Characterization and Problems of Saline/Sodic Vertisols and Their Management Options

Abstract

Soil degradation resulting from salinity, sodicity, or a combination of both is a major impediment to optimal utilization of soils in the world. It is a prime threat to land resources, resulting in large economic and associated social consequences. The relative significance of soluble salts depends on natural drainage conditions, soil properties, groundwater quality, irrigation water quality, and management practices. Saline–sodic Vertisols and their intergrades occur in different parts of the world. The majority of these soils occur in lower piedmont plains or valleys. They are mainly derived from the basaltic alluvium and have a clay texture with smectitic clay with a high swell–shrink potential, very low hydraulic conductivity, and imperfect drainage. The productivity of these soils is limited. Taxonomically, these salty soils are classified as Sodic Haplusterts and Sodic Calciusterts. There is an increase in pH in subsoil associated with an increase in the exchangeable sodium percentage (ESP) toward lower horizons. These soils have high concentrations of neutral salts and sodium in the exchange complex. The very high clay content of these soils can be attributed to their formation from basaltic parent material. These soils do not show any salt efflorescence on the surface. Initiation of alkalinization is operative in these soils in subsurface layers as a consequence of salt accumulation and its progress in an upward direction along with capillary rise of soil solution during dry periods. The soils are strongly to moderately alkaline with an ESP of 5–26. The soils are reported to be calcareous in nature with a tendency toward an increase in calcium carbonate with depth.

The saline/sodic Vertisols in the Purna River valley have a higher clay content of smectite at the subsurface and are prone to severe problems of drainage. These soils pose serious problems owing to high exchangeable sodium, poor physical condition, and nutrient deficiency. The problems of these soils are native sodicity, poor hydraulic conductivity, high calcium carbonate, compact and dense subsoil, incomplete leaching of salts due to poor drainage, and high swell–shrink potential, resulting in water stagnation in the kharif season and wide cracks in the dry season. Soil chemical degradation in terms of increases in ESP and the exchangeable magnesium percentage (EMP) in saline–sodic Vertisols adversely affects hydraulic and other properties important for crop growth. Clay dispersion leads to destabilization of the soil structure and breaking of the soil capillary network, ultimately affecting the water transmission characteristics of the soil.

The decadal change in soil degradation in the Purna valley shows that there has been an increase in pH along with the ESP of the soils over a period of time under the prevailing climate. The soil degradation in the Vertisols of the Purna valley demonstrates that despite low levels of sodicity, the soils have low hydraulic conductivity due to large amounts of smectite clay and high exchangeable sodium in the subsoil. Management options are available for amendment and sustainable productivity of salt-affected swell–shrink soils. The use of amendments (gypsum), land configuration, tillage, and improvements in drainage need to be instituted for amelioration. Innovative approaches include crop residue incorporation, green manuring with dhaincha and  sunhemp, and application of organic manure, compost, and spent-wash press-mud compost. Integration of chemical amendments and organic conditioner, along with bio-inoculants, has been found to be beneficial in improving the air–water relationship in sodic soils. Distribution of gypsum in a powdered form before sowing of crops, and mixing of it into surface soil, are recommended for increasing the productivity of cotton, sorghum, and green gram, besides improving the physical and chemical characteristics of sodic soils in the Purna valley.