Open Agriculture. 2017; 2: 317–328 Research Article Open Access Aitor García‐Tomillo*, Tomás de Figueiredo, Arlindo Almeida, João Rodrigues, Jorge Dafonte Dafonte, Antonio Paz‐González, João Nunes, Zulimar Hernandez Comparing effects of tillage treatments performed with animal traction on soil physical properties and soil electrical resistivity: preliminary experimental results DOI 10.1515/opag-2017-0036 in BD observed after tillage in the 0-0.05 m soil depth Received January 31, 2017; accepted April 12, 2017 increased after operations in all treatments. The increase was higher in the tractor sub-plot (15%) than in those where Abstract: Soil Compaction results from compressive animal traction was used (8%). Before operation Ks class forces applied to compressible soil by machinery wheels, was rapid and fast in all samples, and after operation this combined with tillage operations. Draft animal‐pulled value was reduced to 33% in T, whereas it reached 83% in equipment may also cause soil compaction, but a huge C. Electrical Resistivity Tomography (ERT) was useful as a gap exists on experimental data to adequately assess their tool to identify the alterations caused by tillage operations impacts and, actually, animal traction is an option seen on soil physical status. These preliminary results confirm with increasing potential to contribute to sustainable the potential of animal traction as an option for mountain agriculture, especially in mountain areas. This study was agri‐environments, yet it requires much wider research to conducted to assess the impacts on soil compaction of soundly ground its assets. tillage operations with motor tractor and draft animals. In a farm plot (Vale de Frades, NE Portugal) treatments Keywords: Animal traction, Soil compaction, Saturated were applied in sub‐plots (30 m x 3 m), consisting in a two hydraulic conductivity, Electrical Resistivity Tomography way tillage with tractor (T), a pair of cows (C) and a pair of donkeys (D). Undisturbed soil samples (120) were taken before and after operations for bulk density (BD) and saturated hydraulic conductivity (Ks). The relative changes 1 Introduction Soil structure degradation, often called soil compaction, *Corresponding author: Aitor García‐Tomillo, Centro de Investigaciones Científicas Avanzadas (CICA), grupo AQUASOL-Facultad de Ciencias, is regarded as one of the most serious form of land Universidad de La Coruña. Campus A Zapateira s/n 15008 A Coruña, degradation caused by conventional farming practices Spain, E-mail: [email protected] which negatively disturbs the soil physical status. Antonio Paz‐González, Centro de Investigaciones Científicas According to the European Environmental Agency Avanzadas (CICA), grupo AQUASOL-Facultad de Ciencias, (2012) compaction is one of the key threats affecting Universidad de La Coruña. Campus A Zapateira s/n 15008 A Coruña, soils. It occurs even in no-tillage systems because of Spain Tomás de Figueiredo, Arlindo Almeida, Centro de Investigação de the compressive forces applied to soil by tractor wheels Montanha (CIMO), Instituto Politécnico de Bragança (ESA/IPB), (Batey 2009). Compaction alters soil structure by crushing Campus de Santa Apolonia, 5300-253 Bragança, Portugal aggregates or combining them into larger units, increase Jorge Dafonte Dafonte, Departamento de Ingeniería Agroforestal, soil bulk density, and decrease the number of coarse Escuela Politécnica Superior de LugoUniversidade de Santiago de pores (Needham et al. 2004; Delgado et al. 2007). The Compostela, Campus de Lugo, 27002 Lugo, Spain problem is magnified because, being mainly a sub- João Rodrigues, João Nunes, Associação Portuguesa de Tracção Animal‐ APTRAN, Bragança, Portugal surface phenomenon, soil compaction is commonly Zulimar Hernandez, Grupo de Edafología, Departamento de considered as the type of land degradation most difficult Geología y Geoquímica, Facultad de Ciencias, Universidad to locate and rationalise. Unlike erosion and salinity Autónoma de Madrid, Tomas y Valiente, s/n, Cantoblanco, Spain that give strong surface evidence of their presence, soil © 2017 Aitor García‐Tomillo, et al., published by De Gruyter Open. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License. 