Chapter 4 — Lesson 3 ମୃତ୍ତିକା ସମ୍ବଳ

Soil is the loose upper layer of the earth's crust, made of mineral particles, decayed organic matter called humus, water, air and living organisms, in which plants grow. It is the most important renewable natural resource, because it is the medium of plant growth and so supports all life on land. Soil is the product of the long interaction of rock, climate and life, and it takes millions of years for the soil to form up to a few centimetres in depth.

Soil formation begins with the weathering of rock, the breaking of solid rock into loose particles by natural forces. Physical weathering splits rock by changes of temperature, by frost and by the growth of roots in cracks; chemical weathering decomposes minerals through water, oxygen and acids; biological weathering is the work of plants, animals and micro-organisms. The particles thus produced form the mineral skeleton of the soil. Dead plants and animals decompose into humus, which darkens the soil, binds particles and supplies nutrients.

Five factors govern the process. The parent rock supplies the material and decides the texture and mineral content; granite yields sandy, acidic soils, basalt yields clayey, dark soils, and limestone yields calcareous soils. Relief decides whether the products of weathering remain in place or are carried away; steep slopes have thin soil, valleys and plains deep soil. Climate is the most powerful factor: temperature and rainfall control the speed of weathering and of decay, and in warm wet climates leach soluble matter out of the soil; heavy rain produces leached, acidic soils like laterite, while dry climates produce saline or sandy soils. Living organisms, from bacteria and earthworms to forest trees, add humus, mix the soil and create its structure. Time allows all these processes to go deeper, so that old surfaces have mature soils with distinct layers while young river deposits are hardly weathered at all.

Because the factors vary from place to place, soils vary. The alluvium of the Mahanadi delta is the transported product of many rocks; the red soil of Keonjhar is the residual product of gneiss weathered in place; the black soil of the western Odisha patches comes from basalt; the laterite of the plateau edges is the product of heavy rain leaching an old surface. Understanding formation is therefore the key to understanding the map of soils that follows.

Soils are also constantly changing. Cultivation, manuring and irrigation alter them, and erosion removes them. A soil can be built up by good management or destroyed in a few seasons by careless use. This is why soil is called a renewable but exhaustible resource.

If a pit is dug through a mature soil down to the rock, the walls show a series of layers called horizons, differing in colour, texture and composition. The sequence of horizons is the soil profile, and reading it tells the story of the soil's formation.

The top layer is the O horizon, a thin layer of leaf litter, twigs and partly decomposed plant material, well developed in forests and almost absent in cultivated fields.

Below it lies the A horizon, the topsoil. It is the darkest layer because it is rich in humus, and it is the zone of most biological activity: roots, earthworms, insects and bacteria live here. It is also the layer from which rain washes soluble minerals and fine clay downward, a process called leaching or eluviation. The topsoil is the most fertile layer, and it is the layer that erosion removes first. Its depth varies from a few centimetres on a hillside to a metre or more in a flood plain.

The B horizon, the subsoil, lies below. It receives the clay, iron, aluminium and other materials washed down from the A horizon, a process called illuviation, and is therefore often denser, lighter in colour, and reddish or yellowish from iron. It contains less humus and fewer organisms but stores water and nutrients for deep roots. In laterite soils the B horizon can harden into a crust.

The C horizon is the layer of partly weathered rock fragments, broken and altered but not yet soil. It is the parent material from which the horizons above have developed.

The R horizon at the base is the solid, unweathered bedrock.

The thickness and clarity of these horizons depend on the factors of formation. A soil on a young alluvial plain, deposited by floods every year, has hardly any horizons because there has been no time for them to develop; the Mahanadi delta soil is of this kind, layered by deposition rather than by soil processes. A soil on an old plateau surface under a wet climate, like the laterite of the Eastern Ghats, has deep, well-marked horizons. A soil on a steep slope may have only a thin A horizon directly on rock.

The profile matters for farming and conservation. Crops feed mainly on the A horizon, so its loss by erosion is the loss of fertility; a farmer who sees pale subsoil at the surface has already lost the best part of the field. Deep-rooted trees draw water from the B horizon, which is why afforestation succeeds on soils that will not support crops. Hard pans in the B horizon stop drainage and cause waterlogging. Knowledge of the profile is thus the beginning of soil management.

