Nitrogen mineralization controlled by N/P ratio of plant residues from riparian buffer strip

•We identified the relationship between N mineralization and chemical composition of residues from riparian buffer strip.•N/P ratio was better than lignin content and lignin content was better than N content in controlling N mineralization.•The critical levels were calculated for N, LG, LG+CE contents, and N/P, C/N, LG/N, CE/N and (LG+CE)/N ratios of residues.•N/P ratio in riparian plant residues could be the most important influencing factor on soil inorganic N dynamics.

Soil nitrogen (N) transformation rates are mostly likely related to chemical composition and element ratio of plant residues while contradictory results are also reported. We conducted a laboratory incubation experiment for 100 days under controlled conditions (25 °C and 50% water holding capacity) to investigate the relationship between N mineralization and initial chemical characteristics of 11 diverse plant residues from riparian buffer strip of Danjiangkou Reservoir. The plant residues had a wide range of N, cellulose (CE), hemicellulose (HC) and lignin (LG) contents, and carbon/N (C/N), N/phosphorus (N/P), LG/N and CE/N ratios. A principal component analysis (PCA) showed that the mean N content of the residues was negatively associated with LG and LG + CE contents and LG content was highly positive correlated with C/N and CE/N ratios. Net N mineralization ranged widely (5.1–120.3 mg N kg−1 soil) and was highly correlated with plant N content (r2 = 0.71, P < 0.01), LG content (r2 = 0.72, P < 0.001) and N/P ratio (r2 = 0.76, P < 0.001). The critical levels, i.e. the break point between net N mineralization and net N immobilization were 9.4 g kg−1 for N content, 212.9 g kg−1 for LG content, 343.3 g kg−1 for LG + CE content, 4.1 for N/P ratio, 43.8 for C/N ratio, 16.5 for LG/N ratio, 19.9 for CE/N ratio and 34.6 for (LG + CE)/N ratio of the plant residues, respectively. A multiple regression model demonstrates N/P ratio of the plant residues to be the most important factor for predication of the net effects of plant residue on soil mineral N dynamics.