LONG-RUN PRICE RISK IN U.S. AGRICULTURAL MARKETS

The last three years have realized significant structural changes in the U.S. agricultural policy environment. These changes include nearly complete planting flexibility and the elimination of target-price-based income support for agricultural producers. Many have questioned the extent to which such policy changes may influence the variability of agricultural prices. This analysis uses price series dating from 1944 to develop a multivariate framework to evaluate the long-run (inter-season) determinants of endogenous variability for the prices of corn, wheat, and soybeans. An annual measure of price variability is calculated from monthly spot market cash prices for each of the three commodities. The generalized method of moments estimation technique is used to model the price variability measure as a function of several supply and demand variables hypothesized to be relevant. Several explicit policy variables are tested for their effect on output price variability as well as on the variable parameter estimates. Output price variability is found to be sensitive to stocks, demand shocks, yield shocks, input price variability, and policy factors. Results vary somewhat for corn, wheat, and soybeans. Implications for recent farm policy changes are offered.Agricultural and Food Policy, Demand and Price Analysis,

Adsorption and desorption dynamics of citric acid anions in soil

The functional role of organic acid anions (e.g. citrate, oxalate, malonate, etc) in soil has been intensively investigated with special focus either on (i) microbial respiration and soil carbon dynamics, (ii) nutrient solubilization, or (iii) metal detoxification. Considering the potential impact of sorption processes on the functional significance of these effects, comparatively little is known about the adsorption and desorption dynamics of organic acid anions in soils. The aim of this study therefore was to experimentally characterize the adsorption and desorption dynamics of organic acid anions in different soils using citrate as a model carboxylate. Results showed that both adsorption and desorption processes were fast, reaching a steady state equilibrium solution concentration within approximately 1 hour. However, for a given total soil citrate concentration(ctot) the steady state value obtained was critically dependent on the starting conditions of the experiment (i.e. whether most of the citrate was initially present in solution (cl) or held on the solid phase (cs)). Specifically, desorption-led processes resulted in significantly lower equilibrium solution concentrations than adsorption led processes indicating time-dependent sorption hysteresis. As it is not possible to experimentally distinguish between different sorption pools in soil (i.e. fast, slow, irreversible adsorption/desorption), a new dynamic hysteresis model was developed that relies only on measured soil solution concentrations. The model satisfactorily explained experimental data and was able to predict dynamic adsorption and desorption behaviour. To demonstrate its use we applied the model to two relevant scenarios (exudation and microbial degradation), where the dynamic sorption behaviour of citrate occurs. Overall, this study highlights the complex nature of citrate sorption in soil and concludes that existing models need to incorporate both a temporal and sorption hysteresis component to realistically describe the role and fate of organic acids in soil processes

Effects of Cutting Ashe Juniper Woodlands on Small Mammal Populations in the Texas Hill Country

We studied the effects of cutting Ashe juniper (Juniperus ashei Bucholz) woodlands on populations of small mammals at Friedrich Wilderness Park, north of San Antonio, Texas. Three patches of juniper ranging from 1.8 ha to 2.4 ha were cut to provide habitat for endangered black-capped vireos (Vireo atricapillus Woodhouse). We trapped small mammals along transects placed in the treated patches and in untreated areas of the park from October 1995 to May 1996 and again from October 1996 to March 1997. Three species of small mammals were trapped, but Peromyscus pectoralis Osgood (white-ankled mouse) was the most common species captured. Peromyscus pectoralis was more abundant in the treated patches in which the juniper had been removed. Trapping success in the three treated areas was consistently higher (average of 12%) than in the untreated Ashe juniper woodlands (average of 3%). Mice that colonized treated patches survived longer than mice in control areas. Each year the number of P. pectoralis increased during the winter and spring, with juveniles accounting for up to 32% of captures. The management of habitat for an endangered species, such as the black-capped vireo, enhanced the biodiversity of small mammals in this study

