• Korean Journal of Soil Science and Fertilizer
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• v.1 no.1
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• pp.43-60
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• 1968

In order to find the effects of nitrogen type (ammonium sulfate and urea fertilizer) and fertilized depth, (0~10cm, 0cm, 5~10cm, 10~15cm, 15~20cm, and 20cm below) on leaching and absorption of nitrogen in paddy soil, and growth and yields of rice, the pot culture experiment was carried out, using the variety Jaekun, one of the Korean leading variety. Experimental results were Summarized as follows: 1. No variations of the pH of percolating water were induced by the differences of nitrogen types and their fertilized depth (Table. 2). 2. The leaching of nitrogen was less in ammonium sulfate and top soil fertilizing plots than in urea and subsoil fertilizing plot, and the growth of rice in early stage was more promoted in ammonium sulfate and topsoil fertilizing plots (Table. 1, 7 and 8). 3. Leachng of nitrogen through the percolating water almost came to an end at the most numerous tiller stage (Table 1). 4. The absorption of nitrogen of each part of the rice plant in the harvesting stage correlated closely with the yields of each part (Table 5, 6, 9 and 10) and the leaching of nitrogen in the early stage was inversely proportion to the absorption of nitrogen of rice plant in the harvesting time (Table 1, 5, 6, 9 and 10). 5. The number of spikes was more numerous in ammonium sulfate plots than in urea plots on an average, so that the yields were higher in the ammonium sulfate plots than in urea plots although no differences in the grain number per spike were found in above two plots. The number of spikes was more numerous in topsoil fertilizing plots than in subsoil fertilizing plots, but the grain number per spike was less in former than in latter, so that no difference in yields was found. The absorption of nitrogen correlated closely with the yields in complete paddy grains (Table 5, 9, and 10). 6. At the ammonium sulfate fertilizing plots, the number of spikes was more numerous in topsoil fertilizing plots than in subsoil fertilizing plots, (among the each of the topsoil plots, 0~10cm and 5~10cm fertilizing plots kept more spikes than the 0cm fertilizing plots), but the grain number per spike was less in former than in latter (among the each of topsoil plots, no differences were found), so that no significant difference in yields was showed between the topsoil and subsoil fertilizing plots, but the results showed the tendency that the yields were highest in 0~10cm plots and the lowest in 20cm below plots. At the urea fertilizing plots, the number of spikes decreased in proportion to the increasing of fertilized depth, but no variations were found in the grain number per spike, so that the yields decreased in proportion to the increasing of fertilized depth. The absorption of nitrogen correlated closely with the yields in complete paddy grains (Table 5, 6, 9, and 10). 7. When fertilized in topsoil, the number of spikes was more numerous in ammonium sulfate plot than in urea plot, but the grain number per spike variated reversely, so that no differences were found in the yields between the ammonium sulfate and the urea plots, when fertilized in subsoil, both the number of spikes and the grain number per spike were larger in ammonium sulfate than in urea plot, so that the yields were also higher in ammonium sulfate plots (Table 5, 6, 9 and 10). 8. The weight of straw and its nitrogen absorption were higher in ammonium sulfate plot than in urea plot and decreased in proportion to the increasing of fertilized depth. Among the each of topsoil fertilizing plots, the 0~10cm and the 5~10cm fertilizing plots excelled the 0cm plot (Table 5, 6, 9 and 10). 9. No significant variations in the fertilizer treatments were found in the characters of heading date, maturing date, length of culm, length of spike, weight of empty grain, 1,000 grain weight, and one liter weight.

