Irrigation Management


Growers have long been concerned about water quality, but today water quantity has emerged as a leading consideration in managing irrigation. Today we not only have to focus on reducing contaminants caused by leaching and runoff, but irrigation systems have to be managed so that the amount of applied water closely matches crop water requirements. Poorly managed irrigation systems can cause soil damage, environmental problems, and contribute to low water use efficiency. As California’s population increases and water becomes more scarce, irrigation management practices will have to become ever more precise. A great deal of effort and resources have been dedicated to improving irrigation management in recent decades with great success. Yet there is still room for improvement and evolving practices and technologies continue to emerge. Going forward, data collection and data management will be critical to “real time” water and energy management.

Soil moisture monitoring and irrigation scheduling

One of the best actions growers can take is to accurately predict the timing and amount of irrigation water. There are a variety of methods for determining when and how much to water crops. Simply monitoring soil moisture levels to help determine when to irrigate can significantly optimize water and energy use, maximize yields, improve water use efficiency, and greatly reduce soil erosion. There are several effective, low-cost methods for assessing soil moisture. Combining soil moisture monitoring with a method of irrigation scheduling can produce multiple benefits.

In irrigation scheduling, different factors related to a specific crop and context are assessed to determine water requirements. There are various techniques and software programs readily available for growers to utilize developing irrigation schedules. One method of irrigation scheduling relies on actual weather data in conjunction with crop coefficients to estimate crop water demand. Watering based on evapotranspiration (ET) or plant needs should be used as a method for planning a watering budget and soil/plant-based irrigation schedule to determine irrigation events. One issue with irrigation scheduling is that growers may not have surface water available when needed, this is particularly true with drip/micro irrigation systems.This may create an over reliance on groundwater.

Irrigation systems can be controlled manually or be automated. Recent technological developments include the use of sensors and controls to manage irrigation systems. Automated irrigation systems utilize weather station data and/or moisture sensor data to determine when and for how long to water crops. Sensors are placed into the ground to monitor soil moisture and connected to a control system. The control system can use real-time data from the sensor or a combination of inputs to determine irrigation timing and amount. The sensor tells the computer how much moisture there is in the soil, which determines if water is required. Automated systems typically save on labor, yet tend to be associated with higher equipment costs. Though automated irrigation systems with moisture sensors and weather stations are being more widely adopted, their cost-effectiveness largely depends on the experience of the grower, crop, and irrigation method.

Drip and micro-irrigation

One of the more efficient forms of irrigation can be micro- or drip irrigation. Drip irrigation employs drip emitters that slowly apply water to crop root zones. Drip irrigation usually consists of a pressurized tubing system that is run along crop rows. These tubes are fitted with emission devices at specific distances to allow water to drip from the emitters.

Micro-irrigation is typically used on tree crops. The two distinct features of micro-irrigation are the need for high irrigation frequency and localized water application to only part of the crop’s potential root zone. These two factors are the framework that make up difference between micro-irrigation and traditional surface (flood) irrigation methods. Research shows that there is a minimum level of available soil moisture required for plants to maintain growth. A well managed micro-irrigation system should maintain a moisture level above the predetermined threshold. Over-irrigation should be avoided, because saturated soils can injure a plant by causing inadequate root aeration promoting root rot and/or loss of nutrients.

Another application of drip irrigation is subsurface drip irrigation (SDI). This is the irrigation of crops through buried plastic tubes containing emitters spaced at repeating distance (E.G 8, 12, 18 or 24 inches). The tubing and emitters are generally buried 2 to 10 inches (5 to 25 cm) below the soil surface. In the United States, SDI is most widely used for the irrigation of annual row and field crops, but it can be used for permanent crops as well. In other parts of the world, SDI is successfully used for the irrigation of permanent crops. SDI is an efficient irrigation system that greatly reduces evaporation from the soil surface, often resulting in substantial water savings when compared with flood or sprinkler irrigation. As with drip irrigation, sub-surface drip adoption has proceeded slowly due to the high initial cost and intensive management requirements.

Center pivot technology

Center pivot technology is typically used on large fields with soils with relatively high infiltration rates. Pivots are commonly used on row crops and vegetables. Sprinkler heads can be lowered to just inches above the tops of the plants, which minimizes water loss from evaporation and wind drift. The technology is both labor and water efficient.