SHORT-RUN DEMAND RELATIONSHIPS IN THE U.S. FATS AND OILS COMPLEX

Fats and oils play a prominent role in U.S. dietary patterns. Recent concerns over the negative health consequences associated with fats and oils have led many to suspect structural change in demand conditions. We consider short run (monthly) demand relationships for edible fats and oils. In that monthly quantities of fats and oils are likely to be relatively fixed, we utilize an inverse AIDS specification. Our analysis consists of two components. In the first, we utilize a smooth transition function to model a switching inverse almost ideal demand system (IAIDS) that assesses short-run demand conditions for edible fats and oils in the U.S. Our results suggest that short-run demand conditions for fats and oils experienced a rather rapid structural shift in the early 1990s. Although this shift generally made price flexibilities more elastic, differences in flexibilities across regimes are modest in most cases. Our results suggest that decreases in marginal valuations for most fats and oils in response to consumption increases are rather small. Scale flexibilities are relatively close to -1, suggesting near homothetic preferences for fats and oils. An important distinction occurs for lard and tallow, which exhibit a very elastic scale response. This suggests that scale increases in the consumption of edible fats and oils will significantly decrease consumers' marginal valuation of these animal fats. A second segment of our analysis considers dynamic extensions to the IAIDS model that recognize habit effects. Although nested hypothesis testing supports the dynamic specification over the static IAIDS model, price and scale flexibilities are quite similar to the static case.Demand and Price Analysis,

Inhibition of protein crystallization by evolutionary negative design

In this perspective we address the question: why are proteins seemingly so hard to crystallize? We suggest that this is because of evolutionary negative design, i.e. proteins have evolved not to crystallize, because crystallization, as with any type of protein aggregation, compromises the viability of the cell. There is much evidence in the literature that supports this hypothesis, including the effect of mutations on the crystallizability of a protein, the correlations found in the properties of crystal contacts in bioinformatics databases, and the positive use of protein crystallization by bacteria and viruses.Comment: 5 page

Coupled root water and solute uptake - a functional structural model

Understanding the distribution and fate of solutes in the soil-plant continuum is of interest for regulatory authorities, customers and producers. For example pesticide legalization requires certain modelling and experimental studies before the substance can be released on the market. The modelling approach used in these procedures, however, does not hold detailed information about the fate of the solute in the plant root system, but treats the root system only as a linear sink term. Uptake is determined as fraction of transpiration of the concentration in the dissolved phase. With an increasing availability of more detailed modelling approaches within the last years, we focus on a more comprehensive description of pesticide uptake by plant roots. R-SWMS is a three dimensional model for water movement in soil and plant roots (1). It also includes solute transport within the roots, which is realized as a particle tracking algorithm (2). We coupled this model to Partrace, another particle tracking algorithm that solves the convection-dispersion-equation in the soil. Active or passive solute transport across the root membrane is possible. While active transport, namely Michaelis-Menten kinetics, requires energy input from the plant, passive transport can be either driven by advective water uptake and/or by the local concentration gradient between root and soil. Root membrane conductance is determined by the lipophilic properties of the solute. Within the root system solutes are transported via the advective water flux. We further implemented microbial decay and sorption to both soil and roots. Benchmarking the coupled 3D model with an analytical solution for a single root at steady state flow conditions showed a good agreement. Using this new approach we could derive global uptake parameters in silico and compare the simulation results to data from hydroponic experiments. The detailed modelling approach enables tracking solutes in time, space and phase within the soil and root system. This novel simulation tool can be used to investigate the influence of soil properties, root system architectures, solute properties, meteorological conditions as well as plant management strategies on plant solute uptake to gain a deeper understanding of solute uptake and transport parameters

Verification and intercomparison of reactive transport codes to describe root-uptake

