Nitrogen leaching monitoring from a tropical paddy field using soil-water samplers

A study on the monitoring of Nitrogen (N) leaching was conducted in acid-sulfate clayey soil in the central region of Thailand. The objective of study was to measure the N leaching to shallow groundwater from a tropical paddy. N inputs to and outputs from field were measured by direct method. Inputs of N to the site were commercial fertilizer, precipitation, irrigation water and soils. Outputs of nitrogen from the site were leaching to groundwater, harvested crops, loads in surface runoff, soils and loss from the field. Leaching loss was calculated from daily fluxes of water percolation and soil water N concentrations extracted by vacuum lysimeter. Based on the three month observation, average leaching of NO3-N and TKN to groundwater was found to be 0.04 kg (.) ha(-1) (.) d(-1) and 0.17kg (.) ha(-1) (.) d(-1) respectively. It was also observed that fertilizer application increased NO3-N concentration at five-fold in groundwater. This indicates that groundwater aquifers under paddy fields are vulnerable due to NO3-N leaching. Furthermore, result showed that loss of N inputs as outflow to the water from the field corresponded to 19.02% of total applied N. This indicates that about 20% of fertilizer input is responsible for water pollution if the same conditions prevail. It is recommended to formulate strategy and plan to change existing cultivation practice in order to minimize the water pollution.