REMOTE-SENSING TECHNIQUE FOR MAPPING SALT-AFFECTED SOILS

The salt affected soils of Etah, Aligarh, Mainpuri and Mathura districts have been mapped into S 1: < 10 per cent of the area covered by salts, S2: 10-30 per cent, S3: 30-50 per cent, S4: 50-75 per cent and S5: > 75 per cent using an integrated approach of image interpretation. The dull white tone of salt affected and sandy soils have posed problems in their discrimination, on TM false colour composite, however, the problem of spectral similarity was solved through integration of interpretation of thermal data (10.4-12.5 mum) with TM FCC (bands 2, 3, 4) interpretation. The discrimination of salt affected soils was significantly better on data between March and first week of April because of maximum contrast. Out of 1.75 m ha of the total geographical area, the salt affected soils account for 11.8 per cent. Another 16.2 per cent is likely to be affected with this problem if similar degraded conditions prevail there. The values of pH: 8.7 and ECe: 1.3 dsm-1 of S1 soils group them into non saline and mildly alkali class. Similarly low ECe: 4.4 dSm-1 and high pH: 9.8 for S3 soils and high ECe: 24.0 dsm-1 and very high pH: 10.7 of S4/S5 soils, placed the soils into alkali and sodic classes respectively. The gypsum requirement based on pH values varies from 1 to 15 t ha-1.