Unlocking the potential of contract farming: lessons from Ghana

This paper analyses sorghum contract farming in north-east Ghana in order to explore ways of making such arrangements viable for small farmers. The analysis draws on the convergence of sciences approach, which sees both science and social relations (interactions among the relevant stakeholders) as important for developing small farmer-relevant agricultural innovations (technology, procedures, new forms of organisation). The study reveals that the failure and problems encountered in this particular contracting scheme were both technical and institutional. The technical issues were a combination of pest problems, the environment and the sorghum variety chosen. The institutional issues involved the contractual arrangements and relations between the contracting parties. The authors argue that if contracts are to be fair, they must allow for compensation, contingencies and production risks. But scientific knowledge is required in order to adequately incorporate these elements

Aging Effects Across the Metal-Insulator Transition in Two Dimensions

Aging effects in the relaxations of conductivity of a two-dimensional electron system in Si have been studied as a function of carrier density. They reveal an abrupt change in the nature of the glassy phase at the metal-insulator transition (MIT): (a) while full aging is observed in the insulating regime, there are significant departures from full aging on the metallic side of the MIT, before the glassy phase disappears completely at a higher density $n_g$; (b) the amplitude of the relaxations peaks just below the MIT, and it is strongly suppressed in the insulating phase. Other aspects of aging, including large non-Gaussian noise and similarities to spin glasses, also have been discussed.Comment: 4+ pages, 5 figures; minor changes, accepted for publication in PR

Nonequilibrium Relaxations and Aging Effects in a Two-Dimensional Coulomb Glass

The relaxations of conductivity have been studied in the glassy regime of a strongly disordered two-dimensional electron system in Si after a temporary change of carrier density during the waiting time t_w. Two types of response have been observed: a) monotonic, where relaxations exhibit aging, i.e. dependence on history, determined by t_w and temperature; b) nonmonotonic, where a memory of the sample history is lost. The conditions that separate the two regimes have been also determined.Comment: 4 pages; published versioi

From laser cooling to aging: a unified Levy flight description

Intriguing phenomena such as subrecoil laser cooling of atoms, or aging phenomenon in glasses, have in common that the systems considered do not reach a steady-state during the experiments, although the experimental time scales are very large compared to the microscopic ones. We revisit some standard models describing these phenomena, and reformulate them in a unified framework in terms of lifetimes of the microscopic states of the system. A universal dynamical mechanism emerges, leading to a generic time-dependent distribution of lifetimes, independently of the physical situation considered.Comment: 8 pages, 2 figures; accepted for publication in American Journal of Physic

Growing grass for a green biorefinery - an option for Ireland?

Growing grass for a green biorefinery – an option for Ireland? Mind the gap: deciphering the gap between good intentions and healthy eating behaviour Halting biodiversity loss by 2020 – implications for agriculture A milk processing sector model for Irelan

Huge (but finite) time scales in slow relaxations: beyond simple aging

Experiments performed in the last years demonstrated slow relaxations and aging in the conductance of a large variety of materials. Here, we present experimental and theoretical results for conductance relaxation and aging for the case-study example of porous silicon. The relaxations are experimentally observed even at room temperature over timescales of hours, and when a strong electric field is applied for a time $t_w$, the ensuing relaxation depends on $t_w$. We derive a theoretical curve and show that all experimental data collapse onto it with a single timescale as a fitting parameter. This timescale is found to be of the order of thousands of seconds at room temperature. The generic theory suggested is not fine-tuned to porous silicon, and thus we believe the results should be universal, and the presented method should be applicable for many other systems manifesting memory and other glassy effects.Comment: 4+ pages, 4 figure

Spatially heterogeneous dynamics in granular compaction

We prove the emergence of spatially correlated dynamics in slowly compacting dense granular media by analyzing analytically and numerically multi-point correlation functions in a simple particle model characterized by slow non-equilibrium dynamics. We show that the logarithmically slow dynamics at large times is accompanied by spatially extended dynamic structures that resemble the ones observed in glass-forming liquids and dense colloidal suspensions. This suggests that dynamic heterogeneity is another key common feature present in very different jamming materials.Comment: 4 pages, 3 figure

Adaptations of cowpea varieties (Vigna unguiculata (L.) Walp.) to the environmental variability in Benin

