Abstract:
Agricultural contamination of groundwater with nitrates in Batticaloa is of prime importance, due
to the intensive use of inorganic N fertilizers, together with excess irrigation on highly permeable
soils. The objective of this study was to evaluate the applicability of LEACHM-N on nitrate
leaching in sandy regosols under laboratory conditions. Leaching behaviour of NO3
- - N was
evaluated through laboratory experimentswith those predicted by LEACHM-N,a one dimensional,
water flow, solute transport and plant uptake model. To perform laboratory column studies, PVC
pipes of 20, 30 and 40 cm depths and 8.9 cm internal diameter were used to represent soil profile at
three depths. Each column was fertilized with KNO3, at the rate of 0, 70 and 140 kg N/ha. Three
water application rates (7mm, 14mm and 30mm) were combined with each of these fertilization
rates in each column. The leachate samples were collected and analyzed for nitrate nitrogen
colorimetrically using spectrophotometer. LEACHM-N produced satisfactory predictions for all
the treatments in 20cm column. The accuracy of prediction was found to be decreasing when the
column depth was increased and the decrease in rate of irrigation. In most treatments the simulated
results showed no significant difference between LEACHM-N predicted and measured losses.
Comparisons of simulated NO3
- - N losses in the columns showed reasonable match with the
measured values as indicated by their non significant mean difference values. For most of the
treatments in 20cm column, the mean difference values were non significantwith higher correlation
coefficient values and lower Root Mean Square Error values. Therefore it can be concluded that
LEACHM-N predictions are successful and could be used as a decision making tool at field
conditions to evaluate nitrate leaching
