Soil and rumen microbial responses to photooxidized grass straw Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2r36v2526

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  • 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 liquid portions. 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 rumen applications. 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.
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