View Full Table | Close Full ViewTable 1.

The influence of N and water treatments on grain yields, yield losses due to N stress (YLNS), and yield losses due to water stress (YLWS) at Aurora, SD, in 2002, 2003, and 2004.

 
Variable Grain yield YLNS YLWS
kg ha–1
Yield potential of the soil
 Medium (dryland) 8500 1390 2120
 High (irrigated) 9630 1140 1270
P value 0.004 >0.05 <0.01
N rate, kg ha–1
 0 7510 2830 1660
 56 9040 1360 1600
 112 9890 430 1680
 168 9800 430 1830
P value <0.001 <0.01 >0.05
 LSD(0.05) 400 415
Year
 2002 9070 1630 1350
 2003 9660 1180 1160
 2004 8450 980 2570
P value <0.001 <0.01 <0.01
 LSD(0.05) 290 300 300



View Full Table | Close Full ViewTable 2.

The influence of year, soil yield potential, and a fertilizer cost/corn price ratio of 2.80, 5.59, or 11.27 on the economically optimum N rate (EONR) at Aurora, SD, in 2002, 2003, and 2004.

 
Yield potential of the soil EONR
Year 2.80 ratio 5.59 ratio 11.27 ratio
kg N ha–1
2002 medium (dryland) 156 140 106
high (irrigated) 140 126 97
2003 medium 132 124 108
high 131 123 107
2004 medium 117 107 88
high 121 113 95
P value 0.635 0.616 0.680
2002–2004 medium 135 124 100
high 131 120 106
P value 0.554 0.622 0.863
2002 medium–high 148 132 102
2003 medium–high 132 124 107
2004 medium–high 119 110 92
P value 0.128 0.160 0.199
LSD(0.05)



View Full Table | Close Full ViewTable 3.

The influence of the fertilizer cost/corn price ratios of 2.80, 5.59, and 11.27 on the correlation coefficients (r) between delta yield, the economically optimum N rate (EONR), and yield at the EONR at all study sites. A significant r value at P < 0.05 is 0.33.

 
Delta yield
EONR
Yield at EONR
Parameter 2.80 ratio 5.59 ratio 11.27 ratio 2.80 ratio 5.59 ratio 11.27 ratio 2.80 ratio 5.59 ratio 11.27 ratio
Delta yield, 5.59 ratio 1.00 1.00
Delta yield, 11.27 ratio 0.98 0.99 1.00
EONR, 2.80 ratio –0.09 –0.10 –0.14 1.00
EONR, 5.59 ratio 0.11 0.10 0.07 0.97 1.00
EONR, 11.27 ratio 0.56 0.57 0.57 0.64 0.80 1.00
Yield at EONR, 2.80 ratio 0.73 0.71 0.66 –0.25 –0.13 0.21 1.00
Yield at EONR, 5.59 ratio 0.72 0.71 0.67 –0.26 –0.14 0.20 1.00 1.00
Yield at EONR, 11.27 ratio 0.70 0.69 0.67 –0.30 –0.18 0.18 0.98 0.99 1.00



View Full Table | Close Full ViewTable 4.

The influence of N recommendation model on root mean square errors and bias. Data from all study sites were included in this analysis. For the constant N value calculations, the average NO3–N concentration as reported by the South Dakota Soil Testing Laboratories between 2002 and 2005 was used to estimate NO3–N (Gerwing and Gelderman, 2005). The constant N approach is recommended for fields where a soil sample is not collected.

 
RMSE
Fertilizer/corn price ratio South Dakota model Western Minnesota model Iowa model Nebraska model Modified South Dakota model
2.80 1871 (–16)† 1955 (–38) 3670 (48) 2042 (–21) 1935 (–27)
5.59 1414 (–5) 1832 (–36) 2107 (29) 1560 (–20) 1309 (–13)
11.27 2205 (17) 2316 (–36) 1629 (18) 1780 (–28) 1765 (9)
Replacing measured NO3–N with a constant
2.80 1456 (–11) 1972 (–34) 1555(–19) 1287 (–21)
5.59 1006 (1) 1742 (–33) 1091(–16) 670 (–8)
11.27 1812 (23) 2082 (–32) 1608(–28) 1140 (15)
Bias values in parentheses.



View Full Table | Close Full ViewTable 5.

The influence of the state recommendation model and fertilizer cost/corn price ratio on the economically optimum N rate (EONR) and the N recommendations from South Dakota, western Minnesota, Iowa, and Nebraska. For the constant N value, the average NO3–N concentration as reported by the South Dakota Soil Testing Laboratories between 2002 and 2005 was used to estimate NO3–N (Gerwing and Gelderman, 2005). The constant N approach is recommended for fields where a soil sample is not collected.

 
Fertilizer/corn ratio EONR South Dakota model Western Minnesota model Iowa model Nebraska model Modified South Dakota model
kg N ha–1
Measured NO3–N
2.8 139 122 105 179 120 114
5.59 128 122 92 157 110 114
11.27 105 122 69 122 100 114
Replacing measured NO3–N with a constant
2.8 139 128 109 122 120
5.59 128 128 95 113 120
11.27 105 128 73 100 120