University of Florida
Citrus Research & Education Center
Spatial Soil-Tree-Diaprepes Variability in Biological Zones at the Field Scale
Hong Li, Jim Syvertsen, Arnold Schumann, Clay McCoy and Robin Stuart
The ongoing study has been conducted in an orange grove near
Southport in Osceola County. The site is nearly flat with a slope of 02%. Soils consist of sand muck over clayey materials, very poorly
drained, subject to flooding, and classified as Floridana sand. The
soils were formed in sandy marine sediments at the edges of
Tohopekaliga Lake. ‘Hamlin’ trees on Swingle citrumelo rootstock
were severely damaged by Diaprepes, and commercially abandoned.
Spatial variability of soil properties is thought to be linked
to the distribution frequency of Diaprepes abbreviatus
(L.), a major pest of citrus and some agricultural crops in
Florida. Diaprepes adults damage leaves, and larvae
pupate in soil and damage roots (Fig. 1). We assumed
that Diaprepes frequency was related to spatial soil
variability.
• Plot of diaprepes against soil EC shows a small correlation
coefficient , r = 0.14 (Fig. 3).
• The boundary analysis shows that as related to soil EC, the
Diaprepes present a skewed distribution pattern similar to a
log-normal distribution (Fig. 3).
• Diaprepes are within a soil EC range of 20- 60 mS m-1. There
is one measurement falling outside the boundary (Fig. 3).
Fig. 3. Log-normal distribution pattern of Diaprepes
Fig. 2. Diaprepes infested tree locations and rates,
and positions of traps and soil sampling
• Soil EC measurements: using electromagnetic induction EM38
instrument measuring across the whole block (9.5 ha).
• Soil sampling: from surface to 1.2 m at an increment of 0.3 m at
each Diaprepes trap on 2 Nov. 2002 (Fig. 2).
• Soil (0-0.3 m) parameters measured:
• Water table depth, moisture, sand, clay & silt
• pH, soil organic matter content (SOM), cation exchange
capacity (CEC) & base saturation (BS)
• Major and minor cations (P, K, Mg, Ca, B, Zn, Mn, Fe & Cu)
• Statistics: Semivariogram, Proc Variogram (SAS)
• Principal component analysis (PCA), Proc Princomp (SAS).
• Determine soil-Diaprepes distribution patterns
Mean & standard deviation (SD) of variables (Table 1)
• Delineate soil-Diaprepes biological zones
• Diaprepes frequency is highly variable with location: CV 65%.
• Determine soil-Diaprepes linear correlation relations
• Soil moisture & SOM are generally high across the grove.
• Assess autocorrelation distance for soil-Diaprepes
variables using semivariogram
• Sand content is very low compared to the average sand content
for citrus soil in Florida (94%): poorly drained.
• Soil pH is low for citrus growth (optimum pH 6.0-6.5).
Approach
H0: Diaprepes frequency was related to soil EC (EM 38)
H1: Diaprepes frequency was related to other soil
parameters that determine EC
Fig. 1. Diaprepes adults damage leaves and lay eggs
on leaves (left). Diaprepes larvae feed on
roots and pupate in soil (right).
Semivariogram (autocorrelation distances)
• Three biological zones of Diaprepes were delineated
based on the spatial soil EC patterns (Fig. 4).
• In zone A, soil EC is low with few Diaprepes.
• Zone B is higher in soil EC and lower in Diaprepes.
• Zone C is lower in soil EC and higher in Diaprepes.
• Diaprepes distribution increased with distance
then stabilized at a distance of 200 m (Fig. 6a).
• In individual zones, correlations between soil EC &
Diaprepes are significant for zone B and C (Fig. 4).
Zone B
r = 0.52*
• Water table depth was significantly correlated with Fe (r = 0.28*), which was associated with tree rate (Table 3).
• In the spring 2003, soil was flooded in the NE corner of the
shallow area (Fig. 5), where is the low elevation area.
• Tree leaf stomatal conductance was significantly lower in the
flooded area than in the non-flooded area (Fig. 5). Flooding is
the critical component in citrus growth.
a
Shallow
• Water table depth, moisture, sand, silt, pH, CEC, EC, BS and H:
relatively stable, CV 9-33%.
