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Aromatic Plants as a Tool for Phytoremediation of Salt Affected Soils

Introduction

Soil, a non-renewable resource, is central to all primary production system. ‘ Salt-affected’ is a general term used for soils which contain soluble salts or exchangeable sodium and/or both, in such amounts that can retard growth and development of plants. Such soils cause reduction in crop yield and are required to be managed and remediated for sustainable agriculture. Mostly, salt-affected soils exist in arid and semi-arid regions but are also found in some humid to sub-humid climatic areas, where conditions are favourable for their development. Over the years, in countries like India, due to high population rate, the landmass has suffered from different types of extreme pressure on crop lands and also from degradations. In arid and semi arid region, indiscriminate use of canal water for irrigation often causes accumulation of harmful salts in soil which limits crop productivity. Salt affected soils are distributed in 120 countries covering 1074 M ha and it reduced crop productivity to 7-8% at the global scale (Yadav 2003). In India, about 6.74 M ha (Table 1) land has been affected by salinity and alkalinity problems in different parts of country comprising Uttar Pradesh, Gujarat, West Bengal, Rajasthan, Punjab and Haryana (Figure 1). These types of land are either lying barren or producing less than their normal potential. Most of the traditional agricultural crops on majority of such soils either failed to grow or would give very poor return without substantial investment on reclamation of these lands. Sometimes, the problem of secondary salinization is more serious, since it usually represents losses of productive agricultural lands. The vast occurrence of soil salinity and alkalinity is a serious factor adversely affecting targeted crop production and economic utilization of land resources. This necessitates either development of land by suitable reclamation and management practices or its proper utilization by growing salt tolerant crops.

Phytorernediation is one of the important options for reclamation of salt affected soil. “Phytorernediation is the application of plant-controlled interactions with groundwater and organic

Table 1. Extent and distribution of salt affected soil in India and in the world.

Distribution of salt affected soils in India (based on map prepared by NRSA, Hyderabad, CSSRI Kamal and

Figure 1. Distribution of salt affected soils in India (based on map prepared by NRSA, Hyderabad, CSSRI Kamal and

LUP, Nagpur).

Salt affected soils

Saline soils (million ha)

Alkali soils (million ha)

Coastal saline soils (million ha)

Total (million ha)

India

1.711

3.788

1.246

6.744

World

676.8

239.28

157.92

1074

Source: www.cssri.org; FAO (2008).

and inorganic molecules at contaminated sites to achieve site-specific remedial goals”. Plants are known to reduce the pollution load of the environment by absorbing certain toxic metals or chemicals through their roots and translocating or accumulating them in less toxic forms in various parts. In phytoremediation method, natural conditions of the environment can be sustained. It is the least destructive method among the different types of remediation methods. Most plants, when grown in contaminated areas, uptake and translocate toxic elements to the harvestable parts. Polluted environments are remodeled using phytoremediation as a sustainable strategy to lower the pollution load.

India is endowed with natural abimdance of diverse flora including enormously large number of aromatic plants which have the potential to grow in wide range of soil including salt affected soil and unculturable waste land. As a result of research and development carried out by various laboratories under Council of Scientific and Industrial Research (CSIR), Indian Council of Agricultural Research (ICAR) and the state and central universities, India has made significant progress in the production and processing of aromatic plants. Evidence from research being carried out in recent past reveals that some of these aromatic plants are well suited to saline and alkaline soils than the traditional agricultural crops because of their tolerance to salts and high benefit cost ratio. Some aromatic glasses, Vetiver (Vetiveria zizanioides (Linn) Nash), Palmarosa (Cymbopogon martinii var. motia), Lemongrass (Cymbopogon flexuosus) and Java citronella (Cymbopogon winterianus), appear suited for growth in salt affected soils, able to withstand salinity in soil and irrigation water to a great extent than traditional agriculture crops. Besides having a usually high benefit to cost ratio, aromatic grasses could be usefiil sources of high value, as essential oils that are in great demand in the cosmetic, pharmaceutical, and flavouring industries of India and abroad. In the following discussion, information regarding the use of aromatic glasses for phytoremediation in saline sodic condition has been presented.

 
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