MSc

The study entitled “Rationalisation of phosphorus and potassium nutrition in
cowpea (Vigna unguiculata (L.) Walp.) in the Southern Laterites” was undertaken at
College of Agriculture, Vellayani, during 2021-2023. The key objectives were to assess the
productivity and quality of cowpea in response to varied doses of phosphorus and potassium
supplemented with foliar nutrition, and to compute the economics.
The field experiment was carried out at the Integrated Farming System Research
Station, Karamana, from December 2022 to February 2023. It was laid out in randomised
block design with (2 x 3 x 2) + 1 treatments, replicated thrice. The treatments comprised
combinations of two levels of P (p1-100 % RDP, p2-50 % RDP), three levels of K (k1 - 100
% RDK, k2 - 150 % RDK, k3 - 200 % RDK) and foliar application at 20 DAS and 40 DAS
(f1 - nano DAP @ 0.4%, f2 - PSAP @ 0.4 %), compared against a control (KAU POP). The
variety used for the study was PGCP-6 and the fertilizer recommendation followed was
20:30:10 kg NPK ha-1
. All other cultural operations were carried out as per the KAU POP.
The treatment, p1 (100 % RDP) resulted in significantly taller plants at 30 DAS, 45
DAS and 60 DAS) with more number of primary branches (45 DAS and 60 DAS), the
highest CGR, RGR and NAR at 15-30 DAS, more number of nodules and the highest total
dry matter production (DMP). The treatment, p2 (50 % RDP) resulted in the highest CGR
and NAR at 30-45 DAS, and RGR at 45-60 DAS. Among the levels of K, 200 per cent
RDK (k3) recorded significantly taller plants (45 DAS and 60 DAS) with more number of
primary branches (45 DAS), RGR, CGR and NAR (15-30 DAS) and total DMP (4917 kg
ha-1
). Foliar application of nano DAP (0.4 %) at 20 DAS and 40 DAS (f1) resulted in more
number of primary branches, LAI and RGR at 60 DAS, and total DMP (4925 kg ha-1
).
Foliar application of PSAP (0.4 %) at 20 DAS and 40 DAS (f2) resulted in more number of
nodules per plant, and CGR and NAR at 30-45 DAS. Among the P x K x F interactions,
p1k1f1 (100 % RDP + 100 % RDK + nano DAP @ 0.4 %) resulted in higher total DMP, and
was on par with p1k3f1. The treatment combination, p2k2f2 resulted in higher NAR and
remained comparable with p2k1f1, p1k1f2 and p1k2f2, at 45-60 DAS. The treatment
combination, p2k1f1 resulted in significantly higher LAI (2.94) at 60 DAS and CGR at 30-
45 DAS. The treatments were superior to control with respect to growth attributes and total
DMP.
The treatments, p2, k1 and f2 resulted in the highest number of pods per plant (23.42,
23.17, 22.57), seeds per pod (16.51, 15.81, 15.88), pod yield (1700 kg ha-1
, 1669 kg ha-1
,
1619 kg ha-1
) and seed yield (1484 kg ha-1
, 1433 kg ha-1
, 1395 kg ha-1
). However, the highest
haulm yields (4451 kg ha-1
, 4235 kg ha-1
) were observed with 100% RDP (p1) and 200%
RDK (k3). Among the interaction effects, p2k1f2 resulted in the highest number of pods per
plant (26.17), pod yield (1892 kg ha-1
) and seed yield (1642 kg ha
-1
) and significantly higher
number of seeds per pod (20.17), which was at par with p2k3f2. The treatments were superior
to control with respect to yield attributes and yield, except haulm yield.
While, p1 (100% RDP) recorded the highest uptake of N and P, and apparent
recovery efficiency of P (AREp), the treatments, p2 (50% RDP) and k1 (100% RDK)
resulted in the highest partial factor productivity (PFPp), agronomic efficiency (AEp) and
physiological efficiency (PEp). While f1 (nano DAP @ 0.4% at 20 DAS and 40 DAS)
resulted in the highest N uptake (247.35 kg ha-1
), f2 (PSAP @ 0.4% at 20 DAS and 40 DAS)
resulted in the highest chlorophyll content at 45 DAS (1.92 mg g-1
) and P uptake (21.55 kg
ha-1
), AEp (24.75 kg kg-1
) and AREp (53.12 %) of P. Among the P x K x F interactions,
p1k3f1 (100 % RDP + 200 % RDK + nano DAP @ 0.4 % at 20 DAS and 40 DAS) resulted
in the highest N uptake (265.11 kg ha-1
) and p1k3f2 resulted in the highest P uptake (28.53
kg ha-1
). The highest PFPp (98.93 kg kg-1
) and AEp (44.84 kg kg-1
) were recorded with
p2k1f2. The treatments were superior to control with respect to NPK uptake, PFPp and AEp.
The seed quality in terms of zinc content was observed to be superior with 50%
RDP (p2) and f1 (nano DAP @ 0.4% at 20 DAS and 40 DAS). The seed crude protein
content responded significantly to K and remained comparable among the three levels of
K.
The treatment, k3 resulted in the highest organic carbon content (1.17 %), available
P (65.27 kg ha-1
) and available K (236.74 kg ha-1
). The treatment, f2 resulted in the highest
soil available P (62.77 kg ha-1
). Among the P x K x F interactions, the highest net gain in
available N (205.10 kg ha-1
), available P (7.67 kg ha-1
) and available K (68.24 kg ha-1
) were
observed with the treatment combinations, p2k3f2, p1k3f2 and p1k3f1 respectively. The
treatments were superior to control with respect to pH, organic carbon, and available NPK
status of the post-harvest soil.
Significantly higher net income and benefit cost ratio were recorded with
p2 (₹62,879 ha-1
,1.99), k1 (₹58,307 ha-1
, 1.92), f2 (₹54,256 ha-1
, 1.85) and p2k1f2 (₹76,120
ha-1
, 2.20).
Considering the yield, economics and phosphorus use efficiency, application of full
dose of N (20 kg ha-1
) along with 50 per cent recommended dose of P (15 kg ha-1
) + 100
per cent recommended dose of K (10 kg ha-1
), supplemented with foliar application of
potassium salt of active phosphorus (0.4%) at 20 DAS and 40 DAS (p2k1f2), could be
adjudged as the best treatment for higher productivity and profitability of grain cowpea in
the Southern Laterites of Kerala (AEU 8).