2. Variable rate technology - Arnold Schumann

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 offtarget 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
Essential equipment for VRT
CANOPY SENSORS
FERTILIZER SPREADER来自CONTROL BOX
RATE CONTROLLER
SPRAYER
Small trees are measured in both horizontal and vertical planes Large trees are measured only vertically
Reduce rates (granular+additives)
RISK
Alternative nutrient sources (organic / waste) Reduce rates (granular controlled release: Citriblen®)
Avoid excesses Spring flush leaf N<3% Fertilize for yield POTENTIAL NET $ GAINS
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
High yield potential
excess Low yield potential
(Round orange early varieties; from Obreza & Morgan, 2008: SL253, p. 52)
Yield ~230 boxes/acre
How does excess N affect insect pests?
Map by courtesy of
Variable rate technology (VRT)
VRT success depends on canopy variability; Now would be an excellent time to exploit VRT
N uptake
Only the healthy canopy should be fertilized - avoid fertilizing bare soil or weeds
Vertical (height) sensing
Horizontal (width) sensing
400
Fertilization of mixed tree sizes; all ages
Fertilizer application rate (kg/ha/y)
300
ln(Y) = 0.5106X + 3.084 R2=0.99
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
Opportunities for lowering fertilization costs
HIGH Reduce rates (ordinary granular) Reduce rates (liquid fertigation)
CONCEPTS: *Keep trees slightly „hungry‟ (improved fertilizer efficiency) *Use more efficient sources *Cut excesses *Precision placement VRT
Advantages / benefits of VRT
“A large citrus grove conducted a test on 222 acres of grove using a traditional fertilizer spreader versus a variable rate fertilizer spreader with eyes. The traditional method required 48 tons per application (3 applications per year). Using the VRT spreader, they reduced the amount applied to 37 tons, a savings of 11 tons per application. On an annual basis, it would result in a reduction of 33 tons applied to the 222 acres (23%). Extrapolating from this 222 acres to the approximately 12,000 acres that is owned by the company would result in an annual reduction of nearly 1800 tons of fertilizer going out – over 80 transport loads (22-ton each)! This company has received cost sharing for 10 VRT spreaders and hope to get funding this year for four more”.
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
Fertilizer treatment: 100% conventional granular 75% Citriblen 50% Citriblen 25% conventional + 50% Citriblen 75% conventional
Yield of „Valencia‟ fruit (boxes/acre)** LSD=86
The current situation
$ The prices of fertilizer have approx. doubled in one year
$ The costs of spraying have approx. doubled since psyllid management was intensified
Psyllids favor new leaf flush; New leaves are succulent and have the highest nitrogen concentration
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:
4-mth-old spring-flush leaf N (%) NS
454
396
437
486
351
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
Variable, targeted rates (granular VRT)
LOW
HIGH
Avoid excess fertilizer
•Maintain round orange leaf N below 3.0% •Fertilize for the yield potential •Minimal risk will result from trimming excesses excess