The study was realized in the context of farmer management of genotype by environment interaction. The objective was to determine the agronomic and morphological characteristics commonly used by farmers to assess farmer named cowpea varieties through a joint farmer researcher characterization. The trial design was a completely randomized block with 70 varieties as treatments, replicated four times. Data were analyzed using Shannon-Weaver diversity Index and the Analysis of Variance. These varieties varied in growth habit, in colours of leaves, stems, flowers, pods and seeds, and in seed shape and texture. The Shannon- Weaver diversity index revealed a high global mean of morphological diversity among the varieties (H’=1.23), ranging from 1.02 for pod pigmentation to 1.61 for seed coat colour. Within regions, this index varied from 0.33 to 1.57, depending on considered characteristic. Farmers used the photoperiodic response of the late varieties to distinguish early-maturing from late-maturing varieties. In a 3-year experiment, the variety by environment interactions, as expressed by variety-specific effects of planting date, season, and year on yield and yield components, were highly significant. The late-maturing varieties have shown longer reproductive period and more pods and seeds per plant, and higher yield than the early ones.Keywords: Diversity, Vigna unguiculata, photoperiodism, varieties, genotype by environment interaction, yield, Benin Adaptations des varietes de niebe (Vigna unguiculata (L.) Walp.) a la variabilite environnementale au BeninDans un contexte de gestion d’interaction génotype x environnement, l’objectif était de déterminer les caractéristiques agronomiques et morphologiques couramment utilisées par les paysans pour évaluer les variétés de niébé. Le dispositif a été un bloc aléatoire complet avec 70 variétés comme traitements, répétés quatre fois. Les données ont été analysées avec l’indice de diversité de Shannon-Weaver et l’analyse de variance. Ces variétés diffèrent par la croissance, les couleurs des feuilles, des tiges, des fleurs, des gousses et des graines, la forme et la texture de la graine. L’indice de diversité a révélé une grande diversité morphologique globale moyenne entre les variétés (H’= 1,23), allant de 1,02 pour la pigmentation des gousses à 1,61 pour la couleur du tégument de la graine. Pour une région donnée, cet indice a varié de 0,33 à 1,57, en fonction de la caractéristique considérée. A partir du photopériodisme, les paysans ont pu séparer les variétés stardives des variétés précoces. Sur 3 ans, les interactions génotype x milieu exprimées par des effets spécifiques de date de semis, de saison, et d’année sur le rendement et ses composantes étaient significatives. Les variétés tardives ont une période de fructification plus longue et ont significativement plus de gousses et graines par plante et de plus hauts rendements que les variétés précoces. Mots clés: Diversité, Vigna unguiculata, variétés, photopériodisme, interaction génotype x environnement, rendement, Bénin

Chromosomal location of genes encoding for resistance to septoria tritici blotch (Mycosphaerella graminicola) in substitution lines of wheat

Chromosomal location of resistance to Mycosphaerella graminicola was studied in substitution lines of resistant Triticum genotypes into the (susceptible) cultivar Chinese Spring (T. aestivum). (Moderately) resistant genotypes for which substitution lines were available were tested in a first screening. We selected a synthetic hexaploid wheat (Synthetic 6x; T. dicoccoides × T. tauschii), T. spelta and the wheat (T. aestivum) cultivars Cheyenne and Cappelle-Desprez. In a second screening the most suitable Argentinian isolates were identified. We decided to use the isolate IPO 92067 (all sets of substitution lines), IPO 93014 (substitution lines of Synthetic 6x, Cappelle-Desprez and T. spelta) and IPO 92064 (substitution lines of Cheyenne). In the final experiments, substitution lines of the selected genotypes into Chinese Spring were grown in two different environments and inoculated with the selected isolates at the seedling stage (lines of all four selected genotypes) or the adult stage (lines of Synthetic 6x and Cheyenne). Resistance was expressed as (reduction in) necrosis percentage or pycnidial coverage percentage; the two measures were highly (linearly) correlated. When tested in the seedling stage, all chromosomes seemed to carry genes effective against M. graminicola. Many genes were effective against only one isolate or in only one environment or their effects only showed in one resistance parameter. Often these effects were minor. Only chromosome 7D of Synthetic 6x was found with a major effect against both isolates tested. When tested in the adult stage, all lines but the one carrying chromosome 4B from the resistant parent seemed to show genes effective against M. graminicola. The line carrying chromosome 7D from Synthetic 6x showed a level of resistance similar to the resistant parent for isolate IPO 92067, but not for isolate IPO 93014. Major genes, effective against both isolates, were also found on chromosomes 5A and 5D from Synthetic 6x. Lines carrying chromosome 1B, 5D or 6D from Cheyenne showed major effects against isolate IPO 92064. For both necrosis percentage and pycnidial coverage percentage, highly significant linear correlations were found between resistance in the seedling stage and resistance in the adult stage. However, the variance accounted for was only small (20-24%; n = 184).Facultad de Ciencias Agrarias y Forestale