Deficit irrigation

Deficit (or regulated deficit) irrigation is providing less water than the crop wants at specific times of the growing season. When properly done, it can increase water use efficiency by maintaining yields or increasing crop quality (wine grapes) per unit of irrigation water applied. However, deficit irrigation has been shown to work only for certain crops and the grower must have prior knowledge of crop yield responses to deficit irrigation. One of the greatest obstacles to implementing deficit irrigation is that it has only been shown effective for a handful of the wide range of crops grown in California. More research on deficit irrigation for specific crops and irrigation methods is needed to ensure guidelines for implementation are successful.

The aforementioned methods and technologies are but a small example of the applications available for irrigation management. Growers are encouraged to consult irrigation professionals or farm advisors before implementing significant changes in their irrigation practices.

Uniformity vs. efficiency

An irrigation technology or practice can be measured in many ways. Two of the most commonly used terms when it comes to measuring an irrigation system’s performance are uniformity and efficiency. In irrigation quite often the terms uniformity and efficiency are used interchangeably, but in reality, they each define a different situation. To be more exact, efficiency is the ratio between how much water the plant beneficially uses compared with how much water the irrigation system applies.

Percent efficiency = 100 x water used by the plant / water applied

Uniformity, on the other hand, relates to how evenly you apply water over an area. Equipment selection and the design of the irrigation system affect the uniformity of your irrigation system. Also, system maintenance can be very important. Download details on Evaluating Sprinkler Irrigation Uniformity (pdf).

System design and management are keys to efficient irrigation systems. This means to get optimum performance from your irrigation system, you must properly design, maintain, and manage it. If you don’t optimize all of these variables, system efficiency will be reduced.

Irrigation Methods in California

Using a survey sent out to California growers, the California Department of Water Resources has put together an overview of irrigation methods used throughout the state. The result is an Excel spreadsheet detailing the results of the Statewide Irrigation Methods Survey. It can be adjusted to look at irrigation methods in specific regions. There are survey results from 1991, 2001, and 2010. See also an analysis done by Sam Sandoval’s Research Group, a collaborative project at UC Davis: Spatial and Temporal Analysis of Application Efficiencies for the State of California.

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Water Savings

With the recent drought and water shortages, managing and conserving water has been a major concern in California. The methods and applications mentioned above are just a few irrigation management practices that are being practiced today. The basis of irrigation scheduling is to determine the amount of water to apply to a field and when to apply it. In drip irrigation, water is slowly but directly applied to the plant root zone. Water is not wasted on non-growth areas and the plant root zone is maintained at its ideal moisture level when properly scheduled. Drip irrigation can maintain an optimum moisture level in the soil at all times with less water lost to the sun and the wind. Drip irrigation can optimize applied water used on crops and orchards.

Subsurface drip further reduces the loss of water due to evaporation and/or wind. Subsurface drip irrigation does not typically wet the soil surface, so weeds do no germinate. Regulated deficit irrigation has been shown to reduce additional water use. Using the above technologies and methodologies in conjunction can increase total water savings.

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Irrigation scheduling is a practice that all growers who irrigate should be practicing. Irrigation scheduling can be done in various ways and with most if not all crops and scales of production. Free irrigation scheduling software is available, such as the online Wateright program developed by California State University, Fresno.

Drip irrigation is currently being used in trees and vines, particularly in new plantings all over California. With the recent drought and water shortages, more and more farmers are employing drip technology, with total acreage now exceeding flood irrigation in California. Subsurface drip is currently utilized on over 20,000 acres in California, primarily on alfalfa.

There are three measurements important to make sure your irrigation system is applying the right amount of water to the crop. One is weather or ET data, the second is soil moisture levels, and the third is flow information into the field. The information from all three should support good irrigation practices.

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Additional Benefits

The adoption of irrigation methods that optimize water use is essential to establishing agricultural systems that use available water more efficiently and yet maintain crop production capacity. Changes in irrigation practices will likely require reassessment of fertilizer application rates and delivery practices as well. These changes are key to developing efficient and sustainable cropping systems that will benefit the environment, the grower and consumer. For example, the efficient delivery of water and nutrients to crops will likely lead to less greenhouse gas emissions by reducing available nitrogen and making the soil environment less conducive (less water throughout profile) in producing nitrous oxide, the most potent greenhouse gas. Current agriculture fertilization practices throughout the world contribute significantly to nitrous oxide production. The efficient use of fertilizer and water management will allow growers to enhance and diversify their income sources by enhancing the efficient use of inputs and participating in emerging carbon and greenhouse gas markets.

