Deforestation and current management practices reduce soil organic carbon in the semi-arid Chaco, Argentina

BALDASSINI, PABLO; PARUELO, JOSÉ MARÍA

AGRICULTURAL SYSTEMS

ELSEVIER SCI LTD

Año: 2020 vol. 178

0308-521X

The soil is a fundamental component of the C cycle. Land use changes can alter the soil organic carbon (SOC)content, a key determinant of several regulation ecosystem services. Here, we analyzed the effects of land cover(e.g. from forest to cropland) and land use (i.e. management practices) change on SOC in the semi-arid Chaco ofArgentina, a global deforestation hotspot. Using the CENTURY model, we analyzed SOC changes over 20 yearsfor two sites with contrasting rainfall (600 and 800 mm). For each site, we evaluated the effect of differentcombination of management practices (e.g. fertilization, grazing intensity) and land uses (i.e. annual crops andsown pastures). 98.5% of the simulations performed for cropping systems showed a reduction in SOC, with anaverage reduction of 25% respect to the native forest. Wheat proportion in the crop rotation had the highestrelative influence on SOC variation (54%), higher than the proportion of maize (26.4%) and nitrogen fertilization (9.8%). For sown pastures, < 40% of the simulations showed SOC decreases up to 18%. Grazing intensityhad the greatest relative influence on SOC variation in both sites (> 60%), followed by burning (19%), temporary exclusion of cattle (12%) and nitrogen fertilization (4.3%). In most cases SOC changes were mainlyexplained by changes in C inputs (i.e. NPP) rather than by changes in outputs (i.e. respiration and erosion).Therefore, delta SOC showed a strong negative relationship with the Human Appropriation of NPP (R2 = 0.54and 0.67 in cropping systems and pastures, respectively). Overall, our results suggest that land use change hasnegative effects on SOC regardless of the management practices implemented. The few combinations that balanced food production and carbon sequestration were maize monocultures with annual N fertilization, andcattle raising with temporary exclusion and burning suppression. Our results may be used to define managementpractices that allow maintaining soil carbon stocks in the upper soil layer.