Alluvial soil is the most widespread and the most important soil of India, covering about 40 per cent of the country's area. It is a transported soil, made of fine sediments, silt, sand and clay, deposited by rivers. The entire northern plain of the Indus, Ganga and Brahmaputra is made of it, laid down over ages by the three great river systems flowing from the Himalaya. Alluvial soil also extends into Rajasthan and Gujarat through a narrow corridor, and it is found in the eastern coastal plains, particularly in the deltas of the Mahanadi, Godavari, Krishna and Kaveri, and in the valleys of the peninsula.

The alluvial soil consists of various proportions of sand, silt and clay. As one moves inland towards the river valleys, the soil particles appear larger; in the upper reaches of the river valleys, near the place of the break of slope, the soils are coarse and gravelly, and in the lower parts of the plains and the deltas they are fine and clayey. Such soils are more common in piedmont plains such as Duars, Chos and Terai.

Alluvial soils are classified by age. Bangar is the old alluvium, lying on higher ground beyond the reach of floods; it is less fertile, has more concretions of lime called kankar, and is often lighter in colour. Khadar is the new alluvium of the flood plains, renewed by silt every year; it has finer particles, more moisture and higher fertility. Along the Odisha coast the deltas are khadar-like new alluvium, while the older terraces inland are bangar.

Alluvial soils are generally very fertile. They contain adequate proportions of potash, phosphoric acid and lime, which are ideal for the growth of sugarcane, paddy, wheat and other cereal and pulse crops. They are, however, often poor in nitrogen and humus, so they need manuring. Their texture is loamy and easy to work, their depth is great, and they hold water well. Being level and well watered, the regions of alluvial soil are intensively cultivated and densely populated. The colour ranges from light grey to ash grey depending on the depth of deposition, the texture and the time taken to attain maturity.

In Odisha the alluvial soil covers the coastal plain from Balasore to Ganjam, most extensively in the Mahanadi-Brahmani-Baitarani delta of Cuttack, Jagatsinghpur, Kendrapara, Jajpur, Bhadrak and Puri, and in narrower strips along the Subarnarekha, Budhabalanga and Rushikulya, as well as in the inland valley of the Mahanadi around Sambalpur. It is the state's rice bowl, growing paddy, jute, sugarcane, pulses, vegetables and coconut. Near the coast it grades into saline alluvium, and in the delta it is subject to flood and to waterlogging.

Black soil is the second important soil of India, covering about 15 per cent of the area. It is black in colour and is also known as regur, and because it is ideal for growing cotton it is called black cotton soil. Climatic conditions along with the parent rock material are the important factors for its formation; it developed over the Deccan trap of basalt lava, which spread over north-west peninsular India in the Cretaceous period, and it is made up of extremely fine, clayey material. The type is typical of the Deccan trap region spread over the north-west Deccan plateau, and it covers the plateaus of Maharashtra, Saurashtra, Malwa, Madhya Pradesh and Chhattisgarh and extends in the south-east direction along the Godavari and Krishna valleys into Telangana, Andhra Pradesh and Karnataka. Small patches occur in Tamil Nadu and, in Odisha, in the western districts.

The black soils are well known for their capacity to hold moisture. They are rich in soil nutrients such as calcium carbonate, magnesium, potash and lime, but they are generally poor in phosphoric content. The soil is very clayey and therefore impermeable and sticky when wet. During the hot season it shrinks and develops deep, wide cracks, which allow air to reach deep into the soil; it is said to plough itself, because the surface material falls into the cracks and mixes the soil. In the rainy season it swells, becomes sticky and is difficult to work, so it has to be tilled immediately after the first shower or during the pre-monsoon period. The colour comes from the iron and titanium compounds of the basalt and from humus.

Because it holds moisture for a long time, black soil supports crops even in the dry season without irrigation, which is why the cotton of the Deccan is grown on rain alone. Besides cotton it grows jowar, wheat, linseed, gram, tobacco, sugarcane and citrus. Its fertility is maintained for long periods, but it is poor in organic matter and nitrogen and benefits from manure.

In Odisha black soil is not extensive. Patches occur in Balangir, Sonepur, Bargarh, Kalahandi, Nuapada and parts of Sambalpur and Koraput, where basaltic and other basic rocks or the fine sediments of old lake beds have given a dark, clayey, moisture-retentive soil. These patches grow cotton in Balangir and Kalahandi, as well as pulses, oilseeds, sugarcane and rabi crops that survive on stored moisture. The black soils of the west are among the reasons why cotton is a crop of the state's western districts and not of its coast.

