Arthropod and Soil Microbial Community Size and Composition of Native and Introduced Pastures.

The Texas High Plains has limited water supply for irrigation to produce agricultural crops and livestock. ‘WW-B.Dahl’ Old World bluestem [OWB, Bothriochloa bladhii] is a highly productive, drought-tolerant grass in dryland and limited-irrigation conditions. Some varieties of OWB are rich in essential (volatile) oils which confer a pleasant smell and are suspected of deterring some insects. We characterized the size and structure of the ground-dwelling arthropod and soil microbial communities in different pasture treatments. Visual ratings (1-5 scale) were made for fly densities on cattle grazing OWB alone or OWB+alfalfa (Medicago sativa L.) pastures. Pastures containing OWB had fewer (P<0.01) ground-active arthropods than the alfalfa and native mixed grasses in 2014 and 2015. Numbers of red imported fire ants (Solenopsis spp.) and harvester ants (Pogonomyrmex spp.) were greatest in the native mix and near zero in pastures containing OWB both in 2014 and 2015. The cattle fly ratings in 2014 were lower (P<0.01) for OWB alone than for OWB+alfalfa, but not in 2015 and in 2016. OWB-alfalfa had higher (P=0.002) total FAME than OWB, alfalfa and native mix at 0.5 cm both in June and December. OWB-alfalfa had higher (P=0.048) total FAME than alfalfa and native mix in June at 5-15 cm. Similarly, OWB-alfalfa had higher (P <.0001) total FAME than OWB, alfalfa and native mix in December 2016 at 5-15 cm. OWB had higher total FAME than alfalfa and native mix and alfalfa had higher total FAME than native mix in December at 5-15 cm. The presence of OWB apparently provided an unfavorable environment for colonization by fire ants and harvester ants while still hosting desirable insects and soil microorganisms. OWB had a tendency to reduce horn flies on cattle, but not statistically significant in this trial. OWB is a desirable grass in the Southern Great Plains because of its drought tolerance and insect deterrence. Further research will test links between essential oil presence and insect deterrence on cattle and in the soil-plant biome.