PhD

Banana is well known to be extremely demanding for water and nutrients
and supplemental application of these resources are pre-requisites for higher yield.
Conventional method of application characterized by heavy doses at wider
intervals lead to losses and reduced efficiency of these inputs. A near continuous
system of application possible under drip fertigation minimize these disadvantages
of conventional method of application. Three experiments under the project
"Water and fertilizer use efficiency in drip fertigated banana Musa (AAB)
'Nendran' " were conducted during 1997-98 and repeated during 1998-99 at
Banana Research Station, Kannara and at College of Horticulture, Vellanikkara.
The study aimed to investigate the use efficiency of Water and fertilizers in drip
fertigated banana and to study the dynamics of nutrients applied through drip
fertigation and conventional methods. The rooting pattern of banana as influenced
by methods of irrigation and the leaching loss of nutrients beyond the root zone
under excess water supply were also studied. Based on the results obtained in first
year experimentation, a further dilution of nutrient solution was introduced in the
second year by increasing the quantity of irrigation on pan evaporation basis and
reducing the levels of fertilizer application.
Response of banana var. Nendran to different methods of fertilizer
application (drip fertigation and basin application), to different frequencies of
fertigation (six and twenty four fertilizer splits) and to five different levels of
fertilizer at regular intervals (50 to 250 per cent of present recommendation in the
first year and 25 to 200 per cent in the second year) were tested in the first
experiment. Drip fertigation could register significant improvement in productivity
and response to fertilizer levels over conventional means of fertilizer application
and irrigation when frequency of application was enhanced. Efficiency of fertilizer
application was decided not by quantity of fertilizers, but by dilution and
frequency.

The yield obtained from basin application of the present recommended
fertilizer level viz., 200-115-300 g NPK plant" in six splits was comparable with
that obtained from drip fertigation at 100-60-150 g NPK plant" suggesting an
improved fertilizer use efficiency under drip fertigation.
The second experiment consisted of combinations of different methods
and levels of irrigation. Methods of irrigation included surface drip, subsurface
drip and conventional method, while levels of irrigation were 8, 12 and 16 1 day"
in the first year and 50, 75 and 100 per cent pan evaporation compensation in the
second year. The efficiency of drip fertigation was enhanced by placing the
emitters below the surface (subsurface drip) as evidenced by higher moisture
content in the root zone and a larger production of roots in the limited wet zone.
But higher nutrient concentration consequent to inadequate quantity of irrigation
and higher fertilizer rate negated the benefits of subsurface drip fertigation in the
first year. Water use efficiency of 570 kg ha' mm" of water could be obtained
under subsurface drip fertigation as against 470 kg ha' mrn' in conventional
method resulting in an increased efficiency of 21 per cent in the second year.
Low moisture content in the soil in the first year resulted in the production
of more roots especially secondary and tertiary roots and surface drip had more
roots than conventional method. But when the quantity of irrigation was increased
in the second year, more roots were present in conventional method than surface
drip. Under surface drip 64 per cent of the root length was accumulated in the drip
zone, while under conventional method, roots were more uniformly spread .:
Pot culture study to estimate the leaching loss of nutrients under flooded
condition showed that leaching loss through irrigation water were to the extent of
33.5 per cent and 12.8 per cent respectively for Nand K, when the irrigation was at
100 per cent pan evaporation compensation and fertilizer application at the present
recommended level. Further increase in quantity of irrigation increased Nand K
losses. No leaching loss ofP was observed.

The study has conclusively proved that fertigation is an advantageous
substitute for conventional irrigation cum fertilizer application. The superiority of
fertigation arises from its continuous maintenance of wetting, but not leading to
totally reduced state of environment as well as minimizing the side effects of
synthetic fertilizers affecting soil reactivity, by reducing the unfavourable release
of native element like Fe and Mn and providing prolonged but steady supply of
major nutrients.
The study also convincingly established that it is not the quantity of
nutrient applied or absorbed that decides the yield, but it is the interaction and
metabolic availability of these nutrients. Metabolic availability can be ensured
through higher dilutions and steady applications of nutrients. Drip fertigation is the
only effective tool to serve this purpose.
The effectiveness of drip fertigation can be further enhanced by avoiding
or minimizing the use of fertilizers like single super phosphate, which reduces the
pH of the soil and by scheduling the level of water application through fertigation.
Deeper placement of drip emitter at 30cm as tried in subsurface drip method may
lead to losses and ineffectiveness. Therefore, placement of emitters at 15cm can
make the system more efficient.