Recent PARG Graduates
Dr. Peter Clark (PhD)
Project: The Effect and Mitigation of Vineyard Trellising on EM38 Soil Conductivity Measurements (2006-2009)
Funding Source : University of New England.
Summary:
The EM38 has a widely accepted role in precision agriculture for the efficient mapping of sub-surface apparent electrical conductivity at data densities of the order of 10 m. The resultant high-resolution maps of apparent conductivity enable agriculturists to infer soil properties such as soil moisture and salinity which aid localized crop management decisions. However, when applied to viticulture, previously published research has confirmed that the use of electromagnetic induction instruments, such as the EM38, has been flawed by the interference from the conducting wire and steel-post loops of the grapevine trellising. This has raised questions about the reliability of interpretations made from potentially flawed maps of apparent conductivity in vineyards.
In this research, a combination of component and whole trellis assembly trials confirmed that this interference was separable into two significant components: the steel trellis loops and the trellis-earth system. Furthermore, while these two effects theoretically interact, the contributions from each were found to be conceptually separable in terms of both the EM38 response and possible mitigation or data correction strategies.
An analytical expression was initially developed to predict the interference from steel conducting loops in terms of the mutual inductance from both the transmit and receive coils of the instrument to the Target Loop, the loop’s self-inductance, and its electrical resistance. Increasing the complexity of the loops to reflect real trellis geometries necessitated the use of a numerical analysis program (FastHenry) to calculate the parameters of loop resistance, self-, and mutual-inductance, for substitution into the analytical expression.
Several patterns within the trellis interference were discovered in the simulated vineyard trellising and the commercial vineyard tested. These patterns led to several mitigation/correction possibilities. Future work in the trellis interference on EM38 surveys should focus on the development and refinement of the practical empirical mitigation strategies proposed, rather than further analyses of the detailed mechanism of the trellis-loop and trellis-earth eddy currents because of the difficult to predict post-wire and post-earth resistances, as well as the complexities of the trellis-earth eddy currents.