Assessing the potential for ion selective electrodes and dual wavelength uv spectroscopy as a rapid on-farm measurement of soil nitrate concentration

Current fertiliser recommendations for nitrogen are limited in their accuracy and may be improved by the use of simple on-farm soil rapid tests. This paper investigates the potential for using nitrate (NO₃ ⁻) ion selective electrodes (ISEs) and dual wavelength UV spectroscopy as part of a rapid soil NO₃ ⁻ diagnostic test. Three soil types, representing the major soil types for agriculture in the western UK, were tested. For the three soils, the ISE rapid test procedure gave a near 1:1 response (r² = 0.978, 0.968, 0.989) compared to the internationally-approved standard laboratory method. However, the accuracy of the ISE rapid test was reduced at low soil NO₃ ⁻ concentrations (<10 mg NO₃ ⁻ L⁻¹). We also show that NO₃ ⁻ analysis of H₂O soil extracts by dual wavelength UV spectroscopy was also highly correlated (r² = 0.978, 0.983, 0.991) to the standard laboratory method. We conclude that both ISE and dual wavelength UV spectroscopy have clear potential to be used for the rapid on-farm determination of soil NO₃ ⁻ concentration. Barriers to use of these field-based assessment tools include, farmer perception of cost-benefit, general attitude to new technologies and the ability to generate useful fertiliser use strategies from soil NO₃ ⁻ measurements.