Effect of rice straw application on CH4 emission from paddy fields

The effect of rice straw (RS) incorporated at the time of plowing in the previous cr–p season on CH₄ emission from rice paddies was investigated in a pot experiment. Rice straw that incorporated just before transplanting of rice seedlings (June) into a paddy field was collected after the harvest (October) and at the beginning of the next cropping period (May). Methane emission rates from the rice-planted pots with the application of fresh RS, RS collected in October. and RS collected in Mayas well as the pots without RS application were measured using the chamber method. The composition of organic constituents in the three kinds of RS was estimated by the proximate analysis. The cumulative amount of CH₄ emitted during the first 50–d period was lower in the order of the pots with RS collected in May, pots with RS collected in October, and pots with fresh RS. The cumulative amount of CH₄ emitted throughout the rice growth period from the pots with fresh RS and with RS collected in October was significantly larger while that from the pots with RS collected in May did not differ statistically compared with the total CH₄ emission from the pots without RS. These results suggested that there was an overall decrease in the amount of organic constituents in RS based on the large differences in T-C content and similar composition of organic constituents between the fresh RS and RS collected in May. Significant effect of RS continuously applied during the previous cropping period on the increase in CH₄ emission was discussed.     

Inhibitors of methane production in paddy soils

Global warming is now attracting the world attention. Methane is an important greenhouse gas next to CO₂. Prather et al. (1995) estimated that rice paddy fields account for 14% of all biogenic atmospheric methane. It is considered that methane production from rice paddy fields is increasing along with the increase of the population. Therefore, the development of rice cultivation techniques for reducing methane production is essential, in order to preserve the global environment.     

Phospholipid fatty acid composition of microbiota in the percolating water from a rice paddy microcosm

The microbiota in the percolating water from the plow layer soil in paddy fields was studied based on the composition of phospholipid fatty acids (PLFAs) in a pot experiment. The mean concentrations of PLFAs in the percolating water were 17±5 and 11±4 µg L^-1 in the planted and non-planted pots, respectively. The dominant PLFAs in the percolating water were 16: 0, 16: 1ω7c, 18: 1ω7, 18: 1ω9, il5: 0, and ail5: 0 PLFAs in both the planted and non-planted pots. The dominance percentage of 18: 3ω6c and 17: 1ω8 PLFAs increased at the late stage of rice growth in the planted pots. The percolating water from the planted pots contained in a higher percentage of straight mono-unsaturated PLFAs and a lower percentage of branched-chain PLFAs than that from the non-planted pots. Considerable differences in the PLFA composition in the percolating water were observed between the planted and non-planted treatments and with the duration of the growth period. Principal component analysis indicated that the microbiota in the percolating water was derived from the microbiota in the floodwater and in the plow layer soil. Cluster analysis showed that the similarity of the PLFA composition in the percolating water to the PLFA composition in the plow layer soil was higher than that in the floodwater. The stress factor that was estimated from the trans/cis ratio of 16: 1ω7 PLFA was 0.08±0.04 and 0.14±0.05 in the percolating water from the planted and non-planted pots, respectively, which indicated that the degree of stress on the microbiota in the percolating water from the planted pots was low in a similar way to the degree of stress on the microbiota in the floodwater, while the degree in the percolating water from the non-planted pots was similar to that in the plow layer soil, respectively.     

Influence of surface printing materials on the degradability of biodegradable plastic films in soil

