Management of soil organic matter in semiarid Africa for annual cropping systems

Ensuring sustainable agriculture in semiarid Africa requires the implementation of methods to balance nutrients and to conserve soil organic matter (SOM). There is an urgent need to improve the management of all types of SOM input. In this paper; the authors review a wide range of agricultural practices and discuss their advantages, limitations and feasibility. They distinguish ‘traditional systems’ such as traditional fallow, parkland and manuring from ‘improved systems’ such as ‘improved fallow’, forest fallow, alley cropping, cover crops and application of composted manure. Biomass production (BMP) for ‘improved systems’ is mainly linked: (i) for agroforestry, to the tree species used in forest fallow, to the synchronization of nutrient supply by the soil with the cereal demand in alley cropping, and generally to the efficiency of the root system and its development with the depth; (ii) for cover crops, BMP is mainly linked to the initial soil fertility and to the ecological zone: establishment and management of cover crops are not yet fully mastered under some conditions such as an annual rainfall below 800 mm and/or on very clayey soils; (iii) for manure, BMP is mainly linked to the improvement of fallow in order to ensure sufficient forage resources. Because semiarid Africa is mainly a livestock zone, the authors emphasise manure: constraints, quality indicators and tools used to encourage its production, are analysed. Thus it was concluded that the intensification of manure production and its rational use in semiarid African regions, threatened by drought and malnutrition, is very important: this cannot be separated from the production of plant biomass, whose possibilities have been examined above. This revised version was published online in June 2006 with corrections to the Cover Date.     

N.m.r. study of US Eastern and Western shale oils produced by pyrolysis and hydropyrolysis

Shale oils produced from US Eastern and Western oil shales by pyrolysis and hydropyrolysis processes have been investigated by both ¹H and ¹³C high-resolution n.m.r. techniques. Eastern shale oils produced by hydropyrolysis, and subsequently hydrotreated, were also included. From the n.m.r. data of the shale oils, the average molecular structure parameters were calculated. These parameters quantitatively represent the differences observed in the n.m.r. spectra of the various shale oils because of changes in the chemical composition. Mol percentages of aromatics, olefins, and alkanes were also determined for the shale oils, and show that the composition of the shale oil is dependent upon the geographic origin of the oil shale, the pyrolysis method, and the hydrogenation process. In addition to the study of shale oils, solid-state ¹³C n.m.r. spectra of Eastern and Western oil shales before and after pyrolysis and hydropyrolysis were obtained. The spectral data show that the carbon aromaticities for the Eastern oil shales and shale oils are higher than for the Western oil shale and shale oils. The data also show that hydropyrolysis relative to pyrolysis reduces the amount of residual organic carbon remaining on the spent shales. Carbon aromaticity data for both oil shale and shale oil suggest that the organic moieties present in kerogen may be retained in the shale oils to a greater extent after hydropyrolysis than after pyrolysis.     

SIMULATION OF LIGNIN PYROLYSIS

Model compound pyrolysis reaction pathways and kinetics were used in simulation of both native (e.g.. milled wood) and Kraft lignin thermolyses where either only primary or also secondary reactions are important.

Predicted products fell into one of permanent gases, tight liquids, phenolics and carbonaceous residue fractions. Product yields were more dependent on lignin type than on reaction environment.

Comparison of simulation predictions with experimental pyrolyses of actual lignins, accomplished in terms of both product identities and yields, is encouraging. It is noteworthy that the simulations are strictly a priori and incorporate no actual lignin pyrolysis information.     

Oviposition preference of the diamondback moth (Plutella xylostelld) unaffected by the presence of conspecific eggs orBacillus thuringiensis

Neither toxins fromBacillus thuringiensis Berliner nor conspecific eggs deterred oviposition by the diamondback moth,Plutella xylostella (L.) (Lepidoptera: Plutellidae), in laboratory choice tests. The finding that toxins did not deter oviposition by moths from a susceptible line shows that oviposition preference and larval survival were not associated in this line. Selection for larval resistance to toxins did not significantly alter oviposition preference, which rules out a strong genetic correlation between larval performance and oviposition preference. Failure of conspecific eggs to deter oviposition may not represent lack of association of preference and performance because other evidence suggests that larval performance may not be greatly affected by larval density. These results suggest that the ability of refuges to slow evolution of physiological resistance toB. thuringiensis toxins will not be magnified by an oviposition preference for untreated foliage.     

Metal Electrodes Integration on Macroporous Silicon: Pores Distribution and Morphology

ABSTRACT: In this work a new approach for the one step integration of interdigitated electrodes on macroporous silicon substrates is presented. Titanium/gold interdigitated electrodes are used to pattern p-type silicon substrates prior the anodization in a organic electrolyte. The electrolyte characteristics, conductivity and pH, has been found to affect the adherence of the metal layer on the silicon surface during the electrochemical etching. The impact of the metal pattern on size distribution and morphology of the resulting macroporous silicon layer is analyzed. A formation mechanism supported by finite element simulation is proposed.