Salinity and Alkalinity

Rhizobium and Legume Root Nodulation
Leguminous Plants
The Discovery of Symbiotic Nitrogen Fixation
Rhizobium Classification
Cultural Characteristics
Genetics
Flavonoids Induce Nodualation
Novel Approaches to Extend Root Nodulation
Ecology
Infection
Lectins
Structure of the Nodule
Function of the Nodule
Nitrogenase Hydrogenase Interrelationship
Stem Nodulating Legumes
Factors Affecting Nodulation
Temperature and Light
Hydrogen Ion Concentration
Mineral Nutrition

Salinity and Alkalinity

Salinity and Alkalinity
Saline and alkaline soils are widespread in many parts of the world. In India, such soils prevail in the Indo-Gangetic basin in the north and are not suitable for raising food and fodder legumes. Salinity is caused by the accumulation of soluble salts of calcium, magnesium and sodium, mostly as chlorides and sulphates. Alkalinity is due to the predominance of carbonates and bicarbonates. Application of large quantities of gypsum can ameliorate these soils and render them fit for cultivation. Alternatively, pelleting leguminous seeds with gypsum can also help in the establishment of legume crops.

Some fundamental studies carried out with lucerne plants (Medicago sativa) under bacteriologically controlled conditions on agar slopes have revealed that Rhizobium can tolerate higher levels of all the above-mentioned salts than the corresponding host plant, which reflects the importance of evolving cultivars of leguminous crop plants capable of withstanding salinity rather than attempting to introduce salt-resistant bacterial strains into soil.

In lucerne, higher salinity/alkalinity levels decrease the formation of root hairs and the deposition of mucilage around the roots. Since it is now known that formation of a mucilaginous matrix around innumerable hairs on the root system is a necessary prerequisite in the rhizosphere of a legume for successful entry of rhizobia into roots, it is postulated that salinity / alkalinity in the root region impedes certain steps in the pre-infection stages of legume-Rhizobium symbiosis.

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