Japanese Andosols Research Articles

Potential water repellency influenced CO2 and CH4 release from moist soils: Experiments on water-repellent Japanese Andosols

Soil, the largest terrestrial carbon (C) pool on earth is an important source of greenhouse gasses. Soil water repellency (SWR), a moisture-dependent characteristic, is an important factor that affects microbial decomposition and gas release since it causes non-uniform moisture distributions in the soil matrix. It is not clear whether potential water repellency (PWR), measured on dried soils, can influence carbon dioxide (CO2) and methane (CH4) emissions under unsaturated moist conditions. This study aims to fill this knowledge gap using two water-repellent soils, and one non-repellent soil (NRS; control), under two temperature levels. Samples were collected from water-repellent Chamaecyparis obtusa (CYP) and Cryptomeria japonica (CED) forests, and the NRS was collected from Field Science Center in Ibaraki University, Ibaraki, Japan. Capillary-moistened samples were placed in closed chambers and separately exposed to 25 °C and 35 °C. Gas sampling was conducted in 1, 7, 14, 21, and 28 d. The PWR was measured with separate samples under the same conditions. CED soils showed significantly higher PWR compared with the NRS and CYP. The gas emission per g soil organic C (EGC; mg g−1 SOC h−1) was significantly low in CED soils compared with NRS and CYP, while NRS showed the highest emission. EGC of CO2 and CH4 showed significant strong negative correlations with PWR. The emission of CO2 and CH4 significantly increased with increasing temperature, and the Q10 was significantly high for CH4. Results indicated that the sensitivity to elevated PWR was higher for emission of CO2, whereas the sensitivity to the elevated temperature was higher for the emission of CH4. It was clear that PWR can influence moisture distribution in soil matrix in unsaturated moist soils and the processes that limit gaseous C emission. Further experiments are required on possible processes that enable PWR to influence gaseous C emission from moist soils.

Heat-induced alterations in moisture-dependent repellency of water-repellent forest soils: A laboratory approach with Japanese Andosols

Abstract Soil water repellency (SWR) is a phenomenon that prevents the spontaneous wetting of numerous forest soils. It is a moisture-dependent characteristic, which disappears when soil moisture reaches near saturation. The heat generated during forest fires affects soil characteristics including SWR. The possibility of heat influencing moisture-dependent repellency (MDR) is not well understood. The present study aimed to investigate the effects of different heating temperatures (HT) and exposure durations (ED) on MDR using water-repellent Japanese Cedar (CED) and Japanese Cypress (CYP) forest soils. Soil samples collected from 0–5 cm depth were exposed to heat separately at 50, 100, and 150 °C (H T) for 1 h and 2 h durations (E D). The MDR of heated and non-heated soils was determined using the water drop penetration time (WDPT) test in a drying process. During the drying process of the tested soils, SWR appeared and then increased with drying to reach an extreme level (WDPT ≥3600 s) that persisted for a range of decreasing moisture contents, and declined to be non-repellent again (WDPT = 0 s). The critical moisture content at which soils become water-repellent with drying (CMC), the highest and the lowest moisture contents when soils showed maximum SWR (HMCmax and LMCmax, respectively), and the integrated area below the MDR curve (SWR) decreased with increasing HT in both CED and CYP soils. The moisture content at which soils become non-repellent again during drying, MCNR, was independent of the type of soil and heat treatment. The range of moisture contents between HMCmax and LMCmax, where soils show maximum SWR during drying, decreased with increasing HT, from 50 to 150 °C in CED and from 100–150 °C in CYP. The SWR showed strong positive linear correlations with CMC and HMCmax. The heat generated during wildfires can alter the MDR and all the related repellency parameters of water-repellent forest soils. SWR prevails over a narrower range of moisture contents in heated soil compared with non-heated soils. Further investigations with higher temperature levels using different soil types would be important for a comprehensive understanding of the heat impacts on MDR.

A simulation model (PostPLANT-Soil) for predicting pesticide concentrations in succeeding leafy vegetables: I. Validation with experimental data in a Japanese Andosol field.

