Variable rate fertilization and spraying to cope with high prices

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Variable rate fertilization and spraying to cope
with high prices

• A.W Schumann, H.K. Hostler
• Citrus Research and Education Center
• University of Florida

2008 Citrus Expo, T.S. Fay Edition September 4,
2008 Lake Alfred, FL
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The current situation
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The current situation
Rapid tree removal from groves infected with HLB
is causing more open spaces and resets than ever
before
HLB trees removed! -should not be fertilized or
sprayed
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Variable rate technology (VRT)
VRT success depends on canopy variability Now
would be an excellent time to exploit VRT
Only the healthy canopy should be fertilized -
avoid fertilizing bare soil or weeds
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Opportunities for lowering fertilization costs
CONCEPTS Keep trees slightly hungry (improved
fertilizer efficiency) Use more efficient
sources Cut excesses Precision placement VRT
HIGH
Reduce rates (ordinary granular)
Reduce rates (liquid fertigation)
Reduce rates (granularadditives)
RISK
Alternative nutrient sources (organic / waste)
Reduce rates (granular controlled release
Citriblen)
Avoid excesses Spring flush leaf Nlt3 Fertilize
for yield
Variable, targeted rates (granular VRT)
LOW
HIGH
POTENTIAL NET GAINS
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Avoid excess fertilizer

• Maintain round orange leaf N below 3.0
• Fertilize for the yield potential
• Minimal risk will result from trimming excesses

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Yield 230 boxes/acre
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How does excess N affect insect pests?

• Plants that are over-fertilized with nitrogen
  increase susceptibility to herbivorous insects

Leaf miner

• The higher levels of amino acids, which are the
  primary food source used by insects and mites,
  can increase their reproductive ability

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Psyllids favor new leaf flush New leaves are
succulent and have the highest nitrogen
concentration
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What about controlled release fertilizer?

• Citriblen 15-3-19 was designed for mature
  citrus. Results so far show that it works well
  LOW RISK.
• 2008 yields after a three year study on the ridge

Fertilizer treatment 100 conventional granular 75 Citriblen 50 Citriblen 25 conventional 50 Citriblen 75 conventional
Yield of Valencia fruit (boxes/acre) LSD86 454 396 437 486 351
4-mth-old spring-flush leaf N () NS 2.93 3.01 2.76 2.95 2.75

• The high price (2x) of Citriblen limits cost
  savings
• Other benefits are lower application, freight
  costs

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VRT for lowering fertilization spraying costs

• With VRT,
• risks are low (normal fertilization or spraying
  per tree)
• fertilizer spray savings can be high (40
  measured)
• it only works if the tree canopy in a grove is
  variable
• a perfect solid hedgerow canopy will not benefit
  from VRT

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Advantages / benefits of VRT

• Up to 40 immediate fertilizer or spray savings
  have been measured
• Less fertilizer or pesticide spray per acre means
  less freight and fuel costs
• Less refilling of the spreader or sprayer labor
  and fuel saving
• Reduced leaching of soluble nutrients and
  off-target spray drift due to precision placement
  of agrochemical - Citrus BMPs are enhanced
• Reduced weed vigor due to lower nutrient
  availability in off-target areas
• Payback of the investment in VRT equipment is
  rapid, often in one season

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Advantages / benefits of VRT
Recent estimates suggest that if the whole Fl
citrus industry adopted VRT, even a minimal 10
saving in only fertilizer would be worth 16
million per year
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Essential equipment for VRT
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• Small trees are measured in both horizontal and
  vertical planes
• Large trees are measured only vertically

Vertical (height) sensing
Horizontal (width) sensing
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Fertilization of mixed tree sizes all ages
(sensor 4 height)
(sensor 3 height)
(sensor 2 height)
(sensor 1 width only, no hedgerow)
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Useful tips for VRT fertilization

• Use control boxes with automatic look-ahead and
  ground speed sensing so that variable rates are
  synchronized correctly with the trees
• Use fast proportional hydraulic valves avoid
  slow servo valves
• Use a system gain of 1.0 in the DICKEY-john
  controller

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Useful tips for VRT fertilization

• Calibrate the VRT spreader
• The lowest rates should not be less than 50
• Use a gate height calculator to estimate the gate
  height for best performance
• Adjust the canopy sensors for the desired target
  tree height

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A well-tuned VRT system can correctly and
precisely fertilize (or spray) any size tree
(Video clip)
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Current and future developments

• Automated look-ahead VRT controller for both
  spreaders and sprayers in one device

• Advanced features wireless configuration,
  buffers, fill-in sensing, selective by size class
• Future sensing
• by camera

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Additional information Citrus Industry, January
March 2008
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Conclusions / Summary

• Reduce fertilization and spraying costs by
  choosing options like VRT with the lowest risk,
  and by eliminating excesses

• Avoid applying excess fertilizer. Many commercial
  groves have 3 leaf N. Aim for 2.4-2.6 in 4-6
  month old spring flush leaves taken from
  non-fruiting branches of mature round orange

• More nitrogen more canopy growth (leaf flush
  size expansion) more psyllids leaf miners

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Acknowledgements
Jodie Whitney, Bill Miller, Sherrie Buchanon,
Gerald Perkins, Sharath Cugati
Gapway Groves
Florida Agricultural Experiment Station