Back to the future? Conservative grassland management can preserve soil health in the changing landscapes of Uruguay

Abstract

Abstract. The “soils of the Anthropocene” are predominately agricultural. To understand them, we analyzed agri- and silvicultural intensification of Uruguayan grasslands (GLs) in a country-wide survey on fertility proxies, pH and trace metals in topsoils originating from different land uses across the whole country. Thus, our results reflect interactions of both the natural diversity of Uruguayan soil formation and the impacts of land use change. We observed a loss of nutrients, trace metals and organic matter from GLs, croplands and timber plantations (TPs). As an example, the cation exchange capacity was 160 % higher in native forests (NFs) compared to GLs and lowest in TPs, reaching only half of the cation exchange capacity (CEC) in GLs. Acidification of topsoils continues as three-fourths of all samples are “extremely acidic” and “very strongly acidic”. Topsoils of riverine forests accumulate more trace metals compared to the other uses. We assume an accumulation in the topsoils of riverine forests, where high levels of nutrients, trace metals and organic carbon (OC) are found. The translocation of nutrients and organic matter across the landscape to the erosion base depends on local land use trajectories. Increasing soil acidification is driving a positive feedback loop, and land use intensification has lead to degradation of local black soils within a few decades. Our data raise questions about the resilience and carrying capacity of Uruguayan soils with regard to currently implemented highly productive management forms, including the use of TPs for carbon sequestration, and supports more conservative forms of extensive management on the GL biome.