Determination of the timing and amount of irrigation of winter cover crops with the use of dielectric constant and capacitance soil water content profile methods

Abstract

A well-managed irrigation scheduling system needs a rapid, precise, simple, cost-effective and non-destructive soil water sensor that allows for measurements at different depths and different locations across the cropped area. Two soil water content profile measurement methods were used and compared to determine the timing and amount of irrigation of three winter cover crops (Avena sativa, Secale cereale and Lolium multiflorum): the PR1 profile probe dielectric and Diviner 2000 capacitance methods. The laboratory-measured retentivity relationship was used to define the fill (0.39 m³ m⁻³) and high refill point (0.34 m³ m⁻³). Soil water content was measured two to three times per week starting from 50 days after planting (DAP) until 164 DAP. After the last rainfall event of 8 mm (142 DAP), the next irrigation was predicted graphically using the PR1 measurements to be five days later and seven days for the Diviner 2000. This difference occurred since the Diviner 2000-measured soil water contents at the rooting depth were slightly higher than those obtained using the PR1 method. The amount of irrigation estimated using graphical and mathematical methods were in good agreement.