Citation: Yadav, J.S.P., Sen, H.S. and Bandyopadhyay, B.K. Coastal soils -

Coastal Soils — Imperatives for Improved Management for Higher Agricultural Productivity and Issues Related to Livelihood Security with Special Reference to India

J.S.P. Yadav¹, H.S.Sen² and B.K.Bandyopadhyay³

Of all the major ecosystems, which factor in agriculture or food production, ‘coastal’ has a significant role, wherein about 50-70 % of the global population live within 100 km of the coastline covering only about 4 % of earth’s land. Besides, the ecosystem is highly risk prone and vulnerable causing colossal damage to lives and properties, and this is further compounded due to climate change. Agriculture, on the coastal plain is constrained by a number of technological, social or anthropological, and climatic factors limiting the productivity. The different problem soils, their characteristics and distribution, soil, water and crop related constraints along with management options have been discussed.

The paper highlights the role of drainage for desalinization of salt affected soils; influence of seawater intrusion for salinization of the field and need to develop location-specific optimization models; use of surface water for irrigation with minimum dependence on underground water; and need to develop location-specific integrated water management models under varying soil salinity and water management scenarios. For improved fertility management of crops on salt affected and lowlying soils integrated approach for supply of nutrients has been suggested in order to attain higher nutrient-use efficiencies and reduced expenditures. It also highlights the need for classification of lowlying soils including the problem ones with respect to soil quality. Because of higher rates of C sequestration and lower CH₄ emissions, coastal wetlands were found to be more valuable C sinks per unit area than other ecosystems in a warmer world, suggesting elaborate studies on monitoring SOC pool. In the field of improved crop management with reference to salinity and related constraints the factors affecting production system and the future research agenda by appropriate blending of biotechnology with traditional practices have been discussed. The need for a holistic ‘coastal’ watershed approach with focus on hydrology and conservation plans has been emphasized.

The paper also highlights the need for appropriate disaster management protocol and identifies the key strategies for integrated coastal area management for livelihood security with particular reference to climate change.

(Key words: Coastal ecosystem, Soil & water management, Crop management, Seawater intrusion, Integrated water management, Water quality & resource utilization, Soil quality, Carbon sequestration, Watershed approach, Integrated area management for livelihood security & rehabilitation, Climate change)

Introduction

Of all the major ecosystems, which factor in agriculture or food production being at the very base of poverty alleviation programme, ‘coastal’ has a significant role. Nearly 40 % of cities larger than 500,000 population are located in the coast. Overall, about 50-70 % of the global population

_____________________________________________________________________________ ¹ Former chairman, Agricultural Scientists Recruitment Board, ICAR, New Delhi, 110 012; ² Former Director, Central Research Institute for Jute & Allied Fibres (ICAR), Barrackpore, Kolkata 700 120; ³ Officer-in-Charge, Central Soil Salinity Research Institute, Regional Station Canning Town, South 24 Parganas, West Bengal, 743 329 [Address for correspondence, Postal: Dr. H.S.Sen, 2/74 Naktala, P.O. Naktala, Kolkata 700 047, West Bengal; Email: hssen2000@hotmail.com,hssen.india@gmail.com]

live within 100 km of the coastline covering only about 4 % of earth’s land (Poyya and Balachandran, 2008), thereby drawing heavily on coastal and marine habitats for food, building sites, transportation, recreational areas, and waste disposal. According to another estimate (Wikipedia, 2009^a), coastal areas (within 200 km from the sea) share less than 15 % of the earth surface area, and there is prediction that three-fourth of the world population are expected to reside in the coastal areas by 2025. In India, according to the Department of Ocean Development, there are 40 heavily polluted areas along the Indian coast (Dubey, 1993).Coastal ecosystems have an economic value beyond their aesthetic benefit supporting human lives and livelihoods. By one estimate (Poyya and Balachandran, 2008), the combined global value of goods and services from coastal ecosystems is about US$ 12-14 trillion annually—a figure larger than the United States' Gross Domestic Product worked out in 2004. Yet, the agricultural productivity in this ecosystem is generally lower than the country’s average. Different countries with coastal boundaries have varying proportion of the total area exposed to the sea, expressed as coast/ area ratio, which along with the total coastline length, population density and anthropogenic factors, topography and related soil properties, protection measures undertaken, and natural disasters caused by the sea and their interactions with climate and under-sea tectonic movement of the earth, influence not only the agricultural production but also the nature and extent of vulnerability of the ecosystem per se in a country.

The problems of livelihood in these areas are compounded manifolds owing to a series of technological, administrative and socio-economic constraints. Unfortunately, at the global level,

until very recently, not much serious and concerted attention has been paid for mitigating the

problems for sustainable development in the coastal ecosystem. Attempt for improving on the

agricultural front, which is the focal theme of this paper, though should be at the central stage from daily livelihood point of view in this ecosystem, is still in the back seat in majority of the areas. This is possibly because of the ‘slow-poisoning kind of effect’ of this sector, arising out of poor agricultural practice and/ or inability for the poor to pay for the commodities as a result of insufficient food production, that normally goes un-noticed among the poverty-stricken mass, vis-à-vis catastrophic effects with heavy toll on lives and properties due to climatic disasters. Exceptions are India, Bangladesh and possibly a few other countries paying concerted attention on the coastal ecosystem for improvement in agricultural front in particular.

‘Coastal plain’ is the landward extension of the continental shelf or the sea and used for agriculture and allied activities as well as for few other occupational purposes but is not always

distinctly differntiated from the other ‘main’ components included under the ecosytem (Table 1).

Rather, coastal plain may in some cases include few such main components within its spatial boundary, and are in dynamic equilibrium with each other. In other words, though at a given time the area under each is well demarcated and thus may be estimated with some degree of precision, it may alter, even considerably, over a long time from one component to another because of geomorphologic changes due either to or a combination of natural, hydrological and anthropogenic factors, in support of which there are plenty of examples all over the globe. This is mainly because of the vulnearable nature of the coastal ecosystem, much more than any other ecosystem.

Soils in the coastal plain, hereinafter also referred to as ‘coastal soils’, are flat, low lying land available for cultivation, nature and extent of which depend on various constraints and other factors influencing it. Soil and water management related constraints and factors affecting agricultural productivity along with issues related to integrated coastal area management impacting on livelihood security are discussed in this paper.

Coastal soil classes: Characteristics and distribution

Global overview: The global distribution and salient characteristics of coastal soils are presented in Table 2. Areas quoted under different soil groups do not appear to have been precisely made since the coastal plains are not yet well defined.

Indian context: Of the two coastlines in India length of the East coast is higher than that of the West. The continental shelf is more stable than the coast. The continental shelf of 0-50 m depth spreads over 1,91,972 sq km and that of 0-200 depth over 4,52,060 sq km area. The shelf is wide (50-340 m) along the East coast. The Exclusion Economic Zone is estimated at 2.02 million sq km.

