dry condition is reached at 1,000,000 kPa suction (pF = 7). All water below wilting point is called unavailable water. When the soil moisture content is optimal for plant growth, the water in the large and intermediate size pores can move about in the soil and be easily used by plants. The amount of water remaining in a soil drained to field capacity and the amount that is available are functions of the soil type. Sandy soil will retain very little water, while clay will hold the maximum amount. The available water for the silt loam might be 20% whereas for the sand it might be only 6% by volume, as shown in this table. The above are average values for the soil textures. Water flow Water moves through soil due to the force of gravity, osmosis and capillarity. At zero to 33 kPa suction (field capacity), water is pushed through soil from the point of its application under the force of gravity and the pressure gradient created by differences in the pressure of water; this is called saturated flow. At higher suction, water movement is pulled by capillarity from wetter toward drier soil. This is caused by water's adhesion to soil solids, and is called unsaturated flow. Water infiltration and movement in soil are controlled by six factors: Soil texture Soil structure. Fine-textured soils with granular structure are most favourable to infiltration of water. The amount of organic matter. Coarse matter is best and if on the surface helps prevent the destruction of soil structure and the creation of soil crusts. Depth of soil to impervious layers such as hardpans or bedrock The amount of water already in the soil Soil temperature. Warm soils take in water faster while frozen soils such as permafrost may not be able to absorb depending on the type of freezing. Water infiltration rates range from 0.25 cm per hour for high clay soils to 2.5 cm per hour for sand and well stabilized and aggregated soil structures. Water flows through the ground unevenly, in the form of so-called gravity fingers, because of the surface tension between water particles. Tree roots, whether living or dead, create preferential channels for rainwater flow through soil, magnifying infiltration rates of water up to 27 times. Flooding temporarily increases soil permeability in river beds, helping to recharge aquifers. Water applied to a soil is pushed by pressure gradients