Jiyoung Shon

Impacts of Climate Change on Rice Production and Adaptation Method in Korea as Evaluated by Simulation Study

Air temperature in Korea has increased by over the last 100 years, which is nearly twice the global average rate during the same period. Moreover, it is projected that such change in temperature will continue in the 21st century. The objective of this study was to evaluate the potential impacts of future climate change on the rice production and adaptation methods in Korea. Climate data for the baseline (1971~2000) and the three future climate (2011~2040, 2041~2070, and 2071~2100) at fifty six sites in South Korea under IPCC SRES A1B scenario were used as the input to the rice crop model ORYZA2000. Six experimental schemes were carried out to evaluate the combined effects of climatic warming, fertilization, and cropping season on rice production. We found that the average production in 2071~2100 would decrease by 23%, 27%, and 29% for early, middle, and middle-late rice maturing type, respectively, when cropping seasons were fixed. In contrast, predicted yield reduction was ~0%, 6%, and 7%, for early, middle, and middle-late rice maturing type, respectively, when cropping seasons were changed. Analysis of variation suggested that climatic warming, fertilization, cropping season, and rice maturing type contributed 60, 10, 12, and 2% of rice yield, respectively. In addition, regression analysis suggested 14~46 and 53~86% of variations in rice yield were explained by grain number and filled grain ratio, respectively, when cropping season was fixed. On the other hand, 46~78 and 22~53% of variations were explained respectively with changing cropping season. It was projected that sterility caused by high temperature would have no effect on rice yield. As a result, rice yield reduction in the future climate in Korea would resulted from low filled grain ratio due to high growing temperature during grain-filling period because the fertilization was insufficient to negate the negative effect of climatic warming. However, adjusting cropping seasons to future climate change may alleviate the rice production reduction by minimizing negative effect of climatic warming without altering positive effect of fertilization, which improves weather condition during the grain-filling period.

Yield of maize ( Zea mays L.) logistically declined with increasing length of the consecutive visible wilting days during flowering

Under future climate conditions, the frequency and severity of drought are expected to increase. Maize (Zea mays L.) is susceptible to drought, especially at flowering. The objective of this study was to investigate the effect of consecutive days of visible wilting (DAW) during tassel emergence using two types of Korean maize hybrids, Gwangpyeongok (Gwp; normal) and Ilmichal (Ilmi; waxy). Traits related to plant growth and yield were measured at harvest. Drought stress during tassel emergence significantly reduced the number of green leaves per plant. Silking was delayed due to drought stress during the stage of tassel emergence, although anthesis was only slightly affected, which resulted in an increase in the anthesis-silking interval (ASI). For each DAW, ASI increased by 1.6 days and 0.8 days for Gwp and Ilmi, respectively. The number of green leaves and ASI showed strong correlation with DAW length and grain yield, which suggested that those factors may be selective traits for drought tolerance at flowering. The filled grain number per plant declined logistically with increasing DAW due to reductions in kernels per row and percentage of filled grains. The filled grain number per plant significantly declined starting at 5 and 10 DAW in Gwp and Ilmi, respectively, which indicated that drought stress effects are dependent on drought severity and the genetic characteristics of specific hybrids. Probit analysis revealed that DAW causing 50% reduction in maize grain yield was about 4.7 and 6.3 days in Gwp and Ilmi, respectively, which resulted in about 13.6% and 9.2% reduction in grain yield per day of DAW, respectively. These results indicate that Gwangpyeongok is more sensitive to drought stress during flowering than Ilmichal.

Statistical assessment of the late marginal heading date for normal maturation of temperate japonica rice in South Korea

The late marginal heading date (LMHD) for normal maturation has been assessed to infer the range of late transplanting date and applicability of a new cropping system. A minimum threshold temperature for grain filling can be used to determine the late marginal heading date that would allow normal maturation. In this study, a statistical procedure was developed to determine the threshold temperature for 40 days of the grain-filling period. The threshold temperature was chosen to be the minimum temperature at which grain-filling ratio and weight are minimally affected. To identify the threshold temperature, grain-filling ratio and weight, which were observed at two sites for 2 years in Korea, were compared with a range of cumulative temperature during 40 days in the late season. As a result, cumulative temperature of 800℃, which is equivalent to, on average, 20℃ during 40 days of grain-filling period, was determined to be the threshold temperature for normal grain filling in the late season. The LMHD for normal maturation was also determined from cumulative probability density function of dates from which the threshold temperature of 800℃ was met during the last 15 years as well as 33 years. Our results suggested that it would be better to use the cumulative density function of those dates derived from the last 15 years rather than 33 years because current climate conditions could be better represented by the density function derived from recent years.

Impact of the consecutive days of visible wilting on growth and yield during tassel initiation in maize ( Zea Mays L.)