Effect of surface printing on the biodegradability of plastic films was studied. Biodegradable films (polybutylene-succinate (PBS)) printed with four kinds of gravure inks were placed in soil for 1 year. The inks consisted of carbon black-pigment with four kinds of resins: poly-(ε-caprolactone) (PCL), nitrocellulose-polyamide blended resin (NT), polyvinyl chloride-vinyl acetate copolymer (V), and nitrocellulose (NC). Degradation of film specimens printed on one side and both sides as well as the control film without printing was monitored every 3 months by collecting sample specimens for the measurement of weight loss. No appreciable degradation was observed until 6 months after placement in soil for the control specimens and until 9 months for the printed specimens. And the degradation of the PCL- and NC-printed specimens with one-side printing and V-printed specimens with both-side printing was significantly slower than that of the control specimens without printing after 9-month placement at p < 0.05. Only after 12 months of placement, was the degradation significantly faster for the specimens printed on one side than for those printed on both sides except of the specimens printed with NC. There was no difference in biodegradability among PCL, NT, NC, and V resins. Specimens printed on both sides did not show any appreciable weight loss after 1 year in soil (percentage of maintenance of weight exceeding 98%). Microscopic observation indicated that the degradation mainly proceeded from the non-printed side to the printed side cross-sectionally.     

Microbial mineralization of organic nitrogen into nitrate to allow the use of organic fertilizer in hydroponics

Hydroponics is an excellent technique for the cultivation of vegetable crops and other plants, but organic fertilizers cannot be used in conventional hydroponic systems, which generally use only inorganic fertilizers, because organic compounds in the hydroponic solutions generally have phytotoxic effects that lead to poor plant growth. Few microorganisms are present in hydroponic solutions to mineralize the organic compounds into inorganic nutrients. In this article a novel and practical hydroponic culture method that uses microorganisms to degrade organic fertilizer in the hydroponic solution has been developed. Soil microorganisms were cultured by regulating the amounts of organic fertilizer and inoculum, with moderate aeration. The microorganisms mineralized organic nitrogen via ammonification and nitrification into nitrate at an efficiency of 97.6%. The culture solution containing the microorganisms was usable as a hydroponic solution, and organic fertilizer could be directly added to it during vegetable cultivation. Vegetables grew well in the organic hydroponic system. Organic hydroponics based on this method is therefore a practical tool for the utilization of organic sources of fertilizer.     

Geographic distribution of Waxy gene SNPs and indels in foxtail millet, Setaria italica (L.) P. Beauv.

To elucidate diversity and evolution of the Waxy gene in foxtail millet, Setaria italica, we analyzed sequence polymorphism of Waxy gene in 83 foxtail millet landraces collected from various regions covering the entire geographical distribution of this millet in Europe and Asia. We found a unique geographic distribution pattern at the sequence level of gene haplotypes and also found a large diversity in East Asian landraces. We also found a higher degree of genetic polymorphism in a non-waxy phenotype than in other low amylose types, supporting the hypothesis that low amylose types recently originated from non-waxy type.     

Assessment of the decay risk of airborne wood-decay fungi III: decay risks at different sampling sites

The decay risk of airborne wood-decay fungi in the same volume of air was investigated by using an air sampler over the course of a year at three different sampling sites. Japanese cedar disks measuring 7.8 cm in diameter and about 3 mm in thickness, and with a moisture content of about 100 % were placed in a “BIOSAMP” air sampler and then exposed to 1000 l of air in the northern, central, and southwest parts of Japan. The exposed disks were incubated for 20 weeks in a damp container maintained at 26 ± 2 °C and degraded by fungi trapped on the disks. The decay risk was calculated from the mass loss during incubation, and the factors affecting the said risk were explored. The results showed that sampling sites apparently do not affect decay risk, even though the Scheffer’s climate indexes of the sites were quite different. The relation between the sampling month and decay risk reveals that decay risk remains virtually the same year-round. Relative humidity on a sampling day is one of the key factors affecting decay risk in sampling conducted at the central or southwest site. In contrast, no weather factors influenced decay risk at the northern sampling site.     

