Ph.D

Cowpea, a vital leguminous crop in the semi-arid regions of tropics and sub
tropics, plays a key role in sustainable agriculture and nutritional security. However,
the productivity of cowpea remains low in various regions of India. There is a critical
need to enhance the productivity of cowpea with limited resources to achieve nutritional
security for the growing population. The research program entitled, ‘Nutrient use
efficient technologies for enhancing productivity of cowpea [Vigna unguiculata ( L.)
Walp.]’ was conducted from October 2021 to May 2023 at Instructional Farm, College
of Agriculture, Vellanikkara, with the objective, to enhance the nutrient use efficiency
and yield of cowpea through fertilizer microdosing, nano NPK and designer seeds.
The investigation consisted of three experiments viz., standardization of
fertilizer microdosing and seed treatment for cowpea, standardisation of nano fertilizer
dose and seed treatment for cowpea and on field evaluation of nutrient use efficient
technologies in two different cowpea varieties (Anaswara and PGCP 6) and the field
experiments were repeated for three seasons (summer 2022, rabi 2022 and summer
2023).
The experiment on standardization of fertilizer microdosing and seed treatments
for cowpea consisted of five levels of fertilizer microdosing (25%, 50%, 75% NPK as
per POP, NPK as per POP, and absolute control) and three levels of seed treatments
(designer seeds, rhizobium treated seeds, and untreated seeds). Among fertilizer
microdosing levels, microdosing (50%) exhibited the best growth and yield parameters
followed by microdosing (25%). The percentage increase in grain yield with
microdosing (50%) was 19% compared to NPK as per POP. Nutrient uptake and soil
nutrient availability were higher in microdosing (50%). Partial factor efficiency (PFE),
agronomic efficiency (AE) and apparent recovery efficiency (ARE) of N, P and K were
significantly higher in microdosing (25%). Among seed treatments, designer seeds
demonstrated superiority in terms of growth, yield and nutrient use efficiency. Designer
seeds resulted in earlier flowering and led to a 114 per cent increase in grain yield
compared to untreated seeds. Regarding interaction effect of treatments, microdosing
(50%) with designer seeds showed the best performance followed by microdosing
(25%) with designer seeds. Based on these results, microdosing 50% with designer
seeds and microdosing (25%) with designer seeds were selected for field study.
The experiment on standardization of nano fertilizer dose and seed treatment
for cowpea consisted of six levels of nano fertilizers (2/3, 1/2, 1/3, 1/4 NPK as per POP
applied as nano fertilizer (NF), NPK as per POP and absolute control) and three levels
of seed treatments (designer seeds, rhizobium treated seeds, and untreated seeds).
Among nano fertilizers, 2/3 NPK as per POP applied as NF showed significantly higher
growth and yield parameters. This treatment resulted in a 14% increase in grain yield
compared to NPK as per POP and a 137% increase compared to the absolute control.
Significantly higher PFE and AE of N, P and K were recorded in 1/4 NPK as per POP
applied as NF. Among seed treatments, designer seeds demonstrated the highest
efficiency in terms of growth, yield, and nutrient use efficiency. Considering interaction
effect, the application of 2/3 NPK as per POP applied as NF along with designer seeds
resulted in 50 per cent increase in grain yield, while 1/4 NPK as per POP applied as NF
along with designer seeds led to a 48 per cent increase in yield compared to the
recommended dose of NPK as per POP of KAU with untreated seeds. Based on these
findings, 2/3 NPK as per POP applied as NF with designer seeds and 1/4 NPK as per
POP applied as NF with designer seeds were selected for field study.
Experiment on field evaluation of nutrient use efficient technologies, consists
of eight treatments viz., best two treatments from experiment I viz., microdosing (25%)
with designer seeds, microdosing (50%) with designer seeds, best two treatments from
experiment II viz., 2/3 NPK as per POP applied as NF with designer seeds, 1/4 NPK as
per POP applied as NF with designer seeds, STCR equation based NPK with designer
seeds, soil test based NPK with designer seeds, NPK as per POP with designer seeds
and absolute control.
Results on field evaluation of nutrient use efficient technologies using cowpea
variety Anaswara revealed that microdosing (50%) with designer seeds showed
increased growth parameters viz., plant height, number of branches, dry matter
production per plant, crop growth rate and relative growth rate. Significantly highest
grain yield was recorded in microdosing (50%) with designer seeds. Despite reducing
the fertilizer dose to 50%, this treatment resulted in a 16% yield increase compared to
the NPK as per POP with designer seeds. Total chlorophyll content at different growth
stages and protein content in grains were higher in 1/4 NPK as per POP applied as NF
with designer seeds. Soil parameters did not exhibit a consistent trend across treatments.
Regarding nutrient use efficiencies, significantly higher partial factor efficiency and
agronomic efficiency of N, P and K were recorded in 1/4 NPK as per POP applied as
NF with designer seeds. While considering the economics, microdosing (50%) with
designer seeds showed higher net returns and a better B:C ratio. Despite the higher yield
observed with 2/3 of NPK as per POP applied as NF with designer seeds, the elevated
cost of nano fertilizers rendered it less profitable.
The field evaluation of nutrient use efficient technologies using cowpea variety,
PGCP 6 revealed that microdosing (50%) with designer seeds and 2/3 NPK as per POP
applied as NF with designer seeds performed best in terms of growth and yield
parameters. The highest yield was recorded in microdosing (50%) with designer seeds
followed by 2/3 NPK as per POP applied as NF with designer seeds. Reducing the
fertilizer quantity by 50 per cent from NPK as per POP with designer seeds,
microdosing (50%) with designer seeds resulted in an 86 per cent increase in yield.
Throughout the growth stages, consistently higher total chlorophyll content and protein
content in grains were observed with 1/4 of NPK as per POP applied as NF with
designer seeds. Soil parameters did not show a consistent trend across treatments.
Significantly higher PFE and AE of N, P and K were recorded with 1/4 NPK as per
POP applied as NF with designer seeds. In terms of economics, microdosing (50%)
with designer seeds demonstrated higher net returns and better B:C ratio. Despite
achieving a higher yield with 2/3 of NPK as per POP applied as NF with designer seeds,
the high cost of nano fertilizers made this treatment less profitable.
From the results of field experiments conducted for both cowpea varieties
(Anaswara and PGCP 6), microdosing (50%) with designer seeds can be recommended
as an economically viable and nutrient use efficient technology for enhancing cowpea
productivity.