EXPLAINING THE ADOPTION AND DISADOPTION OF SUSTAINABLE AGRICULTURE: THE CASE OF COVER CROPS IN NORTHERN HONDURAS

Although technology adoption has been the subject of a great deal of economic research, that focused on the economics of adoption of low-input "sustainable" systems has been much more limited and recent. This paper attempts to explain the recent decline in the use of cover crops using in maize farming in the Department of Atlantida, Honduras. In the early 1970's, farmers in the region began rotating maize with the velvetbean (mucuna ssp.), a system learned from Guatemalan immigrants. Tohe mucuna-maize system decreased the labor required for maize farming even as it increased yields, prevented erosion, and conferred a variety of other agronomic benefits. By 1992, estimates show that the system had diffused among more than 60% of farmers in the Department. Both due to this widespread dissemination, and the fact that diffusion was largely spontaneous (unassisted by extensions and NGOs), the maize-mucuna system has become a widely acknowledged "success story" of sustainable agriculture diffusion. However, recent anecdotal evidence, confirmed by the survey research reported here, shows that by the late 1990s, use of the system had begun to decline sharply. Various hypotheses about the cause of this decline were investigated in this research, including whether the abandonment of the mucuna-maize system is attributable to a generalized decline in maize cultivation, changes in land tenure and distribution, a burgeoning cattle industry, infrastructural improvements, widespread infestations of noxious weed (rottboellia cochinchinensis), or limitations in farmer management. Modeling techniques evaluated two land-use decisions: whether to adopt mucuna-maize and the contingent decision of whether to abandon the system, once adopted. Bivariate probit analysis is used in the econometric analysis. Descriptive statistics and econometric results indicate that age, level of income from non-maize sources, the presence of rottboellia, and access to a road or highway are significantly related to the abandonment of overcropping. Meanwhile, greater dedication to maize, diversification into high value crops, greater experience with the system, and annual reseeding of mucuna are associated with continued use of the mucuna-maize rotation. The empirical results overall demonstrate that the phenomenon of maize-muchuna adoption and abandonment is a highly complex process. The results have policy implications for the "farmer to farmer" model of extension as well as the promotion of mucuna-maize as a sustainable agriculture technique. In the first case, less emphasis on diffusion and greater attention to farmer-to-farmer teaching of crop system dynamics may be important for the durability of cover crop systems. Regarding the second, cover crop species like mucuna should not be viewed as "silver bullet" solution to sustaining low-input agriculture: indeed, exclusive rotation of mucuna with maize may eliminate critical sources of plant and animal species diversity, ultimately undermining the system itself.International development, Sustainable agriculture, Adoption, Disadoption, Farmer management, Crop Production/Industries,

Building the Terrestrial Planets: Constrained Accretion in the Inner Solar System

To date, no accretion model has succeeded in reproducing all observed constraints in the inner Solar System. These constraints include 1) the orbits, in particular the small eccentricities, and 2) the masses of the terrestrial planets -- Mars' relatively small mass in particular has not been adequately reproduced in previous simulations; 3) the formation timescales of Earth and Mars, as interpreted from Hf/W isotopes; 4) the bulk structure of the asteroid belt, in particular the lack of an imprint of planetary embryo-sized objects; and 5) Earth's relatively large water content, assuming that it was delivered in the form of water-rich primitive asteroidal material. Here we present results of 40 high-resolution (N=1000-2000) dynamical simulations of late-stage planetary accretion with the goal of reproducing these constraints, although neglecting the planet Mercury. We assume that Jupiter and Saturn are fully-formed at the start of each simulation, and test orbital configurations that are both consistent with and contrary to the "Nice model." We find that a configuration with Jupiter and Saturn on circular orbits forms low-eccentricity terrestrial planets and a water-rich Earth on the correct timescale, but Mars' mass is too large by a factor of 5-10 and embryos are often stranded in the asteroid belt. A configuration with Jupiter and Saturn in their current locations but with slightly higher initial eccentricities (e = 0.07-0.1) produces a small Mars, an embryo-free asteroid belt, and a reasonable Earth analog but rarely allows water delivery to Earth. None of the configurations we tested reproduced all the observed constraints. (abridged)Comment: Accepted to Icarus. 21 pages, 12 figures, 5 tables in emulateapj format. Figures 3 and 4 degraded. For full-resolution see http://casa.colorado.edu/~raymonsn/ms_emulateapj.pd

