Summary
The use of the 1:5 weight extract in soil analysis presents some difficulties. Conductivity determinations as a means of assessing the salt status are unreliable for those soils containing appreciable amounts of gypsum, and it is also desirable that the soil organic matter content be known when interpreting the analytical data.
These objections are largely overcome by using saturation extracts. The principal drawback with this method is, however, its laborious procedure.
In an investigation at the Experiment Station at Naaldwijk very good results were obtained using an extract made by adding sufficient field-moist soil to two parts of water until the total volume had increased by one part (1:2 volume extract). The analytical data for conductivity, chloride, nitrogen, phosphate, potassium and magnesium in this extract were very closely related to data obtained by the saturation extract. The correlation coefficientes being between 0.943 and 0.982.
The weight ratio water: soil of the 1:2 volume extract was highly correlated with the organic matter content. In soils low in organic matter the ratio was about 1:1, and with very peaty soils (40 per cent organic matter) about 3 1/2:1.
For precise preparation of the 1:2 volume extract it is necessary to use soil samples at field capacity. A visual check on this condition appeared to be possible.
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Sonneveld, C., van den Ende, J. Soil analysis by means of a 1:2 volume extract. Plant Soil 35, 505–516 (1971). https://doi.org/10.1007/BF01372683
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DOI: https://doi.org/10.1007/BF01372683