We developed a simulation model for predicting pesticide concentrations in succeeding leafy vegetables (PostPLANT-Soil), which includes the process of pesticide uptake from plant roots. To validate the model, we compared pesticide concentrations simulated by the model with values measured from field experiments in an upland Andosol. The model validation showed that pesticide concentrations in the plant shoot were correlated with the concentrations in the soil solution rather than those of the water-extracted pesticides. The model successfully simulated the concentration changes in plant shoots when the simulated concentrations of the pesticides in the soil solution were fitted to the measured values by considering the key parameter - the corrective coefficient for the soil adsorption coefficient. However, the simulated shoot concentrations at the appropriate harvest period exceeded the measured values. This indicates that the leafy vegetable used in this study may have some metabolic capacity for the pesticides.

Effects of a new compost-chemical fertilizer mixture on CO₂ and N₂O production and plant growth in a Chernozem and an Andosol

ABSTRACT Composts are an attractive organic-farming alternative to chemical fertilizers and are used for carbon sequestration to increase soil carbon storage. In Japan, a new type of mixed compost fertilizer called compost-compound fertilizer mixture (CCFM) has been registered. It exhibits several merits for organic farming; that is, it is odorless, easy to handle, and has a controllable nutrient content. CCFM consists of compost mixed with chemical fertilizer, such that nutrient content can be effectively adjusted. Although it has been pointed out that pellet composts generate more greenhouse gas emissions (GHGEs), such as carbon dioxide (CO₂) and nitrous oxide (N₂O), the mechanism involved is not clearly understood. To investigate the effect of CCFM on GHGEs, soil microbial properties and plant growth, incubation and pot experiments were conducted in a Hungarian Chernozem and a Japanese Andosol. Both soils were incubated with 1) CCFM prepared using pig manure mixed with chemical fertilizer, 2) chemical fertilizer only, or 3) no fertilizer. A pot experiment was conducted using Komatsuna (Brassica rapa). In the Chernozem, the maximum N₂O production rate was observed after chemical fertilizer treatment. The emission factors of chemical fertilizer and CCFM were 0.25% and 0.19%, respectively. In contrast, N₂O production was not detected in the Andosol. Meanwhile, CO₂ production was higher (P < 0.05) in the Chernozem than in the Andosol; furthermore, it was higher under CCFM than under chemical fertilizer treatment, with 7.5% of amended carbon changing to CO₂, thus suggesting that dominant carbon remained in the soil. Microbial biomass increased faster in the Andosol than in the Chernozem and the change was faster under the CCFM than under the chemical fertilizer or control treatments. In the pot experiment, CCFM tended to enhance plant growth in both soils. These experiments showed that CCFM has a soil-carbon storage effect with less resultant GHGEs, especially in Andosols, thereby leading to a more sustainable agriculture. Nonetheless, further studies are required for long-term experiments with other crops.

Air-drying and drying-rewetting effects in Japanese Andosols subjected to long-term organic rice farming

ABSTRACT Paddy fields are generally submerged during the growing season and drained in the fallow season, and occasionally stimulating the air-drying effect and drying-rewetting effect on soil nitrogen (N) mineralization and soil carbon (C) decomposition. It is important to understand how these two effects take place in Andosol field under organic farming. To elucidate these effects, we incubated fresh, air-dried, and dried-rewetted paddy soil anaerobically under flooded condition. Soils were from the fields subjected to organic rice farming (ORF) for 4–5 years (4ORF), 8–9 years (8ORF), and 12 years (12ORF) with only rice residues and fallow weeds as organic matter applied, and cnventional rice farming (CRF). Soil samples were collected from plow layer of 0–15 cm depth after the rice harvest. The results showed that air-dried and dried-rewetted treatments could significantly increase N mineralization potential in 8ORF and 12ORF. The air-drying effects were not significantly changed in 4ORF, but significantly increased in 8ORF and 12ORF as compared to CRF. The drying-rewetting effects of C decomposition potentials were highest in 12ORF significantly. The N mineralization potential of air-drying effect showed no significant difference compared to drying-rewetting effect on conventional and organic rice farming. The ratio of C decomposition to N mineralization after 8 weeks incubation was higher in fresh soil (at 7.26–8.61) than those in air-dried (at 4.09–4.35) and dried-rewetted (at 3.94–4.26) soils. These indicated that the easily decomposable soil organic matter under the anaerobic flooded condition from fresh soil was changed by air-drying and drying-rewetting treatments. The slow increase of N mineralization and C decomposition with years of organic farming suggest the slow increase of fallow weed, the biomass of which gradually increase with years. The specific behavior of 12ORF soil suggest the transition of soil condition from a transitional state to an established state.

