Non-volcanic Soils Research Articles

Physiological, biochemical and molecular responses of the soil microbial community after afforestation of pastures with Pinus radiata

Afforestation and deforestation are key land-use changes across the world, and are considered to be dominant factors controlling ecosystem functioning and biodiversity. However, the responses of soil microbial communities to these land-use changes are not well understood. Because changes in soil microbial abundance and community structure have consequences for nutrient cycling, C-sequestration and long-term sustainability, we investigated impacts of land-use change, age of stand and soil physico-chemical properties on fungal and bacterial communities and their metabolic activities. This study was carried out at four sites in two geographical locations that were afforested on long-established pastures with Pinus radiata D. Don (pine). Two of the sites were on volcanic soils and two on non-volcanic soils and stand age ranged from 5 to 20 y. Microbial communities were analysed by biochemical (phospho-lipid fatty acids; PLFA) and molecular (multiplex-terminal restriction fragment length polymorphism; M-TRFLP) approaches. Both site and stand age influenced microbial properties, with changes being least detectable in the 5-y-old stand. Land use was a key factor influencing soil metabolic activities as measured by physiological profiling using MicroResp. Pasture soils had higher microbial biomass ( P < 0.001), and metabolic activities ( P < 0.001), and basal respiration rates were up to 2.8-times higher than in the pine soils. Microbial abundance analysis by PLFA showed that the fungal to bacterial ratio was higher in the pine soils ( P < 0.01). Community analysis suggested that soil bacterial communities were more responsive to site (principal component 1; P < 0.001) than to land use (principal component 5; P < 0.001). In contrast, the fungal community was more affected by land-use change (principal component 1; P < 0.001) than by site, although site still had some influence on fungal community structure (principal component 2; P < 0.001). Redundancy analysis also suggested that bacterial and fungal communities responded differently to various soil abiotic properties, land-use change and location of sites. Overall, our results indicate that the change in land use from pasture to P. radiata stands had a direct impact on soil fungal communities but an indirect effect, through its effects on soil abiotic properties, on bacterial communities. Most of the changes in bacterial communities could be explained by altered soil physico-chemical properties associated with afforestation of pastures.

Nitrogen and carbon cycling in a New Zealand pumice soil under a manuka (Leptospermum scoparium) and kanuka (Kunzea ericoides) shrubland

Shrubland communities dominated by manuka (Leptospermum scoparium J. Forst. and G. Forst.) and kanuka (Kunzea ericoides var. ericoides ((A. Rich) J. Thompson) are widespread throughout New Zealand. They frequently colonise disturbed land surfaces and are important for erosion mitigation, and also for their capacity to act as a carbon (C) sink. We here investigate C and nitrogen (N) cycling in 3 stands (~26–56 years old) that had established on a repeatedly burned forest site on a Podzolic Orthic Pumice soil in the Turangi area, central North Island. For comparison, limited measurements of N cycling were also made at other manuka–kanuka sites on non-volcanic soils. Leaf N concentrations at the Turangi site were 11.8–13.9 g/kg, and lower than those at many of the other manuka–kanuka stands. Total annual litterfall and N content increased with stand age, as did total N concentrations in FH material and mineral soil (0–100 mm depth). Total C concentrations in mineral soil did not, however, differ significantly in the 3 stands. Levels of soil microbial C and N, rates of carbon dioxide production, and metabolic coefficients (qCO2 values) suggest C cycling could be fairly rapid at this site. In contrast, rates of net mineral-N and nitrate-N production were low to very low compared with those in similar pumice soils under angiosperm–conifer forests, and in the non-volcanic soils under other manuka–kanuka stands. Low N availability and tight N cycling at the Turangi site are thereby strongly suggested. No definitive explanation for the atypically low N availability at this site is apparent, although the possible effects of previous forest burnings may have been a contributing factor. The continued growth of these shrubs, nevertheless, shows they can compete successfully for the N that does become available through gross N mineralisation in the Turangi ecosystem.

