Table 5. Nitrate, sulfur and sulfate concentrations in winter forage rape and perennial ryegrass and potential methane reduction from nitrate and sulfate.
| Measures | Forage rape | Perennial ryegrass | P b |
|---|---|---|---|
| (n = 4) a | (n = 4) | ||
| Period 1 | |||
| Total N (mol/kg) | 2.52 ±0.061 | 2.11 ±0.021 | <0.001 |
| Nitrate-N (mmol/kg) | 135 ±26.0 | 13 ±3.0 | 0.004 |
| Total sulfur (mol/kg) | 0.15 ±0.010 | 0.10 ±0.001 | 0.003 |
| Sulfate (mmol S/kg) | 63 ±6.9 | 39 ±0.9 | 0.015 |
| CH4 (g/kg DM intake) | 13.6 | 19.5 | |
| CH4 difference (g/kg DM intake) compared to perennial ryegrass | −5.9 | ||
| Potential maximum CH4 difference (g/kg DM intake) from nitrate c | 2.0 | ||
| Potential maximum CH4 difference (g/kg DM intake) from sulfate c | 0.4 | ||
| Unexplained CH4 difference (g/kg DM intake) | −3.5 | ||
| Period 2 | |||
| Nitrogen (mol N/kg) | 1.77 ±0.034 | 1.77 ±0.018 | 1.000 |
| Nitrate (mmol N/kg) | <7.1d | 15 ±2.4 | 0.004 |
| Total sulfur (mol S/kg) | 0.10 ±0.002 | 0.09 ±0.001 | 0.004 |
| Sulfate (mmol S/kg) | 28 ±1.3 | 34 ±0.8 | 0.011 |
| CH4 (g/kg DM intake) | 17.8 | 22.9 | |
| CH4 difference (g/kg DM intake) compared to perennial ryegrass | −5.1 | ||
| Potential maximum CH4 difference (g/kg DM intake) from nitrate c , d | −0.1 | ||
| Potential maximum CH4 difference (g/kg DM intake) from sulfate c | −0.1 | ||
| Unexplained CH4 difference (g/kg DM intake) | −5.3 |
a The number of field replicates of forage samples. Values are means ± SEM.
b P value for the difference between forage rape and perennial ryegrass.
c The reduction of 1 mol nitrate or 1 mol sulfate uses 4 mol H2, which decreases methane formation by 1 mol [19].
d Detection limit for nitrate was 7.1 mmol/kg (100 mg N/kg). For the calculations of CH4 reductions and P values, it was assumed that nitrate-N was 7.0 mmol/kg.