New definition of the qualifiers for Dystric and Eutric should be noted for the classification of Andosols with WRB2014

ABSTRACT The WRB (World Reference Base for Soil Resources) 2014 adopted ‘effective base saturation (EBS),’ which is the ratio of exchangeable bases (Ca + Mg + K + Na) to effective CEC (Ca + Mg + K + Na + Al), instead of base saturation (BS), the ratio of exchangeable bases to the cation exchange capacity, as the criterion for the addition of qualifiers concerning the condition of exchangeable bases. An EBS of less than 50% was defined as Dystric conditions, and that of 50% or more was defined as Eutric conditions. These newly defined qualifiers were applied to 49 soil samples from grasslands of Andosols in central Kyushu and 132 horizons from a database of Japanese Andosols. It was found that 80% of the samples met the criterion for Eutric conditions according to WRB2014, despite their small amount of exchangeable bases and low BS, whereas only 2% were Eutric when the criterion of WRB2006 (BS ≥ 50%) was used. In the case of uncultivated soils, the definitions of Dystric and Eutric according to WRB2014 corresponded mainly to non-allophanic and allophanic soils, respectively. All pedons of allophanic Andosols were classified as Eutric, but those of non-allophanic Andosols were classified as Dystric, according to WRB2014, because of the high EBS recorded in them. Conversely, all pedons were classified as Dystric based on the WRB2006 criteria. These characteristics of the Dystric and Eutric qualifiers in the classification of Andosols according to WRB2014, which is related to the variable charge of the samples, should be noted for the proper understanding and management of base conditions of Andosols.

Carbon and nitrogen stocks and their mineralization potentials are higher under organic than conventional farming practices in Japanese Andosols

ABSTRACT This study aimed at understanding whether and how long-term organic rice farming affects soil carbon (C) and nitrogen (N) stocks and their mineralization potentials in submerged rice paddies in Tochigi, Japan. An incubation experiment was carried out to assess the impacts of internal nutrient cycling after organic farming (OF) for 4–5 years (4OF), 8–9 years (8OF), and 12 years (12OF), compared with a conventional rice field (CF). Soil samples were collected at 0–15 cm and 15–20 cm in flooded rice fields after harvest in October 2013. pH and bulk density at 0–15 cm were significantly lower in 12OF fields than in CF fields (by 0.22 unit pH and 17.5%, respectively). Compared with CF, 12OF fields showed significant differences in soil organic carbon (SOC) and total nitrogen (TN), but 4OF and 8OF fields did not. In 8OF fields, the C decomposition (Co) and N mineralization (No) potentials were significantly higher (by 34.0% and 35.6%, respectively, at 0–15 cm, and by 67.1% and 24.5% at 15–20 cm) than in CF fields. Similarly, in 8OF fields at 0–15 cm, the Co:SOC and No:TN ratios were 19.8% and 23.2% higher, respectively, than in CF fields. Co, No, Co:SOC, and No:TN in 12OF fields were higher than those in CF fields, demonstrating the effects of prolonged organic rice farming. Additionally, in 12OF fields, C and N stocks were significantly higher (by 15.5% and 17.2%, respectively, at 0–15 cm, and by 4.8% and 12.1% at 15–20 cm) than in CF fields. Our findings suggest that long-term organic rice farming increases soil C and N stocks as well as C and N mineralization in Japanese Andosols.

Comparison of soil sorption parameters of pesticides measured by batch and centrifugation methods using an andosol.

We compared the soil sorption coefficient (K d) measured by batch and centrifugation methods using a Japanese andosol and ten pesticides. Although the K d values measured by both methods increased with time, those obtained via the batch method tended to be higher during the test period. The difference in K d values between the two methods affected pesticide concentrations estimated in the soil solution, and the results estimated using K d values obtained via the batch method underestimated the observed trends.

