The effect of nitrate and organic matter upon mobility of selenium in groundwater and in a water treatment process

Kesterson Reservoir in Merced County, California was formerly used as a storage and evaporation facility for Se-contaminated agricultural drain water. Very little Se entered the shallow aquifer below the ponds with percolating pond water. With few localized exceptions, most of the Se was removed from the water and retained in the first decimeter of soil, which was rich in decaying organic matter. Where it was present in groundwater, Se was nearly always associated with nitrate. Nitrate induces mildly oxidizing conditions (Eh ≈ 350 mV) and inhibits microbial fixation of Se. In the absence of nitrate, relatively reducing conditions prevail in the groundwater (Eh ≈ -50 mV), and Se is quickly removed. Selenate follows oxygen and nitrate in the order that soil microbes utilize electron acceptors. The process of Se removal from water by soil was reproduced in the laboratory, and the effect of nitrate was confirmed. This natural process might be applied to water treatment for Se removal. The deep water ecosystem at Kesterson Reservoir was highly productive. Vegetation growing in water treatment ponds should supply enough organic matter to maintain anaerobic conditions in the sediment. This process, including algae culture, was operated in an outdoor 79 cm column for 100 days. At percolation rates of 15 and 30 m yr^?1 Se removal averaged 94%, with an additional 2% converted to volatile compounds.     

Five native tree species and manioc under slash-and-mulch agroforestry in the eastern Amazon of Brazil: plant growth and soil responses

Throughout the Amazon of Brazil, manioc (Manihot esculenta) is a staple crop produced through slash-and-burn agriculture. Nutrient losses during slash-and-burn can be large and nutrient demand by food crops so great that fields are often abandoned after two years. In recent decades, farmers have reduced the fallow phase from 20 to ~5 years, limiting plant nutrient accumulation to sustain crop yields. Improved fallows through simultaneous planting of trees with food crops may accelerate nutrient re-accumulation. In addition, slash-and-mulch technology may prevent loss of nutrients due to burning and mulch decomposition may serve as a slow-release source of nutrients. This study in Pará, Brazil, in a 7-year-old secondary forest following slashing and mulching of the vegetation, involved two main plot treatments (with and without P and K fertilizers) and two sub-plot treatments (with or without a N₂-fixer Inga edulis). A mixed-culture of trees and manioc was planted in all plots. P and K fertilizer increased tree mortality due to weed competition but growth of surviving trees in four of the five tree species tested also increased as did biomass production of manioc. In the N₂-fixer treatment trends of greater growth and survival of four of five tree species and manioc biomass were also observed. Fertilization increased the biomass of competing vegetation, but there was a fertilizer by N₂-fixer interaction as I. edulis caused a reduction in competing biomass in the fertilized treatment. After one year, fertilization increased decomposition of the mulch such that Ca, Mg, and N contents within the mulch all decreased. In contrast, P and K contents of mulch increased in all treatments. No influence of the N₂-fixer on 0–10 cm soil N contents was observed. Two years after establishment, this agroforestry system succeeded in growing a manioc crop and leaving a well-maintained tree fallow after the crop harvest.     

Quantitative expression analysis of GH3, a gene induced by plant growth regulator herbicides in soybean

Symptoms resembling off-target plant growth regulator (PGR) herbicide injury are frequently found in soybean fields, but the causal agent is often difficult to identify. The expression of GH3, an auxin-regulated soybean gene, was quantified from soybean leaves injured by PGR herbicides using real-time RT-PCR. Expression of GH3 was analyzed to ascertain its suitability for use in a diagnostic assay to determine whether PGR herbicides are the cause of injury. GH3 was highly induced by dicamba within 3 days after treatment (DAT) and remained high at 7 DAT, but induction was much lower at 17 DAT. GH3 was also highly induced at 7 DAT by dicamba + diflufenzopyr, and to a lesser extent by the other PGR herbicides clopyralid and 2,4-D. The non-PGR herbicides glyphosate, imazethapyr, and fomesafen did not significantly induce GH3 expression above a low constitutive level. These results indicate that a diagnostic assay for PGR herbicide injury based on overexpression of auxin-responsive genes is feasible, and that GH3 is a potential candidate from which a diagnostic assay could be developed. However, time course analysis of GH3 expression indicates the assay would be effective for a limited time after exposure to the herbicide.     

