In this study, fiber yield and changes of fiber qualities proportionately with jute growth and effects of cultural conditions on plant growth, fiber yield and fiber qualities are investigated. Their summaries are as follows:
1. The different sowing date experiments are studied on changes of yield and qualities in developmental process of jute fibers. From this experiments were made of clear that fiber yield indicates considerable increase with plant growth in the early sowing, but comparatively slow in the late sowing.
In the case of the early sowing, fiber tensile strengths show a little change, and in the late sowing, ones are weak in the early growth stage of the plant, and become considerablely strong with subsequent growth stage. Decortication of stem becomes gradually more difficult with the plant growth and fibers increase in coarseness and hardness by degrees. For the above-mentioned reasons, it seems to the authors that a reasonable harvest time of jute in Japan is at about 20 days after the flowering.
2. From results of this study on effects on fiber yield and fiber qualities by different sowing date there is no remarkable difference recognizable in the period from the first 10 days of May to the first 10 days of June.
But, with lateness of sowing date there is some decrease in fiber tensile strengths and in the period between the second 10 days of June and the third 10 days of July, fiber yields considerably decrease, and so fiber tensile strength are inclined reversely to strong in case of late sowing.
3. With the increase of soil moisture, plant growth becomes better and fiber yields increase also, and on the other hand attacks of stem rot diseases increase somewhat. Length and width in single fiber become larger with increase of soil moisture, but considerable difference is not indicated in fiber tensile strength, and on the other hand fiber tensile strength when there is low moisture, becomes stronger.
4. In density of planting, it seeme to the authors that reasonable density of plantings is 100 stocks per 3.3 m²in area, and dense planting is rather better than sparse planting with suflicient weeding, responsible fiber yields are possible in broadcast seeding, and fiber tensile strength shows little eflect of density of planting, but in dense planting it is somewhat more apparent.
5. Jute cultivated in upland fields inverted from paddy lowland fields indicate higher fiber yield, softer and brighter fiber qualities than ones in upland fields.
In above-mentioned field conditions, fiber tensile strengths are stronger in the early sowing, but the reverse is true in the late sowing.

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