Characterization of the perylenequinone pigments in Japanese Andosols and Cambisol

ABSTRACT The green fraction of humic acid (Pg) and the chloroform-extractable green fraction (CEGF) are characteristic soil organic matter (SOM) components. These alkaline solutions are green-colored due to the presence of 4,9-dihydroxyperylene-3,10-quinone (DHPQ) chromophore. While both of which are potential indicators for the effect of land use and paleoclimatic environment in the fields of soil science as well as geochemistry, CEGF as well as its relationship with Pg in soils are not yet fully documented. In this study, we firstly investigated the chemical properties of soil CEGF fractions by ultraviolet–visible (UV–Vis) and infrared (IR) method. Two CEGF components were separated by sequential liquid-liquid extraction using aqueous ammonium hydroxide (NH4OH) followed by aqueous sodium hydroxide (NaOH). Results showed that the UV–Vis spectral shape of NH4OH-extractable component is very similar to that of DHPQ, except that it is red-shifted. The solubility and UV–Vis spectrum of the NaOH-extractable fraction were completely identical with those of synthesized DHPQ. Their IR spectral shapes were also almost the same. Subsequently, the distribution of CEGF in humic acid (HA), fulvic acid (FA) and humin (HN) from Japanese Andosols and Cambisol was quantitatively evaluated by sequential extraction. Most of CEGF was detected in the HA (60–78%) and HN (22–40%), but not in the FA. While the UV–Vis spectral shape of CEGF extracted from Andosols HAs showed a relatively higher proportion of DHPQ than its derivative, the opposite was observed in Cambisol HA, whose CEGF is similar to that of sclerotium grain (one of the possible origin of CEGF). These results suggest the diversity of CEGF-producing soil fungi. Quantitative data also indicated that 35–49% of Pg consisted of a chloroform-soluble fraction (i.e., CEGF) and the remaining 51–65% of Pg was chloroform-insoluble. Based on these results, we propose that CEGF is composed of DHPQ and DHPQ-derivatives and that CEGF is one of the major fractions of Pg.

Tillage, fertilizer type, and plant residue input impacts on soil carbon sequestration rates on a Japanese Andosol

ABSTRACTTo identify efficient field management practices for enhanced soil carbon sequestration suited to crop rotation-based Andosol fields in northern Japan, the impacts of a combination of tillage, fertilizer type, and plant residue input on soil carbon sequestration rates were studied in a 4-year field experiment (April 2007 to March 2011). The rates of changes in soil organic carbon over the entire study period were determined by soil carbon stock change and by net ecosystem carbon budget. Across eight field management treatments and two replicates for each treatment, the rates of changes in soil organic carbon determined by net ecosystem carbon budget were positively correlated with the rates determined by soil carbon stock change (r = 0.766, n = 16). The arithmetic means of the rates determined by net ecosystem carbon budget (1.24 Mg C ha−1 year−1) were greater than those determined by soil carbon stock change (−0.18 Mg C ha−1 year−1) because decomposing crop residues and composted cattle manure in soil were included in the calculation of the net ecosystem carbon budget but were excluded in the calculation of soil carbon stock change (decomposing crop residues and composted cattle manure in soil samples were removed by sieving in measuring the soil carbon stock change). Both methods led to the same conclusion that soil carbon sequestration was significantly enhanced by composted cattle manure application and increased input of plant carbon from crop residues and green manure but was not enhanced by reduced tillage. The p values for net ecosystem carbon budget were smaller than those for soil carbon stock change in analysis of variance; therefore, the net ecosystem carbon budget was more sensitive to field management practice than the soil carbon stock change.