Table 1. Descriptive statistics of Diaprepes & soil variables
Mean SD
CV
Diaprepes
Water table (m)
Moisture (%)
Sand (%)
Clay (%)
Silt (%)
pH
-1
SOM (g kg )
CEC (Cmol kg-1)
EC (mS m-1)
BS (%)
34
0.9
26
53
32
15
4.9
80
15
35
57
65
22
30
33
44
29
8.2
37
26
30
16
22
0.2
7.7
17
14
4.4
0.4
30
4.0
10
9.3
Variables Mean SD
P
K
Mg
Ca
B
Zn
Mn
Fe
Cu
H (%)
mg kg-1
22
12
114
42
260
94
1263 512
0.3
0.2
3.1
2.4
5.5
2.1
36
14
0.1
0.07
21
4.6
CV
55
37
36
41
67
77
38
39
70
22
Fig. 4. Diaprepes - soil EC biological zoning
94
Deep
gs
Flooded
Medium
Principal component analysis (PCA)
• PCA contains 10 variables including soil moisture,
SOM, CEC, EC, K, Mg, Ca, B, Zn, H & Diaprepes.
Water table depth
Shallow
(m)
Deep
Correlation relations of soil-tree-Diaprepes
• Diaprepes was negatively correlated with CEC, Mg & Ca (Table
3), which shows that Diaprepes frequency is high in lower Mg
and Ca concentration areas. Limestone was applied at a rate of
7.4 t ha-1 across the grove in the spring 2002.
• Tree rate was negatively correlated with soil Fe (Table 3), which
was correlated with water table depth (shown above).
• SOM is highly correlated with sand, soil moisture, pH, CEC, EC,
K, Mg, Ca, B, Mn, Fe, & H (- 0.40 < r < 0.90) (Table 3).
12500
10000
Soil Mg
Diaprepes
900
7500
600
300
5000
0
1500
1200
(a)
Range
Range
SOM
(b)
2500
0
200
EC
160
900
120
600
300
80
40
(d)
Range
Range
0
0
0 50 100 150 200 250 0 50 100 150 200 250
Measurement distance (m)
(c)
Fig. 6. Semivariograms and spatial correlation
ranges of Diaprepes (a), soil Mg (b), soil organic
matter, SOM (c) & electrical conductivity, EC (d)
• The PC1 accounts for 50% of the total variance in
the data, 17% for PC2, and 13% for PC3. Together,
the PC1, PC2 & PC3 account for 80.4% of the total
variance in the data to explain soil-tree-Diaprepes
relations (Table 2).
Table 2. PCA correlation matrix
Eigenvalue Difference Proportion Cumulative
(variance)
(%)
(%)
PC1
6.04
3.98
50.3
50.3
PC2
PC3
2.06
1.55
0.50
0.76
17.1
13.0
67.4
80.4
Table 3. Linear correlations of Diaprepes, tree rate & soil physico-chemical properties
Diap†
Non-flooded
• Semivariance of SOM and EC ranged within 50-100
m (Fig. 6ad), and pH, CEC, sand, K & Ca ranged
within 50-100 m (semivariograms not shown).
• The first principal component PC1 has the highest
eigenvalue, which is the variance. Difference in
variance is 3.98 for PC1-PC2, and 0.50 PC2-PC3,
and 0.76 PC3-PC4 (Table 2).
152 gs
Fig. 5. Soil water table & flooding vs. leaf water stress
• Mg, Ca & Fe were high and variable: liming practices.
Variables
b
Leaf stomatal conductance (gs)
• P, Zn, Mn, Cu & BS were poor across the grove.
Zone C
r = 0.56*
Soil water table depth, soil flooding & leaf water stress
• Like soil EC, water table depth can be delineated into north,
center and south zones as shallow, deep and medium zones
(Fig. 5).
• Soil magnesium had a low and a similar variance
within a distance of 100 m (Fig. 6b).
1500
1200
Zone A
120 r = 0.14 ns
100 n = 50
80
60
40
20
0
0 10 20 30 40 50 60 70
EC (mS/m, EM 38)
Objectives
• Analyze soil-tree-Diaprepes relations using principal
component analysis (PCA)
Soil EC-Diaprepes biological zoning
Diaprepes
• Infested tree classification: A total of 2244 trees were rated. There
were 4 rates ( 1 to 4) as very bad, bad, medium and good trees.
Rate 1 & 2 account for 63% of the infested trees.
• Diaprepes adult population measurement: using Tedder’s traps
(n = 50) in a 35 x 25 m grid in a 5-ha area (Fig. 2).