Practically, no systematic study was earlier made to demarcate the coastal soils based on well-

Table 2. Main soil groups in coastal areas and associated characteristics

Soil group1	Estimated total area (x 106 ha)	Essential features and major locations at the coast
Histosols	275	Solanchaks often adjacent to coastal mangrove peats. It comprises soils formed in `organic soil material'.
Anthrosols	NA	Old cultivated sites, excluding paddy soils, formed or profoundly modified through human activities such as addition of organic materials or household wastes, irrigation or cultivation.
Leptosols	1,655	It accommodates very shallow soils over hard rock or highly calcareous material but also deeper soils that are extremely gravelly and/or stony.
Cryosols	1,800	Cryosols comprises mineral soils formed in a permafrost environment.
Fluvisols	350	Fluvisols are genetically young, azonal soils in alluvial deposits.
Solanchaks	260-340	Coastal salt lakes, lagoons, pans; soils of marine origin under mangrove; neutral chloride-sulphate soils of marine origin; acid sulphate soils of marine origin under mangrove.
Gleysols	720	Sandy to loamy, in riverine or coastal areas soils that, unless drained, are saturated with ground water for long enough periods.
Podzols	485	Sandy deposits affected by illuviation and cheluviation, coniferous vegetal cover with ash-grey subsurface horizon, bleached by organic acids.
Sesquisols	60	Usually ancient land surfaces truncated by modern coastal erosion or in close proximity to sea, older coastal plains.
Ferralsols	750	These are ‘classical', deeply weathered, red or yellow soils of the humid tropics, dominated by low activity clays, also known as Oxisols.
Planosols	130	These are acid, seasonally wet soils, contain lower clay content at the surface than in the slowly permeable deeper horizons.
Solonetz	135	This are soils with clay illuviation horizon that has a high proportion of adsorbed sodium and/ or magnesium ions, also known as alkali soils.
Calcisols	800	Calcisols are soils having substantial secondary accumulation of lime.
Alisols	> 100	Alisols are strongly acid soils with high activity clays in their subsoils.
Acrisols	> 900	Acrisols holds soils that are characterized by accumulation of low activity clays in an argic subsurface horizon and by a low base saturation level.
Luvisols	650	These are soils having marked textural differentiation within the soil profile, with the surface horizon depleted of clay but with accumulation of clay in a subsurface `argic' horizon.
Lixisols	435	This consists of strongly weathered soils in which clay has washed out of an eluvial horizon down to an argic subsurface horizon that has low activity clays and a moderate to high base saturation level.
Cambisols	1,500	These were formed under the influence of glaciation during the Pleistocene, partly because the soil's parent material is still young but also because soil formation is comparatively slow in the cool, northern regions.
Arenosols	900	This consists of sandy soils, both those developed in residual sands and those developed in recently deposited sands in deserts and beach lands.
Regosols	260	Regosols is a taxonomic rest group containing all soils that could not be accommodated in any of the other Reference Soil Groups. These are essentially shallow, weakly developed mineral soils in the initial stage of soil formation, present at all coastal landscapes.

¹ Reference Group of Soils on the basis of documents prepared by FAO: After endorsement of the World Reference Base for Soil Resources (WRB) as a universal soil correlation tool by the International Union of Soil Sciences (IUSS), the Reference Base (RB) working group endeavoured to promote the system further. Sources: FAO (2001), Finkl (2005), Beek et al. (1980)

defined scientific indices valid for the different sub-ecosystems in this country. Notable among the past works was that of Yadav et al. (1983) who suggested 3.1 million hectare area (including mangrove forests), while Szabolcs (1979) suggested 23.8 million hectare under coastal salinity in India. The coastal saline soil has been used by various workers almost synonymously with coastal soil per se which is not correct since all coastal soils are not saline in nature. None of the above estimates appears to have been made on sound scientific basis. However, the latest compilation made by Velayutham et al. (1998) on the soil resources and their potentials for different Agro-ecological Sub Regions (AESR) of India show total 10.78 million hectare area under this ecosystem (including the islands) in India, which was the first scientific approach for delineation of the coastal soils.

Factors limiting plant growth and management

Coastal soils in a number of situations are constrained by various technological factors limiting the agricultural productivity and therefore, merit attention. The salient factors are: (i) Excess accumulation of soluble salts and alkalinity in soil, (ii) Pre-dominance of acid sulphate soils, (iii) Toxicity and deficiency of nutrients in soils, (iv) Intrusion of seawater into coastal aquifers, (v) High depth to underground water table rich in salts, (vi) Periodic inundation of soil surface by the tidal water vis-à-vis climatic disaster and their influence on soil properties, (vii) Heavy soil texture and poor infiltrability of soil in many areas, (viii) Eutrophication, hypoxia and nutrient imbalance, (ix) Erosion and sedimentation of soil, and (x) High population density.

Seawater intrusion

Salinization is a major form of land degradation in agricultural areas, including the coastal soils. Statistics about the extent of total salt affected soils in the world vary according to authors; however, general estimates are close to 1 billion hectare, which represent about 7% of the earth’s continental extent. Although estimates are available of the total salt affected soils of the world (Abrol et al., 1988) no separate estimates for the coastal soils are yet available except for India (3.1 Mha, Yadav et al., 1983) and Bangladesh (1.4 Mha, Salim et al., http://www.preventionweb.net/files/8199_Salinity.pdf).

Salinity build-up in coastal soils takes place mainly due to salinity ingress of ground water aquifers, for which the main factors responsible are: (1) excessive and heavy withdrawals of ground water from coastal plain aquifers, (2) seawater ingress, (3) tidal water ingress, (4) relatively less recharge, and (5) poor land and water management.

Attempts have been made on modeling of ground water behaviour with respect to seawater intrusion. Salt (Maimone, http://cms.ce.gatech.edu/gwri/uploads/pdfroceedings/1999/MaimoneM-99.p) water intrusion takes several forms. Horizontal intrusion occurs as the saline water from the coast slowly pushes the fresh inland ground water landward and upward. Its cause can be both natural (due to rising sea levels) and man induced, (say, by pumping of fresh water from coastal wells) (Fig. 1a). Pumping from coastal wells can also draw salt water downward from surface sources, such as tidal creeks, canals, embayment (Fig. 1b). This type of intrusion occurs within the zone of capture of pumping wells, which is local in nature, where significant drawdown of the water table causes induced surface infiltration. A third of intrusion is called ‘upconing’ (Fig. 1c). Upconing also occurs within the zone of capture of a pumping well, with salt water drawn upward toward the well from the salt water layer or well existing in deeper aquifers. .

(a) (b) (c) Fig. 1 Different forms of salt water intrusion (a) horizontal movement towards supply well, (b) induced downward movement from surface sources such as creeks, (c) upconing beneath a supply well (Source: Maimone, http://cms.ce.gatech.edu/gwri/uploads/proceedings/1999/MaimoneM-99.pdf)

Under natural conditions, fully steady state conditions in ground water systems may not be achieved since recharge from surface water bodies and rainfall events cannot be controlled. However, steady state simulation of seawater intrusion phenomenon is of utmost priority for which different management models at varying degrees of success have been reported. One such optimization model was developed for planning and managing saltwater intrusion into coastal aquifer systems using the simulation/ optimization approach for (Da Silva et al., (https://repositorium.sdum.uminho.pt/bitstream/1822/8682/1/Optimal%20Management%20of%20Grondwater%20Withdrawals%20in%20Coastal%20Aquifers.pdf) managing water resources in the areas. The model suggests the best location of the wells with specific flow rate, and thereby, the best policies to maximize the present value of economic results of meeting water demands and to keep under control the saltwater intrusion. Besides, different practical approaches that can be employed for control of seawater ingress into aquifers are listed, applicability of which is subject to (Anon, http://megphed.gov.in/knowledge/RainwaterHarvest/Chap11.pdf) techno-economic viability. These are: (1) Modification of ground water pumping and extraction pattern, (2) Artificial recharge, (3) Injection barrier, (4) Extraction barrier, (5) Subsurface barrier, (6) Tidal regulators/ Check dam/ Reservoirs. In India very sporadic work has been done in this respect, as for example, in Tamil Nadu (Chennai) and along Saurashtra Coast in Gujarat state (Mangrol-Chorwad-Veraval area). More of such attempts at various locations should be tried out on pilot scales in India and other countries.

Soil salinity

Salt accumulation in soil affects plant growth in the coastal soil in much the same way as in inland soils except for the effects due to specific toxicity of ions under given situations. Three major types of salt affected soils exist in the coastal plain.

A. Saline soil or solanchak: Soils contain excess soluble salts ( > 4 dSm^-1) with below 8.5 and lower than 15. Salts are composed mainly of sodium, calcium and magnesium among the cations, and chloride, sulphate, carbonate and bicarbonate among the anions. In majority of the situations, salt concentration along with its composition at the crop root zone varies not only spatially but also temporarily depending upon the soil type, salt-rich ground water characteristics and its rate of recharge into the root zone, and nature and distribution of rainfall along with other relevant climatic parameters.

