Characteristics of rooting and early growth of transplanted rice nursling seedlings with several plant ages in leaf number

The rooting and development of transplanted rice seedlings (Oryza sativa L. ) are affected by the characters of the seedlings and the amount of damage to roots incurred by transplanting. Experiments were conducted to examine t he influences of these factors on the rooting and early growth of transplan ted rice nursling seedlings. To obtain these seedlings with different plant ages in leaf number and seedling characters, seedlings were placed in a da rk nursery chamber (32 degreesC) for 2 days, then raised for 3-7 days in a temperature-controlled greenhouse set at a day/night cycle of 24/19 degrees C under different seeding densities (200 g and 300 g per nursery box). The seedlings were continuously grown under the same temperature conditions aft er transplanting. The number of roots at 8 days after transplanting was hig her in seedlings with older plant ages compared with younger plants. Howeve r, transplanting injury, indicated by the rate of leaf emergence at 0-4 day s after transplanting, was observed when the plant age of a transplanted se edling exceeded 2.6 in leaf number. This was primarily due to an imbalance between the total length of the leaf blade and that of the roots. Furthermo re, this transplanting injury was aggravated by high-density seeding. These results suggest that the characters of seedlings greatly degrade when a pl ant exceeds an age of 2.6 in leaf number.