The Importance of Water for a Young Orchard

Study on Irrigating Fledgling Peach Plants in the Southeastern United States Shows Interesting Initial Results

Another year has started and peach trees that were planted early this season are starting to grow actively.  Every time that we visit young orchards, the trees are bigger and bigger.  However, it is also important to know that the season is unfortunately starting with a drought across the southeastern U.S. (see figure 1).  What does this mean for these young preach trees?

Figure 1. U.S. drought monitor for the southeast region on April 18, 2017. Scale intensity: Yellow colors indicate mild drought and orange/red colors indicate severe to extreme drought. Source: http://droughtmonitor.unl.edu/Home/RegionalDroughtMonitor.aspx?southeast.

Peaches evolved in Asia in humid and subtropical conditions; thus, chances are that peaches naturally have high water requirements and are sensitive to water stress.  However, peaches do not tolerate waterlogging.  Appropriate and precise irrigation management is required for optimal growth and tree health.  Currently, accurate and precise irrigation management for agricultural crops has become a subject of intense interest, due largely to current problems with drought affecting several regions of the world and changes in regulations in water use.  Although peach tree irrigation has been researched over the last decades, these have been mostly done in Mediterranean regions of the world and/or using adult plants.  In these studies, irrigation has shown several benefits such as increase on plant size, fruit yield, and fruit size.

Although irrigation has been proved to benefit plant growth, there is a lack of irrigation studies for young plants in the Southeastern U.S.  This preliminary report presents the benefits that irrigation brings to young peach trees during their first years of growth.

ABOUT THE STUDY

Drought has been reported in the southeastern United States in nine years since 2001.  Because of the drought, plants are not receiving the proper amount of water for optimal growth, which negatively affect the transpiration and photosynthetic rate of the plants.  In an effort to better understand the effects of irrigation of young peach plants, Dr. Dario Chavez (peach specialist), Dr. Marc van Iersel (irrigation physiologist), and Mr. Bruno Casamali (PhD student) from the Department of Horticulture at the University of Georgia started a project on May 2015.  A total of 240 plants of ‘Julyprince’ grafted onto ‘Guardian’ were planted at the Georgia Peach Research and Extension Program field plot, located at Dempsey Farm, Griffin, GA.  Half of the plants received irrigation, while the other half didn’t receive irrigation.  These plants were divided in two major plots, one with drip irrigation and another with micro-sprinkler irrigation.  One of the objectives of the study was to test these two different irrigation systems since they deliver water differently and have different irrigation efficiencies.  The other objective was to test irrigation for young peach plants.  

The irrigation system is controlled by a network of sensors that measure the amount of water in the soil every 20 minutes.  If the soil moisture readings drop below a pre-established threshold of soil moisture, the network communicates with a set of solenoid valves that turn the irrigation on and off as needed, keeping the soil moisture above the limit.  The soil moisture sensors are located at eight and 16 inches underground near the plant being monitored and connected to a wireless node (see figures 2 and 3).

Figure 2. Soil moisture sensors located at 8” and 16” deep in the soil.

Figure 3. Wireless node where the soil moisture sensors are connected.

ABOUT THE INITIAL DATA

Results for the 2016 season of one-year-old plants are very promising.  Each irrigated plant received on average 0.59 gallons of water per day from June to August.  During the peak of the summer (mid- to late-July), each plant received 0.72 gallons of water per day on average.  Plants that were irrigated had canopy volume and trunk cross-sectional area (related with trunk diameter) 2.2 and 1.6 times bigger, respectively, than plants that were not irrigated.  Results of canopy volume and trunk cross-sectional area are important descriptors of the greater plant vigor induced by irrigation compared with the lack of irrigation.  Figure 4 is a good example of an irrigated plant, while figure 5 shows a non-irrigated plant.  It is noticeable that irrigated plants have a bigger and denser canopy, with more healthy foliage than the non-irrigated plants, which appears to have a stunted growth, with some wilting foliage.        

Figure 4. Irrigated plant.

Figure 5. Non-irrigated plant.

Another parameter measured during the Summer 2016 was photosynthetic rate (irrigated plants had 1.8 times greater photosynthetic rate than non-irrigated plants, on average).  Although photosynthetic rate of a single leaf in the plant cannot be directly correlated with plant growth, greater photosynthetic rate is an indicator that the plant has more capability of carbon fixation during photosynthesis, which might induce better plant health.  Furthermore, we measured the leaf and stem water potential of the plants as indicators of how tight the water is adhered to the plant tissues.  The tighter the water is held by tissues, the more difficult it is for the plant to utilize the water for metabolic processes.  As expected, non-irrigated plants had water more tightly attached to the tissue than the irrigated plants, which is not desired.  Thus far, the results of this experiment are very interesting.  Irrigated plants appear to have a better field establishment and growth than non-irrigated plants.

WHAT IS EXPECTED FOR THIS SEASON’S DATA?

This season will be the first year of fruit production.  We expect to collect data on fruit yield and quality.  If the results from last year are repeated this year, we are confident that we will be able to generate guidelines of irrigation practices for young peach plants for the southeastern United States.  Irrigation guidelines will be an important material for peach production, since it will contain information about the water requirements of the plants, helping to irrigate plants more efficiently.  

CREDIT

by BRUNO CASAMALI, PhD Graduate Student, Peach Research and Extension Program, Department of Horticulture, University of Georgia, Griffin, GA; and DARIO J. CHAVEZ, Assistant Professor and Peach Research and Extension Specialist, Department of Horticulture, University of Georgia, Griffin, GA.