サブタレニアン・クローバ(サブ・クローバ)は一般に秋まきで冬期間によく生育し,クローバ類の中では窒素固定能が比較的高いので地力の維持増進に効果がある.また,本草は一度作付すれば,夏作物を栽培しながち,その裏作に再び自生するReseedingという性質をもつ.ここでは,サブ・クローバ種子の生態的特徴を把握し,土中での種子の生存状態を明らかにすることで,耕耘環境下でのサブ・クローバを連年自生化する方策について考察した.
収穫直後のサブ・クローバ種子を土壌表層においたとき,それらは夏季期間中はほとんど発芽せず,秋季に一斉に発芽した.これは,夏季期間中の高温環境が種子の発芽に適さないことと,同時に表層では硬実が進まず気温の低下にともなって,秋季に一斉発芽したものと考えられた.これに対し,土中5～10cmに埋設した種子は,土中で硬実が進行し,秋季まで生存する種子が多くなった.土中で硬実の進行した種子は,発芽環境下におかれても発芽しなかった.このため,これらの硬実種子は土中でも比較的長期間にわたって生存するものと考えた.
一般に硬実種子の減少は日内の変温の影響が大きいとされており,今回の実験においても土中5～10cmの種子が表層の種子に比べて硬実が進行したことは,土中は表層に比べて日内の変温が少ないことによるものと考えられた.従って,圃場表層で結実した種子をロータリ耕耘で土中に埋没させると,表層に残った種子は,夏季には発芽せずに秋季の降雨と同時に発芽するので植生を再形成する.一方,土中に埋没した種子の一部は硬実を示し土中埋土種子として生存し,発芽環境が整ったときに出芽し,その幼植物はサブ・クローバの植生の再形成に役立つものと考えた.このことから,サブ・クローバは夏ロータリ→秋不耕起などの耕耘環境下において植生を再形成することが推察された.

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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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