Breeding density: brood stage is refers to the unit in the area of feeding bird-flu brood only number.
饲养密度：在育雏阶段是指单位育雏面积上饲养的雏鸡只数。
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Adequate root number, deep root system, and efficient root activity per unit of root biomass will be needed for high-yield rice in the future breeding programs.
Increasing yield level per unit area is forever theme for rice breeding aim, and advancing photosynthesis efficiency is one of key factors for improving grain yield.