The identification of local soil variability caused by within-field differences of macronutrients and ecological features is of paramount importance for the effectiveness of precision agriculture. We present several spatial statistical and econometric techniques to capture local differences in soil variation, ecological characteristics, and yield more effectively than the analytical techniques traditionally used in agronomy. The application of these techniques is illustrated in a case study dealing with precision agriculture in the West African Sahel. The production of millet on acid sandy soils constitutes a typical example of low soil fertility areas exhibiting small absolute but large relative differences in crop production conditions over short distances. (R.J.G.M. Florax), r.l.voortman@sow.vu.nl (R.L. Voortman), brouwbar@bos.nl (J. Brouwer). URLs: http://www.feweb.vu.nl/re/master-point, http://www.sow.vu.nl/ Tel.: +31-20-4449321; fax: +31-20-4449325. 0169-5150/02/$see front matter 0 2002 Elsevier Science B.V. All rights reserved.PII: S 0 1 6 9 -5 1 5 0 (0 2 ) 0 0 0 6 8 -3

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Compared to other continents, the economic growth performance of Sub-Saharan Africa has been poor over the last four decades. Likewise, progress in agricultural development has been limited and the Green Revolution left Africa almost untouched. The question raised in the literature is whether the poor performance is a question of poor policies or of an unfavorable biophysical environment (policy versus destiny). This paper, with a broad perspective, analyzes adaptation of current land use to environmental conditions in Africa and compares the physical resource base of Africa with Asia. In doing so, we search for unifying principles that can have operational consequences for agricultural development. We argue that some specificities of the natural resource base, namely local homogeneity and spatial diversity of the predominant Basement Complex soils, imply that simple fertilizer strategies may not produce the yield increases obtained elsewhere.

SummaryAbout a decade ago, the main OECD countries decided to promote the use of biofuels so as to reduce greenhouse gases, to contribute to energy self-sufficiency and to create additional demand for agricultural commodities. The introduction of mandatory blending requirements and lavish subsidies spurred fast adoption of this technology. In the course of 2008, the already existing controversy about the effectiveness of this strategy culminated as the resulting upward shift in demand contributed to staggering rises in food prices on world markets. It is uncertain as yet whether this will tone done current ambitions among policy makers to expand biofuel production. The paper shows that high ratios of energy prices to food prices are needed to make biofuel production profitable without the mandatory blending and subsidies. Yet, even if food-based biofuels disappeared, the issue remains that rising high energy prices will promote intensified use worldwide of land for energy crops, requiring huge amounts of mineral fertilizers and putting nature under additional pressure. In policy terms, this defines three major tasks. The first is replacing the current excise taxes on energy carriers by a uniform carbon tax, so as to mitigate greenhouse gas emissions in an efficient manner, the second to prevent price fluctuations on the oil markets from destabilizing food markets, as happened in recent years. Introduction of upper limits on the use of food for biofuel could prove effective here. The third, much wider, task is to make the transition to a partly biomass based energy production possible and sustainable, that is establishing fair distribution of property and user rights over the lands, while safeguarding biodiversity and soil fertility and maintaining adequate labour standards and living conditions, also during periods that these become non-profitable following a drop in energy prices.