# **1. Introduction**

Since independence in the 1960s, Sub-Saharan African countries (SSA) have undergone exceptionally fast population growth. They also have faced urbanization and some economic growth, which would have tended to increase the demand for agricultural products. The rising population has resulted in farm sizes that in many areas are now close to Asian levels (Headey and Jayne, 2014; Otsuka and Place, 2014). On the other hand, urbanization has created new market opportunities for the farmers. Under the theory of intensification of farming systems of Ester Boserup (1965) and Hans Ruthenberg (1980), both population growth and market access can lead to a virtuous cycle of higher use of organic manure and fertilizers and investments in mechanization, land and irrigation that have the potential to offset the negative impact of population growth on farm sizes, maintaining or increasing per capita food production, and even increase farmer’s income (The BR model of intensification). The increase in output, however, comes at the cost of an increase in labor and other inputs per hectare cultivated. The positive outcome has been realized in those tropical areas of the world where technical change has added impetus to productivity growth. However another outcome was observed by Geertz (1963) in Java prior to the Green Revolution, in which the intensification triggered by population growth and market access was insufficient to lead to enough productivity growth to make today’s farmers better off than their parents, and that instead they became worse off. Geertz called this process agricultural involution. Since the 1960s, biological technical change in SSA has been lagging behind the rest of the world, and so have fertilizer use, mechanization and investment in irrigation (World Bank 2008).

The literature on agricultural intensification in Africa developed significantly in the 1980s and has resumed over the past decade. It generally finds that in most areas studied intensification has progressed along the lines predicted by Boserup and Ruthenberg, and that agricultural involution is confined to few areas. These studies have been done using samples of locations for intensive studies. Under the Intensive Agricultural Surveys (ISA) that have been imbedded in broader Living Standard Measurement Studies (World Bank, 2009), national household data for six African countries is becoming available that contains the intensification and technology variables as well as income. These panel data will over time present a unique opportunity to test the BR model in different countries and different agroclimate zones, and to see whether there are signs of involution. At the present cross section data are available for six countries, while panel data are or will become available for all countries over the next few years. As we will show, only panel data over a sufficient period of time will be able to rigorously test the BR theory.

In this paper we are setting the stage for such later studies by describing the status of intensification across the six countries (Ethiopia, Malawi, Niger, Nigeria Uganda and Tanzania). Following Binswanger et al. (1993) we also study the impact of the agro-ecological endowment and access to markets of the environments in which the farmers live on population density, infrastructure and agricultural variables including output, and use of modern inputs. We construct a single variable for each of these, the agro-ecological potential derived from the potential yield estimates of Toth et al. (2012), and market access (measured by an urban gravity variable) of the environments in which the farmers live. Since AEG and UG are clearly exogenous to the status of intensification, input use and investment, we can estimate causal effects rather than just correlations. Among other findings we show that population density and infrastructure have evolved over time so that we observe higher densities, and better infrastructure and market access in areas with high agro-ecological potential and a high UG.