# How is PF calculated 1

## Usable field capacity of the soil up to 100 cm

Method namenFK-100 PD, classified
Method ID101
editorKlaus Friedrich & Thomas Vorderbrügge
Input dataFine soil of the horizon (rep.)
Humus content (rep.)
Mightiness (rep.)
Packing density
Type of peat
Decomposition level
Substance volume
Correction factor for coarse soil proportion (72)
Characteristic valuesNFKS (level)
was standingJuly 1, 2003, version 1
swellAG Boden (1994): Soil Science Mapping Instructions. 4th edition; Hanover.
HLUG (2003): Soil characteristic value tables
ExplanationThe usable field capacity (nFK) of a soil or horizon is that part of the field capacity that is available for vegetation. It thus contains the amount of water that a horizon remote from the groundwater can hold back in natural storage at suction pressures of pF 1.8-4.2 after sufficient saturation against gravity. The calculation is first made for each horizon. The results are added up and classified based on a depth of 100 cm. The method gives the representative NFK up to 100 cm for a cover / use differentiated substrate unit.
Remarks

### 1. Calculation of the usable field capacity

To calculate the usable field capacity of a horizon for mineral soils, the usable field capacity in mm / dm is first determined from the basic data soil type (rep.) And packing density on the basis of the characteristic values. This is corrected accordingly by additions depending on the organic matter and finally multiplied by the thickness of the horizon (dm). For horizons with a high proportion of coarse soil, the calculated values ​​are multiplied by the correction factor for the proportion of coarse soil (72).

nFK horizon (mineral soil) (mm) = [nFK (mm / dm) + HZ (mm / dm)] × [HM (cm) / 10] × [KoF]

in which:
HM = thickness of the horizon
KoF = correction factor for the coarse soil share

In the case of organogenic horizons (H), depending on the substance volume, the type of peat and the decomposition level, the usable field capacity (mm / dm) is taken from the characteristic value tables. This value is then multiplied by the thickness of the horizon in dm (HM).

nFK horizon (peat soil) (mm) = nFK (mm / dm) × HM (cm) / 10

The calculated values ​​of the horizons are added up in a second step. The value of a horizon that exceeds a depth of 100 cm is proportionately included in the calculation. If the profile description is shorter than 100 cm, a depth of up to 100 cm is assumed for the horizon described last.

### 2. Classification of the usable field capacity

The classification corresponds to the information in Tab. 60 of KA4 (AG Boden 1994), but the effective root space is used as the reference depth.

nFK up to 100 cmDesignation of the nFK level
0 - 60very low (1)
>60 - 140low (2)
>140 - 220medium (3)
>220 - 300high (4)
>300very high (5)