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Colored shading nets increase yields and profitability of highbush blueberries

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The highbush blueberry (Vaccinium corymbosum L.) develops naturally under storey of deciduous forests. In Chile, there is a need to produce fruit earlier in the season, which has forced growers to plant under greater environmental stresses (temperature, radiation, and relative humidity). In this context, colored shading nets can alleviate stresses and affect yield and fruit quality. This research was set up to study the effects of shading nets (color, shading degrees) on environmental conditions faced by plants, as well as vegetative growth, yield and quality of fruit produced, as well as economical performance in highbush blueberries. The experiment started in 2003 in an orchard cv. Berkeley planted in Miraflores, Chile (Lat. 36°04'S; Long. 72°47'E) in 1994 at 3 x 1 m. Black, white, gray and red nets and 35 and 50% shading plus a control treatment (no net) were tested. Nets were set each season at 3.5 m height at fruit set and remained until early leaf fall. With respect to control, white 35 and 50, gray 35 and 50 and red 35%, decreased PAR radiation in 29%; while red 50, black 35 and black 50 decreased PAR in 41, 47 and 53% respectively. Colored nets did not consistently affect air temperature, soil moisture and relative humidity. Yields (wt/plant) over control were increased in year 1 and 2 by 90.5 and 44.6% respectively for white 50%, 59.6 and 24.9% (gray 35%) and 84.2 and 31.9% (red 50%). Black net, commonly used by growers, had long term negative effects on yield; thus for black 35%, yields were 37.2 and -8.3, while for black 50%, yields were -3.2 and -28% of control, respectively. Higher yields were due to greater fruit number, since nets did not affect fruit size or soluble solids. In season 1, black nets increased shoot and internode length, and leaf size, while shoot number and leaf length/width ratio were unchanged.
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193
Colored Shading Nets Increase Yields and Profitability of Highbush
Blueberries
J.B. Retamales, J.M. Montecino, G.A. Lobos and L.A. Rojas
Department of Horticulture
Universidad de Talca
Talca
Chile
Keywords: light manipulation, Vaccinium corymbosum L., photoinhibition, fruit set
Abstract
The highbush blueberry (Vaccinium corymbosum L.) develops naturally under
storey of deciduous forests. In Chile, there is a need to produce fruit earlier in the
season, which has forced growers to plant under greater environmental stresses
(temperature, radiation, and relative humidity). In this context, colored shading nets
can alleviate stresses and affect yield and fruit quality. This research was set up to
study the effects of shading nets (color, shading degrees) on environmental conditions
faced by plants, as well as vegetative growth, yield and quality of fruit produced, as
well as economical performance in highbush blueberries. The experiment started
in 2003 in an orchard cv. Berkeley planted in Miraflores, Chile (Lat. 36°04’S; Long.
72°47’E) in 1994 at 3 × 1 m. Black, white, gray and red nets and 35 and 50% shading
plus a control treatment (no net) were tested. Nets were set each season at 3.5 m
height at fruit set and remained until early leaf fall. With respect to control, white 35
and 50, gray 35 and 50 and red 35%, decreased PAR radiation in 29%; while red 50,
black 35 and black 50 decreased PAR in 41, 47 and 53% respectively. Colored nets did
not consistently affect air temperature, soil moisture and relative humidity. Yields
(wt/plant) over control were increased in year 1 and 2 by 90.5 and 44.6% respectively
for white 50%, 59.6 and 24.9% (gray 35%) and 84.2 and 31.9% (red 50%). Black net,
commonly used by growers, had long term negative effects on yield; thus for black
35%, yields were 37.2 and -8.3, while for black 50%, yields were -3.2 and -28% of
control, respectively. Higher yields were due to greater fruit number, since nets did not
affect fruit size or soluble solids. In season 1, black nets increased shoot and internode
length, and leaf size, while shoot number and leaf length/width ratio were unchanged.
INTRODUCTION
Blueberries are under storey fruit crops native from southern (Vaccinium ashei) or
northern (V. corymbosum) areas of United States (Eck, 1988). Worldwide area planted
with blueberries has increased greatly in the last decade, since benefits for health derived
from their consumption have been demonstrated (Kalt et al., 2001). In Chile, plantings are
increasing at a rate of 500-800 ha/year. Due to high fruit prices at the beginning of the
export season in the southern hemisphere, a large proportion of the expansion in Chile has
occurred in areas with high temperature and light intensity, which could reduce
photosynthesis, carbohydrate accumulation, and fruit yields (Darnell, 1991).
Colored shading nets have been investigated in ornamentals and fruit crops (Oren-
Shamir et al., 2001; Shahak et al., 2004) in these crops, depending upon the degree of
shading and the color used, they have altered the amount and quality of light received by
plants, which has triggered changes in branching, shoot extension, fruit set and fruit
quality. In this context, the use of shading nets could alleviate the environmental stress
faced by blueberry plants and have effects on their growth, fruit yield, and economical
performance (Oren-Shamir et al., 2001).
