Chung-Guk Kim

Allelopathic Effects of Common Ragweed (Ambrosia artemisifolia var. elatior) on the Germination and Seedling Growth of Crops and Weeds

Competitive ability, allelopathy, made the common ragweed (Ambrosia artemisiifolia var. elatior ) one of the most dangerous weeds in Korea. The aim of this research was to evaluate the role of common ragweed as test species under laboratory bioassay and glasshouse conditions. Inhibition effect of the leaf extract was higher than that of stem and root parts extracts on germination and seedling growth of weeds. The 5% concentration of leaf extract of common ragweed inhibited the germination rate of Echinochloa crus-galli, Digitaria sanguinalis and Cyperus microiria by 68.3, 74.6 and 87.3%, respectively, as compared to the control. Generally, increasing incorporation concentration inhibited seedling growth of weeds. Incorporation of 5% common ragweed residue significantly reduced the plant length of E. crus-galli, D. sanguinalis and C. microiria by 48, 63 and 68%, respectively, as compared to the control. Also, the values of dry weight were 72, 78 and 71%, respectively. Contrarily, the emergence rate of soybean and corn was not affected by the incorporation of 5% concentration of common ragweed residue. However, the dry weight was inhibited by 37 and 28%, respectively. These results suggest that common ragweed had the ability to control some weed species using toxic compounds like natural herbicide.

Change of Weed Community in No-till Corn with Legume Cover Crops as Living Mulch

, Ki-Yeong Seong, Duk-Young Song, Weon-Tai JeonHyun-Suk Cho, Kwang-Ho Jeong and Ui-Gum KangABSTRACT Cover crop can be used to suppress weeds by competition for light and nutrient. Objective of this study was to evaluate the effectiveness of legume cover crops on change of weed community in no-till corn cultivation. Two legume cover crops, hairy vetch and crimson clover were grown in the field, and succeeding corn was sown on 4 May, 2010. The distribution of weed was surveyed at 15 April, 1 June, and 20 August. At 15 April, the weed biomass in hairy vetch field was higher than in crimson clover field. The dominant weeds were Capsella bursa-pastoris L. and Stellaria aquatica L. in hairy vetch and crimson clover fields, respectively. At vegetative stage of corn, occurred weeds in hairy vetch and crimson clover fields were four and six species, respectively, while the weed was occurred with nine species in conventional. Also the dry weight of weed was decreased by 82 and 75% in hairy vetch and crimson clover fields compared to conventional. On the other hand, after harvest of corn, occurred weed in hairy vetch, crimson clover and conventional was five, four and five species, respectively. Dry weight percentage of occurred weed in conventional was 23.5%, and the value was higher than 13.8 and 14.7% in hairy vetch and crimson clover fields, respectively. Stellaria aquatica L. as winter annual weed only occurred in cover crop field during corn growing season. It is these possibilities that low soil temperature and light interception by soil cover of legume cover crop.Keys words: cover crop; crimson clover; green manure; hairy vetch; weed community.

Evaluation of waterlogging tolerance with the degree of foliar senescence at early vegetative stage of maize ( Zea mays L.)

Maize is highly susceptible to waterlogging, which is becoming one of worldwide abiotic threats in many agricultural areas. This study was evaluated to establish the screening method and to find tolerant maize genotypes. Six Korean maize inbred lines were subjected to waterlogging at V3 for 15 days using a big size pot with single maize plant (big pot method) and a box containing 31 maize plants at a time (box method). The degree of foliar senescence and the number of senescent leaves were better indicators for selecting waterlogging tolerant maize genotypes than SPAD value and plant height. The degree of foliar senescence revealed that KS124, KS140, and KS141 are tolerant, and KS85 is susceptible to waterlogging at the early growth stage. These responses of foliar senescence were in clear accordance with those of plant grain yield, which was supported by stress tolerance index for grain yield. The box method also showed the similar response of foliar senescence to the big pot method. Therefore, this box method based on foliar senescence may be simple and efficient for large-scale screening of maize germplasm against waterlogging stress. It was concluded that foliar senescence can be a good indicator for selecting tolerant maize genotypes against waterlogging at the early growth stage.

