Management of rice production systems to increase productivity

lowland rice, and lesser risk associated with its production. Both nitrogen and
phosphorus play important roles in its growth and yield, but nitrogen is most
often the limiting nutrient and is required in the in greatest quantity for rice
production. The nitrogen effect is manifested quickly on plant growth and
ultimately on yields. Hence the fertility status of a soil depends to a great
extent on the nitrogen status of the soil (Sinha and Prasad, 1980). Organic
matter is the major source of nutrients, especially N, in low‐input rice
cultivation systems. Experiments have shown that, even in the case of high
yields of rice, N derived from soil still makes up about 76 to 80% of the total
uptake of N of a single‐cropped rice (Ponnamperuma, 1984). Generally, the
higher the organic matter content, the higher is the N‐supplying capacity of
the soil.
Ideal cultivars would be those that perform well under low soil fertility
but also respond well to applied fertilizer and are drought‐tolerant. Cultivars
with relatively high harvest index (HI) are generally found to be more efficient
in nutrient‐use, i.e. giving higher yield per unit of nutrient uptake (Vose, 1990,
Inthapanya et al., 2000). Grain yield can be analyzed in relation to acquisition
and utilization efficiency of nitrogen. Genetic variation for grain yield under
different nitrogen fertility conditions is examined. Once genetic variations in
nitrogen uptake and utilization efficiency are found, then physiological or
morphological factors that are responsible for such variations can be further
examined. The traits responsible for high yield once identified can be used as
selection criteria in plant breeding programs, if suitable screening procedures
can be developed.
The increase in rice production to feed a growing world population will
require a threefold increase in applied N at present levels of N fertilizer‐use
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