Subsurface Drip Irrigation Guide - Page 2

The issue boils down to proper design, installation, and operation. Any irrigation system design that takes into account the type of soil, the plant material being watered, the available water source and all of the other external factors needed will translate into a good system. If down the road the plant material show signs of stress, there are two possible scenarios. Either the system was improperly designed or the system is improperly set.

We'll talk later about the importance of the charts we use in helping you determine the type and amount of dripperline based on the soil type and the plant materials being watered. For now, we need to introduce a concept called "pulsing."

Pulsing is the frequent on-off cycling of a zone of dripperline for the purpose of moving water as far outward, upward and downward as possible.

While some may think that increasing the watering time is the way to push the water farther out, it isn't. Neither is using a dripper with a flow rate above our recommendations. In fact, both go counter to what you should do.

Long run times allow the soil to become super-saturated with water. As such, the soil loses its ability to hold water against gravity, (field capacity) and the water becomes "gravitational."

Capillary Action: The radial (outward and upward) movement of water through the soil that fills the spaces between particles with capillary moisture.

Capillary Moisture: The water held in pore spaces by the surface tension between the water and the soil particles. This is the primary source of water for plants and is also referred to as "available moisture."

Gravitational Water: Free water in the soil which moves downward due to gravity. After a soil has been saturated, the gravitational water percolates downward, leaving the soil at field capacity.

Field Capacity: As much water as the soil can hold against the influence of gravity. If a soil is saturated by rainfall or irrigation and then allowed to drain freely for 24 hours, the soil is usually at field capacity.

Infiltration Rate: The rate at which water enters the soil. This rate varies greatly, and may impose a limitation upon the design of an irrigation system since water application rates in excess of the infiltration rate may result in runoff and erosion.

As we discussed earlier, a dripperline system should be run every day or every other day to establish and maintain a consistent moisture balance in the soil. It is this consistent moisture level that will allow the water to radiate as far outward, upward and downward as far as possible, and it is precisely because of this that you will achieve optimal plant growth. Should plant materials show signs of stress in an otherwise well-designed system, the culprit is typically improper watering.

Before we move on, some people may ask about water quality. That is, what kind of water should I use, or more importantly not use.

Netafim dripperlines are designed to operate for a lifetime regardless of whether the water comes from a municipal source, a lake, or a well. All that is required is a way of removing debris from the water and for that we use a filter. For water with dissolved minerals such as calcium, there are some simple and straightforward ways of dealing with that as well.

Calcium can become a problem in water when it has a chance to precipitate and dry. When it does it can cake into a hard obstruction and possibly become a problem. But calcium has a very hard time affixing itself to polyethylene, which is what Netafim dripperline is made from. In many cases, this will eliminate any problem. But to further reduce the chance of drying and caking, we recommend that the dripperline be buried subsurface and irrigated daily. By doing so, the surrounding soil will keep the environment moist and preclude any problems.

Dripperlines can be used virtually any place where you can use overhead sprinklers because sprinklers and dripperline are trying to accomplish the same thing. Both are trying to create an even wetted pattern throughout the soil profile.

Problems with sprinklers arise though because they are less capable of delivering a consistent balance of water throughout the zones:

• Sprinklers throw water through the air. Sometimes it is windy, sometimes it isn't. Sometimes it is very dry, and other times it isn't.
• Sprinkler performance can also be negatively impacted by changes in pressure. Water pressure changes during the day alter performance, as does the ever-decreasing pressure down a sprinkler lateral.
• Even identical sprinklers farther downstream on a piping lateral do not perform the same as sprinklers closer to the beginning of the line.
• Choosing the proper sprinkler nozzle based on radius and arc can create even more imbalance in a zone, along with how the radius adjustment is set and if the head is properly set to grade.
• Trees, plants, shrubs, flowers, and other natural or man-made obstructions further hinder the proper performance of a sprinkler.

Conclusion: Even if the sprinklers are laid out and installed properly, there are many influences out of a designer or contractor's control that play a major role in the erratic application of water.

Dripperline irrigation on the other hand relies on soil as its transportation medium. As water leaves the dripper, it is captured by the soil. Just like a napkin that absorbs a drop of water and the water spreads upward and outward, water moves outward, upward, and downward away from the dripper outlet into the outlying soil.

Note: For those who do not think that water could possibly move upward against gravity, hold a napkin vertically as you dip it into some water.

In order to simplify the process of choosing the proper dripperline flow rate, dripper interval and row spacing, Netafim has developed guidelines based on the answers to these simple questions. Try answering these questions with a sprinkler!

If you have a very rocky, shaly soil, it could be labor intensive to install dripperline. Once installed, however, it will work fine. If you live along an ocean coastline, where plants may benefit from having the salt spray washed off the leaves, sprinklers may be an option, or may be used in conjunction with a dripperline system. Lastly, if you are relying on the irrigation system to break down and water-in granular fertilizers and chemicals, dripperline may not be your best choice.

The rationale for aerating is to relieve soil compaction, ensuring that there is good pore space between soil particles and that there is enough oxygen in the soil. One of the reasons aeration is necessary is that the soil can become compacted by foot, vehicular, or mower traffic.

Aeration can be done several ways, among them core, deep tine and water injecting.

Our work has shown that a properly installed and irrigated subsurface dripperline actually requires less aeration, if any, when compared to an overhead sprinkler system.

Because of the dripperline's ability to create a very uniform, wetted pattern that reaches far below the surface, the pore spaces of the soil are actually filled with water. As such, they are more resilient to traffic and less likely to compact.

If core aeration will be done, the tines must be set to a depth less than the depth of the dripperline. Knowing this ahead of time is important, as you may need to install the dripperline consistently at a depth of 6 inches, while ensuring that any aeration is done no deeper than 4 inches.

If deep tine aeration is going to be used on a project, it is probably not logical to use dripperline. The risk of substantial damage may be too great.

If a water-injecting aerator unit is being used, an area should be tested to determine what pressure the injector should be set so it does not damage the dripperline.

Subsurface Drip Irrigation Guide - Page 2