of organic matter and plant nutrients from soil by erosion are brought to a minimum.

ix. Preserves the moisture already held by the soil.

iii. Contour Ploughing and Cultivation:

Ploughing is carried out in contour. At every 3 meters, deep contour furrows are opened and a small section bund is formed every 10 meters to check the flow of rain water. These types of ridges and furrows formed along the contour at intervals of 3 to 6 meters help to form plots for moisture conservation during rainfall and to reduce loss of soil. The primary effect of contour ploughing and cultivation is to create a large volume of rain water storage on the soil surface thus reducing runoff.

These practices ensure moisture conservation during normal rains. But during heavy rains, after the soil is saturated, the water starts moving faster. To arrest this momentum, bunds are constructed which are stabilized with a vegetative cover. In India, contour cultivation on 2 per cent slopes reduced soil loss by 28 per cent and runoff by 61 per cent, compared to traditional up-and-down ploughing. It is most effective on 3 per cent to 8 per cent slopes.

Advantages:

a. Contour cultivation lays the foundations of sustainable land use system.

b. Promotes in situ moisture conservation.

c. Ensures uniform distribution of soil moisture.

d. It should be used in conjunction with strip cropping, terracing, bunding etc.

e. It increases yield of crops.

iv. Strip Cropping:

This consists of growing erosion permitting and resisting crops in alternate strips. The soil, which flows from the strips growing erosion permitting crops, is caught by the alternating strips of erosion resisting crops. In between rows of fruit trees, the erosion resisting crops like grasses and legumes with rapid canopy development should be grown, e.g., Ber + Cenchrus glaucus + Stylosanthes hamata.

Strip cropping is to be done in combination with other farming practices like good crop rotations, contour cultivation etc., to achieve the best results. There are four types of strip cropping system viz., contour strip cropping, field strip cropping, buffer strip cropping and wind strip cropping.

The widths of the strips of erosion resisting and erosion permitting crops depend upon several factors like slope, soil texture, rainfall characteristics, type of crops, etc. Depending upon the topography, the widths of the strips will vary. In general, the steeper the slope the greater is the width of the erosion resisting crop and smaller the width of erosion permitting crop.

Crop Widths for Strip Cropping:

a. Contour Strip Cropping:

Erosion resisting and erosion permitting crops are planted in strips along the contour at right angles to the direction of natural slope.

b. Field Strip Cropping:

Field strip cropping consists of strips of uniform width running generally perpendicular to the direction of the erosive force. These strips run across the slope, but not always exactly on the contour. This is useful on regular slopes and with the soils possessing high infiltration rates.

c. Buffer Strip Cropping:

The strips of grass or legume crops laid out between contour strips of crops in regular rotations. These buffer strips may be wide or narrow and of even or variable widths. In buffer strip cropping, permanent strips of grasses are planted either in badly eroded areas or in areas that do not fit into a regular rotation.

d. Wind Strip Cropping:

In wind strip cropping, the crop strips are laid out at right angles to the direction of the prevailing winds irrespective of the direction of the land slope. The objective is to control wind erosion rather than water erosion.

v. Cropping System:

Changes in the cropping system that will help reduce soil movement include intercropping, alley farming, use of grass strips, and pasture improvement. Conversion of cultivated land into grassland can reduce erosion by at least 10 per cent. Growing of fodder crops for livestock provides an opportunity to integrate animal husbandry and erosion control.

Producing sufficient fodder grasses reduces the need to graze animals; cutting and carrying feed may reduce the space needed by the animals and allow for more crop land. Alternating strips of protected plants (vegetables) with protective plants (fodder grasses) will trap suspended particles and reduce soil movement. The use of protective grass strips is effective only if grazing is avoided.

a. Crop Rotation:

Crops like groundnut, soybean, green gram etc., should be included in crop rotation as these crops are having high soil binding capacity and act as erosion resisting crops. This helps to conserve soil fertility. E.g. Maize/sorghum – groundnut.

b. Mixed Cropping:

Mixed cropping is the system of growing more than one crop together on the same land without any distinct row arrangement. Erosion permitting and erosion resisting crops are grown in the same land for effective soil and water conservation. This system helps in utilizing the nutrients in the soil profile effectively as they possess varied rooting system. E.g. Fodder maize + fodder cowpea.

Cover Crops:

Cover crops such as Pueraria phaseoloides, Centrosema pubescens, Setaria spp. and Stylosanthes spp. provide another technique of achieving in situ mulch. These crops conserve soil water, improve water use efficiency, weed control and soil organic matter.

It is the most satisfactory method of building organic matter content of soil. The effectiveness of cover crops in soil and moisture conservation, however, depends on species characteristics including ease of establishment, vigour of growth, depth of rooting, rapidity of establishment of surface cover etc.

