Can the PR1 capacitance probe replace the neutron probe for routine soil‐water measurement?

Abstract. A study was conducted to compare the performance of the PR1 capacitance probe (Delta-T Devices) in measuring soil volumetric moisture content (θ) with two established standard methods: the neutron probe (Didcot Instruments) and the gravimetric method. Over a two-year period, the three methods were used to measure θ in glasshouse plots containing crops of either oilseed rape (Brassica napus L.) or bambara groundnut (Vigna subterranea L.). The PR1 probe gave variable performance depending on the depth and soil profile where the measurements were made. In most cases, the PR1 probe significantly overestimated θ. In some cases, it significantly underestimated θ or gave similar values to the other methods. Despite this frequent overestimation of θ, the PR1 probe adequately registered the relative changes in θ Its measurements were linearly and positively related to those of the gravimetric and neutron-probe methods. However, the regression lines significantly deviated from the 1:l line. This paper discusses the possible reasons for the unsatisfactory performance of the PR1 probe and the practical problems associated with the installation of its access tubes.

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