The System of Rice Intensifi cation (SRI) 105Younger seedlings with higher root–shoot ratio encourage
root–shoot growth along with higher rates of cytokinin
synthesis
A most important crop production objective during the early growth period is to
secure the optimum number of tillers per square metre. Tiller production and
panicle development (at later growth stage) is related to cytokinin synthesis in the
root along with the number of phyllochrons of growth completed.
Transplanting single seedling per hill further enhances root
growth and root activity when grown with AWD during the
vegetative period
To realize the full potential of tiller development, it is necessary to improve the
light-receiving efficiency of the plant, prevent lodging and to improve the physical
condition of the plant. This could be enhanced by further root growth and activity
(1) by minimizing inter-plant competition and (2) by reducing leaf area density
which will ensure more erect and upstanding leaves without any shading effect. At
the same time, AWD will encourage root growth into deeper layers of soil. This
will maximize the roots’ surface area for better nutrient uptake. Greater root length
will also minimize water stress should the plant be exposed to drought conditions
during any period of crop growth.
AWD enhances microbial response and regulates the most
available nitrogen forms in the rhizosphere
AWD should balance the NO 3 :NH 4 ratio in the rhizosphere with higher root
length density for higher biomass production and should also regulate cytokinin-
auxin production for better tiller development. This effect could be further
enhanced when the soil has sufficient organic matter to reduce leaching loss of
NO 3 along with higher root growth at deeper layers of soil.
Shallow flooding during the post-anthesis period maintains
higher cytokinin content with higher root activity
Cytokinins are high nitrogen-demanding compounds so cytokinin production
increases sharply during high root nitrogen events which could be induced by sup-
plying the NH 4 form of nitrogen by shallow flooding during the grain-filling stage.
This would be better realized with higher root surface area and higher cation
exchange capacity as high root nitrogen events result from increased root absorp-
tion of nitrogen from the soil as well as mobilization of stored nitrogen in the
rhizosphere.