The equipment is suitable for the determination of pF curves in the range of pF 2.0-4.2 (0.1-15 bars of soil moisture tension). Furthermore, the sets are suitable for the calibration of soil moisture blocks or other soil moisture measurement equipment. The standard set contains inter alia: two extractors with ceramic plates (0.1 MPa, 0.3 MPa and 1.5 MPa and 1. 3 and 15 bars) and accessories, soil sample rings, a pressure control panel and a compressor. Several ceramic plates with soil samples can be placed in the extractor at the same time. The pressure control panel is standard equipped with two manometers 0-2 MPa and 0-0.4 MPa (and 0-20 bars and 0-4 bars). The supplied compressor (220V / 50 Hz) is specifically designed for this purpose: maximum pressure 2.0 MPa (20 bars), built in safety precautions, completely guarded and quiet
Moisture is removed from the soil samples by raising the air pressure in an extractor. A porous ceramic plate serves as a hydraulic link for water to move from the soil to the exterior of the extractor. The high pressure air will not flow through the pores in the plate because these are filled with water. The smaller the pore size, the higher the pressure can be before air will pass through. During the test run at any set pressure in the extractor, soil moisture will flow around each of the soil particles and out through the ceramic plate and outflow tube. Equilibrium is reached when water flow from the outflow tube ceases. At equilibrium, there is an exact relationship between the air pressure in the extractor and the water tension in the samples (and hence the moisture content). Accuracy of equilibrium values will not be above that of the regulation of air supply. Therefore, the pressure control panel has independent double regulators.
Compared to other methods, such as compaction, centrifugation, molecular absorption etc, the advantages are as follows:
- Relatively simple method.
- Reliable way of removing soil moisture from soil samples under controlled conditions without disturbing the soil structure.
- The method may be used on prepared samples or undisturbed samples. The soil structure is not disturbed. The characteristic pF curves may be developed for each soil type. These curves relate the moisture tension at which the moisture is held in soil to its moisture content. Studies of soil moisture movement and of quantity and availability of soil moisture have shown this relationship to be important for plant growth.
|Art.-Nr.: 146000||Set for pF determination using the ceramic plate method|
If the properties of the moist soil sample are known, the following values may be determined:
- The pore volume of the soil
- The pore size distribution of the soil
- The capillary rise capacity
- The air and moisture contents of the soil with a given ground water level
- Determination of the field capacity and available soil moisture
- Water tension with respect to the germination time of seeds