Pórusvíznyomás

Pórusvíznyomás, also known as matric potential or soil matric potential, refers to the water pressure within the tiny pores of soil or porous materials, such as unsaturated soils, plant tissues, or other porous media. This concept is fundamental in soil physics, hydrology, and plant biology, as it influences water movement, retention, and availability to plants.

In unsaturated soils, water is held within the pores by adhesive and cohesive forces between water molecules and soil particles. The pórusvíznyomás describes the energy status of this water, measured relative to free water (where pressure equals atmospheric pressure). It is typically expressed in units of pressure, such as kilopascals (kPa), and can be negative, indicating tension or suction, as water is pulled away from the soil particles.

Key factors affecting pórusvíznyomás include soil texture, organic matter content, and the degree of saturation. Coarser soils, like sands, have larger pores and lower water-holding capacity, resulting in less negative matric potentials compared to finer soils, such as clays, which retain water more tightly. The presence of organic matter can also enhance water retention by increasing the number of small pores.

In plant science, pórusvíznyomás is critical for understanding water uptake. Plants extract water from the soil when the matric potential in their roots becomes more negative than that of the surrounding soil, creating a gradient that drives water movement. Excessive negative matric potentials can lead to water stress, affecting plant growth and productivity.

Measurement of pórusvíznyomás often involves tensiometers, which detect the suction pressure in the soil, or psychrometers, which assess water potential in plant tissues. These tools help in monitoring soil moisture conditions and optimizing irrigation practices to maintain optimal water availability for plants.