View Full Table | Close Full ViewTable 1.

Average total N rates applied by producers to normal N treatments for different N management categories for corn after soybean (C–S) and corn after corn (C–C) in 125 on-farm evaluation studies conducted between 2007 and 2010 across Iowa.

 
N management category† No. of trials C–S C–C
kg N ha−1
Fall manure 52 189 (122, 259)‡ 220 (167, 271)
Fall AA 32 173 (100, 212) 201 (183, 228)
Spring AA 10 142 (118, 160) 192 (133, 213)
Spring UAN 17 140 (100, 167) 174 (133, 205)
Sidedress N 14 154 (111, 178) 171 (133, 192)
Manure-injected liquid swine manure; AA, anhydrous NH3; UAN, urea–NH4NO3; sidedress N, sidedress AA or UAN.
Minimum and maximum values are given in parentheses.



View Full Table | Close Full ViewTable 2.

Parameter estimates and standard errors for field-level multilevel binary logistic regressions for identifying the probability of a profitable yield response to N fertilizer using observations of the corn stalk nitrate test (CSNT) and relative green reflectance (RGR) or green reflectance (GR) of the late-season digital aerial imagery of the corn canopy across 125 on-farm evaluation trials conducted during 4 yr.

 
Parameter Estimate SE (SD)
CSNT
Fixed effect†
 Intercept 0.37** 0.14
 CNST 0.000326*** 0.0000074
Random effect
 Location (1.21)
RGR
Fixed effect
 Intercept –8.36*** 0.77
 RGR 7.62*** 0.69
Random effect
 Location (1.01)
GR
Fixed effect
 Intercept –3.10*** 0.41
 GR 0.031*** 0.0038
Random effect
 Location (1.29)
**Significant at P < 0.01.
***Significant at P < 0.001.
Fixed parameters shown are for the field-level models, which were estimated from intercepts that varied and slopes that were constant across 125 trials.