Vegetative Hedges:

Grasses prevent soil erosion and improve soil structure. Growing of several grasses and legumes on bunds helps in stabilizing bunds by their maximum root growth and canopy coverage, e.g. Anjan, marvel, rhodes, napier, blue panic. Vetiver and Cenchrus are found suitable as vegetative hedges under rainfed conditions.

Vetiver slips are to be planted within 24 hours of uprooting and root dipping either in Azospirillum or in 5% Glucose solution for better establishment. These are to be planted at 15-20 cm spacing in zig-zag manner for effective soil moisture conservation and higher yield.

Windbreaks and Shelter Belts:

Wind influences plants physiologically and mechanically. It is necessary to have wind breaks in areas where the land is silted up due to wind erosion. A wind break consists of five rows of species planted at an interval of 500 meters. Wind breaks act as a barrier against the wind speed and make the land in between the wind breaks suitable for cultivation by averting evaporation of soil moisture.

Shelter belts consist of several rows of trees planted at right angles to the prevailing wind around the periphery of horticultural plantation areas. This is to avoid high wind speed during the flowering season and to prevent the dropping of fruits. The species for a shelter belts is selected in such a way that it would not affect the horticultural crops by infecting them with pests.

(2) Mechanical Measures:

Mechanical measures require engineering techniques and structures.

These measures are adopted:

a. To divide a long slope of land into a series of shorter ones in order to reduce the velocity of runoff water.

b. To retain the water in the land for long period so as to allow maximum water to be absorbed and held in the soil and less water flows down the slope of the land at non- erosive velocity.

c. To protect the soil against erosion by water.

i. Contour Bunding:

Earthen bunds of 1m basal width, 0.5m top width and 0.5 m height along contours at a lateral distance of every 60m, or a fall of 1 to 1.5m are constructed. The slope of land is thus broken into smaller and more level compartments which hold soil as well as rain water. It is suitable for light and medium textured soils.

Contour bunding is made on land where the slope is not very steep and the soil is fairly permeable (alluvial, red, laterite brown soil, shallow and medium black soil). Clayey or deep black cotton soils are not suitable for this type of bunding. Contour bunds are also called level terraces, absorption type terraces or ridge type terraces. The size, cross-section and inter bund spacing depend upon the nature of rainfall, soil and slope of the area.

Main Functions:

(a) It reduces the length of slope, which in turn reduce soil erosion.

(b) Permits more water to recharge into the soils.

Limitations:

(a) It is suitable for areas, which receive the annual rainfall up to 600 mm and soils of

(b) Greater permeability.

(c) Not suitable for clay soils.

(d) Not suitable for land slopes greater than 6%.

Contour Bund Specifications:

Spacing between Contour Bunds:

ii. Graded Bunding:

When a grade is provided to a contour bund then it is called as graded bund (channel terraces). This bunding is suitable for high rainfall areas as the bunds are slightly graded longitudinally which helps in draining surplus water. For safe removal of excess runoff water, it is essential to provide suitable outlet structures at proper places so that no damage is done to bunds e.g. Stone outlets, channel weirs or pipe outlets in low rainfall areas and grass outlets in heavy soils.

Main Functions:

(a) It reduces length of slope, which decreases erosion.

(b) It disposes the excess water safely to a suitable point.

Limitations:

(a) It is not recommended on the land slopes less than 2% or > 8%.

(b) Suitable only in medium and high rainfall areas (> 600 mm).

(c) It requires establishment of grassed waterway as an outlet for the disposal of surplus water.

Graded Bund Specifications:

Suitability of Contour Bund and Graded Bund:

Terracing:

A terrace is an embankment or ridge of earth constructed across the slope to control runoff and minimize soil erosion. A terrace reduces the length of the hill side slope, thereby reducing sheet and rill erosion and prevents formation of gullies. These terraces are made in the lands having slope of 6 to 10%. Two major types of terraces viz., Broad based terrace and Bench terrace.

a. Broad Based Terrace:

A broad based terrace is defined as a surface channel or embankment, which is formed across the land slope.

This terrace is classified into two types’ viz.:

(a) Graded terrace (or) channel terrace and

(b) Level terrace (or) ridge terrace

(a) Graded Terrace:

This type of terrace is also known as channel type terrace which is constructed to drain runoff water from the land. This terrace reduces length of slope thus reducing soil erosion. Sometimes, the graded terrace is also used as drainage channel and hence referred as drainage terrace.

