PhD

A research project entitled "Enhancing the productivity of the rice-fish/prawn
farming system in Pokkali lands" was carried out from 1999 to 2001 at the Rice Research
Station, Vyttila under the Kerala Agricultural University. The objective of the research
project was to characterise the Pokkali rice-fish/prawn system through critical analysis of
the component factors, so as to evolve an ideal technology to have higher productivity
from Pokkali lands.
Four experiments were conducted to achieve the above objective. The first
experiment entitled "Response of rice to applied N in tidal and non-tidal situations studied
the role of tides on regulation of soil chemical properties and enrichment of plant nutrients
in Pokkali soils. This pot culture study revealed the significant contribution of tides on
increasing the soil pH, available K, straw yield and productive tillers. The soil pH showed
significant positive correlation with available K.
The field experiment entitled "Tidal effect on Pokkali soils and performance of
rice" compared the performance of three rice cultivars under the tidal and non-tidal
situations and studied the influence of tides on the chemical properties of Pokkali soil
during the low saline rice cr~p phase and high saline post rice phase. The tidal influx
brought about significant changes in the chemical properties of the soil. It significantly
increased the soil pH, organic carbon, available P and, available and exchangeable K.
Though the difference was not significant, the electrical conductivity and, available and
exchangeable Na were higher under the tidal situation. Tidal regime favoured higher

grain, straw and biomass production while non-tidal situation favoured a higher grain :
straw ratio.
The Na content in plant tissues were two to three fold higher under the tidal regime
than the non-tidal situation up to the flowering stage and both the regimes had almost same
Na content subsequently. N content was always higher under the tidal situation
irrespective of the plant tissue, varieties and year of study. Among the varieties Vyttila-3
and Cut. 1026 had the lower Na content and Na : K ratio which implied the effective saline
tolerant mechanism operating within them.
Two levels each of lime, silica, phosphorus and sulphur, tried individually during
the first year and in combination subsequently, caused considerable variation in soil
chemical characters and, growth, physiological characters and yield of rice. The
ameliorants significantly increased the electrical conductivity and exchangeable K of the
soiL The sulphur application decreased the soil pH while lime increased it. Lime
application increased the availability of K and Na, while lime + phosphorus combination
increased the exchangeable K and Na. Higher levels of ameliorants considerably increased
the availability of Na compared to the lower levels and the non-ameliorated control
,
treatment. Sulphur at 600 kg ha" had the highest grain Mn, leaf Mn and Ca at harvest,
specific leaf weight and, significantly higher grain, straw and biomass production.
The field experiment entitled "Plant ideotype suited to rice-cum-fish culture in
Pokkali fields" evaluated the compatibility of three rice varieties of varying plant
architecture with three fish treatments. The rice varieties revealed to have significant
variation for light infiltration, growth characters, yield, yield attributes and biomass

production. Considering the light infiltration, grain yield. biomass production and B:C
ratio CuI. 1026 was more suitable for rice-fish culture in Pokkali fields. Among the fish
species tried male Tilapia (Oreochromis mosambicuss) gave higher survival rate (38.9%)
and fish yield (224.2 kg ha"). Selective culture of Tiger prawn (Penaeus monodon) after
the rice-fish dual culture recorded a survival rate of 49.00 per cent, growth rate of 20 gin
74 days and an yield of 425 kg ha-I. The integrated farming system involving rice-fish
dual culture during the low saline phase and selective culture of Tiger prawn subsequently
is capable of increasing the productivity and income from Pokkali lands.