We all want to have a green lawn but do we really know how much water is needed? It is easy to find ourselves overwatering. In fact, it has been shown that we waste about 50% of water that is used on landscape and this is mostly due to overwatering.
Here are some helpful tips for proper watering.
What is ET? ET stands for evapotranspiration and is the loss of water by evaporation from the soil and transpiration from plants. The main factors that affect the rate of evapotranspiration are temperature, wind, and soil moisture. Most everyone knows what evaporation is but transpiration might be a new term for you. It is the loss of water from the plant and is mainly through the stomata of the leaves. When we have this information we can know how much water to supplement with our irrigation systems. How do we use ET to determine the amount of water our plants need? First, we start with a reference ET, or ETo. Then we multiply this reference ET by our landscape coefficient (KL), also known as the crop coefficient (KC) or plant factor (PF).
ETo x KL = Plant water need
For example, in Utah on a summer day the ETo might be .3 and the typical KL for turfgrass is .7, giving us a Plant Water Need of .21 inches
Optimal water scheduling
To determine the optimal watering schedule, we need to look at our ET, precipitation rate of the sprinkler heads, and also take in to account conditions such as soil type and how sunny or shaded a particular zone is. The precipitation rate of each head can be found in product manuals provided by the manufacturer. You may have a zone of Rain Bird 3500 rotors with blue nozzles that have a precipitation rate of 0.53 inches per hour. If we find our plant water requirement to be .42 we can do some simple math to find out how long that zone should run. In order to apply .42 inches of water this zone would need to run for 47 minutes. Discovering this for each zone will make sure we are watering the correct amount.
Another important factor is to make upgrades to the system improving its efficiency. Some upgrades include matched precipitation rates, pressure regulating heads, and rain sensors. Getting matched precipitation rate is done by being consistent with types of heads and nozzles within a zone. This will improve your distribution uniformity. The higher the distribution uniformity, the more efficient the zone is. Distribution uniformity can be found by doing a cup test.