Fig. 1: Sample origin and relationship between emission factors (EFs) and soil pH and nitrogen (N) fertilization rates.
From: Intermediate soil acidification induces highest nitrous oxide emissions
Geographic locations of sites included in the meta-analysis (a). Relationships between soil pH and coarse EFs (b) or averaged EFs (c), and the relationship between N fertilization rates and coarse EFs (d). A second-order polynomial fit described the hump-shaped relationship between pH and EFs (b, EF = −0.0913pH2 + 1.030 pH−1.826) or averaged EFs at each pH incremental (c, EF = −0.1000 pH 2 + 1.198 pH−2.537), which reached its maximum at pH = 5.6 (b) or 6.0 (c), respectively. Linear regression model with two-sided test was used for the statistical analysis (n = 3562 in b; n = 58 in c; n = 3786 in d). The error bands (shaded areas) in (b and c) represent the 95% confidence intervals around the best-fit regression line, and the blue dashed line in (d) indicates an insignificant relationship. Statistics (adjusted R2 and P-values) for polynomial regression are indicated. The exact P-values: P < 0.001 in (b and c). Source data are provided as a Source Data file.
