Soil Health - An Overview

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Soil Health An Overview

M. Dhakshinamoorthy, Professor of Soil Science, IMTI, Trichy 15

Highlights

Soil health is an indicator of environmental health and, like humanhealth, provides an overall picture of the condition of manyproperties and processes; the terms soil health and soil qualitycanbe used interchangeably.

Soil health or quality is the soil's fitness to support crop growthwithout resulting in soil degradation or otherwise harming theenvironment.

Soil quality changes slowly because of natural processes, such asweathering, and more rapidly under human activity; land use andfarming practices may change soil quality for the better or for theworse.

Soil health deteriorates mainly through erosion by wind and water,loss of organic matter, breakdown of soil structure, salinization, andchemical contamination.

Introduction

Soils are used for many purposes, such as road and buildingconstruction, waste disposal, and crop production. The most practicaldefinitions of soil quality relate to the soil's function, or what it does. Thedefinition of soil health commonly used by agriculturalists has emphasizedsoil productivity -- a healthy soil produces abundant, high-quality crops.But, over the past 10 years, our thinking about agriculture has shifted. Weno longer see it as a closed operation, but rather as part of a much-broaderecological system, which interacts with, and affects other parts of, thesystem. We need a new definition of soil health that goes beyondproductivity and connects with the environment as a whole. To that end, wedefine soil health for agriculture as the soil's fitness to support crop growthwithout resulting in soil degradation or otherwise harming the environment.

The terms soil health and soil quality can be usedinterchangeably. Soil health is the term commonly used by producers andby the popular press. Soil quality is the term favoured by researchers andused most often in scientific writing. Some writers have attempted to jointhe terms by referring to soil health/quality.


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Pesticides

Soil gets enormous quantities of pesticides through out the year andsuch indiscriminate use of pesticides caused adverse changes in biologicalbalance and lead to an increase in cancer cases and other diseases throughthe toxic residues. Investigations indicated that many vegetables,processed grains, milk and butter contained significant amounts of DDT.ICMR reported that the 51 % of food items were contaminated withpesticides and 20 % had residues above the maximum residue limit (Fig. 2)when compared with the world average it was quiet high in India. The dailyintake of these residues with food could be hazardous in long run causingcarcinogenicity, reduced life span and fertility, increased cholesterol andmany metabolic and genetic disorders.

Fig.2. Pesticide residues in food commodities-National and Global scenario

Jeevan Rao (1997) reported that, 8-10% DDT and 13-15% HCHapplied to the sandy loam soil becomes bound with in one year. Persistenceand metabolism of organo phosphorous and carbonates were more undersub tropical condition in India. A large number of these pesticides have highimmobility in soils and therefore build up to toxic levels with their repeateduse. These pesticides affect the soil microbial activities with consequentimpact on soil fertility as well as soil health and finally resulting in landdegradation. The chemical residues need to be kept well within theprescribed MRL values for both domestic as well as export markets.

Persistence of pesticides in soil is affected by many factors like soil

pH, leaching, soil micro organisms and adsorption by soil clay and organicmatter. Detectable level of aldicarb residues was found in soil upto 90 daysin clay loam soil. High level carbofuran residues were found in laterite soilthan in black, alluvial and red soil (Chandrasekaran and Regupathy, 1993).

Jayakumar (1995) reported that the ester form of 2, 4-D compoundsare volatile and the gases evolved injured the susceptible crops like cottonand tomato. The gas may also move in porous soil, thus causing injury to


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germinating seeds. The loss of pesticides through volatilization may bereduced by soil incorporation and using special formulations such agranules. Herbicides may interact chemically with other pesticides in thesoil, resulting in enhanced phytotoxic effects. The oxidatiosn of 2, 4-D B to2, 4-D results in an increased phytotoxicity.

Krishnamurthi (1999), collected water samples from 8 locations ofLower Bhavani Project Canal water in Erode district and the results showedthat maximum residue level of 0.811 ppm of HCH and was detected inChithode area and minimum at Akkarainagamam area (0.043 ppm). Itclearly shows the deviation of pesticide used for pest control programmesin these areas. The above referred discussion revealed that soil acts as areservoir for pesticide residues.

Industrial Effluents

In Tamil Nadu there are about 17,000 polluting industries out ofwhich about 700 are large units, 2200 medium ones and 14,000 small units.Out of these, 450 are large units, 1000 are medium units and 6,500 aresmall units, which are in the red category or highly polluting industries(Hindu, 1997).

