Soil water availability improved by site preparation in a Pinus halepensis afforestation under semiarid climate

Abstract

An afforestation experiment with the drought resistant species Pinus halepensis Miller was conducted in a degraded semiarid rangeland of southeastern Spain to evaluate the influence of site preparation on soil moisture and seedling performance. Three different land preparation treatments were tested: manual terracing, mechanical terracing and mechanical terracing with organic amendment addition. Mechanical terracing (+/− organic amendment) always included subsoiling. Soil moisture to a depth of 1 m was monitored by the neutron scattering method during a 28-month-period. The study revealed significant differences among land treatments with respect to soil moisture content and water uptake by the seedlings. Mechanical terracing increased soil water storage up to 40% more effectively than manual terracing. Analysis of moisture depletion rates at different soil depths indicated that seedling access to the water stored into the deeper layers of the profile was constrained by high soil penetration resistance in the manual terraces. As a result of limited water availability, seedling survival after the dry summers of 1994 and 1995 was only 62% in this treatment (98% in the mechanical terraces). The addition of urban solid refuse (USR) further increased the water reserve in the mechanically terraced soils (up to 40%), due to enhanced water infiltration and diminished evaporation from the soil surface. Early root penetration to the deeper and wetter layers of the profile also contributed to increased water availability for the seedlings in the mechanical terraces+USR. Two years after planting, only the seedlings in this treatment were able to deplete homogeneously the moisture stored into the soil profile to a depth of 1 m.