Role of fertilisation regimes on the yield and nutritional benefiits of cowpeaamaranth intercropping systems.
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Date
2020
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Abstract
Several African leafy vegetables (ALVs) contribute to food and nutritional security of rural
communities, particularly due to their ability to grow in marginal soils. These ALVs such as
amaranth and cowpea among others provide valuable macro- and micronutrients that are
key to rural household dietary needs. The aim of this study was to assess the effect of
fertiliser application on the symbiotic nitrogen fixation, enzymatic phosphatase activity, agro
biological properties, nutrition as well as recommended daily allowance in an intercropped
Amaranthus cruentus (amaranth) and Vigna unguiculata (cowpea) farming system. The
nitrogen fixation and nutritional yield of cowpea-amaranth intercrop study was motivated by
limited information relating symbiotic nitrogen fixation and fertilisation of ALVs, such as
cowpea and amaranth grown under intercropping system, in addition to nutritional yield.
Field trials were conducted at the Agricultural Research Council (ARC), Vegetables and
Ornamental Plants campus situated in Roodeplaat, Pretoria, South Africa, during 2014/15
and 2015/16 summer seasons from November to January. The 2 x 4 factorial experiments
were laid out in a completely randomized design (CRD) with four replications. The factors
evaluated were intercropping (amaranth and cowpea) and fertiliser (control, 25%, 50%, and
100% of the recommended NPK levels). Soil sampling was done before land preparation
and soil nutrient analysis was done at the Agricultural Research Council–Soil, Climate and
Water (ARC–SCW). The application of nitrogen, phosphorus and potassium were guided by
the soil analyses results and recommendations on both seasons. Vigna unguiculata was
sown directly in the soils and amaranth was transplanted approximately four weeks after
planting amaranth in the nursery. Irrigation was done based on reference evapotranspiration
(ET) and a crop factor for each crop. Collected data included acid and alkaline phosphatase
activity, phosphorus in the soils, phosphorus in the cowpea and amaranth plants, as well as
biomass of cowpea and amaranth at physiological maturity. In the rhizosphere of cowpea
and amaranth grown as sole crops, there was a higher acid and alkaline phosphatase
activity as compared to those on intercropping. The highest rhizospheric phosphatase
activity occurred when both crops were grown without fertilizer or 25% NPK. Applying NPK
activates soil-bound phosphorus (P) using root exudates, which is important for the
production of ALVs. The results showed a reduction in symbiotic N2 fixation of cowpea with
the increase fertiliser addition.
The above ground and above ground edible biomass of amaranth increased proportionately
to the rate of fertiliser application up to 100% NPK, but in cowpea it only increased up to
50% NPK. Nutritional yield of iron and zinc increased with the increase in fertiliser application
amounts on cowpea and amaranth. The land utilisation values were greater than one, hence
an advantage of intercropping. Cowpea was more aggressive, showed high actual yield
losses and high competitive ratio relative to amaranth. More income could be obtained from
intercropping cowpea and amaranth compared to the respective sole crops at 100% NPK.
In the experiment on the potential of intercropped amaranth and cowpea to meet nutritional
requirements, the seasonal above ground and above ground edible biomass of amaranth
and cowpea increased with fertiliser application up to 100% NPK. More above ground and
above ground edible biomass on amaranth and cowpea were obtained in sole cropping
when compared to intercropping. Macro and trace nutritional element contents were highest
at 100% NPK fertiliser level. The lowest nutritional contents of macro and trace elements
was recorded at the control. Overall, amaranth and cowpea contributed to the recommended
daily allowance of calcium, magnesium, iron, and zinc, where there was more at the 100%
NPK fertiliser level. The research demonstrates the benefits of grain leguminous crops in
soil nutrient fertility enhancement and inorganic fertilization with intercropping in managing
micronutrient deficiency to meet the nutritional needs of rural communities. Moreover, the
study demonstrated the benefit of applying 25%NPK to 50%NPK fertiliser on the above
ground and above ground edible biomass of amaranth and cowpea. In sum, macro and trace
elements that are crucial for the nutritional health of rural communities were improved, thus
contributing more to the recommended daily allowance, which limits food and nutrition
insecurity, and fosters sustainable development.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.