Research has suggested that many farmers often under-irrigate, some from lack of knowledge and information, while others under-irrigate as a deliberate decision to save water or benefit from the quality of crop. In reality, providing crops with too much water is much more harmful than providing crops with too little. Another important note is that although the initial cost of these systems at the outset are generally high, their relative cost over a life span of 15-40 years is offset by the improved quality, uniformity, and higher production associated with the technology or practices. Secondary benefits include stretched water supply and money saved on energy and water costs.

By increasing the use of every drop of water we are also supporting agricultural jobs. With a large portion of California’s population dependent on these jobs, water is essential to keeping California’s economy flourishing.

Better managing irrigation water may have energy benefits as well, especially if the water source for irrigation is groundwater. By more efficiently managing irrigation, growers should need to pump less groundwater and therefore should be able to reduce energy use. This provides a bill savings. California’s Investor Owned Electric and Gas Utilities offer incentive (rebate) programs for switching from flood to drip irrigation in many instances. Contact your utility account representative to learn how you can participate in these energy efficiency incentives.

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For information on water efficiency and dry farming from past Wine Grape Workshops hosted by the Community Alliance with Family Farmers, click here.

Soil Moisture Monitoring | Irrigation Scheduling | Drip Irrigation | Subsurface Drip Irrigation| Support Organizations | Irrigation Technology Companies | Data & Analysis

Beneficial Management Practices for Efficient Irrigation and Nutrient Management
In 2012-13, American Farmland Trust held focus groups with specialty crop growers in California to identify obstacles to the adoption of irrigation and nutrient beneficial management practices (BMP).

CropManage: Online Irrigation and Nutrient Management Tool
An irrigation and nutrient management tool and blog for leafy greens developed by Michael Cahn.

From the Field: Boosting Agricultural Production Through Water Use Efficiency
Western SARE publication with an economic evaluation of alternative (low-water use) Crops for the Great Basin, Irrigation Alternatives for Sustainable Water Use of Processing Tomatoes, an investigation of water management policy and its effects on water use by agriculture in Arizona, and a look into water management in Sonoma County Grape Production.

Advance Pumping Efficiency Program (APEP) is a PG&E sponsored program managed by the Center for Irrigation Technology at Fresno State. More information can be found at

Tips on Irrigating Vegetables
Webpage from the UCCE Small Farm Conference describes general concepts for pre irrigation, when to irrigate, soil monitoring, and how to pick the best irrigation system for your vegetable crops.

Soil Moisture Monitoring

A Little Bit of Water, A Lot of Impact.
NASA Earth Observatory
An article about the affects of moisture in soil, written by Kathryn Hansen.

A Practical Way of Measuring Soil Moisture.
By Esteban Herrera, Extension Horticulturist
One direct method of measuring soil moisture from the College of Agriculture, Consumer and Environmental Sciences, New Mexico State University.

CAFF Irrigation Efficiency and Dry Farming Wine Grape Growing Workshops
CAFF held a series of irrigation efficiency and dry farming workshops from 2013-2016. Find links to the handouts, presentations, panel recordings and more.

Making Sense of Soil Moisture Sensors.
UC Davis.
UC Davis Cooperative Extension evaluation of soil moisture sensors in Kern County.

Measuring and Conserving Irrigation Water. By Mike Morris and Vicki Lynne.
This ATTRA manual describes how to find the net water application rate for any irrigation system and how to calculate the number of hours the system should be operated. Also offers suggestions for irrigating with limited water supplies.

Measuring Soil Moisture for Irrigation Water Management.
By Hal Werner. An overview of various methods of soil moisture monitoring using direct methods.

Soil Moisture Monitoring for Irrigation Management
Audio recording with the presentations and pictures from our 2014 workshops in Paso Robles are also currently available online as an educational resource for growers.

Soil Moisture Monitoring: Low-Cost Tools and Methods. Published by ATTRA.
A good overview of soil moisture monitoring, with a focus on lower-tech direct monitoring.

