The influence of soil pH on denitrification: progress towards the understanding of this interaction over the last 50 years

Results from the pioneering research on the interactions between pH and denitrification in soil from the 1950s to the present are reviewed, the changing perceptions of this complex relationship are discussed, and the current status of the subject is assessed. Facets of this relationship that are analysed in detail include the direct or indirect influence of pH on overall denitrification rates in soils, changes in the composition of gaseous products that depend on pH, methods for measuring the process, the concept of an optimum pH for denitrification, and the adaptation of microbial denitrifying communities to acidic environments. The main conclusions to be drawn are as follows. Total gaseous emissions to the atmosphere (N₂O, NO and N₂) have repeatedly been shown to be less in acidic than in neutral or slightly alkaline soils. This may be attributable to smaller amounts of organic carbon and mineral nitrogen available to the denitrifying population under acid conditions rather than a direct effect of low pH on denitrification enzymes. Numerous laboratory and field studies have demonstrated that the ratio N₂O:N₂ is increased when the pH of soils is reduced. The relation between soil pH and potential denitrification as determined by various incubation methods remains unclear, results being influenced both by original conditions in soil samples and by unknown changes during incubation. The concept of an optimum pH for denitrification has been frequently proposed, but such a term has little or no meaning without reference to specific attributes of the process.     

Relative Abundance of Carsonella ruddii (Gamma Proteobacterium) in Females and Males of Cacopsylla pyricola (Hemiptera: Psyllidae) and Bactericera cockerelli (Hemiptera: Triozidae)

Carsonella ruddii (Gamma Proteobacterium) is an obligate bacterial endosymbiont of psyllids that produces essential amino acids that are lacking in the insect’s diet. Accurate estimations of Carsonella populations are important to studies of Carsonella-psyllid interactions and to developing ways to target Carsonella for control of psyllid pests including pear psylla, Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae) and potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae). We used two methods, namely fluorescence in situ hybridization and quantitative polymerase chain reaction (qPCR), to estimate relative abundance of Carsonella in bacteriocytes and whole bodies of psyllids, respectively. Using these two methods, we compared Carsonella populations between female and male insects. Estimations using fluorescence in situ hybridization indicated that Carsonella was more abundant in bacteriocytes of female C. pyricola than in those of males, but Carsonella abundance in bacteriocytes did not differ between sexes of B. cockerelli. Analyses by qPCR using whole-body specimens indicated Carsonella was more abundant in females than in males of both psyllids. Neither fluorescence in situ hybridization nor qPCR indicated that Carsonella populations differed in abundance among adults of different ages (0–3 wk after adult eclosion). Using fluorescence in situ hybridization, Carsonella was observed in ovarioles of newly emerged females and formed an aggregation in the posterior end of mature oocytes. Results of our study indicate that female psyllids harbor greater populations of Carsonella than do males and that sex should be controlled for in studies which require estimations of Carsonella populations.     

Establishing Conservation Easements on Forested Riparian Buffers: Opportunities for Long-term Streamside Protection

Forest riparian buffers are an important means of conserving land. The Conservation Reserve Enhancement Program (CREP) offers financial incentives to landowners to install forested riparian buffers under 10–15 year contracts. This study explores whether Pennsylvania CREP participants who had established a riparian buffer would also place it under a permanent conservation easement. A mail questionnaire was developed and administered to 685 CREP participants. It was found that the majority of the respondents are likely to leave their buffer intact when the CREP contract expires, but are hesitant to agree to conservation easements. Property rights, education and finances are among the key issues affecting acceptance of conservation easements.     

