Soil Moisture, Soil Water and Soil Tension

Soil Moisture:  Previously the only accurate way to measure soil moisture on site was by use of the neutron probe, nowadays it is very easy and safe with TDR technology.  The award winning TRIME TDR device for example generates a high-frequency-pulse (up to 1GHz) which propagates along the wave guides generating an electromagnetic field around the TRIME-probe. At the end of the wave guides, the pulse is reflected back to its source. The resulting transit time and dielectric constant are dependent on the moisture content of the material.  This highly complex but extremely easy to use technology should not be confused with capacitance or FDR techniques which, although acceptable for general relative measurements cannot be used for serious research. In particular accuracies can be seriously compromised in clay rich or very organic soils. TDR, and in particular TRIME TDR  on the other hand returns results in line with the accuracy of the now discontinued neutron probe. TRIME TDR can be single point, multipoint, profiled or networked. A huge additional advantage is the availability of data from these systems to report a signal which can interpret the soil conductivity.

Soil Water: Extraction of water from the soil spaces or pores is an important research facility for anyone involved in the cultivation of crops. Methods of extraction follow fashions. Yesterday’s best material is vilified today.  At Van Walt we’ve concentrated on two sampling methods. For general soil water extraction, especially when larger volumes of samples are required we supply ceramic cups. These are cheap and work well when simple analyses such as residual nitrates are needed. Unfortunately ceramic cups can interfere with the chemistry of certain elements, compounds or measurements such as for example pH and Phosphorus and other metals.  When a large range of analyses need to be carried out then the Rhizon samplers have become very useful and are now more or less the researcher’s favourite in the UK and many parts of Europe. Rhizon samplers are made of a porous and inert polymer.

Soil Tension: In crop irrigation studies soil tension is an important measurement. A vast array of different tensiometers is available for this purpose with manual or electronic readout facilities.