ABSTRACT
The growth of vegetation and crops is broadly controlled by climate primarily through constraints due to temperature, rainfall and exposure to wind. The leaf water potential has a 'floating value' which responds to both the evaporative demand and the availability of soil water in order to maintain a balance between water supply and demand. This lower limit of water availability occurs when the soil water suction is about 1.5 MP and is termed the permanent wilting point. During gentle rain, water infiltrates the soil surface as rapidly as the rain falls with no accumulation of water on the surface. With increased intensity the rate at which the soil can accept water, known as its infiltration capacity. This condition is known as ponding which is the precursor of surface runoff and erosion. The amount of water stored in the soil was insufficient to maintain the potential evaporation and irrigation would probably have increased crop growth.
