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Summary: Green soybean (edamame), an early-harvested soybean, is a popular vegetable in Asia and is recognised as a healthy vegetable in the other parts of the world. In Japan, edamame yield has gradually decreased over the last 30 years, despite similar cultivation areas. Damage caused by the soybean cyst nematode (SCN), Heterodera glycines , is one of the main causes. We surveyed the distribution of SCN in different locations and found a wide distribution of SCN across Japan. Different control measures are available, such as chemical control using fumigants or a granular type of nematicide, solarisation, and rotation with non-host crops. We are developing a new type of biological control method, which comprises short-term field cultivation and soil incorporation of mung bean. This method not only decreases the SCN density in soil but also mitigates soil erosion and nitrate leaching. For future SCN control it is essential to establish an environmentally friendly management strategy. [ABSTRACT FROM AUTHOR]

This study explores the complex relationship between soil electricity generating capacity, bacterial community dynamics, and soil chemical and physical properties across diverse regions of Japan. First, soil samples were systematically collected and analyzed. Subsequent investigations evaluated soil microbial biomass carbon, dissolved organic carbon (DOC), and total dissolvable iron (DFeT) concentrations. In the experiments, soil samples underwent a rigorous 60-day microbial fuel cell trial, wherein power density and total energy output were measured. Significant variations in power density were observed among different soil samples; specifically, a sugarcane field designated as Okinawa-3 and a peach orchard soil as Nagano-2 demonstrated relatively high total energy output. Analysis of soil bacterial community structures identified some families which showed positive correlations with increased electricity generation capabilities. Correlation analyses revealed associations between these bacterial communities and key soil parameters, particularly with DOC and DFeT concentrations. Redundancy analysis revealed intricate connections between soil properties and electricity generation capacities. Particularly noteworthy was the positive correlation between Acidobacteriaceae and DOC, as well that between Sphingomonadaceae and electricity generation, highlighting the crucial roles of soil microbial communities and chemical compositions in driving electricity generation processes. [ABSTRACT FROM AUTHOR]

To determine nitrogen (N) fate and environmental impact of applying anaerobic digestion slurry (ADS) to rice paddy (Oryza sativa L.), a field experiment was established using three treatments based on contrasting N application rate. The ADS (with ammonium-N accounting for >80 % of total N) treatment at a conventional application rate of 270 kg N ha-1 was compared to a negative control (no N fertilizer) and a positive control of urea applied at 270 kg N ha-1. The N budget showed the following distribution of applied N from ADS and urea: 41.3 ± 5.1 % for ADS and 36.6 ± 4.4 % for urea recovered by the rice plant (including straw, grain, and root), 16.4 ± 3.7 % for ADS and 7.4 ± 1.8 % for urea lost via ammonia volatilization, 0.26 ± 0.15 % for ADS and 0.15 ± 0.12 % for urea lost by direct N2O emission, 1.9 ± 0.5 % for ADS and 2.3 ± 0.8 % for urea leached downward, 0.70 ± 0.15 % for ADS and 0.67 ± 0.12 % for urea discharged with floodwater drainage, and 39.4 ± 8.4 % for ADS and 53.0 ± 9.1 % for urea retained by soil or lost by N2 emission. Compared to urea application, ADS application impacts the environment mainly through gaseous N losses rather than water N losses. ADS application had a positive impact on rice grain yield and reduced chemical fertilizer use. Considering the wide distribution of paddy fields and the ever-increasing quantities of ADS, ADS may serve as a valuable N source for rice cultivation, although mitigating ammonia and N2O losses should be further investigated. © 2012 Springer-Verlag Berlin Heidelberg.

Chrysanthemum is a very popular flower in Japan and is known to be infected by many soil-borne plant pathogens including nematodes. A nematode survey in six chrysanthemum fields in Okinawa, Japan, found Pratylenchus, Meloidogyne, and Paratylenchus (P. dianthus). The first two genera are known as plant pathogens against chrysanthemum, however, Paratylenchus dianthus has not been reported previously. Chrysanthemum seedlings were grown in pots containing soil infected only with P. dianthus for two months in 2017 and 2018. The nematicide imicyafos was applied in triplicates to half of the pots (treated) while the other half were left without the nematicide (non-treated). Plant height and dry plant weight of the imicyafos treated plants exceeded those of the control plants. Also, single-photon avalanche diode value of chrysanthemum leaves was higher in imicyafos treated plants than in the non-treated plants at two-month after planting. The results suggest that P. dianthus may suppress the growth of chrysanthemum. For high-throughput nematode diagnosis, a real-time PCR primer set specific to P. dianthus was developed and its sensitivity to quantify P. dianthus was confirmed with a proper calibration curve. The calibration curve was developed in a simplified approach by using serially diluted DNA extracted from individual nematodes.

