Studies On The Growth And Regulation Of The Seedling Growth And The Long-term Age Stage Of Mechanical Transplanting Of Rice

In 2004-2006, with Wuyujing 3 and Yangjing 9538 as materials, the seedling nurse of mechanical transplanting and effect of seedbed fertilizing on seedling growth were investigated, the seedling growth in the long-term age stage and the effect of plant growth regulator on seedling growth were observed. The results were as follows:(1) The contents of available N, P, K were increased quickly by application of inorganic fertilizer in the seedbed. The increase in available N exhibited an exponent curve, and which was higher under high level of fertilization than under low level, and was faster in hill soil than that in alluvial soil. Available P content increased linearly with the increase in fertilizing level, there was significant difference between soil types. The velocity increase in hill soil was more quickly than that in alluvial soil. The trend of increase in available K content was similar to that in P, but the difference of velocity increase between different types of soil was not significant. During the seedling raising period, available nutrient consumption had its own characteristics. High fertilization trended to high consumption, and the consumption of available N was quicker than those of available P and K.(2) Seedbed fertilization significantly affected the seedling growth and seedling quality. The seedling height increased with seedbed fertilizing levels, indicating the fertilizing level could control seedling height, the dry seedling weight, dry weight per unit height, the base stem thickness, leaf SPAD values and nitrogen content of seedlings increased with fertilization levels in a suitable range, suggesting that the seedling growth can be controlled by seedbed soil fertilizing. However, root activity, root number, root length, increased first and then decreased with the fertilizing level, and they were more sensitive to the fertilizing level than the seedling aboveground, indicating the roots could grow well under proper fertilizing level. Root / shoot ratio decreased with the increase in fertilizing level, which showed high fertilizing level was more effective on the part aboveground than that underground, and strong seedlings of mechanical transplanting should have suitable root / shoot ratio. The results of metabolites between carbon and nitrogen showed the nitrogen content and usable sugar in seedling decreased with seedling age. The nitrogen content in seeding was about 30 mg/g in suitable transplanting period. The nitrogen content in seeding increase with fertilizing level, but difference among fertilizing levels decreased with seedling age. The soluble sugar in seedling decreased with fertilizing levels. Ratio of sugar/nitrogen negatively correlated with seedbed soil fertilizing level, and the correlation coefficients were 0.9623 in alluvium soil and 0.9614 in hill soil. The results suggested that sugar and nitrogen metabolism were mainly controlled by soil fertilizing level. The rooting ability of seedlings decreased in too low or too high fertilizing level. Seedbed fertilizing could shorten the time the seedling to regreen and revive after transplanting, but it had no significant effect on the tilling velocity. The results showed that, only in a suitable fertilizing level, the strong seedling with suitable shape and root/shoot ratio for mechanical transplanting can be raised.(3) The seedling which couldn't be transplanted in time at suitable stage in seedling dishes was named long-term age seedling. In early long-term age stage (from sowing to 28 day after sowing), the part aboveground still could maintain certain growth. Seedling dry weight and dry weight per unit height still increased slightly, but leaf (SPAD) value decreased quickly. The part underground grew stagnantly, and root length, root number stopped increasing, the root activity and root/shoot ratio decreased quickly. In severe long-term stage (36 day after sowing), seedling height increased quickly, the seedling dry weight to height ratio descended significantly, leaf (SPAD) value kept in a low level. The root activity and growth were in the lowest level. The seedling sugar metabolism was more sensitive, when compared with nitrogen metabolism, thus sugar to nitrogen ratio in seedling in the severe long–term age stage decreased significantly. Under different fertilization levels, there was significant difference in rice seedling growth characteristics. The base stem thickness under high fertilizing level changed slightly, but seedling height increased quickly, dry weight per unit height decreased significantly, the part underground grew slowly, root number, root length, root activity and root/shoot ratio decreased significantly, when compared with low fertilizing level. The above result showed that in long-term age stage especially in the severe stage, rice seedling growth was mostly decided by growth condition and seedling raising condition in suitable transplanting stage. The rice seedling in the low fertilizing level could maintain higher sugar to nitrogen ratio in long-term age stage, thus keep better nutrition status for the seedling growth. (4) All the growth regulators could influence the seedling growth obviously. There had obvious effects during the suitable transplanting stage. Compared to the control, ABA could increase the seedling quality, such as seedling height, the base stem thickness, root length, root/shoot ratio, root weight and so on. The activity of peroxidase and catalase were significantly increased, Ethylene inhibitor could very significantly promote the usable sugar, nitrogen content and the activity of peroxidase than that of control. GA inhibitor could significantly promote the root length, usable sugar and nitrogen content, the activity of peroxidase and catalase obviously; MET could control the seedling height, it had a certain effect in promote dry weight per unit height, the base stem thickness, root dry weight, root/shoot ratio, root activity, usable sugar content, the activity of peroxidase and catalase. In the long–term age stage, the aboveground dry weight, dry weight per unit height and the base thickness which used ABA were still obviously higher than that of control, but the difference became slight, such as root/shoot ratio, the activity of peroxidase and catalase, some indices were even reversed than that of control; The seedling quality which used ethylene inhibitor had no difference with the control, except the usable sugar content significantly higher than the control; The seedling which used GA inhibitor had higher base stem thickness and useable sugar content than the control, while leaf SPAD value was less than the control, other indices has no difference with the control; the seedling treated with MET still had the effect of control the seedling height, and the seedling height obviously lower than the control, the usable sugar and nitrogen content, the activity of catalase obviously higher than the control. But to the severe long-term age stage, the effect of each treatment that used before the suitable stage had already disappeared, there was no obviously regulation to the seedling.