An evaluation of nutritional constraints on sweet potato (Ipomoea batatas) production in the central highlands of Papua New Guinea

Sweet potato (Ipomoea batatas) is the staple food crop in the highlands of Papua New Guinea (PNG). Declining crop productivity, however, appears to be threatening the sustainability of sweet potato-based farming systems within the region, a probable cause being the exhaustion of soil nutrient reserves in continuously cultivated sweet potato gardens. To assess the extent of the problem, a survey of sweet potato gardens was conducted across four of the highlands provinces and information on soil and crop variables was obtained for old gardens (cultivated over many seasons) and new gardens (newly brought into cultivation) on soils of volcanic and non-volcanic origin. Crop leaf nutrient data collected in the survey were interpreted using the Diagnosis and Recommendation Integrated System (DRIS), to try to identify the main nutritional constraints on tuber production in different garden types on soils of volcanic or non-volcanic origin. The results suggested that K deficiency was the primary cause of poor crop production in almost a third of sweet potato gardens, but was more of a problem in old gardens than in new. Phosphorus deficiency was also a problem on volcanic soils, and S deficiency on non-volcanic soils. These latter deficiencies, however, were at least as prevalent in new gardens as in old. Important factors contributing to K and S depletion from garden systems were the removal of K and S-rich vines from cultivation areas, the shortening of fallow periods and the burning of weed and crop residues, the latter releasing S (SO2) to the atmosphere. Correction of K and S deficiencies may require the recycling of old vines back to sweet potato cultivation areas and the adoption of a zero-burn policy for fallow management. Correction of P deficiency may necessitate the use of P-accumulating fallow species, e.g. wild Mexican sunflower (Tithonia diversifolia), to extract the P fixed by sesquioxide and allophanic minerals

Methane uptake in soils from Pinus radiata plantations, a reverting shrubland and adjacent pastures: Effects of land-use change, and soil texture, water and mineral nitrogen

Afforestation and reforestation of pastures are key land-use changes in New Zealand that help sequester carbon (C) to offset its carbon dioxide (CO 2) emissions under the Kyoto Protocol. However, relatively little attention has been given so far to associated changes in trace gas fluxes. Here, we measure methane (CH 4) fluxes and CO 2 production, as well as microbial C, nitrogen (N) and mineral-N, in intact, gradually dried (ca. 2 months at 20 °C) cores of a volcanic soil and a heavier textured, non-volcanic soil collected within plantations of Pinus radiata D. Don (pine) and adjacent permanent pastures. CH 4 fluxes and CO 2 production were also measured in cores of another volcanic soil under reverting shrubland (mainly Kunzea var. ericoides (A. Rich) J. Thompson) and an adjacent pasture. CH 4 uptake in the pine and shrubland cores of the volcanic soils at field capacity averaged about 35 and 14 μg CH 4–C m −2 h −1, respectively, and was significantly higher than in the pasture cores (about 21 and 6 μg CH 4–C m −2 h −1, respectively). In the non-volcanic soil, however, CH 4–C uptake was similar in most cores of the pine and pasture soils, averaging about 7–9 μg m −2 h −1, except in very wet samples. In contrast, rates of CO 2 production and microbial C and N concentrations were significantly lower under pine than under pasture. In the air-dry cores, microbial C and N had declined in the volcanic soil, but not in the non-volcanic soil; ammonium–N, and especially nitrate–N, had increased significantly in all samples. CH 4 uptake was, with few exceptions, not significantly influenced by initial concentrations of ammonium–N or nitrate–N, nor by their changes on air-drying. A combination of phospholipid fatty acid (PLFA) and stable isotope probing (SIP) analyses of only the pine and pasture soils showed that different methanotrophic communities were probably active in soils under the different vegetations. The C18 PLFAs (type II methanotrophs) predominated under pine and C16 PLFAs (type I methanotrophs) predominated under pasture. Overall, vegetation, soil texture, and water-filled pore space influenced CH 4–C uptake more than did soil mineral-N concentrations.

Application of the DLCA model to “natural” gels: The allophanic soils

Volcanic soil comprises weathering products such as allophane, originating from a leaching process of volcanic ashes and glasses. These soils are interesting in terms of mitigation of the greenhouse effect (C sequestration), because they are known for accumulating more C than non-volcanic soils. Allophanes are natural amorphous silicates and have physical features very close to those of synthetic gels. Knowledge of the allophanic soil structure is required to understand the sequestration mechanism. In this paper, nitrogen adsorption-desorption experiments, measured on allophanic soil samples, show that the hydraulic diameter (Dh) is shifted towards smaller size while the pore volume (Vp) and specific surface area (S) increase, when the allophane content of the soil increases. We introduce a numerical model to simulate the structure of this “natural gel”. The algorithm is based on Diffusion-Limited Cluster-Cluster Aggregation in which larger particles hinder the DLCA. As a function of the relative content of allophane (gel) and larger particles, the textural properties (Vp, S, Dh) of the different simulated structure are calculated using a simple triangulation method.