No nematicide has been registered for controlling plant-parasitic nematodes in sugarcane in Japan. Greenhouse and field experiments were conducted to evaluate the efficacy of the phenylpyrazole insecticide fipronil (0.3–0.45 kg a.i./ha) against the root-lesion nematode, Pratylenchus zeae, which is an important plant-parasitic nematode species associated with sugarcane (Saccharum spp. hybrids) in Okinawa, Japan. Both experiments showed a reduction of P. zeae population densities in sugarcane roots to 27 to 56% of the non-treated control after 7 wk in the greenhouse experiment and 3 months in the field experiment (two trials). In contrast, P. zeae population densities in soil were not reduced by the fipronil treatment. At harvest, sugarcane yields in the field experiment were significantly increased by 6 to 8% in the fipronil treated plots compared to the non-treated control. The data showed that fipronil reduced numbers of P. zeae in sugarcane roots at the early stage of sugarcane seedling growth resulting in increased sugarcane yields. This is the first report of nematicidal activity of fipronil against P. zeae under field conditions.

This study aimed to evaluate the suppressive potential of different soils on soybean cyst nematodes (SCN) and to estimate the suppressive mechanism. Fifteen soils (designated as soil A to O) from different agricultural fields with varying organic inputs were added with SCN-infested soil and grown with a green soybean variety. The SCN density in the soil at 6 weeks of soybean growth was markedly different depending on the soils used, indicating a different level of disease suppressiveness. No significant correlation was observed between the SCN density and any of the soil physicochemical and biological characteristics tested. Then, to estimate a suppression mechanism, F-soil that showed the lowest density of SCN was added to the SCN-infested soil with or without streptomycin to kill bacteria and grown with soybean. SCN density was not increased by the addition of streptomycin, indicating that soil bacteria may not be involved in the suppressiveness of F-soil. In total, 128 fungal strains were isolated from the rhizosphere of F-soil and inoculated in a combination or singly in the SCN-infested soil. After repeated screenings, five strains were selected since the SCN density was consistently decreased by them. Sequence analysis showed that they were closest to Clonostachys rosea, Aspergillus niger, Aspergillus fumigatus, Fusarium oxysporum, and Cylindrodendrum alicantinum. All five strains significantly reduced the mobility of second-stage juveniles (J2). Further, C. rosea a2, A. niger a8, and F. oxysporum a25 significantly decreased hatching. Overall, the present study demonstrated that soil fungi played an important role in SCN suppression in F-soil. [ABSTRACT FROM AUTHOR]

Phosphorus (P) addition is thought to have a minimal effect on the priming of preexisting soil organic carbon (C) mineralization after C addition. We hypothesized and tested that positive priming effects are driven by microbial P-mining under P-limitation when a relatively small amount of glucose is added to N-rich and P-poor tropical forest soils with N2-fixing trees. The results showed that the addition of glucose alone (C) and the addition of C together with mineral N (CN) induced positive priming effects, while the addition of C together with mineral P (CP) and the addition of CNP did not, suggesting that positive priming effects occurred through microbial P-mining. The acid phosphatase activities were not much different in all treatments. The results support our hypothesis and suggest that positive priming effects will occur through microbial P-mining, independently of the hydrolysis of organic P esters with phosphatases, under P-limitation in N-rich and P-poor tropical forest soils. [ABSTRACT FROM AUTHOR]