318 A. García‐Tomillo, et al. compaction requires physical input before it is uncovered as non-invasive and less time and labour consuming and its extent, nature and cause resolved (Mc Garry and (e. g., electrical resistivity tomography – ERT (Besson Sharp 2003). Soil structure is the way the solid particles et al. 2004) and apparent electrical conductivity – ECa and pores are arranged. The pores between aggregates (Al-Gaadi 2012; Brevik and Fenton 2004). ERT has been are most important, because not only they distribute air, used to study the spatial and temporal variability of many water and nutrients throughout the soil, but also they are soil physical properties (Samouelian et al. 2005). It has used by plant roots to anchor and sustain a healthy crop been also applied to detect the effects of tillage in soil above ground. Soil compaction reduces the pore space physical properties (Besson et al. 2013; Rossi et al. 2013), between aggregates and a compacted soil, where large, to describe soil tilled layer (Besson et al. 2004), to estimate continuous soil pores are lost or reduced in size, does soil water content (Samouelian et al. 2005; Seladji et al. not provide adequate space for the storage or movement 2010; Dafonte et al. 2013) and saturated hydraulic of air and water, leading to slow permeability to water conductivity (Farzamian et al. 2015). Electric conduction and to restricted aeration (Mooney and Nipattasuk 2003). occurs within the water-filled pores and at the surface of Soil compaction, due to the collapse or decrease of pore clay particles. Consequently, electrical resistivity would spaces, is the most common cause of physical restriction depend on soil bulk density and more generally on soil for root growth and development. Thus, crop growth, structural status (Besson et al. 2004). yield and quality are negatively affected causing economic Dominantly applied to assess the effects of costs to farmers. The economic cost and the difficulty to be mechanized and tractor pulled agricultural practices detected make soil compaction a serious risk in the global on soil structural degradation, extensively reported “food security challenge”. in literature, the above mentioned methods are also The main causes of compaction are compressive forces applied in other research contexts such as that of animals from tractor tyres and tillage implements (especially wandering over the soil. In fact, compaction is also caused mouldboard plough and rotary equipment). Compaction by compressive forces acting on soil under the hooves may occur on the surface of the land, within the tilled layer of livestock or other animals, as it is the case of animal or below it, or even at greater depths (Batey 2009). Traffic trampling (da Silva et al. 2003). Effects of grazing animals of wheeled farm machines is common in most agricultural on soil physical properties are described by Drewry et al. operations even in zero tillage systems (Tullberg et al. (2008). Soil compaction caused by grazing animals 1990). Soil compaction by wheels is characterised by a through hoof action may be more widespread within the decrease in soil porosity localised in the zone beneath paddocks as compared to that caused by mechanical the wheel and rut formation at the soil surface (Hamza implements, which is limited to the wheel (Drewry 2006; and Anderson 2005). Tilling, harvesting and spreading Sigua and Coleman 2008). This comparison draws the of chemicals or fertilisers are the common operations attention to the difference between localized impacts in most farms. Most of these operations are performed and widespread impacts on soil in an area subject to by heavy, wheeled machines. In mechanized cropping compressive forces over the ground. Actually, data lack systems the continual use of tillage implements, especially in literature regarding the effects of draft animals acting disc ploughs, disc harrows, mould-board ploughs and in timely tillage operations. Under these circumstances, rotovators, over long periods of time frequently results in it can be hypothesized, but it is far from being fully the formation of dense plough pans containing few pores parameterized, that the moving load represented by large enough to be penetrated by crop roots. animals pulling tillage equipment determines a localized Methodological approaches for assessing soil impact with discontinuous spatial pattern. Besides, compaction are all focused on changes in soil physical animal traction operations are performed at a lower speed status after enduring compressive forces. Soil physical and with a lower load over the soil, when compared with properties related to air and water storage and movement tractor pulled operations, these two factors affecting soil are currently assessed (porosity, soil water characteristic structural degradation under mechanized conditions. curve, hydraulic conductivity, and air permeability), as For mechanized soil management, speed depends on these properties largely reflect the impacts of those forces on the type of implement to get a better result: 5 to 7 km.h-1 key soil functions. Measurement of parameters describing for a moulboard plough or 5 to 10 km.h-1 for a cultivator soil mechanical behaviour, such as shear strength and (Ortiz-Cañavate