ABSTRACT
More than 800 million ha of land throughout the world is affected by salt levels. The soil types most affected by excess salt are found in 30% of Australian soils (Flowers and Colmer 2008). Excess salt in soils can have two origins: (i) natural causes, i.e., weathering of parent rocks, deposition of oceanic salts carried in wind and rain (10 mg/kg of NaCl would deposit
1Laboratoire de Biologie et Physiologie Végétales (LBPV), Faculté des Sciences Exactes et Naturelles, Université des Antilles et de la Guyane, BP. 592, 97159, Pointe-à-Pitre, Guadeloupe, France. 2Laboratoire Commun de Microbiologie (LCM) IRD/UCAD/ISRA, Centre de Recherche de Bel Air, BP. 1386, CP. 18524 Dakar, Sénégal. 3Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM), UMR113, Campus de Baillarguet, A10/J, 34398 Montpellier, Cedex 5, France. 4Département de Mycologie et de Botanique, Université de Lille, BP. 83, F-59006 Lille cedex, France. *Corresponding author: amadou.ba@ird.fr, amadou.ba@univ-ag.fr
10 kg/ha of salt for each 100 mm of rainfall per year); (ii) human causes, i.e., excess amounts of fertilizers, irrigation with brackish water (20% of irrigated lands in the world are affected), and (iii) increased sea level caused by global climate changes. Subsequently, two main groups of salted soils exist: saline soils (soluble salts) and alkaline sodic soils (adsorbed sodium). Saline soils affect plant growth without changing the physical properties of soil. Soil is classifi ed as saline when electrical conductivity ECe is ≥ 4 dS m-1 (~40 mM or 2.4‰ NaCl) and generates an osmotic pressure of 0.2 MPa. Saline soils cover 397 million ha worldwide (FAO 2005). Sodic soils affect plant growth and soil structure by saturating the adsorption complex by Na+, which causes soil structure to evolve to an unstable state of dispersion. This can be overcome through the fl occulant power of Ca++ from gypsum (CaSO42H2O). Soil is classifi ed as sodic when Exchangeable Sodium Percentage (ESP) is ≥ 15% of cation exchange capacity. Sodic soils cover 434 million ha worldwide (FAO 2005).
