Peach Irrigation in an El Nino Year

Monitoring Weather Patterns, Soil Moisture in Orchards, and More

CREDIT
by MERCY OLMSTEAD, Ph.D.,
Stone Fruit Specialist and Assistant
Professor, University of Florida,
Gainesville, FL

AS WE CONTINUE headlong into the winter season and many of the peach or­chards are resting for a couple of months, what will this year bring? According to the Climate Prediction Center and the International Research Institute for Cli­mate and Society, a strong El Niño was present for the fall months and will peak during the 2015-2016 winter months. Sea surface temperatures at the equator are well above normal (Figure 1), influ­encing weather patterns across the Unit­ed States (U.S.).

In the southeastern U.S., an El Niño year typically brings to Florida cooler and wetter weather. Unfortunately for peach trees, they are not tolerant of flooding. Thus, this dry period before the peak of the El Niño season is a good time to assess your orchard site and make any drainage improvements nec­essary. Additional trenching, drain tile installation, and grading to direct water away from low spots will help to reduce standing water and flooding in orchards.

The increased precipitation that may come with the 2015-2016 winter may contribute to advancing trees out from ecodormancy after trees are defoliated. Recent warm temperatures are not help­ing to slow the advancement (Figure 2), and a few orchards may have trees that are starting to flower and set fruit. Al­though impossible to control precipita­tion, orchards that have begun emerging from dormancy should not be heavily irrigated, depending upon previous rain­fall events. Precipitation amounts for all Florida Automated Weather Network sites can be found at fawn.ifas.ufl.edu/.

Although water stress can reduce fruit set and de­lay leaf emergence, significant transpiration (i.e., water movement from roots to the shoots) in the tree will not occur until there is significant leaf area. Soil moisture status will also determine irrigation scheduling in the late winter and early spring.

TOOLS FOR MEASUREMENT OF IN-FIELD SOIL WATER STATUS

There are a number of tools to determine soil water status, and while some may be expensive, there are in­expensive and effective options for in-field monitoring. Soil water status will be influenced by the amount of sand, loam and clay in the soil, and much of the peach acreage in Florida is based on sandy soils that drain very well, reducing excessive soil moisture. However, these types of soils need to be irrigated frequently for short periods to most effectively provide water to peach root systems.

There are three main classes of monitoring soil moisture— volumetric, tensiometric, and hand-feel  of these three classes, volu­metric are perhaps the most expensive and require the most knowledge for in­terpretation of the data.

VOLUMETRIC METHODS estimate soil water content by measuring how fast an electromagnetic pulse is affected by water in the soil. These methods in­clude neutron moderation, time domain reflectometry (TDR), frequency domain, amplitude domain reflectometry, phase transmission, and time domain trans­mission (Muñoz-Carpena, 2015). While neutron moderation and TDR are fairly expensive, the other volumetric methods are less expensive and can be used for ir­rigation scheduling. While soil and site specific calibration are required, the ac­curacy on sandy soils is excellent.

TENSIOMETRIC METHODS are less expensive and include such tools as tensiometers, gypsum blocks, heat dis­sipation probes, soil psychrometers, and granular matrix sensors. These have lower resolution and accuracy than volumetric methods, but their low cost is attractive for season long in-field measurements. However, they are not recommended for sandy or coarse soils (Muñoz-Carpena, 2015), in which much of the citrus and stone fruit or­chards are planted in Florida.

Finally, the “HAND-FEEL” METHOD is the most inexpensive, as it is free! Dig­ging up soil from within the root zone and squeezing the soil to determine the amount of water can help to determine how much irrigation to apply. The ability of the soil to form a ball, ability to rib­bon, amount of loose particles, presence of soil/water stains on fingers and soil color are all used to determine the rela­tive water content of the soil (Klocke and Fischbach, 1998; USDA-NRCS, 1998).

Different soil textures have vary­ing amounts of available water capacity (AWC), which is the amount of water that can be extracted from that soil layer by the plant (Table 1). As in­dicated below, our coarse soils on the ridge and in good production areas have fairly low available water capacity, as well as ability to store water near the root zone.

As you begin to think about irrigation for the next production year, consider using irrigation sensors or tools to help schedule irrigation sets. Early results from or­chards in two Central Florida locations indicate that the amount of water cur­rently being applied can be reduced by as much as 50 percent without reducing yield or fruit size. In pecans produced in the southeastern U.S., recent research has shown that a 38 percent reduction in irrigation did not affect tree water stress, yield or quality (Wells, 2015). We look forward to verifying our initial results in 2016, to save water, and help growers become more efficient.

Thank you to the Southwest Florida Water Management District for funding this research.

 

REFERENCES

Klocke, N.L. and P.E. Fischbach. 1998. Estimating Soil Moisture by Appearance and Feel. Publication G84-690-A, Nebraska Cooperative Extension Service, Lincoln, NE.

Muñoz-Carpena, R. 2015. Field Devices for Monitoring Soil Water Content. Publication #BUL343, Electronic Data Information Service, University of Florida Extension, Gainesville, FL. https://edis.ifas.ufl.edu/ae266

United States Department of Agriculture – National Resources Conservation Service. 1998. Estimating Soil Moisture by Feel and Appearance. Program Aid Number 1619. http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/ nrcs144p2_051845.pdf.

Wells, L. 2015. Irrigation water management for pecans in humid climates. HortScience 50:1070-1074.