Salinity in soil has a dual effect on plant growth via osmotic effect on plant water uptake and specific ion toxicities (Sheldon et al., 2004, US Salinity Laboratory, 1954). Several factors, such as temperature, humidity, stage of plant growth, moisture, soil texture, soil fertility, etc., as well as their interactions influence plant response to soil salinity, which are not uniform and therefore present a complex mechanism. However, relative tolerance of crops to different salinity levels provide useful selection guidelines for saline soils for which an excellent review has been made by Maas (1986), which may not be applicable universally. A ‘threshold’ for a crop is defined as the value below which crop growth is generally not affected due to salinity. This threshold varies for different crops. According to Maas and Hoffman (1977) relative yield can be calculated using equation 1.

(1)

in which, = the salinity threshold (dSm^-1) and = the percent yield decrease per unit salinity increase.

B. Alkaline or sodic soil or solonetz: These soils contain exchangeable sodium in a quantity sufficient ( > 15) to interfere with the growth of most plants. In such soils is generally < 4 dSm^-1 but the higher than 8.5. The soil colloids are usually in a state of deflocculation. The saline-sodic soil, upon alternate wetting and drying, develop dense subsoil with a columnar structure, and such soils are designated as solonetz.

The alkaline or sodic clay colloids in a dispersed state cause poor physical properties primarily in respect of moisture and solute transport, aeration and thermal flux, thereby adversely affecting the plant growth. Nature and extent of the adverse effect depend not only on the soil type including nature and amount of clay, moisture and fertility level, but also upon nature and amount of salt in the soil solution and of the soil, as well as their interactions. In these soils when of the soil solution exceeds 8.5, availability of some nutrients may be restricted resulting in nutrient imbalances.

The relative tolerance of various crops to is given as: wheatgrass > barley > wheat > rice > tall fescue > oats (Pearson and Bernstein, 1958), which may not be valid universally. An exhaustive review on response of plant to nature and extent of salt and sodicity in soil has been made by Gupta and Abrol (1990).

C. Acid sulphate soils: Acid sulphate soils either contain sulphuric acid or have the potential to form sulphuric acid when exposed to oxygen in the air. These soils occur naturally in both coastal (tidal) and inland or upland (freshwater) settings, as a consequence of the deposition of large amounts of organic matter, such as decaying vegetation, in a waterlogged setting. These waterlogged wetlands and mangroves or highly reducing environments are ideal for the formation of sulphide-containing minerals, predominantly iron pyrite (FeS₂) in sulphidic material, which can react with the oxygen in the air to form sulphuric acid (sulphuric materials). Left undisturbed, these soils are harmless, but when excavated or drained, the acid drains into waterways, or reacts with carbonates and clay minerals in soils and sediments to form sulphates – liberating dissolved iron, calcium, magnesium and other elements such as copper (CSIRO, 2009).

Most acid sulphate soils occur in the tropics, in low lying coastal land formerly occupied by mangrove swamps. Their most important characteristics are a field of below 4 and a generally high clay content. Other properties such as organic matter content and cation exchange capacity may vary widely. The total area of actual and potential acid sulphate soils is rather small: about 10 million hectares are known to occur in the tropics, and the world total probably does not exceed 14 million hectares in South and Southeast Asia, West and Southern Africa, and along the South American and Australian coastlines. In addition, some 20 million hectares of coastal peats, mainly in Indonesia, are underlain by potential acid sulphate soil.

The growth of most dry land crops on acid sulphate soils is hampered by the toxic levels of iron and aluminium and the low availability of phosphorus. Toxic levels of dissolved iron plus low phosphorus are the most important adverse factors for wetland rice. In the near-neutral potential acid sulphate soils (Sulfaquents, Sulfic Fluvaquents), high salinity, poor bearing capacity, uneven land surface, and the risk of strong acidification during droughts are the main disadvantages. Young acid sulphate soils (Sulfaquepts) in which the pyritic substratum occurs near the surface are often more acidic than those soils (Sulfic Tropaquepts, Sulfic Haplaquets) in which this horizon is found at greater depths.

Soil & water management

Drainage and desalinization: Leaching requirement is related to , of irrigation water, and to, root zone salinity, through the expression (Rhoades, 1984):

(2)

where, is the salinity of the saturation extract of the soil at 10 percent reduction in yield. The total depth of water that needs to be applied to meet both the crop demand and the leaching can be estimated from the equation:

(3)

where, is the irrigation water depth, is the crop evapotranspiration, and is the leaching fraction.

Leaching requirement depends largely, among other factors, on the irrigation water quality and method employed, soil texture, salinity tolerance limit of the crop grown, etc.

Adequate drainage for desalinization of the soil and removal of water congestion needs necessary attention along with appropriate flood control measures in the coastal low-lying areas. Different aspects of flood control and drainage in coastal areas have been discussed (CSSRI Canning, 1988, Rao, 1991) with respect to India. It was suggested that the land should be protected from tidal inundation through protective embankments, generally, with 3:1 slope at the river end and 2:1 slope in the country end having 1 m free board above the high tide level. Brick pitching of the earthen embankments, wherever possible, and planting of wind breaks (Nanda and Rai, 1979) in areas having problems of coastal sand dunes proved useful. It was suggested to install one-way sluice gates on the river banks or any other suitable location to drain out excess water from the land during low tides in river. Specific design of the sluice gates will depend on the drainage coefficients which have been worked out for different coastal tracts in India (Druvanarayana, 1977, Rao and Dhruvanarayana, 1979). Few attempts made in other countries for successful desalinization of heavy textured coastal soils along with improvement of soil properties include use of subsurface tile drains combined with moling perpendicular to the former (Moukhtar et al., 2003), and open surface drains along with moling perpendicular to it (Abdel-Mawgoud et al., 2003), both conducted in Egypt, and subsurface drains alone, in Portugal (Mann et al., 1982).

Significantly, efforts were made to develop models to desalinize the salty soil through drainage under specified conditions. Different agro-hydro-salinity models, viz. ‘SALTMOD’, ‘DRAINMOD-S’ or ‘SAHYSMOD’ (Oosterbaan, 2002, 2005), developed based on sound principles of moisture and solute transport, for unconfined (phreatic) and semi-confined aquifer, have been tested in the field mostly under arid or semi-arid conditions in order to predict the water distribution and salt balance in the soil profile following different practices of drainage and their response on crop function. A study was undertaken to simulate the effect of different drain depths on the amount of drainage water, root zone salinity, and depth of water table in the Konya–Çumra Plain, Turkey. SALTMOD model was tested with data collected from the Karkın pilot area and effects of current irrigation–drainage practices on root zone salinity and drain discharge rate were evaluated (Bahceci et al., 2006). SALTMOD model was also applied in coastal clay soils of Andhra Pradesh in India where subsurface drainage system was laid out at several drain spacings. The study suggested that the model could be used with confidence to evaluate various drain spacings of subsurface drainage system and facilitate reasonable prediction of the reclamation period (Singh et al., 2002). Further, relative performance of artificial neural networks (ANNs) and the conceptual model SALTMOD was studied in simulating subsurface drainage effluent and root zone soil salinity in the coastal rice fields of Andhra Pradesh, India (Sarangi et al., 2006). Three ANN models, viz. Back Propagation Neural Network (BPNN), General Regression Neural Network (GRNN) and Radial Basis Function Neural Network (RBFNN) were developed for this purpose. Considering coefficient of determination, model efficiency and variation between the observed and predicted salinity values as evaluation parameters, the SALTMOD performed better in predicting root zone soil salinity and the BPNN performed better in predicting the drainage effluent salinity. Therefore, it was concluded that the BPNN with feed forward learning algorithm was a better model than SALTMOD in predicting salinity of drainage effluent from salt affected subsurface drained rice fields. Singh and Singh (2006) compared different models suggesting design of the most appropriate location-specific drainage system under varying water management scenarios covering salt water intrusion, runoff, soil erosion, backwater flow, waterlogging and salinity in the coastal plains in India.

