机插稻超秧龄秧苗的生长特点研究

Growing Characteristics of Rice Seedlings of Over-Optimum Age for Mechanical Transplanting

水稻机插移栽中秧苗不能及时机插而生长过度,形成超秧龄秧苗。本试验以扬粳9538为供试品种,在不同床土培肥条件下,观测了超秧龄秧苗的生长特征。在超秧龄初期阶段(至播种后28d),秧苗地上部仍维持一定的生长,秧苗干重和单位苗高干重尚有一定增加,尚能维持糖氮代谢。但秧苗叶色(SPAD值)迅速下降,地下部生长停滞,根长、根数停止增加,根系活力迅速下降,根冠比明显降低。在严重超秧龄阶段(至播种后36d),苗高依然快速增加,单位苗高干重大幅下降,秧苗叶色维持在较低水平。根系活力低,根系生长处于最低水平。超秧龄生长过程中秧苗糖代谢反应敏感,氮代谢相对稳定,糖氮比在严重超秧龄时大幅下降。床土肥力显著影响超秧龄秧苗生长,高培肥水平下的秧苗茎基粗没有显著变化,但苗高迅速增加,单位苗高干重大幅降低,地下部生长较低培肥处理更弱,根数和根长较低,根系活力下降迅速,根冠比与低培肥处理相比大幅减小。床土培肥水平对秧苗的碳氮代谢影响显著,高培肥处理的超龄秧苗营养状态更为劣化。以上结果表明,超秧龄阶段特别是在严重超秧龄阶段的秧苗生长,很大程度上取决于育秧阶段(适栽期)的育秧条件和生长状况,低培肥处理的秧苗在超秧龄生长中糖氮比能维持相对较高的水平,从而维持秧苗相对较好的营养状态。

The rice seedlings grown for a long time and not suitable for mechanical transplanting are called as ＂seedlings of over-optimum age＂. In this study, Yangjing 9538 was planted in seedling raising plates with different treatments of seedbed soil fertilizing levels. In the stage of 28 days after sowing, the above ground parts of seedlings could still maintain a few growth, seedling dry weight and the dry weight perunit of seedling height still had a little increment. But leaf color （SPAD） descended quickly. The roots grew stagnantly, root length and number of roots stopped increasing, the activity of root and root/shoot ratio descended quickly, and obviously. In the stage of 36 days after sowing, the seedling height increased quickly none the less, the dry weight per unit of seedling height descended significantly, seedling leaf color kept in a low level. The activity of root was low and the root system growth activity was in the lowest level. The seedling sugar metabolism was sensitive to the stage when the seedlings were at over-optimum age, while nitrogen metabolism was blunt, so the ratio of seedling sugar to nitrogen in the stage of 36 days after sowing descended significantly. The characteristics of seedling growth in the stage when the seedlings were at over-optimum age affected significantly by different fertilization levels. Under high level of fertilization, the basal part width of shoot wasn＇t changes obviously, but seedling height increased quickly, so the dry weight per unit of seedling height descended quickly; the roots grew weakly than these under low level of fertilization, root number and root length were less, the root system growth activity descended quickly, root/shoot ratio descended obviously. The seedbed soil fertilization level affected carbon and nitrogen metabolisms obviously, nutrition decreased largely under high level of fertilization. The above results showed that, rice seedling growth in the stage of 28 days especially 36 days after sowing was decided by the growing condition in a very great degree. The rice seedling in the low fertilization level can maintain higher sugar to nitrogen ratio in the stage when the seedling were at over-optimum age, and keep better nourishment for seedling growth.