A laboratory study on the effects of fertilizer addition on mobilization, percolation and leaching of calcium ions in soils of Anuradhapura district

Abstract

This study aims to investigate the effect of fertilizer addition to limestone soils around Thirappane, in Anuradhapura District. Groundwater is the primary source of freshwater in this area. There is evidence that the degree of hardness of groundwater in the area has increased over the years, probably as a result of long-term and large-scale application of chemical fertilizer. Our results show that the exchangeable and total calcium ion concentrations in the soil of non- agricultural increases with depth of the soil profile, indicating the existence of calcium deposits beneath the soil profile. Columns (Dimensions ~ 4.00 cm2 x 100 cm) were filled with soil (up to 60 cm height in each column) from the study area and 0.5% (w/w) of nitrogen fertilizers (Ammonium sulfate and urea) were introduced to the columns to study the effects of fertilizers on properties of soil. Deionized water (100.0 mL) was added by using a dropper from the top of each column and it was allowed to pass through the soil at a rate of 1 mL/minute. The highest effect on the calcareous soil was shown by fertilizer containing ammonium sulfate. After running the columns for 30 days, it was observed that the pH of the leachate in the column introduced with urea, had gradually declined while the calcium ion concentration had gradually increased, whereas the pH of the leachate, in the column introduced with ammonium sulfate fertilizer, showed a rapid decrease and the calcium concentration was very high, compared to the control. Total calcium ion concentration had decreased down the soil sample columns while exchangeable calcium ion concentration increased. The pH value had also decreased down the soil profile. This indicates the dissolution of calcium carbonate in the soil due to the increment of acidity. This highlights that mobilization, percolation, and leaching of calcium ions in the soil change with nitrogen fertilizer application, potentially contributing to increased groundwater hardness