(b) Level Terrace:

Level terraces are constructed for conserving moisture and controlling soil erosion. They are suitable for low to moderate rainfall regions as they trap and hold the rain water on their top, which get infiltrated into the lower soil profile. This type of terrace is called as conservation terrace.

b. Bench Terracing:

Bench terracing consists of construction of series of platforms along contours cut into hill slope in a step like formation. These platforms are separated at regular intervals by vertical drops or by steep sides and protected by vegetation and sometimes by packed stone retaining walls. These types of terraces are generally constructed on the land of 16 to 33% slope.

Bench terraces convert the long uninterrupted slope into several small strips and make protected platforms, which are suitable for farming. Bench terraces are classified into three type’s viz., hill type bench terraces, irrigated type bench terraces and orchard type bench terraces based on the purpose of their use. But, Rama Rao (1974) has classified the bench terraces on the basis of slope of bench as level bench terraces, bench terrace sloping outward and bench terrace sloping inward.

(a) Level Bench Terraces:

This type of bench terraces consists of level top surface which are adopted in medium rainfall areas with highly permeable soils. This terrace is also known as irrigated bench terrace / table top or paddy terraces because they have level top surface that can easily impound rain water. Most of the rainfall is absorbed by the soil and less quantity of water is lost as surface drainage as no slope is given to the benches. These types of terraces are also used where irrigation facilities are available.

(b) Bench Terraces Sloping Outwards:

These are adopted in low rainfall areas with permeable soils. A shoulder bund is essential which provides stability to the outer edge of the terrace. It helps in retaining the surface runoff. These are called as orchard type bench terraces. In these terraces, the rainfall coming over the area is to be conserved by retaining the shoulder bund and the rainfall thus conserved will have more time for soaking into the soil.

(c) Bench Terraces Sloping Inward:

These terraces are adopted in areas of heavy rainfall with less permeable soils, where large portion of rain water is drained as surface runoff. A drainage channel is provided on the inner side to drain excess runoff. These drains ultimately lead to a suitable outlet. This is known as hill type bench terrace. Potato is cultivated widely in these terraces in Nilgiri hills of Tamilnadu and North Eastern hill regions.

iii. Compartmental Bunding:

Small bunds of 15 cm width and 15 cm height are formed in both the directions (along and across slope) to divide the field into small compartments of 40 sq. m size (8 × 5 m). It is suitable for red soils and black soils with a slope of 0.5 to 1%. The bunds can be formed before planting or immediately after planting with wooden plough for effective soil and moisture conservation.

(a) Micro Catchments:

Cultivation of fruit crops in the dryland areas requires appropriate soil and moisture conservation techniques as these areas receive low rainfall and the soils possess high infiltration rate. Therefore, it is essential to develop catchments area for each tree for proper soil and moisture conservation. The size of catchments depends on the slope of land, water requirement, runoff coefficient and canopy of fruit tree.

(b) Basin Listing:

Small basins of 10-15 cm depth and 10-15 cm width at regular intervals are formed by using basin lister. These basins conserve rain water, which can be utilized for fruit production.

(c) Trench Planting:

Deep trenches of 0.5 to 1.0 m are formed across the contours and the fruit trees are planted. These trenches conserve soil and moisture thus promoting the growth of fruit trees.

(d) Farm Ponds:

Farm ponds are small storage structures constructed at the lowest point of a farm to collect and store runoff water. The runoff from various parts of the catchments area is properly guided through grassed water ways into the farm pond. The size of farm pond depends on the quantity of rainfall, soil type, area of catchments and estimated runoff.

Advantages:

i. The harvested water can be used for protective irrigation to fruit crops at critical stages.

ii. Minimizes erosion as the runoff is properly guided through grassed water ways.

iii. Stored water can be used as drinking water for animals, and for fish rearing.

iv. Construction of farm ponds helps in raising ground water level.

Water is essential for all life and is used in many different ways for food production, drinking and domestic and industrial uses. It is also part of the larger ecosystem on which bio diversity depends. Precipitation, converted to soil and groundwater and thus accessible to vegetation and people, is the dominant pre-condition for biomass production and social development in drylands.

Crop production under rainfed conditions in the arid and semiarid regions is often affected by droughts during the monsoon season because of prolonged dry spells associated with break in monsoon. Sometimes, heavy rainfall occurs even in the drier regions because of severe cyclonic activity in the Bay of Bengal. Rainwater management, for mitigating moisture stress is crucial for improving productivity, particularly during the years of drought.

Lack of water is caused by low water storage capacity, low infiltration capacity, large inter-annual and annual fluctuations of precipitation and high evaporative demand. To alleviate these problems, proper agronomic measures and land configurations for conserving soil and moisture should be adopted, which will improve the fertility status of soil and moisture regime thus favouring production of crops in dryland areas.