Efficient use of nitrogen is becoming important due to increasing N fertilizer prices and the growing concerns about NO3- contamination of ground and surface waters. Researchers are interested in whether N rates can be tailored to better fit certain

1
Introduction Efficient use of nitrogen is
becoming important due to increasing N fertilizer
prices and the growing concerns about NO3-
contamination of ground and surface waters.
Researchers are interested in whether N rates can
be tailored to better fit certain hybrids.
Previous studies have shown mixed results. Tsai
et al. (1984) found that yields of hybrids
differed in their response to N, and classified
hybrids as two types high fertility or low
fertility. However, Bundy and Carter (1988) found
that hybrids required similar rates of N to
achieve maximum yield. Commercial seed corn
companies are also trying to develop hybrids with
higher N use efficiency, and thus, less need for
N fertilizer.
  Yield efficiency Yield efficiency   N uptake efficiency N uptake efficiency   N utilization efficiency N utilization efficiency
Hybrid 2005 3-yr avg.   2005 2-yr. avg.   2005 2-yr. avg.
  ---kg grain/kg N--- ---kg grain/kg N---   ------------------- -------------------   ---kg grain/kg N--- ---kg grain/kg N---
440 55.9 45.2   55.6 49.7   99.4 101.6
442 31.0 42.5   41.1 48.5   74.7 84.4
576 37.6 39.4   48.9 50.3   79.8 92.5
583Bt 36.0 37.3   50.8 51.5   69.7 78.6
625 27.7 43.4   39.0 42.9   69.6 86.1
645 30.1 38.3   48.1 46.2   71.6 82.0
710 33.2 37.9   36.1 38.0   85.6 97.0
727 35.6 37.3   40.8 42.7   91.8 99.5
795B 23.4 39.5   31.5 39.9   72.6 87.6
                 
LSD.10 15.8 NS   12.1 NS   NS 14.4
Objective Determine how nine commercial corn
hybrids differed in their response to N rate,
measured as differences in economically optimum N
rate (EONR), yield at EONR, fertilizer N use
efficiency (FNUE), and the economic return to N
at the optimum N rate
Table 4. FNUE measured as yield efficiency, N
uptake efficiency and N utilization efficiency by
hybrid.
Materials and Methods This study was conducted
for 3 years in Urbana, IL. In 2003 and 2004, the
soil type was Dana silt loam, and in 2005, it was
Flanagan silt loam. Corn followed corn. The plots
were arranged in a split plot design in an RCBD
with 4 replications. The main plots consisted of
5 N rates (0, 67, 135, 202, 270 kg N/ha) and the
subplots were 9 Burrus hybrids (440, 442, 576,
583Bt, 625, 645, 710, 727 795B). Nitrogen was
sidedressed as 28 UAN at the V5-V6 growth stage.
A costprice ratio of 8.52 (0.09/kg corn
0.77/kg N) was used to calculate EONR. Data were
analyzed using the Proc Mixed procedure in SAS,
with years and reps (nested in years) as random
factors, and hybrids and N rates as fixed
factors. Yield data were fit to the
quadraticplateau model in Proc NLIN. FNUE
parameters were calculated at a given N rate
using the following equations -Yield
efficiency YieldEONR Yieldzero N
EONR -N uptake efficiency Plant N
contentEONR Plant N contentzero N



EONR -N utilization efficiency
YieldEONR Yieldzero N
Plant N
contentEONR Plant N contentzero N Net return to
N was calculated for each hybrid as (Optimum
yield yieldzero N) price of corn (EONR N
price).
Fig. 1. Yield response to N by hybrid across
years.

