Geophysics applied to agricultural projects – case history from South Africa
Zetica recently carried out an electromagnetic survey over approximately 1,000ha to select optimal areas for installing overhead irrigation (centre pivots) on previously unused agricultural lands in northern Kwazulu-Natal, South Africa. The criteria for locating pivots for cotton growing include well drained soils and low acidity values both of which can be indirectly mapped using ground conductivity. The blue – green colours in the image below left show optimal soils to a depth of 0.5-1.0m below ground level.
A real-time kinetic GPS system was integrated with the ground conductivity survey to produce accurate topography maps which also formed a critical part of the design of the irrigation infrastructure. An interpretation map was produced (below right) showing preferred soils overlain on topography to assist in the design of the irrigation infrastructure (example of pivot below centre).
Given the investment of over £2million in infrastructure on this project, where return on investment is a direct function of crop yield, the importance of a detailed geophysical survey to accurately map properties of the soils especially in heterogenous areas, cannot be overstated. Geophysics also plays a role in the ongoing monitoring of soil properties to facilitate targeted remediation as soils become depleted.
In the UK, resistivity is commonly used to delineate the boundaries of different soil types.
Images of the results from a resistivity survey carried out by the Australian Centre for Precision Agriculture on a wheat field, compared with actual wheat yield indicate a strong spatial correlation between each information layer (resistivity data below left, yield data below right).
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