How Often Should Plants Be Watered?
It all depends upon the type of plant being watered; the environment and the soil conditions.
Water will infiltrate into the soil at different rates in different soils. Moisture will evapourate more in windy consitions an/or in warmer conditions. Water can also be lost through plant foliage; or stopped from reaching the soil by plant foliage.
There are a lot of factors that interact to affect irrigation; and this course is designed to help you better appreciate the factors and the interactions.
The zone between wilting point and field capacity is important in irrigation, with the aim being to keep moisture levels within this zone. It has been found generally that plants take most of their requirements from the upper half of the root zone and as a consequence only about half of the available water is used. Irrigation is therefore generally required when approximately half of the available water is used up. The amount of water to be applied to a crop is therefore half of the available water in the root zone of the crop when the soil is at field capacity.
Irrigation applications are timed according to how quickly the plants use the available moisture, and are generally dependant on climatic conditions and the availability of nutrients. The rate at which water is supplied by irrigation is also important and is governed by soil infiltration rates (the rate at which water will pass into the soil). If water is supplied at a rate greater than the ground can absorb it, then runoff may occur and water may be wasted and lost to the plants. The following table gives an indication of infiltration rates for some soils.
The ideal situation is where application rates are equal to infiltration rates. Infiltration rates can also be affected greatly by compaction which causes reduction in pore space and hence space available for water and its passage.
Compaction becomes very important when designing irrigation systems for areas that are likely to suffer from a lot of traffic such as bowling greens, golf tees and popular lawn areas. Compacted soils are likely to have infiltration rates as low as 5 10 mm/hr. Measures that may have an effect on increasing infiltration rates such as coring of bowling greens should also be considered when irrigating, and application rates should be adjusted accordingly