Irrigation Timing in Fruit Trees

By Celina Callo Simonnet, Kathryn Carter, Rebecca Shortt and Erika DeBrouwer, OMAFRA

The importance of irrigation for tree fruit

Irrigation is important in producing high quality tree fruit (apples, peaches, plums, nectarines, cherries and pears) in Ontario. Research has shown that irrigation not only increases yields, fruit size and fruit quality, but it can also lengthen tree life and improve tree growth and photosynthesis (Casamali et al, 2021).

Irrigation is even more critical for high-density apple orchards, where the economic success of the orchard depend on obtaining high yields in the third, fourth, and fifth years to repay the establishment costs. To obtain these yields trees need excellent tree growth during the first three years. Research has shown that when tree growth is poor in high density apple orchards it results in delays in cropping in new orchards, and the total profits are reduced by 66% over the 20-year life of the orchard (Robinson et al., 2013: Precision irrigation management in apples). Since access to water is important in ensuring tree growth, it is important to have an irrigation system in place for high density orchards.

Recently, the cost of energy for irrigation has been rising. Applying the proper amount of water at the necessary times is vital for reducing costs of production. Therefore, determining when to irrigate is essential for optimum crop response and efficient use of resources.

Critical timings for irrigation for tree fruit

Critical periods for the irrigation of apples, pears, peaches, nectarines, plums and cherries are during flower formation, early fruit set, and during final fruit swell (2-4 weeks before harvest (Penn State Extension, 2017: Irrigation for fruit and vegetable production). Access to water during these times is critical to producing a high-quality crop.

Determining water needs of the crop

Precipitation in Southwestern Ontario averages 300-400 mm (12-16 inches) during the growing season, while the crop water demand may be 500-600 mm (20-24 inches) (OMAFRA, 2004). In Ontario we have been very dry in 2021 . Recent rains in ceratin areas have helped, but how do we know if the rain is enough to satisfy the trees needs?

Knowing when to irrigate

There are several methods to evaluate the need for irrigation, including, soil moisture monitoring, monitoring moisture stress in plants, evapotranspiration, and soil moisture/tree stress.

Evapotranspiration

Evapotranspiration (ET) or weather-based irrigation, calculates irrigation needs on a water budget approach. ET is the total daily loss of soil water by transpiration from plants and evaporation from the soil surface. Each type of soil will hold a certain amount of water reservoir and this reservoir is reduced on a daily basis based on the daily ET and crop maturity level (young plants use less water than fully grown). Precipitation will add to the soil water reservoir. In the spring when your soil is saturated or after irrigating to the full rooting depth your soil water reservoir is full. The daily ET (measured in inches or mm of water) for fully grown plants is reduced from the reservoir total and must be replaced during an irrigation event. Additional information can be found at Using ET Data to Make Irrigation Decisions – ONfruit.

Soil moisture

Soil moisture probes can be an inexpensive and relatively easy way to evaluate the amount of water available to the plant. Soil moisture sensors can help in determining when to irrigate, and when to turn off the irrigation to avoid wasting water. In 2013 and 2014 OMAFRA conducted a demonstration trial evaluating various different soil moisture sensors in orchards. The results of the trial showed that some locations were slower to irrigate then they should have been and the plants may have been experiencing water stress. Also, in some sites with drip irrigation, monitoring soil moisture allowed growers to turn off irrigation earlier then they anticipated, as they had reached adequate water levels. Drip irrigation recommendations are based on soil moisture measurements.

When measuring soil moisture, there are several methods available to growers (OMAFRA, 2019):

• Tensiometers: Directly measures the soil-water potential
• Electrical Resistance Blocks: Indirectly measures soil-water potential by measuring the resistance across a block that is buried in the soil
• C-probe: This tool uses capacitance sensors to collect soil-water readings
• Time domain reflectometry: Probes inserted into the soil measure the velocity of electromagnetic waves in the soil (Figure 9). These waves are slowed by soil moisture. For additional information on soil moisture monitoring please see Monitoring Soil Moisture to Improve Irrigation Decisions (gov.on.ca)

The amount of moisture in the soil can also be approximated by using the hand feel method. Dig down to a depth of 12-16 inches, if the soil is still moist and you can readily ball soil up in your hand, there is probably adequate moisture. Fruit trees can also show visual signs of stress including wilting leaves, lack of shoot growth and leaf drop. These symptoms may not appear until photosynthesis has been reduced by 40%, which limits grower’s ability to respond in a timely manner to water stress.

Evaluating water stress in plants

Evaluating water stress in plants is an ideal method of determining the need for water, as some soils may store water well, but may not release it readily to the plant (i.e. clay). In addition, some varieties and rootstocks may be more susceptible to water stress then others.

Sensors that evaluate plant water stress are now available. Some are not practical because they are time consuming (e.g. pressure bombs). Some are promising but still require more research to understand how to interpret the readings (e.g. NDVI software for use with drones or dendrometers).

As technology continues to develop these tools they will be valuable to growers as they may provide better insight into the water stress of the plants.

Conclusion

Irrigation in fruit trees is important for fruit sizing, fruit development, and tree health. Lack of access to sufficient water will have long term effects on tree structure and productivity. Making sure that trees have access to water during critical periods of fruit development is very important. There are a variety of different methods to determine a crops irrigation needs.

References

Cassamali et al, 2021. Plant Growth and Physiological Responses to Improved Irrigation and Fertilization Management for Young Peach Trees in the Southeastern United States in: HortScience Volume 56 Issue 3 (2021) (ashs.org) Irrigation. Washington State University Tree Fruit. http://treefruit.wsu.edu/web-article/irrigation/

Growing Big Peaches – Irrigation is a Must! – ONfruit 

Irrigation management. British Columbia Tree Fruit Production Guide. https://www.bctfpg.ca/horticulture/irrigation-air-quality/irrigation-management/#:~:text=Irrigation%20Timing%3A%20Irrigate%20at%20night,when%20applied%20to%20dry%20trees.

Ministry of Agricultural, Food, and Rural Affairs. (2002). Irrigation scheduling for fruit crops. http://www.omafra.gov.on.ca/english/crops/facts/90-069.htm

OMAFRA, AAFC, OFA (2004). Irrigation Management, BMP series OMAFRA, 2019 Monitoring Soil Moisture to Improve Irrigation Decisions (gov.on.ca)

OMAFRA, 2019 Monitoring Soil Moisture to Improve Irrigation Decisions (gov.on.ca) 

Penn State Extension 2017 Irrigation for Fruit and Vegetable Production (psu.edu)

Rutgers Best Management Practices for Irrigating Peach Trees (rutgers.edu)

The Role of Dendrometers for Irrigation Management in Apple | WSU Tree Fruit | Washington State University

Growing Big Peaches – Irrigation is a Must! – ONfruit