Abstract:
Paddy cultivation is the largest global consumer of water, and it also significantly contributes to water pollution.
Investigating the water footprint of paddy agriculture can provide insights into how pollutants affect the
ecosystem. This study aimed to quantify the total water footprint for paddy grown in Sri Lanka's Low Country
Intermediate Zone under supplementary irrigation. A lysimeter study was carried out to determine the amount of
leached nutrients below the root zone. The experimental design was a Complete Randomized Block Design
(CRBD) with two factors (cropping season and gradient) and two levels (Yala and Maha; upper and lower). The
green and blue water footprints for both sites were estimated using the CROPWAT 8.0 model by crop water
requirement option. The results revealed that the loss of NO3-N through leaching accounted for 8.61 ± 1.84 kg/ha
(8%), and the leaching losses of PO4
3-
- P were 0.49 ± 0.1 kg/ha (2%) under controlled runoff conditions during the
experimental period. The nitrogen fertilizer-induced grey water footprint (WFgrey) for one tonne of rice produced
was 193 ± 27 m3
/t, and the phosphorous fertilizer-induced WFgrey was 61 ± 7 m3
/t. The study identified nitrate as
the critical element for water pollution. The estimated total water footprint (WFtotal), which was the sum of green,
blue, and grey water footprint, was 1409 ± 95 m3
/t under controlled runoff conditions, while the global average
value is 1325 m
3
/t. The estimated value is about 6% higher than the global average value. Therefore, these
findings demonstrate the need for further research
