Gypsic and Petrogypsic Horizons - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 174

Chapter 17
Gypsic and Petrogypsic Horizons

17.1 Introduction

Gypsum-rich soils are important because they (1) comprise 200 million ha globally
and are important in rainfed and irrigated crop production (Boyadgiev and Verheye
1996 ), (2) are useful for paleoclimatic interpretations (Khademi and Mermut 2003 ;
Buck and Van Hoesen 2005 ), (3) enable an understanding of the roles of parent
material and climate in soil formation (Carter and Inskeep 1988 ; Taimeh 1992 ),
(4) elucidate the desertification process (Florea and Al-Joumaa 1998 ), and (5) have
been useful in the application of Landsat Enhanced Thematic Mapper (ETM) data
in digital mapping of soils (Nield et al. 2007 ).
In Soil Taxonomy (Soil Survey Staff 2010 ), the requirements for a gypsic
horizon include (1) a thickness of

> 15 cm, (2) a concentration of > 5 % gypsum

(of which > 1 % is secondary), and (3) the product of the gypsum content and

thickness is 150. The petrogypsic horizon is (1) cemented or indurated with

gypsum (with or without other cementing agents), (2)

>

> 5 mm thick and (3) contains

40 % gypsum. In the WRB (IUSS Working Group WRB 2007 ), the gypsic
horizon is defined similarly as in ST, but the petrogypsic horizon requires (1) a
thickness of

>

10 cm and (2) a concentration of 5 % gypsum (of which 1%is

> > >

secondary), and (3) the horizon is indurated.
The properties and genesis of gypsum-rich soils have been studied in the USA
(Neher and Bailey 1976 ; Reheis 1987 ; Carter and Inskeep 1988 ; Buck and Van
Hoesen 2005 ), Spain (Herrero et al. 1992 ; Mach´n and Navas 1998 ; Cant´n
et al. 2003 ; Sierra et al. 2009 ), Australia (Chen 1997 ), Syria (Florea and
Al-Joumaa 1998 ), Iran (Toomanian et al. 2001 ; Khademi and Mermut 2003 ), and
Jordan (Taimeh 1982 ). Herrero and Porta ( 2000 ) reviewed the terminology for
gypsum-rich soils and suggested that gypseous be used for soils with abundant
gypsum and gypsiferous be used for those with smaller concentrations of gypsum.
Herrero ( 2004 ) and Herrero et al. ( 2009 ) made suggestions for improving the
classification of these soils in Soil Taxonomy and the WRB.