98 The Global Food System
discussed later. In addition, higher root quantity should enhance both nutrient
and water-absorbing functions. This assumption is in agreement with the finding
of Hanada (1976) where tiller bud formation was promoted by the application of
kinetin to the rice roots at the five leaf stage.
In summary, careful transplanting at the 2–3 leaf stage should yield improved
results as seedlings enjoy the benefit of both endosperm nutrition and of newly
formed roots. However, careful and early transplanting requires increased skill, and
hence labour; but once farmers realize that there is a set of options to evaluate in
growing and transplanting seedlings that will have an impact on production and
yield without heavy demands for costly inputs, rigid traditional practices will be
seen in a new light.
Transplanting single seedlings with wider spacing
Plants grown with wider spacing have more area of soil around them to draw
nutrients from. Such plants also have better access to solar radiation for better
photosynthesis. Hence they perform better as individual plants. Consequently,
there should be no mystery about why SRI plants invariably perform better than
conventionally managed rice in terms of yield per plant. The reason for the devia-
tion of this linearity in the case of grain yield per plot is that the yield is not entirely
dependent on the performance of the individual plant. It is also a function of the
total number of panicles per plot and on the other key yield-contributing param-
eters, number of filled grains per panicle and grain weight. Clearly, spacing is
critical in modifying the components that influence final yield. In this regard,
Takeda and Hirota (1971) showed that grain yield was unchanged between plant-
ing densities from 10 to 100 hills per m^2.
There is significant interaction between varieties and spacing. Generally, long-
duration varieties do better with wider spacing than short-duration varieties
(Baloch et al, 2002). This is in agreement with the recent finding of Stoop (2005)
who suggested that long-duration varieties will perform better under SRI manage-
ment practice. These responses support the hypothesis (Kira et al, 1953) that, with
increasing planting density, biomass yield reaches a ceiling value that is limited by
the supply of resources. The supply of resources mainly depends on the root sys-
tem activity. So, it can be suggested that wider spacing allows roots to grow pro-
fusely along with production of more tillers per plant.
Under SRI management it can be suggested that early transplanting provides
a longer vegetative growth period, and single seedling per hill reduces competition
and helps to minimize the shading effect on lower leaves. This helps lower leaves
to remain photosynthetically active, for much longer; and, in turn, root activity
remains higher for a longer period due to the plant’s enhanced supply of oxygen
and carbohydrates to the roots (Tanaka, 1958; Horie et al, 2005). Further, higher
root activity, in turn, supplies cytokinins to the lower leaves, delaying senescence
and helping to maintain photosynthetic efficiency of the plant at later growth
stages. This outcome has been confirmed by a recent research finding where single