Special issue on proximal soil sensing

Abstract

Thisspecialissuepresentsa collection ofarticlesdescribingthere-search presented at the Second Global Workshop on Proximal SoilSensing (PSS) hosted by McGill University, Montreal, Quebec, Canadaon May 15–18, 2011 and held under the auspices of the InternationalUnionofSoilSciences(IUSS)WorkingGrouponProximalSoilSensing(WG-PSS).Sixtyscientistsfrom18countriesparticipatedinthework-shopwhere currentscientific andtechnologychallenges pertainingtothe field of PSS were discussed.PSS is defined as the use of field-based sensors to obtain signalsfrom the soil when the sensors' detector is in contact with, or closeproximity to (within 2 m) the soil (Viscarra Rossel and McBratney(1998), Viscarra Rossel et al., 2011). The sensors detect signals corre-sponding to physical measures, which can be linked to different soilsand their properties. According to a proposed classification (ViscarraRossel et al., 2011), proximal soil sensors may be described by themanner in which they measure (invasive or non-invasive), the sourceof their energy (active or passive), the way in which they operate(stationaryormobile),andtheinferenceusedinmeasuringthetargetsoil property (direct or indirect).In terms of the physical phenomena involved in the measure-ments, a large number of PSS systems use the soil's ability to reflector emit energy in different parts of the electromagnetic spectrumfrom high-frequency gamma-rays and X-rays to ultraviolet, visible,infra-red and radio-waves. PSS systems may rely on the ability ofsoil particles to conduct and accumulate an electrical charge, whileothers quantify the mechanical interaction between the sensor andsoil, and others use ion-selective potentiometry.Whatever the approach, proximal soil sensors facilitate the collec-tion of large amounts of (spatial and temporal) data using cheaper,simpler, and less laborious techniques, which, as a whole, are veryinformative. The measurements can be made in the field from thesurface or within the soil profile, and this information is produced al-most instantaneously. Hummel et al. (1996), Sudduth et al. (1997),Adamchuk et al. (2004) and Shibusawa (2006) provide a review ofmobile (on-the-go) proximal soil sensing solutions. A book entitled“ProximalSoilSensing” (ViscarraRosselet al., 2010) includes selectedresearch articles presented at the first High Resolution Digital SoilSensing and Mapping Workshop hosted by the University of Sydney,Sydney, Australia on February 5–8, 2010.ThisspecialissuebeginswiththeworkofLueckandRuehlmannaswellasthatofSudduthetal.whoexploretheextendibilityofelectricalresistivity mapping to determine both spatial and vertical changes insoil physical characteristics. Hedley et al. illustrate the potential forthe use soil electrical conductivity maps to be integrated with a wire-less sensor network to optimize soil water management. Althoughmost of the articles pertain to agricultural landscapes, De Shmedt etal. used electromagnetic induction sensing as an archeological tool.Articles by Nocita et al., Ramirez-Lopez et al., Brodsky et al., Kodairaet al., and Kweon et al. focus on the analysis of optical soil reflectancemeasurements in the visible and near-infrared parts of the electro-magnetic spectrum. Dierke et al. have studied the capabilities ofgamma-ray radiometry, while Van Meirvenne et al. and Piikki et al.have looked into combining gamma-ray with other sensors to im-provethequalityofsoilmeasurements.Benedettoetal.haveintegrat-ed several different types of PSS systems. Finally, Coulouma et al.discuss the use of seismic sensors.This selection of diverse and interesting research results will ex-tend your knowledge of the applicability of PSS methods to improveyour understanding of spatial and temporal soil variability. We hopethat this issue will stimulate additional research worldwide to exam-ine new and creative approaches to proximal soil sensing. We also in-vite any interested colleagues to participate in the future activitiescoordinated through the IUSS WG-PSS (www.proximalsoilsensing.org).References