• Magazine of the Korean Society of Agricultural Engineers
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• v.11 no.1
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• pp.1534-1548
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• 1969

This experiment was conducted, making use of the 'NONG-RIM6' arecommended variety of rice for the year of 1968. Main purposes of the experiment are to explore possibilities of; a) ways and means of saving irringation water and, b) overcoming drought at the same time so that an increased yield in rice could be resulted in. Specifically, it was tried to determine the effects of the Rotation irrigation method combined with differentiated thickness of lining upon the growth and yield of rice. Some of the major findings are summarized in the following. 1) The different thicknesses show a significant relationship with the weight of 1,000 grains. In the case of 9cm lined plot, the grain weight is 23.5grams, the heaviest. Next in order is 3cm lined plot, 6cm lined plot, control plot, and wheat straw lined-plot. 2) In rice yield, it is found that there is a considerably moderate significant relationship with both the different thickness of lining and the number of irrigation, as shown in the table. 3) There is little or no difference among different plots in terms of a) physical and chemical properties of soil, b) quality of irrigation water, c) climatic conditions, and rainfalls. 4) It is found that there is a significant relationship between differences in the method of rotation irrigation and the number of ears per hill. The plot irrigated at an interval of 7 days shows 17.4 ears and plot irrigated at an interval of 6 days, 16.3 5) In vinyl-treated plots, it is shown that both yield and component elements are greatest in the case of the plot ith whole of $3cm/m^2$ Next in order are the plot with a hole of $2cm/m^2$ the plot with a hole of $1cm/m^2$ In the case of the plot with no hole it is found that both yield and component elements are decreased as compared to the control plot. 6) The irrigation water reqirement is measured for the actual irrigation days of 72 which are the number subtracted the days of rainfall of 30 from the total irrigation days of 102. It is found that the irrigation water requirement for the uncontrol plot is 1,590mm as compared to 876mm(44.9% saved) for the 9cm-lined plot, 959mm(39.7% saved) for the 6cm-lined plot 1,010mm(36% saved) for the 3cm-lined plot and 1,082mm(32% saved) for the wheat straw lined plot. In the case of the Rotation irrigation method it is found that the water requirement for the plot irrigated at an interval of 8 days is 538mm(65% saved), as compared to 617mm(61.6% saved) for plot irrigated at an interval of 7 day 672mm(57.7% saved) for plot irrigated at an interval of 6day, 746mm(53.0% saved) for the plot irrigated at an interval of 5 days, 890mm 44.0% saved) for the plot irrigated at an interval of 4 days, and 975mm(38.6% saved) for the plot irrigated at an interval of 3 days. 7) The rate of evapotranspiration is found 2.8 around the end of month of July, as compared to 2.6 at the begining of August 3.4 around the end of August and 2.6 at the begining of August 3.4 around the end of August and 2.6 at the begining of September. 8) It is found that the saturation quantity of 30mm per day is decreased to 20mm per day though the use of vinyl covering. 9) The husking rate shows 75 per cent which is considered better.

• Journal of Preventive Medicine and Public Health
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• v.6 no.1
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• pp.51-63
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• 1973

This paper illustrate residual hearing and socio-medical background on the hearing impaired children, 207 comming to Deaf School. attached to Hankuk Social Work College, Taegu, Korea. The survey was performed through interview with their parents and testing by diagnostic audio-meter (TRIO, AS 105 type) at soundproof room from March 10, to November 28, 1973. The results obtained were as follows. 1) The attendance rate of the compulsory primary school was markedly lower tendency in female than male according to directly proportional to prevalence rate of deafness among them. If was showed the deeper gap in the more superior school (middle and high school). 2) Who entered at the suitable age to each school (six years old to primary school, 12 years to middle and 15 years to high) was 11.3%. And who were enrolled in school age to each school (6-11 years for primary. 12-14 years for middle and 15-17 years for high) was 45.9% (43.7% in male, 50.0% in female). 3) As causative disease, congenital case, were 23.6% included of 13.5% of heredity and 10.1% of troubles during pregnancy; the total acquired cases were 47.9%, it was classified as 11.6% of convulsion from any other diseases, 7.7% of measles, 7.7% of other febrile diseases, 3.4% of drug (the most of streptomycin) intoxication, 2.4% of meningitis, 1.5% of epidemic encephalitis and 31.3% of other diseases; and unknown cases were 28.5%. 