The soil samples were collected and analysed for particle size distribution, pH, EC, CaCO3, organic carbon, cation exchange capacity and exchangeable cations. The soils are slightly alkaline (pH 8.5-8.9), having low electrical conductivity (0.05-0.8 dsm-1), low organic carbon (0.01-0.4%) and variable calcium carbonate content. The low organic carbon content (<0.4%) of these soils is due to limited biological activity and rapid decomposition of biomass under the prevalent torric conditions.
Based on the difference in soil texture, drainage and profile development, the soils were grouped into five soil series. The soil - physiographic relationship was established. The soils were classified as per Soil Taxonomy (Soil Survey Staff, 1996) as Ustic Torripsamments (Soil Series 1 and 2), Coarse loamy Ustic Haplocambids (Soil Series 3 and 5), Fine loamy Ustic Haplocambids (Soil Series 4). The final soil map (Fig. 1) was prepared on 1:50,000 scale.
Ground Water Quality
The ground waters of study area are alkaline in reaction (pH >7.0). These waters have varying levels of salinity (0.31 to 2.36 dS m-1), SAR (0.40 to 21.57 [me L-1]½) and RSC (nil to 10.60 me L-1) with a mean value of 1.24 dS m-1, 9.97 (me L-1)½ and ---- me L-1 respectively. Sodium is the dominant cation and its value ranged from 0.43 to 34.78 me L-1. Among the anions, HCO3- concentration varied from 1.0 to 13.0 me L-1 with a mean value of 5.88, whereas concentration of Cl- and SO42- varied from 0.75 - 12.25 and 0.21 - 14.17 me L-1, respectively.
Depending upon the EC and RSC values (Sood et al., 1998), the ground waters of the area have been grouped into three ground water quality categories viz. good, marginal (sodic) and poor. The ground water quality map (Fig. 2) of the area shows that the category-I (good) occupy 35 per cent of total geographical area of the block. Since these good quality ground waters have least salinity and sodicity hazard, their use over the years is not likely to be hazardous in the soils having clay content even >30% which are fairly to moderately well drained with water table not shallower than 1.5 metre.
Marginal-sodic ground waters occupy highest area (59%) of the block. These waters are low in EC and calcium but high in sodium and bicarbonate. The indiscriminate use of these waters will result in precipitation of calcium and magnesium as insoluble carbonates thereby, building up higher levels of exchangeable sodium in the soil exchange complex. This will lead to formation of dispersed and relatively impermeable soils. These waters can preferably be used in light textured, well drained and permeable soils, if good quantity of organic manures are added. The poor quality ground waters which are unsuitable for irrigation due to high EC, RSC or both occupy six per cent of total area. These waters should not be used for irrigation purposes otherwise they will cause serious problems of soil salinization and sodification ultimately severely restricting the crop yields and deteriorating the soil healthy.
Landuse
Landuse mapping of the study area has been undertaken using two dates IRS 1B LISS II data. Five major landuse categories at level I were identified and mapped (Fig. 3). These categories have been subdivided based on the differences in tone, texture, pattern, association etc. and eleven categories at level II were identified and mapped. The map was rechecked using April 1996 data. There are 34 inhabited and one uninhabited villages in this block. The study reveals that more than 89 per cent of TGA of the block is double cropped and only 4.32 per cent area is single cropped. The area under settlements and village ponds is 3.46 and 0.36 per cent respectively. Nearly, 2.28 per cent of TGA is under wasteland category which includes salt-affected, waterlogged and sandy areas.
Resource Constraints
The study area has a variety of problems associated with soil and water which are listed below :
- Arid and semi-arid climate
- Low, erratic, ill-distributed rainfall
- High wind velocity especially during summer months (April-June)
- Poor underground water in large area (65%)
- Thick sand cover (sand dunes) in some area.
- Poor retention of water and nutrients in coarse textured soils.
- Inadequate and erratic supply of canal water.
- Poor marketing facilities and absence of processing units especially for horticultural produce.
Based on the information on landuse, soils and ground water quality, the following major constraints in the study area were identified (Table 1) and a resource constraint map of the area was prepared on 1:50,000 scale (Fig. 4)
- Poor ground water quality.
- Coarse textured soils primarily in sand dune areas.