Drip irrigation is an efficient method for delivering water directly to a tree’s root zone, minimizing waste from evaporation and runoff. The core component of this system is the emitter, a small device that regulates the flow of water. Selecting the correct “size” for these emitters is an important step in designing an effective system, as the size determines the rate at which water is applied to the soil. This decision is not based on the tree’s total water need, but rather on how quickly the soil can absorb the moisture without pooling or being wasted.
Understanding Emitter Flow Rates
The size of a drip emitter is defined by its flow rate, which is universally measured in Gallons Per Hour (GPH). Standard GPH rates commonly available for tree irrigation systems include 0.5 GPH, 1 GPH, 2 GPH, and 4 GPH.
The technology within the emitter also influences its performance, specifically the distinction between pressure-compensating (PC) and non-PC emitters. PC emitters are recommended for trees because they contain an internal diaphragm that maintains a consistent flow rate regardless of pressure variations in the line. This feature ensures that a tree at the beginning of a long irrigation line receives the same volume of water as a tree at the end. Non-PC emitters, which are less expensive, have a flow rate that fluctuates with pressure changes, making them less reliable for systems with varying distances or slopes.
Matching Flow Rate to Soil Type
The primary factor determining the emitter’s GPH flow rate is the soil’s absorption rate. Matching the water application rate to the soil’s ability to absorb it is necessary to prevent surface runoff or deep percolation past the root zone.
For clay soils, which have fine, tightly packed particles and a very slow absorption rate, a low flow rate emitter is necessary to prevent ponding on the surface. Emitters with a lower output, such as 0.5 GPH or 1 GPH, are ideal for clay, as the water spreads significantly more laterally than vertically.
Conversely, sandy soils are coarse and porous, allowing water to drain quickly with little lateral spread. To ensure deep saturation in sandy soil before the water drains away, a higher flow rate emitter, such as 2 GPH or 4 GPH, is used. Loam soil, which is a balanced mixture of sand, silt, and clay, has a moderate absorption rate. A mid-range emitter flow rate, typically 1 GPH or 2 GPH, provides an effective balance between preventing runoff and achieving deep penetration.
Calculating Emitter Quantity and Placement
Once the correct GPH flow rate is selected based on the soil type, the focus shifts to determining the total number of emitters needed. The quantity of emitters is determined by the size of the tree, which is often measured by its canopy diameter or drip line.
To calculate the number of emitters, the total required daily water volume must be converted into a total required GPH. This figure is then divided by the GPH rating of the chosen emitter. For instance, if a tree requires a total of 4 GPH, and a 1 GPH emitter was selected, four individual emitters would be required.
Proper emitter placement is important to ensure adequate coverage of the root zone, which should ideally wet 50% to 60% of the area beneath the canopy. Emitters should be positioned near the tree’s dripline, as the most active water-absorbing roots are concentrated there. As the tree grows and its canopy expands, the emitters must be moved outward. Using multiple emitters in a ring pattern around the tree, rather than a single emitter, promotes healthy root distribution and avoids the development of a confined, localized root ball.