Use of amendment: For non-saline sodic soil, incorporation of relatively soluble calcium salt like gypsum, phosphogypsum, iron salt like pyrite, CaCl₂, sulphuric acid (H₂SO₄), or other acid formers like sulphur (S), lime-sulphur (9 % Ca + 25 % S), ferric sulphate, aluminum sulphate, etc. to replace exchangeable sodium from the clay complex, along with recommended water and crop management practices, have been reviewed by many, notable among them was by Gupta and Abrol (1990), for reclamation of these soils in general. Occurrence of non-saline sodic soil is, however, much less in the coastal plain than in inlands, and, in case of the former, attempts made for experimental verification have mostly been limited to the use of locally available organic waste, like paper mill sludge or other industrial effluent as well.

Management for acid sulphate soils: For reclaiming or improving potential and young acid sulphate soils following approaches have been suggested: (i) pyrite and soil acidity can be removed by leaching after drying and aeration, and (ii) pyrite oxidation can be limited or stopped and existing acidity inactivated by maintaining a high water table, with or without (iii) additional liming and fertilization with phosphorus, though liming may be often uneconomic in practical use. The reclamation method cited at (ii) above, for maintaining a high water table to stop pyrite oxidation and inactivate existing soil acidity, has the advantage that its effects are usually noticeable much quicker. Upon waterlogging, soil reduction caused by microbial decomposition of organic matter lowers acidity and may cause the pH to rise rapidly to near-neutral values. Such attempt was made by O’Sullivan et al. (2005) in Australia which is one of the worst sufferers (Thomas et al., 2003). The method is particularly suitable with rice cultivation, but even in oil palm plantations in Malaysia, maintaining a shallow water table has given far better results than deeper drainage with intensive leaching. The crucial factor is, of course, the availability of fresh water for irrigation. The less toxic and deeper developed older acid sulphate soils are moderately suitable for rice and can be improved by sound agronomic practices (Beek et al., 1980). In the Muda irrigation project in Malaysia, where patches of Sulfaquepts occur among better soils, improved water management and intensive irrigation have dramatically increased the productivity of these highly acid soils.

Large scale engineering schemes for reclaiming potentially acid, and usually strongly saline, coastal swamp are however rarely economic. The injudicious reclamation of seemingly suitable land in coastal swamps by excluding salt water through diking and by excavating fishponds has led to the destruction and abandonment of thousands of hectares of mangrove land in Southeast Asia and Africa. However, Beek et al. (1980) were also of the view that unless sufficient fresh water is available and other pre-requisites for good water management exist, the potential acid sulphate soils as young and strongly acidic in character should not be reclaimed, but are better left for other types of land use, say conservation, forestry, fisheries and, sometimes, salt pans, etc.

In India, for the coastal acid sulphate soils of Sundarbans, application of lime, superphosphate and rock phosphate have been found beneficial in improving the soil properties and rice growth (Bandyopadhyay, 1989). Application of Ca-rich oystershell, which is available in plenty, was found beneficial, if applied in powdered form, as an inexpensive alternative soil ameliorating agent. In this soil continuous submergence for one year could not improve the soil properties substantially.

Mongia et al. (1989), while reporting for two soils in Andaman Islands observed that application of lime and phosphorus may be beneficial for lowland rice, but the soils should be leached of excess salts in case of high soil salinity before using these amendments. In another study on mangrove (Avecenia marina) muds in this island, it has been reported that liming significantly depressed the concentrations of Al, Mn and Fe. Exchangeable Al content also decreased with lime application. The depression of exchangeable Al may be due to precipitation of trivalent Al and Al (OH)₃ in the presence of high concentration of OH^- ions. Lime application, in general, also reduced the exchangeable and extractable Fe contents of the soil.

Integrated water management: The coastal plain represents, in majority of the cases, aquifer present at large depths containing fresh water, which has no consequence to salt accumulation in the crop root zone, but are often combined with water table, rich in salts, present at a very shallow depth (generally not exceeding a depth of 2 m below the soil surface). The net salt loading in the root zone will be positive (salinity will build up) or negative (desalinization will take place) depending upon the relative rate of recharge of salts by upward rise to rate of downward flux of salts by leaching. The relative salt loading will thus be treated generally as positive during dry season, and negative (waterlogging on the soil surface) during wet season due to high rainfall, and the process will be repeated each year in a seasonally cyclic mode.

IWMI analyses that globally, out of 110,000 cubic kilometers rainfall received annually, about 56 % is evapotranspired by various landscape uses including forest products, livestock grazing lands and other forms of biodiversity, and 4.5 % by rainfed agriculture, in addition to another 2 % utilized for irrigated agriculture, aquaculture and livestock mainly through withdrawal from the ground water. The balance about 38 % comprises of evapotranspiration losses from other open surface sources including rivers, wetlands, lakes, etc. for supporting aquaculture, other forms of biodiversity (1.3 %), cities and industries (0.1 %), and runoff losses (36 %) to the ocean (Molden, 2007). Thus, in the field of agriculture, while 4.5 % of rainwater is used for rainfed cultivation only 2 % of the total rainwater is used for irrigated agriculture mainly by withdrawing water from the underground. The colossal loss of 36 % water holds the key to create higher storage opportunities by reducing the runoff losses. In the coastal plain being at the lowest topographical elevation, the scope for intervention of runoff amount received from the upper reaches should be much higher, and thus the scope for higher storage.

On the other hand, in view of the susceptibility of the coastal plains to seawater intrusion and its adverse impact on soil and plant growth, the practice for use of ground water, even if in small quantity, for irrigation should be very carefully exercised, for which suitable optimization model may be used as discussed earlier, if not eliminated altogether. It should not be difficult to avoid using the underground water, if properly planned, by increasing the surface storage of runoff water by an equivalent amount or more. Thus, water management in the coastal plains should principally revolve round creating more fresh surface water sources and their proper management with little dependence on the subsurface source in order to maintain stability of the ecosystem.

In spite of the coastal ecosystem presenting a delicate equilibrium among the different components, there is, however, no firm strategy, as of now, for exploitation of water resources for irrigation and other purposes for long term solution in any sector. The European Commission (2007) observed, based on a study by Spanish researchers, how an inappropriately planned coastal development could lead to increasing water consumption to unsustainable levels, due to which future planning for sustainable development, based particularly on water resources, should be such as not to disturb the ecosystem in the long run. The degradation of the environment through pollution, which has so far been neglected, will need to be given serious consideration particularly for the coastal soils.

Sen and Oosterbaan (1992) presented a practical working method on integrated water management for Sundarbans (India) through surface gravity induced drainage during summer/ wet season (through land shaping)-cum-excess rainwater storage for irrigation during dry season. They computed for the same region drainable surplus, which may be stored for irrigation during dry (deficit) period. Ambast and Sen (2006) developed a computer simulation model and a user-friendly software ‘RAINSIM’ for the same, primarily for Sundarbans region for small holdings, based on the hydrological processes, and the same tested duly for different agro-climatic regions in India. The software may be used for (i) computation of soil water balance, (ii) optimal design of water storage in the ‘On-farm reservoir (OFR)’ by converting 20 % of the watershed, (iii) design of surface drainage in deep waterlogged areas to reduce water congestion in 75 % of the area, and (iv) design of a simple linear programme to propose optimal land allocation under various constraints of land and water to arrive at a contingency plan for maximization of profit. They also reported use of remote sensing and GIS in mapping lowland lands, vegetation, crop yield estimation, along with performance assessment of irrigation/ drainage systems. Similar models may be tested and validated under wide variety of situation in India and other countries.

Improved irrigation water sources and methods: No single irrigation method can be expected to be universally the best, particularly as the criteria applied may not be the same. We do not intend to make any detailed discussion on different practices here but would like to highlight that in actual practice, application efficiencies of surface systems range between about 30 and 60% with the latter figure being found in modern, well designed and managed systems; sprinkler systems generally achieve efficiencies in the range of 60–85%, and drip systems commonly operate at 85–95% efficiency (Rawitz, 2008).

Different sources of irrigation water, other than surface freshwater storage, are discussed below.