4) 31.4% of who included congenital cases lost their hearing within six months old, 11.6% in 6-11 months. 9.7% in 1-2 years old and 14.0% in 2-3years old. Consequently we obtained that the most cases 90.0% were lost their hearing within 3 years after birth. 5) According to qualities of hearing leases the most of cases were perceptive, 197(97.5%), only two cases were conductive, and eight cases were mixed. 6) The status of residual hearing according to average grade of hearing loss. $B(=\frac{a+2b+c}{4}$ as table 13) were as follows. Two cases were normal (one was mute and another was severe speach disorder). Ten cases, moderate. Moderately severe cases were 40 (19.3%). Severe cases, 38(18.4%). Scale out, profound cases, 48 (23.3%). And impossible testing cases because that were infantile or had some mental disorder were 69 (33.3%). 7) The using rate of hearing aides was only 12.0%. Among them who had some more residual hearing and could showed hearing effect with hearing aide have used more many proportionary but who were difficult to expect that effect were rare.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.10 no.2
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• pp.97-114
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• 1977

The fresh water prawn, Macrobrachium rosenbergi(de Man) is a very common species in Indopacific region, which inhaits both fresh and brackish water in low land area, most of rivers and especially aboundant in the lower reaches which are influenced by sea water. It is one of the largest and commercial species of genus Macrobrachium, which is commonly larger than $18\~21cm$ in body length, from the basis of eye-stalked to the distal of telson. As a part of the researches in order to investigate the possibilities on transplantation and propagation of this species, this work dealt with the problems on the effects of chlorinities upon zoeal larvae and post-larvae 1). metamorphosis rate and optimum chlorinity for metamorphosis to post-larve, 2). tolerance and comparative survival rate on various chlorinties, from fresh water to sea water $(19.38\%_{\circ}\;Cl)$, which reared for six days upon each stage of zoeal larvae, 3). accomodation rate on chlonities which reared for twelve days after transmigration into variant chlorinities of the range from $3.68\%_{\circ}$ Cl to $1.53\%_{\circ}$ Cl in the way of rearing of the range from $3.82\%_{\circ}$ Cl to $11.05\%_{\circ}$ upon each stage of zoea, 4). tolerance on both of fresh and sea water upon zoeal larva and post-larva under the condition of $28^{\circ}C{\pm}1$ in temperature and feeding on Artenia salina nauplii, 5). relationship between various chlorinities and grwth of post-larvae under the condition of $28^{\circ}C$ in tmperature and feeding on meat of clam. Thus these investigations were performed in order to grope for a comfortable method on seedmass production. Up to the present, the study on the effects of chlorinity upon earlier zoeal larvae and post-larvae of Macrobrachium species has been scarcely performed by workers with the exception of Lewis(1961) and Ling (1962,, 1967), even so their works were not so detailed. On the other hand, larvae of several species of this genus were reared at the water which mixed sea water so as to carry out complete metamorphosis to post-larva by workers in order to investigate on earlier 1 arval and earlier post-larval development, such as Macrobrachium lamerrei (Rajyalakshmi, 1961), M. rosenbergi and M. nipponense (Uno and Kwoa, 1969; Kwon and Uno, 1969), M. acanthurs (Choudhury, 1970; Dobkin, 1971), M. carcinus(Choudhury, 1970), M. formosense(Shokita, 1970), M. olfersii (Duggei et al., 1975), M. novaehallandiae (Greenwood et al., 1976), M. japonicum (Kwon, 1974) and M. lar (Shokita, personal communication), and there fore it is regarded that chlorinity is, generally, one of absolute factors to rear zoeal larvae of brackish species of Macrobrachium genus. Synthetic results on this work is summarized as the follwings: 1) Zoeal larvae required different chlorinities to grow according to each stage, and generally, it is regarded that optimum range of living and growing is from $7.63\%_{\circ}Cl\to\;7.63\%_{\circ}Cl$, and while differences of metamorphsis rate, from first zoea to post-larva, is rarely found in this range, and however it occurs apparently in both of situation at $7.63\%_{\circ}Cl$ below and $16.63\%_{\circ}Cl$ above and moreover, metamorphosis rate is delayed somewhat in case of lower chlorinity as compared with high chlorinity in these situations. 2) Accomodation in each chlorinity on the range, from fresh water to sea water, is different according to larval stages and while the best of it is, generally, on the range from $14.24\%_{\circ}Cl$ to $8.28\%_{\circ}Cl$ and favorite chlorinity of zoea have a tendency to remove from high chlorinity to lower chlorinity in order to advance larval age throughout all zoeal stages, setting a conversional stage for eighta zoea stage. 