Using microirrigation to optimize crop water use in strawberries

Strawberry (Fragaria × ananassa Duch.) is a small berry fruit from the Rosaceae family that is well appreciated and consumed worldwide. In the U.S., strawberries are primarily grown in California and Florida, which account for 91% and 8% of production, respectively. Although Florida has the smaller market share, strawberry production in Florida occurs during the off-season for California. The Florida growing season starts in late September to mid-October to supply fresh strawberries from November to March, when the price is higher than during the rest of the year. In 2022, strawberries were planted on 10,600 acres in Florida, resulting in a production value of $511 million.

Strawberry management practices

Water use in strawberry production in Florida is unique due to its heavy reliance on both sprinkler and drip irrigation systems. Typically, commercial strawberries are planted on raised beds covered with black plastic mulch, with plants in twin rows in a staggered fashion. The plastic mulch serves as a tarp for soil fumigation to control soil-borne pathogens and weeds, and as mulch for conserving soil moisture, warming the soil during the cooler months and keeping the berries clean. The drip tape installed in the center of the beds provides water and fertilizer during the growing season, whereas sprinkler irrigation is used at the beginning of strawberry growing season for bare-root transplant establishment and later in the season for freeze protection. Typically, impact sprinklers are used with fixed square spacing to supply water during both phases.

Although availability of strawberry plug transplants has increased, bare-root strawberry transplants still predominate because of the higher cost of plug transplants. The bare-root transplants have impaired root systems, which make them vulnerable to heat stress during plant establishment, as they are unable to uptake water from the soil efficiently and withstand the high temperatures associated with black plastic mulch (see fig. 1). Consequently, an overhead sprinkler irrigation system is required to maintain a cooler microclimate around the transplant crowns to foster the growth of new roots and avoid the desiccation of the plants (see fig. 2).

Overhead sprinkler irrigation is not only used during transplant establishment but also later in the growing season during winter to protect flowers and fruits from cold injury when there is a potential drop in air temperature to freezing and near freezing. Typically, growers turn on their sprinkler systems for cold protection when the temperature reaches 34 degrees and keep them on during the cold event generally until the sun melts the ice.

Both management practices use significant amounts of water. For example, the establishment phase for bare-root transplant can last 10-14 days with water applied for eight to 10 hours a day to lower the plastic mulch temperature to promote establishment and early growth. This accounts for one-third (~ 374-534 hundred thousand gallons/acre) of the total water use over the growing season, 97% of which flows off the plastic mulched beds. In Florida, between late September to mid-October this water use accounts for 14.7 million cubic meters of water, which not only lowers the aquifer levels but also constrains water availability for metropolitan areas in west-central Florida, which is the major strawberry growing area in Florida.

Similarly, large volumes of water may be used during the freeze events. For example, a single freeze event can require the use of approximately 2-3 acre-inches of water. The magnitude of water use for freeze protection of strawberries when multiple events occur in a season can have adverse environmental effects. In 2009-10 and 2010-11, for example, water use for approximately 13 freezing and near freezing events occurred per season, resulting in 750 dried wells and 140 sinkholes (Aurit et al., 2013).

Research station and on-farm trial results

One way of conserving water during strawberry plant establishment and freeze protection is the use of micro/low-volume sprinklers. So, in a Southwest Florida Water Management District-funded study designed at the Plant Science Research and Education Unit in Citra, Florida, we have evaluated the efficacy of commercially available micro/low-volume sprinklers for decreasing water application during bare-root transplant establishment and freeze protection without adversely affecting plant survival, growth and yield.

One way of conserving water during strawberry plant establishment and freeze protection is the use of micro/low-volume sprinklers.

We compared four commercially available micro/low-volume sprinklers with a standard impact sprinkler. The sprinklers were selected based on the wetting diameter, operating pressure and cost to retrofit the existing conventional impact sprinkler system. The layouts of the sprinklers were consistent with the manufacturers’ guidelines for sprinkler spacing and operating pressure.

The two-year study revealed that all four micro/low-volume sprinklers significantly reduce water use. Two of the systems reduced the cumulative water use by 65% and 27% in plant establishment phase and 62% and 23% in freeze/frost protection phase, respectively. The lower water application for frost/freeze protection with the low-volume sprinkler systems did not result in more flower and fruit injury than the impact sprinkler system. Additionally, no significant difference in yields was observed in terms of strawberry transplant survival, plant growth and yield.

To further validate the water savings, an on-farm trial was established in a grower’s field in Plant City, Florida, during the 2022-23 growing season, where the best performing micro/low-volume sprinkler (based on the PSREU trial) was compared with the grower’s sprinkler. On-farm results revealed water savings of 57% during the transplant establishment phase and 63% over the freeze/frost phase without any adverse effect on growth and yield with the micro/low-volume sprinkler when compared with plots managed with the grower’s sprinkler.

All equipment shown or referenced is used solely as an example and not as an endorsement by UF or authors.

Vivek Sharma, PhD, is an assistant professor, precision water management specialist, agricultural and biological engineering department, University of Florida.

Josue St. Fort is a graduate research assistant in the school of natural resources and environment at the University of Florida.

Carlene Chase PhD is an associate professor in the horticultural sciences department in the University of Florida.