Study On Simple And Convenient Techniques In Raising Medium-Seedlings For Mechanical Transplanting Of Rice

In 2002-2003, with Wu Yun Jing 7 and Wu Yu Jing 3 as materials, the morphology of the seedlings, seedlings quality , grain yield and its components were investigated under various treatments of sowing densities, seedbed soil fertilizing and seedling ages in raising medium-seedlings for mechanical transplanting of rice. The results are as follows:(l)When the seedling was transplanted at the leaf age of just after 3, the main indices of seedling quality such as root-developing ability in field, the ratio of dry weight to seedling height, above ground dry weight and the stem thickness at the base, were worsened with the increase of the sowing densities. The indices for the least density ( 170.7 grains/dm2) treatment were significantly or obviously superior to other treatments, but its grain yield was significantly lower than others else due to higher empty hill percentage and fewer seedlings per hill in field. Although there existed a decreasing trend in seedling quality with the increase of the sowing densities from 229.4grains/dm to 400. 1 grains/dm", the differences among the densities were not significant for grain yields, indicating that the sowing density for the strongest seedling was not the suitable density for the seedling nursery with two-layer plastic film for mechanical transplanting. The suitable sowing density was around 230 of grains/dm2 for the purpose of extending suitable seedling transplanting period.(2)The peak of seedling dry weight appeared at the 20th day after sowing when the leafage of the seedling was 3.8~4.1 for all the density treatments except for the least density (170.7 grains/dm2) treatment. The seedling dry weight decreased or ceased increasing, and seedling quality got worse thereafter. The higher the density, the quicker the speed of the seedling deteriorating would be. So the critical suitable transplanting time for these densities was at the 20th day after sowing or a little earlier when the leafage was 3.8~4.1.(3)The main indices of seedling quality, such as root-developing ability and dry weight of seedlings nursed in high levels of fertilizing, were significantly higher than those in low fertilizing levels ;Furthermore, tillers of the seedlings nursed in the high levels developed earlier ,and the peak tillers was greater ,but the ratio of productive tillers were lower and spikelets per panicle were less ,the difference among treatments in grain yield was not significant ,but the trend which yield was raised with the increase of fertilizer levels was obvious. According to these results, the appropriate indices for vigorous seedlings of Wu Yun jing 7 were as follows :12 cm for seedling height ,2.7 mm for thickness of fake-stem ,1.0~2.0 for the ratio of sugar to nitrogen .(4) At seedling age of 16d to 2 Id, the main indices of seedling quality, such as the root-developing ability , the sugar content of stem and sheath and the ratio of dry weight to seedling height were improved. At seedling age of 21 d to 35d, the seedling quality obviously went worse, the sugar content of stem and sheath and the ratio of dry weight to seedling height decreased. The ratio of seedlings to seeds and living seedlings of paddy field decreased with the prolonging of seedling age , seedlings per hill were reduced and empty hill percentageincreased, the number of seedlings in paddy field decreased. The number of seedlings in paddy field in the high sowing density treatment was higher than that of the low sowing density, it was reduced with the increase in fertilizer levels at seedling age of 16d and high sowing density. It was raised with the increase in fertilizer levels at seedling age of 21d and 35d. The results adequately indicate the interaction effects on quality among sowing density , seedbed fertilizing and seedling age. It has referenced value in getting convenient measures of seedling for mechanical transplanting.(5)The grain yield was significantly decreased with the prolonging of seedling age. The influence of sowing density on yield wasn't significant. The effect of seedbed fer...