Effects of climate and land-use on physicochemical properties of gneiss-derived soils in tropical drylands: Evidence from northeastern Brazil

Abstract

Gneisses are rocks formed by metamorphism and their resistance to weathering plays an important role in the physical and chemical properties of soils in tropical drylands. In this study, we evaluated the effects of climate including semi-arid, dry sub-humid, wet sub-humid, and humid, and land-use encompassing forest restoration, agriculture, and pasture and their interactions on the physical and chemical properties of the surface horizon of fifty-five soil profiles originating from gneiss saprolite in the tropical drylands of northeastern Brazil. Our results have shown that climatic extremes such as semi-arid and humid climates contributed to the formation of soils with low nutrient availability, notably Ca2+ (2.1–3.4 cmolc kg−1), Mg2+ (1.4–1.5 cmolc kg−1) and P (3.5–6.3 mg kg−1). In general, the drier ecosystems presented, on average, 63.5% and 51.7% less C and N, respectively, than wetter ecosystems. In contrast, soils in a more humid climate had, on average, 56.0% and 39.6% more silt and clay, respectively, than those in the semi-arid climate. The land-use analysis indicated that soils under pasture had, on average, 32.2%, 24.2%, 66.6%, 40.4%, and 35.8% less Ca2+, Mg2+, K+, C, and N, respectively, than soils under agricultural cultivation. Overall, both agriculture (4.8 mg P kg−1) and pasture (5.0 mg P kg−1) on average, reduced the available P content of soils by 75% when compared to soils under forest (19.7 mg P kg−1). The interaction between climate and land-use indicated that regardless of the climatic conditions, pastures intensified soil degradation, showing a reduced correlation with properties related to soil fertility. For all climatic conditions, extensive pastures should be carried out considering the animal stocking rate supported by natural vegetation to reduce the risk of environmental degradation. We concluded that the interaction between a semi-arid climate and extensive pasture represents the condition of the highest level of degradation in the physicochemical properties of gneiss-derived soils in tropical drylands.