Non-invasive imaging of roots with high resolution X-ray micro-tomography

X-ray micro-tomography is a well-established technique for non-invasive imaging and evaluation of heterogeneous materials. An inexpensive X-ray micro-tomography system has been designed and built for the specific purposes of examining root growth and root/soil interactions. The system uses a silver target X-ray source with a focal spot diameter of 80 (mu)m, an Xray image intensifier with a sampling aperture of about 100 (mu)m, and a sample with a diameter of 25 mm. Pre-germinated wheat and rape seeds were grown for up to 8–10 days in plastic containers in a sandy loam soil sieved to < 250 (mu)m, and imaged with the X-ray system at regular intervals. The quality of 3 D image obtained was good allowing the development and growth of both root axes and some first-order laterals to be observed. The satisfactory discrimination between soil and roots enabled measurements of root diameter (wheat values were 0.48–1.22 mm) in individual tomographic slices and, by tracking from slice to slice, root lengths were also measured. The measurements obtained were generally within 10% of those obtained from destructive samples measured manually and with a flat-bed scanner. Further developments of the system will allow more detailed examination of the root:soil interface.