Impact of the Repeated Tractor Passes on Some Physical Properties of Silty Loam Soil

Soil compaction caused by machinery traffic in agriculture is a well recognised problem in many parts of the world as one of the most important factor responsible for soil physical degradation and has important consequences on crop production and environment (Soane and van Ouwerkerk, 1994; Keller and Arvidsson, 2004). It is estimated to be responsible for the degradation of an area of 68 million hectares worldwide (Flowers and Lal, 1998), of which 33 million hectares were located in Europe (van den Akker and Canarache, 2001). Soil physical properties represent a group of properties having a substantial impact on the different physical-chemical and biological processes in soil and hence they should be kept optimal (Lal, 1991). Soil compaction induced by vehicle traffic has adverse effects on a number of key soil propreties such as bulk density, mechanical impedance, porosity and hydraulic conductivity (Radford et al., 2000; Hamza and Anderson, 2005). It may decrease soil porosity and change pore shape and size distribution (Pagliai et al., 2003), decrease aeration (Czyz et al., 2001), decrease water infiltration and increase preferential flow (Kulli et al., 2003), including increase surface runoff resulting in soil erosion (Feige and Horn, 2000). From a management point of view, it is useful to identify the process responsible for changes in soil physical properties so that farming systems and practices can be adopted to either ameliorate, avoid or minimise soil compaction problems and reduce the subsequent risk of poor agronomic performance (Chan et al., 2006). Trends in machinery development over the last few decades, introducing machines of a greater size and weight, have increased the problems of finding tyres and inflation pressures, capable of keeping soil compaction low (Pagliai et al., 2003). In order to reduce the ISSN 1330-7142 UDK = 631.372 : 631.482’511