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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 J. B. Solie Sarkey’s Professor, ASAE Fellow D. Zavodny Research Engineer Paper Number: 051119
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 • 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 • 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 • 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 • 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
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 • 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 Paper Number: 051119
Spring 2003 App. Rates/Results Paper Number: 051119
Spring, Fall 2004 Paper Number: 051119
2004 App. Rates/Results Sprayed plots: averaged 10 kg/ha biomass better than hand application Paper Number: 051119
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 • When should we apply post-emergence N fertilizer in spinach? • Once approximately 45 days post seeding (50% ground cover stage) Paper Number: 051119
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
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? Acknowledgments Support through funding from the USDA Special Research Grant Number 2003-06134 Paper Number: 051119