Journal of Agricultural Science; Vol. 8, No. 6; 2016 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 120 Soil Physical Quality of Brazilian Crop Management Systems Evaluated with Aid of Penetrometer Daniel Gonçalves Gomes Junior 1 , Rubismar Stolf 1 , José Geanini Peres 1 , Victor Meriguetti Pinto 2 & Klaus Reichardt 2 1 Department of Natural Resource and Environmental Protection, Federal University of São Carlos, Araras, SP, Brazil 2 Soil Physics Laboratory, University of São Paulo, Center for Nuclear Energy in Agriculture, Piracicaba, SP, Brazil Correspondence: Klaus Reichardt, Soil Physics Laboratory, University of São Paulo, Center for Nuclear Energy in Agriculture, P.O. Box 96, Piracicaba, SP 13416-970, Brazil. Tel: 55-193-429-4712. E-mail: klaus@cena.usp.br Received: March 24, 2016 Accepted: April 29, 2016 Online Published: May 15, 2016 doi:10.5539/jas.v8n6p120 URL: http://dx.doi.org/10.5539/jas.v8n6p120 Abstract Crop management affects soil attributes as well as its quality. We evaluated the following soil physical attributes: saturated hydraulic conductivity (K 0 ), soil resistance (RP) and soil bulk density (BD), in Araras-SP, Brazil. Areas with sugarcane (Saccharum officinarum), soybean (Glycine max), physic nut (Jatropha curcas L.) and native forest presented an increase of soil compaction in the 0.10 m surface layer for the three attributes in a following order: native forest <physic nut < soybean < sugarcane. Significant regressions were obtained for RP × K 0 ; BD × K 0 and BD × RP. Penetrometer measurements were essential to indicate differences among areassugarcane, native forest, physic nut and soybean; but for the measurements of K 0 , only between sugarcane and native forest. RP measurements confirm anthropogenic changes in the soil profile up to the 0.3 m depth. In the “Canarache soil resistance classification” soils showed “low resistance” “without limitations to root development” for native forest and physic nut; “medium resistance” for soybean area with “some limitations to root development” and “high resistance” for sugarcane with “limitations to root development”. The use of penetrometers is discussed in relation to the readiness of field measurements. Keywords: saturated hydraulic conductivity, soil compaction, impact penetrometer 1. Introduction Intensive crop use can lead to soil degradation also affecting soil physical attributes. One of the soil parameters used as an indicative of physical soil quality is the saturated hydraulic conductivity (K 0 ). Considering that water and air flow better in pores of larger diameter, the parameters K 0 and the macroporosity (MP) can be taken as indicators of soil compaction. External pressures applied to soils, coming from management practices reduce preferentially larger pores. In this way, low values of MP imply low values of K 0 , low soil aeration and an increase of soil resistance to penetration (RP) of roots (Stolf, Thurler, Bacchi, & Reichardt, 2011; Mollinedo et al., 2015). Additionally to the importance of K 0 in the evaluation of soil compaction, RP has also been correlated with other soil physical parameters (Marques, Texeira, Reis, Junior, & Martins, 2008; Ramos et al., 2011; Mollinedo et al., 2016). K 0 is also essential in the description of water movement in soils, like the processes of infiltration, drainage, fertilizer losses, erosion, and leaching of chemicals (Warrick, 2002; Mesquita & Moraes, 2004). RP for the evaluation of the compaction status of a soil is one of the most employed practices because measurements are carried out directly in the field, without the need of a laboratory backup. Measurements are fast, approximately 1 min to sample a profile down to 0.50 m (Stolf, Murakami, Maniero, Silva, & Soares, 2012). Therefore, a large number of studies are found in the literature comparing native forest, orchards and other agro-forestry systems of low machinery impact, with agricultural systems (Martins et al., 2010; Portugal et al., 2010; Cardoso, Silva, Cury, Ferreira, & França, 2011; Iarema, Fonte, Fernandes, Shaefer, & Pereira, 2011; Ramos et al., 2011; Silva et al., 2011). Penetrometers have also been used in pastures (Ramos et al., 2010; Silva Filho, Cottas, & Marini, 2010; Cardoso et al., 2011; Castagnara et al., 2012; Moura, Marasca, Meneses, Pires, & Medeiros, 2012) and in crops with intense traffic of machinery as in areas of sugarcane and soybean (Machado et al., 2010; Debiasi & Franchini, 2012; Ecco, Carvalho, & Ferrari, 2012; Silva, Nunes, Caldeira, Arantes, & Souza,