|Abstract or Summary
- Straw has many uses, as feed, roughage, animal bedding, but
these requirements are not sufficient to utilize the available production.
In areas where grasskseed is produced, post-harvest straw is
burned in the field to help prevent crop disease the following year.
This treatment is very wasteful in terms of straw utilization and also
produces considerable air pollution. Straw can be incorporated in
the soil, but this process requires added nitrogen to prevent reduced
crop productions the following year. Obviously, new uses are needed
to assist in the profitable elimination of excess straws.
One possibility would be to alter the straw photolytically to
produce a material more readily decomposible by soil or rumen microorganisms.
Increased microbial utilization would rapidly return
to the soil many basic chemical components taken out during crop
production. If the level of energy derived from straw in the rumen
could be increased significantly by photolytic treatment, a nutritive
feed could be produced. A study of the effects of ultraviolet light on
the soil and rumen microbial utilizability of straw consequently
might be of considerable value.
In this study, finely ground Newport Kentucky Bluegrass (Poa
pratensis) straws or Annual Ryegrass (Lolium multiflorum) straws
were mixed with distilled water in 0.5% w/v concentrations and exposed
to ultraviolet light emitted from a mercury-vapor lamp. Gaseous
oxygen or 30% hydrogen peroxide were used as electron acceptors
in the photooxidation process.
Growth studies, with an Aspergillus sp. isolated from local
soil, on the liquid portion of irradiated straw mixtures were used to
evaluate the effect of ultraviolet irradiation in the presence of oxygen.
Straws irradiated with ultraviolet light in the presence of varying concentrations
of 30% hydrogen peroxide were used to evaluate soil and
rumen microbial responses.
Fungal responses to the liquid portion of photolyzed straw
showed a positive correlation with a carbonyl compound utilization.
Fungal growth was depressed in liquid portions removed from hydrogen
peroxide irradiated straws where negligible carbonyl containing
compounds were found.
Soil microbial activity increased significantly when straws
irradiated in the presence of 30% hydrogen peroxide were mixed with soil in vitro. The increased activity corresponded with the utilization
of hemicellulose-like compounds formed on the exposed surfaces
of straw particles by the photooxidation process. When these
newly formed compounds were decomposed the microbial activity
decreased to the same level as non-treated straws.
Hydrogen peroxide photooxidized straws exhibited decreased
rumen digestibility when tested in vitro. When these photooxidized
straws were washed with distilled water and oven dried before digestion
studies, the reduction in digestibility was significantly greater.
The primary action of ultraviolet light on straw appears to be
with the molecules found on the straw particle surfaces. The role of
oxygen appears to be very important in the photooxidation process
since recombination of ruptured bonds is interfered with by activated
oxygen, resulting in new compound formation. Many of these compounds
are water soluble and are retained in solution during irradiation
with oxygen. When hydrogen peroxide is used the availability of
oxygen active species is much greater and the soluble compounds
are rapidly decomposed photolytically to carbon dioxide and water,
thus reducing the availability of nutrients for microbial growth in the
Apparently, many complex aromatic and polymeric straw structures
are ruptured photolytically, followed by combination with oxygen
to form open chain and cyclic products. Soil incorporation studies
indicate that many of these compounds are similar to hemicelluloses.
Rumen studies indicate that either optimum in vitro parameters
were not maintained or some photolytic compound or compounds are
formed which are inhibitory to the rumen microflora. Further investigation
is required in order to obtain conclusive results for future
All data, except those from rumen studies, indicate that treatment
of straw with ultraviolet light in the presence of oxygen does
alter the molecular structure in such a way as to increase its mi
crobial utilizability. This process, therefore, has promising possibilities
for new uses of straw and warrants further investigation.