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Variable Rate Nitrogen Application on Row Crop Spinach. 2005 ASAE Annual International Meeting. C. L. Jones Research Engineer N. O. Maness Professor - Hort./Landscape Architecture M. L. Stone Regents’ Professor, ASAE Fellow

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variable rate nitrogen application on row crop spinach

Variable Rate Nitrogen Application on Row Crop Spinach

2005 ASAE Annual International Meeting

C. L. Jones Research Engineer

N. O. Maness Professor - Hort./Landscape Architecture

M. L. Stone Regents’ Professor, ASAE Fellow

J. B. Solie Sarkey’s Professor, ASAE Fellow

D. Zavodny Research Engineer

Paper Number: 051119

nitrogen mismanagement causes
Nitrogen Mismanagement causes:
  • Nitrogen Use Efficiency (NUE): 40-70 %
  • Leaching and groundwater contamination
  • Ozone depletion from gaseous losses as N2
  • Loss of profit
  • Health hazard due to nitrate build-up in foliage

Paper Number: 051119

current best practices
Current “Best” Practices
  • 50 to 110 kg N/ha applied at planting
  • Side dress application after emergence:
  • Rate depends..
  • soil type
  • seasonal variation
  • cultural practice
  • Soil testing: limited by economics, resolution, time

Paper Number: 051119

objectives
Objectives
  • Answer the following:
    • When should we apply post-emergence N fertilizer in spinach?
    • How should we determine in-season N application rates?
    • Does variable rate application of N in row crop spinach work?

Paper Number: 051119

past spinach research
Past Spinach Research
  • Readily responsive to nitrogen
  • NDVI (normalized difference vegetation index) is a good predictor of chlorophyll content
  • Chlorophyll content and NDVI may be used to estimate photosynthetic capacity and productivity
  • NDVI may be used to estimate nitrogen needs in spinach

Paper Number: 051119

equipment
Equipment
  • GreenSeeker™ active multispectral sensors (NTech Industries, Ukiah, Calif.)
    • Handheld
    • Applicator mounted
  • LED’s emit red and NIR light
  • Photodiode receives reflectedlight, produces a voltage
  • Data used to calculate NDVI:

Paper Number: 051119

determining in season response
0

0

100

125

75

150

0

0

100

Determining In-Season Response
  • Non-N-limiting strips

Stamp Calibration Plots

Paper Number: 051119

experiment design
Experiment Design
  • Oklahoma Vegetable Research Station, Bixby, Oklahoma
  • Spring, 2003… Spring, 2004… Fall, 2004
  • “San Juan” and “Fidalgo” varieties
  • Overhead sprinkler irrigation
  • Severn very fine sandy loam, prior year fallow, preplant herbicide application

Paper Number: 051119

spring 2003
Spring 2003

Paper Number: 051119

spring 2003 app rates results
Spring 2003 App. Rates/Results

Paper Number: 051119

spring fall 2004
Spring, Fall 2004

Paper Number: 051119

2004 app rates results
2004 App. Rates/Results

Sprayed plots: averaged 10 kg/ha biomass better than hand application

Paper Number: 051119

comparison vrt vs non vrt
Comparison: VRT vs. Non-VRT

2003:

for plots yielding approx. 16,000 kg/ha

non-VRT plot: 132 kg N/ha

VRT plot: 81 kg N/ha

Fall 2004:

VRT plots treated with approx. 75 kg N/ha total: 21,000 kg/ha

non-VRT plot treated with 75 kg N/ha: 13,000 kg/ha

Paper Number: 051119

conclusions
Conclusions
  • When should we apply post-emergence N fertilizer in spinach?
    • Once approximately 45 days post seeding (50% ground cover stage)

Paper Number: 051119

conclusions15
Conclusions
  • How should we determine in-season N application rates?
    • Compare NDVI of plot to best NDVI in stamp or calibration plots

Paper Number: 051119

conclusions16
Conclusions
  • Does variable rate application of N in row crop spinach work?
    • Yes! Examples:
      • Spring ‘04: 43% improvement
      • Fall ‘04: 53% improvement over non-VRT plots

-VRT plots were visibly more uniform in color, texture, and size

Paper Number: 051119

questions
QUESTIONS?

Acknowledgments

Support through funding from the USDA Special Research Grant Number 2003-06134

Paper Number: 051119