Sustaining conservation agriculture: Lessons learned from the EU project KASSA

The questioning of the sustainability of conventional plough-based agriculture led to the emergence of alternative concepts and practices such as conservation agriculture (CA), which is currently spreading in many places. CA-based systems are said to rely on the simultaneous use of three main components: (1) reduced tillage or no-tillage and direct seeding for less disturbance of the soil and proper crop establishment; (2) soil cover to mitigate erosion, reduce weeds, and improve soil fertility and functions; and (3) crop rotation to control pests and diseases. These systems are thought to respond to production-protection requirements; interest in their applicability and results is growing. Knowledge Assessment and Sharing on Sustainable Agriculture (KASSA) is an EU-funded project that intended to extract lessons from past research on CA. It did it through a step-by-step and iterative process that took place within four regional platforms: Asia, Europe, Latin America, and the Mediterranean. In the four platforms of KASSA, implementation of the concept of CA gave rise to many farming practices. The no-till¿based systems are the most common: in some places, they are about to replace completely the conventional plough-based systems. However, soil cover and sound crop rotation are still hardly practiced because of biophysical conditions; low biomass production; competition from livestock; lack of adapted varieties, of implements, and of knowledge; and general market conditions. The absence of these components makes the systems rely mainly on using chemicals to control weeds, pests, and diseases. The reduction in production costs CA systems provide often acts as a powerful argument for their introduction and adoption. But this argument alone is risky because (1) the development and fine-tuning of these systems is knowledge-consuming and (2) their suitability and efficiency are highly sensitive to local biophysical, social, cultural, technological, institutional, market, and policy environments. Furthermore, there are relatively few scientific data on CA systems; particularly, their long-term agronomic, environmental, and socioeconomic impacts are still not well understood. Substantial systemic and multidisciplinary research effort is needed to understand the functioning of CA systems and their socioeconomic and ecological sustainability conditions. (Résumé d'auteur

Barrier modification in sub-barrier fusion reactions using Wong formula with Skyrme forces in semiclassical formalism

We obtain the nuclear proximity potential by using semiclassical extended Thomas Fermi (ETF) approach in Skyrme energy density formalism (SEDF), and use it in the extended $\ell$-summed Wong formula under frozen density approximation. This method has the advantage of allowing the use of different Skyrme forces, giving different barriers. Thus, for a given reaction, we could choose a Skyrme force with proper barrier characteristics, not-requiring extra ``barrier lowering" or ``barrier narrowing" for a best fit to data. For the $^{64}$Ni+$^{100}$Mo reaction, the $\ell$-summed Wong formula, with effects of deformations and orientations of nuclei included, fits the fusion-evaporation cross section data exactly for the force GSkI, requiring additional barrier modifications for forces SIII and SV. However, the same for other similar reactions, like $^{58,64}$Ni+$^{58,64}$Ni, fits the data best for SIII force. Hence, the barrier modification effects in $\ell$-summed Wong expression depends on the choice of Skyrme force in extended ETF method.Comment: INPC2010, Vancouver, CANAD

Theory of charge dispersion in nuclear fission

By introducing charge asymmetry as a new dynamical collective coordinate in the asymmetric two-center shell model, the nuclear charge dispersion in the fission of 236U is calculated without using any free parameter. The agreement between theory and experiment is quite good