• Results
• The N rate hybrid interaction for yield was
  significant in 2004, 2005 and across years (Table
  1)
• Across years, maximum yields were reached at N
  rates ranging from 140 to 228 kg N/ha (Fig. 1)
• Optimum yields were significantly different among
  hybrids in each year and across years, with 583Bt
  and 795B having consistently higher optimum
  yields in each year (Table 2)
• EONR values were significantly different among
  hybrids in 2004 and across years, with hybrid
  583Bt having the highest EONR values in both
  instances (Table 2)
• Net return to N (NRTN) was significantly
  different among hybrids in 2004 and 2005, and
  583Bt had the highest NRTN in both years (Table
  3)
• NRTN values were correlated with optimum yields
  in 2004 and 2005, but were only correlated with
  EONR values in 2004
• Yield efficiency and N uptake efficiency were
  significantly different among hybrids in 2005,
  while N utilization efficiency was significantly
  different among hybrids across 2004 and 2005
  (Table 4)
• Some hybrids that had higher optimum yields and
  EONR values tended to have lower yield
  efficiency, and thus lower FNUE (Tables 2 4)
• NRTN values were not correlated with yield
  efficiency in 2005

Hybrid 2003 2003   2004 2004   2005 2005   3-yr avg. 3-yr avg.
  EONR OY   EONR OY   EONR OY   EONR OY
  kg N/ha Mg/ha   kg N/ha Mg/ha   kg N/ha Mg/ha   kg N/ha Mg/ha
440 171.0 12.8   145.3 13.1   80.8 10.0   132.4 12.0
442 147.5 12.7   152.5 14.6   188.9 10.3   139.6 12.5
576 181.6 13.2   173.0 15.2   70.2 8.9   145.7 12.5
583Bt 215.1 13.7   228.9 15.9   173.7 11.0   205.9 13.5
625 139.4 13.2   152.2 14.8   127.5 9.7   139.7 12.6
645 130.9 13.3   181.2 15.1   109.2 9.7   140.4 12.7
710 178.6 13.2   197.5 14.3   72.4 9.4   152.8 12.3
727 144.4 12.3   194.7 14.6   116.0 10.1   153.5 12.3
795B 178.5 14.2   174.7 15.7   163.0 11.0   169.2 13.6
                       
LSD.10 NS 0.8   33.5 0.7   NS 0.9   38.2 0.7
Table 2. Economically optimum N rates (EONR) and
optimum yields (OY) by hybrid.
Hybrid 2003   2004   2005   3-yr avg.
------------------------------/ha-------------------------------- ------------------------------/ha-------------------------------- ------------------------------/ha-------------------------------- ------------------------------/ha-------------------------------- ------------------------------/ha-------------------------------- ------------------------------/ha-------------------------------- ------------------------------/ha--------------------------------
440 269.1   453.6   319.3   347.3
442 421.0   572.9   213.5   402.4
576 373.5   595.7   160.7   379.6
583Bt 381.4   734.7   355.8   490.6
625 360.3   500.3   189.4   350.0
645 347.8   500.0   172.6   340.2
710 423.3   537.2   173.4   380.1
727 232.3   613.3   259.0   371.7
795B 433.3   722.1   241.5   468.4
               
LSD.10 NS   89.8   94.9   NS

• Conclusions
• The two Bt hybrids seemed to have a higher
  response to N
• Further research to compare Bt hybrids against
  non-Bt counterparts
• Hybrid maturity did not consistently affect
  hybrids response to N in either yield or FNUE
• Net return to N was closely associated with
  optimum yield
• FNUE by itself may have limited economic value as
  a hybrid trait

Fixed effect Grain yield Grain yield Grain yield Grain yield
  Across years 2003 2004 2005
  ----------------------------PrgtF------------------------- ----------------------------PrgtF------------------------- ----------------------------PrgtF------------------------- ----------------------------PrgtF-------------------------
Nitrogen rate 0.0005 lt.0001 lt.0001 lt.0001
Hybrid 0.0576 0.0280 lt.0001 lt.0001
Nitrogen rate Hybrid 0.0699 0.5967 0.0245 0.0025

• Literature Cited
• Bundy, L.G. and P.R. Carter. 1988. Corn hybrid
  response to
• nitrogen fertilization in the Northern
  Corn Belt. J. Prod. Agric.
• 1 99-104.
• Tsai, C.Y., D.M. Huber, D.V. Glover, and H.L
  Warren. 1984.
• Relationship of N deposition to grain
  yield and N response of
• three maize hybrids. Crop Sci. 24
  277-281.

Table 3. Net return to N by hybrid. Values are
calculated at the economically optimum N rate for
each hybrid each year, using an N price of
0.77/kg N and a corn price of 0.09/kg corn.
Table 1. Test of fixed effects for yield.