Water & Nutrient Management: Soil Moisture-Based Irrigation Systems.
Acknowledging that sensor-based measurement systems are a key factor in effective water management, this “Virtual Field Day” website from the University of Florida includes a range of good publications and videos on soil moisture monitoring and irrigation management. Several types of soil moisture sensors are also described in detail.

Irrigation Scheduling

Automatic Irrigation Based on Soil Moisture for Vegetable Crops.
By Rafael Muñoz-Carpena and Michael D. Dukes.
A University of Florida paper on soil moisture monitoring and automated irrigation scheduling.

Determining Irrigation Amount
A UC Cooperative Extension document on irrigation scheduling for wine grapes includes detailed calculations and worksheets to determine your vineyard water use, irrigation system application rate and uniformity, and number of hours to irrigate.

Efficient Irrigation Scheduling
By Dr. Clint Shock, Oregon State University Malheur Experiment Station.
Irrigation scheduling tips, using potatoes as an example.

Irrigation Scheduling: A Guide for Efficient On-Farm Water Management
By David A. Goldhamer. This guide discusses how to measure soil, atmospheric, crop, and irrigation factors to determine the most efficient irrigation schedule.

Irrigation Scheduling
Facts and calculations about irrigation scheduling by Colorado State University.

Irrigation System Selection
The intent of this paper is to summarize considerations for the most common types of irrigation systems.

Irrigation Technology: Smart Water Solutions for State’s Farmers
This 2008 Ag Alert article discusses water saving irrigation technologies being used by farmers across the state, including smart controllers, reusing and recycling irrigation water, and center pivot irrigation technology.

Limited Irrigation Management
An article about best management practices as recommended by Colorado State University.

Three Most Common Methods- Measuring Vine Water Status
This article from Practical Winery and Vineyard Magazine compares three methods for scheduling irrigation events for wine grapes: leaf water potential, stem water potential, and pre-dawn leaf water potential.

UC Drought Management
A web resource covering irrigation scheduling (includes evapotranspiration scheduling, soil moisture monitoring and plant-based irrigation scheduling) and individual crop deficit irrigation information.

Water Budget Method of Irrigation Scheduling
A short description of the water budget method of irrigation scheduling, and how to useCIMIS ETO to help determine irrigation schedules.

CSU Fresno.
The WATERIGHT site was developed by the Center for Irrigation Technology at California State University, Fresno with significant support from the US Bureau of Reclamation.WATERIGHT is designed to be a multi-function, educational resource for irrigation water management. The site is designed for three audiences: homeowners, commercial turf growers, and agriculture.

Drip Irrigation

Drip Irrigation: An Introduction.
Oregon State University.
The ins and outs of drip irrigation, including management of drip systems.

Drip Irrigation
Washington State University.
A good overview of drip irrigation design and management. Also includes rules and regulations specific to the Washington context.

Drip Irrigation for Home Gardens.
Colorado State University.
A complete overview of installing drip systems in home gardens. Useful also for small farms.

Drip vs. Furrow Irrigation
A study on drip irrigation vs. furrow irrigation at the University of Arizona.

Maintaining Microirrigation Systems
This publication from the University of California Agriculture & Natural Resources discusses the maintenance issues of microirrigation systems that can be used on tree crops, row crops, and trees and vines.

Micro-Irrigation Scheduling and Management
A study on micro-irrigation scheduling and management from Fresno State.

Micro-Sprinkler Irrigation for Orchards
A fact sheet from the Colorado State University Extension.

Practical and Efficient Drip Technology.
By Toro.
Information and resources on drip technology by manufacturer Toro.

Selecting Drip Irrigation for Vineyards
Important considerations for the purchase of a drip irrigation system for vineyards.

Subsurface Drip Irrigation

SDI On The Great Plains.
Kansas State University.
A portal to subsurface drip irrigation resources and information.

Subsurface Drip Irrigation
By Kenneth H. Solomon and Greg Jorgensen.
A research report outlining what works and what doesn’t.

Subsurface Drip Irrigation.
Colorado State University.
A report covering SDI basics as well as crops, materials, placement, cost, operation and maintenance.

Subsurface Drip Irrigation.
University of Nevada.
A publication addressing operation, costs and benefits, and components of SDI systems.

