title: Performance Evaluation of Proximal Sensors for Soil Assessment in Smallholder Farms in Embu County, Kenya.
abstract: Four proximal soil sensors were tested at four smallholder farms in Embu County, Kenya: a portable X-ray fluorescence sensor (PXRF), a mobile phone application for soil color determination by photography, a dual-depth electromagnetic induction (EMI) sensor, and a LED-based soil optical reflectance sensor. Measurements were made at 32-43 locations at each site. Topsoil samples were analyzed for plant-available nutrients (N, P, K, Mg, Ca, S, B, Mn, Zn, Cu, and Fe), pH, total nitrogen (TN) and total carbon (TC), soil texture, cation exchange capacity (CEC), and exchangeable aluminum (Al). Multivariate prediction models of each of the lab-analyzed soil properties were parameterized for 576 sensor-variable combinations. Prediction models for K, N, Ca and S, B, Zn, Mn, Fe, TC, Al, and CEC met the setup criteria for functional, robust, and accurate models. The PXRF sensor was the sensor most often included in successful models. We concluded that the combination of a PXRF and a portable soil reflectance sensor is a promising combination of handheld soil sensors for the development of in situ soil assessments as a field-based alternative or complement to laboratory measurements.
authors.affiliation: Regional Office for Africa, International Center for Tropical Agriculture (CIAT), P.O. Box, 823-00621 Nairobi, Kenya. kristin.piikki@slu.se.|Department of Soil and Environment, Precision Agriculture and Pedometrics, Swedish University of Agricultural Sciences (SLU), Box 234, SE-53231 Skara, Sweden. kristin.piikki@slu.se.
authors.forename: Kristin
authors.initials: K
authors.lastname: Piikki
authors.affiliation: Regional Office for Africa, International Center for Tropical Agriculture (CIAT), P.O. Box, 823-00621 Nairobi, Kenya. mats.soderstrom@slu.se.|Department of Soil and Environment, Precision Agriculture and Pedometrics, Swedish University of Agricultural Sciences (SLU), Box 234, SE-53231 Skara, Sweden. mats.soderstrom@slu.se.
authors.forename: Mats
authors.initials: M
authors.lastname: Söderström
authors.affiliation: Department of Soil and Environment, Biogeochemistry, Swedish University of Agricultural Sciences (SLU), Box 7014, SE-75007 Uppsala, Sweden. jan.o.eriksson@slu.se.
authors.forename: Jan
authors.initials: J
authors.lastname: Eriksson
authors.affiliation: School of Agriculture, University of Embu (UoEm), Embu, P.O. Box 6, 60100 Embu, Kenya. jjamkenya@yahoo.com.
authors.forename: Jamleck
authors.initials: J
authors.lastname: Muturi John
authors.affiliation: Ministry of Agriculture, 60100 Embu, Kenya. patrickireri66@gmail.com.
authors.forename: Patrick
authors.initials: P
authors.lastname: Ireri Muthee
authors.affiliation: Department of Soil and Environment, Precision Agriculture and Pedometrics, Swedish University of Agricultural Sciences (SLU), Box 234, SE-53231 Skara, Sweden. johanna.wetterlind@slu.se.
authors.forename: Johanna
authors.initials: J
authors.lastname: Wetterlind
authors.affiliation: Veris Technologies Inc., 1925 Clay Ridge Ct., Salina, KS 67401, USA. lunde@veristech.com.
authors.forename: Eric
authors.initials: E
authors.lastname: Lund
keywords: East Africa; proximal sensor; soil assessment; subsistence farming