Top Summer Practices to Prime Your Field for Success
Summer is a critical period for the growth of new fruiting wood, which is needed for the following year’s blueberry crop. The goal is to produce vigorous and healthy summer growth that will initiate flower buds in late summer and fall that will form the bases for next year’s crop. Along with postharvest pruning, fertilization, and pest and disease management, proper irrigation practices are critical for producing healthy summer growth of sufficient vigor to sustain productivity year after year. A typical blueberry field in Florida often consists of a light sandy soil with pine bark incorporated into the soil, or with beds of pine bark on top of the soil surface. The pine bark provides organic matter and helps maintain an acidic soil pH. However, neither sandy soils nor non-decomposed pine bark have high water holding capacities (they do not retain large quantities of water after wetting). Moreover, blueberry plants have shallow root systems that lack root hairs, making them drought susceptible during periods of high water demand (Figure 1).
Figure 1. An excavated ‘Meadowlark’ southern highbush blueberry (SHB) plant. Note the shallow, fibrous root system typical of SHB.
Combining the shallow root system of the blueberry plants with the low soil water holding capacity typically found in blueberry fields demonstrates the need for careful irrigation management to supply plant water needs without leaching nutrients or moving water below the root zone.
The amount of water used by a blueberry plant is usually highest in mid to late summer, but it can depend on many factors including plant canopy size (which usually increases throughout the summer following postharvest hedging and topping), and weather conditions. Research has shown that mature blueberry plants use an average of about 2 gallons of water per day during peak periods of water use from July through September. However, these are average values that vary considerably from day to day based on daily weather conditions. Plant water use changes significantly with changing weather conditions throughout the year. In north-central Florida, blueberry water use declined significantly during fall and winter when compared to summer. For example, average October water use was 40% less than at its peak in September and declined further during winter months.
The amount of water available for uptake by a well-irrigated plant will be limited by the depth and spread of the root system and the ability of the soil to retain water (soil water holding capacity) as discussed above. During normal irrigation, there is no advantage to applying water below the depth of the root zone. Therefore, irrigation water is usually applied frequently and in relatively small amounts to avoid water and nutrient loss below the root zone, especially in pine bark bed plantings where the roots are mainly limited to the bark media. Over-irrigation can lead to inefficient water and nutrient use and leaching of nutrients and other chemicals below the root zone. During periods of high water demand, light irrigations applied multiple times per day will increase water use efficiency and reduce potential leaching of fertilizers and pesticides compared to longer, less frequent, irrigation events. The chemical and physical properties of blueberry beds are dynamic. As pine bark decomposes, its water holding capacity generally increases, however, the root profile depth decreases, requiring reapplication of bark at approximately two- to three-year intervals to maintain an adequate root zone volume.
To irrigate efficiently, root system depth and spread, and the depth and spread of the wetted zone from irrigation, should be known. Rooting depth can be estimated by lightly digging, or collecting core samples, from the beds within the rootzone of the plants and observing the depth of the roots. Soil moisture sensors can supply data on water content at different soil depths, providing growers with information needed for proper irrigation scheduling. The goal is to keep soil moisture within a targeted range by replacing water lost through evapotranspiration. Knowledge of crop water demand, root system depth, wetting pattern of the irrigation system, and the water holding characteristics of the soil will help achieve this goal. Common types of moisture sensors include those that measure soil water content (volumetric), and those that measure soil water tension (the force of adhesion of water to soil particles). Sensors measuring soil water content can indicate both when and how much to irrigate. See UF EDIS Publication BUL343, Field Devices for Monitoring Soil Water Content (Munoz-Carpena, 2021) for more details. Sensors that measure water tension such as tensiometers may not work well in most Florida blueberry fields because of the high sand and bark content of the soil. Sensors should be placed within the rootzones, in accessible areas. Positioning sensors at different depths will provide information about water movement in the root profile. Sensors positioned near the soil/bark surface will indicate when irrigation is needed. Sensors positioned near the bottom of the root zone will help determine how much water is needed. If only one sensor per site is used, it should be placed at a depth in the middle of the root zone. Multiple sensors may be needed to account for differences in the fields such as slope, drainage, plant age and size, pine bark age, condition, amount used, and cultivar.
Developing an efficient and effective irrigation program for blueberries in Florida can be challenging. Knowledge of varying blueberry plant water needs throughout the year, the nature of the blueberry root system, soil and pine bark bed characteristics, and proper use of soil moisture sensors will help growers develop efficient irrigation practices that avoid drought stress and excessive water use and associated leaching of fertilizers and other chemicals.
Suggested reading
Literature Cited and Further reading
Munoz-Carpena, R. 2021. Field devices for monitoring soil water content. University of Florida Cooperative Extension Service. Publication BUL343. https://edis.ifas.ufl.edu/pdf%5CAE%5CAE26600.pdf
Phillips, D. A. and J.G. Williamson. 2021. Irrigation Practices for Southern Highbush Blueberry. University of Florida, Cooperative Extension Service. Pub. HS1432. https://edis.ifas.ufl.edu/pdf/HS/HS1432/HS1432-Dx4nsu6ek6.pdf
CREDITS:
JEFF WILLIAMSON, Horticultural Sciences Department, UF/IFAS
& DOUG PHILLIPS, Gulf Coast Research and Education Center, UF/IFAS