Heavy metal containing effluents discharged either into the system orapplied as an irrigation water on the agricultural lands have a potential ofcontaminating the adjoining drinking water bodies and aquifers. Industriesdischarge large quantities of effluents, industrial wastes as well as by-products to the environment. Paper industries annually dispose nearly onelakh tonnes of lime sludge, a by-product of paper mill, which contains

calcium carbonate along with sodium. This lime sludge, although useful foramending acid soil, the content of sodium in fresh slurry may build highsodium status in the soil. Further, the sludge, if not disposed by the usertimely, heaps of it make the land barren.

The Ni, Pb, Cd and Cr content of the effluent samples fromelectroplating industries and sewage farms located at Gowndampalayam,Ganapathy, Peelamedu, Ukkadam and Avarampalayam were above thetoxic level as prescribed by ISI standard limits for effluents. This might posea problem of heavy metal contamination in food chain, if it passeduntreatedly on the land (Fig.3)


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0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

Ni Pb Cd Cr Cu Zn

Con

tent(

S1 S2 S3 S4 S5

S1- Sewage water ; S2 - Electroplating ; S3 - Textiles ; S4 - Dying ;S5 Foundry

Fig. 3. Heavy metal characterization in various industrial effluents

The major constituent of tannery and textile effluents are are Cl-

, Naand Cr3+ which affect the soil health. Pickling is the process for tanning skinwhich includes treatment with H2SO4 and NaCl. By this process the proteinis made permanently resistant to bio degradation by commonmicroorganisms. Formaldehyde, unreacted acrylic monomers and toxicmetal-based pigment formulation are released form tannery industry thataffects soil quality. The effluents generated from tanning and textileindustries are characterized by high values of BOD, COD, Na and dissolvedsolids. Besides it also contains high amount of heavy metals especially Ni,Cr, Pb and Cd. The soil samples collected from industrial areas in Erodedistrict were assessed for its total heavy metal content and it was above

the critical limits (Table 2).

Table 2. Range and mean values of the total heavy metal content ofthe soil collected from Erode district

Place of collection

Concentration (mg kg-1)

Cr Ni

Range Mean Range Mean

RN Pudur 126 468 261 96 187 141

Agraharam (Big) 288 446 322 73 176 116Agraharam (Small) 98 156 103 66 178 125

Sunnambuoodai 147 5216 4314 76 788 126

Vairapalayam 129 589 357 55 169 134

Chavadipalayam 79 496 269 46 169 118

Pasur 63 146 109 64 189 138


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(Source : Krishnaasamy et al., 2004)

The addition of tannery effluents will cause deflocculation of soilparticles and will destroy the soil microstructure. Similarly, deleteriouseffects such as increase in sodicity, EC and pH have been observed by the

discharge of textile effluents on land. Salinization and alkalization of thesoil and ground water will occur under the land on which tannery and textileeffluents are applied.

The steel and allied industries, dispose huge amounts of basic slags.Similar to lime sludge, basic slag has ameliorative properties of acid soils,but high contents of iron and manganese in it will be additive to the ironrich acid soils. Moreover the slag is very hard to crush for use. Deposits ofthe by-product if remain unused may pollute the soil. During manufacture ofcement, small particles of lime stones in the form of dust, float inatmosphere and subsequently settle on the soil and vegetation causing

pollution.

Press mud, a by-product of sugar industries, although a good organicmanure, when disposed uncontrolled, the effluent increases the salt contentof the soil. The Thermal Power Plants use coal daily for combustion, as aresult of which, these plants discharge fly ash daily which is a rich source ofheavy metals such as iron, manganese, zinc, copper, lead, nickel,chromium, cobalt and radio active substances like thorium and uranium.These heavy metals leaking into the soil cause hazards to environment.

Phosphatic fertilizer factories release ammonia gas and sulphuric acidto the environment, which are absorbed in soil and cause toxicity.Phosphogypsum, the by-product of these industries deposited around thefactories cause soil pollution by release of free acid and excess sulphur. Thecomposition and volume of waste waters discharged vary from industry toindustry, but broadly the effluent is reported to contain toxic elements suchas Cd, Cr, Cu, Fe, Mn, Pb and Zn. Accumulation of heavy metals beyond thepermissible limits adversely affect the soil health and in turn, human andanimal health (Krishnasamy et al., 2004)

FertilizersSynthetic fertilizers with instant ability to refurbish depleted nutrients

is a key component for sustainable soil fertility management. However,more than 50% of fertilizer applied to crops is left behind as residues.Rajendra Prasad (2000) reported that, ammonia emanates from ureaapplied to agricultural fields contribute to acid rain, while nitrates producedin soil contributes to ground water pollution. The nutrient imbalance arises


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due to excessive use of single nutrient fertilizer have serious consequences.Commercial fertilizer may contain a great range of heavy metals but thehighest values for heavy metal are found in phosphatic fertilizers. Cdcontent in rock phosphates ranges from 1-90 mg/kg (Chhonkar, 2003).