Silicon availability of the nursery bed soils and effects of silicon fertilizer applied on the growth and silicon uptake of rice Oryza sativa L. seedlings

(pp. 41–46) Silicon availability in 36 commercial nursery bed soils was evaluated by four methods the phosphate buffer (pH 6.2, 40 mmol L−1), incubation, supernatant and acetate buffer (pH 4.0, 1 mol L−1) Methods. The influence of silicon availability in the nursery bed soils on the silicon uptake of rice Oryza sativa L. cv. Hitomebore seedlings and the effect of silicon fertilizer application were examined in a glass house in 2002. The results revealed that the best correlation between silicon content in rice seedlings and available silicon in soils was obtained with the phosphate buffer-solution method (r = 0.86). More precise evaluation of available silicon was achieved by grouping soils based on these phosphate absorption coefficients (PAC). The correlation coefficients between silicon content in rice seedlings and available silicon in soils were 0.92 and 0.72 for volcanic soils (PAC > 1500) and non volcanic soils (PAC < 1500), respectively. We concluded that the phosphate buffer method is the most easily adjusted method for estimation of silicon availability in nursery bed soils, and silicon fertilizers should be applied when silicon availability in non-volcanic nursery bed soils goes below 200 mg kg−1, whereas the level is less than 350 mg kg−1 in volcanic soils.

가축분 퇴비의 시용량에 따른 제주 밭토양의 부식의 형태별 함량 변화

우리나라 최남단에 위치한 제주도에 가장 많이 분포하고 있는 화산회 밭 토양과 비화산회 밭 토양에 가축분 퇴비를 0, 50, 100, 150 ton/ha 해당량을 시용한 후 토양 부식의 함량 변화를 조사하여 문제점을 살펴본 결과는 다음과 같다. 부식의 분포도는 화산회 토양은 대부분 A type이었으며 일부 밭토양에서 B type에 속하여 화산회 토양은 부식화가 진행되었음을 알 수 있었으며 비화산회 밭토양은 대부분 Rp, B type으로 존재하여 동일한 결과를 얻을 수 없었다. 질산태 질소 함량과 부식함량과의 관계는 화산회 토양은 <TEX>$R^2=0.5263$</TEX>, 비화산회 양은 <TEX>$R^2=0.524$</TEX>의 정의 상관관계를 나타내었다. 탄소의 함량과 부식 함량과의 관계는 화산회 토양은 <TEX>$R^2=0.469$</TEX>, 비화산회 밭 토양은 <TEX>$R^2=0.550$</TEX>의 정의 상관관계를 보이고 있다. In Jeju island, the southernmost island of Korea, the field soils are mostly consisted of volcanic and non-volcanic soils. Animal manures of 0, 50, 100, and 150 MT/ha were treated to analyse the humus content changes by application amounts and the soil types. The results are as follows; Humus distribution type was A in the most of the volcanic soils while a few soils was type B, and it was possible to confirm that the humus process has occurred in the soils. Most of the non-volcanic soils was Rp and B type, therefore, the humus content change pattern was different from the volcanic soils. The nitrate-nitrogen content and the humus content showed positive correlation of <TEX>$R^2=0.5263$</TEX> in the volcanic soils, while that of non-volcanic soils was <TEX>$R^2=0.524$</TEX>. The carbon content and the humus content showed positive correlation of <TEX>$R^2=0.469$</TEX> in the volcanic soils, while that of non-volcanic soils was <TEX>$R^2=0.550$</TEX>.

A comparison of the RUSLE, EPIC and WEPP erosion models as calibrated to climate and soil of south-central Chile

Adequate modelling of soil erosion is important for conservation planning, especially in developing countries where there is increasing competition for limited soil resources. In this study, the RUSLE, EPIC and WEPP models were used to estimate soil erosion from small grain production in south-central Chile, a region having a Mediterranean type climate and volcanic soils with distinctive properties compared to non-volcanic soils. The models were compared for their consistency with historical rates of erosion and those calculated using the previously calibrated USLE model. Of the models, WEPP permitted the most adequate parameterization for both climate and volcanic soil, and calculated erosion rates that were in overall agreement with field and USLE values.

