Management of rice production systems to increase productivity

1.0Mpa, a range in soil water potential that does not strongly restrict water
uptake by most plants (Nye and Tinker 1977; Chapin, 1991).
Because the rate of ion diffusion to the root surface is usually the rate‐
limiting step in nutrient uptake by plants, reduction in water availability may
affect plant growth substantially. According to Chapin (1991), the effects of
low soil water content on nutrient availability may be nearly as important as
the direct effects of water stress on plant growth. Evidence is that tissue
concentrations of growth‐limiting nutrients (nitrogen and phosphorus) often
decline during water stress, whereas one would expect these elements to
increase in concentration if water directly restricts growth more strongly than
it affects nutrient uptake. Second, experimental manipulations indicate that
adding nutrients enhances growth of some desert annuals more than adding
water (Gutierrez and Whitford, 1987; Chapin, 1991). Nitrogen is the most
limiting nutrient, but under drought conditions, phosphorus is relatively
important.
The timing, frequency and amount of rainfall during the growing
season determine the land productivity in a rainfed environment. For
increasing productivity and stabilizing yield, technologies and strategies that
minimize the effects of uncertain water availability are needed (Saleh, 1995).
One management option for upland rice is the use of low‐input rice
varieties. The requirement of nitrogen by rice varies with location, variety,
season, and management practices. The amount of nitrogen to be applied for
rice is dependent upon a number of factors, such as likely losses of N through
leaching, immobilization, mineralization and denitrification, environmental
factors (solar radiation and temperature), plant characteristics (tillering
potential, leaf area index, resistance to lodging and length of growing cycle),
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