We thought that subterranean clover (Trifolium subterraneum) has the greatest potential of any annual clovers as a cool season cover crop. So we attempted to investigate the relationship between the persistence of sub clover seedling emergence after seed maturing and seed survival in the soil on the supposition that seeds are buried by tillage.
The seeds of sub clover both of Mt. Baker and trikkla which set at the soil surface germinated little during the summer, as these seeds immediately after seed maturing germinated little at high temperature. These seeds sprouted simultaneously in the early autumn, as the decrease of the hard seed ratio of sub clover seeds was effected by fluctuating temperature at soil surface. On the other hands, almost sub clover survived seeds buried at 5-10cm showed hard seeds, so these seeds germinated little in early autumn and will survived for several years in the soil.
Therefore we thought that the fields tilled by rotary after sub clover seed maturing, these seeds at soil surface will distribute within the depth of rotary share, over half of the seeds at the soil surface will emerge in early autumn and will reestablish the good stands. Other seeds which were distributed to lower depths by rotary tillage will remain in the soil to make a seed bank. The hard seeds in the deep soil layer will survive for several years, and if these seeds are redistributed to the soil surface by rotary tillage, they may soften rapidly and emerge. These seedlings will be useful to success for good stand. So rotary tillage will make an adequate soil seed bank of sub clover.

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The effects of seedling age on uniformity in growth, rootability and adaptability to automatic plug transplanter were investigated in cabbage plug seedlings for their timely transplantation. Growth of plug seedlings and fresh weight of cabbage head were recorded after transplanting. Major findings:
1. There was a positive corelation between the seedlings age and their uniformity in growth in nursery plug system.
2. This uniformity in growth is contributed to the limited size of the plug for root growth.
3. The seedlings with 2.5 leaves were inferior to any older seedlings in rootability.
4. The age of transplanted seedlings had no effect on their subsequent growth.
5. The number of leaves increased as seedlings aged in nursery plug system.
6. The seedlings with 5.0 leaves were considered unsuitable for use in the automatic plug transplantes due to their large size and thier spreading shape.
7. The head weight in cabbage was higher when older seedlings were used in transplanting.
From these observations, taking all factors (including cost and management time in raising seedlings) into consideration, we conclude that 3.5 leaves aged plug seedlings were suitable for timely transplanting in automatic mechanical transplantation of cabbage cultivar Matsunami.

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The characteristics of the noise produced by some agricultural machines were investigated. The intensity with which such noise reaches the operator's ears and its consequential effect on the operator, particularly with respect to sound level temporary threshold shift (TTS), were also studied. The results are as follows:
1) The noise produced by agricultural machines spread concentrically from the engine and muffler parts. Attenuation values were about 2-4dB/m starting from 2m radial distance from the noise source and farther.
2) Maintaining a distance of equal to or more than 2m from the noise source to the other workers provide less danger from temporary hearing loss. However, proper communication between the operator and the other workers could be negatively affected.
3) The agricultural machines used in the test had produced noise that enter the ears of the operator at 85-102 dB levels. However, the Labor Ministry's guidelines for noise injury prevention indicates a maximum safe level of 85 dB only. As such, continuous use of the machines tested in this experiment could be quite unsafe and dangerous to the ears.
4) The most prevalent sound frequency levels that were observed near the operator's ear while the various agricultural machines were being tested were those that belong to the 30, 50, 60, 70, and 120Hz (power spectrum).
5) Sound level TTS of ± 5 dB was observed on the operator's hearing ability after using some of the test machines for 1-3 hours. However, TTS levels of 5-15 dB were observed immediately after the use of most of the machines until an hour after stopping the work. Hearing loss recovery then starts until full recovery was achieved at around 3 hours after the working period. Noise levels near the operator's ear while using the test machines were 85-93 dB.
6) All of the machines that were tested caused TTS levels of equal to or more than 15 dB. This is true for both the hearing abilities by air conduction and by bone conduction that were measured. Most of the temporary threshold shifts were observed at 250, 500 and 8000Hz, and 250, 500, and 2000Hz for the air conduction and bone conduction hearing abilities, respectively.
7) The data collected from the use of the different test machines indicated that the hearing ability by bone conduction is more easily influenced by noise as compared to that of air conduction. Furthermore, sound level TTS is not solely influenced by noise but also affected by machine vibration and work intensity. Likewise, the effect of noise is not fully dependent on the noise intensity near the operator's ear but also influenced by the sound frequency, especially at the low frequency band.
8) Considering the fact that as much as 15 dB of sound level TTS results from as short as 1-3 hours of agricultural machine work, it is necessary to reduce machine noise. Suppressing the noise level could definitely enhance the work environment by ensuring the safety and comfort of the operator and of the other workers in the field.

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