Herbicide resistances in Amaranthus tuberculatus: a call for new options

Amaranthus tuberculatus is a major weed of crop fields in the midwestern United States. Making this weed particularly problematic to manage is its demonstrated ability to evolve resistance to herbicides. Herbicides to which A. tuberculatus has evolved resistance are photosystem II inhibitors, acetolactate synthase inhibitors, protoporphyrinogen oxidase inhibitors, and glyphosate. Many populations of A. tuberculatus contain more than one of these resistances, severely limiting the options for effective herbicide control. A survey of multiple-herbicide resistance in A. tuberculatus revealed that all populations resistant to glyphosate contained resistance to acetolactate synthase inhibitors, and 40% contained resistance to protoporphyrinogen oxidase inhibitors. The occurrences of multiple-herbicide resistances in A. tuberculatus illustrate the need for continued herbicide discovery efforts and/or the development of new strategies for weed management.     

Multi-scale environmental heterogeneity as a predictor of plant species richness

Ecological theory predicts a positive influence of local-, landscape-, and regional-scale spatial environmental heterogeneity on local species richness. Therefore, knowing how heterogeneity measured at a variety of scales relates to local species richness has important implications for conservation of biological diversity. We took a statistical modeling approach to determine which metrics of heterogeneity measured at which scales were useful predictors of local species richness, and whether the heterogeneity-local richness relationship was always positive. Local plant species richness data came from 400-m² vegetation plots in North and South Carolina, USA. At each of four scales from within plots to across regions, we used either GIS or field data to calculate measures of heterogeneity from abiotic environmental variables, vegetation productivity data, and land cover classifications. Among all predictors at all scales, we found that no measure of heterogeneity was a better predictor of local richness than mean pH within plots. However, at scales larger than within plots, measures of heterogeneity were correlated most strongly with local richness, and each of the three classes of variables we used had a distinct scale at which it performed better than the others. These results highlight the fact that ecological processes occurring across multiple scales influence local species richness differently. In addition, relationships between heterogeneity and richness were usually, though not always, positive, underscoring the importance of processes that occur at a variety of scales to local biodiversity conservation and management.     

The crossbred sire: experimental results for cattle

Results comparing crossbred bulls relative to straightbred bulls for various reproduction traits (such as puberty, sperm concentration, pregnancy rate and weaning rate) and progeny growth traits (birth and weaning weight) were summarized separately for Bos taurus X Bos taurus (Bt X Bt) and Bos indicus X Bos taurus (Bi X Bt) crosses. The Bt X Bt and Bi X Bt crossbred bulls were 1.8 and 5.0% younger, respectively, at puberty than straightbred bulls. Also, sperm concentration of Bt X Bt and Bi X Bt crossbred bulls was greater than straightbred bulls by 36.4 and 56.0%, respectively. Pregnancy rate and weaning rate of cows exposed to straightbred and crossbred bulls indicated advantage values of .2 and 4.0%, respectively, for Bt X Bt crossbred bulls. Corresponding advantage values for Bi X Bt crossbred bulls over straightbred bulls were 1.4 and 3.7%, respectively, for these two traits. Birth and weaning weights were similar for calves sired by straightbred and Bt X Bt crossbred bulls as well as for calves sired by straightbred and Bi X Bt crossbred bulls.     

The North American Animal Disease Spread Model: a simulation model to assist decision making in evaluating animal disease incursions

The North American Animal Disease Spread Model is a stochastic, spatial, state-transition simulation model for the spread of highly contagious diseases of animals. It was developed with broad international support to assist policy development and decision making involving disease incursions. User-established parameters define model behavior in terms of disease progression; disease spread by animal-to-animal contact, contact with contaminated personnel or equipment, and airborne dissemination; and the implementation of control measures such as destruction and vaccination. Resources available to implement disease control strategies, as well as the direct costs associated with these strategies, are taken into consideration. The model records a wide variety of measures of the extent of simulated outbreaks and other characteristics. The graphical interface and output visualization features also make it a useful tool for training and preparedness exercises. This model is now being used to evaluate outbreak scenarios and potential control strategies for several economically important exotic animal diseases in the United States, Canada, and elsewhere. NAADSM is freely available via the Internet at http://www.naadsm.org.