1.1 Background to the Study
There is no question about the need to increase the yield potential of rice in
response to global population increases and arable land decreases. One of the
approaches to meeting this goal is breeding new varieties. Many high-yielding
varieties have been released, and the introduction of novel genes has made
significant progress (Matsuoka et al. 2013; Surridge 2014), yet the practical
impacts are limited. Some gains have come from a crop management approach,
with site-specific crop management (SSCM) being introduced to attain better
yields with reduced by optimized fertilizer input (Dobermann et al. 2012).
Dealing with water scarcity is also a challenge for the future in rice-growing
regions. Alternate wetting and drying (AWD) rice cultivation and aerobic rice
cultivation have been developed to address this issue (Bouman et al. 2007).
However, yields of rice under such management have remained mostly
unchanged or decreased slightly. Development of innovative management
technologies that will boost rice yield as well as increase water productivity, in
particular reducing water requirements, remains to be achieved.
To elucidate the conditions that must be satisfied to raise rice yields up to their
potential is an important research goal. For example, Horie et al. (2005)
suggested – based on their review of past scientific knowledge and their
research data (Takai et al. 2006) – that a higher crop growth rate (CGR) at the
late reproductive stage (2 weeks before heading) would be the most effective
change for realizing higher yield. This concept implies that a high CGR can
sustain an increase in spikelet numbers by controlling their degeneration
together with high dry matter production which will contribute to boosting yield
potential. However, research on crop management systems to achieve high
yields closer to the yield potential in a stable manner is not sufficient. This is
one reason why grass-root techniques such as System of rice intensification
(system of rice intensification) have attracted researchers’ attention.