Boundary Analysis of Diaprepes frequency: Skewed
log-normal distribution
Semivariogram (mS/m)2 Semivariogram (mg/kg)2
A study of soil-tree-Diaprepes root weevil relations was
conducted in a 9.5-ha citrus grove near Southport in
Osceola County in Florida beginning in 2002. The
objectives of the study were to assess spatial variability
of soil, ‘hamlin’ tree (Swingle citrumelo rootstock) and
Diaprepes root weevil, to delineate Diaprepes biological
zones, and to determine soil-tree-Diaprepes relationships
using principal component analysis (PCA). Soil electrical
conductivity (EC) was measured using electro-magnetic
induction EM38, and Diaprepes adult population (using
Tedder’s traps), soil pH, organic matter content, P, K, Ca,
Mg, B, Zn, Fe, Cu, and other properties were measured in
a 35 x 25 m grid across the grove. Boundary analysis
showed that Diaprepes had a log-normal distribution
pattern as related to soil EC. Three biological zones of
Diaprepes were delineated based on the spatial patterns
of soil EC, and correlations between soil EC and
Diaprepes were significant within zones. Diaprepes
frequency was high in low Mg and Ca concentration
areas, as shown by their negative correlation coefficients.
Diaprepes tended to increase with distance then stabilize
within a semivariogram range of 200 m. Soil Mg had a low
and similar variance within a distance of 100 m. The PCA
quantified that the first, second and third principal
components (PC1, PC2 and PC3) together accounted for
80.4% of the total variance in the data. The results
suggest that Diaprepes variability is weighted on the
importance of Mg and Ca concentrations that explain soiltree-Diaprepes variability.
Introduction
Results and Discussion
Semivariogram
Materials and Methods
Semivariogram (g/kg)2
Abstract
Tree Rate
SWC† Sand
Clay
pH
SOM† CEC† EC†
P
K
Mg
Ca
B
Zn
Mn
Fe
Cu
H
1
-0.11
1
Pearson correlation coefficients
Diap
Tree Rate
SWC
Sand
Clay
pH
SOM
CEC
EC
P
K
Mg
Ca
B
Zn
Mn
Fe
Cu
H
1
-0.14
-0.21
0.14
-0.11
-0.19
-0.12
-0.25*
-0.14
0.04
-0.06
-0.31*
-0.26*
-0.13
0.04
0.15
0.14
0.08
0.26*
1
- 0.15
1
0.17
- 0.32*
1
- 0.16 0.31* -0.97** 1
0.16
-0.40** 0.21
-0.27*
- 0.06 0.90** -0.23 0.25*
- 0.03 0.79** -0.09 0.06
0.013 0.47** -0.15 0.13
0.18
-0.02 0.17
-0.19
0.20
0.37** 0.11
-0.10
- 0.04 0.53** -0.12 0.07
0.04
0.55** 0.04
-0.09
0.12
0.27* 0.23
-0.25*
0.2
0.06 0.28* -0.27*
0.02
0.17
0.12
-0.06
-0.42** -0.16 -0.05 0.08
0.03
0.06
-0.11 0.12
0.12
-0.02 -0.04 0.12
1
-0.46** 1
-0.08 0.80**
0.075 0.48**
0.22
0.03
0.17
0.41**
0.14
0.46**
0.31* 0.55**
0.33** 0.34**
0.29* 0.2
-0.51** 0.26*
-0.18 -0.29*
0.07
0.06
-0.78** 0.05
1
0.59**
1
0.16
0.49**
1
0.47** 0.47** 0.45**
0.79** 0.48** -0.04
0.90** 0.61** 0.24
0.60** 0.48** 0.47**
0.34** 0.39** 0.52**
0.06
0.21
0.47**
-0.29* -0.38** -0.33*
0.11
0.02
0.41**
-0.38** -0.31* -0.15
1
0.37**
1
0.51** 0.77**
1
0.57** 0.33* 0.78**
1
0.54** 0.04
0.54** 0.90**
1
0.22 ns -0.13 -0.16 0.01
0.11
1
-0.59** -0.28* -0.32* -0.25* -0.25* -0.07
1
0.25* 0.04
0.07
0.19
0.19
0.26* -0.12
-0.31* -0.62** -0.68** -0.48** -0.28* 0.50** 0.24
† Diap: Diaprepes; SWC, soil gravimetric water content; SOM, soil organic matter; CEC, Cation exchange capacity; EC, electrical conductivity
Conclusions
Diaprepes frequency was significantly correlated to soil Mg, Ca and CEC, indicating previous soil liming practices may have determined Diaprepes frequency. Diaprepes
frequency pattern and soil EC present a log-normal distribution. Soil-Diaprepes correlations can be better described using biological zoning. The first principal component
PC1 accounts for 50%, and PC1, PC2 & PC3 account for 80.4% of the total variance that explain spatial soil-tree-Diaprepes variability.
Acknowledgement
We thank Florida Citrus Production Research Advisory Council for funding, and Ian Jackson, Angel Hoyte, and Jill Dunlop for assistance in this study.