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Variable Rate Nitrogen Application on Row Crop Spinach. 2005 ASAE Annual International Meeting. C. L. JonesResearch 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

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Variable rate nitrogen application on row crop spinach l.jpg

Variable Rate Nitrogen Application on Row Crop Spinach

2005 ASAE Annual International Meeting

C. L. JonesResearch Engineer

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

M. L. Stone Regents’ Professor, ASAE Fellow

J. B. SolieSarkey’s Professor, ASAE Fellow

D. Zavodny Research Engineer

Paper Number: 051119


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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


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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


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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


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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


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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


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Determining In-Season Response

  • Non-N-limiting strips

Stamp Calibration Plots

Paper Number: 051119


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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


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Spring 2003

Paper Number: 051119


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Spring 2003 App. Rates/Results

Paper Number: 051119


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Spring, Fall 2004

Paper Number: 051119


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2004 App. Rates/Results

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

Paper Number: 051119


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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


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Conclusions

  • When should we apply post-emergence N fertilizer in spinach?

    • Once approximately 45 days post seeding (50% ground cover stage)

Paper Number: 051119


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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


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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


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QUESTIONS?

Acknowledgments

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

Paper Number: 051119


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