PhD

Para rubber (Hevea brasiliensis Muell. Arg.) grown in varied soil and
climate condition in traditional rubber growing regions of India. Variability in
soil and climate influences performance of rubber and for this site specific
management helps to increase input use efficiency and enhance crop production.
Geospatial analysis under GIS environment helps to integrate soil and climate
variability and identify the limitations and potential areas for enhancing the
rubber production without horizontal expansion of rubber cultivation. Hence the
present study was undertaken with the following objectives
1. To develop soil, climate, rubber area and rubber yield database to
understand the variability of rubber productivity.
2. To prepare rubber distribution map and delineate productivity
constraint area map of rubber in Kanaykumari and Kasargod.
3. To study the soil nutrient dynamics and phenology of rubber in
different growing environments.
Objectives of the present study were addressed by conducting two
experiments. Under experiment I, two districts - Kanyakumari and Kasargod -
were selected and identified 60 holdings in each district distributed over different
Soil Management Unit (SMU). Recorded girth and Tapping Panel Dryness (TPD)
observations and collected surface soil sample (0-30 cm) from identified holdings
and analyzed for major nutrient and physical parameters. Using GPS reading
developed holdings soil database and generated soil nutrient map and brought
under GIS platform to identify the soil constraint areas. Water balance approach
was followed to delineate climate constraint area in each district. Rubber
distribution map was developed for each district using satellite image and
overlayed with soil and climate constraint map to know the extent of rubber area
under soil and climate constraint. Under experiment II, Kottayam district was
selected for studying the soil nutrient dynamics of mature rubber plantation in
relation to phenology and growing environment. Identified two holdings in each
of three elevation classes; 0-100, 100-300 and > 300m. Collected surface soil
samples and recorded rubber phenology at monthly interval. Soil samples were
analyzed for pH, OC, nitrogen, exchangeable Al. Recorded annual litter fall and
mineralization potential. Rainfall and temperature were recorded at one location
in each of the three elevation classes.
Mean soil OC, available P, K, Ca and Mg varied significantly between
Kanyakumari and Kasargod district. Soil available P and K were significantly
higher in Kanyakumari where as soil OC, available Ca and Mg were significantly
higher in Kasargod. Within the district, soil OC, available P, K and Ca showed
high spatial variability. Rainfall distribution was distinctly different in two
districts. Well distributed rainfall with less dry period and long growing period
was seen in Kanyakumari. In Kasargod rainfall was concentrated between June-
September, as a result dry period was longer and growing period was shorter.
During December to March period moisture stress level was more in Kasargod
compared to Kanyakumari. Performance of rubber in terms of girth and rubber
yield was better in Kanyakumari compared to Kasargod. Average per tree rubber
yield (g/tree/tap) during dry period and annual yield per unit area (kg/ha/year)
was significantly higher in Kanyakumari compared to Kasargod. Incidence of
Tapping Panel Dryness (TPD) was significantly more in Kasargod compared to
Kanyakumari. Leaf nutrient content showed balance level of N, P and K and
deficiency of Ca and excess of Mg in Kanyakumari. In Kasargod leaf K was
balanced, whereas Mg was in excess and deficiency of nutrient was in the order
of P>Ca>N.
Rubber showed a distinct signature compared to other vegetation. Satellite
based rubber area was estimated with good accuracy and rubber area was
comparable with ground statistics. Ovrelay analysis indicated that considerable
extent of rubber area in Kanyakumari distributed over area without moisture
stress but same was not seen in Kasargod. In general all rubber area in Kasargod
comes under poor to very poor moisture adequacy during summer compared to
only 48 per cent rubber area in Kanyakumari experienced poor moisture
adequacy during summer. In Kanyakumari 28 per cent of rubber area distributed
over low available P, medium in OC, K and high Ca and Mg followed by 18 per
cent over area medium in OC, available P ,K and high in available Ca and Mg. In
Kasargod, 61 per cent rubber area distributed over low available P, medium K
and high in OC, available Ca and Mg. In Kanyakumari district soil cation (Ca and
Mg), and soil OC factors showed significant relation with rubber growth and
yield. In Kasargod only topography factor showed significant relation with rubber
yield.
In Experiment II rubber showed distinct phenological difference over
elevation with rubber in high elevation showing early wintering compared to low
elevation. Number of new leaf flushes was more in low elevation compared to
high elevation. Annual litter addition did not vary along elevation; however rate
of litter decomposition was slow at high elevation compared to low elevation. In
general maximum and minimum temperature was low at high elevation where as
no marked difference in quantity and distribution of rainfall was seen along
elevation. Soil OC was significantly higher at high elevation compared to low
elevation, but mineralization of soil OC and total N was significantly low at high
elevation compared to low elevation. Peak soil total N was observed for short
period at high elevation indicating the short growing period compared to low
elevation. Wide gap between potential and actual NO3 and NH4 nitrogen at low
elevation compared to high elevation indicated the loss at low elevation through
leaching and denitrification. At low and medium elevation, rubber active growth
stage coincided with peak N mineralization whereas peak rubber yield period
coincided with low N mineralization. But at high elevation both active growth
and peak yield coincided with peak N mineralization. At high elevation, climate
factor showed significant positive relation with next month rubber yield
indicating the climate limitation at high elevation. At low elevation, climate
factor and soil reaction factor did not show significant relation with next month
rubber yield indicating mineralization and climate are not limiting at low
elevation.