Soil physical quality of Luvisols under agroforestry, natural vegetation and conventional crop management systems in the Brazilian semi-arid region

The imposition of agricultural systems changes the natural equilibrium of the soil to an extent that it becomes dependant on management practices and soil resilience. Agroforestry systems (AFs) mimic characteristics of natural ecosystems such as multistrata canopy and deep rooting and may minimize the consequences of these changes by providing soil protection and maintenance of conditions similar to those under natural vegetation. This study evaluates the physical properties of a Luvisol at a site where since 1997 alternative agro-forestry systems (AFs) (agrosilvipasture-AGP and silvipasture-SILV), conventional crop management (CCM) and natural vegetation (NV) have been maintained. Undisturbed soil cores were collected in 2005 and submitted to a range of matric suction for which soil bulk density (BD), soil penetration resistance (Q) and soil water content (theta) were determined. Water retention and penetration resistance were used to determine the least limiting water range (LLWR) and the slope of the soil water retention curve at its inflection point (S-value). Particle size, total organic carbon (TOC) and particle density were determined using the disturbed soil samples. Water retention and porosity followed the sequence NV>SILV>CCM>AGP. The AFs studied (AGP and SILV) improved or maintained soil physical quality when compared to NV with no significant differences between the S-values of 0.044, 0.042 and 0.050, respectively. However, the S-value of 0.035 for CCM indicates that this management was unable to maintain soil physical quality on the same levels as AFs and NV. The decrease of LLWR with BD occurred for all treatments, and the BD at a maximum effect (LLWR=0) which is called the critical BD (BDc), was, respectively, 1.69, 1.62, 1.56 and 1.56 Mg m(-3) for AGP, SILV, NV and CCM. The larger values of LLWR for AFs (AGP and SILV) are similar to the value for NV, with associated superior aeration, matric suction and reduced resistance to penetration by roots. Indices such as LLWR and S-value were suitably sensitive and could be used in future research, but it is important to identify other potential indices for these situations that can show how quickly changes in soil quality may occur. (C) 2011 Elsevier B.V. All rights reserved.