Field capacity

Subfield Capacity is defined as the amount of water that can hold an initially water-saturated soil against gravity in 2 to 3 days yet. The field capacity is of great importance in practical issues of agricultural and horticultural products, eg in matters relating to water supply of the plant, the plant availability of water-soluble nutrients, the removal of soluble substances and irrigation.

Determination

The determination of water content by drying is carried out before a sample of soil in the laboratory over 24 hours at 105 ° C and a weight determination of the soil sample before and after drying. The difference of the measured weights gives the water content. The value is specified ( example values ​​see pore volume ):

• As a percentage (vol. - %)
• By volume [ cm3 cm -3] or
• Based on a certain floor level [mm / dm ].

Because the drainage behavior of a soil, among other things strongly on the type of soil (or their stratification ) depends, agreement has been reached with regard to the determination of field capacity in the laboratory for non- groundwater- influenced soils on a convention: the water content at a soil water tension of 1.8 pF.

The full field capacity is reached in central European latitudes mostly towards the end of winter (March / April). And then the soil is fully saturated with water; in the coarse -and macro- pores is still contain air. The floor can thus in precipitation have a higher water content than determined by the field capacity.

Related to the pore size

The field capacity is, inter alia, of pore size distribution dependent (see pore volume ). Usually it is assumed that pores with a diameter greater than 10 or 50 microns, the water can not hold by capillary forces; the water seeps through the ground.

Also stored in the soil retained water is not fully available to plants. The part of the field capacity (FC ), which can be absorbed by plants through the roots, is the field capacity ( field capacity ), often referred to as ground water storage:

Dead water ( TOT) is less than 0.2 microns so strongly held in the pores by the adhesive forces that plants can not solve it. Here the water tension over 15,000 hPa or 15 is bar, this value is also called permanent wilting point ( PWP ).

• Soil Science
• Hydrology