Abstract:
Rice is one of the important food crop for growing population which demands high levels of
nitrogen typically supplied in the form of nitrogen base straight chemical fertilisers. Nitrate
which is the most significant and common nitrogen leaching form mainly occurs in paddy
cultivation, that leaches below the crop root zone represents economically and environmentally
undesirable by directly elevating nitrate levels in shallow ground water in defuse way. By the
way, Grey Water Footprint (GWF) which is a quantitative arithmetic method is favorable in
understanding the ecological impact and disastrous way the freshwater gets polluted. This study
was designed to quantify the leaching losses of nitrate and grey water footprint. In order to
obtain high yield with the availability of excess fertilizer with subsidy, farmers normally do not
follow the department recommendation of fertilizer application. Therefore, a field experiment
was carried out in a selected farmer paddy field in Kurunegala District, which is one of major
paddy cultivation areas in the Low Country Intermediate Zone, Sri Lanka. The lechate form the
study plots were collected using non-weighable lysimeter arranged in a randomized block design
with three replicates at the upper and lower ends of the site and analyzed for nitrate (NO3
-)
content. Drained water was collected from each lysimeter just below the root zone at 7 to 14 day
intervals and analyzed for nitrate content in 2015 and 2016, for four consecutive cropping
seasons. The study revealed that the highest concentration of nitrate in leached water was not
exceed 12 mg/L which is below the threshold value of drinking water, 50 mg/L (as NO3
-). The
quantified leached nitrate amount 3 kg/ha for each cropping season represent the 3% of total
applied nitrogen without showing statistical significant differences. Though Nitrate leached from
paddy cultivation in the given settings did not exceed the maximum permissible level, it
contributes the considerable amount of leaching losses of nitrogen to the sallow ground water in
defuse way. The quantified leaching run-off fraction of 0.15424 value related fertilizer induced
Grey water footprint values were 209 and 191 m3/ton for 2015 and 2016 correspondingly. The
GWF values emphasize that if leached water itself from paddy fields to be contaminated with the
water resources without adding above said amount of fresh water to the leached water to
assimilate pollutants, it would be adversely affected to the nearby water resources.
