LO 3.6 - Capillary Action & 3.7 - Available water

25% When this is the case there is enough water available for plant growth and sufficient air in the soil. Soil Water

After full saturation of soil… * The water that drains away comes from the macropores. It is called gravitational water. Once this water has drained, the macropores contain air, the micropores and mesopores still contain water and all of the particles are surrounded by a film of water. This is what’s known as Field Capacity. Soil Water

Capillary action: * Water molecules are attracted to the walls of the tube – they ‘stick’ to the walls and the strength of that attraction is enough to pull the water up the tube against gravity – higher in a narrower tube. * For capillary action to work in a soil there must be enough mesopores that will hold water against gravity, and these mesopores must be connected together. Capillary Action

• Some water will be taken up by plants. • Depending on weather conditions, water will also be lost from the surface of the soil through evaporation. When complete, All that will be left in the soil is the thin film of water surrounding the soil particles and the water tightly held in the micropores. Soil Water

Permanent Wilting Point: * The film of water around the soil particles becomes thinner, the water is held more tightly, and plants are not able to take it up. This is known as hygroscopic water or unavailable water. * It is the point at which plants are no longer able to take up water and is the Permanent wilting point. Soil Water

Importance of Water movement in soil: * Soil formation * Plant growth * Transport of nutrients (and pollutants) Soil Water