Baryon Destruction by Asymmetric Dark Matter

We investigate new and unusual signals that arise in theories where dark matter is asymmetric and carries a net antibaryon number, as may occur when the dark matter abundance is linked to the baryon abundance. Antibaryonic dark matter can cause {\it induced nucleon decay} by annihilating visible baryons through inelastic scattering. These processes lead to an effective nucleon lifetime of 10^{29}-10^{32} years in terrestrial nucleon decay experiments, if baryon number transfer between visible and dark sectors arises through new physics at the weak scale. The possibility of induced nucleon decay motivates a novel approach for direct detection of cosmic dark matter in nucleon decay experiments. Monojet searches (and related signatures) at hadron colliders also provide a complementary probe of weak-scale dark-matter--induced baryon number violation. Finally, we discuss the effects of baryon-destroying dark matter on stellar systems and show that it can be consistent with existing observations.Comment: 26 pages, 6 figure

Water Delivery and Giant Impacts in the 'Grand Tack' Scenario

A new model for terrestrial planet formation (Hansen 2009, Walsh et al. 2011) has explored accretion in a truncated protoplanetary disk, and found that such a configuration is able to reproduce the distribution of mass among the planets in the Solar System, especially the Earth/Mars mass ratio, which earlier simulations have generally not been able to match. Walsh et al. tested a possible mechanism to truncate the disk--a two-stage, inward-then-outward migration of Jupiter and Saturn, as found in numerous hydrodynamical simulations of giant planet formation. In addition to truncating the disk and producing a more realistic Earth/Mars mass ratio, the migration of the giant planets also populates the asteroid belt with two distinct populations of bodies--the inner belt is filled by bodies originating inside of 3 AU, and the outer belt is filled with bodies originating from between and beyond the giant planets (which are hereafter referred to as `primitive' bodies). We find here that the planets will accrete on order 1-2% of their total mass from primitive planetesimals scattered onto planet-crossing orbits during the formation of the planets. For an assumed value of 10% for the water mass fraction of the primitive planetesimals, this model delivers a total amount of water comparable to that estimated to be on the Earth today. While the radial distribution of the planetary masses and the dynamical excitation of their orbits are a good match to the observed system, we find that the last giant impact is typically earlier than 20 Myr, and a substantial amount of mass is accreted after that event. However, 5 of the 27 planets larger than half an Earth mass formed in all simulations do experience large late impacts and subsequent accretion consistent with the dating of the Moon-forming impact and the estimated amount of mass accreted by Earth following that event

Direct and Enantioselective Organocatalytic α-Chlorination of Aldehydes

The first direct enantioselective catalytic α-chlorination of aldehydes has been accomplished. The use of enamine catalysis has provided a new organocatalytic strategy for the enantioselective chlorination of aldehydes to generate α-chloro aldehydes, an important chiral synthon for chemical and medicinal agent synthesis. The use of imidazolidinone 3 as the asymmetric catalyst has been found to mediate the halogenation of a large variety of aldehyde substrates with the perchlorinated quinone 1 serving as the electrophilic chlorinating reagent. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. The capacity of catalyst 3 to override the inherent bias of resident stereogenicity in the chlorination of enantiopure β-chiral aldehydes is also described. Catalyst quantities of 5 mol % were generally employed in this study