Overmature periurban Quercus–Carpinus coppice forests in Austria and Japan: a comparison of carbon stocks, stand characteristics and conversion to high forest

Periurban coppice forests have a long history and tradition in Austria, as well as in Japan. Although developed in a slightly different context, such forests faced nearly the same fate during the last century. While these once served biomass almost exclusively as a feedstock for thermal energy, their significance decreased with the increasing use of fossil fuels and coppice management was consequently abandoned, or these forests were converted into high forests with different management aims. This study tries to assess the status of periurban forests that were previously managed as coppice in a comparative approach between Vienna (Austria) and Tokyo (Japan) in view of rising demands for biomass. The focus is to present stand structure, biomass and C stocks, as well as a comparison with high forest in typical stands close to the urban area. In Japan, we further directly assessed the consequences of coppice to high forest conversion on soil chemistry. While lower diameter classes are dominated by Carpinus, Quercus is only found in larger diameter classes, indicating the overmature character of both stands due to the lapse from a recognized system of coppice management with occasional fuelwood harvesting in the past decades. Total C stocks are comparable, but soil organic carbon is significantly higher in Japanese Andosols. The conversion of coppice to high forest in the 1960s in Japan had a notable impact on soil chemistry in our plots. There may be multiple benefits for restoring coppice management to these periurban forests. This includes increased biomass production capabilities and carbon sequestration as well as a better habitat provision and a higher biodiversity.

Effects of land-use type and nitrogen addition on nitrous oxide and carbon dioxide production potentials in Japanese Andosols

Land-use type and nitrogen (N) addition strongly affect nitrous oxide (N2O) and carbon dioxide (CO2) production, but the impacts of their interaction and the controlling factors remain unclear. The aim of this study was to evaluate the effect of both factors simultaneously on N2O and CO2 production and associated soil chemical and biological properties. Surface soils (0–10 cm) from three adjacent lands (apple orchard, grassland and deciduous forest) in central Japan were selected and incubated aerobically for 12 weeks with addition of 0, 30 or 150 kg N ha–1 yr–1. Land-use type had a significant (p < 0.001) impact on the cumulative N2O and CO2 production. Soils from the apple orchard had higher N2O and CO2 production potentials than those from the grassland and forest soils. Soil net N mineralization rate had a positive correlation with both soil N2O and CO2 production rates. Furthermore, the N2O production rate was positively correlated with the CO2 production rate. In the soils with no N addition, the dominant soil properties influencing N2O production were found to be the ammonium-N content and the ratio of soil microbial biomass carbon to nitrogen (MBC/MBN), while those for CO2 production were the content of nitrate-N and soluble organic carbon. N2O production increased with the increase in added N doses for the three land-use types and depended on the status of the initial soil available N. The effect of N addition on CO2 production varied with land use type; with the increase of N addition doses, it decreased for the apple orchard and forest soils but increased for the grassland soils. This difference might be due to the differences in microbial flora as indicated by the MBC/MBN ratio. Soil N mineralization was the major process controlling N2O and CO2 production in the examined soils under aerobic incubation conditions.

Contribution of nitrification and denitrification to nitrous oxide emissions in Andosol and from Fluvisol after coated urea application

Nitrogen (N) fertilizers applied on agricultural fields are an important source of nitrous oxide (N2O). The use of coated fertilizer is known to mitigate fertilizer derived N2O emissions; however, according to previous studies, the effectiveness of coated fertilizer as a mitigation option varies depending on the soil types. We hypothesized that this variability was due to the contribution of nitrification and denitrification to N2O emissions depending on the soil and fertilizer types. Two contrasting Japanese soils, Andosol and Fluvisol, were repacked in columns and treated with either urea or coated urea, and soil N2O emissions were monitored for 30 days at 55% water-filled pore space under laboratory conditions. Contribution of nitrification and denitrification to N2O emissions were determined for soils without fertilizer application and for soils at 7 and 28 days after urea or coated urea application, using a 15N tracer technique. The results imply that >60% and >80% of N2O emissions in Andosol were derived from nitrification at 7 and 28 days after application, respectively, regardless of the fertilizer types used. In Fluvisol, nitrification-derived N2O contributed 59 ± 55% and 82 ± 8% of soil N2O emissions at 7 and 28 days after application, respectively, when coated urea was applied, whereas the domination of nitrification-derived N2O to soil N2O emissions was not observed when urea was applied to Fluvisol. Soil ammonium () was depleted at 4 weeks after fertilizer application in Andosol, but was still available in Fluvisol at the same period, regardless of fertilizer types used. In Andosol, nitrification-derived N2O emissions increased when the availability was high but this was not the case for Fluvisol, when urea was applied, and we believe that the response of nitrifying microbes to the amount of available controls the differing trend of N2O emissions after the application of urea or of coated urea.