Spectrophotometrical characteristics in the near infrared region in beech (<Emphasis Type="Italic">Fagus crenata</Emphasis>) and pine (<Emphasis Type="Italic">Pinus densiflora</Emphasis>) litters at the various decomposing stages

We examined the relationships between the absorptional characteristics in the near infrared region and the chemical changes of decomposing beech (Fagus crenata) and pine (Pinus densiflora) litters. Spectra as well as the concentrations of chemical substances approached each other and converged with decomposition, although both initial characteristics differed markedly between beech and pine. This indicated that the fundamental chemical structures were almost the same, although their organochemical composition differed. Specific absorption bands for lignin, polysaccharide, and protein were identified at 2,140 and 1,670 nm, 2,270, 1,720, 1,590, and 1,216 nm, and 2,350 nm, respectively. Absorbance at 1,670 nm, peculiar band of aromatics, showed a positive correlation with lignin concentration, which suggested the relative increment of aromatics due to condensed lignin in decomposing litters. Absorbance at 2,140 nm, characterized as the C–H bond in HRC = CHR, showed a negative correlation with lignin concentration, which suggested the decrements of some structures such as side-chains in lignin polymers unrelated to aromatics. Absorbance at 2,270, 1,720, and 1,216 nm, specified to O–H/C–O/C–H bonds in saccharide, might reflect the change of polysaccharide during decomposition because they showed a positive correlation to polysaccharide concentration. In the same way, absorbance at 2,350 nm, identified to the C–H/CH₂ bonds in protein, showed a negative correlation to nitrogen concentration in decomposing litters, which might indicate that the C–H/CH₂ bonds in protein decreased with decomposition due to microbial consumption of carbon in protein. Our findings suggested the possibility that the spectral changes indicate the litter digestibility during decomposition and that also explain the compositional change in decomposing litters.     

The effects of within-species and between-species variation in wood density on the photodegradation depth profiles of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa)

Low density wood is more rapidly eroded than denser wood when exposed to the weather, possibly because it is more susceptible to photodegradation. Fourier transform infrared microscopy was used to examine: (1) the depth of photodegradation in earlywood and latewood of sugi (Japanese cedar) and earlywood of hinoki (Japanese cypress) exposed for up to 1500 h to artificial sunlight emitted by a xenon lamp (375 W/m² within the 300 to 700 nm spectral range); and (2) the relationship between the density of wood tissues and depth of photodegradation. The depth of photodegradation varied between species (sugi and hinoki) as well as within a growth ring (sugi earlywood and latewood), and there was an inversely proportional relationship between depth of photodegradation and wood density. These findings may explain why low density earlywood is more rapidly eroded than latewood during weathering, and more generally, why there is an inverse relationship between the density of wood species and their rate of erosion during artificial and natural weathering. Part of this work was presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, August 2004     

Using landscape metrics and topographic analysis to examine forest management in a mixed forest,Hokkaido, Japan: Guidelines for management interventions and evaluation of cover changes

In this study, we identified the distribution characteristics of a mixed forest of coniferous and broad-leaved trees (a typical forest type in Hokkaido, Japan) using landscape metrics and topographic factors, and attempted to apply this knowledge to examine forest management. This approach provides a new perspective (i.e., the landscape structure) on forest management, which traditionally has been determined on the basis of individual forest stands. We first created a cover type map of the study area by means of aerial photo interpretation. The characteristics of each cover type identified from the photographs were determined using landscape metrics for each cover class. We digitized a forest administrative map (1:20,000 scale) using 20-m contours, and imported this into GIS software to produce a terrain model; on this model, we overlaid the cover types. Our examination of landscape metrics showed that most of the natural forest could be managed similarly. However, our examination of topographic characteristics revealed exceptions (e.g., areas that are difficult to regenerate) that will require particular attention when managing the natural forest. Based on the information we obtained, we proposed a guideline for sustainable forest management. From the land cover map, we proposed an “improved” cover type map to illustrate the development of a high growing stock of forest based on forest management. We compared the current cover map with the “improved” cover map and demonstrated that the improved form would have more significant effects on fauna that do not recognize differences in the proportion of the dominant species types than on those that can recognize these differences. Our results show how the information obtained using landscape metrics and terrain models is an essential tool for various stages of forest management planning.