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Variable Rate Fertilizer at Reduced Scales. Randy Taylor Biosystems and Agricultural Engineering Oklahoma State University. 2010 NUE Conference Stillwater, OK. Field Scale Variability. Macro-variability Likely tied to soil type, landscape position, or something else Micro-variability. - PowerPoint PPT Presentation
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Variable Rate Fertilizer at Reduced Scales
Randy TaylorBiosystems and Agricultural Engineering
Oklahoma State University
2010 NUE ConferenceStillwater, OK
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Field Scale Variability
• Macro-variability– Likely tied to soil type, landscape position, or
something else• Micro-variability
0
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App
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Rat
e, g
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RX_RATERATE
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Variability View from Equipment
• Longitudinal– Down-the-row– Response time issues
• Lateral– Across the boom– Boom divisions
A greater distance between the control and delivery points means a lower resolution and increased scale.
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Liquid Systems
• The initial sub-meter application system met market resistance
• However, sensor based VRA has found commercial success
• Section control systems have also renewed the interest in sub-boom width application
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Accepted Resolution
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0 20 40 60 80 100
Min
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Res
pons
e Tim
e, s
Application Scale, ft
5 mph10 mph15 mphLimit
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Reduced Scale
0.0
0.5
1.0
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0 5 10 15 20
Min
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Res
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e Tim
e, s
Application Scale, ft
5 mph10 mph15 mphLimitLimit
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Liquid Systems
• Most commercial rate controllers can be set to about a 2 second response time.
• Multiple control sections will require multiple control valves and possibly flow meters.
• Pulse width modulation and binary valve systems have promise.
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Granular VRT
• Granular distribution/delivery systems follow two basic designs– Gate/belt or chain/spinner– Metering wheel/air boom
• While both systems can be used for variable rate application, reducing the application scale to a partially width is really not feasible
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Spinner Spreaders• Reducing application scales
with spinner spreaders is really not feasible.
• The material is centrally metered and distributed.
• Furthermore, VRA with spinner spreaders is a challenge.– Spread distribution patterns
are typically a function of flow rate onto the spinner
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Air Boom Systems
• The material is centrally metered, but patterns are created locally.
• The primary challenge is lag time from the metering system to the point of application
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Potential Solutions
• The central hopper/conveying system might be a good model to follow
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Section Control System Speed
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Rate Controllers and Tuning
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0.0 0.2 0.4 0.6 0.8 1.0NDVI
Pres
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GPA 1 gpa/0.05 NDVI
2.5 gpa/0.05 NDVI
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App
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Rat
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RX_RATERATE
• Prescriptions should not be developed without considering rate controller performance.
• Worry about the macro variability within the field.
• Are you capturing the general trend?