Given that rice husk biochar has been shown to modulate salinity in salt-affected acid soils, the objective of this study was to investigate the effects of organic amendment of salinized acid soils on P fractions, enzyme activities, and associated rice yield. Four treatments, viz. Rice–Rice–Rice, [RRR]; Fallow–Rice–Rice, [FRR]; Fallow–Rice–Rice + 3 Mg ha−1 of compost [FRR + Comp]; and Fallow–Rice–Rice + 10 Mg ha−1 of biochar [FRR + BC] were established at Ben Tre and Kien Giang sites, Viet Nam, over six consecutive crops. Soil properties at harvest of the sixth crop showed that there were diverse patterns of fractionation between P forms with respect to treatment. Overarchingly, biochar increased labile and moderately labile inorganic P and organic P by 30% to 70%, respectively, whilst compost had a relatively modest effect on these pools. Soil phosphatase activities at crop tillering increased following the FRR + Comp and FRR + BC treatments compared with those in RRR, except for acid phosphatase at Ben Tre. At harvest, there were no significant differences between the enzyme activities among the treatments. Rice yield was positively correlated with the more labile forms of P, soil C, and acid phosphatase activity. In the absence of organic amendments, there was no effect of triple versus double rice crops being grown in one-year cycle. Repeated application of biochar (10 Mg ha−1 × 5 times) showed potential to increase grain yields and total soil C in salt-affected acid soils, via modulation of P transformations to more plant-available forms. [ABSTRACT FROM AUTHOR]

Mung bean residues stimulate the hatching of soybean cyst nematode (SCN). In our previous study, combined incorporation of mung bean residues and biochar into soil can be effective in suppression of the soybean cyst nematode (SCN), Heterodera glycines, in the upper layer soil. However, there are no data available as to whether such effects are transmissible, and could for example be manifest in subsoil zones where such incorporation is confined to topsoils, via water-based pathways. We evaluated the effects of leachate passage from a biochar-amended soil in an upper soil zone to a lower zone in a microcosm-based system, upon a range of physicochemical properties and density of SCN. Disturbed soil was filled in a total of 9 cylindrical cores with two layers. The upper layer (0–15 cm) was amended with biochar at rates equivalent to 0, 0.3% or 1.8%, with bulk density set at of 1.1 g cm−3. The lower layer (15–25 cm) without biochar amendment was compacted to 1.2 g cm−3. Mung beans were grown for two weeks and incorporated into the upper layer. Water was surface-applied to the cores 4, 6, and 8 weeks after mung bean incorporation. After 16 weeks, the upper and lower layer soils were separately collected and assayed. The presence of biochar in the upper layer reduced the abundance of free-living nematodes, mainly bacterivorous, but increased that of a predator genus Ecumenicus in this zone. In the lower layer of soil under a biochar-amended upper layer, available P and soluble cations were increased as were abundances of total nematodes including Ecumenicus, resulting in greater maturity index, basal and structure indices. Notably, SCN density was decreased in lower zones by more than 90% compared to zero-biochar controls. This demonstrates that the effects of biochar upon soil properties, including impacts on biota and plant pathogens, are transmissible. [ABSTRACT FROM AUTHOR]

Summary: Hirschmanniella diversa and H. imamuri parasitise the lotus, Nelumbo nucifera. Hirschmanniella spp. are the most important pests of lotus cultivation in Japan, but the distribution and species dominancy are not fully understood. In this study, we aimed to collect Hirschmanniella spp. individuals from lotus roots in the major lotus cultivation areas in Japan and identify them morphologically and molecularly using the 18S, D2-D3 regions of rRNA and mitochondrial cytochrome c oxidase subunit I (mtCOI). Hirschmanniella oryzae , commonly known to cause damage on rice in Japan, was also obtained and analysed for inter- and intraspecies sequence variations. All individuals of the genus Hirschmanniella extracted from lotus roots in 16 fields in ten prefectures were identified as H. diversa morphologically and molecularly. This result revealed that H. diversa is a dominant Hirschmanniella species parasitising lotus in Japan. Meanwhile, intraspecific sequence variations in H. diversa were relatively higher in the mtCOI (1-21 bases, ≦5.3%) than in the 18S rRNA and D2-D3 of 28S rRNA (0.0-0.3% and 0.0-0.4%, respectively) and in those of H. oryzae. Based on the mtCOI sequences, five haplotypes were identified and each haplotype was distributed in relatively close regions or regions in which the same lotus cultivars were grown, although further studies are required to verify this assertion. The morphological and genetic variations were higher in H. diversa than in H. oryzae (no intraspecific sequence variation in mtCOI), suggesting that H. diversa was not a recent invasive species. [ABSTRACT FROM AUTHOR]