Effects of Subsurface Micro-irrigation on Water Use Efficiency and Hazelnut Tree Growth

Because irrigation practices and their impact on growing operations and management practices are a result of many factors including seasonal and annual weather pattern changes, various irrigation methods may have simultaneous benefits and disadvantages, and measurements can’t be completed in a short study. Single year results do not provide an adequate evaluation of a cover crop’s potential (UC Davis Publication 3338). That is why multiple year experiments such as the one we are proposing are important to find out what works best with a given farm, its microclimate, soils, set of equipment, and other factors. In the case of long-term irrigation methods of hazelnut trees, benefits of each irrigation method may take several years to become apparent. For this project, education and outreach will include field days (pre- and post-harvest), irrigation in orchards “How-To” guide that will be distributed for free to orchardists in the region, articles in trade publications, and sharing the research results via social media outlets.

The project will take place on a 13.4-acre hazelnut growing operation on ZD Farms of Oregon in the northern Willamette Valley of Oregon where 1,100 hazelnut trees have been planted in the last 4-years.  The orchard is broken into 5 irrigation zones of hazelnut trees ranging from 129 trees to 324 trees and ranging in age from 3-years to 4-years.  The orchard has standard drip micro-irrigation systems supplying each tree with a single emitter and with drip supply tubing surface distributed.  The project will include comparison of SDI and vertical watering pipes to existing drip system in the field designated Field 2 where 154 trees of the oldest variety are available and growing in the same soil type.  4 rows from this field, each with 27 trees will be selected, prescreened and 1 each row setup with SDI micro-irrigation, with 2 vertical pipe emitters per tree, with 3 vertical pipe emitters per tree and a control row with the existing drip system.  Evaluation will be made on a quarterly basis for relative tree growth as well as core samples made for water displacement characteristics at the root level for each irrigation type.  This layout of trees and irrigation variations allows for the various systems to utilize the same water source and soil type leaving the key variables to be in the irrigation methods allowing for more efficient project management and monitoring. There is also good vehicle access, plenty of parking, and field accessibility for our educational field days.

Update 2021;

As of this writing, the main headers have been installed, the sub-lines feeding the rows have been installed and each control or test tree has been setup as intended.  There are 2 control rows, two PVC subsurface rows and 2 manufactured sub-surface drip rows setup.  The field is an irregular shape and therefore the number of trees in test for each type, control or deep drip option varies and is outlined in the following table;

Table: Irrigation Type per Row Per Number of Trees in the Test

In summary there are 45 trees considered control trees using the common surface drip method. 

There are 40 trees that utilize a 2 drip/tree PVC system for deep drip.  

There are 31 trees that utilize the deep drip system from DRI.

Notes on the system setup:

• In all rows, the same drip emitter was used for the control, the PVC deep drip system and the DRI deep drip system.
• In each row, the feed system has been setup separate so each row can be not only controlled independently but also can be monitored through the use of flow meters on each row.
• The flow meters are recorded at the beginning of the season, throughout the season and at the end of the growing season to give a total amount of water provided as well as the calculation for water per tree per season.
• All rows are fed by a common header line that is charged (filled) prior to opening the row feed valve to initiate the flow to the tree emitters.
• All control valves are currently setup to come on at the same time and remain on for the same duration.  In future tests there may be some variability in the "on time" for each row to setup different conditions of the test.
• Future plans are to utilize the common feed header to a) fertilize the entire orchard section using organic fertilizers to determine the response between deep drip irrigation and surface drip irrigation and b) to utilize rain water captured in the irrigation scheme for each drip type.

Each tree, control trees and trees with the in test setups have been measured at a noted height and document for growth status at the beginning of last seasons growing season and will be measured once again at the beginning of this growing season.  This method of measurement will be statistically utilized to determine the impact of each irrigation system on the tree rows growth.

SARE Project Discussion 2020

Final Report 2022

Although this represents the final report for this project, it is expected that our team will write a phase 2 project to continue the efforts and determine conclusively which system results in the best use of water for a hazelnut orchard.

To make a systems comparison, the following different systems are discussed.

General Discussion of Each Orchard Irrigation System

The surface drip system used in this project is a very common means of irrigation for many growing applications where you provide irrigation water from a source, through a series of delivery tubes in the tree rows, to emitter tubes to the final emitters.  These emitters give a controlled level of water for irrigation to each tree and the entire system can be controlled from central control point(s).  There are many variations of this system but this represents a common one.

From website sources, the following is a chart showing the general cost per acre for this type of irrigation system compared to subsurface irrigation systems.

So in this analysis the above ground or surface systems range from $500 to $3,000 per acre and the subsurface systems range from $1,000 to $4,000 per acre.  For this kind of an increase in cost per acre, there must be benefits that are obtained for an agricultural organization to choose the subsurface system, which is a part of the intent of this study to determine.

DRI Product Information.

The following is a list of benefits from the DRI Deep Drip Emitters.

1. SAVES WATER: By DIRECT DELIVERY of water to the root, unlike surface watering systems that lose enormous amounts of water to run-off and evaporation.

2. AFFORDABLE:

3. EASY TO INSTALL: Each unit takes an average of 30 - 60 seconds to install.

4. CONNECTS TO YOUR EXISTING EMTTER: So you don’t have to replace any parts! The DRI-12 is a simple addition to what you already have.

5. PROMOTES DOWNWARD ROOT GROWTH: This improves the plants resistance to drought and disease. Drip systems can encourage J-root and shallow root development making the vine or tree more vulnerable.

6. REDUCES MINERAL BUILD-UP ON EMITTERS: Warm air flowing around drip emitters causes water loss to evaporation. This process results in a calcification build up causing clogging. The DRI-12 seals, contains and directs water to the root zone without air interference.

