Water Vapor Movement in Soils

• Two types of water vapor movement occur in soils, Internal and External. Internal movement occurs within soil i.e. in the soil pores and external movement occurs at land surface and water vapor is lost by surface evaporation.
• Water vapor moves from one point to another point in soil due to vapor pressure difference. Water vapor will move from the moist soil (high vapor pressure) to dry soil (low vapor pressure).
• Also, water vapor moves from the zone of low salt concentration to high salt concentration (e.g. around fertilizer granule) because salt lowers the vapor pressure. In uniformly moist soil, if the temperature is lowered, vapor pressure will decrease and water vapor will move towards this cooler part.
• However, heating will cause water vapor to move away from the heated area because the vapor pressure is increased by the process of heating.