Management of rice production systems to increase productivity

transport to the root‐soil interface is impeded by the diminished rate of
diffusion and mass flow (Yamboa and O’Toole, 1984). The low nitrogen
concentration under zero and low‐input application rates was not conducive
for effective nitrogen uptake under the dry soil conditions that prevailed for
most of the growing season.
According to Fukai et al. (1999); Graham and Welch (1996) plant species
and varieties within species do differ in nutrient uptake efficiency, and dry
matter accumulation per unit time and growth duration. Genotypes also
differ in the efficiency with which nutrients are used in the proportion of total
dry matter production and in the proportion and quantity of nutrients
translocated to the grain. The low‐input rice varieties develop a massive
biomass during the early growth stages forming a broad canopy, and
phenomenally after panicle initiation becomes compacted and the leaves seem
to reduce in size. It is hypothesized that this relative reduction in canopy size
is as a result of nutrient translocation from stem and leaves into the panicle for
grain production. The stem N content is affected both by fertility and
available moisture levels. During the driest year of experimentation stem N
content increased drastically, even though grain production diminished
(Figure 6).
Tissue N concentration was below 1.2% in 2000 and 2001 cropping seasons
independent of N application rates. In 2002, a relatively drier year, the N
tissue concentration ranged between 0.8 and 1.0% for zero the application rate.
For the 160 N application rate tissue N concentration ranged between 1.1 and
1.5%. This is much higher than that recorded in the years with normal rainfall.
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