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CHARACTERIZING SOIL STABILITY IN HIGH SAND CONTENT SOILS AND MIXTURES James R. Crum Crop and Soil Science Department, M.S.U.

INTRODUCTION

Soils are an intragal part of the turf grass system and the particle-size of that soil (sand) is the most important physical property. Particle-size distribution (texture) influences or controls porosity, bulk density, cation exchange capacity, plant available water-holding capacity, soil strength, and soil stability. Particle-size is the primary property specified within the USGA specifications for putting green construction because of it's influence on soil behavior. These specifications, listed below in Table 1, center on not having a large amount of very large

particles (VCoS and Gravel) nor a large amount of«10

VFS, silt and clay) fines, a majority of particles in the

medium and coarse sand size range is preferred. This produces a rootzone mixture with a large proportion of macropores that allow for rapid water movement and drainage. Since putting greens constructed on these materials have a low plant available water holding capacity, the different materials (rootzone, intermediate, and gravel) are stratified, or layered, to increase the ability of the sandy rootzone to hold plant available water.

Table 1. USGA Specifications for the particle size of the rootzone mixture to use in Putting Green Construction.

N9me

.......

......

..JI

.~:

(bv

..

-

F. Gravel

2.0-3.4 mm

Not more than 10% of the total particles in this range, including a maximum of3% fine gravel (preferably none).

VCoS

1.0-2.0 mm

CoS

0.5-1.0 mm

A minimum of 60% of the particles must fall in this range.

MS

0.25-0.5 mm

VFS

0.05-0.15 mm

Not more than 5%

Total particles in this range shall not

Silt

0.002-0.05 mm

Not more than 5%

exceed 10%.

FS

0.15-0.25 mm

No more than 20% can fall in this range.

Clay

under 0.002 mm

Not more than 5%

The uniformity of the soil and distribution of grain size among the different particle size classes dictate the porosity and soil stability (Adams et. aI, 1985; Baker, 1983; Gibbs et. aI, 1989). Sands that are uniform (tending to one or a few "ad1acent" size classes) lack the right amounts and sizes of particles that will fit together (smaller particles fitting into the void space of the larger particles) and provide stability against movement. We have tried to explain the stability problem with uniform sands as being similar to tossing round marbles on the floor

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