Title: Sandy Soil Microaggregates: Rethinking Our Understanding of Hydraulic Function

Abstract

Core Ideas Sandy soil microaggregates are comprised of a solid sand core encrusted with fines. Thick films control a significant proportion of water retention in coarse sandy soil. Three water pools drain sequentially: capillary water, thick films, and adsorptive films. Film seepage rates should be considered when irrigating sandy soil. This study investigated the peculiar structure of microaggregates in coarse sandy soils that exhibit only external porosity and investigated their control on soil hydrology. The microstructure underpins a hydrologic existence that differs from finer textured soils where aggregates have internal porosity. Understanding the impact of these microaggregates on soil hydrology will permit improved agricultural irrigation management and estimates associated with ecosystem capacity and resiliency. Microstructure was investigated using a digital microscope, and aspects of the structure were quantified by sedimentation and computed microtomography. Sandy soil microaggregates were observed to be comprised of a solid sand‐grain core that is coated with fines, presumably cemented by organic media. This microstructure leads to three distinct water pools during drainage: capillary water, followed by thick films (1–20 μm) enveloping the outer surfaces of the crusted microaggregates, followed by adsorbed thin films (<1 μm). The characteristics of the thick films were investigated using an analyticalmore » model. These films may provide as much as 10 to 40% saturation in the range of plant‐available water. Using lubrication theory, it was predicted that thick film drainage follows a power law function with an exponent of 2. Thick films may also have a role in the geochemical evolution of soils and in ecosystem function because they provide contiguous water and gas phases at relatively high moisture contents. And, because the rough outer crust of these microaggregates can provide good niches for microbial activity, biofilm physics will dominate thick film processes, and consequently hydrologic, biologic, and geochemical functions for coarse sandy soils.« less

Authors:

Paradiś, Ashley ^[1]; Brueck, Christopher ^[2]; Meisenheimer, Douglas ^[2]; Wanzek, Thomas ^[1]; Dragila, Maria Ines ^[1]

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+ Show Author Affiliations

1. Dep. of Crop and Soil Science Oregon State Univ. Corvallis OR 97331
2. Dep. of Chemical, Biological and Environmental Engineering Oregon State Univ. Corvallis OR 97331

Publication Date:

Thu Sep 07 00:00:00 EDT 2017

Sponsoring Org.:

USDOE

OSTI Identifier:

1582114

Grant/Contract Number:  

DE‐FG02‐94ER14466

Resource Type:

Publisher's Accepted Manuscript

Journal Name:

Vadose Zone Journal

Additional Journal Information:

Journal Name: Vadose Zone Journal Journal Volume: 16 Journal Issue: 9; Journal ID: ISSN 1539-1663

Publisher:

Wiley Blackwell (John Wiley & Sons)

Country of Publication:

United States

Language:

English