1. Citrus Research and Development Foundation, Inc.
CPDC– Nutrient / HLB Summary
Jim Syvertsen , CRDF Horticulture Project Manager
700 Experiment Station Road • Lake Alfred • FL • citrusrdf.org

2. CRDF Nutrition / HLB Summary
Gruber, Barrit Boman, Brian Wright, Alan UF
Nutrition for IR GF for HLB, fruit drop, postharvest fruit storage
7/1/2014
9/1/2016
$360,000
1: Newly planted red GF trees-- Foliar EN & HLB 2: Mature trees-- EN Supplemental fertilizer, HLB, fruit drop ACP & postharvest storage
England, Gary Total
Mid Florida Citrus Foundation grove
10/1/2012
9/30/2015
237,500
1: …nutritional practices to maintain the productivity of groves.
Graham, Jim Total
Phytophthora, Calcium carbonate reductions root health
7/1/2012
3/31/2016
942,409
3: HLB roots, Phytophthora, phosphite, high carbonate well water + acidification, rootstocks and root health
Grosser, Jude Total
Rootstocks, HLB, Nutrition
4/1/2012
9/30/2018
684,326
3: Rootstocks & constant optimal nutrition, TigerSul manganese and slow release sodium borate overdoses (combinations, delivery, economics)
Morgan, Kelly Total
Calcium bicarbonate, acid + S and HLB
5/1/2014
4/30/2017
349,491
1: HLB, calcium bicarbonate, soil pH & nutrient uptake, water use, root density
Rouse, Bob Total
Optimizing ground & foliar nutrients; vector control
4/1/2010
6/30/2014
925,659
2: HLB nutritional sprays, SARs, and aggressive psyllid control program
Schumann, Arnold
Nutrition, tree performance, roots
5/1/2010
6/30/2018
1,609,205
7: HLB, ACPS, nutrition, B, tree productivity, mitigation with EN, root efficiency
Stansly, Phil Total
HLB, Nutritional and Insecticidal
7/1/2010
2/14/2016
948,465
4: Vector control, ACP management , foliar nutrients, mulch, cost/benefit
Total
$ 6,057,055

3. Boman’s foliar ENP Well fertilized 6 yr-old ‘Ruby Red’ / SO at 160 # N etc. (all sufficient)
4 trees/ trt x 5 reps
Units per tree
Percentage change compared to control
Treatment
Fruit size
 Yield
Yield 
Foliar ENP
Small         
Med.   
Large
Box/Tr
Med.  
Control 90
109 41
3.3
KP+M
113
168 63
4.8 26 53 55 47 Ca 93
115 38 3 5 -7 1
KN+KP+M
103
144 36
3.8 14 32
-12 16
KN+KP+M+Ca
133 48
3.9 22 17 20
DKP+KP+M
102
155 60
4.3 13 42
KN+KP
105
150 45
4.1 37 11
DKP+KP
125
3.7
KN+M
119 31 21 24
DKP+M 82
127 56 -9
p -value
0.704
0.405
0.217
0.305 NS
No significant effect of ENP on Canopy Volume, LAI, Yield or fruit size
Importance of P phosphite (KP) and Dipot. phosphate (DKP)
Economic analyses KP
Potassium phosphite M
Micronutrients KN
Potassium nitrate Ca
Calcium nitrate (soil)
DKP
Dipotassium phosphate

4. Boman
Average concentrations of macro and microelements in leaves of grapefruit trees for the seasons Sampling Date
N P K Ca Mg Fe Cu Mn Zn B
% % % % % mg/kg mg/kg mg/kg mg/kg mg/kg
Jul

5. 6 yr-old ‘Ruby Red’ red grapefruit (Citrus paradisi) on Sour Orange (Citrus x aurantium) rootstock. Well fertilized.
“…despite these positives results for most variables evaluated, significant differences were not observed due to high variability in the field”
Dipotassium poly phosphate (DKP) + low biuret urea (4N-20P-22K) applied at 19L/ha. The research results suggest that treatments KP + Micros, DKP (dipotassium mono and diphosphate)+KP+M and KN+KP showed increases in number of fruit per tree as well as increases in the production of medium and large size fruit. The calcium nitrate applied to the soil had low impact on yield. According to the results, the most relevant components appear to be potassium phosphite (which is present in the treatments with the best results) accompanied by applications of micronutrients and a source of nitrogen (especially DKP).

6. Nutrient Study Results on HLB Affected Trees – Update – Kelly T
Nutrient Study Results on HLB Affected Trees – Update – Kelly T. Morgan – March 24, 2017
Irrigation studies –
Evapotranspiration (ET) models are as effective as soil moisture sensors
Higher average water content in blocks irrigated daily, with significantly lower fruit drop.
However, no significant increase in yield was found.
Two-year greenhouse study (2013 to 2015) using individual lysimeters
water use in trees are proportional to ET rates,
Hamlin and Valencia trees use similar amounts of water,
HLB affected trees use 25% less water than healthy trees resulting
reduced water uptake by HLB affected trees were proportional to reduction in tree leaf area.