Black soil is prone to sheet erosion when bare, and its heavy clay causes waterlogging where drainage is poor, so it needs careful management: bunding, crop rotation with pulses to add nitrogen, and timely tillage.

Red and yellow soil covers about 18 per cent of India and is the dominant soil of the eastern and southern peninsula. It develops on the crystalline igneous and metamorphic rocks, chiefly granite and gneiss, in areas of low to moderate rainfall in the eastern and southern parts of the Deccan plateau. It is found along the piedmont zone of the Western Ghats, in a long stretch, and in large parts of Odisha, Chhattisgarh, Jharkhand, southern Uttar Pradesh, Madhya Pradesh, Tamil Nadu, Karnataka and Andhra Pradesh.

The soil develops a reddish colour due to the diffusion of iron in the crystalline and metamorphic rocks; the iron oxide coats the particles. It looks yellow when it occurs in a hydrated form, that is, when the iron oxides have taken up water, usually in the lower, moister parts of the landscape. The red colour is therefore a sign of good drainage and oxidation, and the yellow colour of wetter conditions.

Red soils are generally poor in nitrogen, phosphorus, humus and lime, though they may be fairly rich in potash. They are loamy to sandy in texture, porous and well drained, and therefore do not hold water well. Their fertility is moderate to low, and they respond well to irrigation, manure and fertiliser; where these are available they give good crops of rice, ragi, maize, groundnut, pulses, tobacco, potato and fruit. Where they are thin and dry, only millets and coarse crops are grown, and much of the red soil area lies under forest or scrub.

In Odisha red soil is the most extensive soil of the state, covering the greater part of the interior: the northern plateau of Mayurbhanj, Keonjhar and Sundargarh, the central tableland of Angul, Dhenkanal, Boudh, Balangir and Bargarh, the Mahanadi valley uplands of Sambalpur and Jharsuguda, the hills of Kandhamal and Gajapati, and the Koraput-Rayagada-Nabarangpur-Malkangiri region in the south-west. It is derived from the granites, gneisses and khondalites of the Eastern Ghats and the peninsular shield. Being poor in nutrients and easily eroded on slopes, it supports rain-fed rice in the lowlands, and millets such as ragi, pulses, oilseeds like niger and groundnut, and maize on the uplands; with irrigation from Hirakud or tanks it gives good paddy. The red soil regions coincide with the state's forests, its mineral belt and its tribal population.

Red soil needs organic manure to build humus, lime to correct acidity, and bunding to prevent erosion. Where it is well managed, as in the irrigated tracts of Bargarh, it is productive; where it is neglected on slopes, it is the most eroded soil in the state.

The name laterite comes from the Latin word later, which means brick, because the soil hardens like a brick when it is exposed to air and dries, and it has long been cut into blocks for building. Laterite soil develops in areas with high temperature and heavy rainfall. It is the result of intense leaching caused by tropical rains: the heavy rain dissolves and washes down the soluble constituents, lime and silica, and leaves behind the insoluble oxides of iron and aluminium, which give the soil its red colour and its hard, porous, gravelly character. With rain, lime and silica are leached away, and soils rich in iron oxide and aluminium compounds are left behind.

Laterite soils are found on the higher, older surfaces of the humid tropics: the summits and edges of plateaus in Karnataka, Kerala, Tamil Nadu, Madhya Pradesh, the hilly areas of Odisha and Assam, and the edges of the Western Ghats and the Eastern Ghats. In Odisha laterite occurs as a discontinuous belt along the transition between the interior uplands and the coastal plain, in parts of Balasore, Mayurbhanj, Keonjhar, Jajpur, Cuttack, Khordha, Nayagarh, Puri and Ganjam, and as caps on plateaus in the interior; the red laterite ground of Khordha and around Bhubaneswar is a familiar example.

Humus content of the soil is low because most micro-organisms, particularly the decomposers like bacteria, get destroyed by the high temperature. Laterite soils are therefore poor in organic matter, nitrogen, phosphate and calcium, while iron oxide and potash are in excess. They are acidic, coarse, porous and infertile in their natural state, and for agriculture they need adequate doses of manure and fertiliser and, often, irrigation. Their advantage is that they are deep and easy to work, and they respond to management.