Phosphate adsorption coefficient can improve the validity of RothC model for Andosols

The conventionally-modified RothC model for Andosols required pyrophosphate-extractable aluminum (Alp) for changing humus decomposition rate of the original RothC model. However, any Japanese soil database, which were derived from national soil survey projects, did not have the Alp dataset, and thus the conventionally-modified RothC model required Alp prediction from soil organic carbon (SOC) content. From this reason, there is a risk of Alp prediction error in the run-up to predict the SOC turnover. Objectives of this study were (1) to explore the alternative soil property for re-modifying the conventionally-modified RothC model and (2) to validate the re-modified model against long-term experimental data sets of Japanese Andosols. Phosphate adsorption coefficient (PAC), which is an indicator of the content of amorphous aluminum (Al) and iron (Fe) compounds, was tested to replace Alp using three Andosols database. A stability factor, H(f), was defined as the factor needed to divide the decomposition rate constant of the humus pool so that the modeled SOC level matched the measured level. Phosphate adsorption coefficient showed positive correlation with the H(f). The H(f) was regressed by the exponential equation using PAC as an independent variable, and its R 2 value was higher than in the Alp derived regression. We incorporated the PAC derived regression into the original RothC model as the PAC-modified RothC model. From the comparison of the models validity, the PAC-modified RothC model showed low mean error with low root mean square error in the long-term experimental data sets. These results indicate that PAC can replace Alp for changing the decomposition rate of humus pool in RothC model with accuracy enhancement.

Nitrification Inhibitor Reduces Nitrous Oxide Production from Different Soil Profiles of an Andosol Soil

A laboratory incubation was conducted to evaluate nitrous oxide (N2O) production during nitrification and the effect of a nitrification inhibitor on N2O production from different profiles in a Japanese orchard Andosol. Soils were collected from five profiles: A1, A2, Bw1, Bw2, and BC. The soils were treated with ammonium sulfate at the rate of 200 mg N kg−1 with or without dicyandiamide (DCD) and incubated under aerobic conditions for 32 days. The net nitrification rate without DCD during the first 8 days was greater in the surface soils than in the subsurface soils. Accordingly, the surface soils showed a greater cumulative N2O production than the subsurface soils. Application of DCD significantly reduced the nitrification rate and thus N2O production from any depths of soils by 33.8 to 62.9%. Our study showed that substantial N2O was produced from the subsurface soil, although the amount was less than from the surface soils.

Seasonal changes in herbage production and soil phosphorus contents in Japanese lawngrass (Zoysia japonica Steud.) and tall fescue (Festuca arundinacea Schreb.) pastures

AbstractSeasonal changes in the above‐ground phosphorus (P), soil total P (TP), soil Olsen P (OP) and soil microbial biomass P (MBP) were investigated for 2 years in Japanese lawngrass (Zy) and tall fescue (Tf) pastures on Japanese Andosol, with the goal of clarifying P characteristics in the Zy pasture in comparison with the Tf pasture. The soil P attributes were measured in two soil layers (root mat layer, 0–2.5 cm depth; under layer, 5–10 cm depth). The P concentration of the above‐ground herbage in the Zy pasture, which was higher than the standard value and similar to those in the Tf pasture, might have contributed to the large amounts of the above‐ground P mass. The lack of plowing management and the coverage with Japanese lawngrass might have changed soil TP. The TP, the OP and the OP/TP in the Zy pasture were higher than those in the Tf pasture, and the TP, the OP and the OP/TP at the root mat layer were higher than those at the under layer. A large amount of the TP and high P availability in the soil caused the large amounts of OP. Soil pH, soil microorganisms and MBP might have affected soil P availability in the Zy pasture. Plant litter in the root mat layer of the Zy pasture may have increased soil P accumulation and its availability, which might be reasons for the high P uptake in the present study. Japanese lawngrass pasture may be a system with improved soil P utilization efficiency based on P cycling.

