Report on the Agricultural Experiment Stations, 1952 Page: 47
The following text was automatically extracted from the image on this page using optical character recognition software:
SOIL SCIENCE 47
hibit plant growth to any great extent. In practice, successful results
are often obtained with less than 40 pounds of PCP per acre, indicating
that the chemical is active in a relatively shallow soil layer. Since
the amount required to be effective is so much less than that found to
retard plant growth, it is concluded that there is little danger of
harmful residual toxicity in the soil from the use of the usual field
rates of applications of PCP.
Experiments with 2,4-D compounds at the California station show
that little toxicity remained in the soil by the time of the second cropping,
that breakdown of the materials was slower in neutral and alkaline
soils than in acid ones, and that the fixation on the clay fraction
was so pronounced that leaching with 320 centimeters of water did not
free the soils of 2,4-D. The three forms of 2,4-D used acted alike when
mixed with the soil, perhaps because the salt forms revert to the parent
acid form through hydrolysis.
The Utah station found that DDT, chlordane, and benzene hexachloride
(BHC) were still toxic to ammonifying and nitrifying bacteria
in soils following a 3-year storage period. Although the inhibition
of these bacteria was less than in the two previous years, all
three materials showed toxicity in concentrations of 0.1 percent and
above. The DDT content of the soil had declined, but the rate of
breakdown was not as pronounced as between the first and second
The greatest percentage decomposition of DDT occurred in the soils
with the highest content of organic matter, and at the lowest rates
of application. The experiments showed that DDT is slowly decomposed
by soil micro-organisms. Since the toxic concentrations of
DDT, chlordane, and BHC are considerably higher than the recommended
rates of usage, the Utah scientists believe that where these
rates are not exceeded there is little or no reason to fear harmful
results from accumulations in the soil. Another herbicide, aromatic
solvent, did not injure either the ammonifying or nitrifying bacteria
when added in irrigation water in concentrations as high as 2,400
parts per million.
Decomposition of Organic Matter
Plants grown at the Iowa station (coop. USDA) in an atmosphere
of radioactive carbon dioxide were incorporated into the soil in order
to determine the effects that green manure crops have on the decomposition
(mineralization) of the organic matter already present
in the soil. Corn and soybean crops were used, and the rate and
extent of their mineralization were followed over a 6-month period by
measuring the radioactive CO2 produced. The breakdown process of
the native soil organic matter was speeded up by the addition of the
fresh crop residues, especially during the first few weeks following
application. The rate of mineralization of the native soil organic
matter was stimulated to the greatest extent in the soil with lowest
organic matter content (Monona silt loam). Actually the rate of decomposition
of the organic matter already present in this soil was
almost twice as rapid following the incorporation of corn residues,
as in the absence of the corn residues. Very little of the crop residues
remained in any of the soils at the conclusion of the incubation period,
Here’s what’s next.
This book can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Book.
United States. Office of Experiment Stations. Report on the Agricultural Experiment Stations, 1952, book, January 1953; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5990/m1/49/: accessed October 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.