Two publications from the University of Nebraska-Lincoln Extension.
Advantages and Disadvantages of Subsurface Drip Irrigation
Drip Irrigation Design and Management Considerations for Windbreaks

Subsurface Drip Irrigation
Information and research on SDI from University of Arizona’s subsurface drip irrigation demonstration and research project.

Support Organizations

California Irrigation Management Information System (CIMIS)
CIMIS is a program in the Office of Water Use Efficiency (OWUE), California Department of Water Resources (DWR) that manages a network of over 120 automated weather stations in the state of California. Weather data from these stations is free and available online, can be used to schedule irrigations. The website also provides Resources on irrigation management and Evapotranspiration equations.

California Water Institute
An academic center of excellence for research, education and policy analysis of issues involving water resources based at CSU Fresno.

CSU Water Resource and Policy Initiative
CSU’s system wide academic excellence into an important resource for addressing the complex issues about water confronting California today and in its future.

International Center For Water Technology
ICWT was established in 2001 to educate, promote, and assist in the development and adoption of innovative technologies that improve water utilization, reduce energy demand, and positively impact air quality. Based at CSU Fresno.

Irrigation Association
The Irrigation Association is the leading membership organization for irrigation equipment and system manufacturers, dealers, distributors, designers, consultants, contractors and end users.

Irrigation Management Society
The Irrigation Water Management Society is a non-profit organization dedicated to the wise and efficient use of water in landscape, golf and agriculture.

Irrigation Training and Research Center at Cal Poly
ITRC provides irrigation training, research and technical support. The website includes many examples of their results, including downloadable papers and reports, valuable public databases, and samples of completed projects.
Self-described as the web’s motherlode of irrigation information. Includes free tutorials on drip irrigation design and installation and many other irrigation-related information.

Managing/Monitoring Irrigation Water Videos
These YouTube videos are two of eight produced by USDA’s Natural Resources Conservation Service in California In December 2011. The videos provide a quick glimpse into some of the Agency’s most popular conservation opportunities.
Irrigation Water Management: Theres a Plan for That
Irrigation Flow Measurement: Theres a Plan for That

Mobile Irrigation Labs
The Department of Water Resources’ mobile irrigation labs help growers across California evaluate their current irrigation systems and make recommendations on improvements. These labs are operated by local Resource Conservation Districts .

NRCS Technical Guide
NRCS provides a set of key technical resources to guide on-farm water (and other resource) management practices. These include information and recommendations about specific practices related to irrigation management as they pertain to local areas. Visit the online Field Office Technical Guide (eFOTG) and click through to the map to your county for details. Once there, you can search through practices listed in Section IV of the pull-down menu in the left-hand column of the page. Here, you may also find information about financial support that may be available for implementing these practices. In addition to practice-specific assistance, the eFOTG provides key data to help growers in resource management decision-making, including natural resource information (Section II in the pull-down menu) about local soil (e.g. web soil survey), water, air, plant and animal resources; planning tools for developing resource management systems (Section III); and other useful tools and information.

NRCS Irrigation Page
A comprehensive one-stop-shop that includes information on irrigation components, training, methods, management models, and lots more.

The Center For Irrigation Technology
An independent research and testing facility, the Center for Irrigation Technology (CIT) assists designers, manufacturers and users of irrigation equipment to make the technological advances. Based at CSU Fresno.

UC Irrigation Education Material
The UC Department of Land, Air and Water Resources hosts this site that collects UC research-based information on irrigation.

Irrigation Technology Companies

Tested Irrigation and Water Management Equipment
These irrigation and water management equipment companies have submitted their equipment to third party testing at Fresno State. To find out more about the products you are interested in and have been tested, contact the companies directly and ask about the equipment and the certification results.

Tested Supervisory Control and Data Acquisition Equipment
Supervisory Control and Data Acquisition Systems (SCADA) have become a valuable tool for irrigation districts and other water users, allowing more accurate, fast, and reliable water service. A wide variety of SCADA options are now available, from providing simple remote monitoring capabilities, to full automatic control of canal and water delivery systems. This list of SCADA services was put together by the Cal Poly Irrigation Training and Research Center, which tests and advises on local water delivery and control systems.

Data & Analysis

Application Efficiency
The Department of Water Resources and UC Davis compiled this Spatial and Temporal Analysis of Application Efficiencies for the State of California, a map-based portal detailing how well different irrigation systems perform when delivering a specific amount of water.