Effects of tillage and fertilizer on nematode communities in a Japanese soybean field

No-tillage (NT) cropping systems develop distinct soil ecosystems characterized by a diverse soil fauna and slow fungal decomposition. However, nematode community analyses sometimes fail to detect these characteristics because the treatment before study or the sampling period is too short or the studies are not comprehensive. Different nematode taxa may occur depending on the geographic region and soil type, thereby affecting the usefulness of nematode analyses for soil biological assessment. However, studies in Asia are scarce. Thus, in this 2-year study, we compared nematode populations, community structures, and soil physicochemical properties between long-term NT and conventional tillage (CT) treatments combined with chemical (CF), organic (OF), or no (NF) fertilizer treatments in a Japanese soybean field. We then examined whether nematode diversity and community indices could detect differences among the treatments in the Japanese andosols. Although the effects of tillage on nematode densities were significant, the overall trend in NT–CT differences was not clear, except for omnivores and Meloidogyne. The effects of tillage on nematode diversity and community indices were apparent: diversity indices, maturity index (MI) and related indices, structure index, and channel index were higher, whereas enrichment index (EI) was lower in NT because of higher densities of K-strategy taxa, fungal and facultative root feeders, and lower densities of r-strategy bacterial feeders. Fertilizer treatments also affected nematode densities: most feeding groups were less abundant in NF and predatory nematodes were more abundant in OF than in other treatments. OF increased nematode diversity via an increase in microbivorous and predaceous nematodes. However, the effects of fertilizer on most community indices were not apparent. Interactions between tillage and fertilizer effects were significant for Pratylenchus and total nematode densities, MI, and EI. Among the soil properties differing among treatments, Ca and Mg content, cation exchange capacity, and percent total nitrogen affected nematode community structure. In conclusion, nematode community analyses using index calculations are useful for assessing soil biological properties under different tillage treatments in Japanese andosols, as well as in soil types in other countries. However, index calculations were less sensitive at detecting fertilizer treatment effects, probably because of simultaneous increases in r- and K-strategy nematodes and OF compost that was too decomposed. Other community analyses such as indicator species analysis or diversity evaluations should be used to detect fertilizer effects.

Vertical distribution of chloroform-extractable green fraction in several Andosol and Cambisol profiles

The vertical distribution of the content of the chloroform-extractable green fraction (CEGF) in the soil profiles of four Japanese Andosols, one Japanese Cambisol and one Nepalese Cambisol was examined using a colorimetric method with an ultraviolet and visible spectrophotometer. In addition, the relationship between the CEGF content and the soil chemical properties was examined by statistical analysis. CEGF was detected in all the soil samples, and the content ranged from 0.02 to 1.16 g kg−1. The CEGF content in the surface A horizon of the Andosol tended to be higher than in the Cambisol. The vertical distribution of the CEGF content in three soil profiles (two Andosol profiles and one Nepalese Cambisol) revealed maximum values in the subsurface horizon. In the Japanese Cambisol, the content of the CEGF was highest in the surface horizon. In the remaining two Andosol profiles containing a buried humus horizon, the content of the CEGF was highest in the buried humus horizon and the distribution was considerably different from that of organic carbon. Statistical analysis showed that the content of the CEGF displayed a significant positive correlation (P < 0.001, n = 36) with the contents of dithionite-citrate-bicarbonate-extractable Al (Ald), and with oxalate-oxalic acid-extractable Fe and Al (Feo and Alo, respectively). Furthermore, the content of the CEGF showed a significant positive correlation with the content of Alo (r = 0.944, P < 0.01, n = 6) in the soil with the highest content of CEGF in the profile. It was, therefore, suggested that CEGF is actively produced in humus-rich soils like Andosols, and that Ald, Feo and, in particular, Alo were associated with the vertical distribution of CEGF in the soil profiles.

