Growth, physiology and yield responses of Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata to plant density under dripirrigated commercial production
Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata are traditional leafy vegetables with potential to improve nutritional security of vulnerable people. The promotion of these crops is partly hindered by the lack of agronomic information. The effect of plant spacing on growth, physiology and yield of these three leafy vegetables was evaluated under commercial-scale production at Roodeplaat, Pretoria over two summer seasons, 2011/12 and 2012/13. A randomised complete block design was used with plant density (100 000, 66 666 and 50 000 plants ha−1) as a factor. Chlorophyll content index (CCI), chlorophyll fluorescence, stomatal conductance, leaf number, leaf area index (LAI) and biomass were measured in situ. Planting at 100 000 plants ha−1 resulted in lower (P < 0.05) LAI, CCI and biomass per plant for A. cruentus and C. olitorius. Total yield of A. cruentus, C. olitorius and V. unguiculata was higher (P < 0.05) at 100 000 plants ha−1 relative to 50 000 and 66 666 plants ha−1. For A. cruentus and C. olitorius, higher leaf attributes (CCI, plant height, leaf number, biomass per plant and LAI) were obtained and this indicated that traditional leafy vegetables can be produced commercially under lower densities using a drip irrigation system. Using 66 666 plants ha−1 is suitable for commercial production of A. cruentus and C. olitorius, whereas 50 000 plants ha−1 may be recommended under low water availability. For V. unguiculata 100 000 plants ha−1 is recommended.
Keywords: chlorophyll content index, chlorophyll fluorescence, production, stomatal conductance