Ecological Modelling 256 (2013) 6–15 Contents lists available at SciVerse ScienceDirect Ecological Modelling jo u r n al hom ep age : www.elsevier.com/locate/ecolmodel Modeling biopore effects on root growth and biomass production on soils with pronounced sub-soil clay accumulation Thomas Gaiser a,∗ , Ute Perkons b , Paul Martin Küpper b , Timo Kautz b , Daniel Uteau-Puschmann c , Frank Ewert a , Andreas Enders a , Gunther Krauss a a University of Bonn, Institute of Crop Science and Resource Conservation, D-53115 Bonn, Germany b University of Bonn, Institute of Organic Agriculture, D-53115 Bonn, Germany c University of Kiel, Institute of Plant Nutrition and Soil Science, D-24118 Kiel, Germany a r t i c l e i n f o Article history: Received 26 October 2012 Received in revised form 7 February 2013 Accepted 12 February 2013 Keywords: Luvisols Biopores Root growth Biomass production Spring wheat a b s t r a c t Soils with subsoil clay accumulation account for more than 20% of the global land surface. These soils are characterized by vertical differences with respect to soil texture and increasing bulk density below the topsoil, which in turn affects root penetration into the subsoil. Biopores are preferential pathways for roots and assist in overcoming physical barriers like high density soil layers. An integration of these rela- tionships into cropping systems models at the field scale is on-going. This paper presents a new approach to model the effect of biopores on root development in soils with clay accumulation at the plot scale. In this approach, the effect of biopores on root elongation rate depends on bulk density and on a biopore- root growth threshold (MPRT), which is the biopore volume at which the resistance of soil strength to root penetration is completely offset by the density of the biopores. The approach was integrated into a model solution of the model framework SIMPLACE (Scientific Impact assessment and Modeling PLatform for Advanced Crop and Ecosystem management). MPRT was parameterized for spring wheat using the inverse modeling approach based on root observations from a multi-factorial field experiment on a Haplic Luvisol. The observed biopore densities (>2 mm diameter) were between 300 and 660 pores m -2 (equiv- alent to a volumetric proportion of 0.38–0.83%) depending on the preceding crop. Observed soil bulk densities ranged between 1.31 and 1.62 g cm -3 . For spring wheat, the best fit between simulated and observed root densities in different layers was obtained with a MPRT of 0.023 m 3 m -3 (equivalent to 2.3% of soil volume). The mean simulated total above ground biomass was sensitive to MPRT and had the best agreement with observed values when a MPRT between 0.023 and 0.032 m 3 m -3 was used in the simulations. Scenario simulations with the parameterized model at the same site demonstrate the importance of biopores for biomass production of short-cycle spring wheat when prolonged dry spells occur. The simulations allow a rough quantification of the biopore effects with respect to root elongation rate and biomass production at the plot scale with the potential to be extended to the field scale. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In recent decades, significant progress has been made in the modeling of crops including root growth. The focus of many mod- eling efforts was on simulating the response of crops to diverse climate, soil and management conditions, e.g. CropSyst (Stockle et al., 2003), DSSAT (Jones et al., 2003), APSIM (Keating et al., 2003a), STICS (Brisson et al., 2003a) and the different models developed at Wageningen University (van Ittersum et al., 2003). However, most models consider effects of soil structural properties in a simplified way, using mainly soil bulk density as a proxy for penetrability of ∗ Corresponding author. Tel.: +49 228 732050; fax: +49 228 732870. E-mail address: tgaiser@uni-bonn.de (T. Gaiser). the soil layers (Keating et al., 2003b; Williams and Izaurralde, 2005). Soil bulk density affects simulated root penetration rates and in some cases extension of lateral roots (Brisson et al., 2003b). In soils with little vertical differentiation of bulk density and low macrop- ore density, this simplification may yield satisfactory results when simulating root growth and development. However, in soils with pronounced vertical differences with respect to soil structure and macropore density, such simplified assumptions may lead to uncer- tain rates of root growth and of water and nutrient uptake. This is due to the fact that macropores generated by roots do not reduce soil bulk density, because the reduction of density in the voids created by the roots is largely compensated by the increased soil density of the root channel walls (Hirth et al., 2005; Young, 1998). Vertical differences with respect to soil texture and bulk density are characteristic features of soil types with clay accumulation 0304-3800/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecolmodel.2013.02.016