Crop Yields and Global Food Security. Will Yield Increase Continue to Feed the World?

Tony Fischer, Derek Beyerlee and Greg Edmeades jointly represent more than 100 years of expertise in agronomy, crop physiology and agricultural economics. They served many different international institutions but have a career at the International Wheat and Maize Improvement Centre (CIMMYT) in common. These three distinguished scientists put together a great book summarising and reviewing the developments in crop yields and their effect on global food security. As the sub-title of the book reveals, they also look ahead into the next decades. The book has been written in the context of the question whether progress in crop yield is sufficient to meet the future demand for staple crops (i.e. an estimated 60 per cent higher in 2050 than in 2010) without substantial increases in real prices. After an introduction of this question and definitions of the key concepts, the book reviews the progress in yields of the world's major commodities. Wheat, rice, maize and soybean are treated in separate chapters, while other coarse grains (barley, sorghum and millet), pulses, rapeseed, peanuts, sunflower, sugarcane, sugar beet, cassava, oil palm, potato and sweet potato are elaborated in somewhat less detail (partly because much less data are available). Each commodity is addressed for its major mega-environments. A mega-environment is defined as a commodity-specific term, referring to broad areas facing similar agro-ecologies in terms of weather, abiotic and biotic stresses and cropping system requirements. For each mega-environment, representative regions are used as illustrations. As the book is highly quantitative in nature, the examples are by definition those regions for which data are available. This also implies that the book has some emphasis on regions from the western world and from Asia, while Sub-Saharan Africa (SSA) is under-represented as detailed measurements of farm and potential yields are more scarce (or inaccurate) for this part of the world. That is of course an issue, as an important part of the increase in demand will occur in SSA. In the book both progress of on-farm yields (i.e. average actual farm yields) and potential yields (either irrigated or water-limited (rainfed)) are estimated. The first are derived from surveys and statistics and the latter from comparative or single variety experiments. Comparative variety experiments allow the assessment of genetic progress of potential yields by relating the measured yields in well-managed experiments (preferably avoiding any growth stress) to the year of release of the variety. As such the book heavily relies on observed data, which makes it a truly unique asset of observed farmers' and experimental yields. A drawback is that the book is somewhat idiosyncratic in using in a few cases own definitions, such as expressing the yield gap in relative deviations from farm yields. This is clearly different from the majority of the literature that expresses the yield gap as (a relative) deviation from the potential yield. This is not so convenient, as the potential yield is a much more typical and stable feature of an environment and it is more intuitive to compare yield gaps across the globe to express it as a percentage of the potential yield. Another limitation of the book is perhaps the downside of its strength. It relies heavily on experimental data, and hence the estimations of yield gaps may be somewhat conservative for those cases where good data on potential yields are lacking. For instance, experiments that approach potential yields are really scarce in some parts of the world, including SSA. After assessing yield gaps, the book continues with chapters about the causes of increases in potential yields (including the scope for further increases), climate change, resource use efficiency, trends in total factor productivity and policies. Although these chapters are clearly less comprehensive, they are helpful overviews. Finally, the book returns to the key question: will progress in crop yield be sufficient to meet the future demand for staple crops to avoid substantial increases in real prices? This question can be rephrased as: will crop yields (at farm level) linearly increase by at least 1.1 per cent per year (relative to 2010 yield)? Progress in farm yields depends on progress in potential yields and on closing the yield gap (the difference between potential and actual yields). Over the past decades, progress in potential yields had a larger contribution to increases in crop yields than closing the yield gaps (although with differences between crops). Of course the progress in potential yields has to go with the proper agronomy to harvest the greater potential. The authors conclude that looking ahead, the most feasible way to increase yields is to narrow the substantial yield gaps in some parts of the world. The book is a fantastic source of data on progress in actual and potential yields of the world's major food crops. It is also a clear text on the principles underlying progress in both types of yields and on resource use efficiencies. We can only hope the book will be updated every 10 years, so it remains the key source for progress in crop yields for a wide audience.