Resolving The Moth at Millimeter Wavelengths

HD 61005, also known as "The Moth," is one of only a handful of debris disks that exhibit swept-back "wings" thought to be caused by interaction with the ambient interstellar medium (ISM). We present 1.3 mm Submillimeter Array (SMA) observations of the debris disk around HD 61005 at a spatial resolution of 1.9 arcsec that resolve the emission from large grains for the first time. The disk exhibits a double-peaked morphology at millimeter wavelengths, consistent with an optically thin ring viewed close to edge-on. To investigate the disk structure and the properties of the dust grains we simultaneously model the spatially resolved 1.3 mm visibilities and the unresolved spectral energy distribution. The temperatures indicated by the SED are consistent with expected temperatures for grains close to the blowout size located at radii commensurate with the millimeter and scattered light data. We also perform a visibility-domain analysis of the spatial distribution of millimeter-wavelength flux, incorporating constraints on the disk geometry from scattered light imaging, and find suggestive evidence of wavelength-dependent structure. The millimeter-wavelength emission apparently originates predominantly from the thin ring component rather than tracing the "wings" observed in scattered light. The implied segregation of large dust grains in the ring is consistent with an ISM-driven origin for the scattered light wings.Comment: 10 pages, 6 figure

A unified model explains commonness and rarity on coral reefs

Abundance patterns in ecological communities have important implications for biodiversity maintenance and ecosystem functioning. However, ecological theory has been largely unsuccessful at capturing multiple macroecological abundance patterns simultaneously. Here, we propose a parsimonious model that unifies widespread ecological relationships involving local aggregation, species-abundance distributions, and species associations, and we test this model against the metacommunity structure of reef-building corals and coral reef fishes across the western and central Pacific. For both corals and fishes, the unified model simultaneously captures extremely well local species-abundance distributions, interspecific variation in the strength of spatial aggregation, patterns of community similarity, species accumulation, and regional species richness, performing far better than alternative models also examined here and in previous work on coral reefs. Our approach contributes to the development of synthetic theory for large-scale patterns of community structure in nature, and to addressing ongoing challenges in biodiversity conservation at macroecological scales

Competition in the 1990s

https://deepblue.lib.umich.edu/bitstream/2027.42/154101/1/cole-competition1994.pd

Indo-Pacific biodiversity of coral Rreefs: deviations from a mid-domain model

Understanding the nature and causes of global gradients in species richness is a perennial ecological problem, and recent work has highlighted the need to assess these gradients relative to an appropriate statistical expectation. This paper examines latitudinal and longitudinal gradients in species richnesses of corals and reef fishes in the Indo-Pacific domain and compares them with gradients predicted by a mid-domain model in which geographic domains are located at random between the latitudinal and longitudinal boundaries of this region. We test for significant differences between observed and predicted species-richness patterns, and we identify regions that are enriched or depauperate in species, relative to expectation. In addition, we move beyond previous mid-domain analyses by directly comparing observed spatial distributions of geographic ranges with those predicted by a mid-domain model. This comparison indicates precisely how species-richness anomalies are produced by nonrandomness in the distribution of species ranges. For both corals and fishes, large and statistically significant differences exist between observed latitudinal and longitudinal species-richness gradients and those predicted by mid-domain models. Longitudinally, species richness is markedly higher than predicted along the African coast and, to a lesser extent, within the Indo-Australian Archipelago (IAA), and it is markedly lower than expected in the eastern Pacific. Latitudinally, species richness becomes increasingly higher than predicted as one moves from the equator to the tropical margins; then it becomes sharply lower than predicted beyond the tropics. Unexpectedly, differences between observed and predicted spatial distributions of range endpoints and midpoints reveal a pattern of nonrandomness that is highly congruent with the hypothesis that gyres in the Indian and Pacific Oceans, with the IAA forming a porous boundary between them, have a major influence on Indo-Pacific species-richness patterns. Our analyses indicate that the perspective offered by a focus on explaining nonrandomness in the location of geographic ranges (rather than explaining why species numbers vary in space) is likely to dramatically alter our assessments of alternative explanations for global species-richness gradients