A 22-year (1990–2012) field experiment was conducted to assess the effects of different fertilization and cropping regimes on the quantitative changes of total N and organic N forms in the topsoil (0–20 cm) and subsoil(20–40 cm) of a Mollisol in Northeast China. This study included nine fertilizer treatments on maize monoculture [no fertilizer (CK), N, NP, NK, PK, NPK, NPK combined with maize straw (NPKS), NPK combined with pig manure (NPKM), and 1.5’ the rate of NPKM (1.5NPKM)] and one fertilizer treatment with maize-maize-soybean rotation (NPKMR). Compared with the CK treatment, the application of mineral fertilizers alone or in combination with straw generally had no significant effect on the contents of total N and organic N forms, whereas the combined application of mineral fertilizers with manure significantly increased their contents. Manure levels and cropping regimes had no significant effect on the total N content in the topsoil. By contrast, the hydrolysable unknown N content significantly increased with the increasing manure levels, and the amino sugar N content was significantly lower in rotation than in monoculture treatment. Our results imply that manure application integrated with continuous maize cropping can be considered as an optimized strategy for improving soil fertility.

Rhodiola sachalinensis A. Bor (family Crassulaceae), a perennial herbaceous plant, is distributed mainly in the mountainous areas of China, Japan, Korea, and Russia. It is widely used as a traditional Chinese medicine with adaptogenic properties, cardiopulmonary protective effects, and central nervous system activities (3). Currently, it is extensively cultivated in northeastern China. In August 2010, widespread (>60% of plants were symptomatic) damping-off was observed in a seedling field in Linjiang, China. Leaves and stems near the ground were affected first, with dark lesions forming on the stem and the lowest leaves exhibiting wilt. The wilt spread rapidly over the entire plant with leaves becoming grayish brown and water soaked and then turned black and died. Root rot, defoliation, and damping-off were also observed. Six isolates with morphological characteristics of Rhizoctonia solani Kühn were isolated from symptomatic stems when plated on potato dextrose agar (PDA). Mycelium was branched at right angles with a septum near the branch and a slight constriction at the branch base. Fungal colonies were initially white, turned brown with age, and produced irregularly shaped, brown sclerotia after 8 days on PDA. Hyphal cells removed from cultures grown at 25°C on 2% water agar were determined to be multinucleate when stained with 1% safranin O and 3% KOH solution (1) and examined at ×400 magnification. The internal transcribed spacer (ITS) region of the nuclear rDNA was amplified by using the primers ITS4/ITS5 (2). The ITS sequences (715 bp) were identical in these six isolates (GenBank Accession No. FR878087) and had 100% sequence identity with R. solani AG-4 HG-II (GenBank Accession No. HQ629873) along with numerous other accessions from this AG subgroup. Pathogenicity tests were performed on healthy, potted seedlings of R. sachalinensis. Twenty plants were inoculated near the base of the stem with a 0.6-cm-diameter mycelial plug from 3-day-old PDA cultures for each isolate. Twenty plants inoculated with only PDA plugs served as controls. The plants were covered with plastic bags and kept in a greenhouse at 20 to 25°C for 72 h. All inoculated plants showed characteristic symptoms as previously observed in the seedling field 13 days after inoculation, while control plants remained healthy. R. solani AG-4 HG-II was reisolated from symptomatic tissues on inoculated plants. To our knowledge, this is the first report of R. solani AG-4 HG-II causing damping-off on R. sachalinensis in China. References: (1) R. J. Bandoni. Mycologia 71:873, 1979. (2) D. E. L. Cooke et al. Mycol. Res. 101:667, 1997. (3) T. F. Yan et al. Conserv. Genet. 4:213, 2003.