제주 밭토양에서 가축분 퇴비의 시용에 따른 양분의 이동양상

Recently, saw dust manure has been widely used in horticultural crop production in Korea. Animal manure is produced by decaying of livestock manure mixed with saw dust, and contained higher nutrients and ion concentration than the traditional manure made from rice straw and grasses. Therefore, a continuous application of the animal manure disregarding to soil characteristics may be ruined the soil conditions. This study was conducted to investigate the transportation of the nitrogen, phosphate, potassium, and ion concentration of the animal manure applied to volcanic and non-volcanic soils in Jeju islana Soil chemical analysis were done before and 180 days after animal manure application. After animal manure application, -N moved up to 90cm in volcanic soil, while the movement was limited to 60 cm in non-volcanic soil. Phosphate concentration was high up to 30 cm, where crop roots are mainly distributed, in volcanic soil, however, the phosphate moved up to 60 cm in volcanic soil. Exchangeable potassium moved up to 90 cm in volcanic soil, but the movement wns limited up to 60 cm in non-volcanic soil. For both soil types, no significant different in ion concentrations was observed up to 60 cm in soil depth, though the concentrations were higher in volcanic ash soils as compared to the non-volcanic ash soils.

Evaluation of soil nitrogen status in japanese agricultural lands with reference to land use and soil types

The nitrogen content of agricultural soils collected from throughout Japan was characterized according to the form and availability, and with reference to land use and soil types. In total, 147 plow layer soil samples were collected—80 from paddy fields and 67 from upland fields to include various soil types. Soil N was separated into four fractions: inorganic extractable-N (Iex-N), fixed NH4 +-N (Ifix-N), organic mineralizable-N (Omin-N), and organic stable-N (Osta-N). In the analysis, the total-N content was determined by the dry combustion method. The lex-N content was determined by extraction with a 2 mol L-1 KCI solution and the lfix-N content by extraction with a HF-HCI solution after removal of organic-No The Omin-N content was evaluated as the potentially mineralizable N based on a long-term incubation method and the Osta-N content was calculated as the difference between the contents of total-N and the above-mentioned three fractions. The average total-N content was 2,593 mg kg-1, of which the contents of lex-N, lfix-N, Omin-N, and OstaN were 37, 124, 159, and 2,273 mg kg-1, respectively. Thus the available fraction (Iex-N and Omin-N) accounted for 7.6%, and the stable fraction (Ifix-N and Osta-N) for 92.4% of totalN on the average. Assuming that the plow layer depth was 15 cm and the bulk density was 1.0 Mg m-3 , the amounts of total-N, lex-N, lfix-N, Omin-N, and Osta-N were 3,890, 56, 186, 239, and 3,411 kg ha-1 , respectively. The amount of the available fraction (295 kg ha-1) was comparable to the total annual N input (266 kg ha-1), whereas the amount of the stable fraction (3,597 kg ha-1) was more than ten times larger. In relation to land use, the lex-N content was lower (both absolute and relative contents) in paddy soils (32 mg kg-1, 1.4%) than in upland soils (43 mg kg-1, 1.8%), whereas the Omin-N content was higher in paddy soils (200 mg kg-1, 8.9%) than in upland soils (108 mg kg-1, 4.4%). No differences due to land use were observed in the stable N fraction. In contrast, differences due to soil types which were not observed in the available fraction were clearly observed in the stable fraction (Ifix-N and Osta-N), Le. the lfix-N content was higher in non-volcanic soils (156 mg kg-1, 10.0%) than in volcanic soils (54 mg kg-1, 1.6%) whereas the Osta-N content was higher in volcanic soils (3,639 mg kg-I, 93.0%) than in non-volcanic soils (1,632 mg kg-1, 80.1%). Accordingly, the 42.4% of variance of the lfix-N content was explained by the clay and Alo contents and 48.1% of variance of the Osta-N content by the Alo content. These findings showing that, in Japanese agricultural soils, the available N fraction was strongly affected by the land use, whereas the stable N fraction was mainly determined by the soil types, should be taken into account in the management of soil N in agricultural practices and N dynamics in agricultural fields.

