Net Nitrogen Mineralization or Immobilization Potential in a Residue-Amended Calcareous Soil

Abstract

Developing more sustainable agricultural systems that are less dependent on external inputs such as inorganic nitrogen (N) fertilizer that may affect environmental quality requires alternative N sources such as plant residues. However, to be effective it is important to screen plant material for their potential to mineralize N during the decomposition. The objective of this study was to establish statistical relationships between the fate of N from 14 diverse plant residues during an 8-week incubation in a calcareous soil at 25°C and 50% water holding capacity. The residues had a wide range of N, cellulose, hemicellulose, and lignin concentrations and C:N ratios. The N content of the residues was negatively associated with C:N ratio(r = − 0.83, P < 0.001), cellulose (r = − 0.69, P < 0.01), hemicellulose (r = − 0.59, P < 0.05), and lignin:N (r = − 0.67, P < 0.01). Net N mineralization or immobilization (Nm/i) ranged widely (−59.7 to 622.2 mg N kg−1) and significantly correlated with N concentration (r = 0.96, P < 0.001), C:N (r = − 0.69, P < 0.01), and lignin:N ratio (r = − 0.68, P < 0.01) of the plant residues. The critical levels of N concentration, C:N ratio, and lignin:N ratio of the plant residues at which neither N mineralization nor immobilization would occur were 11.0 g kg−1, 45, and 6.5, respectively. Nitrogen concentration of the plant residue was the most important factor for prediction of the net effects of plant residue on soil mineral N dynamics.