Land use change and organic matter storage and composition in an arid soil of Argentina.

VAZQUEZ, C.; IRIARTE A.; ROMERO C.M.; MERLO C.; LUCINI E.; KOWALJOW, E.; MERILES J.M.

Congreso; Synergy in Science: Partnering for Solutions.; 2015

Soil organic matter (SOM) storage and composition in woody ecosystems may change asresult of long-term grazing and soil cultivation, particularly in arid environmentscharacterized by a high risk of desertification. The impact of land use change on the storage(0-20 cm) of total organic matter (TOM), humic substances (HS), humic acids (HA), andfulvics acids (FA) were studied in a Mollic Ustifluvent soil within three productive sites,total-and selective-clearings with livestock (TC-livestock and SC-livestock), total clearingwith irrigated agriculture (TC-agriculture), and an undisturbed site (CR) located in theChaco region of central-western Argentina. Total organic matter content was higher in CRand TC-agriculture relative to livestock clearing (TC and SC) sites. The concentrations ofHS, HA, and FA were all reduced substantially (50-75%) by land use change (i.e.conversion of native woodlands to livestock systems). The type of clearing (TC and SC)did not affect HS concentration among livestock systems. Humic substance composition,assessed by Fourier Transform Infrared Spectroscopy (FT-IR) and UV-VIS (E4/E6), wasaffected by land use and management. A pronounced peak (aliphatic C-H stretching) wasreported in TC-livestock, which doubled the intensity founded for the remaining sites. Theband 1268-1279 cm-1, attributed to phenols, was only detected in livestock clearing sites.Polysaccharides (C-O stretching, 1032-1023 cm-1 band) was 3.0 times higher in TCagriculturethan in TC-livestock. Low values were obtained for the E4/E6 ratio in CR,indicating a relatively high degree of condensation of aromatic substances in undisturbedsoils. It would appear that, a) the conversion of native woodlands to livestock systemsfavors soil C losses, b) higher SOM storage observed in TC-agriculture may reflect greaterresidue accumulation at the soil surface. It is also concluded that FT-IR is a sensitivemethod to evaluate how management practices affect the storage and chemicalcharacteristics of HS.