Green Seeker Research in Virginia S B Phillips

Green. Seeker Research in Virginia S. B. Phillips, W. E. Thomason, and J. G. Warren Virginia Tech 2005 Nitrogen Conference Columbia, Missouri August 10 -12

Virginia N Algorithm Employs the same concepts and strategies as the OSU algorithm l 1) Collect NDVI measurements from high-N reference, 0 -N reference, and target corn canopies 2) Estimate base grain yield potential using target NDVI/DAP

Yield Prediction Model y = 95. 463 e 36. 91 x r 2 = 0. 59

Virginia N Algorithm Employs the same concepts and strategies as the OSU algorithm l 1) Collect NDVI measurements from high-N reference, low-N reference, and target corn canopies 2) Estimate base grain yield potential using target NDVI/DAP 3) Estimate optimum grain yield potential using target NDVI/DAP multiplied by a response index (typically high. N NDVI/target NDVI) 4) Calculate N requirement as {[(N removed in optimum grain-N removed in base grain)/NUE]+(100 -starter)}

2004 Results Summary Across 5 locations in Virginia, predicted grain yields were within 5% of actual yields obtained under optimum fertilization l Optimum sidedress N rate averaged across locations was 85 lb N/acre; sensor-based rate recommendations averaged 36 lb N/acre, which resulted in a 16% yield reduction l Applying N on a by-plant basis resulted in N reductions of 10 lb/acre without affecting grain yield at 3 sites; at 2 other sites, grain yields were significantly reduced following by-plant fertilization l

Current and Future Objectives Refine current methods of determining variable topdress N rates and incorporate into sensor-based fertilization algorithms l Continue working toward development of a regional strategy l Demonstrate sensor-based, variable-rate N fertilization strategies on grower farms using the Green. Seeker RT 200 l

2005 Research 10 sites across Virginia l Irrigated and non-irrigated l Conventional and no till l Starter N (0, 50, 100, 150, 200 lb N/acre) l Sidedress N (0, 25, 50, 75, 100, 150, 200 lb N/acre) l Resolution (2. 5, 5, 10, 20 row ft) l Plots will be fertilized and harvested using conventional plot equipment l

2005 Research

Regional VRT Study Painter, VA Starter N 0 40 160 NDVI SR CV NE OK MO VA . 3772. 4658 23. 4623. 3812 23. 5209. 3253 25 120 --- 33 17 -- 158 93 -- 92 107 --- 111 38 7 5 72 52 53 51 Blacksburg, VA 0 40 ------- ---

RT 200 Field Trials