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| a pF = log of cm water column. | |||
| b 1 bar = 105Pa. | |||
| c Corresponds to an approximate water content of 10% in sand, 35% in loam and 45% in clay. | |||
| d Field capacity is not constant but varies with soil type between pF 1.5 and 2.5. | |||
| Height of Water Column [cm] | pFa | barb | Remarks |
|---|---|---|---|
| 107 | 7 | 104 | Dry Soil |
| 1.6 · 104 | 4.2 | 16 | Wilting point |
| 104 | 4 | 10 | |
| 103 | 3 | 1 | |
| 6 · 102 | 2.8 | 0.6 | |
| 3.3 · 102 | 2.5 | 0.33c | |
| 102 | 2 | 0.1 | Range of Field capacityd WHC (approximation) Water saturated soil |
| 60 | 1.8 | 0.06 | |
| 33 | 1.5 | 0.033 | |
| 10 | 1 | 0.01 | |
| 1 | 0 | 0.001 | |
Water tension is measured in cm water column or in bar. Due to the large range of suction tension it is expressed simply as pF value which is equivalent to the logarithm of cm water column.
Field capacity is defined as the amount of water which can be stored against gravity by a natural soil 2 days after a longer raining period or after sufficient irrigation. It is determined in undisturbed soil in situ in the field. The measurement is thus not applicable to disturbed laboratory soil samples. FC values determined in disturbed soils may show great systematic variances.
Water holding capacity (WHC) is determined in the laboratory with undisturbed and disturbed soil by saturating a soil column with water by capillary transport. It is particularly useful for disturbed soils and can be up to 30 % greater than field capacity (1). It is also experimentally easier to determine than reliable FC-values.