Table 2. The number of on-farm experiments, maize yield without N, medium N rate, grain yield at the medium N rate and N rate, grain yield, GHG emission intensity of N fertilizer use, N fertilizer production and other sources for regional N management approach and field-specific N management.
| Subregion | na | Yield without N (Mg ha−1) | Medium N rate (kg ha−1) | Yield for medium N rate (Mg ha−1) | Regional N management approach | Field-specific N management | ||||||||||
| N rate (kg ha−1) | Grain yield (Mg ha−1) | GHG emission intensity (kg CO2 eq Mg−1 grain) | N rate (kg ha−1) | Grain yield (Mg ha−1) | GHG emission intensity (kg CO2 eq Mg−1 grain) | |||||||||||
| N fertilizer use | N fertilizer production | Other sources | Total | N fertilizer use | N fertilizer production | Other sources | Total | |||||||||
| NE1 | 132 | 6.40±1.01b | 153±6 | 8.98±1.09 | 150 | 8.85 | 91 | 141 | 49 | 280 | 158±26 | 8.87±1.11 | 91±19 | 149±32 | 49±7 | 289±55 |
| NE2 | 62 | 6.82±1.23 | 147±21 | 9.05±1.51 | 150 | 9.18 | 87 | 136 | 49 | 272 | 155±25 | 9.13±1.48 | 87±14 | 143±23 | 51±8 | 281±42 |
| NE3 | 126 | 6.50±1.26 | 162±15 | 9.48±1.38 | 164 | 9.01 | 96 | 151 | 50 | 298 | 165±20 | 9.10±1.25 | 92±18 | 153±29 | 50±8 | 295±53 |
| NE4 | 77 | 6.92±1.66 | 204±28 | 8.93±1.59 | 188 | 8.76 | 113 | 178 | 55 | 346 | 191±49 | 8.84±1.48 | 117±37 | 183±53 | 57±9 | 356±94 |
| NCP1 | 348 | 6.58±1.13 | 194±22 | 8.23±1.13 | 178 | 8.13 | 115 | 182 | 58 | 355 | 179±27 | 8.14±1.19 | 113±23 | 185±36 | 59±9 | 357±64 |
| NCP2 | 59 | 6.91±1.13 | 213±30 | 8.67±0.95 | 177 | 8.37 | 111 | 176 | 55 | 342 | 185±33 | 7.59±1.12 | 129±30 | 208±45 | 62±9 | 399±80 |
| NW1 | 100 | 6.30±1.06 | 190±34 | 8.35±1.03 | 181 | 8.13 | 117 | 185 | 59 | 360 | 180±44 | 8.13±1.12 | 115±29 | 184±45 | 59±9 | 357±77 |
| NW2 | 309 | 8.12±1.83 | 190±20 | 10.53±1.71 | 176 | 10.38 | 89 | 141 | 47 | 277 | 182±34 | 10.48±1.82 | 91±25 | 148±37 | 48±9 | 288±68 |
| NW3 | 7 | 7.23±1.74 | 221±9 | 10.33±1.59 | 219 | 9.83 | 118 | 185 | 46 | 349 | 215±16 | 9.85±1.56 | 116±20 | 185±30 | 46±7 | 347±57 |
| SW1 | 78 | 5.70±1.30 | 217±22 | 7.63±1.20 | 174 | 7.46 | 123 | 194 | 63 | 379 | 191±39 | 7.56±1.19 | 134±34 | 214±53 | 63±11 | 412±93 |
| SW2 | 368 | 5.59±1.13 | 195±22 | 7.72±1.18 | 183 | 7.71 | 125 | 197 | 66 | 387 | 184±38 | 7.77±1.26 | 125±33 | 202±52 | 67±12 | 394±92 |
| SW3 | 60 | 6.00±1.09 | 207±25 | 8.29±1.33 | 186 | 8.10 | 121 | 191 | 65 | 376 | 191±37 | 8.38±1.33 | 120±28 | 192±44 | 65±11 | 376±78 |
| National c | - | 6.60 | 187 | 8.69 | 174 | 8.56 | 108 | 171 | 56 | 334 | 178 | 8.55 | 109 | 185 | 57 | 343 |
a
n: number of observations.
b
Mean ± SD.
c
National values are computed from the regional values weighted by area. The regional weights are as follows:
NE1, 4.5%; NE2, 14.9%; NE3, 4.7%; NE4, 6.4%; NCP1, 25.6%; NCP2, 6.0%; NW1, 10.4%; NW2, 7.3%; NW3, 2.6%; SW1, 3.5%; SW2, 7.9%; SW3, 6.2%.