3) Optimum chlorinity of living and growth upon postlarvae is on the range of $4.25\%_{\circ}Cl$ below, and in proportion as approach to fresh water, growth rate is increased. 4) Post-large are able to live better in fresh water in comparison with zoeal larvae, which are only able to live within fifteen hours, and by contraries, post-larvae are merely able to live for one day as compared with ?미 larvar, which are able to live for six days more in sea water $19.38\%_{\circ}Cl\;above$. 5) Also, in case of transmigration into higher and lower chlorinities in the way of rearing in the initial chlorinities $ 3.82\%_{\circ}Cl,\;7.14%_{\circ}Cl\;and\;11.05%_{\circ}Cl$, accoodation rate is a follow: accomodation capacity in ease of removing into higher chlorinities from lower chlorinities is increased in proportion as earlier stages, setting a conversional stage for eighth zoea stage, and by contraries, in case of advanced stages from eighth zoea it is incraesed in proportion as approach to post-larva stage in the case of transmigration into lower chlorinity from higher chlorinity. On the other hand, it is interesting that in case of reciprocal transmigration between two different chlorinitiess, each survival rate is different, and in this case, also, its accomodation in each zoea stage has a tendency to vary according to larval stages as described above, setting a conversional stage for eighth zoea stage. 6) It is likely that expension of radish pigments on body surface is directly proportional to chlorinity during the period of zoea rearing, and therefore it seems like all body surfacts of zoea larvae be radish coloured in case of higher chlorinity. 7) By the differences that each zoeal larvae, postlarvae, juvaniles and adult prawn are required different chlorinity for inhabiting in each, it is regarded that this species migrats from up steam to near the estuary of the river which the prawns inhabits commonly in natural field for spawning and growth migration. 8) It had better maintainning chlorinities according to zoeal stage for a comfortable method on seed-mass production that earlier larva stages than eighth zoea are maintained on the range from $8\%_{\circ}Cl\;to\;12\%_{\circ}Cl$ to rear, and later larva stages than eighth zoea, by contraries, are gradually regula ted-to love chlorininity of the range from $7\%_{\circ}Cl\;to\;4\%_{\circ}Cl$ according to advance for post-larva stage.

• Applied Biological Chemistry
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• v.9
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• pp.125-147
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• 1968

This experiment was carried out as a part of the studies on reasonable application of nitrogen in rice plant to determine: (I) Nitrogen absorption. and rooting of rice seedlings as affected by urea foliar application at late seedling stage (II) Effect of leaf prunning and foliar application of urea at late heading stage on the maturation and yield of rice (III) Effect of foliar application of urea and its time during the stage of ear formation on yield of rice plant. Results obtained are summarized as follows. Exp.I: Nitrogen absorption and rooting of rice seedlings as affected be urea foliar application at late seedling stage. 1 : The foliar application of urea plots$(T_{1},T_2)$ snowed mare N-content than non-urea foliar application plot(T0) at lane seedling stage, being significant among treatments and foliar application of urea seemed more effective in increasing the N-content of seedlings. and promoted root settlement and early growth alter the transplanting. 2 : The carbon contents of the plants of $T_1$, and $T_2$ at late seedling stage increased than T0, and the carbon contents. of $T_1$ and $T_2$ plots became higher in amount in proportion to the nitrogen absorption as compared with those of $T_0$. 3 : C/N ratio appeared significant among soil application plots($N_1, \;N_2$) and foliar application of urea plots ($T_1$, $T_2$ and $T_0$). C/N ratio was lower in case of increased amount of nitrogen. The higher contents of nitrogen and carbon and lower C/N ratio resulted in the increment of root numbers and root lengths. Exp.II: Effect of leaf prunning and foliar application of urea at late heading stage on the maturation and yield of rice. 1 : There was a highly significant decrease in the maturing rate by severe leaf prunning. In the mean time, significant increase in maturing rate was observed with urea foliar application and it was found the more frequent application the more effective for higher maturing rate with a moderate significance. A correlationship between the level of prunning and maturing rate was enumerated to 0.961 of correlation coefficient, which indicated an increased maturing rate by the increased number of remaining leaves. 2 : The 1.000 grain weight, grain weight and hulled rice yield increased by leaf prunning in order (plot a$A_1$, $A_3$, $A_2$ and $A_0$ were 89.8%, 89.4%, 87.8% and 87.5% respectively, showing the highest of rate in $A_1$ and $A_3$ in methods of ear fertilization and being highly significant between its treatment. 