Effects of Different Planting Dates on Growth and Yield Component in Two Ecotypes of Soybean at Paddy Field Condition in the Mid Part of Korea

This experiment was carried out to investigate the differences of the growth and yield characteristics at different planting dates in two soybean ecotypes from 2012 to 2013. Three summer types of soybean varieties, Seaol, Chamol, Hanol and three autumn types, Hwanggum, Taegwang, Daepung were planted 4 times from 1 May to 1 August in paddy field at the experimental field of National Institute of Crop Science in Suwon, Korea. Emergence rate was shown to difference among the varieties and the lowest planting at 29 June cause of the severe drought in 2012. The emergence period and days to flowering shortened as planting date delayed regardless of varieties. Emergence period more reduced in 2013 than in 2012 and days to flowering was more shortened in the summer types than in the autumn types. Stem height, number of main stem nodes, stem diameter were different among the summer types and the autumn types and reduced as planting date delayed. Number of main stem nodes and number of branch were different but no difference were observed in the stem height and stem diameter between 2012 and 2013. The number of pod per plant was the highest planting at 21 May and the lowest planting at 1 August and more in the autumn types than in the summer types. The number of seed per plant was the highest at planting 29 June and the lowest at planting 1 August and more in the autumn types than in the summer types and more in 2012 than in 2013. It was observed that one hundred seed weight was reduced rapidly planting at 1 August and heavier in the summer types than in the autumn types and heavier in 2013 than in 2012. Seed yield was the highest at planting 29 June and the lowest at planting 1 August, and 85kg/10a higher in the autumn types and 47kg/10a higher in 2012 than in the summer types and 2013, respectively.

Evaluation of Winter Annual Weed Vicia angustifolia as Green Manure

Vicia angustifolia L. is native plant of winter annual leguminous weed in Korea. Objective of this research was to investigate the effects of V. angustifolia as green manure for rice production in sustainable agriculture. Seed size of V. angustifolia was smaller than that hairy vetch as control plant, while seed number in same amount was approximately 1.4-fold higher. V. angustifolia started stem elongation in early April. In addition, flowering and dead-ripe stages of the plant reached at May and June , respectively. Growth of V. angustifolia-barley mixed cropping system in upland was promoted up to 101 cm of plant length compared to 46.6 to 60.9 cm that grown in paddy. Biomass yield of V. angustifolia was 14.5 kg in single cropping system of paddy soil, and the amount of nitrogen was 65 kg . Moreover, self-reseedling of fallen seed from V. angustifolia grown in previous year in paddy soil was significantly higher than that hairy vetch plant. These results suggested that V. angustifolia can be uses as green manure in addition to reducing the mineral fertilizer application in rice production for sustainable agriculture.

Common Ragweed-Derived Phenolic Compounds and Their Effects on Germination and Seedling Growth of Weed Species

Phenolic compounds, which are products of secondary metabolism, have been demonstrated to be widespread growth substances in plants. The objectives of this study were to identify the phenolic compounds in common ragweed (Ambrosia artemisiifolia var. elatior) by HPLC and to evaluate their effects on germination and seedling growth of three weed species. Under controlled conditions in Petri dishes at 25℃, 10 -3 and 10 -4 M solutions of phenolic compounds were evaluated in seed germination tests. Four phenolic compounds (caffeic acid, ο-coumaric acid, ρ -coumaric acid and ferulic acid) in common ragweed plant were identified and their concentration was increased from the stage before flowering through full flowering stage. Treatment of ο- and ρ-coumaric acids delayed the seed germination of Digitalia ciliaris, while the treatment of caffeic acid delayed the seed germination of Echinochloa crus-galli. In time to 50% germination (T50), phenolic compounds at 10 -4 M promoted in Cyperus microiria and E. crus-galli but the level of 10 -3 M delayed the T50 of those weeds. The ο-coumaric acid inhibited seed germination and seedling growth of the tested weeds and especially it perfectly inhibited the root growth of E. crus-galli.