Maize (Zea mays L.) is a major crop with different uses but shows significant susceptibility to drought stress. Recent climate change has caused prolonged drought stress, but in most countries maize production relies on rain-fed cultivation. This study was to investigate the impact of the consecutive days of visible wilting (DAW) during tassel initiation (V6) using two types of Korean maize hybrids, Gwangpyeongok (GWP) and Ilmichal (Ilmi). The traits related to plant growth and yield were measured at harvest. Drought stress during tassel initiation linearly reduced plant elongation and dry matter accumulation with the length of DAW increasing but did not affect the leaf number per plant. Our results from the simple linear regression analysis indicated that silking of GWP and Ilmi would be delayed by 0.78 and 0.61 days per DAW, respectively, which was similar to anthesis. Still, little change was observed for interval between anthesis and silking under the same condition. The kernels per row were very dependent on the length of DAW but the rows per ear were not. The percentage of filled grains and the 100- grain weight were significantly reduced only at 15- or 20-DAW and more markedly so in Gwangpyeongok at 20-DAW. The filled grain number per plant showed a gradual logistical decline mainly due to decreases in the kernels per row. All these reductions may be because initiation and growth of tassel, ear, and kernels and internode elongation beginning around V6 are sensitive to water deficits. Probit analysis revealed that the DAW to cause 50% reduction in plant grain yield was about 12 and 20 days in GWP and Ilmi, resulting in about 4.5 and 2.7% reduction a day of DAW, respectively. These results indicate that Gwangpyeongok may be more sensitive to drought stress during tassel initiation than Ilmichal.

A Late-Maturing and Whole Crop Silage Rice Cultivar `Mogwoo`

`Mogwoo`, a new high yield and whole crop silage rice (Oryza sativa L.) cultivar, was developed by the rice breeding team of the National Institute of Crop Science, RDA, Suwon, Korea, from 1999 to 2009, and was released in 2010. It was derived in 1999 from a cross between Dasanbyeo, having a high yield, and Suweon431/IR71190-45-2-1. A promising line, SR25848-C99-1-2-1, selected by the pedigree breeding method, was designated the name of `Suweon 519` in 2007. This cultivar has about 155 days of growth period from seeding to heading, and is tolerance to lodging, with erect pubescent leaves as well as a long and thick culm. This cultivar has the same number of tillers per hill and higher spikelet numbers per panicle compared to Nokyang. `Mogwoo` has longer leaves compared with other Tongil-type varieties. This new variety is resistant to grain shattering, leaf blast, bacterial leaf blight, and small brown planthopper. The biomass yield of `Mogwoo` was 1,956 kg/10a in a regional test over three years. The result shows that `Mogwoo` is adaptable to central and south-east plain areas of Korea.

Importance of National Crop Productivity in View of CO 2 Balance

Crop production in a country is very crucial not only in a country`s crop self-sufficiency, but also in carbon recycle. Crop can capture and store the emitted by cereal food consumption. However, imported cereal food is not concerned in carbon recycle and this hinders the accurate estimation of carbon recycle. Korea imports major grain products including wheat, corn, soybean, and rice and about 90% of the grain composition consists of carbohydrate, protein and lipid. Carbon portions in carbohydrate, protein and lipid are 45, 53, and 77%, respectively. When the carbon portions are digested and converted into completely, one ton of rice, wheat, corn, and soybean can release 1.51, 1.63, 1.56, and 1.56 tons of to the atmopshere, respectively. Based on this premise, the evolved calculated from imported grains for the last 4 years in Korea was over 21 MT of . This amount is equivalent to 4.8 billion US dollars in the conception of carbon tax. These results suggest that a decrease in a cereal import(i.e, an increase in a country`s crop self-sufficiency) can lower release to the atmosphere.

Changes of Weedy Rice Occurrence in Repeated Wet Direct Seeding and Alternate Transplanting/Wet Direct Seeding of Rice

Weedy rice is one of the major problems in direct-seeded rice field, resulting in poor rice quality and low grain yield. This study was carried out to evaluate the conversion effect to machine transplanting after wetdirect-seeding for 3 years on weedy rice occurrence, in comparison of repeated wet-direct-seeding. Occurrence of weedy rice in the continuous wet-hill-seeded and broadcasted field for 3 years increased 4 folds, when compared with that in machine transplanted rice paddy. In the first year of wet-direct-seeded field converted from machine transplanting, weedy rice occurrence did not increase, demonstrating lesser weedy rice in wet-hill-seeded than broadcasted field. These results indicate that alternate cultivation of wet-hill-seeding and machine transplanting is more effective to prevent weedy rice occurrence than the repeated wet-direct-seeding method for 3 years.

Comparison of Statistic Methods for Evaluating Crop Model Performance

The objective of this short communication is to introduce several evaluation methods to crop model users because the evaluation of crop model performance is an important step to develop or select crop model. In this paper, mean error, mean absolute error, index of agreement, root mean square error, efficiency of model, accuracy factor and bias factor were explained and compared in terms of dimension and observed number. Efficiency of model and index of agreement are dimensionless and independent of number of observation. Relative root mean square, accuracy factor and bias factor are dimensionless and not independent of number of observation. Mean error and mean absolute error are affected by dimension and number of observation.