Investigations of agronomic practices to improve the establishment and yields of Amaranthus Hybridus and Cleome Gynandra
Abstract
Many people are becoming increasingly aware of the importance of indigenous
African leafy vegetables in meeting their household food security, and are therefore
producing them in their home gardens and farms. There is however not enough
information regarding agronomic practices for their optimum productivity. In an
effort to investigate viable techniques of producing indigenous leafy vegetables
among local communities, this study was carried out to test agronomic practices that
can be used to improve the establishment, growth, productivity and quality of two
dominant indigenous African leafy vegetables (IALVS) namely, Amaranth us
hybridus and Cleome gynandra.
The effects of seed sowing depth on emergence and early seedling development of
Amaranthus hybridus and Cleome gynandra, was investigated in a glasshouse study.
Eight sowing depths (1.5, 3.5, 7, 10, 15, 20, 25 and 30 mm) were imposed on seeds
of two African indigenous (Amaranthus hybridus and Cleome gynandra) and exotic
(Spinacia oleracea and Brassica napus) leafy vegetable species using a split plot
design with four replicates. Exotic vegetables had significantly higher (p<0.05)
seedling emergence (95%) than the indigenous ones (60%). Among the indigenous
species, Cleome gynandra had a higher emergence (70%) than Amaranthus
hybridus (61 %). However, there were no significant differences on emergence
amongst the exotic vegetables. Exotic vegetables also had significantly higher
(p<0.05) mean plant height (8.6 cm) than indigenous vegetables (1.01 cm). In all the
vegetable species, both emergence and plant height decreased with deeper sowing
due to higher soil strength. The biomass yields of the seedlings were reduced with
deeper sowing although the differences were not significant. There were however
significant differences (p<0.05) among the biomass yields of the vegetable species
at different sowing depths. Generally, significantly higher biomass yields (6.4
g/plant) were obtained in exotic species compared with indigenous ones (0.2
g/plant). The results suggest that seeds of indigenous African leafy vegetables were
more sensitive than the exotic ones to deeper (>10mm) sowing and their emergence
was more adversely affected by soil strength at this depth. Both deep (15-20mm)
and shallow (<10mm) sowing depths reduced the emergence of seedlings of both
species of IALVS studied. It was thus concluded that an optimum stand of IALVS
can be obtained if the seeds are sown at optimum depth of 10 mm.
The effects of applying kraal manure (cattle, goat and control) and leaf cutting
management (cutting edible tender tips only, cutting all leaves and cut all the leaves
only at the end) on leaf biomass yield of indigenous African leafy vegetables
Cleome gynandra and A. hybridus were studied. The plants were grown in large
PVC pots laid in a randomized complete block design and leaves were cut five
times before the final harvest. Applications of kraal manure improved leaf biomass
yield of both vegetables and the yield was increased with successive cutting where
kraal manure was applied. Plants that were grown in soil amended with goat manure
produced significantly higher total fresh leaf biomass yield (470.86 g pot⁻¹) than
those under cattle manure (328.42 g pot⁻¹) in C. gynandra. A similar observation
was made in A. hybridus plants.
The results showed that fresh leaf biomass of C. gynandra and A. hybridus were
increased when kraal manure was added. The yield was higher in goat manure when
all the leaves were cut than in cattle manure for both vegetables. It was observed
that in all the cutting techniques, plants that were not amended with kraal manure
produced the lowest crude protein content while the highest CP content was
obtained from the plants that were amended with kraal manure across all the cutting
techniques. The biomass yields of both vegetable species in the treatments with
manure increased progressively with each harvesting while those in the control
declined. Plants where all the leaves were cut produced significantly higher total
yields (371 g pot⁻¹) compared with cutting only edible tender leaves (342.83 g pot⁻¹)
and cutting all the leaves at the end (165.35 g pot⁻¹). A combination of goat manure
and cutting all leaves gave the highest fresh leaf biomass yield (571.99 g pot⁻¹)
while the corresponding yield for cattle manure was (439.69 g pot⁻¹). The results
revealed variations among the two manure types with goat manure being superior to
cattle manure. It was concluded that the yields of Cleome gynandra and
Amaranthus hybridus could be increased by adopting an appropriate manure and
leaf cutting technique.
In order to determine the influence of phosphorus fertilizer and leaf cutting
techniques on biomass yield and quality of leaves of amaranthus (Amaranthus
hybridus) and cleome (Cleome gynandra), an experiment was conducted in pots
where single super phosphate (SSP) fertilizer was applied at rates equivalent to 0,
20, 40 and 60 kg ha⁻¹. Phosphorus application significantly (P<0.05) increased leaf
biomass yields compared with the control. The biomass yields of both species
increased with increasing P level with plants that received 60 kg P ha⁻¹ producing
significantly (P<0.05) higher total fresh leaf yield (266.7 g pot⁻¹) than in 20 and 40
kg ha-1. Application of P fertilizer also contributed to increased fresh stem and root
biomass of both C. gynandra and A. hybridus. In both vegetable species, highest
fresh leaf yield was obtained from the plants whose leaves were all cut leaving
mature leaves and stems while lowest yields were obtained when plants were cut
once at final cut. There was a high moisture content in plants whose leaves were cut
throughout while the lowest moisture content was obtained from plants that were
cut once at the end. The biomass yields increased with increasing P rates across all
cutting techniques in both vegetable species. A combination of fertilizer at 60 kg P
ha-l and cutting all leaves throughout produced highest fresh leaf yield. The results
indicated that crude protein was decreased when leaves were cut once at end of the
study across all the phosphorus rates. Highest crude protein content was obtained
when all leaves were cut at all P rates in both vegetable species. It was concluded
that leaf cuttings with high rates of P fertilizer can contribute to improved biomass
yield production of the two indigenous African leafy vegetables.
In both C. gynandra and A. hybridus, the crude protein in leaves was enhanced by
application of kraal manure with goat manure producing higher crude protein than
cattle (14.2% vs 13.4%, respectively) and (12.2% vs 11.44%, respectively).
Application of phosphorus significantly (P<0.05) increased the crude protein
content of vegetable leaves. Frequent cut of leaves enhanced crude protein
production while cutting leaves once at final cut produced lowest crude protein. It
was concluded that the crude protein content of IALVS can be improved by P
fertilizer and frequent cut of leaves of IALVS.
Not withstanding the limitation of practical application of pot growth experiments,
the significance of this study is that, the findings can help to promote the production
of IALVS by providing the necessary agronomic information for their cultivation.
The results of this study indicate that planting depth and fertility management are
important for improving productivity and should however be confirmed under
different field conditions and for longer experimental duration to provide
recommendations for farmers.