Testing the suitability of the Rothamsted Carbon model for long-term experiments on Japanese non-volcanic upland soils

We evaluated the suitability of the Rothamsted Carbon (RothC) model for long-term experiments on Japanese non-volcanic upland soils using 6 long-term experimental data sets: 2 Brown Lowland Soils, 2 Yellow Soils, 1 Gray Lowland Soil, and 1 Brown Forest Soil. The predicted changes in the content of soil carbon with time were very close to the observed values in almost all the treatments at all the 6 sites. These 6 sites were distributed from North to South across Japan and included a variety of climatic conditions, soil textures, and land management practices. We therefore concluded that the RothC model adequately simulated changes in the soil carbon content with time in Japanese non-volcanic upland soils.

RELATIVE MOBILITY OF ATRAZINE, 2,4-D AND DICAMBA IN VOLCANIC SOILS OF SOUTH-CENTRAL CHILE 1

Herbicide mobility has been studied extensively in nonvolcanic soils but not in the volcanic soils that are important to the agricultural systems of many regions, including Pacific-Rim countries. Volcanic soils have unique properties that include high contents of organic carbon and soil water at 1500 kPa tension, low bulk density and saturation of bases, and the presence of amorphous clay. We hypothesized that the chemical and physical characteristics of these soils would affect the mobility of selected herbicides. Therefore, thin-layer chromatography was used to measure the relative mobility of atrazine, diethylamine salt of 2,4-D, and dicamba in volcanic soils of south-central Chile, including Arrayan silt loam (Typic Haploxerands), Santa Barbara silt loam (Typic Haploxerands), Arenales loamy sand (Dystric Xeropsamments), and weathered Collipulli clay loam (Xeric Palehumults) series. Dicamba was the most mobile herbicide in all of the soils; atrazine was the least mobile herbicide in the weathered Collipulli soil and in the surface horizons of the Arrayan and Arenales soils, but 2,4-D was the least mobile in the Santa Barbara soil. Herbicide mobility in the allophanic soils (Arrayan, Santa Barbara, and Arenales) could be estimated using the contents of soil organic matter and 1500 kPa water, and also soil pH. The relative mobility of atrazine was greater than expected in the Arrayan and Santa Barbara soils and was probably caused by the protonation and subsequent repulsion of atrazine by positively charged soil surfaces. The relative mobilities of 2,4-D and dicamba were smaller than expected in the Santa Barbara soil and were attributed to the retention of dissociated 2,4-D and dicamba by positively charged soil surfaces.

