Application of Dexter’s soil physical quality index: an Irish case study

Abstract

Historically, due to a lack of measured soil physical data, the quality of Irish soils was relatively unknown. Herein, we investigate the physical quality of the national representative profiles of Co. Waterford. To do this, the soil physical quality (SPQ) S-Index, as described by Dexter (2004a,b,c) using the S-theory (which seeks the inflection point of a soil water retention curve [SWRC]), is used. This can be determined using simple (S-Indirect) or complex (S-Direct) soil physical data streams. Both are achievable using existing data for the County Waterford profiles, but until now, the suitability of this S-Index for Irish soils has never been tested. Indirect-S provides a generic characterisation of SPQ for a particular soil horizon, using simplified and modelled information (e.g. texture and SWRC derived from pedo-transfer functions), whereas Direct-S provides more complex site-specific information (e.g. texture and SWRC measured in the laboratory), which relates to properties measured for that exact soil horizon. Results showed a significant correlation between S-Indirect (S i ) and S-Direct (S d ). Therefore, the S-Index can be used in Irish soils and presents opportunities for the use of S i at the national scale. Outlier horizons contained >6% organic carbon (OC) and bulk density (B d ) values <1 g/cm 3 and were not suitable for S i estimation. In addition, the S-Index did not perform well on excessively drained soils. Overall correlations of S i with B d and of S i with OC% for the dataset were detected. Future work should extend this approach to the national scale dataset in the Irish Soil Information System.

Water Related Properties to Assess Soil Quality in Two Olive Orchards of South Spain under Different Management Strategies

“…Therefore, the S index is a new version of the maximum value of the specific water capacity, similar to the stability index of Childs. This index has been shown to be related to some agronomic and edaphic characteristics suggested for the evaluation of soil quality [19][20][21]. Assouline and Or [22] choose the tangent to the soil water retention curve at the inflection point to estimate the water content and the pressure head at the state of field capacity.…”

Evaluating pedotransfer functions of the Splintex model

“…A similar approach was used by Fenton et al . (), who derived an SPQ index based on VGM parameters by applying Rosetta (Schaap et al ., ) to evaluate soil structure; this might be an alternative option when information on soil structure is important. In this context, we evaluated the indices air capacity (AC), crop available water content (AW), relative field capacity (RFC) and macroporosity (Mac) (Reynolds et al ., ), calculated by: in which θ (0 m), θ (0.1 m) and θ (1.0 m) are the volumetric soil water contents (m 3 m −3 ) at tensions ( h ) of 0, 0.1 and 1.0 m, respectively.…”