Childhood cancer in Texas counties with moderate to intense agricultural activity

With few established risk factors, cancer remains the second leading cause of death for children in the U.S. Agricultural pesticide use is one of many suspected factors that may contribute to the etiology of childhood cancer. This study tests the hypothesis that birth in Texas counties with moderate to intense agricultural activity increases childhood cancer risk. This case-control study analyzed 6974 cases and controls ages 0 to 14, identified through the Texas Cancer Registry and Texas birth records, respectively. Exposure data were obtained from the Census of Agriculture. Percent cropland in the county of birth and total county-specific pesticide exposure incorporating the EPA's carcinogenicity classification served as surrogates for pesticide exposure. Cancer sites examined include: all cancers, leukemia, lymphoma, CNS tumors, and several specific subsites. Elevated, although not statistically significant, ORs for the association between birth in counties with > or =50% cropland were produced for all CNS tumors (OR = 1.3, 95% CI = 0.9-1.8), astrocytoma (OR = 1.4, 95% CI = 0.8-2.2), and PNET (OR = 1.3, 95% CI = 0.7-2.5). A similar pattern was not observed using the index of total county-specific pesticide exposure. Although imprecise, these exposure assessment methods represent novel applications of agricultural census data. Although a pattern of increased risk was observed between percent cropland and CNS tumors, this study's results do not support an association between birth in Texas counties with moderate to intense agricultural activity and childhood cancer. Due to study limitations, such an association should not be ruled out. Future research should incorporate individual-level data from various sources to increase precision and decrease misclassification in the exposure assessment.     

Boots on the ground: construction management of urbanizing irrigated farm land

Since its inception, in 1885 the Buckeye Irrigation Canal has delivered irrigation water in the Buckeye Valley, southwest of Phoenix, Arizona. Throughout its tenure the owners of the canal have consulted design professionals for its engineering needs. Early engineering in 1885 established canal alignments, delivery points and channel capacity. Until recently, the Buckeye Valley was a rural area relying on agricultural revenues to drive the local economy. Now, due to the recent housing market boom new homes started springing up like corn in September driving the existing open-channel laterals below grade into a patch work redesigned pipeline system. Because of these changes, professional construction managers are an enormous benefit to the Buckeye Water Conservation and Drainage District (BWCDD), the owner of the canal.As a result of this urbanization, contractors working for home developers are installing irrigation pipelines and systems with the focus of completing the project as quickly and economically as possible. Irrigation providers, on the other hand, focus on meeting the agricultural needs of their clients with consistent and uninterrupted water delivery. The services of a professional construction manager help both entities achieve their respective goals, shield BWCDD from construction of sub-par systems and risk, maintain uninterrupted service to growers and providing the technical expertise to communicate with both BWCDD and contractors.Construction managers provide a number of services to rural irrigation districts under-going urbanization. They team with an irrigation district by:

• Understanding irrigation design concepts;
• Understanding agricultural demands;
• Providing a thorough knowledge of construction practices and standards;
• Creating long-term design functionality;
• Reducing stress on and increasing productivity of personnel;
• Coordinating construction activities with water deliveries;
• Verifying constructed facilities perform as designed, which reduces maintenance costs.

Construction managers represent an irrigation district in the field by:

• Reviewing development plans for adherence to current construction standards and practices and coordinates construction schedules with water delivery needs;
• Observing construction for proper installation;
• Clarifying installers understanding of plans and specifications;
• Coordinating interruptions in service;
• Tracking multiple construction projects;
• Explaining agricultural practices to contractor personnel;
• Providing a single point of contact for construction related correspondence.

These “boots on the ground” create a local presence with a focus on the specific needs unique to an irrigation district. They provide a liaison while minimizing the impact to its growers.This paper will discuss the strain of urbanization on an irrigation district and the benefits of an engineering consulting firm to manage construction projects. The benefits include expertise, technical resources, design capability, coordination and inspection. Construction managers can help protect an irrigation district from being overwhelmed by rapid urbanization.     

Plasma progesterone concentration in the hen in relation to the ovulatory cycle

The concentration of peripheral plasma progesterone was measured by a double isotope derivative assay in hens slaughtered at various stages during the ovulatory cycle. A peak value was obtained 2 to 6 h before ovulation and basal levels were reached at ovulation. No secondary peaks were observed during the cycle. Similar results were obtained using a protein‐binding assay on plasma from individual birds taken serially during the cycle. Birds which did not ovulate on a particular day showed no peak of progesterone. In two birds sampled at the beginning of a laying cycle, the progesterone peak was of longer duration.