MATERIALS AND METHODS
The trial was initiated in October 2003 in a commercial orchard of highbush cv.
Berkeley planted in 1994 at 3 × 1 m. The orchard is located in Miraflores (Lat. 36°04’S;
Proc. XXVII IHC - Cultiv. Utiliz. Asian, Sub-Trop., Underutilized Hort. Crops
Eds.-in-Chief: Dae-Geun Oh and Chieri Kubota
Acta Hort. 770, ISHS 2008
194
Long. 72°47’E). A completely randomized design with 3 replications of 12 plants per
treatment was used. The area destined to each treatment was 108 m2, which comprised a
plot of three rows with two plants each. To allow complete effect of nets, only six central
plants were selected for measurements and six equivalent plants were used as control (no
nets). The combination of 4 colors of net (white, black, gray and red) and 2 intensities of
shading (35 and 50%), plus control treatment (no net), generated 9 treatments. In each of
the two seasons, nets (Polytex, Iquique, Chile), were placed on a wire frame at 3.5 m
height at fruit set (October 8-10) and removed at the onset of leaf fall (March 30).
Temperature, relative humidity (HOBO, H8 sensors, Onset Co., Bourne, MA), and
PAR radiation (LI-190SA sensor, Licor Biosciences, Lincoln, USA) were recorded every
15 min. Soil moisture was measured weekly with tensiometers (Model R, Irrometer Co.,
Riverside, USA) set at 30 cm depth. Vegetative growth measurements (leaf length and
width, shoot number and length, and internode length), were done on 6 central plants in
each experimental unit on April 3, 2004. To determine yield per plant and fruit production
curves, fruit were hand-picked twice per week between 12/13 and 01/24 each season.
Fruit weight was established on a sample of 100 fruit collected in each replication and
each harvest.
Data were analyzed through ANOVA; mean separation was done using Duncan’s
multiple range test.
RESULTS AND DISCUSSION
Black nets reduced PAR radiation to 50% of their levels in open field; there was
no correlation between the level of shading and the PAR levels under the shade (Fig. 1).
Treatments generated minor differences in temperature, relative humidity and soil
moisture (data not shown).
Black nets generated longer shoots and larger leaves (length and width) but had no
significant effects on shoot number as compared to control plants (Table 1); similar
effects of shading were observed by Baraldi et al. (1994), in peaches. The treatments
white 50%, gray 35% and red 50%, had yields that were 26-91% greater than control
plants; on the other hand, yields under black 50% ( a shade commonly used by growers in
Chile), were similar to the control in the first season and significantly inferior in the
second year (Table 2). Treatments had no significant effect on fruit soluble solids or
weight (Table 3). Since the treatments were established after bloom each year, once
flower induction had already occurred (Eck, 1988), the differences in yield must have
been caused by the influence of shading on fruit set. In these regards, Shahak et al. (2004)
have reported increased fruit set after shading 6 weeks before harvest apples cv. Smothee
and cv. Top Red and peaches cv. Hermosa. In climates with high incidence of radiation
(such as Central Chile), this positive effect of shading on fruit set and yield could be due
to the reduction of stressful conditions in midday hours which would avoid supraoptimal
light levels, plant heating and photosynthesis inhibition (Dale, 1992; Ort, 2001); greater
partitioning of carbohydrates towards shoot in black nets (Table 1) would explain their
failure to produce higher yields. In the days following fruit set in blueberries, shoots,
roots and leaves are competing for carbohydrates, water and nitrogen (Darnell and
Birkhold, 1996); in these circumstances, developing fruit under shade treatments would
have more water availability and a greater supply of carbohydrates from young
developing leaves (Raveh et al., 2003), this situation would allow more availability of
these compounds to the fruit and would increase fruit set. The greater fruit set would
influence photosynthetic rate through a feed back mechanism, as has been demonstrated
in several species (Flore and Lakso, 1986; Birrenkott and Stang, 1990; Matthew and
Pellny, 2003). Is it also possible that some of the effects of the nets are due to changes in
the light quality of the transmitted light, since it has been demonstrated that colored
shading nets alter the quantity and quality of light that reaches the plants (Oren-Shamir et
al., 2001; Shahak et al., 2004). Plants can detect the quality, quantity and orientation of
light and use it as a signal to optimize their growth and development in a given
environment (Rajapakse et al., 1999).