With proper treatment laterite soils have been made productive. In the hilly areas of Karnataka, Kerala and Tamil Nadu they are suitable for growing tea and coffee; the red laterite soils of Tamil Nadu, Andhra Pradesh and Kerala are more suitable for crops like cashew nut. In Odisha the laterite belt grows cashew, which thrives on the poor sandy laterite of the coastal uplands of Ganjam, Puri, Khordha and Balasore, as well as mango, coconut, sabai grass, and rain-fed rice and millets in the low patches; large parts remain under scrub jungle and sal.

Laterite is also a building material and a source of aluminium: the great bauxite deposits of the Eastern Ghats plateaus of Koraput, Kalahandi and Rayagada are themselves a product of the same laterisation process, in which prolonged leaching concentrated aluminium oxide into ore. Laterite soil erodes readily when the vegetation is removed, and its hardened crust, once exposed, is nearly impossible to cultivate, so the protection of vegetation on laterite land is a first rule of conservation.

The last two soil types of India occupy the driest and the highest parts of the country and, though small in Odisha, complete the national picture.

Arid soils range from red to brown in colour. They are generally sandy in texture and saline in nature; in some areas the salt content is so high that common salt is obtained by evaporating the water. Owing to the dry climate and high temperature, evaporation is faster than rainfall, and the soil lacks humus and moisture. The lower horizons of the soil are occupied by kankar, nodules of calcium carbonate, because of the increasing calcium content downwards; the kankar layer formation in the bottom horizons restricts the infiltration of water. After proper irrigation these soils become cultivable, as has been the case in western Rajasthan, where the Indira Gandhi canal has turned desert into farmland. Arid soils are found in western Rajasthan, parts of Gujarat, Haryana and Punjab, and in the rain-shadow areas of the peninsula. They support bajra, jowar, pulses and, with irrigation, wheat and cotton. Odisha, being humid, has no true arid soil, though the sandy soils of the coastal dunes share some of the character.

Forest or mountain soils are found in the hilly and mountainous areas where sufficient rainforest is available. The texture varies according to the mountain environment where they are formed: they are loamy and silty in valley sides and coarse-grained in the upper slopes. In the snow-covered areas of the Himalaya these soils experience denudation and are acidic with low humus content; the soils found in the lower valleys are fertile. Forest soils are generally immature and thin on slopes, dark and rich in humus under dense forest, and often acidic because of leaching. They support the forests themselves, tea and fruit orchards in the hills, and terraced cultivation of rice, maize and potato in valleys.

Odisha's hill soils belong to this class. On the slopes of the Eastern Ghats in Koraput, Kandhamal and Gajapati, and on the Similipal massif of Mayurbhanj, the soil under forest is brown to dark, loamy on the lower slopes and gravelly above, rich in leaf humus where the forest is intact, and quickly lost when the forest is cleared for podu cultivation. Coffee is grown on such soils in the Koraput hills, and orchards of mango, orange and pineapple have been tried. The mountain soils of Odisha are thus mixed soils, combining the red and laterite material of the parent rock with the humus of the forest, and their value depends entirely on keeping the forest cover.

Together the six soil types describe the whole of India, and in Odisha the red, laterite, alluvial, black and mountain soils, with the coastal saline soils treated in the next section, describe the whole of the state.

Drawing the national types together, the soils of Odisha may be mapped in six groups, each tied to a region and a kind of farming.

Red soil is the most extensive, covering more than half the state across the northern plateau, the central tableland and the Eastern Ghats: Mayurbhanj, Keonjhar, Sundargarh, Angul, Dhenkanal, Boudh, Balangir, Sambalpur, Jharsuguda, Kandhamal, Koraput, Rayagada, Nabarangpur and Malkangiri. Derived from granite, gneiss and khondalite, it is light, well-drained, acidic and poor in nitrogen and humus. It grows rain-fed paddy in the lowlands, ragi, maize, niger, groundnut and pulses on the uplands, and paddy with irrigation.

Laterite soil forms a discontinuous belt between the uplands and the coast, in Balasore, Mayurbhanj, Keonjhar, Jajpur, Cuttack, Khordha, Nayagarh, Puri and Ganjam, and caps plateaus in the interior. Coarse, acidic and infertile, it grows cashew, mango, coconut and sabai grass, with rice and millets in the hollows, and much of it lies under scrub and sal.