7. ALLOWS YOU TO DIRECT LIQUID FERTILIZERS TO THE ROOT ZONE: This minimizes the loss of fertilizers to run-off and displacement.

8. REDUCES WEED GROWTH: Because the DRI unit goes directly into the ground it will not provide an easy source of food and water for pests as do drip systems.

9. ENVIRONMENTAL BENEFITS OF THE DRI design: Besides saving water, the DRI unit considerably reduces the amount of fertilizers entering our rivers and streams as a result of run-off from surface watering systems. The DRI design also lessens the impact of toxins in our waterways because of its controlled underground delivery.

10. ECONOMIC BENEFITS OF THE DRI design: A Napa Valley area vineyard recently lost 2,500 vines on their hillside vineyard due to drought and an inefficient surface watering system. That kind of crop loss is happening all over the globe. DRI increases revenues by preventing losses such as this.

Note; it can be said that the White PVC deep drip system shares most if not all of these above listed benefits.

DRI provides a video of the installation at Print (dri-products.com) and the following instructions for installation of the DRI-18 that we installed.

The DRI-18 unit is used for large heritage landscape trees. Start by poking a hole about 22 inches deep about 4 to 6 feet away from the base of your tree. Insert the DRI-18 unit so the top of the soaker, with the 1/4 inch tubing, is buried about 3 inches below the surface of the soil. Compact the dirt to fill the hole around the extending 1/4 inch tubing. Attach the 1/4 inch tubing to a drip emitter with a “woodpecker-type” nipple. The flow rate of the emitter should be appropriate for your tree size and soil type.

An expected advantage of the DRI-18, which is a foam emitter the length of the unit, is the even distribution of water along the length of the tube where the White PVC tube system would mostly distribute water at the last 3” of the emitter tube.

White PVC Subsurface Irrigation System

The white PVC subsurface Irrigation system is a DYI set of components using ¾” PVC tubing cut to length and with approximately a 3” notch or saw cut from the bottom up for water delivery range. From HomeDepot, a 10’ long piece of ¾” PVC pipe can be purchased for approximately $7.00 or a price of $0.70/lineal foot.  Therefore, the base tube for a 2’ long piece would be about $1.40/piece.  Added to that would be a ¾” PVC pipe cap (slip x slip) at $0.82 and the total materials, not counting the drip tube and emitter would be $2.22 each.

Labor required would be;

1. Cut ¾” PVC to length, estimated at 60 seconds to cut 1 10’ long PVC tube (12 seconds per piece)
2. Notch 3” at the end of PVC pipe estimated at 20 seconds each
3. Drill hole in ¾” PVC pipe cap, estimated at 30 seconds each

So labor is estimated at about 1 minute each for the basic setup of a chop saw, a band saw and a drill press.  As labor costs vary, it’s difficult to quantify the cost but a a loaded rate of $20/hour (non-skilled labor) it would be less than $0.50 so the total labor and materials for this option, not considering the cost of tools, would be less than $3/tube.  Likely a minimum of 2 tubes are required per tree.

Other factors to consider are the impact of each drip irrigation system on the operations of the orchard like vegetation control, damage to the drip emitters through seasonal activities and the general impact on operations.  Here are our thoughts for these areas.

• Above native vegetation in the Orchard;
  • Theres an increase in vegetation around the trees from the surface drip options that is less obvious in the other two methods.
  • The DRI subsurface system has distribution of the irrigation water at or just below the surface so although it has less vegetation growth tendencies than the surface drip system, it still provides some water to the native vegetation to support growth around the to of the delivery tube.
  • The PVC tube subsurface system provides most of the delivery of wat to the lowest 2” to 3” of the tube so less water is provided to native vegetation except at an extreme level.
• As it is our practice to not completely eliminate the vegetation around the trees as is common in most hazelnut orchards through the use of herbicides, our practice is to do a much-reduced application of herbicides throughout the growing season.
  • Therefore, our practices include more mowing and “weed whacking” to which the two deep drip systems often get in the way of causing damage to the pipes and emitters.
  • Subsurface irrigation systems have seen damage to their delivery tubes coming from the tree line header at a higher percentage than the normal surface drip system as they are spread out further from the trunk of the tree resulting in more frequent contact from week whacking.
  • This is an area that we need to work on to obtain the low level of vegetation around the trees, keep our minimum practice of reduced herbicide application but equally minimize the work and the damage to the tubes and emitters. We will be working on these practices in this next phase.
• In the rest of our orchard, our practice is to roll out our tree line header lines prior to the irrigation season and roll them back up in the fall after irrigation is completed. This practice a) allows us to reuse and maintain the header lines year on year without off season damage, and b) allows us to mow between the trees in off season until we need to roll out the lines for the next season.
  • The surface drip systems support this method of installation and removal seasonally and we are well suited for this process.
  • The DRI foam subsurface drip system would require more disassembly of the lines from the tree line headers before they can be rolled up causing potentially damage to the insertion points in the plastic tubes requiring more annual replacement needs. Also the DRI-18 units inserted into the ground, unless removed annually, would still be in the way of the process of mowing or weed whacking between the trees.
  • The white PVC tubes inserted into the ground have the same impact regarding the need to mow or weed whack around the trees however the removal of the lines can be done easier as they have simple caps that can be pulled from the PVC tubes thus allowing us to roll them up like we do with our other surface drip system.

We also have not worked with these systems long enough to know the life of them and/or the ongoing maintenance needs of each.  These we will consider and work on as we continue to use them in our operations.

Effects of Subsurface Micro-irrigation on Water Use Efficiency