Surveys of weed species on upland fields were conducted in Korea to investigate the occurrence of weed flora from April to May 2014 for winter crop fields and from July to August 2014 for summer crop fields. From the nation-wide survey, 375 weed species in 50 families were identified and classified to 162 annuals, 78 biennials and 135 perennials. Based on the occurrence ratio, the most weed species belonged to Compositae (73 species). 44 and 25 weed species belonged to Poaceae and Polygonaceae, respectively, and these 183 weed species in the most five families accounted for 49% of total weed occurrence. While 287 weed species in 45 families occurred in the winter crop fields, 339 weed species in 47 families occurred in summer crop fields. The most dominant weed species in Korean upland fields were Digitaria ciliaris, followed by Portulaca oleracea, Acalypha australis, Chenopodium album, Rorippa palustris etc. 129 weed species in 25 families were considered as exotic weeds. Based on the importance analysis, the highest value was C. album followed by Amaranthus lividus, Conyza canadensis etc. This information could be useful for estimation of future weed occurrence, weed population dynamics and establishment of weed control methods in upland fields of Korea.
This study was conducted to evaluate the effect of soil amendments on changes in enzyme activity in soils polluted with As. The effects of S and calcium superphosphate (CSP) on the activities of dehydrogenase, urease, arylsulfatase (ASF), β-glucosidase, and phosphatase (PHA) were measured in paddy soils. In CSPamended soil, As concentration in soil solution was lowest and rice growth increased. However, the activity of PHA was significantly lower for CSP-amended soil (0.9 -1.4 µmol h -1 g -1 ) than control and S-amended soils (2.3 -2.7 µmol h -1 g -1 ). As availability was reduced in CSP-and S-amended soils, and in those soils, the activities of ASF were approximately two times higher (2.4 -3.9 µmol h -1 g -1 ) than that in control (1.3 -2.0 µmol h -1 g -1 ). Overall, ASF activity could be used as an index for evaluating changes in quality of As-polluted paddy soils after amendment treatment.
Warming trends and concomitant increases in frost-free period are expected to alter cropping systems and subsequent land productivity in temperate climate regions. Our agricultural and food systems need to adapt to such changes. Here, we examined how nitrogen (N) availability would affect productivity of rice double cropping in combination with its ratoon regenerated from their parents rice plant (Oryza sativa, cv. Jomyeong) with early maturing habit. For main cropping season, rice plants were transplanted in experimental paddy field (35°10'N, 26o53'E, alt. 33.0m) of Chonnam National University, on April 25, 2016, and grown under local farmers' agronomic practices. After main crops harvested on August 17, ratoon rice plants were grown at five different levels of N availability [0 (N0), 9 (N9), 18 (N18), 28 (N28) and 37 (N37) kg N ha -1 ] and harvested on November 20. Unexpectedly, plant height of ratoon rice was unaffected by N availability. However, aboveground biomass (AGB) and yield of ratoon rice were significantly affected by N availability, displaying an increase of 56.5 kg ha -1 and 26.3 kg ha -1 per unit (1 kg ha -1 ) increase in N fertilization, respectively. As a result, while at N0, the AGB and yield of ratoon rice plants were 4.14 Mg ha -1 and 1.46 Mg ha -1 , respectively, they increased to 6.32 and 2.35 Mg ha -1 at N37, corresponding to 47% and 41% of those (i.e. 13.39 Mg ha -1 in AGB and 5.68 Mg ha -1 in yield) of main rice plants. Under high N availability, the greater number of regenerated tillers and panicle per m2 contributed to greater ratoon rice productivity. Combined annual productivity of the main and ratoon seasons ranged from 17.5 to 19.7 Mg ha -1 for AGB and from 7.1 to 8.0 Mg ha -1 for yield depending on N availability. The results suggest that ratoon rice double cropping could provide an ample opportunity to consolidate national food security in the warming world by increasing annual land productivity.
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