Air permeability and diffusivity of an Andisol subsoil as influenced by pasture improvement strategies

Abstract

In southern Chile, grazing systems over volcanic ash soils play an important role for the development of the region. The productivity of these grazing systems should be improved by Pasture Improvement Strategies (PIMs), which in the case of the present study were established 5 years before this analysis. Often topsoil properties were measured while those for describing the functioning of the pore system (e.g., air permeability) in the subsoil (> 0.45 m) are missing. For subsoil samples, these parameters were determined to compare the long-term effect of three PIMs (i.e., NFNP: not-fertilized and not-ploughed, FNP: fertilized but not-ploughed or fertilized and CP: ploughed). Two depth intervals (D1: 0.45 - 0.55 m, D2: 0.55 - 0.65 m) within the same subsoil horizon of a Duric Hapludand were considered. Results show that the subsoil was influenced by tillage. The transformation to an improved pore system was e.g. indicated by increased means of pore indices (C3 ) for FNP (123.5%) and CP (46%) as compared to NFNP for D1 (Ψm = -6 kPa). The soil air diffusivity values in these subsoil samples were in a range comparable to those reported for non-volcanic but sandy soils in Europe and were generally larger in D2 than in D1. We concluded that soil properties were still in transition to a new equilibrium. Thus, measurements of subsoil properties should be repeated in time intervals to better understand gas transport processes in cultivated Chilean soils that origin from volcanic ash.