Phytoremediation for enhancing agricultural productivity of salt affected soils

Abstract

About 7% of world’s total arable land is classified as salt affected lands; while in India it is around 6.7 million hectare (mha). With the requirement for more food driving agriculture to find new areas and methods for greater productivity, the reclamation of the barren-lying salt affected lands attains utmost importance. Though there are multiple methods to manage and bring back such soils, vegetative remediation is of interest, being more cost-effective and environment friendly. The other methods (leaching, organic/chemical amendments) have restrictions depending on type of soil, availability of water, chances for loss of soil nutrients and beneficial micro-organisms; in addition to being more expensive to farmers. Phytoremediation can be defined as the cultivation of salt-tolerant or accumulating (halophyte) plants for the reduction of soil salinity and/or sodicity. There are several halophytes which can be grown at very high levels of electrical conductivity. For examples Eucalyptus occidentalis and E. sargentii (useful landscape trees) can withstand salinity over 30 dS m-1. About 290 tree species of economic importance have been documented which could tolerate salinity levels of 7 to 8 dS m-1. These plants provide multiple benefits like accumulation of salts from wider and deeper zones depending on its root system, simultaneously preventing its seepage into groundwater. Studies have reported three mechanisms of halophytes: excluder, accumulator, and conductor plants; which are to be considered while selecting plants for this purpose. Several plants have been studied by many researchers for its soil reclamation abilities. Phytoextraction was seen to be more beneficial for EC and SAR reduction under non-leaching conditions, over other treatment options. Salt uptake by different species were seen to vary from 90 to >5000 kg ha−1 year−1. In this aspect, the potential of native vegetation also needs to be taken into consideration. This achieves utmost importance in arid zones of western India where only salt tolerant species like like Khara Lana (Haloxylon recurvum), Lani (Salsola barysoma), Luni (Sueda fruticosa) etc. may be used. These halophyte shrubs have a prime role in the rehabilitation and reclamation of salt affected lands. The efficiency of extraction may further increase with adoption of integrated management techniques (combination with amendments, biological techniques, agricultural practices and land management process). Establishment of perennial trees also allow for a more extended period of remediation. However, there is a great need to develop the proper agro-management techniques and conditions to maximize productivity of halophytic species and for genetic improvement of halophyte characteristics.