3 : 1000 grain weights were highly significant between time of application, showing a tendency of increase of weights with the time lagging until days before earings as that of maturing rates. High significance was recognized between methods of ear fertilization, showing the highest in $A_2$ 23.18 gr. 4 : Yields per $3.3m^2$ were not significant between time of ear fertilization, whereas were highly significant between methods of ear fertilization. Those of $A_1$, $A_3$, $A_2$ and $A_0$ were 1.486 kg, 1.491 kg, 1.381 kg and 1.328 kg, respectively, showing the highest in $A_1$ and $A_3$. 5 : Hulling ratios showed significant different between time of ear fertilization, showing the highest in $T_2$, whereas those of methods of ear fertilization were highly significant between its treatment, Those of $A_1$, $A_3$, $A_2$ and $A_0$ were 84.72%, 84.06%, 83.29%, and 82.56% respectively, showing the highest m $A_2$ and $A_3$ among others. 6 : Yields of hulled rice per $3.3m^2$ showed significant different between time of ear fertilization, showing the highest in $T_1$ 1.192 kg. Whereas, those were highly significant between methods of ear fertilization. Those of $A_1$, $A_3$, $A_2$ and $A_0$ were 1.259 kg, 1.254 kg, 1.149 kg and 1.095 kg, respectively, showing the highest in $A_1$ and $A_2$. 7 : Contents of nitrogen on rice plant increased in case of nitrogen application as ear fertilizer and showed that the case of urea foliar application was more effective than that of soil application, showing the increased nitrogen content of rice plant was accompanied by carbon content.

• Journal of Korean Society of Forest Science
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• v.15 no.1
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• pp.1-38
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• 1972

1. Objective of the Study The objective of the study was to make fundamental suggestions for drawing a forest insurance system applicable in Korea by investigating forest insurance systems undertaken in foreign countries, analyzing the forest hazards occurred in entire forests of Korea in the past, and hearing the opinions of people engaged in forestry. 2. Methods of the Study First, reference studies on insurance at large as well as on forest insurance were intensively made to draw the characteristics of forest insurance practiced in main forestry countries, Second, the investigations of forest hazards in Korea for the past ten years were made with the help of the Office of Forestry. Third, the questionnaires concerning forest insurance were prepared and delivered at random to 533 personnel who are working at different administrative offices of forestry, forest stations, forest cooperatives, colleges and universities, research institutes, and fire insurance companies. Fourth, fifty three representative forest owners in the area of three forest types (coniferous, hardwood, and mixed forest), a representative region in Kyonggi Province out of fourteen collective forest development programs in Korea, were directly interviewed with the writer. 3. Results of the Study The rate of response to the questionnaire was 74.40% as shown in the table 3, and the results of the questionaire were as follows: (% in the parenthes shows the rates of response; shortages in amount to 100% were due to the facts of excluding the rates of response of minor respondents). 1) Necessity of forest insurance The respondents expressed their opinions that forest insurance must be undertaken to assure forest financing (5.65%); for receiving the reimbursement of replanting costs in case of damages done (35.87%); and to protect silvicultural investments (46.74%). 2) Law of forest insurance Few respondents showed their views in favor of applying the general insurance regulations to forest insurance practice (9.35%), but the majority of respondents were in favor of passing a special forest insurance law in the light of forest characteristics (88.26%). 3) Sorts of institutes to undertake forest insurance A few respondents believed that insurance companies at large could take care of forest insurance (17.42%); forest owner's mutual associations would manage the forest insurance more effectively (23.53%); but the more than half of the respondents were in favor of establishing public or national forest insurance institutes (56.18%). 4) Kinds of risks to be undertaken in forest insurance It would be desirable that the risks to be undertaken in forest insurance be limited: To forest fire hazards only (23.38%); to forest fire hazards plus damages made by weather (14.32%); to forest fire hazards, weather damages, and insect damages (60.68%). 5) Objectives to be insured It was responded that the objectives to be included in forest insurance should be limited: (1) To artificial coniferous forest only (13.47%); (2) to both coniferous and broad-leaved artificial forests (23.74%); (3) but the more than half of the respondents showed their desire that all the forests regardless of species and the methods of establishment should be insured (61.64%). 