• KOREAN JOURNAL OF CROP SCIENCE
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• v.35 no.4
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• pp.370-374
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• 1990

A field experiment was conducted to investigate the influence of water weevil damage on growth and grain guality in rice. Plant height was shortened, number of tillers per hill decreased and maximum tillering stage delayed in damaged field by rice water weevil. Heading date was delayed by 1-2days, culm lenght shortened, panicle lengthened, number of panicles decreaced, number of panicles per spikelet increased, ripened grain ratio decreased in damaged field by rice water weevil. Yield per 10a was decreased 4-22% in damaged field compared with that in undamaged field by rice water weevil, yield loss in late transplanting (June 23) was larger than that in early transplanting (May 20). Imperfect kerml rice, especially green kernel rice, was increased in damaged field by rice water weevil.

• Korean Journal of Agricultural Science
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• v.13 no.1
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• pp.33-43
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• 1986

Long-term fertilizer application have been carried out at experimental farm of the Yeongnam Crop Experiment Station from 1967 to 1983 to obtain basic informations about longterm effect of fertilizer regime, especially, compost and chemical fertilizer on the soil chemical properties and the rice growth. 1. Rice yields obtained from the non-fertilized plot and PK applied plot were significantly reduced compared to NPK applied plot by 43% and 53%, respectively, primarily due to decrease of leaf area, crop growth rate, number of panicles and number of spikelets and delayed flowering. 2. No visible phosphorus-symptom and yield loss were obserbed at the plot that phosphorus was not included even though phosphorus content in the soil and rice plant were lowered. 3. The plot that was not received potassium resulted in yield loss by 9% compared to NPK applied plot due to decrease in potassium content in soil and rice plant, and spikelt number. 4. Available phosphorus, silica, and exchangeable potassium in soil significantly increased by adding compost to NPK applied plot and hence, increased grin yield by 6 to 9% compared to applied plot through improvement of nutrient uptake efficiency. 5. Grain yield of compost applied plot lowered by 30% than NPK applied plot due to decreased nutrient uptake efficiency and delayed rice growth while this yield was higher than Non-fertilized plot.

• Proceedings of the Korean Society of Crop Science Conference
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• 1987.06a
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• pp.26-27
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• 1987

• Korean Journal of Weed Science
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• v.31 no.3
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• pp.289-293
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• 2011

Field experiments were conducted to predict rice yield losses caused by Echinochloa crus-galli (L.)P. Beauv., Bidens frondosa L. and Aeschynomeme indica L. at a range of plant densities under machine transplanted rice cultivation in different regions of Korea in 2006, and to determine their economic threshold levels (ET). All data were fitted to Cousens' rectangular hyperbola to estimate parameters for predicting rice yield loss. The rice yield loss models of Bidens frondosa L. was predicted as y=5.43/(1+0.0113x), $R^2$=0.963, A. indica was y=5.47/(1+0.0332x), $R^2$=0.976 and E. crus-galli y=5.43/(1+0.01552x), $R^2$=0.950. The mean competitivities represented by the parameter, whose reciprocal ($1/{\beta}$) is a weed density reducing crop yield by 50%. Those of E. crus-galli, B. frondosa and A. indica were 0.01552, 0.01113 and 0.0332 in normal-season machine transplanting of Korea, respectively. Single year mean economic thresholds (ET) of A. indica were 0.5, 0.6 and 0.7 plant $m^{-2}$ with the application of flucetosulfuron, flucetosulfuron+imazosulfuron GR and flucetosulfuron+imazosulfuron+carfentrazone GR herbicides, respectively. Meanwhile ET values of 1.6, 1.9 and 1.9 plants $m^{-2}$ for B. frondosa, 1.2, 1.4, and 1.4 plants $m^{-2}$ for E. crus-galli.

• Korean journal of applied entomology
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• v.21 no.4 s.53
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• pp.216-221
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• 1982

This experiment was conducted in Jeonnam to investigate the effects of fertilizer amounts at two application levels on disease severity of bacterial leaf blight, yield and qualify of rice grains using nineteen rice cultivars. Incidence of bacterial leaf blight was more severe in the field with higher amount of fertilizer application. Disease severity was also different depending upon maturity of rice cultivars of early maturing group, however, the flag, second and third leaves were diseased in rice cultivars of medium late maturing group. Such differences were more obvious in the field with higher amount of fertilizer application than in the field with ordinary fertilizer application. Rice cultivars such as Taebaegbyeo, Hangangchalbyeo, Baegunchalbyeo, Palgwangbyeo and Milyang 42 were resistant whereas rice cultivars such as Milyang 30, Geumgangbyeo, Nagdongbyeo and Jinjubyeo were susceptible to bacterial leaf blight in both treatments. However, fertilization rate and percentage of ripeness were decreased resulting in heavy loss of yield. The rate of green-kerneled rice was increased resulting in poor qualify.

