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Soil moisture measurement

pF determination

The pF-curve, or moisture characteristic of the soil, measures how easily plants can access water in the soil. This accessibility differs per soil type, but with the right instruments, the characteristic pF-curves can be determined for each. These curves relate the soil suction, or how tightly moisture is held in the soil, to its moisture contents. We offer multiple lab instruments that help determine the full pF-range.

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pF determination

Water relations are among the most important physical phenomena that affect the use of soils for agricultural purposes. Insight in these relations help establish effective irrigation and fertiliser practices for the commercial growing of food stuffs. But it also influences engineering purposes.

The relationship between soil water retention and moisture content is important in studies of soil moisture movement and of quantity and availability of soil moisture for plant growth. Moisture in the soil alone isn't enough, the suction needs to allow plant roots to extract it.

pF determination helps to get insight in these soil moisture characteristics. These are many methods to do this, and Royal Eijkelkamp offers equipment for the following:

Sandbox method

This method is suitable for insight in the wettest part of the curve, pF 0 to 2.0. It requires undisturbed samples, taken in soil sample rings. 

Sandbox/kaolin method

This method shapes the largest part of the curve, pF 2.0 to 2.7. 

Membrane apparatus

This instrument determines the driest range of the pF-curve, from 3.0 to 4.2. 

Ceramic plates

The sets with ceramic plates are suitable for the pF-range of 2.0 to 4.2. In addition, it can be used for the calibration of soil moisture blocks or soil moisture measurement equipment. 

The soil moisture retention curve

pF determination is really about researching a characteristic of the soil: how tightly does it hold on the water? The higher the soil retention curve, the harder plants have to work to extract the water. This means that, even with high soil moisture contents, the plants can wilt.

In general, clay soils have a higher soil suction that sandy soils. This means that it's always important to research both soil moisture and suction to make the best decisions about additional irrigation. 

Michiel van Kampen

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Need advice choosing the right product for your application? Our specialist Michiel is happy to help.