(i) Marginally saline water

Water quality or suitability for use is judged on the potential severity of problems that can be expected to develop during long term use. Water quality problems, however, are often complex and the principal considerations for evaluation are: (i) the type and concentration of salts in water; (ii) nature of soil-water-plant interactions to affect plant growth; (iii) the expected severity of the problem following long term use of the water; and (iv) the management options that are available to prevent, correct, or delay the onset of the problem (Ayers and Westcot, 1994).

Minhas and Rao (2007) and Gupta (2008) discussed the prospects for use of poor quality water on soil properties and plant growth in coastal plains with special reference to India. The former workers emphasized the use of fresh water layer floating on the denser (saline) underground water through skimming, while both suggested the use of fresh water alone stored at the surface as well as consumptive use through judicial combination of saline and fresh water available at the surface and at subsurface depths. The scope for consumptive use for improvement of crop yield is though limited, it is a useful way of vegetable production, in particular, in some countries, particularly in coastal areas having limited fresh water resources. In Hanoi (Viet Nam), say, 80% of vegetables are irrigated with water mixed with wastewater, while, in Kumasi (Ghana), informal irrigation, much of it using wastewater, covers 11,900 hectares, about a third of the officially recorded irrigated area of the country (Molden, 2007).

(ii) Ground water skimming

Various skimming well configurations such as single, multi-strainer, radial collector and scavenger wells are possible to selectively abstract fresh water from thin layers overlying saline ground water. Single well is used in unconfined aquifers in most parts of India, while multi-strainer well with relatively shallower penetration than single well can be used for water table control with diminished upconing in fresh layer of restricted depth. There are sporadic reports on the use of these systems in different marginally saline regions in India. Scavenger wells involve simultaneous abstraction of fresh and saline waters through two wells having screens in different quality zones for controlling the rise of interface. Radial collector wells consisting of an open well and input radial drains on one or more sides involve shallower penetration than a single vertical well operating at the same discharge. Since the radial drains collect water from shallow depths, upconing of saline water from lower depths is prevented (Minhas and Rao, 2007).

Large diameter open skimming wells with sump based Doruvu technology is operated on a large scale in coastal sandy soils of Andhra Pradesh in India. The system popularly known as “Improved Doruvu Technology” is becoming popular among the farmers of the region. This Doruvu system coupled with sprinkler/ drip was found to yield sufficient water for irrigating 3 ha of field crops and 4.5 ha of plantation. Each Doruvu occupies an area of about 200 m² and the water collected from each is sufficient to irrigate 800 m² . As such 10-12 Doruvus are needed for 1 ha area. Using skimming water, the farmers are raising paddy, tobacco, chilli nurseries, vegetables, flowers plants and groundnut using jerries which can reduce water drop effect on tender plants. Besides this, the system also could supply water for dairy and drinking in rural areas (Minhas and Rao, 2007).

(iii) Seawater desalination

Large scale desalination typically uses extremely large amounts of energy as well as specialized, expensive infrastructure, making it very costly compared to the use of fresh water from rivers or groundwater. The large energy reserves of many Middle Eastern countries, along with their relative water scarcity, have led to extensive construction of desalination in this region. By mid-2007, Middle Eastern desalination accounted for close to 75% of total world capacity. The world's largest desalination plant is the “Jebel Ali Desalination Plant (Phase 2)” in the United Arab Emirates capable of producing 300 million cubic meters of water per year. The largest desalination plant in the United States is the one at Tampa Bay, Florida, which began desalinating 25 million gallons (US Gal.) (95000 m³) of water per day in December 2007. The Tampa Bay plant runs at around 12% the output of the Jebel Ali Desalination Plants. World-wide, 13,080 desalination plants produce more than 12 billion gallons of water a day. (Wikipedia, 2009^b). Another major desalination plant is planned for development in the Wonthaggi region to supply up to 150 billion litres of water a year to Melbourne and other cities in Australia. It will be capable of providing around a third of Melbourne's annual water supply and will commence by the end of 2011. The plant will use approximately 90 megawatts of electricity from the Victorian energy grid, which will be offset through the purchase of renewable energy credits (State Government of Victoria, 2009). Its use for irrigation purpose is, however, subject to reduction in the cost of production, which should take place significantly, and its benefit relative to other social uses.

In India, since 1970, there has been significant commercial development using various desalination technologies, including distillation, reverse osmosis and electrolysis (Kumar et al., 2005). This technology is suitable for use in areas where freshwater is scarce, but saline water is available and energy is cheap. Desalination, as currently practised, mostly uses fossil fuels. Solar and wind energy are available in abundance in India and may be explored as alternative sources for this purpose in the coastal states. Current production cost is about Rs 50 per m³. Many facilities in coastal region are using reverse osmosis for desalinization. For example, at Kalpakkam reactor, Tamil Nadu, 1.8 million litres of water is being produced per day. It is expected that as the cost comes down and alternate energy sources are used, desalinization would become commercially viable in the next 6 to 8 years.

(iv) Weather modification

Weather control is the act of manipulating or altering certain aspects of the environment to produce desirable changes in weather; in the present context, rain formation through cloud seeding. This is a common technique intended to trigger rain, but evidence on its effectiveness is mixed. It is used, however, in several different countries, including the United States, the People's Republic of China, and Russia through the use of silver iodide or dry ice in cloud (Wikipedia, 2009^c).

It is thus suggested that location-specific programme on water allocation under different sources should be drawn up for each country, based on all relevant parameters, with the overall target to increase water productivity and cropping intensity phasewise, and conserve the ecosystem at the same time.

Fertility management

Integrated nutrient management: With regard to soil fertility, the coastal soils are usually rich in available K and micronutrients (except Zn), low to medium in available N and are having variable available P status (Bandyopadhyay et al., 1985, Bandyopadhyay, 1990, Maji and Bandyopadhyay, 1991). Major portion of the applied N fertilizer is lost through volatilization (Sen and Bandyopadhyay, 1987).

Effect of salinity on the microbial and biochemical parameters of the salt affected soils in Sundarbans (India) was studied at nine different sites. The study revealed that the average microbial biomass C (MBC), average basal soil respiration (BSR), and average fluorescein diacetate hydrolyzing activity (FDHA) were lowest during the summer season, indicating the adverse effect of soil salinity (Tripathi et al., 2006). It was suggested that integrated nutrient management should be very effective for increasing its use efficiency for higher and sustainable yield of crops (Bandyopadhyay et al., 2006, Tripathi et al., 2007). Bandyopadhyay and Rao (2001) were of the opinion to introduce systems approach involving organic, inorganic and biofertlizers compatible with the farmers’ practice. In coastal soil at Tamil Nadu (India), application of agro-industrial wastes significantly improved soil organic carbon, pH, EC and soil bacteria, fungus and actinomycetes population and enhanced the soil fertility status (macro and micro nutrients) and improved the crop productivity of finger millet. Application of pressmud @12.5 t ha^-1 recorded better growth and yield of finger millet followed by composted coirpith @ 12.5 t ha^-1 (Rangaraj et al., 2007). Use of green manure crops like Sesbania spp. (S. aculeata) has been proved very suitable for saline alkali soils (Keating and Fisher, 1985, Rao, 1986, Evans and Rotar 1986). In favourable climate with proper management, these crops accumulate well over 100 kg N ha^-1, mostly through biological N fixation, in 50-55 days, thereby increasing the yield of the following rice crop significantly (Singh et al., 1991). Likewise, application of green leaves of Glyricidia maculata @ 10 tonne ha^-1 to the puddled soil before rice transplanting has been found comparable in terms of yield with inorganic fertilizer application of N, P and K at 100, 50 and 50 kg ha^-1, respectively (Chavan and Dongale 1994). Buresh and De Datta (1991), however, were of the view that leguminous green manure and its residue normally are able to meet only partially the N requirement for the following high yielding rice variety. They focused attention on the high loss of N under the anaerobic-aerobic soil cycles typical of legume-lowland rice sequence, as well as under higher production of methane and nitrous oxide from the low land rice field. However, in view of rising energy cost and limited input availability, recycling of organic wastes and use of renewable sources of biofertilizers, viz. rhizobium cultures for pulse or legume, and blue-green algae for waterlogged rice field may play a significant role in terms of integrated nutrient management for rice in coastal saline soils (Kundu and Pillai, 1992).