7. Morgan
Nutrient uptake studies – Field studies on foliar applications and lowering soil pH positive response in HLB affected trees.
Five-year study of foliar micronutrient applications (2010 to 2015) on HLB affected trees was conducted in a commercial grove using three rates on Mn, Zn and B with and without KNO3. This study included a zero nutrient spray application treatment.
Similar relationships were found among K, Mn and Zn applications. Leaf Mn and Zn concentrations were below optimum for the control throughout the five years. Treatments of Mn, Zn and B were based on 1.5, 3.0 and 6.0 times IFAS recommendation application rates (prior to HLB). Leaf Mn, Zn and B concentrations increased significantly after application. 3.0 and 6.0 times IFAS recommendations increased tree canopy size and yield but only the 3.0 times IFAS recommendation was significantly greater than the 1.5 and 6.0 time IFAS rate. These results indicate foliar applications of nutrients greater than 3.0 times IFAS promotes increase in canopy volume at the expense of increased fruit yield No increase in canopy volume or yield Increased with leaf B.
A two-year greenhouse study from 2015 to Calcium bicarbonate significantly reduced root densities, leaf area and water uptake (10-15%) of healthy trees but not as much as HLB affected trees (>20%).
A three-year study (2014 to 2017) on irrigation water acidification (pH, 7.5, 6.0, 5.0 and 4.0) + sulfur (Tiger 90). Average mature leaf Ca, Mg , Zn, Fe, Mn, and B concentrations increased in the spring 2016 samples. These results may indicate increased nutrient uptake from soils below pH 6.5
Leaf samples collected at both sites in June to September indicated no significant differences among treatments.
Root density samples taken in February to June indicate a significantly greater root length density from soil pH 7 to 5. Leaf Ca, Mg, Mn, and Zn in November samples were greater for trees treated with sulfur.

8. “Soil pH affects the availability of plant nutrients including
“Soil pH affects the availability of plant nutrients including
phosphorus (P), calcium (Ca), magnesium (Mg),
and the micronutrients. Most Florida soils are acidic in
their native state, so they require lime applications before
planting and every few years thereafter depending
on fertilizer and irrigation water sources. The optimum
soil pH range for citrus is 6.0 to 6.5.”

9. Schumann in progress
Our main goal is to find the reasons for inconsistent responses of HLB-affected citrus to EN programs and to develop feasible and economical remedies that can consistently replicate successful HLB mitigation with ENs in all Florida groves.
Establish nutrient sufficiency guidelines from a very large database of leaf nutrients, tree attributes, soil properties, qPCR, and leaf starch concentrations, across 11 sampling sites in Polk Co.
For example, “little leaf” syndrome on HLB-affected trees related to leaf Mg and Ca (**).
Derive the best causal relationships between leaf nutrients and other site factors such as soil, and tree performance despite HLB.
2) The 2nd objective: Determine soil conditions that favor root hair and VAM proliferation of citrus roots, thus maximizing root-uptake of calcium and other deficient nutrients in HLB- affected citrus trees. Liquid aeroponic conditions.

10. SL253.04: Soil and Leaf Tissue Testing for Commercial Citrus Production
Figure 2. Changes in concentration of N, P, K, Ca, and Mg in citrus leaves with age. The shaded areas denote the recommended sampling period and the optimum concentration range for each element.
                                                                                   

11. Table 2. 
Guidelines for interpreting orange tree leaf analysis based on four- to six-month-old spring flush leaves
from nonfruiting twigs (Koo et al. 1984).
Element
Unit of measure
Deficient
Low
Optimum
High
Excess N %
< 2.2
2.2 – 2.4
2.5 – 2.7
2.8 – 3.0
> 3.0 P
< 0.09
.09 – 0.11
0.12 – 0.16
.17 – 0.30
> 0.30 K
< 0.7
0.7 – 1.1
1.2 – 1.7
1.8 – 2.4
> 2.4 Ca
< 1.5
1.5 – 2.9
3.0 – 4.9
5.0 – 7.0
> 7.0 Mg
< 0.20
.20 – 0.29
0.30 – 0.49
.50 – 0.70
> 0.70 Cl
---
.20 – 0.70 Na
.15 – 0.25
> 0.25 Mn
mg/kg or ppm2
< 18
18 – 24
25 – 100
101 – 300
> 300 Zn
mg/kg or ppm Cu
< 3
3 – 4
5 – 16
17 – 20
> 20 Fe
< 35
35 – 59
60 – 120
121 – 200
> 200 B
< 20
20 – 35
36 – 100
101 – 200 Mo
< 0.06
.06 – 0.09
0.10 – 2.0
2.0 – 5.0
> 5.0