Management of rice production systems to increase productivity

Sta Cruz et al. (1994) identified different morphological and
physiological features that enhance soil nutrient‐use‐efficiency. The following
were identified: growth type, panicle type, and growth duration. Genotypic
difference can also interact with cultural practices and environmental
variables.
Roots can moderate the effects of drought by growing deeper, longer,
or at higher densities within the soil to reach more water, thus increasing the
plant’s water supply, or by changing the rate at which water becomes
available (Gregory, 1989; Sta Cruz and Wada, 1994). Genetic variations are in
several root characteristics associated with increased capacity in rice to extract
available soil water which may be responsible for increased drought
avoidance, have been reported by O’Toole and Chang (1979), Yoshida and
Hagegawa (1982), Ekanayake et al. (1986), and Nguyen et al. (1994).
Generally, genotypes that perform well at low nitrogen levels are tall,
have a low percentage of productive tillers, have high dry matter production,
are susceptible to lodging, and have low panicle‐to‐straw weight ratios. They
grow relatively fast and cover the fields even without nitrogen addition. At
high nitrogen levels, higher growth rates in the early growth stages result in
mutual shading during the middle and late growth stages. This reduces
nitrogen uptake because net photosynthesis is decreased, resulting in fewer
tillers and weaker roots and lower dry matter production. By contrast,
genotypes that respond productively to high nitrogen have short stature, high
panicle‐to‐straw weight ratios, a high percentage of productive tillers, and
slow growth in the early growth stages. This plant type shows little mutual
shading (Tanaka et al., 1964; Sta Cruz and Wada, 1994).
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