Mining of Nutrients in African Soils Due to Agricultural Intensification - Principles of Sustainable Soil Management in Agroecosystems - page 401

15 Mining of Nutrients

in African Soils
Due to Agricultural
Intensification

Eric T. Craswell and Paul L. G. Vlek

CONTENTS
15.1 Introduction .................................................................................................. 401
15.1.1 Soils in Africa ................................................................................... 403
15.1.2 Crop Intensification ..........................................................................404
15.2 Rates of Nutrient Depletion ..........................................................................406
15.2.1 Methodology .....................................................................................406
15.2.2 Nutrient Balances at International and Regional Scales ..................408
15.2.3 Nutrient Balances at National Scale .................................................409
15.2.4 Nutrient Balances at Farm and Plot Scales ....................................... 411
15.3 Drivers of Nutrient Mining ........................................................................... 412
15.3.1 Population Pressure .......................................................................... 412
15.3.2 Low External Nutrient Inputs ........................................................... 413
15.3.3 Climatic Risk .................................................................................... 414
15.4 Addressing the Challenge of Nutrient Mining ............................................. 414
15.4.1 Recycling Nutrients in Peri-Urban and Urban Agriculture .............. 414
15.4.2 Conservation Agriculture ................................................................. 415
15.4.3 Integrated Soil Fertility Management............................................... 416
15.4.4 Policy Issues ..................................................................................... 416
15.5 Conclusions ................................................................................................... 417
Abbreviations ......................................................................................................... 418
References .............................................................................................................. 418

15.1 INTRODUCTION
In the twenty-first century, food security in many African countries remains a
major concern. A recent United Nations report estimates that in sub-Saharan Africa
(SSA—this region is the focus of the chapter, but some reference is made to the
rest of the continent), 218 million people, some 30% of the population, suffer from
chronic malnutrition (FAO 2009). Average cereal yields in the region of 1.2 Mg/ha

401