Visual assessment of soil structure: Evaluation of methodologies on sites in Canada, China and Germany: Part I: Comparing visual methods and linking them with soil physical data and grain yield of cereals

Abstract

Visual observations of soil structure in the field offer the potential of semi-quantitative information for use in extension and monitoring. The aim of the study was to test the diagnostic value of different visual methods of soil structure assessment in relation to measurements of topsoil physical quality and yield of cereals. Visual methods that emphasized aggregate and pore characteristics were considered and included procedures of Peerlkamp [Peerlkamp, P.K., 1967. Visual estimation of soil structure. In: de Boodt, M., de Leenherr, D.E., Frese, H., Low, A.J., Peerlkamp, P.K. (Eds.), West European Methods for Soil Structure Determination, vol. 2, no. 11. State Faculty Agric. Sci., Ghent, Belgium, pp. 216–223], Diez and Weigelt [Diez, T., Weigelt, H., 1997. Bodenstruktur erkennen und beurteilen. Anleitung zur Bodenuntersuchung mit dem Spaten. Sonderdruck diz agrarmagazin. Bayer. Landesanstalt fuer Bodenkultur und Pflanzenbau, Freising-Muenchen., 2nd ed., 16 pp.], Shepherd [Shepherd, T.G., 2000. Visual Soil Assessment. Volume 1. Field Guide for Cropping and Pastoral Grazing on Flat to Rolling Country. Horizons.mw/Landcare Research, Palmerston North, 84 pp.], Werner and Thaemert [Werner, D., Thaemert, W., 1989. Zur Diagnose des physikalischen Bodenzustandes auf Produktionsflaechen. Arch. Acker-Pflanzenbau Bodenkd., Berlin 33, 729–739], FAO [FAO, 2006. Guidelines for soil description, 4th ed. FAO, Rome, 95 pp.] and the Peerlkamp method, modified by [Ball, B.C., Batey, T., Munkholm, L.J., 2007. Field assessment of soil structural quality—a development of the Peerlkamp test. Soil Use and Management 23, 329–337]. Measurements of soil quality included soil density (DBD), strength (penetrometer resistance, vane shear strength), permeability (initial infiltration rate) and biological activity (earthworm counts). The study was conducted on sites in Canada (Elora), China (Luancheng), and Germany (Dedelow). Soils were loamy and silty textured Haplic Luvisols (Elora, Dedelow) and Haplic Cambisols (Luancheng). Results showed that shape and size of aggregates were quickly recognizable diagnostic features of soil structure. Structure scores of most methods gave similar results after standardizing data. Measured soil physical qualities and crop yields correlated significantly with visual soil structure. Unfavourable visual structure was associated with increased dry bulk density, higher soil strength and lower infiltration rate but correlations were site-specific. Biological features like earthworm or root numbers were less reliable indicators of soil structure than aggregate characteristics. Visual soil structure assessment is a useful diagnostic tool and may indicate soil structure states clearly. Methods should be selected according to site conditions and should include a fast method of the Peerlkamp type.