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1- KALABAGH DAM
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SOIL AS SUPPORTING MEDIA FOR PLANT GROWTH
3- PAK-IRAN: GROWING BORDER TRADE

 

SOIL AS A SUPPORTING MEDIA FOR PLANT GROWTH

 

Pakistan loses 20 tons of topsoil per hectare in a year due to floods, rainfall and deforestation

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By Dr. S.M. ALAM
Sep 29 - Oct 05, 2003
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Soil can be defined as a thin layer of the earth's crust, which serves as a natural medium for the growth of plants. Soil, though considered as a non-living thing, acts as a home for various living organisms from small worms and insects, to reptiles, etc. Thus, the soil is an environment of its own. For a healthy-ecosystem, healthy soil is important. The physical properties of any kind of soil largely determines the manner in which it can be used. Properties like water holding capacity, permeability to water, aeration, plasticity and nutrient supply ability, are influenced by the size, proportion, arrangement and mineral composition of the soil particles.

In Holy Quran, there is a world Ard (AI-Ardh), which means earth, ground, land or soil; Earth is a planet on which we live, with the five continents, oceans, seas, lakes, mountains, valleys, great deserts, glaciers, rain forests, savannas, prairies, rich meadows and fertile plains. Its centre is boiling lava, while its surface is covered with a thin layer of disintegrated organic and non-organic solid materials. From this earth, five soil materials are developed. Soil is the main component of the earth. Soil is defined as a 'natural body, engendered from a variable mixture of broken and weathered minerals and decaying organic matter, which covers, the earth in a thin layer and which may supply, when containing, the proper amounts of air and water, mechanical support and in part sustenance of plants. Soil is considered as a natural body with three major components, solid, liquid and gaseous.

Some major soil groups are as follows:

BLACK SOIL: These soils vary in depth from shallow to deep. They are highly argillaceous, very fine grained and dark, containing a high proportion of calcium and magnesium carbonates. But they are poor in phosphorus, nitrogen and organic matter.

ALLUVIAL SOIL: This type of soil differs in constituency from drifting sand to loam and from fine silt to stiff clay. This is also the most important soil group contributing in a major extent to agricultural wealth.

RED SOIL: This is the most predominant type of soil found in the world. These soils are rather shallow, very open in texture, having a pH ranging from 6.6 to 8.0 and are generally poor in nitrogen, phosphorus and humus.

LATERITE: These soils are specially well developed on the summits. Though poor in lime, magnesium and nitrogen they are rich in plant nutrients and especially iron.

 

 

CLAY: Since the soil particles are very fine grained and fine textured, the quality of retaining water is more and hence the water infiltration capacity is low.

SAND: This is found in coastal and river bed areas. These soils are very permeable and drain well, but are less water retentive.

PROBLEMS ARISING DUE TO SOIL LOSS: Deforestation leads to loss of top soil, soil erosion and nutrient leaching. It takes about 2,000 years for the top soil to develop. Due to deforestation, on open, bare land, soil gets dissipated or carried away by monsoon rains and deposited in rivers, tanks and ponds, thus leading to silt formation, thereby reducing their water holding capacity. The exposed poor soil in agricultural lands makes it unfit for cultivation; soil erosion occurs due to wind and rain. Prolonged soil erosion may lead to formation of gullies and may lead to land slides.

ACIDIC SOILS: In humid regions where rainfall is high, the continued leaching of soils results in the replacement of calcium, magnesium, potassium and sodium ions by hydrogen ion, leading to the formation of acidic soils. Lime application neutralizes to some extent the acidity in the soil. Crops like millets, oats, peas and soybeans, can tolerate moderate acidity and trees like Derris indica, Gliricidia and Tamarind can be grown in these soils.

SALINE SOILS: In Pakistan, 6.3 million hectares of land are saline in nature. This soil contains toxic concentrations of soluble salt in the root zone. Because of the white encrustation due to salts, the saline soil is also called white alkali. The salinity may increase due to a rise in the water table, water-logging in the root zone and sea coast irrigation. Excess soluble salts like chloride, sulphate, sodium and calcium will be present. Tree species like Azadirachta indica, Prosopis julliflora, Terminilia arjuna and Albizia lebbeck can be grown in these soils. While planting, ridge-trench method, sub-surface planting and planting in furrow irrigation channels would help to reduce the toxicity of salts.