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To calculate the profitability of the installation of nets, a cost of US$ 1,033 per
year was assumed for purchasing and installing the nets (US$ 3,100 for 3 years). On the
other hand, the treatments that in both seasons yielded significantly higher than the
control (white 50%, gray 35% and red 50%) had a two season average of 26,315 kg
(3,333 plants per hectare), as compared to 17,498 of control plants; the increase in yield
would amount to 8,817 kg. At a net value for the grower of US$ 2.0 per kg, this would
mean a yearly increase in income of US$ 17,634. After discounting the US$ 1,033 in
yearly expenses, if these increases in yield are realized in commercial fields, the
installation of nets in a mature blueberry orchard would mean a net profit to the grower of
US$ 16,601.
CONCLUSIONS
Shading with colored nets produced significant changes in reproductive behavior
and some vegetative parameters of mature highbush blueberries. Certain treatments
(white 50%, gray 35% and red 50%), consistently increased yields; this positive effect on
yield was due to larger fruit set, since flower induction and fruit weight were not altered
by the treatments.
If the yields effects obtained in these trials are sustained in commercial plantings,
the already high profitability of blueberries in southern latitudes would increase even
more. The effects of the use of colored shading nets on fruit quality and postharvest life
are been studied. If no deleterious effects for the use of nets on these aspects are found,
this technology would be highly beneficial for blueberry growers, especially those
producing the crop under high solar radiation environments.
Literature Cited
Baraldi, R., Rossi, F., Faccini, O., Fasolo, F., Rotondi, A., Magli, M. and Nerozzi, F. 1994.
Light environment, growth and morphogenesis in a peach canopy. Phys. Plant.
91:329-335.
Birrenkott, B.A. and Stang, E.J. 1990. Selective flower removal increases cranberry fruit
set. HortScience 25:1226-1228.
Dale, J.E. 1992. How do leaves grow: advances in cell and molecular biology are
unraveling some of the mysteries of leaf development. BioScience 42:423-432.
Darnell, R.L. 1991. Photoperiod, carbohydrate partitioning, and reproductive
development in rabbiteye blueberry. J. Amer. Soc. Hort. Sci. 116:856-860
Darnell, R.L. and Birkhold, K.B. 1996. Carbohydrate contribution to fruit development in
two phenologically distinct rabbiteye blueberry cultivars. J. Amer. Soc. Hort. Sci.
121:1132-1136.
Eck, P. 1988. Blueberry Science. Rutgers Univ. Press, N. Brunswick, USA p.378.
Flore, J.A. and Lakso, A.N. 1986. Environmental and physiological regulation of
photosynthesis in fruit crops. Hort. Rev. 11:111-157.
Kalt, W.A., Howell, A., Duy, J.C., Forney, C.F. and McDonald, J.E. 2001. Horticultural
factors affecting antioxidant capacity of blueberries and other small fruit.
HortTechnology 11:523-528.
Matthew, J.P. and Pellny, T.K. 2003. Carbon metabolite feedback regulation of leaf
photosynthesis and development. J. Exp. Bot. 54:539-547.
Oren-Shamir, M., Gussakovsky, E.E., Spiegel, E., Nissim-Levi, A., Ratner, K., Ovadía,
R., Giller, Y.E. and Shahak, Y. 2001. Coloured shade nets can improve the yield and
quality of green decorative branches of Pittosporum variegatum. J. Hort. Sci. Biotech.
76:353-361.
Ort, D.R. 2001. When there is too much light? Plant Phys. 125:29-32.
Rajapakse, N.C., Young, R.E., MacMahon, M.J. and Oi, R. 1999. Plant height control by
photoselective filters: current status and future prospects. HortTechnology 9:618-624.
Raveh, E., Cohen, S., Raz, T., Fakir, D., Grava, A. and Goldschmidt, E.E. 2003. Increased
growth of young citrus under reduced radiation load in a semi-arid climate. J. Exp.
Bot. 54:365-373.
196
Shahak, Y., Gussakovsky, E.E., Cohen, Y., Laurie, S., Stern, R., Kfir, S., Naor, A.,
Atzmon, I., Doron, I. and Greenblat-Avron, Y. 2004. ColorNets: a new approach for
light manipulation in fruit trees. Acta Hort. 634:609-616.
Tabl e s
Table 1. Influence of net shading (color and % shade) on vegetative blueberry growth of
blueberry plants cv. Berkeley in 2003-2004 seasonZ.
Treatment
(color, % shade)
Shoot
no.
