Nitrogen mineralization of roots of maize and selected woody species

A laboratory experiment was carried out to assess nitrogen (N) mineralization of roots of four woody agroforestry species (Dactyladenia barteri, Senna siamea, Gliricidia sepium, and Leucaena leucocephala) and maize (Zea mays). Addition of Gliricidia and Leucaena roots with high N contents and low carbon (C)-to-N ratio (less than or equal to 14.0) resulted in net N mineralization, while the addition of maize roots with low N and high C-to-N ratio (40.3) immobilized N. Addition of Dactyladenia and Senna roots with intermediate N content and C-to-N ratio immobilized N to a lesser extent. Nitrogen mineralization was negatively and significantly correlated with C-to-N ratio of the added roots. Addition of roots of the five species also differentially affected soil pH during the first 12 weeks of incubation. Soil pH was positively and significantly correlated with the roots initial C-to-N ratio and negatively correlated with their initial N content. At 24 weeks of incubation, the pH of all treatments reverted to initial value.