제주도 감귤원 토양에서 GUS, RF, AF 지수를 이용한 농약의 용탈잠재성 평가

유기물함량이 다른 감귤원 토양을 대상으로 GUS, RF 및 AF 값을 비교하여 감귤원에서 많이 사용되고 있는 농약 종류별 지하수 오염 잠재성을 평가하였다. GUS에 의하면 metribuzin과 metolachlor는 조사된 모든 토양통에서 용탈 가능성이 큰 것으로 평가되었으며, alachlor와 linuron도 대부분 토양에서 용탈가능성이 높은 것으로 평가되었으며 linuron의 경우에는 특히 비화산회토양에서 용탈의 가능성이 매우 높은 것으로 나타났다. Diuron과 diniconazole은 대부분 토양에서 용탈 가능성이 없는 것으로 평가되었고, chlorothalonil과 chlorpyrifos는 유기물 함량에 관계없이 용탈 가능성이 없는 것으로 평가되었다. RF에 의한 평가에서는 diniconazole, chlorothalonil, chlorpyrifos는 모든 토양에서, linuron과 diuron은 일부 비화산회토를 제외한 모든 토양에서 이동성이 매우 낮은 것으로 분류되었으며, metolachlor와 alachlor는 대부분의 토양에서 이동성이 보통인 것으로, metribuzin은 유기탄소함량이 낮은 토양에서 오염 잠재성이 있는 것으로 평가되었다. AF에 의하면 diniconazole, chlorothalonil, chloipyrifos는 화산회토, 비화산회토에 관계없이 지하수 오염 잠재성이 없는 것으로 평가되었으며, 반면 metribuzin은 화산회토, 비화산회토에 관계없이 오염 잠재성이 있는 것으로 평가되었다. Metolachlor는 비화산회토에서 지하수 오염 잠재성이 있는 것으로 평가되었고, alachlor, linuron 및 diuron은 유기물 함량이 낮은 일부 비화산회토에서만 지하수 오염 잠재성이 우려되는 것으로 나타났다. 농약의 용탈잠재성은 용해도, 흡착성, 잔류성 등의 약제 자체의 특성과 함께 유기물 함량, 투수성 등 토양의 물리화학적 특성에 따라서 결정된다. 본 연구의 결과를 보면 이러한 일반적인 원칙이 각 농약의 용탈잠재성 지수에 그대로 반영되었는데, 용해도가 높고, 흡착성이 약하며 잔류성이 긴 약제일수록 대부분의 토양에서 용탈잠재성이 큰 것으로 나타났다. 토양의 특성 중에서는 특히 농약의 흡착에 직접 영향을 미치는 유기물 함량이 용탈잠재성 지수를 결정하는 중요한 요인으로 볼 수 있는데, 본 연구의 결과에서도 일반적으로 유기물 함량이 높은 화산회 토양에서는 농약의 용탈잠재성이 비화산회토양에 비교하여 낮은 것으로 나타났으며, 용해도가 높고 흡착성이 매우 낮은 약제인 metribuzin의 경우에도 투수성이 상대적으로 높은 화산회 토양에서보다 투수성이 낮은 비화산회토양에서 용탈 가능성이 높게 평가된 것으로 보아 대부분 농약의 용탈잠재성을 결정하는데 있어 토양의 투수성 보다도 유기물 함량이 더욱 중요하게 영향을 미치는 것으로 판단할 수 있다. 따라서 비화산회토를 위주로 한 유기물 함량이 낮은 토양이 분포된 지역의 지하수가 농약의 오염에 취약할 것으로 판단할 수 있으며, 이들 지역에서는 용탈잠재성이 높은 것으로 평가된 약제들의 사용을 최대한 제한함으로써 제주도 피하수의 농약 오염을 방지할 수 있을 것이다. 물론 제주도 감귤원에서는 토양의 유기물 함량과 약제의 흡착성을 우선적으로 고려하여 사용할 농약을 선택해야 할 것으로 보이나, 그 외 약제의 잔류성, 사용량, 사용시기와 함께 기후조건, 토양의 투수성, 토층이 깊이, 지하수 깊이 등의 지역적인 특성들이 농약의 용탈잠재성에 미치는 영향도 더욱 구체적으로 파악되어야 할 것이며 농약의 선택 과정에서도 이러한 특성들이 앞으로 고려되어야 할 것이다. Contamination of groundwater by agrochemicals used in the regional-scale Is now a major environmental problem, and this is especially true for Cheju island where virtually all potable water is from groundwater. The objective of this study was to assess leaching potential of eight pesticides in soils of citrus orchards using groundwater ubiquity score (GUS), retardation factor (RF) and attenuation factor (AF). Considering GUS estimated in 30 citrus orchard soils, metribuzin and metolachlor were classified as leacher, alachlor in volcanic ash soils and linuron in non-volcanic soils were classified as leacher, but chlorothalonil and chlorpyrifos were classified as non-leacher. For RF values, metribuzin was classified to be mobile in soils of low organic carbon, metolachlor and alachlor were classified to be moderately immobile in most soils, but linuron, diuron, diniconazole, chlorothalonil and chlorpyrifos were all classified to be very immobile. For AF values, diniconazole, chlorothalonil, and chlorpyrifos were classified to be very unlikely leachable in all of the soils, metribuzin was classified to be likely leachable, and metolahclor, alachlor, linuron and diuron were classified to be leachable only in non-volcanic soils. Although there were some variations in the relative potential of teachability of pesticides estimated with the three different indices, the ranking was essentially determined on the base of the intrinsic properties of the chemicals and environmental properties. Among the eight pesticides, metribuzin, metolachlor, and alachlor, which have high water solubility and low <TEX>$K_{oc}$</TEX> values, have a significant leaching potential especially in non-volcanic ash soils of low organic carbon. But diniconazole, chlorothalonil, and chlorpyrifos, which have low water solubility and high <TEX>$K_{oc}$</TEX> values, were classified to be very immobile in all of the soils. Therefore, to lower the possibility of pesticide contamination of the groundwater in Cheju island, those pesticides which have high water solubility and low <TEX>$K_{oc}$</TEX> values should be used with care in soils of low organic carbon including non-volcanic ash soils.