Shoot
length
(cm)
Internode
length
(cm)
Leaf
length
(cm)
Leaf
width
(cm)
Leaf
length/width
ratio
Control 5.3 39.3 a 2.3 ab 7.9 a 4.5 a 1.75
White 35% 5.1 47.1 ab 2.5 bc 8.5 ab 4.7 ab 1.79
White 50% 5.0 47.5 ab 2.3 ab 8.4 ab 5.0 bc 1.67
Gray 35% 7.3 53.0 abc 2.5 abc 8.4 ab 5.0 bc 1.67
Gray 50% 2.0 54.9 abc 2.5 abc 9.0 bc 5.2 bc 1.73
Red 35% 3.2 39.7 a 2.2 a 8.6 abc 4.9 abc 1.75
Red 50% 4.6 44.8 a 2.6 bcd 8.5 ab 5.1 bc 1.64
Black 35% 3.7 62.6 bc 2.7 cd 9.4 cd 5.4 cd 1.74
Black 50% 4.6 65.7 c 2.9 d 10.0 d 5.8 d 1.72
ZValues within each column followed by the same letter are not significantly different at P=0.01, Duncan’s
multiple Range Test.
Table 2. Influence of shading (color and % shade) on yields (kg fruit/plant) of blueberries
cv. Berkeley in the 2003-2004 and 2004-2005 seasonsZ.
Treatment Harvest season
(color, % shade) 2003-2004 2004-2005
Control 3.79 c 6.71 cd
White 35% 4.20 bc 8.05 bc
White 50% 7.23 a 9.76 a
Gray 35% 6.06 ab 8.43 ab
Gray 50% 5.45 abc 8.36 abc
Red 35% 4.99 abc 7.44 bcd
Red 50% 6.98 a 8.91 ab
Black 35% 5.21 abc 6.19 de
Black 50% 3.67 c 4.86 e
ZValues within each column followed by the same letter are not significantly different at P=0.05, Duncan’s
multiple Range Test.
197
Table 3. Effect of shading (color and % shade) on soluble solids and fruit weight for
blueberries cv. Berkeley in the 2004-2005 seasonZ.
Treatment
(color, % shade)
Soluble solids
(% Brix)
Fruit weight
(g)
Control 13.5 1.72
Red 35% 12.8 1.95
Red 50% 12.7 1.92
Gray 35% 13.4 1.96
Gray 50% 13.3 2.12
Black 35% 13.4 1.87
Black 50% 13.1 1.87
White 35% 13.1 2.07
White 50% 12.9 1.99
Significance ns ns
ZValues within each column followed by the same letter are not significantly different at P=0.05, Duncan’s
multiple Range Test.
ns = non significant differences.
Figurese
-
200
400
600
800
1,000
1,200
1,400
1,600
1,800
Control
White 35%
White 50%
Grey 35%
Grey 50%
Red 35%
Red 50%
Black 35%
Black 50%
Treatment
PAR radiation (umol/m
2/s)
Feb-15-04
Mar-15-04
Fig. 1. Influence of shading (color and % shade) on PAR radiation (µmol/m2/s) available
for blueberry plants cv. Berkeley.
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... Често се използват засенчващи мрежи над културите за намаляване на топлинния стрес (Shahak et al., 2004;Elad et al., 2007;Retamales et al., 2008). ...
... Shading nets over crops are often used to reduce heat stress (Shahak et al., 2004;Elad et al., 2007;Retamales et al., 2008). ...
... The observed values of the temperature factor show higher values during the colder months of the year (at the beginning of the growing season) and lower values during the hottest months of the year. The opinion of many authors that shading nets over crops reduce heat stress was undoubtedly confirmed (Shahak et al., 2004;Elad et al., 2007;Retamales et al., 2008) Of course, in order to fully assess the effect of shading and entomological network on cultivated plants, it is necessary to analyze the other abiotic factors and their interaction. ...
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Growing fruit species through sustainable environmental practices was considered as promising alternative to meet the challenge of various biotic and abiotic stresses threatening the production of fruit and planting material in climate change. Nowadays, various types of nets (shading, entomological, etc.) were used worldwide to protect plant species against environmental conditions, including hail, wind, excess sun light and pests, while improving plant health and quality of the fruits. During the period 2019-2020, in Fruit Growing Institute, Plovdiv a research was conducted to trace the changes, variations and trends of the main climatic factor -- temperature in the production of fruit planting material grown in conditions of shaded field, insects-proof net house and open field (area). In observation of changes in temperature (t,C) its average monthly value was considered. The change of the average annual temperatures in the observed fields showed higher values during the winter and spring months in the insects-proof net house, compared to the reported outdoor temperatures. In a shaded field, lower temperatures were observed in warm spring and hot summer. Throughout the period, there was a continuing trend of increasing temperature. A higher value of the average monthly temperature by 0.9 С -- 1.5 С was observed in the insects-proof net house. The obtained results would be the basis for the development of risk analysis programs for the production of standard and certified fruit planting material in containers.
... Contrary to this, in a different study, the black net showed the smallest PAR reduction [29]. In a few studies where nets with the same shading factor were comparable, similar differences could be found [13,30,31]. Although, as mentioned above, some authors reported that, among tested nets, the black net reduced PAR intensity the most, this was not the case in studies conducted by [6,15]. ...
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