• Journal of the Korean Professional Engineers Association
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• v.1 no.1
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• pp.18-25
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• 1968

Higher yield in rice paddies is greatly dependent on adequately balanced and timely supply of water. A majority of rice paddy in Korea is generally irrigated by rainfall, but in many cases it has to be supplemented by artificial irrigation for optimum rice culture. Although the water requirement of rice plant is for higher Than that of athec crops, submerged condition of rice paddy is not Necessarily required. The moisture requirement of rice plant varies with its growing stages, and it is possible to increase the irrigation efficiency through reduction of water loss due to percolation in rice paddies. An experimental plots were set up by means of sandomized block design with three duplication; (a) All time submerged, (b) Economically controlled, and (c) Extremely controlled. Three different irrigation periods Were (a) Initial sage, (b) Inter-stage, and (c) Yast stage. The topsoil of the three plots were excavated to the depth of 30 cm and then compacted with clay of 6 cm thickness. There after, they were piled up with the excavated top soils, leveled and cored with clay of 6 cm thickness around footpath in order to prevent leakage. The results obtained from the experiments are as follows, 1. There is no difference among the three experiments plots in terms of physical and chemical conditions, soil properties, and other characteristics. 2. Culm length and ear length are not affected by different irrigation methods. 3. There is no difference in the mature rate and 1, 000 grain weight of rice for the three plots. 4. The control plot which was irrigated every three days shows an increased yield over the all the time submerged plot by 17.8 percent. 5. The clay lined plot whose water holding capacity was held 5 days long, needs only to be irrigated every 7 days. 6. The clay lined plot shows an increased yield over the untreated plot ; over all-the-time submerged plot by 18 percent ; extremely controlled plot by 18 percent, and economically controlled plot by 33 percent. 7. It may be saved in water requirement about one Thirds.

• Korean Journal of Weed Science
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• v.31 no.4
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• pp.348-354
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• 2011

This study was conducted to find the levels of reduction in rice yield and to determine economic threshold levels as affected by densities of Scirpus planiculmis and Lindernia dubia in wet seeding rice cultivation. In wet seeding rice cultivation, yield of rice in densities of S. planiculmis (192 per $m^2$) and L. dubia (384 per $m^2$) was reduced by 43 and 22%, respectively. Relationship between rice yield and densities of weeds were predicted with these equations of Y=531.3kg/(1+0.003931x), $r^2$=0.964 for S. planiculmis and Y=547.0kg/(1+0.000792x), $r^2$=0.922 for L. dubia. According to Cousens' method, economic threshold densities of S. planiculmis and L. dubia were calculated by 7.2 and 34.9 per $m^2$, respectively. This result indicated that yield of rice in wet seeding rice cultivation could be reduced by over economic threshold densities of S. planiculmis and L. dubia.

• Korean Journal of Weed Science
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• v.31 no.4
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• pp.340-347
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• 2011

This study was conducted to predict the rice yield loss and to determine the economic threshold levels for direct-seeding flooded rice cultivation from competition to the most serious weeds, Sagittaria trifolia L. and Bidens frondosa L. The rice yield loss models of S. trifolia and B. frondosa were predicted as Y = 497.0/(1+0.003760x), $R^2$=0.869 and Y = 486.0/(1+0.007612x), $R^2$ = 0.887, respectively. In comparison of the competitiveness represented by parameter ${\beta}$, it was 0.003760 in S. trifolia and 0.007612 in B. frondosa, respectively. Economic thresholds calculated using Cousens' equation was negatively related with the competitiveness of weed. The economic thresholds of S. trifolia and B. frondosa were 7.6 and 3.9 plants per $m^2$, respectively.

• Korean Journal of Soil Science and Fertilizer
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• v.19 no.2
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• pp.147-151
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• 1986

A study was carried out to investigate yield, yield components, and change of chemical components in rice plants grown under different concentration of lead compound in nutrient solution of sandy culture. The results obtained are as follows. 1. Increasing lead concentration in culture solutions, pb content in the plant was increased and crop yields were decreased. 2. The critical pb concentration at which yield was declined, was 13.6 ppm. 3. As adding higher concentration of lead in nutrient solutions, concentration of lead in rice plant was significantly increased on leaf blade, and brown rice in pb. 4. Yield loss was closely related to pb content in leaf blade.

• Korean Journal of Environmental Agriculture
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• v.25 no.1
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• pp.71-76
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• 2006

Environment friendly agriculture is nowadays a major fiend to sustain balanced agricultural ecosystem, keeping its productivity. This study was conducted to determine the optimum levels of nitrogen (N) application for improving rice productivity and reducing N loss through N application based on soil diagnosis. four levels of N were applied with 0, 50, 100 and 150% of recommended levels by soil testing in 4 different paddy soils (i.e. normal, sandy, ill-drained and immature soils). Across N treatments, the greatest grain yield was observed in sandy soil and the lowest in ill-drained soil. The grain yield tended to decrease with increasing N application from 50% to 150% of recommended levels, except ill-drained soil. To ensure maximum yield the optimum levels of N application were estimated at 120 kg, 153 kg and 173 kg $ha^{-1}$ in normal, immature and sandy soil, respectively.