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Fluid Journal : Fluid Journal 1993-1995
3 Fluid Journal Summer 1994 Figure 4. Relationship between SPAD reading on V6 carn and corn yield at Crawfordsville, 1993. Figure 3. Effect of N fertilizer rate on corn grain yields at Crawfordsville, 1993. 49 70 80 90 100 110 120 Yield (bu/A) 50 51 SPAD Readings 52 53 54 0 70 80 90 100 110 120 Yield (bu/A) 20 40 60 N Rate (lb/A) 80 100 120 140 180 160 west of Ames is a Nicollet loam (Fine- Loamy, mixed, mesic Aquic Hapludoll). At the Southeastern Iowa Outlying Research Farm near Crawfordsville, soil is Mahaska (Fine, montmorillonitic, mesic Aquic Argiudaoll). Plots. A split plot design with four replications was used at both locations. Main plots were method of N application. Sub-plots were N rates. Fertilizer. Fertilizer source was 28% UAN. Broadcast N was incorporated within 24 hours. Two passes were needed to inject N. Crop was sidedressed at the V6 growth stage (six leaf collars visible on the stalk). Readings were taken with a Minolta SPAD-502 Chlorophyll Meter from ten randomly selected plants in the two middle rows of each plot. Readings were taken halfway between the tip and collar (where the leaf was bent), and midway between the leaf midrib and the leaf edge of the most recently mature leaf. Timing. Fertilizer was applied on April 26, 1993 at Ames and on May 20, 1993 at Crawfordsville. Berghoefer is graduate research assistant and Dr. Killorn is extension agronomist, Agronomy Department, Iowa State University.
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