土壌菌核粒子の形成と生物的意図

Sclerotium grains, the resting structure of an ectomycorrhizal fungus, Cenococcum graniforme (currently, Cenococcum geophilum), are black and spherical, 1-2 mm in diameter have a characteristic hollow structure, and can be easily found in forest soils. The maximum content of sclerotium grains in surface soils of Japanese Andosols is 3.40 g kg-1, which suggests that the contribution of sclerotium grains to forest soils cannot be ignored as one of the soil organic components. This paper introduces the interests of the biological strategies of Cenococcum geophilum and sclerotium grains by reviewing the findings of advanced studies on micromorphological features, chemical composition, and microbial communities of sclerotium grains.Instruments such as scanning electron microscope (SEM) and energy dispersion X-ray fluorescence micro-analyzer (EDX), electron probe micro-analyzer of wave dispersion type (EPMA) and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) were used to obtain the characteristics of sclerotium grains. A basic finding was that C is the major element in sclerotium grains associated with a relatively large concentration of octahedral Al, which suggests an Al-humus complex. The mean concentrations of major elements in sclerotium grains are quantitatively defined as C (47.6%), O (30.2%), H (3.32%), Al (1.4%), N (0.78%). Carbon in sclerotium grains took the form of large amounts of 0-alkyl C and was also associated with aromatic C and methyl C, which strongly showed a characteristic biological origin and completely different spectral feature to humic acids from an allophonic Andosol. AMS 14C age values obtained for sclerotium grains in surface soils of Japanese forest soils were from modern to 1800 yr BP, which proves its stability and long life as an Al-humus complex. Transmission Electron Microscope (TEM) and EDX techniques revealed the micromorphological features of the Al-oxyhydroxide polymorphs found in sclerotium grains. It is assumed that a biochemical process responsible for host fungi induced Al saturation and precipitation under acidic conditions to form Boemite inside the grain. Studies on microbial communities elucidated the predominance of specific species such as Sphingomonas sp.From a further investigation on the distributions of sclerotium grains in profiles of German Podsols, Braunfaherde and Brown Podsols, it is concluded that development of sclerotium grains was not always regulated by low pH but by the content of exchangeable Al and the status of Al in the soil, regardless of soil type. The sclerotium grain was likely to be formed in soils with high ratios (>0.6) of organic bonding Al (Alp) to amorphous Al (Alo), and with high contents of exchangeable Al (Al3+) (> 0.54 g kg-1).The Al accumulation in sclerotium grains and the close relationship between sclerotium grain density and the status of active Al in soils suggest the symbiotic function of Cenococcum geophilum with root by reducing the toxicity of Al under low pH in rhizosphere. Sclerotium grain may also serve as a shelter for microorganisms and preserve their diversity under severe environmental conditions. Although the findings we have are still very limited, the goal of the study is to understand further implications of sclerotium formation in a soil ecosystem, which may help us to learn what strategy is necessary for biota to survive a catastrophe.

Modified rothamsted carbon model for andosols and its validation: changing humus decomposition rate constant with pyrophosphate-extractable Al

We modified the Rothamsted carbon model (RothC) to adopt it to Andosols. We changed the decomposition rate constant of the humus (HUM) pool because the presence of Al-humus complexes in Andosols gives HUM strong stability. In addition, the inert organic matter (IOM) pool was set at zero, because the soil did not contain carbon when it was formed from fresh volcanic ash. H(f) was defined as the factor required to divide the decomposition rate constant of the HUM pool so that the modelled soil organic carbon (SOC) level matched the measured level. H(f) was calculated for 32 Japanese Andosols, and the relationships between H(f) and soil properties such as contents of acid-oxalate-extractable Al, Fe, and Si (Mo, Feo, and Sio) or pyrophosphate-extractable Al (Alp) were analysed. The equation H(f) =1.20 + 2,50Alp(% ), (r 2 = 0.518) was selected to divide the decomposition rate constant of HUM. The modified model was tested for four long-term experimental data sets on Andosols under various climatic conditions, soil textures, and management techniques from north to south across Japan. We obtained considerably improved fits between the contents of modelled and measured SOC by using the modified RothC instead of the original model. Use of this modified model may contribute to the improvement of the performance of existing SOC2 models in modelling Andosols. It can be used for estimating CO2 emission from soils, as well as for planning suitable organic matter management in Japanese Andosols.