The structure of ferrihydrite, a nanocrystalline material

Despite the ubiquity of ferrihydrite in natural sediments and its importance as an industrial sorbent, the nanocrystallinity of this iron oxyhydroxide has hampered accurate structure determination by traditional methods that rely on long-range order. We uncovered the atomic arrangement by real-space modeling of the pair distribution function (PDF) derived from direct Fourier transformation of the total x-ray scattering. The PDF for ferrihydrite synthesized with the use of different routes is consistent with a single phase (hexagonal space group P6(3)mc; a = approximately 5.95 angstroms, c = approximately 9.06 angstroms). In its ideal form, this structure contains 20% tetrahedrally and 80% octahedrally coordinated iron and has a basic structural motif closely related to the Baker-Figgis delta-Keggin cluster. Real-space fitting indicates structural relaxation with decreasing particle size and also suggests that second-order effects such as internal strain, stacking faults, and particle shape contribute to the PDFs.     

Soil Phosphorus and Potassium Mapping Using a Spatial Correlation Model Incorporating Terrain Slope Gradient

Variable-rate fertilizer application requires knowledge of the spatial distribution of soil nutrients within fields. Grid soil sampling might be used for acquiring this information, but is often too expensive for resolving spatial patterns in soil nutrients at the scale of precision fertilizer application. The objective of this study was to determine whether grid sampling efficiency can be improved using cokriging estimates with slope gradient as a secondary variable, which is easily obtained from high-resolution digital elevation models. Soils in two northern Montana wheat fields were sampled at the nodes of a 100-m diagonal grid. Soil test phosphorus and potassium maps were constructed with kriging and cokriging. Co-kriging uses the spatial correlation between two variables to predict for the less intensively sampled variable of interest, often with less estimation error than a univariate method such as kriging. The average estimation variance for cokriging compared to kriging was reduced for all values of the correlation considered. The additional complexity of cokriging might be justified provided a secondary variable exists that is spatially cross correlated with the primary variable of interest.     

The illusion of control: industrialized agriculture,nature, and food safety

I explore the role of nature in the agrifood system and how attempts to fit food production into a large-scale manufacturing model has lead to widespread outbreaks of food borne illness. I illustrate how industrial processing of leafy greens is related to the outbreak of E. coli 0157:H7 associated with spinach in the fall of 2006. I also use this example to show how industry attempts to create the illusion of control while failing to address weaknesses in current processing systems. The leafy greens industry has focused efforts on sterilizing the growing environment and adopting new technologies, while neglecting to change the concentrated structure of processing systems. Repeated breakdowns in these systems illustrate a widening fault line between attempted and failed control of nature in industrial food production.

Growth and fatty acid composition of sesame (<Emphasis Type="Italic">Sesamum indicum</Emphasis> L.) genotypes as influence by planting dates and nitrogen fertilization in semiarid region of Northwest,Pakistan

A field experiment was conducted on silty clay loam soil in the years 2011–2012. Two sesame (Sesamum indicum L.) cultivars (Local Black and Local White) were evaluated using various 3 different sowing dates (20th June, 10th and 30th July) and four agrotechnical level (0, 40, 80 and 120 kg N ha^–1) at New Developmental Farm The University of Agriculture, Peshawar, Pakistan. The objective of this study was to evaluate the effects of sowing dates on growth, yield and oil fatty acid composition of two sesame cultivars grown under different nitrogen fertilization. Results showed that cv. Local Black was characterized by significantly higher content of oil (47%), seed yield (696 kg ha^–1) and oil yield (335 kg ha^–1) while cv. Local White had higher palmitic acid (8%) and linoleic acid (38.7%). Yield and its main components were positively affected by the earlier sowing date. With regard to fatty acid composition, a decrease in oleic and stearic acid and an increase in linoleic and palmitic acid were observed. At early sowing, oleic and palmitic acid decreased whereas linoleic and stearic acid increased. The decrease in the oleic/linoleic acid ratio observed at early sowing, suggests a possible role of temperature on the activity of oleate desaturase in the developing seeds. Intensive technology of cultivation (120 kg N ha^–1), compared to the economical technology (40 kg N ha^–1), significantly increased the seed yield of both sesame cultivars. This was due to higher number of branches, Capsules m^–2, capsules plant^–1, seeds capsule^–1 and 1000 seed weight (g). The intensive technology of cultivation had a beneficial effect on the content of palmitic acid, linolenic acid and oleic acid in sesame seed.     