Quantitative relationship between soil properties and adsorption of dissolved organic matter onto volcanic ash and non-volcanic ash soils

The formation of soil organo-mineral complexes is a key reaction in the carbon cycle in soil, since organic materials acquire a resistance to decomposition due to the formation of the complexes. Adsorption of dissolved organic matter (DOM) onto soil minerals provides a model of this important process. Adsorption of DOM onto samples from Andisols, Inceptisols, and Entisols in batch experiments was compared in terms of the quantitative relationship between the soil properties and the adsorption behavior of DOM. Adsorption behavior was effectively described by a linear initial mass (IM) isotherm, indicating that the adsorption efficiency did not appreciably decline in the range studied even though a large amount of DOM was applied to the soil samples. Samples from Andisols showed a particularly high efficiency of adsorption compared with those from other soils which contained a comparable amount of organic carbon. Explanatory variables useful to predict the efficiency parameter were investigated in 2 steps: firstly the degree of carbon accumulation in the soil samples was examined, and next an index for the amount of ligand exchange sites was examined in combination with the former indices. As a result, an index comprising the total carbon/clay (or total carbon/specific surface area) ratio and the amount of hydroxy ions in the soil extracts with NaF solution was eventually detected. The former represents the degree of carbon occupation on the soil surface, and the latter the amount of ligand exchange sites on labile aluminum. Although the mechanisms involved in the adsorption varied among soils, the selected index was significantly correlated with the adsorption efficiency.

Development of a new multinutrient extraction method for macro- and micro-nutrients in arable land soil

A new multinutrient extraction method was developed for simultaneous extraction of macro- and micro-nutrients in arable land soil. Composition and concentration of the new multinutrient extractant were 0.2 mol L-1 CH3COOH, 0.25 mol L-1 NH4Cl, 0.005 mol L-1 C6H8O7 (citric acid), and 0.05 mol L-1 HCl (pH 1.3). The extraction method consisted of continuous shaking for 30 min with a ratio of air-dried soil to extractant of 1 : 10 (w/v). For boron (B) extraction, the ratio of soil to extractant was 1 : 2 (w/v), and then the extract was filtered. Correlation coefficients between the values of the nutrients extracted with the newly developed method and the values of those extracted with the conventional methods—i.e., NO3-N extracted with KCl, available P extracted with the Truog method, exchangeable K, Ca, and Mg extracted with the Semimicro-Schollenberger method, easily reducible Mn extracted with hydroquinone-ammonium acetate, soluble Zn and Cu extracted with HCI, and available B extracted with hot water—were equal to or higher than 0.91***, respectively. The correlation coefficient for the soil samples, where available P values were below 400 mg P2O5 kg-1 (Truog method), was as low as 0.783***. In the case of paddy soil samples, however, the correlation coefficients were as high as 0.836***, and, in the case of upland soil samples, 0.878**. Values of Ca and Mg extracted with the newly developed method were higher than those of Ca and Mg extracted with the Semimicro-Schollenberger method in one or two soil samples. They may have contained a large amount of Ca and Mg carbonates, because base-saturation percentages exceeded 100. For HCl-soluble Cu, the correlation coefficients were as high as 0.983*** for volcanic ash soil samples, and 0.990*** for nonvolcanic ash soil samples. For available B, multiple correlation coefficient (adjusted by degrees of freedom) increased from 0.925*** to 0.962***, when soil pH(H2O) was included in a multiple regression equation between the values of B extracted with the newly developed method and those of B extracted with the hot water method.

Role of active aluminum in the formation of water-stable macroaggregates

Soil structure is determined by the arrangement of particles in soil and the particles of sand, silt, and clay bind together into aggregates of various sizes by organic and inorganic materials. Structural stability which is the ability of the aggregates and pores to remain intact when subjected to stress, markedly affects crop production and soil erosion (Tisdall 1996). Since water, either directly as rainfall or as surface runoff is the main agent of aggregate breakdown, in the analyzes of stable soil aggregation, the term water-stable aggregation is generally used (Lynch and Bragg 1985). Water-stable aggregates have been divided into micro aggregates < 0.25 mm dia.) and macro aggregates (> 0.25 mm dia.) (Edwards and Bremner 1967; Tisdall and Oades 1982). Microaggregates show a relatively high stability against physical disruption (Edwards and Bremner 1967). On the other hand, macro aggregates are sensitive to soil management (Tisdall and Oades 1982). There are many reports on the relationships between the aggregate stability and the soil physicochemical properties. For example, significant correlations were found between the aggregate stability and the amounts of organic C (Tisdall and Oades 1982), total N, and carbohydrates or the CEC (Chaney and Swift 1984). However, most of these studies were conducted in non-volcanic ash soils. Volcanic ash soils are widely distributed in Japan and are very important soils for crop production. The objective of this study was, therefore, to obtain more information on the relationship between the degree of macro aggregation and the soil physicochemical properties in non-volcanic and volcanic ash soils.

