The System of Rice Intensifi cation (SRI) 99seedling per hill had higher yield compared to three seedlings per hill (San-oh et al,
2006). In addition, they reported that plants with one seedling/hill had greater
numbers of crown roots, root length density and cytokinin content compared to
plants with three seedlings/hill. The photosynthetic rate at later growth stages was
significantly higher in single seedling/hill compared to three seedlings/hill.
However, single seedling/hill may be justified with the concept that the yield-
contributing parameter within the plant can be modified by manipulating intra-
hill interactions; still, inter-hill and row spacing need to be adjusted according to
varietal characteristics (plant height, leaf area index, leaf posture and plant canopy
area) to achieve optimum plant population per plot to realize higher yield poten-
tial under SRI management practices. Once again, farmers are well placed to
experiment with spacing and its relation with varieties and crop yield. Increased
spacing with younger seedlings runs counter to the traditional experiences of rice
farmers and is one aspect of SRI that is approached with much scepticism by farm-
ers who are experimenting with SRI concepts for the first time, with even more
scepticism from neighbouring farmers. However, the impact of these practices on
plant growth is sufficiently spectacular that neighbouring farmers start asking,
‘what variety are you using?’ Regardless of the eventual merits of SRI, it stimulates
self-development and increased ownership by farmers of their production proc-
esses.
Intermittent irrigation
In recent years, the main aim of developing intermittent irrigation of rice has been
to save water. It was reported that 25–50 per cent of water used could be saved by
this method without any adverse effect on rice yield (Ramamoorthy et al, 1993;
Tajima, 1995). In contrast, it has also been reported that intermittent irrigation
increased water consumption and water stress, decreased leaf area index, induced
early senescence and decreased the rate of photosynthesis and net assimilation rate
(Lu et al, 2000). Recently, Belder et al (2005) have found that in aerobic rice cul-
ture, crop growth and yield was limited by water deficits and not by nitrogen
deficiency. However, it was also found that growth is not harmed when plants are
exposed to limited water conditions during their vegetative stage (Boonjung and
Fukai, 1996). These authors concluded that the plant adopts osmotic adjustment
at the vegetative stage which constitutes the most noticeable mechanism of dehy-
dration tolerance in the rice plant (Steponkus et al, 1980). But, any drought stress
at later stages in plants which are not exposed to such drying treatment can cause
great loss, especially when plants are in the early reproductive phase (Kobata and
Takami, 1981).
Interestingly, in HYT, intermittent irrigation served a different purpose.
According to the HYT theory, the so-called ‘broken irrigation’ method was used to
control tillering, improve soil conditions and to maximize efficiency at harvest by
changing the sink–source relationship. The ‘broken irrigation’ method entailed the
following procedure: after flooding the field, water intake was cut so as to let the