Long term field experiment in coastal saline soils in India showed that rice and wheat yield could be maintained even at 50% NPK used in conjunction with FYM or green manure (DARE, 2003-04). In a detailed long term experiment conducted (CSSRI, 1990) in Sundarbans (India) it was observed that grain yield of crops in a rice-barley rotation increased significantly only due to the application of N. Application of P did not show any significant increase in the yield of crops in the initial 8 years, after which the yield of barley alone increased due to P application. Available K content was high in the soil. The experiments conducted so far showed that a basal dose of 11 kg P ha^-1 for rice and 5.5 kg P ha^-1 for barley or for similar upland crops should maintain the fertility status of the soil, whereas the K application may be omitted without any detrimental effect on soil fertility or crop growth. The K removal by the crop was compensated by K added through accumulation and release of non-exchangeable sources.

Soil quality: The importance of improved soil quality in the coastal plains through higher SOC level of the soils was highlighted by Mandal et al. (2008). Very recently, IRRI characterized lowland rice soils (excluding deepwater rice) in Asia in respect of soil quality (Haefele and Hijmans, 2009), and the study included large areas under coastal plains (Fig. 2). They grouped soil qualities into four categories. These were: Good, Poor, Very Poor and Problem soils. ‘Good’ and ‘Poor soils’ represent those with different degrees of weathering but without major constraints; ‘Very Poor’ represents soils with multiple chemical constraints (acidity, deficiency of phosphorous, or toxicities of iron and aluminum); while ‘Problem soils’ represent those with the most frequently cited soil problems, including acid sulphate, peat, saline, and alkaline soils, which partly cause low fertility, and partly soil chemical toxicity.

The above classification raises the issue as to whether or not the problem soils should also be scale-dependent with respect to soil quality assessment? A soil’s quality should be assessed for quality regardless of factors rendering it ‘problematic’ in nature. Amelioration of a ‘problem soil’ should therefore be a pre-requisite for quality assessment, and should not form a separate group as such. Detailed characterization of the coastal plains in respect of soil quality should be undertaken in order to plan for improved fertility management practices with a systems approach for higher and sustainable development in India and other countries. Research so far provides strong indication that low lying coastal soils may be a useful sink for higher organic carbon pool for the terrestrial system.

Crop management

Production system: The coastal areas in countries, in general, are endowed with abundant sunshine, solar as well as wind energy, precipitation, diverse soils, physiography, climate, etc. and therefore, have tremendous opportunities for supporting a host of perennial and annual crops like trees, fruit plants, cereals, root crops, pulses, oilseeds, commercial crops, vegetables, etc. Suitable crop cafeteria should be developed for specific agro-ecologies Several factors, such as temperature, humidity, stage of plant growth, moisture, soil texture type of soil fertility, etc., as well as their interactions, however, influence plant response to soil salinity, which is not uniform and, therefore, present a complex mechanism. Relative tolerance of crops to different levels provide useful selection guidelines for saline soils for which an excellent review was made by Maas (1986) listed in Table 3. A ‘threshold’ ECe for a crop is defined as the value below which crop growth is generally not affected due to salinity. The threshold ECe varies for different crops. According to Maas and Hoffman (1977) relative yield can be calculated using equation 4.

(4)

in which = the salinity threshold (dSm^-1) and = the percent yield decrease per unit salinity increase.

Ambast et al. (1996) described a suitable crop cafeteria for maximizing productivity under rainfed system in Sundarbans (India). Multi-tier cropping systems involving arable, horticultural and plantation crops, as well as agro-forestry, should be given appropriate attention for better land use in a given location. Several benefits relating to sustainability and profitability accruing from the integrated farming have been described by Yadav (2008).

Future strategy of crop improvement, which is possibly the most important component of crop management programme, lies in the evolution of better varieties using appropriate breeding programme. This should be coupled with improved agro-input management practices suited to

Table 3. Relative tolerance of plants

Crop	Tolerance level	Electrical conductivity (dSm-1), ECe		Crop		Tolerance level	Electrical conductivity (dSm-1), ECe
		Thresh-old ECea	50% Yield ECea				Thresh-old ECea	50% Yield ECea
Field crops
Barley	High	8	18	Bermuda	High		7	14
Cotton	High	9	17	Vetch	Moderate		3	8
Sugar beet	High	7	15	Alfalfa	Moderate		2	9
Sorghum	Moderate	5	12	Clover	Low		2	5
Wheat	Moderate	9	12	Veg. & Fruits
Cowpea	Moderate	5	9	Broccoli	Moderate		3	8
Peas	Low	3	5	Spinach	Moderate		2	9
Corn	Low	2	6	Tomato	Moderate		2	8
Rice	Low	3	4	Bean	Low		1	4
Grasses & forages				Strawberry	Low		1	3
Wheat grass tall	High	8	19	Pineapple	Low		1	3

^a‘Threshold’ is the salt level below which crop yields generally are not decreased significantly; 50 % Yield ECe refers to the salt concentration at which crop yield is only 50 % of normal yield attainable at threshold ECe values.

harsh agroecological environments, viz. salinity, alkalinity, acidity and flooding, as well as shallow, semi- and deep-water conditions. The objectives of breeding are development/ identification of genotypes with higher genetic yield ceiling and consolidation of the already achieved yield gains. We need improved seeds/ germplasm for varietal improvement suitable for the adverse ecosystem.

Earlier there was a freedom of germplasm exchange across the countries though CGIAR and other systems which provided benefit to all for varietal improvement programme. Global trade issues, conflict of interests and dominating roles of private sectors on seed/ vegetable business and uncertain roles of CGIAR today have posed a different challenge we must address. Improved crop improvement strategies are lacking, therefore attention should be focused on emphasis on biotechnology for harsh coastal environments for different crops. Genetically engineered salt/ drought tolerant crops should create great impact in changing agricultural scenario in the coastal regions as well (Datta, 2008). However, one might not lose sight of the role of traditional breeding using genetic material adapted to harsh conditions over ages through natural screening, and therefore the ideal strategy should be an appropriate blend of the traditional practice with biotechnology.

Crop improvement strategies in rice: Rice is the natural choice almost throughout the coastal areas for which a major attention should be paid for improvement in its breeding and crop protection strategies. Salt stress in rice seldom occurs in isolation and is always coupled with mineral deficiencies and toxicities, which compound the problem of salt stress (Ismail et al., 2007). Majority of the associated soil stresses include Zn deficiency, Fe toxicity, P deficiency, and also submergence tolerance. Thus, in breeding rice for saline environments, multiple abiotic stress tolerance must be considered. Most of the varieties developed so far through conventional breeding approach are target specific and have narrow genetic background. To increase the parental control it is thus desirable (Singh et al., 2008) to broaden the genetic base and break the stubborn linkages, employ a modified Diallel Selective Mating System (DSMS) at IRRI, and use a permanent breeding scheme for the development of the multiple abiotic stress tolerant genotypes for wide adaptability after slight modification of the Diallel Selective Mating System (DSMS) suggested by Jensen (1970). Ismail et al. (2007) aimed to develop resilient varieties tolerant to salinity and submergence stress. They attempted to combine Sub1A with tolerance to longer duration partial flooding common in coastal areas, as well as with tolerance to salt stress conferred by Saltol, with long term goal to ensure higher and stable food production in coastal areas.

