EFFECT OF NITROGEN - FERTILIZER APPLICATION ON THE MIGRATION OF NITRATES IN PADDY FIELD ECOSYSTEM, A CASE STUDY FROM KOBEIGANE, NORTHWESTERN PROVINCE SRI LANKA.

Abstract

The nitrate anion is very soluble in water and is not influenced by soil colloids, and hence is subject to leaching. The seeping water dissolves soil nitrate and therefore any excess nitrate that are present in this ground water recharge zone are carried to the groundwater. Loss of nitrate is undesirable, because in drinking water it is considered to be a health hazard and it may cause eutrofication. After apply fertilizer the characteristics of nitrates vertical transport in a paddy soil, Daduru Oya basin in intermediate zone, were selected for this study. The main aim of this study is to evaluate spatial variations of nitrate in water, which is seeping to the groundwater. Three artificially constructed wells were established in the paddy field. First sets of samples were collected from constructed wells, dug wells around the paddy fields and nearby tank before the cultivation. To analyses the variation of nitrate in constructed wells, water samples were collected after 3, 7 and 14 days after the fertilizer application. After 2 months of first sampling, second sets of samples were collected from dug wells and tank. The contents of nitrate, phosphate, electrical conductivity, pH, Temperature and rainfall were measured. The result of this study provide evidence that nitrate losses from paddy soils was one of the potential factors relating ground and surface water pollution. Because after fertilizer- application, nitrate and phosphate contents of water collected from constructed wells, dug wells around the paddy field and. nearby tank are increased considerably. The correlation coefficient between the nitrate content and the distance from rice field found to be negative and significant both before and after fertilizer application. This case study clearly illustrates the factors that affect for nitrate and phosphate mobility. Variation of nitrate and phosphate concentrations of water collected from constructed wells mainly depends on rainfall, soil characteristics and type and amount of fertilizer. When nitrate and phosphate concentrations variations were compared in three constructed wells, it was found that nitrate-leaching rate was greater than that of phosphate. This suggest that the different mobilities of nitrate and phosphate losses in different soils.