By Kathryn Carter and John Warbick (OMAFRA)
Why is Irrigation Important for Tree Fruit?
Irrigating peaches is important in increasing fruit size, increasing yields and improving fruit quality, especially in long periods of dry conditions. Irrigation also benefits tree growth, tree health and fruit bud development for next years crop. Research has shown extensive benefits to irrigating young trees such as increased growth, greater fruiting wood structure and earlier fruiting potential.
Critical Timing for Irrigation in Tree Fruit
Certain stages of growth are less sensitive to water stress than other stages. As a result, there are certain times during the season when reducing irrigation is less harmful to the crop.
There are three stages of development for peaches:
Phase 1-Rapid fruit growth occurs in all fruit varieties (early and late season) due to cell division from bloom to approximately 30 days after bloom. Water stress must be avoided during this phase.
Phase 2-Pit Hardening starts 30 days after bloom and continues until 6 weeks before harvest for early maturing varieties and 8 weeks before harvest for late maturing varieties. During this time there is little increase in fruit size, however shoot growth is rapid. Water needs are reduced at this time.
Phase 3- Cell expansion results in a significant increase in fruit size (~66% of the final fruit volume) for all fruit varieties (early and late) from approximately 2–4 weeks before harvest. Water stress must not occur during this final period of fruit growth.
Deciding When to Irrigate
There are several methods to evaluate the need for irrigation including soil moisture monitoring, monitoring moisture stress in plants, evapotranspiration, historical guidelines and soil moisture/tree stress.
Soil Moisture Monitoring
Soil moisture probes can be an inexpensive and relatively easy way to evaluatethe 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. Drip irrigation recommendations are based on soil moisture measurements.
Monitoring Water Stress in Plants
Evaluating water stress in plants is the most accurate methods 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). Although sensors are available to evaluate water stress in plants (ie. pressure bombs, NDVI software for use with drones), currently these are not practical options for most growers.
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. Daily ET in Ontario is available from the following website http://www.onpotatoes.com/cwd.cfm
For a detailed explanation of Irrigation Scheduling using Evapotranspiration please see page 39 in the OMAFRA publication Irrigation Management Best Management Practices.
Estimating water requirements for overhead irrigation based on historical data, is not the most accurate method of determining irrigation needs since the water status for peach trees changes day by day depending on the weather conditions. Historical weather guidelines do not account for these variations and can result in either under or over irrigation. As a general rule, the standard for overhead irrigation for peach trees is 1 inch of rain per week before pit hardening and 2 inches per week from pit hardening through harvest.
Soil Moisture and Tree Stress
The amount of moisture in the soil can 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.
Deciding How Much to Irrigate
The timing for initiating irrigation will depend on the type of irrigation you are using. It is more difficult to catch up during dry conditions with drip irrigation, so the threshold for initiating drip irrigation is lower than that of overhead irrigation. Drip irrigation often involves frequent irrigation applications, while overhead irrigation involves applying a larger amount of water in an application. In addition, drip irrigation is 90% efficient as compared to overhead irrigation which is 60% efficient, so this should be accounted for when calculating your irrigation application rates.
The effective root zone depth for peaches is 24″, and ~ 70% of moisture is extracted from the upper half of the root zone. As a result, irrigations that result in water moving down past 24” will result in wasted water and can cause issues with soil pathogens (crown rot).
Tips for Reducing Water Requirements
Whether you are a grower with irrigation and are looking to reduce your water use, or someone that doesn’t have access to irrigation, there are some opportunities to reduce water requirements in orchards.
Keep cover crops or sod mowed to ensure that it does not compete with the trees for water resources. Maintain a 3 to 4 feet wide weed-free strip to minimize competition with weeds. Finally, mulches (i.e. Composted manure) can increase soil organic matter and increase water holding capacity, and reduce soil temperature, resulting in a 25 percent decrease in tree water demand. Managing tree vigour by managing N applications can also help to reduce the water demands for the tree. Wind breaks also help to reduce the drying of soil allow for more efficient use of irrigation water.
For orchards without irrigation, crop load can be modified with a second thinning to ensure marketable fruit size is still achieved, and reduce competition for water. Using drip irrigation as opposed to overhead irrigation can also allow growers to save more water, as the water is directly reaching its target.
Irrigation is important for fruit sizing, tree growth, fruit bud development and tree health. Developmental stages have a significant impact on the importance the timing and amount of irrigation needed.
Courtney, R. (2016, April 1). Better ways to irrigate. Good Fruit Grower. https://www.goodfruit.com/better-ways-to-irrigate/
Frecon, J.L. (2002). Best management practices for irrigating peach trees. Rutgers Cooperative Extension. https://njaes.rutgers.edu/drought/pdfs/BMP-Irrigating-Peaches.pdf
Hansen, M. (2013 February 15). Saving water in early peaches. Good Fruit Grower. https://www.goodfruit.com/saving-water-in-early-peaches/
Johnson, S., Prichard, T., & Schwankl, L. (2020). Drought strategies for fresh market peaches, plums, and nectarines. University of California Drought Management. http://ucmanagedrought.ucdavis.edu/Agriculture/Crop_Irrigation_Strategies/Stone_Fruit/