It is important, however, to take stock of the varieties (Singh et al., 2008) released so far in different countries through traditional breeding approach. For example, Philippines has released many IRRI developed materials, like IRRI 112 as PSBRc48 (Hagonoy), IRRI 113 as PSBRc50 (Bicol), IRRI 124 as PSBRc84 (Sipocot), IRRI 125 as PSBRc86 (Matnog), IRRI 126 as PSBRc88 (Naga), and IRRI 128 as NSICRc106. In other countries also, many salt tolerant rice varieties have been released for commercial cultivation like CSR10, CSR13, CSR23, CSR27, CSR30, CSR36, Lunishree, Vytilla 1, Vytilla 2, Vytilla 3, Vytilla 4, Panvel 1, Panvel 2, Sumati, Usar dhan 1, 2 & 3 (India); BRRI dhan 40, BRRI dhan 41, BRRI dhan 47 (Bangladesh); OM576, OM2717, OM2517, OM3242, AS996 (Vietnam); and Giza 177, Giza 178, Sakha 104, Sakha 111 (Egypt).

Recent advances in biotechnology particularly in cell and tissue culture, molecular biology and functional genomics as innovative tools for enhancing resistance against insect pests and stabilizing rice yield have been reviewed by Pandey et al. (2008). In a study by FAO/ IAEA on biotechnology for crop improvement at Latin America induced mutations were found to be very effective (Maluszynski, 2002) to obtain mutants carrying different single resistance genes effective against the different lineages of the blast pathogen (Pyricularia grisea). Mutant lines exhibiting a partial resistance to rice pathogens such as rice hoja blanca virus and/or its vector (Tagosodes oryzicolus) in Colombia and Cuba, and stem rot in Uruguay have been documented. These mutants can also be used effectively in crosses for the development of rice cultivars with resistance to these pathogens which have no known resistance genes.

Improvement strategies in other crops: Both breeding and screening germplasm for salt tolerance, in general, for different crops encounter the following limitations (Arzani, 2008): (a) different phenotypic responses of plants at different growth stages, (b) different physiological mechanisms, (c) complicated genotype × environment interactions, and (d) variability of the salt affected field in its chemical and physical soil composition. Plant molecular and physiological traits provide the bases for efficient germplasm screening procedures through traditional breeding, molecular breeding, and transgenic approaches. Salt tolerance in several plant species may operate at the cellular level, and glycophytes are believed to have special cellular mechanisms for salt tolerance. Ion exclusion, ion sequestration, osmotic adjustment, macromolecule protection, and membrane transport system adaptation to saline environments are important strategies that may confer salt tolerance to plants. Cell and tissue culture techniques have been used to obtain salt tolerant plants employing in vitro culture approaches. Doubled haploid lines derived from pollen culture of F₁ hybrids of salt tolerant parents are further regarded as promising tools to further improve salt tolerance of plant cultivars. Enhancement of resistance against both hyper-osmotic stress and ion toxicity may also be achieved via molecular breeding of salt tolerant plants using either molecular markers or genetic engineering.

Methodology for induced mutations by FAO/ IAEA in citrus cuttings using the irradiation method was successfully modified and applied for the development of desired new germplasm with such agronomically important characters as seedlessness, reduced plant growth or thin skin in Latin America. Besides, the phenomenon of high level mutant heterosis was confirmed on a large scale experiment with gamma ray induced wheat mutants in Chile. Similarly, the heterotic effect was also observed in some experiments with barley and rice in other countries (Maluszynski, 2002).

Carbon sequestration

Soil is the world’s largest terrestrial C sink, and is estimated to contain approximately 1600 Pg of C to a depth of one metre (Eswaran et al., 1993). According to West and Post (2002), C sequestration rates in agricultural soils averaged 57 ± 14 g m^–2 yr^–1, mainly through biomass production, reaching a steady state condition within 15 to 20 years.

According to American Geophysics Union and American Waterworks Union the wetlands along the shore could sequester three to eight tons of carbon dioxide per acre every year (Anon, 2008). In a study sediments in a southern California, USA coastal lagoon–wetland complex were cored, radiocarbon dated, and depositional environments were interpreted (Brevik and Homburg, 2004) over a period of 5000 years. This study demonstrated that high levels of organic C are sequestered per unit volume of sediment (35.9±3.2 kg m⁻³), and the mean rate of C accumulation was high (0.033±0.0029 kg C m⁻² year⁻¹) over a long time period (5000 years). Hoffman and Titus (1983) identified the primary factors that might influence future rates of sea level rise, which, in turn, would influence C sequestration in coastal marsh ecosystems. In general, most soil forming processes are so slow that the impact of sea level rise on soil properties should be studied over a long time period. Hussein et al. (2004), in a significant study over the period from 2100 to 2300 AD, established two transects across submerging tidal marsh soils in coastal landscapes in Dorchester County, Maryland to model C sequestration (Fig. 3). Future C sequestration during the first 100 yr would range from 250 to 570 g m^–2 yr^–1, averaging 400 ± 162 g m^–2 yr^–1, which is much higher than the global average at present. Modeling C sequestration thus indicated that coastal marsh ecosystems tend to sequester C by accumulation in the organic horizons continuously with increasing storage capacity as marsh age progresses and its area increases. Thus, C sequestration in coastal marsh ecosystems under positive accretionary balance acts as a negative feedback mechanism to global warming. Choi and Wang (2004) were, however, of the opinion that dynamics of carbon cycling in coastal wetlands and its response to sea level change associated with global warming is still poorly understood. Because of higher rates of C sequestration and lower CH₄ emissions, coastal wetlands could be more valuable C sinks per unit area than other ecosystems in a warmer world. Brigham et al. (2006) stated that the estuarine wetlands sequester carbon at a rate about 10-fold higher on an area basis than any other wetland ecosystem due to high sedimentation rates, high soil carbon content, and constant burial due to sea level rise.

In India, possibly the first ever study made by Bhattacharyya et al. (2000) about a decade back showed SOC pool in two soil strata under different physiographic regions including coastal (Table 4). The data on coastal soils based on soil analyses covering 43 soil series showed the SOC data vary from 2.4 Pg to 10.9 Pg from 30 cm to 150 cm soil depth. It was not clear from the study about the sites of sampling. It should be worthwhile to create databank on SOC and related factors of the past, using radiocarbon dating for wider coverage, for monitoring the changes in India and other countries, and relate them with sea level rise and other relevant factors.

Table 4. SOC stock in different physiographic regions of India (Source: Bhattacharyya et al., 2000)

	SOC stock (Pg)
	Soil depth (cm)
Physiographic region	0-30	1-150	Area (m ha)
Northern Mountains	7.89 (39)1	18.31	55.3
The Great Plains	3.28 (18)	10.53	72.4
Peninsular India	3.64 (17)	13.34	54.7
Peninsular Plateau	3.62 (17)	10.11	105.7
Coastal plains and Islands	2.24 (11)	10.90	40.9
Total	20.99 (100)	63.19

¹ Figure in parenthesis indicates percent of total SOC stock

Watershed approach

In India, the major scheme, namely National Watershed Development Project for Rainfed Areas (NWDPRA) was launched by the Government of India in 1990-91 in 25 States and 2 Union Territories including coastal areas based on twin concepts of integrated watershed management and sustainable farming systems without, however, mandates specifically addressed for the coastal ecosystem. There are, however, a few attempts to address the problems of coastal watersheds by non-government agencies in minor scale in India and few other countries, but lack holistic approach. Significantly, in India UNESCO sponsored a 3-year watershed project on “Salinity Moderating and Proofing of Coastal Aquifers”, which was launched in 2006 in Auroville Bioregion covering 1400 sq km on the Kaluvelly watershed, with the objectives to fight saline water intrusion and sustain all water resources with active participation of users and stakeholders.

Although watershed includes lakes, rivers, estuaries, wetlands, and streams as well as ground water that drains to a common surface water body, a unit present in the coastal ecosystem may not necessarily drain to a common point on a river (Rivernet Watershed Access Lab, 2008). The coastal watershed is characterized broadly, different from inland watershed, by salinity gradients at the mouth of rivers, which are important hydrologically and ecologically, and presence of salt wedge with the incoming tides at the estuaries, where a river meets up with the ocean, resulting in a combination of fresh and salt water known as brackish waters. Coastal watersheds not only include tidal influence but also sea-spray influence. The salt water spray affects even the salinity of the freshwater watershed.

