The vital for plants water seeps away rainfall (Rain, hail, sleet, snow) in the ground. A small proportion is also derived from the condensation formed by condensation (dew, frost), which is directly through the just below the surface Tauwurzeln is recorded. The non-solid soil substance consists of different sized pores, which are filled with air and / or water. The pores can make up 30 to 60% of the total volume. Depending on the pore volume, the porosity results - the ratio of the cavity volume to the total volume. In dry soil all pores are filled with air.
The infiltrating water displaces the air first in the fine pores, until finally, when the soil is moist, only air remains in the coarse pores. Adhesive or capillary water is the water held against gravity, which remains in pores less than 10 μm due to the surface tension of the water (meniscus = concavely curved water surface). The amount of hold water that the soil with its pores can hold against gravity is called water capacity (WK) or field capacity (FK). She is strong of soil type depends and is expressed in% vol (volume) or% mas (weight). For example, 30% vol FK means that one m³ of soil can hold 300 liters of water, which is an average for clay soils.
In the individual types of pores of the soil, the water is bound with different strength, resulting in the so-called water retention capacity. The coarse pores provide above all for a good ventilation. The middle pores contain most of the water available to the plants. And in the fine-pored portion acts very strong adsorption, This force binds some of the water so strongly that it is not available to the plants. Therefore, this proportion is aptly called dead water, which makes up for loam soils up to 150 l / m³. In heavy clay soils with a field capacity of up to 400 l / m³, the dead water can in extreme cases even be up to 300 l / m³. A balance between available water and dead water have loamy soils, which are among the most profitable. In sand or gravel soils the water seeps away very quickly. Here only 100 l / m³ of field capacity can be maintained, of which 50 to 70 l are available.
The trapped in the soil water rises to a lesser extent back to the soil surface and evaporates what you as evaporation (Evaporation) referred. The usable field capacity (minus dead water) is very different for the plants. This water content is absorbed by the roots, with the suction at vines is extremely high compared to other plants and corresponds to a pressure of about 16 bar (only 10 bar for wheat). However, this water only remains in the plant to a lesser extent and evaporates to a greater extent via the stomata of the stomata leaves (Transpiration). If the maximum storage capacity of the soil is exceeded with respect to gravity, percolation (percolation) of the soil occurs.
The excess amount of water seeps deeper and deeper into the groundwater. But that's a good one water discharge required. An optimal water balance is of soil type, precipitation, root penetration depth, as well as the water absorption of greening plants dependent. An improvement of the storage capacity is achieved by introducing organic material such as humus or mulch reached. These substances promote the formation of coarse and medium pores. In clay-rich soils, stones introduced into the soil can be an effective measure. Sufficient rainfall and a balanced water balance are important criteria for the so-called Weinbauwürdigkeit, See also below Weingarten Care,