A STRUCTURAL CLASSIFICATION OF SOIL PORE SPACE: A PROPOSAL

Transcription

1 A STRUCTURAL CLASSIFICATION OF SOIL PORE SPACE: A PROPOSAL Theophilo Benedicto Ottoni Filho Marta Vasconcelos Ottoni Yakov Pachepsky Otto Corrêa Rotunno Filho

2 INTRODUCTION Importance of characterization of the structure of soil pore space: soil functioning and soil ecosystems services agronomic and engineering applications Soil pore space can be characterized with different level of detail Fine details: Computer Tomography; More common way to characterize the pore spaces: Pore size distributions Condensing information on pore size distribution; Defining small number of pores classes For example, macroporosity, mesoporosity, microporosity

3 OBJECTIVE Classify soil pore spaces based on three classes of pores

4 Pore classes Class Definition easily drainable pores ( Formula n 60 n ) x100% ( n ) 100% SUM 100% n x100% n is the total porosity pore classes are defined in terms of saturation degree the definition of each class is based on the functional uses of pores:

5 Porosity Triangle 45% 22%

6 Defining θ60 and θ15000 ~ 2000 European soils - Hypres DATABASE: ~ 3000 soil samples ~ 1000 Brazilian soils 100% - Measurementes on θ15000 and porosity or saturated water content >1% - discarded θobs - θestim Error θ60 ~ 80% - Measurements on θ60 θ θ60 60 cm PFs ~ 20% - no measurements on θ60 60 cm s

7 Results triangles comparison TEMPERATE SOILS POROSITY TRIANGLE TROPICAL SOILS POROSITY TRIANGLE TEXTURAL TRIANGLE SC CL 30 SCL 20 L SL 10 LS S CLAY (%) TEXTURAL TRIANGLE C 40 Silt (%) 50 SiC 60 SiCL SiL 90 Si SAND (%) CLAY (%) SC CL 30 SCL 20 L SL 10 LS S C 40 Silt (%) 50 SiC 60 SiCL SiL 90 Si SAND (%)

8 Results similarities and differences TEMPERATE SOILS AND TROPICAL SOILS PLOTTED TOGETHER 11% 22% POROSITY TRIANGLE +

9 Results similarities and differences POROSITY TRIANGLE AMAZON FOREST POROSITY TRIANGLE SAVANNAS AND ATLANTIC FOREST POROSITY TRIANGLE TROPICAL AND TEMPERATE SOILS

10 Porosity triangle is useful 1. The proposed pore space representation was helpful in characterization the pore space of temperate and tropical soils. We saw similarities and differences based on pore functions; 2. As for some Brazilian soils their pore space was different from the temperate soils. One intriguing consequence is that perhaps the hydraulic PTF defined for temperate soils may not work for the tropical soils, mainly for the heavy Ferrasols, simply because such pore spaces are not found in soils of temperate climates.

11 Structural classification of soil pore space:proposal

12 Structural classification of soil pore space:proposal

13 Other porosity triangles Grouping soils by similarities of the pore size distribution Van Genuchten equation Formula ( n 60) x100% n θr STRUCTURAL TRIANGLE ( 60 n θr n θr θr ) 100% x100%

14 Isolines of log10(α) Other porosity triangles Class A Isolines of m Class D

15 Other porosity triangles Class A Class D

16 Acknowledgments CPRM, USDA and CAPES/Brazil for financial support; scientists who collected and provided data in Brazilian and Hypres databases.

17 Thank you! Marta Vasconcelos Ottoni