Table 3. Total concentration of selected heavy metals and traceelements in fertilizers ( mg kg-1 on dry wt. basis)Fertiliz

ersAs Cd Cr Cu Pb Ni Zn Reference

Urea < 0.04 0.2 Nd 0.6 0.4 0.2 - Raven andLoeppert (1997)

DAP 9.9-16.2

4.6-35.5

5.5 2.41 2.1-3.7

7.4-222

10.3

Raven andLoeppert (1997)

MOP 0.4 0.2 1.0 2.35 0.4-10

0.2 4.59

Raven andLoeppert (1997)

SSP 10.3 15.0 133 3.5 11.0 17 159 Charter et al.(1993)

(Source : Chhonkar, 2003)

Sewage sludge

Sewage sludges are the discharges of city wastes in form of semiliquid to agricultural land through drains. These sludges contain heavymetals of lead, cadmium, chromium, zinc and mercury. Decline in soilmicrobial bio mass, metabolic activity and organic matter mineralizationhave been observed in soils receiving sewage bio solids. Pig and poultry

waste slurries commonly contain 600-900 mg Cu per kg but can contain asmuch as 2000 mg kg-1 (Channey and Oliver, 1996) and if spread on land ona regular basis could cause pollution problems in same soil.

Table 4. Heavy metal content (mg kg-1) of soils treated withsewage and solid waste around Hyderabad

Heavy metals Normal soil Treated soilLead 5.0 170.0Nickel 2.0 10.0Cobalt 5.0 7.0Cadmium 0.4 0.9Chromium 6.0 47.0

Jeevan Rao and Shanta Ram(1999)

Apart from specific industrial effluents, sewage effluents generatedout of the mixture of domestic and industrial waste water, are otherimportant metal contributors to the environment. The sewage generationper annum from 200 major cities of India is about 2600 mm3 (Rattan et al.,


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2000). The Coimbatore city consists of an unorganized set of sewersnumbering 21,000 (Somasundaram, 2001) running through various zonesand finally discharging the sewage into the sewage farm present inUkkadam. The concentration of heavy metals in sewage effluentsemanating from the different cities is of many folds higher than that of tube

well water.

Radio nuclides

Radioactive materials fall out from atmosphere and nuclear weapontest. The waste known as tailings comes from the mines and mills. Thetransfer of radio nuclides along the soil to plant pathway is of particularimportance in the terrestrial environment because of its position in the foodchain. The deposition of radio nuclides on the ground (soil and plant) is thefirst and, in many cases, the only link in the food chain by which theenvironmental contamination is transferred to human beings (excluding

processing losses). In the short term (up to a few weeks following theaccident), the activity deposited on agricultural plants is available forconsumption by human beings and by animals. Later on, the activitydeposited on the soil, as well as the activity that is removed from the plantby environmental processes, migrates in the soil. A fraction of the activitypresent in the soil is then taken up by the roots of the plant and transferredto its aerial parts (Rajarajan et al., 1998). The trees, which are growing inthat soil, yield deformed fruits. Fruits and leaves of some other trees whichare consumed (eg. drumstics) do not taste as sweet as before.

Plant litter is also recognized as a vector in radionuclide migration, as

a lateral transport, recycling or as substrate for mushrooms. For

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I theleaching loss rate exceeded the corresponding loss rate of dry matter sothat concentrations in the litter decreased with time (Sheppard andEvenden, 1990). Three modes of direct deposition of radio nuclides byplants have been identified: through leaves (foliar absorption), throughinflorescence (floral absorption) and through basal parts or surface roots(plant base absorption).

However, the magnitude of transfer depends on various factors: thephysico-chemical characteristics of the radioactive particles contaminatingthe soil, the age of the radioactive contamination, the chemical

characteristics of the radionuclide compounds, the agrochemical andphysical characteristics of the soil (Raja Rajan et al., 1998; Saradha et al.,1998; Balamurugan and Raja Rajan, 2000), the plant species concerned andclimatic conditions.

