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Copyright 2005, Board of Trustees, University
EFFECTS OF SALINITY ON YOUNG GRAPEFRUIT ON FOUR ROOTSTOCKS
BRIAN J. BOMAN '
OBJECTIVES Of : ..*.
1. Document the baseline effects of four salinity levels (500 to 3800 ppm) on
2. Determine salinity effects on growth, yield, and quality of Ruby Red
grapefruit on Sour Orange, Carrizo, Cleopatra mandarin, and Swingle
3. Evaluate the interaction between salinity level and fertilizer source
4. Determine whether there are differences in tree performance between dry
fertilization and liquid applications of ammonium nitrate/potassium
chloride at four salinity levels.
Trees were planted on newly constructed beds on virgin land (Oldsmar
series) at the Ft. Pierce AREC. Water furrows were cut to the depth of the
hardpan (about 36"). 'Ray Red' grapefruit trees were planted on 50' double beds
at a 15 X 22 ft spacing and 116 trees per acre.
The irrigation treatments have water with electrical conductivities of 0.7,
2.3, 3.9, and 5.5 dS/m (roughly 500, 1600, 2700, and 3800 ppm TDS). Sea water
is mixed with shallow well water to obtain the higher salinity levels. Water is
applied with a green base (15 GPH) microirrigation system with all trees having
the same irrigation frequency and duration. One third of the plots for each
salinity level are fertigated using with liquid ammonium nitrate and potassium
chloride combination (NH4NO3 & KC1). Another third are fertigated with a
ammonium nitrate-potassium nitrate solution (NH4NO3 & KNO3). The remaining trees
S are fertilized with a dry mixture of ammonium nitrate and potassium chloride
applied 5-6 times per year. Fertigations are made on plots approximately every
2 weeks during the active growing season. All plots receive the same total rate
of N and K on an annual basis.
Tree plots consist of 2 tree rows, each with 4 trees each on Sour, Carrizo,
Cleo, and Swingle plus a pair of trees on each end used as buffers. Trees were
planted in April and July (sour orange) 1990. The experiment uses a randomized
split plot design with salinity and fertilizer as the main effects and rootstock
as the split plot (4 replications). Rootstocks are randomized within each of the
treatments (Table 1). Table 1. Irrigation salinity levels, fertilization
Other cultural materials, and application methods.
operations for all the
treatments are identical. Treatment Fertilizer Application
The treatment effects are
measured by differences in No. ppm material method
tree growth (trunk
caliper, tree height, and
canopy volume. Fruit 1 500 NH4NO3 & KC1 Fertigation
yield -and juice quality 2 1600 NH4NO3 & KC1 Fertigation
measurements will be taken 3 2700 NH4NO3 & KC1 Fertigation
to analyze effects once 4 3800 NH4NO & KC1 Fertigation
trees come into 5 500 NH4NO, & KNO Fertigation
production. Trunk 6 1600 NH NO & KN Fertigation
diameter was measured 4 7 2700 NHNO3 & KNO3 Fertigation
inches above the bud union 8 3800 NHNO3 & KN3 Fertigation
with a caliper. Trunk 9 500 3& Kl Broadcast
diameter, tree height and 9 500 NH4NO3 & KC1 Broadcast
diameter, tree height, and 3
canopy widths measured on 10 1600 NH4NO3 & KC1 Broadcast
each tree in May 1991 and 11 2700 NH4NO3 & KCl Broadcast
S April 1992. Canopy volume 12 3800 NH4NO3 & KC1 Broadcast
was calculated as: Vol =
Ft. Pierce AREC 93-3
Table 3. Mean tree height, canopy volume, and trunk cross-sectional area for 1991
and 1992 by irrigation water salinity level, fertilization treatment, and
Tree height (m) Canopy volume (m3) Trunk X/C area (cm2)
5/91 4/92 chg' 5/91 4/92 chg' 5/91 4/92 chg'
Cl 1.22a 1.59a
Ca 1.05c 1.43c
Sw 1.18b 1.57a
So 1.15b 1.44c
'Change in measured parameter calculated as: value in April 1992 divided by value
in May 1991.
2Means within the same column for the same group followed by the same letter are
not significantly different according to Duncan's Multiple Range Test (p=0.5).
3Fertilizer treatments are: A = fertigation with NH4NO3+KC1; B = fertigation with
NH4NO3+KNO3; C = dry applications of NH4NO3+KC1.
Rootstocks are: Cl = Cleopatra mandarin; Ca = Carrizo citrange, Sw = Swingle
citrumelo, and So = Sour orange.
Irrigation Salinity (ppm)
Fig. 1. April 1992
trunk cross-sectional area by salinity level and
Irrigation Salinity (ppm)
Fig. 2. April 1992 canopy valume by rootstock and salinity level.