A Controlled‐Temperature Rhizotron

Growth of roots deep in the soil profile often is essential for continued water uptake by dryland crops in subhumid climates. Study of root growth in these situations must be conducted in field‐scale volumes of soil, to allow normal plant development. Additionally, given the importance of temperature to all biological processes, the thermal regime of field soil should be adequately mimicked. We have constructed a rhizotron that meets these criteria. Nine cylinders 0.45 m in diameter and 1.8 m high were fabricated from plastic sewer pipe. Controlled‐temperature water is circulated through plastic tubing embedded in the soil media and wrapped around the columns. Vertical temperature gradients of 15 °C m −1 can be created with horizontal variations of less than 0.4 °C. Diurnal fluctuations in temperature can be produced in the top 0.15 m. Root growth is monitored with root observation tubes installed horizontally at 0.3‐m intervals. Soil volumetric water content is measured by time‐domain reflectometry.