Biotic interferences

The ever-increasing population has tremendous pressure on landresources of the islands and the mangroves are being deforested for


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bringing move land under plough the feed the increasing population. Thesebiotic interferences are likely to affect the heavy metal distribution thus soilhealth is getting degraded. Siva et al (1990) reported that Mangrove mudsare the main reservoirs of heavy metals and mangroves forests are efficientbarriers to heavy metal transport. Higher concentration of Cr metal in the

highly disturbed soil may cause adverse effect on crops due to higher bioavailability in the absence of Mangrove barriers.

Specific elements/ heavy metals:

In the period of human history many novel chemicals have beencreated at the rate of 1000 per year. Without use of many of them humancivilization can not achieve the goals for sustainable development in mostof the economy's sectors, but the same time a very large number of themmay cause a serious damages, related also to the quality and safety ofagriculture products and soil productivity. The most widespread compoundsregarded, as pollutants are industrial chemicals of the types:Cd, Pb, Hg,As

etc.

Cadmium

Cadmium is group II B transition element that is relatively rare in theearths crust (Wood and Wang, 1983). The strong preference of Cd for SHcontaining ligands especially polythiols in enzymes and other proteins is theprincipal basis for its toxicity in biological systems. The presence of Cd inexcess amount may disturb Fe metabolism and cause chlorosis. Cd mimicsZns behaviour and influence the uptake, translocation and other metabolicfunctions of Zn. Major inputs of Cd to soil are due to application of

phosphatic fertilizers, municipal sewage sludge etc.

There are various factors which can influence the availability of Cd toplants viz., pH, CEC, nature and amount of clay minerals, hydrous oxides ofAl, Fe and Mn, organic matter, moisture regimes etc. The application oforganic matter to the soil reduce the availability of Cd by forming insolublemetal organo complexes.

Mercury

Mercury is usually collected from the mineral, mercury sulphide.Mercury is commonly used as fungicide because it is found to be toxic for

many organisms. Atmospheric mercury is usually produced during miningand refilling and incineration of garbage containing wastes from electricalequipment industries, manufacture of chlorine and caustic soda, productionof batteries, pharmaceuticals. Toxicity of mercury is greatest when it is anorganic form, produced by bio transformation of ionic mercury to methylmercury. This transformation is provided by bacterial action on thesediment-bound mercury. Methyl mercury dissolves in water and is easily


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absorbed by organisms. Methyl mercury vapours cause fatal poisoning, i.e.Mina Mata disease in epidemic form in Mina Mata Bay of Kyushu in Japan.This toxicant is persistent because it is not easily removed from the bodyand as a result mercury can remain in the body for 20 to 30 years. Toxicityfrom inorganic mercury is primarily an occupational disease resulting in

central nervous system damage and kidney failure.

Lead

Lead is often used in the manufacturing of storage batteries and asan anti knocking additive in gasoline. Other major sources of lead alsoinclude mining, smelting and refining of lead, nickel and copper ores andfrom automobiles. Lead is believed to cause hypertension, reproductivedisorders neurological and metabolic problems. The critical pointconcerning chronic toxicity of lead is that, it is chemically similar to calciumand therefore it is accumulated in the bone matrix. Whenever the body

triggers calcium release from bones, lead is also released into the bloodstream. This could cause high levels of lead to enter into the blood stream,possibly long after the body was exposed to the lead.

Arsenic

Arsenic is a semi-metal, which although toxic at high concentrations,is essential at very low concentrations for promoting growth. It is generallyused as an insecticide and as a hardener in the making of alloys and semiconductors. Use of pesticides containing arsenic results in elevated levelsof the metal in food and water pollution. Epidemiological studies have

indicated a correlation between low dosage exposure to arsenic and theincidence of cancers. Use of sewage effluents and the sludge is becomingmore common particularly for vegetable production in the suburbs of cities,but it is also proving a source of pollution of soil particularly because of itscontents of heavy metals especially As.

Strategies

The capacity of the fast shrinking soil resource to perform the criticalfunction of entire life support system is undergoing unabated degradationand deterioration due to aforesaid causes. However the country has to raisethe productivity to feed the exploding population, which will not be possible

without judicious management of the sustained soil health. Some of thestrategies to achieve good soil health are

Judicious use of agrochemicals viz., fertilizers and pesticides coupledwith organic manures, biofertilizers and biopesticides will be analternative viable option to reduce the risk of soil contamination

Prevention of degradation and pollution of soil resources through


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technically sound, eco-friendly and cost effective technologies forreducing the contaminants from the industrial effluents. Phytoextraction,the use of plants to extract toxic metals from contaminated soils, hasemerged as a cost-effective, environment-friendly cleanup alternative.

