This study was conducted to establish a weed management system based on the sequential application of pre-emergence (PRE) and post-emergence (POST) herbicides for soybean production in Primorsky krai. Field experiments were conducted for two years in a field located in Bogatyrka, Primorsky krai, Russia (N43°49′, E131°36′). No herbicide application resulted in significant soybean yield loss, 0.03–0.3 t ha⁻¹, which is more than 91.6% yield loss compared with that of the weed-free plot. The PRE application of acetochlor showed good weed control efficacy (greater than 90% weed control) with acceptable soybean safety (less than 10% soybean damage), while the other PRE herbicides performed poorly in terms of weed control. The POST application of bentazon + acifluorfen, bentazon, and imazamox at 30 days after soybean sowing (DAS) showed good weed control efficacy with good soybean safety. Neither the PRE nor POST application alone showed a sufficient soybean yield protection, resulting in much lower soybean yield than the weed-free plot. The sequential application of acetochlor (PRE), followed by either bentazon + acifluorfen (POST) at 30 DAS in 2012 or bentazon + imazamox (POST) at 60 DAS in 2013 showed the best performance in soybean yields, 1.7 t and 1.9 t ha⁻¹, respectively, provided with 724.5 US$ and 1155.6 US$ ha⁻¹ of economic returns. For alternative PRE herbicides of acetochlor, which is now banned, our tests of the sequential application of S-metolachlor with other POST herbicides and the sole application of other PRE herbicides revealed that S-metolachlor and clomazone could also be considered. Our results thus demonstrate that the sequential applications of PRE and POST herbicides should be incorporated into the weed management system for soybean production in Primorsky krai, Russia.

Understanding the effects of nitrogen (N) fertilizer on soybean-weed competition is essential for establishing a practical tool for N application and weed management. A two-year field experiment was conducted in a soybean field located in Bogatyrka (43.82° N, 131.6° E), Primorsky krai, Russia, to investigate the effects of N fertilizer and multiple-weed interference on soybean (Glycine max) yield and to model these effects. Soybean yield loss caused by the interference of multiple weeds including common ragweed (Ambrosia artemisiifolia), barnyard grass (Echinochloa crus-galli), and American slough grass (Beckmannia syzigachne) at different levels of N fertilizer was accurately described by a combined model incorporating inverse quadratic and exponential models into the rectangular hyperbolic model for two parameters Y₀ and β, respectively. The combined model used in our study indicated that the application of N up to 36 kg N ha⁻¹ can increase weed-free soybean yield by 2.2 Mg ha⁻¹ but soybean yield under multiple-weed interference can sharply decrease with increasing total density equivalent, particularly at 36 kg N ha⁻¹. These results, including the combined model, thus can support decision making for weed management under different N uses in soybean cultivation.

Four-year field experiments were conducted to investigate phenotypic traits associated with the biomass yield of 173 Miscanthus sinensis accessions collected from Korea and neighboring East Asian countries. Nine phenological and agronomic traits associated with biomass yield were assessed to investigate their phenotypic diversity and relationships with biomass yield as well as the latitudes of the M. sinensis accessions collection sites. Correlation analyses among phenological and agronomic traits, biomass yield, and collection site revealed that heading date, vegetative growth duration, leaf area, and stem growth traits (stem height, stem diameter, and stem dry weight) were closely related to biomass yield. The latitude of collection site exhibited a significant negative correlation with heading date, and heading date showed a significant positive correlation with biomass yield, indicating the high biomass potential of the accessions originating from lower latitude due to longer vegetative growth. The best biomass yield was mainly observed in M. sinensis accessions from the southern parts of Korea, such as Jeolla and Jeju provinces, with over 20 Mg DM ha⁻¹. Agronomic traits measured in the second year after planting also showed a high correlation with biomass yield measured in the fourth year after planting. In particular, vegetative growth duration, leaf area, stem diameter, and stem dry weight measured in the second year were significantly related to the fourth-year biomass yield. Therefore, these findings suggest that agronomic traits measured in the second year can be used for screening M. sinensis genetic resources and breeding lines with high biomass yield potential.

Senecio vulgaris is an exotic annual winter weed that is problematic in garlic and onion fields in Republic of Korea. The chloroplast DNA was 150,765 bp with 82,907 bp of large single-copy region, 18,214 bp of small single-copy region, and 24,822 bp of a pair of inverted repeats. A total of 104 genes were annotated including 80 protein-coding genes, 20 tRNA genes, and 4 rRNA genes. Twelve genes (ClpP, ndhB, ycf3, rpl2, rps12, trnA, trnI, trnR, trnG, trnL, and trnV) were multiple-copy genes. Senecio vulgaris was closely related to Jacobaea vulgaris in same subfamily resulting from phylogenetic analysis.