Submitted to: International Conference on Precision Agriculture Abstracts & Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/14/2002
Publication Date: 12/1/2002
Citation: SCHARF, P.C., KITCHEN, N.R., SUDDUTH, K.A., DAVIS, J.G., LORY, J. FIELD-SCALE EVALUATION OF VARIABLE N RATE RECOMMENDATIONS FOR CORN. PROCEEDINGS 6TH INTERNATIONAL CONFERENCE ON PRECISION AGRICULTURE. 2002. CD-ROM (UNPAGINATED). AMERICAN SOCIETY OF AGRONOMY. MADISON, WI.
Technical Abstract: The nitrogen (N) fertilizer needs of corn (Zea mays L.)and other crops can vary substantially within and among fields. This may be due to variations in soil N supply, crop N demand, or both. Our objective is to develop and validate systems to predict need for N fertilizer at a field scale. This study investigated the use of 35 mm aerial photographs to detect spatially variable corn N needs for developing variable rate fertilizer maps. Photographs were taken using a 35 mm camera and a UV filter at an altitude ranging from 750 to 1800 m for five Missouri fields representing three different soil types (alluvial, claypan, deep loess). Nitrogen was applied in strips across the field at early vegetative (about V5) stage ranging from 0 to 280 kg N/ha. For three different corn growth stages (V6, V11, R3), digital counts for red, green, and blue bands were compared with SPAD chlorophyll meter readings in order to assess crop N health. Red and green bands were similar to chlorophyll meter readings in predicting differences. Optimum N rates varied widely in all three fields. Within a field, variation was often over 112 kg N/ha. Color bands from photographs taken before side-dress were strongly correlated with soil EC (R**2 equal to or greater than 0.65). Aerial photographs with soil pixels removed poorly predicted grain yield with R**2 values generally 0.3 or less. Our results will be used to explore the potential for aerial images to detect corn N health, explain soil type (Soil ECa) and crop color interactions, and develop in-season variable N fertilizer maps.