Regular monitoring and assessment of soil health is the need of the hourand a system of most appropriate soil health care measures are to beevolved

Increasing the awareness to stakeholders about the importance of soilhealth and also the serious health hazards resulting from the misuse ofthese valuable resources

Suitable models to predict the likely changes in soil health and itsconsequences to the ecosystem should be developed.

A Nation where agriculture, industry and service sector work togetherin symphony, absorbing technology thereby resulting in sustained wealthgeneration leading to higher employment potential and prosperous nation,these are the words delivered by president Abdul Kalam on his republic dayspeech. For achieving this, the aforesaid strategies should be managedtechnically and scientifically well and this will provide a sound solution interms of food security, environmental safety and overall human welfare.Concisely SOIL HEALTH CARE will make a Nation prosperous, healthy,secure, peaceful and happy.

IssuesSOIL DEGRADATION

Industrial wastesPesticides

Fertilizers

Sewage

RadionuclidesBiotic interference

SalinisationWaterlogging

StrategiesSOIL HEALTH CARE

Scientific and Technical

Management

Phytoremediation

INM, IPM. ISFM etcAlternative cropping

Regular monitoringDecision Support SystemsIncreasing awareness


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References

Agnihotri, N.P. 1999. Pesticide safety evaluation and monitoring. AICRP onpesticide residues, IARI, New Delhi, 173p.

Chandrasekaran, J. and Regupathy, A. 1993. Dissipation of carbosulfan incertain soils of Tamil Nadu. Pestology, 17(5): 38-48.

Chaney R.L. and Oliver. D.P. 1996. Sources Potential adverse potentialadverse effects and remediation of agricultural soil contaminants inextended abstracts of first Inter National Conference on Contaminantson the soil environment in the Australatia- Pacific Region. 18-23February 1996. Adelaide, Kulwer, London. 323-359.

Chhonkar, P.K. 2003. Organic farming : Science and Belief. Indian Soc. SoilSci., 51(4): 365-377.

GOI. 2002. Agricultural Statistics at a glance. Ministry of Agriculture, NewDelhi.

Hindu (1997). English Daily news paper on 18th February.

Jayakumar, R. 1995. Herbicide residues in soil plant water system. In :Agricultural Inputs and environment (ed. SP. Palaniappan). ScientificPublishers, Jodhpur,pp. 389-409.

Jeevan Rao, K. 1999. Pesticide pollution in Agriculture. J. Environment andPeople, pp. 14-19.

Jeevan Rao, K. and Shanta Ram, M.V. 1999. Soil contamination due to urbansolid wastes. Abstracts, 2nd international conference on contaminationin Soil Environment in the Australia-pacific region, p9-10.

Kalra, R.L. and Chawla, R.P. 1983. Studies on pesticide residues andpesticide pollution. Final Technical report of the PL 480 Project,Ludhiana, 230 P.

Khurana, M.P.S., Nayyar, V.K., Bansal, R.L. and Singh, M.V.2003. Heavy

metal pollution in soils and plants through untreated sewage water.In: Singh, V.P. and Yadav, R.N. (Ed.). Proceedings of the InternationalConference on water and environment. Allied Publishers, Pvt. Ltd.,New Delhi,pp 487-495.

Krishnamurthi, V.V. 1999. Monitoring of pesticide residues in lower Bhavaniproject canal water. Pestology, 23(8): 34-35.


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Krishnasamy, R., Chitdeshwari,T., Malarkodi, M. and Sherene. T. 2004.Heavy metal dynamics in soils : Implications for their mobility inecosystem and soil productivity. Final Technical Report, 2004 GOI-MEF.Tamil Nadu Agricultural University, Coimbatore.

Rajarajan, A., Balamurugan, J. and Sundararajan, A.R. 1998. Soil to croptransfer of iodine-131 in maize (Zea mays L.). Paper presented at theNational Seminar on Developments in Soil Science, held 16-19,November 1998, at Haryana Agricultural University, Hissar.

Rajendra Prasad. 2000. Nutrient management strategies for the nextdecade : Challenges Ahead. Fert. News, 45: 13-18.

Raven, K.P. and Loeppert. 1997. Trace element composition of fertilizers andsoil amendments. J. Environ. Qual.,26: 551-557.

Sheppard, S.C. and Evenden, W.G. 1990. Leaching of radionuclides from

decaying blueberry leaves: Relative rate independent ofconcentration.J. Environ. Qual. 19: 464-469.

Soil Health - An Overview

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