Legume N mineralization: Effect of aeration and size distribution of water-filled pores

Abstract The relative importance of air-filled porosity and the size distribution of water-filled pores to the mineralization of legume N and soil N were assessed. Seven soils, with or without added legume, were packed to two relative bulk densities and incubated at a constant water potential. Mineralization was measured over 70 d. The accumulation of inorganic N in the amended treatment was described using a two-pool model and in the control using a one-pool model. Biomass C was measured in both treatments. Mineralization was found to be influenced by both the air-filled porosity and the distribution of the volume fractions of pores (VFP) that were water-filled and the relative importance of each was assessed using stepwise variable-selection regression procedures. The parabolic dependence of mineralization on air-filled porosity that has been observed when soils are incubated at different potentials was not obvious in soils equilibrated at a constant potential. Air-filled porosity was positively related to the rate constant of the labile pool and negatively related to the size of the resistant pool in the amended treatment. The rate constant of the control was parabolically related to air-filled porosity, but did not give rise to a predicted maximum in N accumulation within the experimental range of air-filled porosities. The VFP with dia