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Fluid Journal : Fluid Journal 1993-1995
2 Fluid Journal Summer 1994 Figure 2. Relationship between SPAD reading on V6 carn and corn grain yiled at Ames, 1993 Figure 1. Effect of N fertilizer rate on corn grain yields at Ames, 1993. 0 70 80 90 100 110 120 130 Yield (bu/A) 20 40 60 80N Rate (lb/A) 100 120 140 160 180 40 70 80 90 100 110 120 Yield (bu/A) 41 42 43 44 SPAD Readings 45 46 47 48 49 yield is shown in Figure 2. SPAD readings ranged from about 42 to 48, while yield ranged from about 80 to 120 bu/A. There was a strong correlation between yield and SPAD readings. Crawfordsville site SPAD readings at the Crawfordsville site increased with N rate, but were not affected by method of application. SPAD readings ranged from about 50 to 54. Maximum readings were reached at about 125 lbs/A. Ammonium-nitrogen concentration in the surface foot of soil increased with N rates in both broadcast and injected applications at sidedress. Ammonium- nitrogen concentrations were higher in injected than in broadcast treatments. Nitrogen fertilizer was not applied until late in the season. This reduced the amount of N leached. There were higher concentrations of ammonium-nitrogen in injected applications than broadcast. Nitrate-nitrogen concentrations ranged from about 9 to 27 ppm and increased with N rates. Method of application had no effect on nitrate- nitrogen concentration. Nitrate- nitrogen content of the check treatment was below the critical level of 21 ppm, indicating the need for additional N to optimize yield. Grain yields (reported at 15.5 percent moisture) were generally low and ranged from 70 to 110 bu/A (Figure 3) and increased with N rates. Method of application had no effect on yield. Heavy rains and cool temperatures in the spring and summer reduced yields. Maximum yield was reached with about 130 lbs/A of N. The relationship between SPAD readings on V6 corn leaves and corn yields is shown in Figure 4. SPAD readings ranged from 50 to 54. The readings are grouped in two areas, suggesting a difference between deficient N and adequate N. The SPAD readings correlated well with yield. More work needed Results in 1991/1992 were similar, indicating a good correlation between chlorophyll content, as measured in SPAD values at V6 growth stage and corn yield. However, yield and SPAD readings were not as strongly correlated in 1993 because of unusually high amounts of precipitation. SPAD meter readings were not affected by banded N, but showed differences in N availability. However, the narrow range of SPAD meter readings made it difficult to determine a critical value. This narrow range may make it difficult to predict N sidedress amounts. SPAD meter readings were different for each site. This was probably caused by hybrid differences and site specific factors. Our conclusion is using a chlorophyll meter to predict N status of corn is promising. However, because of hybrid/ site effects, some sort of relative scale must be developed. This technology will be adopted only if users are willing to develop adequately fertilized areas in fields and base sidedress N recommendations on SPAD reading differences between the fertilized and unfertilized areas. Experimental design Soil. Soil on site located three miles
Fluid Journal 1996-1998