Table 3. Effect of long-term N fertilization on soil properties.
| pH | TNa (g kg-1) | NO3- N (mg kg-1) | NH4+ N (mg kg-1) | SOCa (g kg-1) | C:N | |
|---|---|---|---|---|---|---|
| Wheat season | ||||||
| Control | 8.12 ± 0.017 ab | 1.19 ± 0.013 c | 5.86 ± 0.87 b | 3.22 ± 0.64 a | 20.57 ± 0.55 b | 17.35 ± a 0.37 a |
| Low-N | 8.00 ± 0.018 b | 1.28 ± 0.019 b | 11.07 ± 1.37 ab | 2.81 ± 0.33 a | 22.11 ± 0.18 a | 17.32 ± a 0.16 a |
| High-N | 7.91 ± 0.016 c | 1.32 ± 0.015 a | 19.86 ± 5.08 a | 2.69 ± 0.06 a | 21.97 ± 0.20 a | 16.69 ± a 0.24 a |
| Source of variation | ||||||
| df | 2 | 2 | 2 | 2 | 2 | 2 |
| SS | 0.08 | 0.03 | 400 | 0.60 | 5.70 | 1.48 |
| F | 26.22 | 33.49 | 6.01 | 0.33 | 12.97 | 2.12 |
| P | ≤ 0.001 | ≤ 0.001 | ≤ 0.05 | 0.68 | ≤ 0.01 | 0.20 |
| Maize season | ||||||
| Control | 7.96 ± 0.028 a | 1.15 ± 0.016 b | 3.06 ± 0.37 b | 1.54 ± 0.23 a | 18.53 ± 0.45 b | 16.43 ± a 0.18 a |
| Low-N | 7.79 ± 0.028 b | 1.24 ± 0.024 a | 14.65 ± 1.13 a | 1.79 ± 0.50 a | 20.28 ± 0.57 a | 16.38 ± a 0.26 a |
| High-N | 7.80 ± 0.006 b | 1.27 ±0.016 a | 14.87 ± 1.06 a | 1.29 ± 0.12 a | 20.73 ±0.32 a | 16.33 ± a 0.08 a |
| Source of variation | ||||||
| df | 2 | 2 | 2 | 2 | 2 | 2 |
| SS | 0.07 | 0.03 | 364 | 0.49 | 10.75 | 0.02 |
| F | 29.78 | 9.28 | 40.87 | 0.65 | 8.69 | 0.07 |
| P | ≤ 0.001 | ≤ 0.01 | ≤ 0.001 | 0.44 | ≤ 0.01 | 0.93 |
Data are the means ± standard error (n = 4).
a TN = total nitrogen, SOC = soil organic carbon.
b Different letters in a column indicate significant differences among treatments at P ≤ 0.05 as determined by fisher’s least significant difference (LSD). Control (No N added), Low (182 kg ha-1 of N), and High additions (225 kg ha-1 of N) in each crop season.