Abstract:
Lysimeter studies are high tier studies and give additional information about leaching of fertilizers. HYDRUS -ID is a
numerical model which can be used to simulate the movement of water and solutes in saturated and unsaturated soil
conditions. Nitrate- N in water bodies is a serious environmental concern in Jaffna peninsula. High amount of nitrate N in the water bodies are suspected due to the intensification of agricultural activities by adding high amount of
inorganic fertilizers. In Jaffna, Carrot was cultivated around 65.7ha of arable land and public market price of carrot
was reached the maximum of Rs 200 and the minimum of Rs20 in year 2011 and the fertilizer application for carrot
also high. Hence a lysimeter study was carried out to evaluate the effect of different levels of fertilizer on the leaching
loss of nitrate-N in calcic red yellow latosol and the possibility of using HYDRUS - ID for the simulation of nitrate
leaching. In lysimeter two levels of fertilizer application; recommended level (RT) and half of the recommended level
of fertilizer (HRT) recommended by the Department of Agriculture, Sri Lanka was used with three replicates. Data
from the lysimeter was statistically analyzed at 95% confidence level and the leaching was simulated by using
HYDRUS-ID in a 50 cm soil column of calcic red yellow latosol. There was no significant difference found between
nitrate concentrations in leachate of two treatments, but significant difference was found in leachate concentration
with the days after sowing. Since the RT consist higher leave length, evaportranspiration is high. The soil nitrate-N
varied as 17.3mg/100g soil and 15.3mg/100 g soil for RT and as 17.9mg/100 g and 21.1mg/100 g for HRT at 10cm
and 30cm depth, respectively because of less root solute uptake in HRT. Measured nitrate-N loss by leaching was
16kgN/ha for RT and 15.2kgN/ha for HRT. In the simulation, nitrate-N leaching loss was 33kg N/ha for RT and 25.7kg
N/ha for HRT. But, the percentage of loss high for HRT in both cases. Through this experiment it can be concluded that
the RT has low potential to leach than the HRT and it is better to reduce the amount of fertilizer at the sowing time
because of less root solute uptake.
