Abstract:
In the North-Eastern region, abstraction of ground water brings lot of iron from the subsurface layers to the surface. The deposition of iron takes place on the surface and in the sub-surface soil due to continuous use of iron-rich groundwater for irrigation. Installation of 1,00,000 Shallow Tube Wells (STW) during the 9th plan under NABARD's funding and another 47,250 STW under the Assam Rural Infrastructure and Agriculture Services Project (ARIASP) has further raised the problem. About 10,000 more STW are proposed under the 10th five-year plan period. Tests carried out indicated that the ground water being used for irrigation contains high iron in most parts of Assam.
The study carried out in the Sonitpur district aimed at to analyze the scenario of gradual deposition of total iron on irrigated soil also gave a picture of threat. The effect of rainfall on the iron deposited soil was also studied for both monsoon and non-monsoon period. The periodical changes in the iron content of the ground water were also studied. The water table fluctuation was also monitored on monthly basis. The soil macronutrient parameters namely, potassium, phosphorus, organic carbon, pH of soil were also analyzed.
Based on the observed data of nearly two years (October, 2000 to August, 2002), it was found that the iron content in ground water was higher (4.63 to 22.92 ppm) in areas located nearer to river Brahmaputra and to the other small rivers than in areas (8.24 to 10.35 ppm) located far off from the rivers. The concentration of total iron was found varied from 409 to 867 mg/kg in surface soils depth ranges 0 to 30 cm, whereas this concentration for the sub-surface soil depth between 30 cm and 60 cm varied 463 to 687 mg/kg. It was found that monsoon rain has an effect on the deposited iron content. On an average, percentage decrease of total iron because of dilution varied from 36 to 47. The paper presents results and analysis of the study conducted in the Sonitpur district along with few suggestions for management of iron rich for its effective use in surface irrigation.
