Microorganisms and Soil Structure

Authors

T. M. McCalla, University of Nebraska-Lincoln

Date of this Version

3-1950

Citation

Transactions of the Kansas Academy of Science (March 1950) 53(1): 91-100.

Comments

Copyright 1950, Kansas Academy of Science. Used by permission.

Abstract

SUMMARY

Laboratory tests were made to determine the effectiveness of different compounds and microbial groups in increasing the stability of Peorian loess lumps against the action of falling water drops. The influence of these on percolation tests in the laboratory was also determined.

Many organic substances-dextrose, sucrose, starch, peptone, cullulose, and gum arabic-did not themselves contribute directly to soil-structure stability, though these substances do furnish energy material for soil microorganisms, which can convert them readily into either microbial tissue or decomposition products that increase soil-structure stability. Lignin, proteins, oils, fats, waxes, resin, and paraffin increased the stability of lumps of Peorian loess to water drops. Organic matter, Vinsol, dodecyl dimethylamine sulfate, and dodecyl dimethyl benzyl ammonium chloride increased stability.

The order of descending effectiveness of different microbial groups for soil lump stabilization against the beating action of water drops was: (1) Fungi, (2) Actinomycetes, (3) certain bacteria, (4) yeasts, and (5) the majority of bacteria used.

The percolation rate of Peorian loess material was increased by certain organic substances, especially if these were in the process of decaying. Water-soluble organic substances like starch and sugar were not immediately effective in increasing percolation.

Coarse organic substances such as straw, cornstalks, and soybean straw in sufficient concentration increased the percolation rate of the Peorian loess by holding up the soil lumps so that the water could run down between them. Organic substances such as sawdust or lignocellulose, added in a finely divided mechanical state, did not increase the percolation rate.

Microorganisms grown at the surface of Peorian loess plugged up the pores, provided the soil was not stirred, so that the percolation rate was decreased. If the soil was treated with microorganisms and then stirred into a lumpy condition, the percolation rate was increased. As micro- organisms act upon organic matter in the soil, they tend to stabilize the soil structure units.