World Congress of Soil Science Logo 18th World Congress of Soil Science
July 9-15, 2006 - Philadelphia, Pennsylvania, USA
International Union of Soil Sciences

Monday, 10 July 2006 - Friday, 14 July 2006

This presentation is part of 131: 1.5A Diffuse Reflectance Spectroscopy, Soil Sensing, Remote Sensing and Image Analysis - Poster

Precise Soil Texture Inventory by an On-the-go Sensor EM38.

Ruprecht Herbst, Humboldt Univ Berlin, Precision Agriculture, Philippstr.13, Berlin, D10115, Germany and Juergen Lamp, C.A.Univ, Plant Nutrition a. Soil Science, WG Soil Informatics, Olshausenstr. 40, Kiel, D24118, Germany.

1. Principle and technique. The soil sensor EM38 from Geonics sends by a coil electromagnetic waves of 14.6 kHz into soil depths from 0 to about 1.5m (max. at 4 dm). Electromagnetic induction (EMI) gener-ates weak alternating currents which induce a bulked response wave being measured by a secondary coil. Thus, the signals can be calibrated to the apparent electrical conductivity of the soil length unit (EC, mS/m). Electrical currents in soils depend on important soil fea-tures: under temperate humid (non-salty) conditions these are mainly the clay content (or tex-ture class) and moisture. The ion-loaded moisture (Stern-) layers near to clay mineral sur-faces are main pathways of currents. Interaction of both parameters can be used to detect tex-ture classes of profiles (or mean clay contents) with a good relative reproducability of areal patterns. Farmland can be surveyed by EC-tracking along the tramlines with a GPS-equipped ATV vehicle, efficiently. A bord laptop syncronizes the streams of EC and dGPS data which are collected each 2-3 s or by a grid of ~10*20 m. Including geostatistical data interpolation and GIS map construction, 50-150 ha can be surveyed per day.

2. Calibrating EC values for texture class prediction. The bulked EC values of the EM38 sonde can be related to texture classes of soil profiles only after calibration by soil augering to 15 dm depth (with “SoilRover” hydraulic borer). Lo-cal deviations of temperature and moisture regimes from standards are corrected by thumb rules (3% and 5% of EC per 1oC. or 1% water, resp.). Also organic matter enrichments (bog-soils) may have specific effects on the EC values and need to be verified. As a regional exam-ple of calibration, the EC ranges of texture classes are given in table 1.

3. Uses of the sensor based soil surveys. With a limited number of calibrating auger profiles (~1/ha) very detailed soil inventories for texture (or clay) profile maps can be achieved. Due to correlations (coefficient r, see table 1) of EC to crop yields and to soil parameters (AWC, CEC: available water and cation exchange capacities in 0-1m depth) several special purpose maps can be constructed for precision farm-ing or soil protection projects, e.g. detailed maps for (a) soil specific liming and base fertil-izer applications (P-, K-,Mg-/Ca-nutrients), (b) target yield based variable seeding and nitro-gen fertilization, (c) variable tillage depth, depending on clay in Ap (with caution, if soil is stratified), (d) tile drain width which relates to texture classes, (e) water percolation rates and nitrogen leaching risks (depending on AWC).

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