Journal of the Society of Agricultural Structures, Japan

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The overall heat transfer coefficients of various agricultural covering materials were measured under winter nighttime downward longwave radiation from 212 to 297 W m⁻² reproduced in an experimental device. Under the downward longwave radiation conditions of this study, the ranges of overall heat transfer coefficients of glass, polyolefin film, fluorocarbon resin film, polyvinyl chloride film, polyvinyl acetate film, and polyethylene film were 5.2–5.7, 5.5–6.4, 5.6–6.4, 6.0–6.9, 6.7–7.6, and 6.7–7.6 W m⁻² °C⁻¹, respectively. The overall heat transfer coefficient tended to increase as the downward longwave radiation decreased. The relationship between downward longwave radiation and the overall heat transfer coefficient could be approximated for each covering material by a straight line. Therefore, it should be possible to calculate the amount of overall heat transmission of a greenhouse more accurately by considering the downward longwave radiation and applying each material’s respective approximate equation. In addition, it was possible to approximate the absorptance (transmittance) of longwave radiation and the overall heat transfer coefficient in each covering material with a quadratic function. Therefore, it should be possible to estimate the overall heat transfer coefficient of covering materials with unknown heat insulation capacity under different downward longwave radiation by measuring the absorptance or transmittance of longwave radiation.

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This study aimed to clarify the characteristics of composting reaction for dairy cattle manure mixed with biochar (rice husk biochar, bamboo biochar, and granular wood) commercially available in Japan. Composting of dairy cattle manure mixed with 10 % biochar (wet weight basis) was performed for 35 days using a lab-scale composting device to analyze compost temperature, microbial activity, and N₂O, CH₄, and NH₃ gas emissions. The results showed that rice husk biochar reduced NH₃ emissions by 59.8 % compared to the control, while bamboo charcoal only reduced NH₃ emissions by 6.8 %. N₂O and CH₄ emissions were reduced by all biochar types, with bamboo charcoal showing the highest suppression among them. On the other hand, the biochar treatments showed the same tendency as the control treatment regarding the increase in the maximum temperature in the initial composting stage and the persis- tence of a high-temperature period above 55°C. In addition, no signiﬁcant differences in cumulative CO₂ emissions or organic matter decomposition rates, representing microbial activity, were observed between the biochar treatments and the control. The results indicate that mixing biochar does not affect the composting process. Although the biochar used in the study did not affect the promotion of composting of dairy cattle manure, some types of biochar were effec-tive materials in reducing NH₃, N₂O, and CH₄ emissions.

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