ALKALINE OR SODIC SOILS: These soils do not contain any neutral salts. Because of high alkalinity resulting from sodium carbonate, the surface soil appears discoloured and black. Such soils have a very low infiltration rate. If the soil texture is heavy, gypsum can be added. Silt and rice husk can also be added to improve the texture. Trees like neem, Albizia lebbeck, Derris indica, Subabul, Prosopis and terminilia arjuna can be planted.

SOIL MANAGEMENT: There are around 16 micro and macronutrients needed for the healthy growth of a plant. During each harvest, the soil's fertility will keep progressively reducing. To protect the fertility of the soil, it has to be tested each time after harvesting. A careless application of fertilizers will only further deplete the soil fertility. It is also not advisable to apply micro and macronutrients simultaneously into the soil. Mixed cropping would help to balance the nutrients in the soil. Although, the problems of soil management vary according to the soils and their situations and the climatic conditions, these are fundamental factors, which govern the choice of soil management practices. The productive capacity of the soil should be improved and maintained by providing adequate organic manure and plant nutrients.

SOIL TEST: For maximum production and rational soil management, knowledge of the soil fertility status and the physical properties is essential. Soil testing is one of the methods of determining the fertility status of the soils, so that recommendation in regard to deficient nutrients or soil amendments can be made.

COLLECTION OF SAMPLES: It is advisable to remove all leaf litter and debris from the top soil and using a soil tube, an auger, a spade or a pick-axe, to dig the soil in a V shape up to a depth of 10 cm and then collect the sample. The soil should be removed from the centre of the land, but manure filled or compost areas have to be avoided.

There are 16 micro and macronutrients essential for plant growth, i.e. nitrogen for leaves, stem growth, seed development; Phosphorous for roots to-spread and absorb water; Potassium for protection from disease, pest resistance, and compensating evapotranspiration; Iron for preparing chlorophyll and for energy development and transfer; Zinc growth stimulator; manganese for absorption of C02 and for transfer of nitrogen; Copper for preparation of primary protein; boron in cell formation and division; molybdenum to absorb nitrogen and to resist excess micro-nutrients; sulphur for chlorophyll and root development; Calcium in cell development and for transfer of food; magnesium for protein preparation as an enzyme catalyst; other nutrients such as carbon, hydrogen, oxygen and chlorine too play vital roles in plant growth.

SOIL POLLUTION: Land is a very valuable but limited resource, as the population increases rapidly. Many highly urbanized cities are faced with acute space problems, as in Karachi, Calcutta or Bombay. Besides the limited availability of land, 175 million hectares of land are becoming less productive every year. Pakistan loses 20 tons of topsoil per hectare in a year due to floods, rainfall and deforestation. 20 % to 50 % of lands under irrigation can go out of cultivation at this rate because of water logging and salinity. The scenario of desertification is compounded by pollution which includes indiscriminate discharge of industrial effluents on land and into water bodies; an increase in the use of fertilizers for agriculture; open defecation by animals and human beings; accumulation of solid waste; this is a major problem in developing countries like Pakistan, where the garbage and refuse products are not degraded and radioactive substances from nuclear plants are released into the soil.

MAJOR SOIL POLLUTANTS AND THEIR EFFECT ON HUMAN HEALTH

Arsenic occurs naturally chronic poisoning leads to loss of appetite and weight, diarrhea, alternating with constipation, gastrointestinal disturbances, peripheral neuritis, conjunctivitis and sometimes skin cancer. Cadmium mining, metallurgy chemical industry and electroplating lead to chronic poisoning and affect the proximal tubules of the kidney, causing formation of kidney stones. Lead smelters storage battery lead poisoning can lead to severe mental retardation or death. Mercury industrial wastes and methylmercuric compounds are much more toxic than other forms of mercury, causes neurological problems and damages renal glomeruli and tubules. Cyanides waste from heat treatment of metals, dismantling of electroplating shops, etc. rapid death may follow due to exposure to cyanide as a result of inhibition of cellular respiration.