Several mathematical models have been developed to simulate processes and interactions in the plant rhizosphere. Most of these models are based on a rather simplified description of the soil chemistry and interactions of plant roots in the rhizosphere. In particular the feedback loops between exudation, water and solute uptake are mostly not considered, although their importance in the bioavailability of mineral elements for plants has been demonstrated. The aim of this work was to evaluate three existing coupled speciation-transport tools to model rhizosphere processes. In the field of hydrogeochemistry, such␣computational tools have been developed to␣describe acid-base and redox reactions, complexation and ion exchange, adsorption and precipitation of chemical species in soils and aquifers using thermodynamic and kinetic relationships. We implemented and tested a simple rhizosphere model with three geochemical computational tools (ORCHESTRA, MIN3P, and PHREEQC). The first step was an accuracy analysis of the different solution strategies by comparing the numerical results to the analytical solution of solute uptake (K or Ca) by a single cylindrical root. All models are able to reproduce the concentration profiles as well as the uptake flux. The relative error of the simulated concentration profile decreases with increasing distance from the root. The uptake flux was simulated for all codes with less than 5% error for K and less than 0.4% for Ca. The strength of the codes presented in this paper is that they can also be used to investigate more complex and coupled biogeochemical processes in rhizosphere models. This is shown exemplarily with simulations involving both exudation and uptake and the simultaneous uptake of solute and wate

Mechanofluorescent Polymer Brush Surfaces that Spatially Resolve Surface Solvation

Polymer brushes, consisting of densely end-tethered polymers to a surface, can exhibit rapid and sharp conformational transitions due to specific stimuli, which offer intriguing possibilities for surface-based sensing of the stimuli. The key toward unlocking these possibilities is the development of methods to readily transduce signals from polymer conformational changes. Herein, we report on single-fluorophore integrated ultrathin (<40 nm) polymer brush surfaces that exhibit changing fluorescence properties based on polymer conformation. The basis of our methods is the change in occupied volume as the polymer brush undergoes a collapse transition, which enhances the effective concentration and aggregation of the integrated fluorophores, leading to a self-quenching of the fluorophores’ fluorescence and thereby reduced fluorescence lifetimes. By using fluorescence lifetime imaging microscopy, we reveal spatial details on polymer brush conformational transitions across complex interfaces, including at the air–water–solid interface and at the interface of immiscible liquids that solvate the surface. Furthermore, our method identifies the swelling of polymer brushes from outside of a direct droplet (i.e., the polymer phase with vapor above), which is controlled by humidity. These solvation-sensitive surfaces offer a strong potential for surface-based sensing of stimuli-induced phase transitions of polymer brushes with spatially resolved output in high resolution

Rotavirus Rearranged Genomic RNA Segments Are Preferentially Packaged into Viruses Despite Not Conferring Selective Growth Advantage to Viruses

The rotavirus (RV) genome consists of 11 double-stranded RNA segments. Sometimes, partial sequence duplication of an RNA segment leads to a rearranged RNA segment. To specify the impact of rearrangement, the replication efficiencies of human RV with rearranged segments 7, 11 or both were compared to these of the homologous human wild-type RV (wt-RV) and of the bovine wt-RV strain RF. As judged by viral growth curves, rotaviruses with a rearranged genome (r-RV) had no selective growth advantage over the homologous wt-RV. In contrast, r-RV were selected over wt-RV during competitive experiments (i.e mixed infections between r-RV and wt-RV followed by serial passages in cell culture). Moreover, when competitive experiments were performed between a human r-RV and the bovine wt-RV strain RF, which had a clear growth advantage, rearranged segments 7, 11 or both always segregated in viral progenies even when performing mixed infections at an MOI ratio of 1 r-RV to 100 wt-RV. Lastly, bovine reassortant viruses that had inherited a rearranged segment 7 from human r-RV were generated. Although substitution of wt by rearranged segment 7 did not result in any growth advantage, the rearranged segment was selected in the viral progenies resulting from mixed infections by bovine reassortant r-RV and wt-RV, even for an MOI ratio of 1 r-RV to 107 wt-RV. Lack of selective growth advantage of r-RV over wt-RV in cell culture suggests a mechanism of preferential packaging of the rearranged segments over their standard counterparts in the viral progeny