ABSTRACT
Rice joined quite late the club of high-yielding, input-responsive crops. This chapter discusses the sink and source capacity in rice and environment effects on both. It reviews information on how source and sink size and explores opportunities to optimize source-sink relationships through management and breeding. The gas exchange and carbon assimilation system of rice is adapted to warm, humid, and—except in upland-adapted rices—water-logged environments. Initial vegetative growth is primed by grain reserves until autotrophy is achieved at the three- or four-leaf stage, 2 weeks after germination. Effects on rice yield, however, are small as compared to drought stress at reproductive stages, which irreversibly reduces the number of fertile spikelets. Most rice crop models are deterministic: they consist of formal, hierarchical rules for the utilization of resources by an individuum or uniform population, based on historical or hypothetical environments. Partitioning rules of the International Rice Research Institute-Wageningen rice models approximate the patterns observed under favorable growth conditions.
