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DIVISION S-6—SOIL & WATER MANAGEMENT & CONSERVATION

Soil Carbon and Nitrogen Organic Fractions in Degraded vs. Non-Degraded Mollisols in Argentina

^a Fellow Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Agrarias, Universidad Nacional de Mar del Plata, Instituto Nacional de Tecnología Agropecuaria (INTA), Unidad Integrada Balcarce, C.C. 276 (7620) Balcarce, Argentina
^b Current address: Department of Agronomy, Kansas State University, Manhattan, KS 66506-5501
^c Estación Experimental La Estanzuela, Instituto Nacional de Investigaciones Agropecuarias (INIA), Colonia, Uruguay
^d INPOFOS Cono Sur, PPI-PPIC, Av. Santa Fe 910, (1641) Acassuso, Buenos Aires, Argentina

^* Corresponding author (fgarcia{at}ppi-ppic.org).

The use of no-tillage has notably increased in the Pampas region of Argentina during the last 10 yr. Two tillage experiments with contrasting previous agricultural use, degraded and non-degraded soils, were evaluated in the southeast of Buenos Aires province, Argentina. The objectives were to: (i) quantify the effects of tillage and N fertilization on quantity and vertical distribution of C and N in the soil organic matter (SOM) and particulate organic matter (POM) fractions as well as potentially mineralizable N (PMN), and (ii) evaluate these fractions as indicators of soil quality. Tillage systems were conventional tillage (CT), minimum tillage (MT), and no-tillage (NT) (main plots), and N fertilization rates were 0, 120, and 150 kg ha^-1 (subplots). Total organic C (TOC), total N (TN), POM-C, POM-N, and PMN were measured at 0- to 7.5- and 7.5- to 15-cm soil depth. In Exp. I (degraded soil) TOC was greater under NT (27 g kg^-1) than under CT (24 g kg^-1) in the 0-N treatments. No differences in TOC and TN were found in Exp. II at 0 to 7.5 cm (non-degraded soil). Carbon in POM and POM-N were greater under NT in the fractions of 212 to 2000 and 53 to 212 µm at 0 to 7.5 cm, but they were similar or greater under CT at 7.5- to 15-cm depth in Exp. I. Stratification of TOC, TN, and POM were observed under NT in Exp. I. Potentially mineralizable N was greater under NT (62 mg kg^-1) in Exp. I, however, no differences in PMN were observed in Exp. II. Carbon in POM 212 to 2000 µm and PMN were the more sensitive indicators of tillage effects, mainly in Exp. I.

Abbreviations: CT, conventional tillage • MAOM, mineral-associated organic matter • MT, minimum tillage • NT, no-tillage • PMN, potentially mineralizable N • POM, particulate organic matter • SOM, soil organic matter • TN, total N • TOC, total organic C

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