The best techniques for soil solution sampling

June 16, 2011

Soil solution sampling is used to monitor the effects of air pollution and other stress factors on soil properties. The 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.

As a general rule sampling can be done by non-destructive or destructive methods. Non-destructive methods involve the installation of a soil solution collector, like a rhizon that samples soil solution at the same point. Destructive methods involve soil sampling and subsequent extraction of soil solution in the laboratory.

A number of reviews and comparison studies have been carried out on the different techniques used to obtain samples of soil solution and as the soil solution sampling technique employed depends on the aim of soil solution monitoring, the following broad recommendations can be made:

– Repeated soil sampling results in considerable disturbance to the site. Therefore,to produce a time series with short sampling intervals, a non-destructive method is the most appropriate.

– For monitoring with large time intervals, repeated soil sampling followed by centrifugation (or a saturation extract when centrifugation is impossible) is also appropriate, especially as this approach reduces spatial variation.

At Van Walt we’ve concentrated on two non-destructive sampling techniques. 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 our 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.

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