We used the AEP/ha variable to calculate AEP per person, a new measure of agro-ecological population pressure. We find that this measure ranks countries quite differently with respect to rural population pressure than rural population density. The AEP/ha of Uganda is by far the highest in among the countries the lowest in Niger, with Tanzania close to the average across countries. However, in terms of AEP per rural person it is the highest in Tanzania followed by Niger, and then only Uganda. Agro-ecological population pressure is therefore the highest in Uganda, followed by Niger and the Tanzania. In terms of rural population density on the other hand, the rank with Uganda the first, and both Niger and Tanzania last. We therefore conclude that agroecological population pressure is so poorly related to population density that rural population density is a poor measure of population pressure on the natural resources.

# **Descriptive results**

Given the rise in population pressure in all these African countries, the improvements in infrastructure and growing urban demand, Africa’s land use intensity has reached permanent cropping in all the countries. Fallow areas have virtually disappeared. Under permanent agriculture high doses of organic and inorganic fertilizers are required to maintain or restore the soil nutrients taken out by the plants. Except for Malawi and Ethiopia the proportion of households using chemical fertilizers is clearly too low to do so. Nor is this compensated by high proportion of households using organic fertilizer, which is high only in the warm semi-arid and the three cool areas. The BR theory also predicts that under pressure from population growth and market access irrigation investment, and other modern technologies would be used more intensively to increase yields. However, these factors also not triggered significant irrigation investments even in semi-arid areas where the payoff to irrigation is high. Unfortunately we do not have data on other land investments, or on mechanization to judge whether expected intensification responses have occurred with respect to these important investments. However, the descriptive analysis suggests that the BR impacts of population pressure and market access have triggered an inadequate response of the farming systems with respect to irrigation and technology use.

An additional inconsistency arises when comparing Tanzania to Malawi, with Tanzania having about 2.4 times the AEP/person as Malawi, i.e., much lower population pressure. Yet cropping intensity is about the same and so is the intensity of use of manure. Use of agro-chemicals is more prevalent in Tanzania than Malawi. The only area where Malawi has greater intensity of input use than Tanzania is in the use of inorganic fertilizers and improved seeds. In addition to being triggered by the forces of intensification, these higher uses are consistent with the longstanding effort of Malawi to increase the use of these two factors, including the significant subsidies that have been provided in recent years.

Of course, our descriptive analysis is in now ways a rigorous test of the BR hypotheses. First of all, there are enormous variations in soils, crops and other biological variables that are likely to have a significant impact on the degree of intensification and its pattern among the different intensification variables. These have been completely ignored in this paper. In addition, there are sharp differences in policies and infrastructure investments that have not been taken into account. It is therefore important that the theory be tested with panel data, where these variations can be aggregated into fixed environment effects.

# **Regression analysis**

We found significant responses of population density and infrastructure, farming systems characteristics, farm technology and profits per ha to our measures of AEP and UG, and the signs are all according to expectations. However there is a sharp divide between the nature of impact of AEP and UG across the variables: 17