Alluvial soil covers the coastal plain and the delta of the Mahanadi, Brahmani and Baitarani, and the river valleys: Balasore, Bhadrak, Jajpur, Kendrapara, Cuttack, Jagatsinghpur, Puri, Khordha, Ganjam and the Sambalpur valley. Deep, loamy to clayey and fertile, it is the rice bowl, growing two crops of paddy where irrigated, plus jute, sugarcane, pulses, vegetables, betel vine and coconut.

Black soil occurs in patches in the west and south-west: Balangir, Sonepur, Bargarh, Kalahandi, Nuapada and parts of Koraput. Clayey and moisture-retentive, it grows cotton, pulses, oilseeds, sugarcane and rabi crops on stored moisture.

Coastal saline soil fringes the shore in Balasore, Bhadrak, Kendrapara, Jagatsinghpur, Puri and Ganjam, where tidal water and sea spray charge the alluvium with salt. Only salt-tolerant paddy varieties grow in the kharif season after the rains wash the salt down; prawn and fish culture, casuarina and coconut occupy much of it, and mangroves grow on the tidal margins. Cyclone surges, such as that of 1999, spread salt far inland.

Mixed and forest soils of the hills, brown loams rich in humus under intact forest on the slopes of the Eastern Ghats and Similipal, support the forests, coffee and orchards in Koraput, and terraced rice and millets in the valleys.

Two facts stand out. First, the productive alluvial and black soils are a minority; most of Odisha's soil is red or laterite, poor and easily eroded, which is why yields are low without irrigation and manure. Second, the soils of the hills depend on the forest above them, which links the fate of the state's agriculture to the fate of its forests, the subject of the next unit.

The denudation of the soil cover and its subsequent washing down is described as soil erosion. It is the removal of the topsoil from the land by natural agents, chiefly running water and wind, at a rate faster than the soil can form. Some erosion is natural and geological, part of the slow shaping of the land, and it is balanced by soil formation. The erosion that concerns us is the accelerated erosion caused by human activity, which removes in years what nature built in centuries. The processes of soil formation and erosion go on simultaneously, and generally there is a balance between the two; this balance is disturbed by human activities such as deforestation, over-grazing, construction and mining, while natural forces like wind, glacier and water lead to the actual removal.

Running water is the principal agent in a monsoon country. Raindrops falling on bare soil break the surface aggregates and splash particles loose; the water then flows over the surface and carries them away. The amount of erosion depends on the intensity of rainfall, the length and steepness of the slope, the type of soil and, above all, the cover of vegetation. Water erosion takes three forms, which are described in the next section: sheet, rill and gully erosion. Rivers in flood also erode their banks and carry the soil of whole fields to the sea, and the sea itself erodes the coast.

Wind is the chief agent in dry regions where the soil is loose and vegetation sparse. Wind blows loose soil off flat or sloping land, sometimes lifting the fine particles high into the air as dust storms and rolling the sand along the surface to form dunes. This is wind erosion, and it is the scourge of Rajasthan and the dry parts of Gujarat and Haryana. Along the Odisha coast, the wind moves beach sand inland over fields and villages, a local form of the same process.

Glaciers grind the rock and soil of high mountains, and sea waves cut back cliffs and beaches; both are natural agents of small concern to farmers except on the coast.

The effects of erosion are severe and cumulative. The topsoil, the most fertile layer with the humus and nutrients, goes first, so yields fall. The land becomes uneven, gullied and hard to cultivate. The eroded material chokes rivers, raises their beds and worsens floods, and silts up tanks and reservoirs, reducing irrigation and power; Hirakud has lost a significant part of its capacity to silt from the eroded catchment. Springs dry up because bare, compacted land absorbs less rain, and the groundwater is not recharged. Erosion thus damages not only the eroded field but the whole river basin below it.

Water erosion progresses through three stages, each more destructive than the last, and a farmer or a geographer should be able to recognise them in the field.

Sheet erosion is the first stage. When water flows as a thin sheet over a large area down a gentle slope, it removes a uniform thin layer of topsoil from the whole surface. The loss is not visible as any cut or channel, only as a gradual paling of the soil as the dark topsoil goes and the lighter subsoil appears, and as a slow fall in yield. Because it is invisible, sheet erosion is the most widespread and, over years, the most damaging form; a millimetre a year across a whole field is a tonne of soil per hectare. It is common on the gently sloping red and laterite uplands of Odisha wherever the fields are left bare after the harvest.

Rill erosion is the second stage. As the sheet of water gathers into small streams, it cuts fine, shallow channels called rills, a few centimetres deep, running down the slope like the marks of fingers. Rills can still be ploughed over and erased, but each rain deepens them and the soil lost through them is much greater than through sheet flow.

