Abstract:
The use of external inputs in the form of inorganic fertilisers is rising across the
world. Rapidly growing crops such as vegetables necessitate high fertiliser
inputs, whilst remaining an attractive cash-crop option for farmers, especially
smallholders in the developing countries. For vegetable farming to be
sustainable, these inputs should be monitored so the crop nutrient use efficiency
is high and the potential for under- and over-fertilisation is low.
Therefore, there is a need for the development of low-cost tools that can bring
site-specific soil information to farmers who do not ordinarily have access to such
knowledge. In recent years, smartphone technology has given rise to a number
of advanced apps that aim to improve agronomic production, especially in the
Southern Hemisphere. The work in this thesis centres around method
development and appraisal for the application of a smartphone-mediated
diagnostic tool for use in soil nutrient screening.
A smartphone application marketed as Akvo Caddisfly, used together with
nutrient-sensitive test strips was repurposed for the analysis of soil samples. The
app was used alongside selected test strip types and underwent rigorous
laboratory testing to evaluate its suitability for soil analysis and to identify its
strengths and weaknesses. The laboratory-based experiments allowed for the
development of soil extraction, filtration and analysis methodologies, through the
utilisation of variable soil samples obtained from Indonesia, an approach
subsequently employed in field conditions in other study sites.
The field-based experiments were undertaken in the People’s Republic of China,
Ghana and Kenya, allowing for a critical appraisal of smartphone-mediated soil
analysis as an effective tool for fertiliser recommendations in smallholder
vegetable production. In China, where frequent over-fertilisation of crops is the
chief cause of soil acidification and heavy metal pollution as well as
eutrophication of waterbodies and high N₂O emissions, smartphone-mediated
soil analysis was employed successfully in identifying over-fertilised plots. In
contrast, in Sub-Saharan Africa, where soil Nitrogen content was low,
smartphone-mediated soil analysis encouraged farmers to apply organic
fertilisers to improve their yields.
Referencing the metadata, which was collected during laboratory and field-based
experiments, a framework for designing and evaluating future in-field soil test kits
was created. The data consisted of a collation of quantitative analyses and
qualitative observations and these were synthesised into a step-by-step process
that can be used at the test kit evaluation stage to reduce the time and costs
associated with their development. Finally, a range of statistical approaches were
employed to investigate the level of agreement between the in-field method and
the accepted laboratory standard methods employed in agricultural soil analysis.
They were described in detail to encourage their wider application in method
comparison studies across environmental science.