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Case Studies

American Farms

American Farms uses several water-saving techniques for their 7,500 acres of vegetable crops. The solid set sprinklers utilized reduce mainline leaks common with mobile systems, which is a major cause of water losses. This sprinkler system also reduces crop damage caused by walking on the beds to move irrigation pipes. Additionally, with the solid set system, it is possible to plant multiple crops per year—as many as 3 to 4 crops per field per year for American Farms.

Adragna Ranch

The ranch shifted from using a gated pipe sprinkler system to low-flow buried pipe sprinklers that distribute water uniformly throughout the walnut grove. From the California Institute for Rural Studies report California Water Stewards

Dixon Ridge Farms

Dixon Ridge Farms suspends irrigation lines in the limbs of their walnut trees, which reduces how often they need to replace the irrigation tubing. It also uses less energy to water the crop, reduces GHG emissions, grows better cover crops and protects against frost.

Fetzer Vineyards

This case study highlights Fetzer’s water stewardship practices, including the installment of water meters to detect leaks and monitor use, carefully timed drip irrigation for maximum efficiency, and pond installments around the property to catch and store river water when flows are high as well as winter and spring rain. This practice of creating on-site water storage is ecologically sustainable because it avoids the use of river water during critical periods, it recharges local groundwater, and it creates wildlife habitat.

Limoneira Company

Limoneira Company has 7,000 acres of fruit and nut crops. In 2004, Limoneira partnered with Agromin Corporation, to produce organic mulch and compost from green waste. Limoneira receives this compost free of charge from Ventura County and uses it on their 3,000 acres of lemon and avocado orchards. This mulch helps reduce water lost through evaporation and provides an improved habitat for beneficial microorganisms. The mulch also improves overall soil structure and nutrient availability, while reducing erosion.

Planting Justice

Although California is the largest food producing state in the country, many residents in cities like Oakland and Richmond live in what are called “food deserts,” defined as places lacking access to fresh produce and food. The San Francisco Bay Area is at the forefront of efforts to transform cities into food producing landscapes. San Francisco and Oakland are adopting urban agriculture as a permanent component of their City’s General Plan. Thiscase study reviews efforts to incorporate water-use efficiency and conservation practices into urban agriculture and describes how one organization in Oakland is utilizing permaculture techniques to address food justice, economic justice, and social justice issues.

Red Rock Ranch

A general description of John Diener’s Integrated On-Farm Drainage Management system, which includes both drip tape and new-generation center pivot sprinklers equipped with smart controllers for precise irrigation scheduling. From the California Institute for Rural Studies report California Water Stewards

Reiter Berry Farms

This video is part of the Water Stewardship video series produced by the Ecological Farming Association. Reiter Berry Farms has pioneered a tension-based irrigation monitoring system that reduces water use by 30%.

Suncrest Nurseries

Suncrest Nurseries is a California Institute for Rural Studies case study of a nursery utilizing tailwater ponds to clean and recycle water in the Watsonville area. Access the full report, California Water Stewards or download just the Suncrest case study.

Tom Roger’s Almond Ranch

Smart irrigation scheduling refers to technologies that help growers determine more precisely when crops need to be watered and how much water they require. With smart irrigation scheduling, growers are able to use their water more efficiently, either by reducing or by keeping constant the amount of applied water, while maintaining or improving yields. Having more precise knowledge of soil moisture levels can also have a number of co-benefits, such as reduced energy and water costs and fewer pests. This case study reviews the science and practice of irrigation scheduling on an almond ranch in Madera County, California.

Vineyard Water Conservation Demonstration Project

This case study reports the results of two years of irrigation demonstration projects and recommendations for best irrigation practices. The first irrigation demonstration project was conducted at Hoot Owl Creek / Alexander Valley Vineyards during the 2009 growing season, and a follow-up demonstration was conducted in 2010. A second site was added at Wildwood Vineyards in 2010 to serve the Sonoma Valley. The demonstration consisted of 6 nonreplicated irrigation “treatments” illustrating 6 common practices used in drip irrigation of vineyards. Irrigation scheduling was conducted independently of the commercial practice being used in the surrounding vineyard block.

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Page Credit

Content for this page was originally developed by Kaomine Vang and Dr. David Zoldoske, California State University Water Resources and Policy Initiative and Sarge Green, CSUFresno California Water Institute. Various others have since contributed content.