• Topics: Agricultural and Biological Engineering  | Blueberry  |  Haman, Dorota Z  | Zazueta, Fedro  | Lyrene, Paul M  |  Smajstrla, Allen G  | Pritchard, Robert Todd 

Water Use in Establishment of Young Blueberry Plants¹

BLUEBERRY PRODUCTION IN FLORIDA

Blueberries show great promise as a Florida fruit crop. Although blueberries are grown in many other states, Florida's climate allows fruit to reach maturity earlier, avoiding competition with growers in other states, thus commanding high prices. This advantage has been increased by the recent introduction of earlier-yielding highbush varieties.

Currently, about 2,100 acres of blueberries are grown in Florida. This acreage is expected to expand as more growers take advantage of Florida's unique market window and new early-yielding blueberry varieties, and as existing growers expand their acreage. Presently, the blueberry acreage is evenly divided between rabbiteye and highbush varieties. However, for the last 10 years, new plantations have been almost exclusively planted to highbush varieties.

Newly developed early ripening highbush varieties are of the greatest interest to Florida growers at this time. These varieties are lower yielding and much more difficult to grow than rabbiteye varieties, but the early ripening fruit brings high prices since it is the only blueberry available at this time. Before May 20, the average price is very high per pound. After June 1, the average price drops to around one dollar per pound. Highbush plants are more difficult to establish and have a shorter life expectancy than the rabbiteye varieties. They are also much more sensitive to water stress and they require frequent irrigation to grow and produce even when well established.

Rabbiteye blueberries are native to Florida. These are relatively easy to grow and are considered the highest yielding type of blueberry for north Florida. The plants are more vigorous, longer living, higher yielding, and later ripening than the highbush variety. However, the rabbiteyes experience some problems with fruit setting due to pollination problems, thus yields do not always reach the expected levels. If pollination problems can be solved, it is very likely that rabbiteyes will again account for a significant percentage of new plantings since they are much easier to grow, and once established, live longer and have higher potential yields. During the establishment period the plants respond very well to irrigation; however, once well established, they are relatively insensitive to drought. In addition, rabbiteye blueberries can be mechanically harvested which results in a significant decrease in production cost.

BLUEBERRY IRRIGATION

The importance of irrigating young blueberry plants has been recognized for some time. In dry years, irrigation is very important during fruit formation. Berry size can be significantly increased in a dry year if irrigation is used to maintain moist soil conditions in the plant root zone. Sufficient moisture is not only critical during fruit production but is also important for the future of the plants since adequate irrigation during bud formation is critical for next year's crop (Lyrene and Crocker, 1991). Irrigation is critical to successful production in Florida because rainfall is typically low during the time of blueberry bud formation.

Blueberries are often grown using organic mulches such as pine bark. The mulch provides protection against high temperatures, decreases evaporation from the soil, and with time, provides organic material to the soil. Organic mulches may also help reduce soil pH which is beneficial to the blueberry plant. Earlier research at the University of Florida demonstrated the importance of an organic mulch ground cover and precise irrigation scheduling on the growth of young rabbiteye and highbush blueberry plants (Haman et al., 1988).

The recommendations presented in this publication were developed based on a three year experiment on water requirements for establishment of young blueberry plants which was conducted at the University of Florida. The project was partially funded by the St. Johns River and the Southwest Florida Water Management Districts. Both native rabbiteye and newly developed early-yielding highbush varieties were studied. Two-year old, container-grown plants were transplanted to the field at the beginning of 1991. The experiment ended in December 1993. Total water use (evapotranspiration) of the plants, irrigation requirements, crop yield, and vegetative plant growth were evaluated for the three years after transplanting. Three different threshold levels of soil water tension were evaluated for scheduling irrigations. The threshold soil tension were set at 10 centibars (cb), 15 cb, and 20 cb.

In Florida, blueberries are usually grown on sandy soils with low water holding capacities and large pore spaces. Thus, water applications must be frequent and relatively small to avoid water losses from the root zone. This requires precise irrigation scheduling. Microirrigation, which was used in the experiment on establishment of blueberry plants, applies water directly to the crop root zone. The amount and placement of water can be precisely controlled with this system to minimize application losses. The microirrigation system was controlled using magnetic switching tensiometers (Smajstrla et al., 1988).

With the microirrigation system used in this study, water was not applied to the grass alleyways between plant rows. Also, organic pine bark mulch minimized evaporation losses from the soil surface. Irrigation requirements would need to be adjusted for other plant sizes, irrigation systems and/or production practices. For example, a greater volume of water would be required with a sprinkler irrigation system because water would be applied to the entire soil surface rather than being limited to the mulched area near each plant.

Figure 1 and Figure 2 present the cumulative irrigation for both varieties of blueberry during three years of the experiment. The significant increase in the slope of the lines during the last year of the experiment for all treatments (with exception of 20-cb highbush) reflects the higher water requirement of the larger plants and the lower rain contribution during that year.

Figure 1. 

Cumulative irrigation over three years of the experiment for Rabbiteye blueberries.

Figure 2. 

Cumulative irrigation over three years of the experiment for Highbush blueberries.

YOUNG BLUEBERRY WATER USE

Water use in gal/acre and inches/acre for the first three years after transplanting for both varieties of blueberries is presented in Table 1 , Table 2 , Table 3 , Table 4 , Table 5 , Table 6 . The numbers were developed for different plant densities depending on the field spacing between the plants. These quantities are relatively small because they are specific for the young, small, microirrigated blueberry plants studied in this research. The portion of the water demand which must be supplied by irrigation depends on system efficiency and rainfall effectiveness and can be calculated using the water budget method.

