Abstract:
Iron (Fe) toxicity is one of the major constraints in lowland paddy soils in Southern Sri Lanka. The toxicity
is associated with reduced soil condition of flooded soils, which increases concentration of iron (Fe2+). Iron
concentrations of natural origin are region-specific, and differ even within localized areas due to various
soil types. Unlike other crops, rice can cope with excess water stress. However, according to the flash
flooding or deep-water flooding the gas diffusion may limit in paddy soils. Flash flooding, may last less
than a few weeks causing after heavy rainfall although the depth of water limits a few meters, however,
deep-water flooding, the water depth reaches several meters for several months. The heavy rainfall during
May 2017 in Mapalana area caused severe floods by damaging the lowland rice cultivated areas. In order
to evaluate the immediate impact of these floods for iron toxicity, the current experiment was conducted
in Mapalana and two sites in Nayimbala. Twelve samples were selected from above areas after one week
of floods when water has completely drained. The collected soil samples from 0-10 cm layer were air dried,
sieved then analysed for pH, EC, colour, NO3
-
-N, NH4
+-N, available K and Fe concentration. All the
samples showed pH values less than 5.6 which can be identified as acidic soils. The Fe content of the soil
samples collected in Mapalana was 1594±308.7 mg kg-1, Nayimbala site 1 was 1050±416.5 mg kg-1 and
Nayimbala site 2 was 1300±198.8 mg kg-1 which was above the critical level of 4.5 mg kg-1 of soil. There
was a positive strong co-relationship in Fe content with K, NH4
+-N. Similar occurrence of a pronounced
peak of Fe immediately after flooding was reported in previous studies. Further studies are continuing on
iron toxicity in respective area.
