Manganese-coated IRIS to document reducing soil conditions

Iron-coated indicatorof reduction in soils (IRIS) devices have been used for nearly two decades to help assess and document reducing conditions in soils, and official guidance has been approved for interpreting these data. Interest in manganese (Mn)-coated IRIS devices has increased because Mn oxides are reduced under more moderately reducing conditions than iron (Fe) oxides (which require strongly reducing conditions), such that they are expected to be better proxies for some important ecosystem services like denitrification. However, only recently has the necessary technology become available to produce Mn-coated IRIS, and the need is now emerging for guidance in interpreting data derived from Mn IRIS. Ninety-six data sets collected over a 2-yr period from 40 plots at 18 study sites among eight states were used to compare the performance of Mn-coated IRIS with Fe-coated IRIS and to assess the effect of duration of saturation and soil temperature as environmental drivers on the reduction and removal of the oxide coating. It appears that the current threshold prescribed by the National Technical Committee for Hydric Soils for Fe-coated IRIS is appropriate for periods when soil temperatures are warmer (\u3e11 °C), but is unnecessarily conservative when soil temperatures are cooler (5–11 °C). In contrast, Mn-coated devices are particularly useful early in the growing season when soil temperatures are cool. Our data show that when using a threshold of 30% removal of Mn oxide coatings there is essentially 100% confidence of the presence of reducing soil conditions under cool (\u3c11 °C) conditions

Bradyrhizobium elkanii nod regulon: insights through genomic analysis

Abstract A successful symbiotic relationship between soybean [Glycine max (L.) Merr.] and Bradyrhizobium species requires expression of the bacterial structural nod genes that encode for the synthesis of lipochitooligosaccharide nodulation signal molecules, known as Nod factors (NFs). Bradyrhizobium diazoefficiens USDA 110 possesses a wide nodulation gene repertoire that allows NF assembly and modification, with transcription of the nodYABCSUIJnolMNOnodZ operon depending upon specific activators, i.e., products of regulatory nod genes that are responsive to signaling molecules such as flavonoid compounds exuded by host plant roots. Central to this regulatory circuit of nod gene expression are NodD proteins, members of the LysR-type regulator family. In this study, publicly available Bradyrhizobium elkanii sequenced genomes were compared with the closely related B. diazoefficiens USDA 110 reference genome to determine the similarities between those genomes, especially with regards to the nod operon and nod regulon. Bioinformatics analyses revealed a correlation between functional mechanisms and key elements that play an essential role in the regulation of nod gene expression. These analyses also revealed new genomic features that had not been clearly explored before, some of which were unique for some B. elkanii genomes

Factors Affecting White-Tailed Deer-Browsing Rates on Early Growth Stages of Soybean Crops

White-tailed deer (Odocoileus virginanus) damage to soybean crops is a concern for soybean producers. Although researchers have documented decreases in the intensity of deer-browse on soybean plants as the growing season progresses, an understanding of the mechanisms driving the decrease in deer-browse is necessary for reduction and mitigation of deer damage to soybean crops. We tested 4 hypotheses to determine why deer-browse rates decrease 3 weeks after plant emergence: (1) plant phenology affects plant palatability; (2) diet change occurs; (3) deer damage induces a plant response making soybean leaves less palatable: and (4) deer consume fewer leaves but the same amount of leaf biomass as the season progresses. We recorded deer-browse in double- and single-crop soybean fields in Little Creek, Delaware, during the 2005 to 2006 growing seasons. To test if plant phenology affected deer-browse, we conducted a forage analysis of soybean leaves at different growth stages. Although forage quality components were variable across the growing season, white-tailed deer dietary requirements were met or exceeded in all cases. We compared deer diet composition using microhistological analyses across the early soybean growing season. The proportion of soybeans in the diet increased from 13 to 37% from late May to early July. We tested for an induced plant response by comparing the browse rates of plots that were protected from deerbrowsing until 4 weeks after plant emergence to plots that received no protection. Although we documented greater browse rates in the protected plots once protection was removed, we also documented that protected plots had taller plants, suggesting that deer may have been attracted to the taller plants. The amount of soybean leaf biomass that deer were consuming across the growing season increased from the early to late growth stages of soybeans. Based on our results, we believe that the increasing biomass of soybean leaves is the most plausible explanation for the decrease in browsing rate that we observed as soybeans matured

Mn-Coated IRIS to Document Reducing Soil Conditions

Iron-coated indicator of reduction in soils (IRIS) devices have been used for nearly two decades to help assess and document reducing conditions in soils, and official guidance has been approved for interpreting these data. Interest in manganese (Mn)-coated IRIS devices has increased because Mn oxides are reduced under more moderately reducing conditions than iron (Fe) oxides (which require strongly reducing conditions), such that they are expected to be better proxies for some important ecosystem services like denitrification. However, only recently has the necessary technology become available to produce Mn-coated IRIS, and the need is now emerging for guidance in interpreting data derived from Mn IRIS. Ninety-six data sets collected over a 2-yr period from 40 plots at 18 study sites among eight states were used to compare the performance of Mn-coated IRIS with Fe-coated IRIS and to assess the effect of duration of saturation and soil temperature as environmental drivers on the reduction and removal of the oxide coating. It appears that the current threshold prescribed by the National Technical Committee for Hydric Soils for Fe-coated IRIS is appropriate for periods when soil temperatures are warmer (\u3e11 °C), but is unnecessarily conservative when soil temperatures are cooler (5–11 °C). In contrast, Mn-coated devices are particularly useful early in the growing season when soil temperatures are cool. Our data show that when using a threshold of 30% removal of Mn oxide coatings there is essentially 100% confidence of the presence of reducing soil conditions under cool (\u3c11 °C) conditions