Abstract
Deforestation of Chacoan native forests and reorientation of land use are transforming the region into agricultural use. The main purpose of this work was to evaluate the impact of different land uses on soil quality in the semi-arid Chaco (Argentina). We assessed the behaviour of soil parameters over four years of experimental conditions: 1) Exclosure pasture (EP) used as reference level, 2) Grazed pasture (GP), 3) Grazed pasture transformed to agriculture with Zero tillage (ZT) and 4) Grazed pasture transformed to agriculture under Conventional tillage (CT). Soil organic carbon, particulate and heavy organic carbon (C), total nitrogen (N), C:N ratio, pH, electric conductivity and soil respiration were measured. Soil samples were taken yearly at 0-5, 5-20 and 20-40 cm of soil depth. Differences among treatments across time were assessed by Analysis of Covariance (ANCOVA) with time (years) as covariate factor, treatments as group factor and individual scores from Principal Component Analysis (PCA) as responses. Correlated changes in the soil characteristics were detected, especially at the top soil layer. Both carbon and nitrogen contents increased in both GP and ZT systems. An opposite trend was found for CT, which also had a negative impact on salinity. Both land use change and management practices in the Chaco region represent the main human activities that modify the landscape; thus, they should be analysed by recognizing heterogeneity on farming practices and identifying their impacts on a specific site. The results of this work reinforce the utility of soil organic carbon as a single parameter for monitoring land management systems, especially for monitoring large region like Chaco that are subject to continuous transformation processes.
Highlights
The major challenge of agricultural production consists of producing food, in terms of both quantity and quality, to support a continuously growing population
The first two principal components of the Principal Component Analysis (PCA) applied on the entire dataset captured 83.88% of total variance
We evaluate the imprint of different land uses on several physical-chemical indicators of soil quality, using for that purpose of long-term dataset spanning for 4 years
Summary
The major challenge of agricultural production consists of producing food, in terms of both quantity and quality, to support a continuously growing population. In recent years South America has experienced an increasing rate of deforestation (Volante et al 2012), especially in the following ecoregions: the Brazilian Cerrado (Mendes Malhado et al 2010), the Chiquitano Forests in Bolivia (Müller et al 2012) and the Gran Chaco in Bolivia, Paraguay and Argentina (Gasparri and Grau 2009). In the Gran Chaco ecoregion large areas of forests were transformed into agricultural land (Hansen et al 2013). These land-use changes are poorly understood, they are likely globally significant. The South American Chaco has recently emerged as a spot of agricultural expansion and intensification, as cattle ranching expands into forests, and later agriculture replaces grazing land (Baumann et al 2017)
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