African leafy vegetables have been shown and suggested to have potential to contribute to
human diets and alleviate malnutrition; however, their levels of utilisation are currently low
especially in South Africa. This is because there is limited access to these crops due to low
availability in the market. Limited access is attributed, in part, to the lack of
commercialisation as a result of limited agronomic information describing optimum
management options for these leafy vegetables. Availability of such information would
contribute to successful commercialisation of these crops. The primary objective of this study
was to establish optimum agronomic management factors for Amaranthus cruentus,
Corchorus olitorius, Vigna unguiculata and Brassica juncea for irrigated commercial
production in South Africa.
Seeds of Amaranthus cruentus, Corchorus olitorius were obtained from the Agricultural
Research Council seed bank; Vigna unguiculata were obtained from Hydrotech and Brassica
juncea seeds were obtained from Stark Ayres. The project consisted of three field studies
whose overall objective was to evaluate growth and yield responses of the selected African
leafy vegetables to agronomic factors under irrigated commercial production. These field
studies comprised of two single factors; summer trials (planting density and nitrogen on three
selected crops) and a combined winter trial (nitrogen, irrigation, plant density and planting
date on a winter crop). Chapter three (3) investigated the effect of plant density on growth, physiology and yield
responses of Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata to three plant
densities under drip irrigated commercial production. The plant density levels of 100 000, 66
666 and 50 000 plants/ha were used in the 2011/12 and 2012/13 summer seasons. Parameters
measured included chlorophyll content index (CCI), chlorophyll fluorescence (CF), stomatal
conductance (SC), leaf number, leaf area index (LAI) and biomass. Amaranthus cruentus and
Corchorus olitorius showed better leaf quality at lower plant density of 50 000 plants ha-1
than at 66 666 plants ha-1 and 100 000 plants ha-1. These results are based on bigger leaves
expressed as leaf area index (LAI), better colour expressed as chlorophyll (CCI) and higher
biomass per plant observed in these crops at 50 000 plants ha-1 in comparison to 66 666 plants
ha-1 and 100 000 plants ha-1. In Vigna unguiculata there were no responses observed in LAI
and CCI. In Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata fresh and dry
mass yield of leaves were higher at 100 000 plants ha-1 compared to other treatments. In A. cruentus and C. olitorius, higher leaf quality parameters (CCI, plant height, leaf number,
biomass per plant and LAI) indicated that these crops can perform better at lower densities of
50 000 than at 66 666 plants ha-1 and 100 000 plants ha-1 Therefore, using 50 000 plants ha-
1 is suitable for commercial production of A. cruentus and C. olitorius. In Vigna unguiculata,
a plant density of 100 000 plants ha-1 produced the highest fresh and dry mass per unit area
without compromising quality in terms of the leaf size (LAI) and colour (CCI). Therefore 100
000 plants ha-1 is a density recommended for commercial production in V. unguiculata.Chapter four (4) was conducted to investigate growth, physiology and yield responses of A.
cruentus, C. olitorius and V unguiculata to nitrogen application under drip irrigated
commercial production. Three nitrogen treatments levels were used viz. 0, 44 and 88 kg N ha-
1 in 2011/12 season and four nitrogen treatments levels viz. 0, 50, 100 and 125 kg N ha-1 were
used in 2012/13 summer season. The nitrogen levels selected for each season were based on
recommendations for Amaranthaceae species, Swiss chard (Beta vulgaris L.var cicla)
derived from soil analysis of the trial (field) site. Parameters measured included chlorophyll
content index (CCI), chlorophyll fluorescence (CF), stomatal conductance (SC), leaf number,
leaf area index (LAI) and biomass. Results showed that application of nitrogen at 44 kg N ha-
1 in 2011/12 summer season and 100 kg N ha-1 in 2012/13 summer season improved LAI,
CCI, biomass per plants and yield in A. cruentus. A similar trend was observed in C. olitorius
except that 44 kg N ha-1 improved stem fresh yield. Further increase in nitrogen fertiliser
above 44 kg N ha-1 during the 2011/12 season and above 100 kg N ha-1 in 2012/13 summer
season reduced leaf quality and yield in both crops. In V. unguiculata, nitrogen application
showed a slight increase in yield values from 0 to 44 kg N ha-1 followed by decrease at 88 kg
N ha-1 in 2011/12 summer season; however, this increase in yield was not significant. During
the 2012/13 summer season, yield in terms of fresh weight was significantly (P<.001)
reduced by applying nitrogen at various levels. However, leaf dry matter content increased
significantly (P<.001) with increase in nitrogen from 0 kg up to 100 kg N ha-1, then remained
unchanged at 125 kg N ha-1. Therefore, the current study recommends that C. olitorius and A.
