R.L. Voortman

African land ecology: opportunities and constraints for agricultural development

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.

Spatial dimensions of precision agriculture: a spatial econometric analysis of Millet Yield on Sahelian Coversands

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.

An empirical analysis of the simultaneous effects of nitrogen, phosphorus and potassium in millet production on spatially variable fields in SW Niger

Low soil fertility is a major constraint for increasing millet production on the acid sandy soils of the West African Sahel. On these soils, all three macronutrients: nitrogen (N), phosphate (P) and potassium (K), may be expected to limit crop yields. The important question is therefore: which of them is the most critical and would, if applied in small amounts, increase yields significantly? This paper addresses this question with an empirical approach, thus avoiding the commonly observed difficulty in the interpretation of agronomic research, caused by the extreme local soil variability which characterizes Sahelian coversands. We actually exploit soil variability by using novel non-parametric techniques for data exploration in combination with spatial methods of parametric model estimation. Apart from N, P and K, the effects of surface crusting, local topography, manure levels, farmer behaviour and spatial dependence are taken into account, since these may confound the true effects of N, P and K. A quadratic formulation conforms best to the data and explains 81 percent of the yield variation. The equation highlights the importance of interactions among variables and thus confirms the possible impact of native soil conditions on the outcome of fertilizer treatments in experimental research. The results of much earlier, multi-year, research are confirmed remarkably well by this single year study. In addition, a spatially explicit assessment on the crop response to increasing nutrient levels highlights that blanket fertilizer applications are inefficient, because yield increases in some places will be accompanied by yield decreases at other sites. Cash-constrained farmers therefore have to resort to precision farming techniques to maximize returns from minimal external input packages. However, a large part of the good explanation of millet yield variability over space derives from spatial autocorrelation, and not directly from topsoil N, P and K. This calls for further research on the factors that affect millet yield and on the characterization and classification of sites, followed by experimental work to design site-specific fertilizer technologies.

Recent historical climate change and its effect on land use in the eastern part of West Africa

There are indications that low rainfall, drought periods and famine become more frequent in West Africa. This may in part be a rather early expression of the effect of global warming but it is very likely that local factors such as drastic changes in land cover due to expanded cultivated area, as required by a growing population, play an important role. Before studying the causative mechanisms of climate change, it first needs to be established that climate did indeed change significantly, and if so, its nature, extent and magnitude have to be quantified. To this effect time series of annual rainfall (1950-1992) for 42 synoptic climate stations in eastern West Africa, covering 5 countries, were analyzed. The data were subjected to several statistical tests for the entire time series and parts thereof. The outcomes were interpolated in a GIS environment to assess the spatial pattern of change. The time series and spatial analysis reveals that climate change is indeed significant in the northern part of the study area and that the degree of change shows a spatial pattern that can be related to the weather system in combination with topography. A remarkable feature is that the clmnge in rainfall is not a gradual one, but consists of a trend break with zero trend before and after the break. This is unexpected because it might imply that causal factors have to be sought under those that do not change gradually. The year of occurrence of the break is around 1970 but varies in time, again according to a geographic pattern. The reduction of rainfall shortens the length of the growing period (LGP) and has a considerable impact on potential crop yields and their variability. The paper shows the serious implications of recent historical climate change for land use in the semi-arid region of West Africa.

RESEARCH NEEDS AND METHODS FOR DECENTRALISED ECONOMIC PLANNING

International debates on food and agricultural policy increasingly endorse the principles of the free market and stress the responsibilities of national governments for active policies to manage development, to achieve food security and to safeguard the environment. This paper argues that consequently policy-oriented research needs to establish databases and develop models, in which both rural and urban households figure prominently and in a properly geo-referenced manner. This will enable the policy analyst to design policies and to monitor their effect on a regional basis. The paper emphasises that policy-oriented research should provide a nationwide perspective, because in relation to sustainability, as far as environmental economics is concerned, virtually all theory and theory-based policy guidelines have been formulated for national economies in their totality. With respect to the representation of agricultural production itself, we discuss a class of spatial estimation techniques that can deal with missing data and account for qualitative observations, and that can make full use of spatially explicit information on crop yield potentials as generated by agro-ecological models.