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

Abstract

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.