Tillage impacts on soil biological activity and aggregation in a Brazilian Cerrado Oxisol V.S. Green a,1 , D.E. Stott b, * , J.C. Cruz c , N. Curi d a Department of Agronomy, Purdue University, 915 West State Street, West Lafayette, IN 47907-2054, USA b United States Department of Agriculture, Agricultural Research Service, National Soil Erosion Research Laboratory, 275 S. Russell Street, West Lafayette, IN 47907-2077, USA c Empresa Brasileira de Pesquisa Agropecuaria, Embrapa Centro Nacional de Pesquisa de Milho e Sorgo, Rod MG424, km 65, CP 151, 35701-970 Sete Lagoas MG, Brazil d Departamento de Cie ˆncia do Solo, Universidade Federal de Lavras, Caixa Postal 37, 37200-000 Lavras MG, Brazil Received 18 June 2004; received in revised form 20 January 2006; accepted 27 January 2006 Abstract Mechanized agriculture is increasing rapidly in the Cerrado region of Brazil, causing concerns about water quality, off-site impacts, and sustainability. Our objective was to determine the impact of tillage on soil biological activity and aggregate stability in an Oxisol typical to the region. Three different tillage practices common to the Cerrado region (no-till, disk harrow, and disk plow) and an area under native vegetation were examined. Five different soil enzyme activities, C- and N-mineralization, organic C, total N, and aggregate distribution were determined. Total N, acid phosphatase, arylamidase, and C- and N-mineralization were the most sensitive to changes in tillage management. For each of these analyses, the no-till system had greater concentrations or activities (18–186%) than disk plow in the 0–5 cm layer. Significant differences observed in the 0–5 cm depth did not necessarily translate into total profile differences to a depth of 30 cm. No-till had significantly greater levels of total N, and C- and N-mineralization (20– 127%) than the disk harrow system. Total N ranged from 1.8 to 2.2 kg m 3 ; C- and N-mineralization (24-day incubation) ranged from 2.8 to 6.8 and 0.04 to 0.10 kg m 3 , respectively, among tillage systems and soil depths. Enzyme activities in all treatments were more strongly correlated with total soil N than with soil organic C (SOC), contrary to the norm in temperate soils where the stronger correlation is with SOC. Mean weight diameter of water stable aggregates was related to SOC (r = 0.73) and total N (r = 0.92), indicating that soil organic matter does play a significant role in stabilizing aggregates in Oxisols. Results indicated the importance of reducing tillage as a means of increasing soil biological activity of the topsoil in the Cerrado region of Brazil. By understanding the effects of tillage on soil biological properties, management systems can be implemented that improve natural nutrient cycling processes and soil structure, resulting in increased agricultural sustainability of tropical ecosystems. Published by Elsevier B.V. Keywords: Biological activity; Aggregate stability; Oxisols; b-Glucosidase; Acid phosphatase; Arylamidase; Arylsulfatase; Fluorescein diacetate hydrolytic activity; Carbon mineralization; Nitrogen mineralization; Tillage; No-till 1. Introduction The Cerrado region covers >200 Mha in the heart of Brazil. Cerrado refers to the common savanna-like vegetation of low trees, scrub brush, and grasses. It is estimated that about 70% of the Cerrado is suitable for agriculture and this area is rapidly being converted to www.elsevier.com/locate/still Soil & Tillage Research 92 (2007) 114–121 * Corresponding author. Tel.: +1 765 494 8062; fax: +1 765 494 5948. E-mail address: destott@purdue.edu (D.E. Stott). 1 Present address: Arkansas State University, College of Agricul- ture, P.O. Box 1080, State University, AR 72467. 0167-1987/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.still.2006.01.004