Fig. 2: Effects of long-term nitrogen fertilization on carbon pools across four field experiments, with results categorized into C-poor and C-rich soils from four sites.
From: Soil organic carbon thresholds control fertilizer effects on carbon accrual in croplands worldwide
a, c Effects of N fertilization on POC and MAOC across four field experiments. Asterisk indicate a statistical significance of the effect based on non-parametric Wilcoxon test (P < 0.05) using the Benjamini and Hochberg (BH) method (n = 4 for N0, n = 8 for N). b, d Effects of N fertilization on POC and MAOC in both C-poor and rich soils. The estimated effect sizes are regression coefficients based on rescaled response variables (with zero mean and unit standard deviation) in the linear mixed-effects model. The points and shades represent mean ± s.e.m. of effect sizes in B and D. Statistical significance is based on Wald type II χ² tests, and 95% CI not overlapping zero indicated significant. POC: particulate organic carbon; MAOC: mineral-associated organic carbon. N0: control (No N addition); N: N addition (results of combining optimized N addition and high N addition). C-poor: combining QZ and CW results; C-rich: combining SP and YA results. Source data are provided as a Source Data file.