RESPONSE OF YOUNG BLUEBERRY PLANTS TO IRRIGATION

Growth of blueberry plants was measured monthly. The volume of each plant canopy was calculated from three measurements: the height, the width along the plant row, and the width perpendicular to the row.

Plant volumes increased each year for all treatments. Both plant size and rate of increase were greater for rabbiteye plants as compared to highbush plants. Among highbush plants only the 10-cb treatment showed significant growth, most of which occurred in the last year of the experiment. During 1993, the 10-cb plants grew almost 2 ft, while the 15-cb and 20-cb highbush plants showed very little increase in height in all three years due to water stress and poor establishment of the root system. Overall, the 10-cb treatment had the highest growth rate for both varieties. In 1993, the rate of growth for the 15-cb and 20-cb treatments was very small and significantly lower than the 10-cb treatment ( Figure 3 ).

Figure 3. 

Blueberry growth during three years of the experiment.

Rabbiteye plant heights increased mainly in the first year after transplanting (1991), especially in the 10-cb treatment. During that year, the 10-cb plants reached approximately 5 ft. The 15-cb and 20-cb treatments were slightly shorter and reached 5 ft at the end of the second year. By the end of 1993, the 10-cb rabbiteye treatment plants were approximately 6 ft tall with 15-cb slightly shorter at 5.6 ft and 20 cb at 5.3 ft.

In 1991, following common practice for young plants to stimulate vegetative growth, the flowers were removed from the plants, preventing fruit from setting. This is reflected in the 1991 plant growth pattern. Most of the plants showed an increase in volume in all months until September. In 1992 and 1993, most of the increase in plant size occurred during the three months after fruit harvest. Little change in plant size occurred during the spring months as fruit was set and grew to maturity.

Fruit production data were collected during the last two years of the research and are presented in Table 5 . The two types of rabbiteye plants yielded differently and for this reason are presented separately.

The fruit for all three cultivars matured at different times of the year, and yields varied as a function of time of harvest. In both years, yields were lowest for the early-producing Sharpblue (highbush) variety, largest for the late-producing Powderblue (rabbiteye) variety, and intermediate for the midseason rabbiteye variety, Premier. This is important since timing of harvest is critical to blueberry growers. Early-producing varieties are in great demand because early yields command much higher market prices.

Sensitivity to water stress was greatest in the highbush variety. Both vegetative growth and yield were strongly dependent on irrigation. Only the well-watered (10 cb) treatment was well established and healthy at the end of three years. The plants in this treatment were much larger and produced significantly more berries. All rabbiteye plants were well established by the end of three years and there were only small differences between the water treatments.

Figure 4 shows the annual distributions of monthly ET for the well-watered rabbiteye and highbush plants as a function of time during the first three years after transplanting. The ET pattern is consistent with the patterns of climate demand as measured by Penman ETo (reference evapotranspiration). In 1991 the peak monthly ET occurred in June. For all three years, the peak monthly ET for both varieties occurred in July. This closely follows the peak climate demand, and it is largely a result of levels of solar radiation and temperatures.

Figure 4. 

Potential evapotransporation calculated from the Penman equation as compared to actual evapotranspiration of highbush and Rabbiteye blueberries.

Evapotranspirational (ET) rates were larger for the rabbiteye plants as compared to the highbush plants. This difference was due to plant size and growth characteristics. The rabbiteye plants are more vigorous and rapidly-growing than the highbush plants.

CONCLUSIONS AND RECOMMENDATIONS

The establishment and water requirements of plants are strongly dependent on the blueberry variety. Two typical types of blueberry plants were evaluated in this experiment: rabbiteye, which is native to Florida, and highbush, which is an introduced variety. Growers are very interested in highbush plants due to their early ripening and the high prices which blueberries bring early in the year.

The rabbiteye variety is easier to establish and easier to grow successfully under Florida conditions. Plants grow rapidly after transplanting, and were relatively insensitive to imposed water stresses up to 20 cb. As compared to highbush plants, rabbiteyes have a deeper root system which allows them to uptake water from a larger volume of soil, resulting in more efficient irrigation scheduling and fewer losses to deep percolation. At the end of the third year of this project, the establishment of rabbiteye blueberries was good under all treatments. There was only small visible difference among plants.

As compared to rabbiteye, the highbush variety is much more difficult to establish and requires more precise water management. Plants exhibit high sensitivity to water stress and require frequent irrigation for good establishment. It takes longer for highbush plants to develop a root system. Most of the roots in this variety are located relatively close to the soil surface, which makes efficient irrigation scheduling more difficult. As a result, more water is lost to deep percolation.

Well-watered highbush plants (10-cb treatment) were very well established at the end of the experiment. However, two drier treatments showed much less vegetative growth and much lower yields than the well-watered plants. It can be concluded that the establishment of highbush blueberries under Florida conditions will not be successful without irrigation, and that irrigations should be scheduled at 10 cb.

REFERENCES

Haman D.Z., A.G. Smajstrla and P.M. Lyrene. 1988. Blueberry response to irrigation and ground cover. Proc. Fla. State Hort. Soc. 101:235-238.

Lyrene, P.M. and T.E. Crocker. 1986. Florida blueberry handbook. Circular 564. Univ. of Fla. Coop. Ext. Ser., Gainesville, FL. 15 pg.

Lyrene P.M. and T.E. Crocker. 1991. Commercial blueberry production in Florida. SS-FRC-002. Univ. of Fla. Coop. Ext. Ser., Gainesville, FL. 49

Smajstrla A.G., D.Z. Haman and P.M. Lyrene. 1988. Use of tensiometers for blueberry irrigation scheduling. Proc. Fla. State Hort. Soc. 101:232-235.

Tables

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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer, Interim Dean.

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