Improved remote sensing detection of wheat powdery mildew using dual-green vegetation indices

In this study, we investigated the possibility of using ground-based remote sensing technology to estimate powdery mildew disease severity in winter wheat. Using artificially inoculated fields, potted plants, and disease nursery tests, we measured the powdery mildew canopy spectra of varieties of wheat at different levels of incidence and growth stages to investigate the disease severity. The results showed that the powdery mildew sensitive bands were between 580 and 710 nm. The best two-band vegetation index that correlated with wheat powdery mildew between 400 and 1000 nm wavelength were the normalized spectrum 570–590 and 536–566 nm bands for the ratio index, and 568–592 and 528–570 nm for the normalized difference index. The coefficients of determination (R ²) for both were almost the same. The optimum dual-green vegetation index was constructed based on a calculation of the ratio and normalized difference between the normalized spectrum within the two green bands. The coefficients of determination (R ²) of DGSR (584, 550) (dual-green simple ratio) and DGND (584, 550) (dual-green normalized difference) were both 0.845. The inverse models of disease severity performed well in the test process at the canopy scale, and indicated that, compared with the traditional vegetation indices of Lwidth, mND705, ND (SDr, SDb), SIPI, and GNDVI, the novel dual-green indices greatly improved the remote sensing detection of wheat powdery mildew disease. Following these results, combined disease severity and canopy spectra were shown to be of enormous value when applied to the accurate monitoring, prevention, and control of crop diseases.     

Cation-ratio and accelerator radiocarbon dating of rock varnish on mojave artifacts and landforms

The first accelerator radiocarbon dates of rock varnishes are reported along with potassium/argon ages of lava flows and conventional radiocarbon dates of pluvial lake shorelines, in an empirical calibration of rock varnish K(+) + Ca(2+)/Ti(4+) ratios with age in the Mojave Desert, eastern California. This calibration was used to determine the cation-ratio dates of 167 artifacts. Although cation-ratio dating is an experimental method, some dates suggest human occupation of the Mojave Desert in the late Pleistocene.     

Conserving copalillo: The creation of sustainable Oaxacan wood carvings

Most accounts of the effect of the global marketplace on deforestation in Africa, Asia, and Latin America emphasize the demand for timber used in industrial processes and the conversion of tropical forests to pastures for beef cattle. In recent years, numerous scholars and policymakers have suggested that developing a market for non-timber forest products (NTFPs) might slow the pace of habitat destruction. Although increased demand for NTFPs rarely results in massive deforestation, the depletion of the raw materials needed to make particular products is common. Many rural households in the Mexican state of Oaxaca have prospered over the past three decades through the sale of brightly-painted, whimsical wood carvings (alebrijes) to international tourists and the owners of ethnic arts shops in the United States, Canada, and Europe. This paper examines a promising project aimed at providing Oaxacan alebrije-makers with a reliable, legal, and sustainable supply of wood. The ecologists, artisans, merchants, and forest owners involved in the project face formidable obstacles. Gaining permission to harvest wood from land belonging to Oaxacan communities requires the negotiation of a complex social, legal, economic, and political landscape. Artisans’ decisions about where to obtain wood rest largely on price, quality, and reliability of the supplier; they are willing to pay a premium for ecologically sustainable wood only if the additional cost can be passed on to consumers. Nonetheless, a group of carvers has begun to buy sustainably harvested wood. This arrangement has economic advantages for both the alebrije-makers and the owners of the forests where the wood is produced. Michael Chibnik is Professor of Anthropology at the University of Iowa. He has conducted fieldwork in Belize, Peru, Mexico, and in various parts of the United States. His research interests include economic anthropology, artisans, work organization, agricultural decision-making, and political ecology. He is the author of Crafting Tradition: The Making and Marketing of Oaxacan Wood Carvings (University of Texas Press, 2003) and Risky Rivers: The Economics and Politics of Floodplain Farming in Amazonia (University of Arizona Press, 1994), and editor of Farm Work and Fieldwork: American Agriculture in Anthropological Perspective (Cornell University Press, 1987). Dr. Silvia E. Purata is a Mexican ethnoecologist based in Xalapa, Veracruz. She is a member of People and Plants International, an organization that works to integrate conservation and the use of natural resources. Purata has conducted research on the methods indigenous peoples use to extract non-timber forest products (NTFPs) in tropical forests and the fate of such systems in varying socioeconomic circumstances. She has also been working on the promotion of forest certification in the Selva Maya.     