6) Range of risks in age of trees to be included in forest insurance The opinions of the respondents showed that it might be enough to insure the trees less than ten years of age (15.23%); but it would be more desirous of taking up forest trees under twenty years of age (32.95%); nevertheless, a large number of respondents were in favor of underwriting all the forest trees less than fourty years of age (46.37%). 7) Term of a forest insurance contract Quite a few respondents favored a contract made on one year basis (31.74%), but the more than half of the respondents favored the contract made on five year bases (58.68%). 8) Limitation in a forest insurance contract The respondents indicated that it would be desirable in a forest insurance contract to exclude forests less than five hectars (20.78%), but more than half of the respondents expressed their opinions that forests above a minimum volume or number of trees per unit area should be included in a forest insurance contract regardless of the area of forest lands (63.77%). 9) Methods of contract Some responded that it would be good to let the forest owners choose their forests in making a forest insurance contract (32.13%); others inclined to think that it would be desirable to include all the forests that owners hold whenerver they decide to make a forest insurance contract (33.48%); the rest responded in favor of forcing the owners to buy insurance policy if they own the forests that were established with subsidy or own highly vauable growing stock (31.92%) 10) Rate of premium The responses were divided into three categories: (1) The rate of primium is to be decided according to the regional degree of risks(27.72%); (2) to be decided by taking consideration both regional degree of risks and insurable values(31.59%); (3) and to be decided according to the rate of risks for the entire country and the insurable values (39.55%). 11) Payment of Premium Although a few respondents wished to make a payment of premium at once for a short term forest insurance contract, and an annual payment for a long term contract (13.80%); the majority of the respondents wished to pay the premium annually regardless of the term of contract, by employing a high rate of premium on a short term contract, but a low rate on a long term contract (83.71%). 12) Institutes in charge of forest insurance business A few respondents showed their desire that forest insurance be taken care of at the government forest administrative offices (18.75%); others at insurance companies (35.76%); but the rest, the largest number of the respondents, favored forest associations in the county. They also wanted to pay a certain rate of premium to the forest associations that issue the insurance (44.22%). 13) Limitation on indemnity for damages done In limitation on indemnity for damages done, the respondents showed a quite different views. Some desired compesation to cover replanting costs when young stands suffered damages and to be paid at the rate of eighty percent to the losses received when matured timber stands suffered damages(29.70%); others desired to receive compensation of the actual total loss valued at present market prices (31.07%); but the rest responded in favor of compensation at the present value figured out by applying a certain rate of prolongation factors to the establishment costs(36.99%). 14) Raising of funds for forest insurance A few respondents hoped to raise the fund for forest insurance by setting aside certain amount of money from the indemnity paid (15.65%); others wished to raise the fund by levying new forest land taxes(33.79%); but the rest expressed their hope to raise the fund by reserving certain amount of money from the surplus money that was saved due to the non-risks (44.81%). 15) Causes of fires The main causes of forest fires 6gured out by the respondents experience turned out to be (1) an accidental fire, (2) cigarettes, (3) shifting cultivation. The reponses were coincided with the forest fire analysis made by the Office of Forestry. 16) Fire prevention The respondents suggested that the most important and practical three kinds of forest fire prevention measures would be (1) providing a fire-break, (2) keeping passers-by out during the drought seasons, (3) enlightenment through mass communication systems. 4. Suggestions The writer wishes to present some suggestions that seemed helpful in drawing up a forest insurance system by reviewing the findings in the questionaire analysis and the results of investigations on forest insurance undertaken in foreign countries. 1) A forest insurance system designed to compensate the loss figured out on the basis of replanting cost when young forest stands suffered damages, and to strengthen credit rating by relieving of risks of damages, must be put in practice as soon as possible with the enactment of a specifically drawn forest insurance law. And the committee of forest insurance should be organized to make a full study of forest insurance system. 