Thesis (M. Sc.(Agronomy)) -- University of Limpopo, 2015 / Cowpea (Vigna unguiculata L. Walp) is an important grain legume grown in many parts
of the world mostly by smallholder (SH) farmers. Low soil phosphorus (P) and drought
stress are major constraints to legume production and threaten food security. Root
architecture is a spatial configuration of the root system which is influenced by moisture
status and P uptake. A field experiment was conducted at Ukulima farm near Modimolle
in Waterberg district during 2012/13 summer growing season. The treatments
comprised of two levels each for soil P (low and high) and moisture status (water stress
and well-watered); and eight cowpea genotypes (Tvu 4632, Tvu 6365, Tvu 9848, Tvu
15445, Tvu 16408, Tvu 15143, Oloyin and IT00K-1217). The low P level implied the
available P in the soil measured in situ, which was less than 8 mg kg-1 while the high P
level entailed fertilization at the rate of 40 kg P ha-1 application to achieve approximately
35 mg P kg-1 of soil . The root traits measured included angle of adventitious and basal
roots, number of basal roots, tap root diameters at 5, 10, 15 and 20 cm soil depths;
lateral branching densities at depth 5,10 and 15 cm, nodule score, deep score,
shallowness score, 3rd order branching density, and 1.5 branching densities at 5 and 10
cm depth. Plant parameters measured were plant height, number of pods per plant,
number of seeds per pod, length of the pods, unshelled weight, shelled weight and
number of primary and secondary branches. Photosynthetic parameters measured were
photosynthetic rate, intercellular CO2 concentration, water conductance, transpiration
rate, vapour pressure deficits, sample cell CO2, sample cell H2O and relative humidity in
the cell. All treatment factors were combined as split-split plot arrangement fitted into
randomized complete block design; with four replicates.
Results indicate that the lateral root branching density at 5 and 10 cm differed
significantly (P≤0.05) across cowpea genotypes. Genotype showed significant effect on
taproot diameter at 10 cm. Moisture status and P level exerted significant effect on
cowpea genotypes 15 cm. There were significant differences (P≤0.05) for lateral root
branching density observed at 5 and 10 cm depth in P rates x genotype interaction.
Statistical analysis showed that P levels and cowpea genotypes had significant effects
(P≤0.05) on mean plant height, biomass and highly significantly effects (P≤0.01) on
number of branches, days to physiological maturity and mean pod length. The
interaction between cowpea genotype and moisture stress condition significantly
(P≤0.05) affected hundred (100) seed weight. Cowpea genotype Tvu16408 obtained
highest grain yield of 3240 kg ha-1 and lowest was by IT00K1217 which obtained grain
yield of 1256 kg ha-1.
Results showed that photosynthetic rate, water conductance, transpiration rate, sample
cell CO2, sample cell H2O, relative humidity in the cell, intercellular CO2 and vapour
pressure deficit differed significantly (P≤0.05) across cowpea genotypes. Soil moisture
condition and cowpea genotype exerted significant (P≤0.01) effect on photosynthetic
rate, water conductance, transpiration rate, sample cell CO2, sample cell H2O and
relative humidity in the cell. Variation in P levels had no significant effect on the
measured photosynthetic parameters. Oloyin genotype had the highest photosynthetic
rate followed by Tvu 4632 while cowpea genotype Tvu 9848 had the least
photosynthetic rate. Interaction of moisture stress and cowpea genotype had a
significant effect on intercellular CO2 concentration. Water stress reduced the
intercellular CO2 concentration of Oloyin, Tvu 6365 and 4632 but resulted in a
significant increase in intercellular CO2 concentration in Tvu 9848 genotype.
Results showed that variation in soil P level exerted a significant (P≤0.05) effect on
grain tissue P content and uptake, and a highly significant (P≤0.01) difference in P
content across the various cowpea genotypes. Moisture stress exerted a significant
(P≤0.05) difference on P uptake. The results showed that P levels and cowpea
genotype variation exerted significant (P≤0.05) effects on P content, P uptake and
nitrogen (N) uptake. Moisture status and cowpea genotype variation exerted significant
(P≤0.05) effects on total N and N uptake. Cowpea genotype Tvu 9848 obtained more
total N content (4.37%), while the lowest total N content was obtained by cowpea
genotype Tvu 15445 with 3035 mg kg-1. The interaction between cowpea genotype and
moisture status exerted a significant (P≤0.05) effect on N and P uptake of immature
green pods harvested. There is a need to conduct more studies to identify cowpea
genotypes, their root architecture and agronomic measures that can do well under
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drought stress and low soil P conditions. Research needs to be conducted to enhance
cowpea productivity under both low soil P and drought stress.
Keywords: cowpea genotypes; moisture stress; phosphorus fertilisation; root traits
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/1585 |
| Date | January 2015 |
| Creators | Thosago, Setshele Standford |
| Contributors | Mariga, I. K., Kutu, F. R. |
| Publisher | University of Limpopo |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xvii, 118 leaves |
| Relation |
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