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Active and Passive Reflectance Sensor Comparison in Cotton

Active and Passive Reflectance Sensor Comparison in Cotton. Kevin F. Bronson. Texas A & M Univ. – Texas Agric. Exp. Stn., Lubbock, TX. Introduction.

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Active and Passive Reflectance Sensor Comparison in Cotton

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  1. Active and Passive Reflectance Sensor Comparison in Cotton Kevin F. Bronson Texas A & M Univ. – Texas Agric. Exp. Stn., Lubbock, TX

  2. Introduction • Previous work has shown that using spectral reflectance with well-fertilized plots/sufficiency index approach can improve agronomic N use efficiency in LEPA and subsurface drip irrigated cotton • We hypothesized that reflectance based management can be used on long plots/stations with near daily N injection • We built a 16-station SDI system that we can inject N daily as farmers do (not 30 lb N/ac doses)

  3. Study objectives • To assess lint yields and N fertilizer use efficiency of UAN (32-0-0) and 28-0-0-5S injected between 1st square and mid bloom and 1st square and peak bloom • To test the GreenSeeker and Cropscan spectroradiometers as in-season N status monitoring tools

  4. Treatments Tr ea t N Source Termination Other a 1 32 - 0 - 0 Mid bloom 90 lb N /ac a 2 32 - 0 - 0 Peak bloom 90 lb N /ac a 3 28 - 0 - 0 - 5 Mid bloom 90 lb N /ac a Peak bloom 4 28 - 0 - 0 - 5 90 lb N /ac 5 32 - 0 - 0 Peak bloom 45 lb N /ac & reflect 6 Zero - N 1 rep/stn only a Treatments 1 - 4 based on 150 lb N/ac – lb NO - N/ac in 0 - 24 in. soil 3 - NO - N in 12 inches of irrigation water ) 3

  5. Plot/station layout (plots are 8, 40-in. rows X 600 ft)

  6. Reflectance methods • Measured zero-N, reflectance-based (includes 30 ft over-fertilized plots), and 32-0-0 to mid bloom weekly between 23 June and 9 August • Cropscan MSR 16 is a passive spectroradiometer. Has 16 upwards and downwards facing radiation tranducers/filters. Height of measurement was 48 inches (24–in. fov). Four spot measures (100 per) per GPS point (4 per 600 foot plot). • GreenSeeker (Green) is an active spectroradiometer and calculated GNDVI and 1/GVI. Wavebands are 530 and 780 nm). Took 6 m of measurements (~100) per GPS point at 34-36 in above canopy.

  7. Green vegetative index (r780/r530) from Cropscan MSR16, 48 inches above canopy, Lubbock, TX, 2005

  8. Green vegetative index (r780/r530) from GreenSeeker, 36 inches above canopy, Lubbock, TX, 2005

  9. Correlations of GVI from cropscan, GreenSeeker and SPAD meter readings at early bloom, and peak bloom, Lubbock, 2005

  10. Summary/What next • Reflectance-based had 65 lb N/ac injected, we hope for same lint yield as soil-test based of 90 lb N/ac. • N Source or timing did not affect GVI. • Will repeat study next year. • May abandon small well-fertilized plots. • Keep the same height above the ground for the GreenSeeker for all plots? • Or maintain the same height above the canopy for GreenSeeker?

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