2) Two kinds of forest insurance organizations furnishing forest insurance, publicly-owned insurance organizations and privately-owned, are desirable in order to handle forest risks properly. The privately-owned forest insurance organizations should take up forest fire insurance only, and the publicly-owned ought to write insurance for forest fires and insect damages. 3) The privately-owned organizations furnishing forest insurance are desired to take up all the forest stands older than twenty years; whereas, the publicly-owned should sell forest insurance on artificially planted stands younger than twenty years with emphasis on compensating replanting costs of forest stands when they suffer damages. 4) Small forest stands, less than one hectare holding volume or stocked at smaller than standard per unit area are not to be included in a forest insurance writing, and the minimum term of insuring should not be longer than one year in the privately-owned forest insurance organizations although insuring period could be extended more than one year; whereas, consecutive five year term of insurance periods should be set as a mimimum period of insuring forest in the publicly-owned forest insurance organizations. 5) The forest owners should be free in selecting their forests in insuring; whereas, forest owners of the stands that were established with subsidy should be required to insure their forests at publicly-owned forest insurance organizations. 6) Annual insurance premiums for both publicly-owned and privately-owned forest insurance organizations ought to be figured out in proportion to the amount of insurance in accordance with the degree of risks which are grouped into three categories on the basis of the rate of risks throughout the country. 7) Annual premium should be paid at the beginning of forest insurance contract, but reduction must be made if the insuring periods extend longer than a minimum period of forest insurance set by the law. 8) The compensation for damages, the reimbursement, should be figured out on the basis of the ratio between the amount of insurance and insurable value. In the publicly-owned forest insurance system, the standard amount of insurance should be set on the basis of establishment costs in order to prevent over-compensation. 9) Forest insurance business is to be taken care of at the window of insurance com pnies when forest owners buy the privately-owned forest insurance, but the business of writing the publicly-owned forest insurance should be done through the forest cooperatives and certain portions of the premium be reimbursed to the forest cooperatives. 10) Forest insurance funds ought to be reserved by levying a property tax on forest lands. 11) In order to prevent forest damages, the forest owners should be required to report forest hazards immediately to the forest insurance organizations and the latter should bear the responsibility of taking preventive measures.

• Journal of the Korean Wood Science and Technology
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• v.13 no.1
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• pp.19-62
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• 1985

This study was performed to investigate: (i) the bending processing properties of silk worm oak (Quercus acutissima Carr.) and Korean red pine (Pinus densiflora S. et Z.) by boiling and steaming treatments; (ii) the effects of interrelated factors - sapwood and heartwood, annual ring placement, softening temperature and time, moisture content. and wood defects on bending processing properties; (iii) the changing rates of bending radii after release from a tension strap, and (iv) the improving methods of bending process by treatment with chemicals. The size of specimens tested was $15{\times}15{\times}350mm$ for boiling and steaming treatments and $5{\times}10{\times}200mm$ for treatments with chemicals. The specimens were green for boiling treatments and dried to 15 percent for steaming treatments. The specimens for treatments with chemicals were soaked in saturated urea solution, 35 percent formaldehyde solution, 25 percent polyethylene glycol -400 solution, and 25 percent ammonium hydroxide solution for 5 days and immediately followed the bending process, respectively. The results obtained were as follows: 1. The internal temperature of silk worm oak and Korean red pine by boiling and steaming time was raised slowly to $30^{\circ}C$ but rapidly from $30^{\circ}C$ to $80-90^{\circ}C$ and then slowly from $80-90^{\circ}C$ to $100^{\circ}C$. 