Bans,tests, and alchemy: Food safety regulation and the Uganda fish export industry

Contemporary regulation of food safety incorporates principles of quality management and systemic performance objectives that used to characterize private standards. Conversely, private standards are covering ground that used to be the realm of regulation. The nature of the two is becoming increasingly indistinguishable. The case study of the Ugandan fish export industry highlights how management methods borrowed from private standards can be applied to public regulation to achieve seemingly conflicting objectives. In the late 1990s, the EU imposed repeated bans on fish imported from Uganda on the basis of food safety concerns. However, the EU did not provide scientific proof that the fish were actually “unsafe.” Rather, the poor performance of Uganda’s regulatory and monitoring system was used as justification. Only by fixing “the system” (of regulations and inspections) and performing the ritual of laboratory testing for all consignments for export to the EU did the Ugandan industry regain its status as a “safe” source of fish. Yet, gaps and inconsistencies abound in the current Ugandan fish safety management system. Some operations are by necessity carried out as “rituals of verification.” Given the importance of microbiological tests and laboratories in the compliance system, “alchemic rituals” provide an appropriate metaphor. These rituals are part and parcel of a model that reassures the EU fish-eating public that all is under control in Uganda from boat to point of export. As a consequence, actual non-compliance from boat to landing site allows the fishery to survive as an artisanal operation. Stefano Ponte is Senior Researcher at the Danish Institute for International Studies, Copenhagen. His research focuses on the role of standards, regulation and quality conventions in the governance of agro-food value chains, with particular focus on Africa. He is co-author of Trading Down: Africa, Value Chains and the Global Economy and The Coffee Paradox: Global Markets, Commodity Trade and the Elusive Promise of Development.     

Reverse leasing and power dynamics among blue agave farmers in western Mexico

We examine changing production relations in the Mexican tequila industry to explore the ways in which large industrial firms are using “reverse leasing arrangements,” a form of contract farming, to extend their control over small agave farmers. Under these arrangements, smallholders rent their parcels to contracting companies who bring in capital, machinery, labor, and other agricultural inputs. Smallholders do not have access to their land, nor do they make any of the management decisions. We analyze the factors that have led some producers to participate in reverse leasing arrangements, while allowing other producers to continue farming independently. In addition, we look at the ways in which farmers are responding to these new production relations and constraints and the strategies that they are using to regain control over the production process.

Ultrafast flash thermal conductance of molecular chains

At the level of individual molecules, familiar concepts of heat transport no longer apply. When large amounts of heat are transported through a molecule, a crucial process in molecular electronic devices, energy is carried by discrete molecular vibrational excitations. We studied heat transport through self-assembled monolayers of long-chain hydrocarbon molecules anchored to a gold substrate by ultrafast heating of the gold with a femtosecond laser pulse. When the heat reached the methyl groups at the chain ends, a nonlinear coherent vibrational spectroscopy technique detected the resulting thermally induced disorder. The flow of heat into the chains was limited by the interface conductance. The leading edge of the heat burst traveled ballistically along the chains at a velocity of 1 kilometer per second. The molecular conductance per chain was 50 picowatts per kelvin.