Of yield gaps and yield ceilings: Making plants grow in particular places

The System of Rice Intensification (SRI) and rice genetic improvement are proposed as two approaches to improving and increasing rice production. In recent exchanges, they have been represented by their respective supporters as starkly contrasting, almost mutually incompatible alternatives. However, advocates on both sides of this argument have tended to stress the genetic and physiological characteristics of rice plants and place less emphasis on the spatially and temporally situated knowledge and management skills of farmers, which are the means by which any agricultural technology is locally adapted and integrated into livelihood strategies, and technological potential is translated into real outcomes in specific settings. Taking this proposition seriously would entail a substantial reorganisation of agricultural research and extension, bridging the historical divide between these two wings of professional agronomy. It would require agronomists of both types to work more collaboratively with farmers. It would also require scientists to produce new kinds of outputs, such as analytical frameworks, heuristics and decision-making tools to help farmers apply scientific insights to their own constrained circumstances. This argument is made with reference to the cases of SRI (a cultivation system that is said to boost farm yields without the need for genetically improved germplasm) and C4 rice (a crop-improvement project intending to 'supercharge' rice photosynthesis to increase rice yields). The paper uses the agronomic concepts of the 'yield gap' and the 'yield ceiling' to offer a perspective on strategic questions about the goals and organisation of agricultural research and extension.