Filling caveats in yield gap analysis

Yield gap analysis has been a well know notion in crop science since the late 1980s, but it has been become popular only recently. It is generally regarded a helpful starting point for mapping the opportunities for sustainable intensification of agricultural systems. Different methods exist to quantify and map yield gaps of our major food crops grown as sole crops (Van Ittersum et al., 2013). In significant parts of the world (e.g. in Sub-Saharan Africa and China), however, crops are not grown as sole crops, but in intercropping systems. This clearly complicates yield gap assessment. Also, at least 30% of the cereals is fed to livestock and livestock products constitute a major and increasing share of our diets. Many of the world’s agricultural systems are in fact crop-livestock systems. Finally, perennial crops are an important source of our nutrition and a component of agricultural systems that increases in relevance. How can the yield gap notion be applied to such more integrated or complex systems and how does it drive model development? Before addressing this question we briefly summarize a global approach with local relevance for sole crops, setting the scene for other systems.