cruentus could be commercialised at 44 kg N ha-1 and 100 kg N ha-1 which were lower
nitrogen application rates than those recommended for Amaranthaceae species. In V.
unguiculata, 50 kg N ha-1 improved leaf number; however, this did not translate to any fresh
yield advantage, implying that the optimum rate for nitrogen application might be lower than 50 kg N ha-1. Therefore, nitrogen rates less than the ones used in the current study are
recommended for V. unguiculata. Chapter five (5) was conducted in winter and it was necessitated by observations made
primarily in the previous studies which focused on the effects of single factors such as plant
density, planting date and nitrogen deficits. Therefore, there was a need to address
interactions between irrigation, nitrogen, spacing and planting date. The objective of this
study was to evaluate growth, physiology and yield responses of Brassica juncea to different
agronomic and management factors in the 2012 and 2013 seasons. The treatments were as
follows: two planting dates in main plot (1 June and 18 July, 2012); two irrigation frequency
in sub main plot (once and three times a week); three nitrogen levels (0, 50, 100 kg N ha-1)
and three plant densities (133 333, 80 000, 50 000 plants ha-1) as subplots. Parameters
measured included chlorophyll content index (CCI), chlorophyll fluorescence (CF), stomatal conductance (SC), leaf number, leaf area index (LAI) and biomass. Results from this study
showed a significant interaction effect on plant height, LAI, CCI and CF. Crops irrigated
thrice or once a week with 50 kg N ha-1 combined with 50 000 plants ha-1 produced tall plants
and bigger leaves (LAI) in the early planting date (1 June) compared to other combinations.
Irrigating three times a week combined with nitrogen application at 100 or 50 kg N ha-1
improved CF for late planting date (18 July) in comparison to other combinations. Irrigating once a week combined with nitrogen application at 100 kg N ha-1 increased CCI. There was
no significant interaction effect on yield. Application of nitrogen at 50 and 100 kg N ha-1
significantly (P>0.05) increased yield in early and late planting dates compared to the control
(0 kg N ha-1), in 2012 and 2013 winter season. Irrigating three times a week led to a
significant (P<0.05) increase in yield in the late planting date (18th July) and early planting date (1st June) in 2013 season. Higher plant density of 133 333 plants ha-1 resulted in
significantly (P<0.05) higher yield in terms of fresh mass and leaf number in the late planting
date 18 July in 2012 and 2013 seasons. However, leaf quality parameters such as leaf size and
colour was compromised at 133 333 plants ha-1 relative to 50 000 plants ha-1. Therefore,
farmers are recommended to plant early, apply 50 kg N ha-1, irrigate thrice a week and utilise
a spacing of 50 000 plants ha-1. The current study indicates that growth and yield of
traditional leaf vegetables can be optimised through improved agronomic practise. / Agriculture and Life Sciences / D. Litt. et. Phil. (Agriculture)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:unisa/oai:umkn-dsp01.int.unisa.ac.za:10500/18999 |
| Date | 06 1900 |
| Creators | Maseko, Innocent |
| Contributors | Beletse, Yacob, Nogemane, Noluyolo |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | 1 online resource (xx, 150 leaves) |
Page generated in 0.0025 seconds