water water everywhere, nor a drop to drink!
The importance of water to agriculture and the environment in general is such that soil hydrology has often been touted as a potential means to develop a Universal Soil Classification System. However soil hydrology is not an inherent soil property but more an emergent property that is a consequence of soil and climate interactions.
From an agronomic perspective the purpose of the hydrology is to maintain sufficient soil solution to: provide the plant and the microbiology with it’s water needs and the principal transport mechanism for the nutrients that the whole system needs.
These three purposes (system transportation and microbe and plant hydration) are then dependent on the frequency and degree of inputs from precipitation or irrigation and the degree to which the soil then retains and drains following such events.
Knowing how these processes interact permits for the means to develop effective and efficient water conservation measures.
Where a farmer relies solely on natural precipitation he has little control over and is largely at the mercy of climate. Therefore the first step in understanding the soil Hydrology is to appreciate the effects and longevity of the effect of precipitation.
Field capacity and the ‘drought point’
Field capacity is a condition in which the soil is moisten to it’s maximum capacity following sufficient drainage.
The drought point is the point at which the the volume of water has dropped to a point where the plant is suffering from water stress and beginning to die.
Knowing these two values tells us the potential water storage capacity of the soil and with crop and climate data allows us to further predict when and to what extent to irrigate.
whilst calculating the field capacity and the drought point can be achieved at any time using a standard and simple laboratory technique (below) it is arguable better to determine this measurement under or following the correct climatic event: following heavy and prolonged rainfall and once the field has drained: when the land is actually at field capacity.