Irrigation efficiency in nurseries: towards a more sustainable approach

irrigated plants inside a hoophouse
Optimal irrigation for model species. Laval University Nursery.
pic of a man
Dr. Charles Goulet

Aided by an abundance of research, nursery container production has matured significantly over the years, resulting in ever-increasing categories and size ranges of plants grown in containers.  While we have also seen corresponding improvements in irrigation technologies in that same timeframe however, the complexity of containerized nursery production means that nursery growers in Canada continue to rely on inefficient overhead irrigation practices.

The constant movement of pots, necessitated by a multitude of factors ranging from decreased inventory during the sales season to winter storage requirements, adds to the already higher costs associated with more efficient drip irrigation technologies. Additionally, the lack of automation typically available for overhead systems means that watering decisions are based primarily on timed irrigation intervals and visual clues to plan irrigation scheduling. The result can be either under or over watering, both of which can have detrimental impacts on plant growth and quality. More recently, reliable access to water has also become problematic for many growers, making water conservation an increasingly important priority.

A research project currently underway by Laval University’s Dr. Charles Goulet entitled Irrigation efficiency in nurseries: towards a more sustainable approach, will offer nursery growers the ability to optimize their irrigation practices by delivering the right amount of water at the right time and to the right plant. This project is part of the “Accelerating Green Plant Innovation for Environmental and Economic Benefit” Cluster and is funded by the Canadian Ornamental Horticulture Alliance (COHA-ACHO), private sector companies, and the Government of Canada under the Canadian Agricultural Partnership’s AgriScience Program, a federal, provincial, territorial initiative.

This current project continues work started by Dr. Goulet under the Growing Forward 2 (2013 – 2018) Cluster program which focused on the use of wireless tensiometers to measure the water available to the plant, thereby allowing for precise irrigation scheduling based on plant needs. This high-tech wireless web-based technology was paired with drip irrigation systems, with or without capillary mats. Both water use and plant growth were measured to determine the impact of each strategy. The researchers were able to conclude that precision irrigation has the potential to significantly reduce water use in nursery plant production as wireless tensiometers provide reliable data to guide irrigation scheduling decisions. Additionally, wireless technology provides considerable operational flexibility by providing the grower with easy access to data.

irrigation at a nursery
Optimal irrigation with automation at the commercial nursery site.

A plant’s water needs can vary widely from species to species, however monitoring the individual needs of each species with tensiometers would be both complicated and expensive. As a result, finding plants with similar watering requirements which can be grouped or clustered in the nursery environment became an important component of this phase one research project. To facilitate the decision-making process on watering practices, such as frequency and volume of water, a series of reference plants representing a good diversity of watering requirements, was determined. As well as being an essential part of the research process, reference plants facilitate the ability for clustering plants according to their very specific cultural requirements.

Initial research was conducted at the University’s production facilities, which incorporates the use of wind tunnels to mitigate as much as possible the impacts of weather events such as rain, temperature and wind, to the research data.  However, as the project was eventually moved to a commercial nursery setting, it became necessary to make several modifications to the project’s overall design. The use of wireless tensiometers provided reliable data to the nursery and the research teams, but the challenges associated with weather factors, especially wind or the knowledge of a pending rain event, ultimately pointed to the option of adopting a hybrid approach to irrigation scheduling.  Ultimately, the final decision to irrigate was made by the nursery’s production team, guided by data provided by the tensiometers.

plants in post with tubes in them
Clustering experiment at Laval University Nursery.

The data collected and lessons learned from the first phase of this research project have largely dictated the design and objectives of the current phase. According to Dr. Goulet, “Due to cost factors, nursery growers will find it necessary to use overhead irrigation systems, but there is a need for precision irrigation management that will allow growers to make the most of their existing systems. To be truly efficient in terms of water use, the different irrigation strategies need to be expanded to meet the requirements of the species and the climate.”

The first objective of the current project is to improve irrigation management in the nursery setting through the use of wireless tensiometers. Specifically, the research will seek to optimize the use of tensiometers to support the practice of clustering. The research will also evaluate how the amount and frequency of watering can influence plant growth. Using several species with very diverse watering requirements, in combination with different irrigation management strategies, (eg: comparing different volumes of water and different irrigation intervals) will help researchers to determine water use and the impact on plant growth. More precise data will be obtained in the first two years by conducting the experiment at the Laval University research facilities and the data obtained will be used to determine irrigation strategies when the research is transferred to a commercial nursery setting.

field grown plants in pots
Soil tension measurement at the commercial nursery site.

Research will also continue into expanding the use of clustering practices. In order to best meet the very diverse watering needs of the very wide range of species that make up the inventory of most growers, the number of reference species will be increased. According to Dr. Goulet, “The clustering process is not as simple as it seems, as the factors that impact overall plant growth include factors such as frequency of watering as well as amount of water applied with each irrigation event. Clustering is not as straightforward as determining plant species with high, medium and low water requirements.”

It will be the objective of the project to increase the list of reference species from the current 10 to a total of 15 species, and the corresponding clustering recommendations will be increased from 50 to 100 species. To ensure accurate data, this component of the research project will use the wind tunnel facilities at Laval University to mitigate the impacts of natural weather events.

shrubs growing in pots in an nursery
Optimal irrigation for clustering species. This photo shows the irrigation mats which were used in the Cluster 2 project; they are not a part of the current project.

To truly live up to its potential, precision irrigation must be supported by a solid automation process. Over the past few years, many models have been developed that integrate various technologies to optimize the irrigation process and the third objective of this project will determine the most useful parameters to automate irrigation in the commercial nursery setting. The research team will evaluate if irrigation controlled by evapotranspiration measurements will provide similar results to irrigation controlled by the new generation of wireless tensiometers, as well as the potential to integrate these technologies.

Again looking at the need to provide practical recommendations for use in the commercial nursery setting, the research will evaluate the various parameters which could be added to the automation process with data obtained from external weather sites, including daily rain forecast, wind speed (to delay a planned irrigation event if the wind is too strong) and evapotranspiration predictions. The ultimate goal is to provide growers with various options depending on their existing systems and their resources to acquire new irrigation technologies.

Weather station
Weather station for irrigation automation.