Carbon enrichment in particulate matter is affected by the interaction between soil type and management

LAURA ANTONELA ITURRI; ROGER FUNK; MARTIN LEUE; MICHAEL SOMMER; DANIEL EDUARDO BUSCHIAZZO

Simposio; Blowing South: Southern Hemiphere Dust Symposium; 2021

Coarse textured soils, with low soil organic carbon (SOC) content, like those of the Pampas, are prone to beeroded by the wind. It is known that wind erosion of these soils, which largely depends on managementpractices and climatic conditions, can modify the physico-chemical composition of the uppermost layer.Little is known on how such changes may affect the composition and enrichment of the particulate matter(PM). Because of this, three soils of the Pampas, spanning from sandy- to sandy loam texture, and with low-(LC), medium-(MC) and high (HC) cultivation intensities, were sampled in two consecutive 10-yearperiods: a more humid and a dryer than the normal for the region. For each soil and in all dates, PM wasseparated by a sorption-based laboratory procedure. Samples were investigated for granulometry, organic Cand mineral (Si-O of quartz and O-H of clay minerals) and organic (C-H of aliphatics, C=O of carboxylicacids, aldehydes, amides and aromatics, and C-O-C of polysaccharides) functional groups. Results show thatPM composition does not differ between soils. This can be explained by the frequent turnover of theuppermost layer due to tillage, constituting a reload of new particles. However, C enrichment of PM of LCand HC, mainly associated with that of C-H groups of plant debris and C-O-C of polysaccharides ofmicrobial origin, was higher than in MC. This can be explained by the dominance of quartz sand grains,side-by-side arranged with fresh and loose organic matter in LC, that determine the ease with which finesized clay and silt and low-density fresh debris, accumulated in PM. The accumulation of C in PM of HCwas related to its presence in polysaccharides as part of fine-sized microaggregates. The better aggregationof MC may explain why C accumulated in lower proportion in its PM. With time and in all sites, PMimpoverished in C and enriched in clay, as shown by the increase in the clay+silt/C ratio. This was explainedby SOC impoverishment after the dryer period, which was related to the decrease of the labile C-H groups,probably caused by the low residue input followed by its rapid oxidation during the dryer phase. LCimpoverished the most, probably due to its low SOC stock mainly composed by C-H groups. The clayenrichment in PM was probably a consequence of the deterioration of soil structure due to frequent tillage.In MC and HC, clay accumulation in PM was significant only when frequent tillage operations wereperformed during the dryer phase. In LC, clay enrichment occurred even during the moister period, and maybe explained by the worse physical conditions of this soil. However, PM of LC and HC prevailed as themost C enriched ones along the time, according to its composition rich in C-H and C-O-C groups easilytransported by the wind. The decrease with time of the proportion of C in PM would affect its distribution inthe ecosystem.