Advanced Zone settings are primarily used for Rachio's "Flex" Scheduling. If you're using Flexible (Monthly / Daily) scheduling, the Rachio controller calculates your watering similar to that of balancing a checkbook. The plant’s soil water storage reservoir is like that of a bank vault.
However, this reservoir can only hold a limited amount of water that is useful for the crop. If you overwater the soil reservoir, it will result in water loss due to deep percolation and/or runoff losses. The turf/crop evapotranspiration (ET), or water loss & use, is the crop’s daily water withdrawal. Irrigation and effective precipitation (aka rain) are deposits to this "bank account".
Advanced Zone Settings Inputs
Available Water (AW) or Available Water Capacity (AWC) is the range of available water that can be stored in soil and be available for growing crops. The AW of a soil is related to texture and structure, the spongier the soil the more water it can hold. Typical AW holding capacities represent the amount of water that can be held in an inch of soil; in short, how much water can be available for plants with the depth of the root zone is known.
Root Depth (RZ) is the soil depth from which a plant extracts most of its water needs. The RZ is equal to effective rooting depth and is expressed in inches within the Rachio software. To determine the depth of the RZ, a soil sample containing the roots must be taken. It is recommended to use a soil probe to minimize disturbance of the soil and to obtain a good quality sample. Once the core is removed from the probe, look for the small roots to determine the number of inches from the top of the core to the deepest root near the bottom of the core. This sampling process should be done in several locations throughout the test area to determine an average depth.
Allowed Depletion (AD) is the maximum amount of Plant Available Water (PAW) allowed to be removed (expressed as a percentage) from the soil before irrigation refill occurs. PAW is the total amount of water held in the plant root zone based on Soil Type and Plant Root Depth. Increased surface evaporation (loss) of water and usually higher rates of transpiration are associated with frequent irrigation events; It is best to irrigate only when the root zone has reached the AD threshold.
- For most landscape purposes, 50% AD represents a reasonable overall value for the typical soils and plants used in landscapes. 50% AD is the Water Manger's choice to irrigate when the soil moisture level is half depleted.
- For sensitive, shallow rooted plants (where little reserve water is available), or very heavy compacted soils, a smaller depletion should be considered (i.e. 30-50%)
- For stress-tolerant plants, such as desert plants, deep root zones, or lighter soils, a larger depletion can be used (i.e. 50-70%)
AD represents a management decision to use the water that is most readily available to the plant. While plants can still extract water from the less available water reserves, the plant will begin to show signs of stress or wilt.
In short, AD is the quantity of water that is easily used by the plants from soil moisture without withdrawing all of the water prior to refilling the soil profile. Additionally, by allowing the soil to dry down, it draws air into the root zone. Roots use this air to breathe & grow; having the appropriate amount of water and air in the soil allows the microorganisms to flourish, enabling the plant (& soil) to be healthy.
Efficiency (DU), also referred to as Application Efficiency or Distribution Uniformity (DU), tells us how efficient the water is being distributed by the sprinklers. The lower the DU the higher the run time needs to be to deliver enough water to the area with the weakest coverage.
- DU is a factor used to adjust the run time to account for non-uniform distribution of irrigation water
- DU is be measured by conducting a catch can audit
If the E/DU is below 0.40, then time and effort should be spent identifying what needs to be done to assure the system is operating optimally. This may include recommendations for improving maintenance or to seek the services of a certified Water Manager to identify the factors that are causing such poor performance. When the uniformity is low, it is hard to justify the amount of additional water needed to minimize stressed areas and achieve an acceptable appearance. When additional minutes of run time become excessive, runoff potential increases, and it becomes more difficult to do proper maintenance if the sprinkler system is operating beyond its desired or designated water window
Factors that contribute to water waste (and poor DU):
- Pressure. In irrigation there are two kinds of pressure, static and dynamic. Static pressure is the pressure of non flowing water at the point of connection. Dynamic pressure is the pressure at a sprinkler head when the system is on. Static pressure determines pipe sizing and size of sprinkler zones, whereas dynamic pressure determines head performance. Both pressures are commonly misunderstood and can have a significant impact on the efficiency of a sprinkler system.
- Different types of sprinklers are designed to operate at different dynamic pressures. Typically, spray head nozzles are designed to perform best at 30 psi, while rotor nozzles are designed to perform best at 45-65 psi. It is important to pay close attention to the nozzle pressure specification because certain dynamic pressures are required to obtain the desired coverage and radius of throw. Under pressurized nozzles typically produce dry rings around the heads, leading to over watering in an effort to compensate for poor coverage. Over pressurized nozzles produce misting and small water droplets that are lost to wind and evaporation. Over pressurized nozzles also use 20-40% more water than properly pressurized nozzles, resulting in excessive, unnecessary water use.
- Head spacing. Head spacing refers to the distance between heads, ultimately dictating nozzle size. Typically spray heads are used when spacing is in the 5 – 15 foot range; rotors are used for radii of 20 feet or more. All sprinkler types perform best when head to head coverage is achieved. Obviously, using 12’ nozzles on heads that are spaced 15’ apart is going to result in coverage issues. Again, it is critical to refer to the manufacturer’s specification to determine the correct nozzle size for the desired radius for the pressure available.
- Nozzle selection. Nozzles for different sprinklers apply water at different rates. Spray nozzles typically apply water at 1.5” – 2.0” / hour; rotor nozzles are usually in the range of .5” - 1” / hour. The rate at which the nozzle applies the water is also a determining factor when scheduling the controller. A nozzle with a lower application rate, theoretically, will have to run longer in order to apply the desired amount of water.
- Nozzle size can also significantly affect the hydraulics of a sprinkler system. Nozzles are not only rated for a radius of throw, they are also rated for flow, referred to as gallons per minute (GPM) and or gallons per hour (GPH) for drip or micro spray nozzles. A common mistake when visually evaluating rotor heads that are under pressurized, and not achieving head to head coverage, is to use a larger size nozzle that is rated for more distance. Under pressurization is more of a GPM issue than an actual pressure issue, i.e., too much water is flowing through the sprinklers than the supply can provide, by increasing the nozzle size the GPM is increased, exacerbating the problem. Decreasing the flow of a zone by using nozzles with lower GPM is the best way to resolve pressure issues if a booster pump is not an option.
Fixed Schedule Tips
If you're using Fixed Schedules, please note they are static and do not automatically update like Flex schedules do. As such, if you make adjustments to any of the Advanced Zones Settings, remember to recreate your watering times for the inputs to be properly calculated.