Gully erosion is the third and worst stage. The running water cuts through the clayey soils and makes deep channels called gullies, too deep and wide to be crossed by a plough. The land becomes unfit for cultivation and is known as bad land. In the Chambal basin such lands are called ravines, and the ravines of the Chambal in Madhya Pradesh, Rajasthan and Uttar Pradesh are the largest badland area in India, several lakh hectares of once fertile plain cut into a maze of gullies. Gullies also form on the deforested slopes of the peninsular hills, including the uplands of western Odisha and the Eastern Ghats, and along the banks of rivers such as the Mahanadi, Brahmani and Baitarani where they cut through alluvium.

The sequence teaches the strategy of conservation: stop erosion at the sheet stage, when it is cheap to control with cover crops and contour bunds, rather than at the gully stage, when it requires expensive check dams and land reshaping. It also explains why gullies grow: once a gully has formed it concentrates the run-off of the whole slope, its head cuts back uphill with every storm, and its sides collapse, so a small gully becomes a ravine unless it is checked.

Besides these, there is stream bank erosion, in which rivers cut away their banks in flood, and landslides on steep, saturated slopes, both common in Odisha's hills and along its rivers in the monsoon. Together, sheet, rill, gully, bank erosion and landslides account for the greater part of the country's degraded land.

Nature balances erosion with soil formation; it is human action that tips the balance, and the causes are the same as those of land degradation studied in the previous lesson, now seen from the soil's point of view.

Deforestation is the first cause. Tree cover breaks the fall of rain, its litter absorbs the impact, and its roots hold the soil; when the forest is cut for farming, timber, fuel, mining or reservoirs, the bare soil is exposed to direct rain and erodes at many times its former rate. In Odisha the felling of forests in the upper catchments of the Mahanadi, Brahmani and Baitarani is the main cause of erosion of the uplands and of the silting of Hirakud and Rengali.

Over-grazing destroys grass cover and compacts the surface, reducing infiltration and increasing run-off. It is a major cause on the commons and forest fringes of western Odisha and across the drier states.

Faulty methods of farming accelerate erosion: ploughing up and down the slope, which turns each furrow into a channel; leaving fields bare between crops; growing the same crop repeatedly, which weakens the soil structure; and cultivating steep slopes without terraces. Shifting cultivation or podu in the hills of Koraput, Kandhamal, Gajapati and Rayagada, with its shortened cycles, leaves burnt slopes bare in the monsoon and is the chief cause of erosion in the Eastern Ghats.

Mining, quarrying and construction strip the surface and pile loose material that washes away with every rain. The iron ore belt of Keonjhar and Sundargarh, the chromite valley of Sukinda, the coal fields of Talcher and the Ib valley and the bauxite plateaus of Koraput all send silt into the rivers below. Road building and settlement on slopes have the same effect. Defective irrigation and drainage cause waterlogging and salinity, which kill vegetation and expose the soil.

The extent of the problem is large. Of India's roughly 130 million hectares of degraded land, more than half is affected by water erosion and a further part by wind erosion. Estimates suggest that India loses several thousand million tonnes of topsoil a year, carrying away with it nutrients worth thousands of crores of rupees. In Odisha a large share of the uplands of the west and the Eastern Ghats, the mined districts and the river banks of the coast show erosion in one form or another; the state's agricultural universities and soil survey organisations have classed a substantial part of the state's area as prone to moderate to severe erosion.

The consequences run through the whole economy: falling yields, silted reservoirs and tanks, worse floods, drying springs, dust and, in the end, the abandonment of land. Since the causes are human, so is the cure, which is the subject of the final sections.

Soil conservation is the set of practices that keep the soil in place and maintain its fertility. Because the causes of erosion are known, the remedies are direct, and they are chosen to suit the terrain.

Contour ploughing. Ploughing along the contour lines, that is, across the slope rather than up and down it, so that each furrow acts as a small bund that decelerates the flow of water down the slopes. It is the simplest measure and the first that a hill farmer should adopt.

Terrace cultivation. Steps can be cut out on the slopes, making terraces. Terrace cultivation restricts erosion by turning a steep slope into a series of level or gently sloping platforms on which water stands and soaks in instead of running off. The Western and Central Himalaya have well-developed terrace farming, and terraced paddy is found in the hill valleys of Koraput and Kandhamal. Bench terraces, contour bunds and graded bunds are variants suited to different slopes.

