Studies into plant water relations of cotton are sometimes constrained by the inability to adequately characterise the root zone or the effectiveness of water uptake. It can be very difficult to measure the depth or lateral movement of roots, or the way roots interact with soil type and irrigation method. This is especially so under field conditions. However, by using a new technique that utilizes an array of multi-level capacitance probes, it is now possible to measure changes in soil moisture in a two-dimensional plane across the root zone and easily follow these changes over time – even under commercial growing conditions.

Capacitance probes are electronic sensors that measure volumetric soil moisture simultaneously at multiple depths and are very effective at tracking small changes over time. When a series of probes are placed in close proximity across the plant line, it creates an array of measurement points tracking changes in soil moisture throughout the root zone. Data from each sensor can be interpolated to provide a colour map, or picture of soil moisture at each point in time. When a series of pictures are run together in a time animation, it is possible to dynamically view the changes in soil moisture, creating a movie depicting root growth and water extraction over the life of the crop.

This technique can be used to compare the root structure and moisture extraction of different varieties, or the effectiveness of different irrigation methods. The continuous data provides the ability to watch the plant ‘drink' on a daily basis and it is now possible to compare above ground stresses with the below ground response. This technique is not only provides a valuable insight into the root response to plant water relations, but the movies are also a highly intuitive method of showing these complex relationships in an easily understood format.