Report on the Agricultural Experiment Stations, 1952 Page: 48
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48 REPORT ON EXPERIMENT STATIONS, 1952
and only small increases occurred in the treated soils as compared with
the controls where no residues had been added.
Until radio carbon became available for research it was not possible
to distinguish between the newly added and the native organic matter
in soils in decomposition studies. These experiments throw new light
on the very important problem of loss of organic matter in soils, and
confirm a belief held by many, but which could not heretofore be
proved, that native soil organic matter "burns out" faster following
the addition of a green manure crop.
The Oklahoma station found that plants take up more fertilizer N
and less of the native soil N on soils low in organic matter than on
soils of high organic matter content. Both ammonium and nitrate
N, labeled with the N15 isotope, were used as fertilizer. Although the
amount of N in the plants was about the same for both sources, there
was a higher recovery of that added in the nitrate form. Residues
from plants grown to contain N15 were added to soils in the greenhouse
to determine the time and rate of biological release of N from the
organic matter as measured by its uptake by growing oat plants.
More of the N in the growing plants was derived from the added organic
matter in the second harvest than in the first, indicating the
importance of crop residues as a source of N during the growing season,
provided conditions are favorable for biological activity.
The Oregon station found that the rate of decomposition of various
tree products, when used as soil amendments, decreased in the following
order: Pea vines, wheat straw, alder sawdust, ponderosa pine
sawdust, cedar sawdust, Douglas-fir cork, Douglas-fir sawdust, young
Douglas-fir bark, hemlock sawdust, old Douglas-fir bark. Cedar sawdust
decomposed very slowly during the first 10 days. Water extraction
increased decomposability of old fir bark but had an opposite
effect on the young bark. Douglas-fir bark and fresh sawdust were
slightly toxic to soil micro-organisms and plant growth, but this toxicity
was overcome by the addition of available N. Various wood
waste mulches harbored exceptionally high numbers of micro-organisms,
whereas the underlying soil contained approximately the same
numbers as unmulched soil.
The commonly observed reduction in carbon dioxide evolution,
when N fertilizer is added to hasten the decomposition of crop residues,
has been explained by experiments at the Oregon station. The
addition of available N resulted in an increase in the number of organisms
and a corresponding increase in CO, production, but for only
24 to 48 hours. This brief increase in CO, production has often been
overlooked in the past. The larger population of micro-organisms
naturally requires more carbon, both for energy and for building
bodily protoplasm. For this reason more organic carbon is tied up
when N is added than when it is not added. This carbon remains tied
up for varying periods of time in the bodies of the micro-organisms.
It is gradually liberated, however, as CO, but does not show up in the
course of the usual 30- to 90-day respiration experiment.
A new product, Orzan (a dehydrated waste sulfite liquor byproduct
of the paper industry), now available as a soil amendment, was
found by the Oregon scientists to be decomposed in the soil in much
the same manner as ordinary plant residues. The rate of nitrification
of the product compared favorably with that of peptone, and its sul
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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/m1/50/: accessed September 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.