Strip cropping. Large fields can be divided into strips, and strips of grass or of a close-growing crop are left to grow between the crops. This breaks up the force of the wind and of surface flow, and the grass strips catch the soil washed from the cropped strips. It is used on gentle slopes and in windy dry regions.

Shelter belts. Planting lines of trees to create shelter also works in a similar way. Rows of trees across the direction of the prevailing wind reduce its speed near the ground, so that it can no longer lift soil. Shelter belts of trees have contributed significantly to the stabilisation of sand dunes and in stabilising the desert in western India, and the casuarina belts along the Odisha coast protect the fields behind them from wind, salt spray and blowing sand.

Afforestation and control of grazing. Planting trees and grass on eroded slopes, catchments, gully heads and wastelands re-establishes the cover that holds the soil; protecting natural regeneration through community forest management does the same at low cost. Rotational grazing, stall feeding and fodder plantations relieve the pressure of animals.

Gully control. Small check dams of stone, brushwood or earth built across gullies slow the water, trap silt and let vegetation take hold; the gully head is protected with a plantation or a stone apron so that it stops cutting back. In badlands, the land can be reshaped and planted, as has been attempted in the Chambal ravines.

Control of shifting cultivation. Settling podu cultivators on permanent terraced fields, horticulture and agro-forestry on the slopes, with secure rights under the Forest Rights Act, removes the cause instead of fighting the symptom; Odisha's programmes in Koraput and Kandhamal follow this line.

These measures are usually combined in a watershed approach, treating the whole catchment from ridge to valley so that water is held at every step and the soil stays where it belongs.

Beyond the hills, soil must be conserved in the cultivated plains, on the coast and on land already damaged, and the methods differ.

In cultivated fields. Crop rotation, alternating cereals with pulses and other crops, keeps the soil structure and returns nitrogen through the legumes. Cover crops and mulching keep the surface covered between main crops so that rain does not strike bare soil. Organic manure, green manure and compost build humus, which binds the soil and holds water; farmyard manure is the traditional strength of Odisha's farming and should not be replaced wholly by chemical fertiliser. Balanced use of fertiliser prevents the acidification and hardening that follow excessive chemical use. Field bunds around paddy plots, universal in the Odisha lowlands, hold water and silt in place. Proper drainage in irrigated tracts prevents waterlogging, and drip and sprinkler irrigation prevent the erosion and salinity that flood irrigation causes on light soils.

Reclamation of saline and alkaline soils. Saline soils are reclaimed by leaching, flooding the field and draining the salt water away, with good subsurface drainage; salt-tolerant crop varieties bridge the period of recovery. Alkaline soils are reclaimed by applying gypsum, which replaces the sodium on the clay, followed by leaching. In the Hirakud command and the coastal delta of Odisha, drainage improvement and salt-tolerant paddy have brought back land that was going out of use.

On the coast. The Odisha shore suffers from blowing sand, salt spray, tidal flooding and cyclone surges. Casuarina shelter belts along the dunes, planted extensively after the super cyclone of 1999, hold the sand and shield the fields. Mangrove restoration in Bhitarkanika, Mahanadi mouth and elsewhere breaks storm waves and traps silt; villages behind intact mangroves suffered far less in 1999 than those without. Dune stabilisation with grasses and creepers, and the protection of coastal wetlands as buffers, complete the coastal set. Embankments keep tidal water out of low fields but need drainage sluices to avoid trapping rain.

Reclamation of mined and industrial land. Mine pits should be backfilled, overburden dumps reshaped and planted with hardy grasses and trees, and topsoil stored before mining and spread again afterwards. Fly ash ponds should be capped and planted or the ash used in bricks and cement. Effluent should be treated before it reaches the land. Odisha's mine closure rules and the reclamation of exhausted iron ore mines in Keonjhar are steps in this direction.

Institutions and people. Soil conservation in India is organised through the soil and water conservation wings of state agriculture departments, the watershed development programmes of the Union and state governments, the agricultural universities and research centres, and the village watershed and forest committees that carry out the work. In Odisha the Directorate of Soil Conservation and Watershed Development and the university at Bhubaneswar lead the effort. Ultimately, however, soil is conserved field by field, by farmers who understand that the dark topsoil under their feet is a resource that took a thousand years to make and can be lost in a single careless season.