MSc

An investigation entitled “Dynamics of iron and aluminium toxicity on
rice (Oryza sativa L.) in saline hydromorphic soils of Kaipad” was carried out at
College of Agriculture, Padannakkad during the academic year 2015 to 2017. The
objectives of the study were to investigate the status of iron and aluminium in
saline hydromorphic soils of Kaipad, evaluate the performance of popular rice
varieties to varying levels of iron and aluminium concentration at different
salinity levels, and examine amelioration strategies for iron and aluminium
toxicity. The study was carried out in four parts namely collection and soil
analysis, incubation study, solution culture and pot culture experiments.
As a part of the initial study, representative surface soil samples were
collected from 15 selected locations of Kaipad areas comprising of Muttil and
Cherukunnu panchayath during the first week of April 2016 to assess the different
physical and chemical properties. The GPS data for the sites were also recorded.
The pH of the soils varied from ultra-acidic to slightly acidic. The electrical
conductivity during the summer months was very high. Among the macro and
micro nutrients studied, very high available K and Ca values were observed and
extreme toxicity of available Fe and Al were also recorded.
An incubation study was conducted with four treatments at two levels of
submergence (5 cm and 10 cm) in factorial CRD. The treatments were fixed
based on the recommendations of KAU POP, 2011 viz. lime (T1); magnesium
sulphate + 1⁄2 lime (T2); phosphogypsum + 1⁄2 lime (T3) and control (T4). The
application of treatments showed a positive effect in reducing iron and aluminium
toxicity. The toxic levels of available Fe were significantly reduced in T 1 at 30
and 120 DAI whereas, at 60 and 90 DAI, T3 was significantly superior in reducing
the iron toxicity. The aluminium toxicity was reduced to minimum level at 30, 60
and 120 DAI in treatment T3. However at 90 DAI, the least aluminium content
was recorded in the soil treated with lime alone.
The solution culture experiment was conducted by maintaining
Hoagland‟s nutrient solution containing 3 levels of iron (400, 800, 1200 mg L-1), 2

levels of aluminium (15 and 30 mg L-1) and 2 levels of salinity (5 and 10 dS m-1)
along with one control in factorial combinations using CRD. The two selected
varieties, Ezhome-1 and Kuthiru were evaluated for their tolerance to iron and
aluminium toxicity coupled with salinity. Maximum iron coating around the roots
with respect to the treatments were displayed in T12 (1200 mg L-1 iron, 30 mg L-1
aluminium and 10 dS m-1 salinity) solution. Increase in levels of iron, aluminium
and salinity significantly reduced the plant height, root dry weight, root length and
root CEC of rice plants.
The pot culture experiment was conducted with seven treatments as
amendments and two varieties Ezhome-1 and Kuthiru in factorial CRD during
July to October 2016. The treatment combinations were: Lime (T1); Magnesium
sulphate + 1⁄2 lime (T2); Phosphogypsum + 1⁄2 lime (T3); Lime + potassium silicate
0.25% + 0.25% boron (T4); Magnesium sulphate + 1⁄2 lime + potassium silicate
0.25% + 0.25% boron (T5); Phosphogypsum + 1⁄2 lime + potassium silicate 0.25%
+ 0.25% boron (T6) and control (T7). The leachate was collected and analysed by
inserting a perforated pipe at the centre of each pot.
The variety Ezhome-1
recorded maximum significant plant height at 30, 60 and 90 DAT. The number of
productive tillers/ number of panicles, grains per panicle, grain yield, straw yield
and 1000 grain weight were also significantly superior in Ezhome-1. Among the
amendments, T6 recorded significantly superior plant height, grain yield, total Ca,
B, Si and lowest Al content in rice.
The treatment T 3 recorded maximum
significant number of panicles, productive tillers, grains per panicle, straw yield,
1000 grain weight and lowest Na and Fe content in plant tissue. The treatments
receiving phosphogypsum + 1⁄2 lime (T 3 and T6) were highly effective in reducing
the toxic levels of available Fe and Al whereas, application of lime (T 4) was
significantly superior in increasing the soil pH, available P and reducing the EC
and exchangeable Na status of Kaipad soil.
The saline hydromorphic soils of Kaipad are having severe constraints of
acidity, extreme toxicity of iron and aluminium coupled with high salinity. These
problems can be ameliorated using combinations of amendments including
phosphogypsum, lime and foliar application of boron and silicon to enhance the

growth and yield of rice crop. Adoption of aforementioned management strategy
could help in improving the soil health and thereby increasing the yield potential
of Kaipad rice.