Faunal-mediated nutrient cycling, especially N mineralization, has the potential to make a significant contribution to nutrient supply to crop plants in production systems involving e.g. green manure cover crops. We investigated the effects of enchytraeids on N mineralization from mung bean residues in microcosm experiments using an organically-farmed soil with an inherently large population of enchytraeids. Enchytraeids promoted N mineralization by 23% after a distinct lag of between four and 12 weeks, concomitant with a substantial increase in population size followed by an almost complete collapse. Nitrogen release from the necromass would have contributed a small but significant fraction of the N mineralized, and the result suggested the presence of other mechanisms. Enchytraeids suppressed nematode populations, while did not affect the mean weight diameter (MWD) of soil aggregates, although mung bean residues increased MWD. We conclude that enchytraeids have potential to play significant roles in mediating N supply to crops but matching supply-and-demand periods may be challenging.

This study examined the accelerated degradation of poly(caprolactone) films using two types of lignin derivatives. The degradation of poly(caprolactone) films was unaffected by the lignin-derivative-capped hydroxy groups, indicating the participation of radicals from phenolic hydroxy groups in lignin derivatives for accelerating the degradation of films. Furthermore, the role of lignin radicals in relation to polymer degradation changed as per the mechanism of polymer decomposition, e.g., the degradation of poly(ethylene carbonate) films was suppressed by feeding lignin derivatives because of the back biting type decomposition nature of poly(ethylene carbonate), which differs from the radical-mediated addition/cleavage type decomposition nature of poly(caprolactone). These results provide an approach of designing bio-degradative materials from lignin, a natural phenolic polymer.

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.

Purpose A method to control soybean cyst nematode (SCN) is to grow green manure which releases hatching stimulants in the absence of host plants. We hypothesized that biochar may improve the efficacy of this control strategy. Methods We evaluated the effects of two hatch-stimulating plants (Vigna radiata and Crotalaria spectabilis) in combination with rice husk biochar on the plant growth, SCN density, and soil nematode community. Plants were cultivated in biochar-amended and unamended soils for one month and then incorporated. Soils were collected periodically for chemical properties, SCN, and nematode community assessment. Results Biochar increased total biomass of V. radiata and C. spectabilis significantly. For V. radiata alone, the number of SCN juveniles (J2) increased at three weeks and then decreased, but in biochar-amended soil J2 prevailed for three to seven weeks after residue incorporation. In soil incorporated with C. spectabilis, J2 were sustained consistently in biochar-amended soil. Nine weeks after residue incorporation, real-time PCR assays revealed that V. radiata reduced the SCN density by 96% and 91%, and that C. spectabilis reduced the SCN density by 72% and 48% with and without biochar, respectively. Incorporation of green manure in biochar-amended soil increased microbial activity and abundance of omnivorous nematodes, notably Ecumenicus and Aporcelaimellus species which were negatively correlated with the SCN density. Specifically, V. radiata increased the composite and enrichment footprints of nematodes, and omnivore and structure footprints were further increased by combination with biochar. Conclusion Biochar may improve the efficacy of a green manure-based strategy to control SCN.

Biochar has the potential for improving soil properties and supporting ecological functions, but it has negative impacts on soil organisms in some cases. This study aimed to assess the effect of biochar application at rates of 0 (B0), 5 Mg ha−1 (B5), 20 Mg−1 (B20), and 40 Mg ha−1 (B40) on soil nematode community under upland and flooded conditions in a short-term microcosm experiment. After biochar application, soil was incubated for 2 to 8 weeks and nematodes were identified for community composition, trophic structures, functional guilds, maturity index and metabolic footprints. The chemical properties of the soils were also analyzed. General linear model revealed that biochar increased soil pH, EC, NO3−-N, available phosphorus, total C, and C/N ratio, particularly in the highest application rate and shifted the composition of nematodes. The greatest abundances of omnivores (Mesodorylaimus, Thornenema), predator (Nygolaimus) and functional guilds of cp5 were observed in B5, resulting in greatest structure footprint and composite footprint, (omnivorous + predator) footprint and total biomass in B5. While abundances of nematodes tended to decrease with the biochar applicate rates, the abundance of Prismatolaimus was the highest in B40. During the 8-week incubation period, the abundances of Achromadora, Alaimus, Aporcelaimellus, Cryptonchus, Mononchus, and Tobrilus remained stable in upland conditions. Under flooded conditions, the abundances of almost all taxa were markedly lower than those under upland conditions irrespective of biochar application, except for Acrobeloides, Alaimus, Aphelenchoides, and Ditylenchus. We highlighted that 5 Mg ha−1 of rice husk biochar can be the optimum in shaping the nematode community.