2. The softening time required to the final temperature was directly proportional to the thickness of specimen. The time required from $25^{\circ}C$ to $100^{\circ}C$ for 15mm-squared specimen was 9.6-11.2 minutes in silk worm oak and 7.6-8.1 minutes in Korean red pine. 3. The moisture content (M.C.) of specimen by steaming time was increased rapidly first 4 minutes in the both species, and moderately from 4 to 20 minutes and then slowly and constantly in silk worm oak, and moderately from 4 to 15 minutes and then slowly and constantly in Korean red pine. The M.C. of 15mm-squared specimen in 50 minutes of steaming was increased to 18.0 percent in the oak and 22.4 percent in the pine from the initial conditioned M.C. of 15 percent The rate of moisture adsorption measured was therefore faster in the pine than in the oak. 4. The mechanical properties of the both species were decreased significantly with the increase of boiling rime. The decrement by the boiling treatment for 60 minutes was measured to 36.6-45.0 percent in compressive strength, 12.5-17.5 percent in tensile strength, 31.6-40.9 percent in modulus of rupture, and 23.3-34.6 percent in modulus of elasticity. 5. The minimum bending radius (M.B.R.) of sapwood and heartwood was 60-80 mm and 90 mm in silk worm oak, and 260 - 300 mm and 280 - 300 mm in Korean red pine, respectively. Therefore, the both species showed better bending processing properties in sapwood than in heartwood. 6. The M.B.R. of edge-grained and flat-grained specimen in suk worm oak was 60-80 mm, but the M.B.R. in Korean red pine was 240-280 mm and 260-360 mm, respectively. Comparing the M.B.R. of edge-grained with flat-grained specimen, in the pine the edge-grained showed better bending processing property than the flat-grained. 7. The bending processing properties of the both species were improved by the rising of softening temperature from $40^{\circ}C$ to $100^{\circ}C$. The minimum softening temperature for bending was $90^{\circ}C$ in silk worm oak and $80^{\circ}C$ in Korean red pine, and the dependency of softening temperature for bending was therefore higher in the oak than in the pine. 8. The bending processing properties of the both species were improved by the increase of softening time as well as temperature, but even after the internal temperature of specimen reaching to the final temperature, somewhat prolonged softening was required to obtain the best plastic conditions. The minimum softening time for bending of 15 mm-squared silk worm oak and Korean red pine specimen was 15 and 10 minutes in the boiling treatment, and 30 and 20 minutes in the steaming treatment, respectively. 9. The optimum M.C. for bending of silk worm oak was 20 percent, and the M.C. above fiber saturation point rather degraded the bending processing property, whereas the optimum M.C. of Korean red pine needed to be above 30 percent. 10. The bending works in the optimum conditions obtained as seen in Table 24 showed that the M.B.R. of silk worm oak and Korean red pine was 80 mm and 240 mm in the boiling treatment, and 50 mm and 280 mm in the steaming treatment, respectively. Therefore, the bending processing property of the oak was better in the steaming than in the boiling treatment, but that of the pine better in the boiling than in the steaming treatment. 11. In the bending without a tension strap, the radio r/t of the minimum bending radius t to the thickness t of silk worm oak and Korean red pine specimen amounted to 16.0 and 21.3 in the boiling treatment, and 17.3 and 24.0 in the steaming treatment, respectively. But in the bending with a tension strap, the r/t of the oak and the pine specimen decreased to 5.3 and 16.0 in t he boiling treatment, and 3.3 and 18.7 in the steaming treatment, respectively. Therefore, the bending processing properties of the both species were significantly improved by the strap. 12. The effect of pin knot on the degradation of bending processing property was very severe in silk worm oak by side, e.g. 90 percent of the oak specimens with pin knot on the concave side were ruptured when bent to a 100 mm radius but only 10 percent of the other specimens with pin knot on the convex side were ruptured. 13. The changing rate in the bending radius of specimen bent to a 300 mm radius after 30 days of exposure to room temperature conditions was measured to 4.0-10.3 percent in the boiling treatment and 13,0-15.0 percent in the steaming treatment. Therefore, the degree of spring back after release was higher in the steaming than in the boiling treatment. And the changing rate of moisture-proofing treated specimen by expoxy resin coating was only -1.0.0 percent. 14. Formaldehyde, 35 percent solution, and 25 percent polyethylene glycol-400 solution found no effect on the plasticization of the both species, but saturated urea solution and 25 percent ammonium hydroxide solution found significant effect in comparison to non-treated specimen. But the effect of the treatment with chemicals alone was inferior to that of the steaming treatment, and the steaming treatment after the treatment with chemicals improved 10-24 percent over the bending processing property of steam-bent specimen. 15. Three plasticity coefficients - load-strain coefficient, strain coefficient, and energy coefficient - were evaluated to be appropriate for the index of bending processing property because the coefficients had highly significant correlation with the bending radius. The fitness of the coefficients as the index was good at load-strain coefficient, energy coefficient, and strain coefficient, in order.