A watershed approach is essentially holistic in nature and for coastal ecosystem, in particular, hydrology and water management form the core components. Thus, for countries with significant coastline having high degree of vulnerability along with low productivity and various socio-economic constraints, either the regions should be clearly identified as ‘coastal watersheds’, or the regions within the existing watersheds should be delineated with focus on hydrology and conservation plans for sustainable solution.

Focus for the coastal watershed areas: The focus should be on conservation plan on those lands and waters that are most important for conserving living resources — native plants, animals, and natural communities — and also of water quality. The Land Conservation Plan should be separately formulated and, if necessary, enacted to prioritize for implementation with location- specific regional strategies for improving productivity of agriculture and other activities, for which areas under different regimes of salinity and hydrology should be identified for appropriate activities, and protecting shorelands for livelihood security. Other specific target areas are maintenance of hydrology of rivers and streams and improvement of surface water storage, estimation of the water balance of the entire watershed through integrated approach of drainage and surface water recharge by appropriate modeling, conservation of flood water discharge from uplands or inland ecosystems for recharging surface water resources, mitigation of problems arising out of sedimentation, seawater intrusion, pollution, hypoxia, eutrophication, etc., sustenance of the ecology as diverse habitat for wildlife, flora and fauna, abundant wetlands, clean water, productive forests, and creation of outstanding recreational opportunities, most importantly, not in piecemeals, into the future with active participation from all stakeholders and public enterprises.

Integrated coastal area management for livelihood security

A multifaceted approach to disaster management

The number of people living within 100 km of coastlines will increase by about 35 percent in 2050 as compared to that in 1995. This type of migration will expose 2.75 billion people to coastal threats from global warming such as sea level rise and stronger hurricanes in addition to other natural disasters like tsunamis (Goudarzi, 2006). The incidents on natural disaster are on sharp increase with time, and the death toll of humans and animals, and along with it proportionate loss of wealth and properties, are horrifying. The enormity of loss of human lives alone can be guaged from the five deadliest toll in the history recorded (Wikipedia, 2009^d) so far as 2-4 million due to China floods (China) in 1931, 0.9-2 million due to Yellow River flood (China) in 1887, 0.5 million due to Bhola cyclone (Bangladesh) in 1970, ≥ 0.3 million due to India cyclone (India) in 1839, and 0.23 million due to Indian Ocean tsunami (India, Sri Lanka, Indonesia, etc.) in 2004. The coastal ecosystem is thus extremely vulnerable due to various natural disasters punctuated by climate change, yet highly important region from economic, ecological, social, and recreational points of view, warranting special attention for rehabilitation with improvement and sustenance in productivity. The multifaceted approach to the management of coastal resources (Scialabba, 1998) has become known as integrated coastal area management (ICAM) or integrated coastal zone management (ICZM).

Salient issues for disaster management: Pomeroy et al. (2006) observed in the wake of the Asian tsunami tragedy, that large volumes of aid and a vast array of actors flew into the affected areas. There is a real risk when rehabilitation responses to this and future disasters developed from simplistic thinking and dominated by easy and ill-considered options, such as replacing lost boats and gear, which can lead to increased fishing capacity, further creating unsustainability of stocks and threats to livelihoods, or providing equipment and infrastructure for new income generating schemes that are poorly suited to the local context. In other words, rehabilitation of coastal livelihoods is not merely about giving people jobs; it requires addressing fundamental social, economic and environmental reforms that affect coastal communities and livelihoods. Notwithstanding, sound integrated coastal planning and management (ICM) must not be beset with contradictions since low-cost programmes on how to save lives are often ignored at vulnerable locations, as experienced in Indonesia following tsunami of 26 December 2004 (Samarakoon, 2007). This was evidenced by the tsunami of 17 July 2006 which killed about 600 people in Java. Sudmeier-Rieux et al. (2006) viewed in the direct aftermath of a disaster that organizations and professionals involved in humanitarian assistance and in environmental management need to work together more closely to develop workable solutions and bring about real integration on the ground. They recommended modular approach on Integrated Disaster Risk Management Cycle suggested by Dolcemascolo (2004), subject to its adaptation based on individual case.

Empowering rural knowledge centre and use of GIS: According to Kesavan and Swaminathan (2006), the imminent threat to livelihood security is from a vicious spiral among environmental degradation, poverty and climate change related natural disasters interacting in a mutually reinforcing manner. The M.S. Swaminathan Research Foundation at Chennai has developed biovillage paradigm and rural knowledge centres for eco-technological and knowledge empowerment, with pro-nature, pro-poor and pro-women orientation, of the coastal communities at risk. Yumuang (http://www.Disaster livelihhod\SYSTEMATIC GEOGRAPHY AND INTEGRATED COASTAL ZONE MANAGEMENT (ICZM) FOR THAILAND.htm) provided some new key concepts and ideas of systematic geography that can be applied in integrated coastal zone management (ICZM) for Thailand. The important tools for studying the fields of systematic geography include: cartography, geographic information systems (GIS), remote sensing, mathematic modeling, and statistics.

Tenure and property rights: The general absence of tenure and property rights with legal forms of representation has been a major obstacle faced by coastal resource users because they were dependent mainly on customary rights (Samarakoon, 2007). Failure to safeguard livelihoods and diminishing income from natural resources was driving increasing numbers of these unskilled and semi-skilled workers to foreign employment, particularly in Bangladesh, India and Sri Lanka where most of the coastal poor lived. A “remittance windfall” has resulted despite governance failure. Carefully designed tenure rights are an instrument that can provide cohesion and political power to enable negotiation for improved governance. The Government of India has enacted Coastal Regulation Zone Act in 1991, considering the vulnerability and importance of the coastal ecosystem, in order to regulate and monitor the activities and their progress. The act defines the coastal stretches as seas, bays, estuaries, creeks, rivers and backwaters which are influenced by tidal action, in the landward side, up to 500 m from the high tide line (HTL) and the land between the Low Tide Line (LTL) and HTL or the intertidal zone, as the CRZ.

National and international initiatives

Apart from the strategies listed above a large number of national and international disaster warning systems and collaborations using advanced electronic and telecommunication networks have been initiated at various levels, a detailed account of which has been presented by Yadav (2007).

Climate change and livelihood

While climate change is not the only threat to natural resources and livelihoods, climate-induced changes to resource flows will affect the viability of livelihoods unless effective measures are taken to protect and diversify them through adaptation and other strategies. The debate over climate change has now reached a stage where all but the most extreme contrarians accept that, whatever may happen to future greenhouse gas emissions, we are now locked into inevitable changes to climate patterns. Many, including the scientists working with the Intergovernmental Panel on Climate Change, (IPCC), have concluded that these changes are already underway. The emergence of this consensus has led to increasing attention being paid to the issue of how to respond (IISD, 2003).

For too long the whole climate change debate has focused at the global level, both in terms of global climate and in relation to the global economic and political system. A Task Force meeting organized in November 2001 by IUCN – The World Conservation Union, the International Institute for Sustainable Development (IISD) and the Stockholm Environment Institute (SEI) was a non-governmental response to the emergence of adaptation as the leading issue in the global climate change debate. It seeks to inform and challenge conventional wisdom in this field, and in particular, to bring together the different perspectives needed for successful adaptation. These perspectives come from four main constituencies—disaster reduction, climate change action, biodiversity conservation, and poverty alleviation—each with their own understandings and responses to the climate change dilemma. Drawing from each of their experiences and emerging priorities, the Task Force identified the need for an integrated approach to climate change adaptation based on the livelihoods of vulnerable communities (IISD, 2003).

The Task Force has tried to present a rationale for adopting an adaptation approach that reduces climate-related vulnerability through ecosystem management and restoration activities that sustain and diversify local livelihoods. This calls for a greater emphasis on micro-level approaches to vulnerability reduction and a closer collaboration between disciplines, agencies and sectors to scale up these activities and integrate them into emerging policy frameworks, needless to mention, with priorities on poverty reduction (IISD, 2003). The guidelines suggested appear to have direct relevance to the coastal ecosystem as well.

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