Microbial ecology in tea soils

The soil chemical properties and microbial numbers in three volcanic ash soils and two non-volcanic ash soils, which had been continuously subjected to the same tea cultivation practices (21 y), were investigated. The results obtained were as follows. 1) pH values of all the soils gradually decreased from the original pH value (near neutral or mildly acid pH) to strongly acid values of about 4 or lower. In contrast, long-term tea cultivation practices resulted in the increase of the total C and N contents in the surface layers (0–20 cm) while the contents remained stable in the subsurface layers (20–40 cm). The increase in the organic matter content in non-volcanic ash soils was presumably due to the accumulation of microbial residues. The availability of P increased markedly. 2) Numbers of bacteria, actinomycetes, fungi, and denitrifiers were higher in volcanic ash soils than in non-volcanic ash soils, and also higher in surface layers than in subsurface layers. The results suggest that in spite of the same cultivation practices, the soil depth and soil type affected the microbial numbers in the tea soils. Numbers of autotrophic NH4 + oxidizers were low in comparison with the numbers of autotrophic NO2 - oxidizers. Influence of soil type and soil depth on autotrophic nitrifiers was not clear. 3) Total C and N contents in the tea soils were parameters closely related to the numbers of bacteria, actinomycetes, and fungi. For actinomycetes and fungi, the prediction could be more accurate, especially for total N content, if the estimations could be made within the same soil layers. The numbers per unit of C or N were higher in the surface layers than in the subsurface layers. 4) High concentration of NO3 --N in the tea soils used suggests that nitrification could occur despite the low pH value (3.2-3.8). The negative relationship between the number of total bacteria or actinomycetes and soil NH4 +-N concentration suggests that some NH4 +-N was converted to organic microbial biomass-No.

Microbial ecology in tea soils

We determined the protease activity to analyze the mechanism of organic nitrogen decomposition (protein degradation) in tea soils. The hydrolyzing activities of N-benzoyl l-arginine amide (BAA), N-benzyloxycarbonyl l-phenylalanyl l-Ieucine (ZPL), and N-benzyloxycarbonyl glycyl l-phenylalanine (ZGP) were investigated at two depths in five acid tea soils, in upland crop Boils and in uncultivated soils (soils with near neutral pH) as controls. Sources of the enzymes and factors that influenced the activities were determined based on the relation between the protease activity and total N, total C, or microbial numbers. 1) In the assay with 0.2 M phosphate buffer (pH 8.1), the BAA-hydrolyzing activity in all the tea soils, upland crop soils and uncultivated soils was the highest, followed by the ZPL-hydrolyzing activity while the ZGP-hydrolyzing activity was the lowest. 2) Both magnitude of the protease activity and substrate specificity varied with depths and soil types. Proteases in the surface layers (0–20 cm) hydrolyzed all the used substrates faster than those in the lower layers (20–40 cm). The proteases in the lower layers hydrolyzed specifically BAA more than those in the surface layers. The BAA- and ZPL-hydrolyzing activities were higher in volcanic ash soils than in non-volcanic ash soils. 3) Tea, upland crop cultivation, and absence of cultivation affected the magnitude of protease activity. The soil cultivated with upland crops (hereafter referred to as “upland crop soils”) and uncultivated soils hydrolyzed specifically BAA more than the tea-cultivated soils (hereafter referred to as “tea soils”). 4) There were close relationships between the soil microbial group and BAA- or ZPL-hydrolyzing activity. It is therefore assumed that the enzymes hydrolyzing BAA and ZPL in the acid tea soils originated from the soil microorganisms.

A new method for measuring microbial biomass nitrogen in soils: Direct extraction after toluene treatment

Abstract Attempts were made to develop a new method for measuring the microbial biomass N in upland soils by direct extraction after toluene treatment. This method which involves the use of ninhydrin reagent for the estimation of nitrogenous compounds released by autolysis after incubation of the soil with buffered (pH 7.0) toluene at 30°C for 24 h, is rapid, sensitive, and precise. The factors responsible for the difference in the value of the K N nin factor between volcanic and non-volcanic ash upland soils were also examined. The results obtained can be summarized as-follows: 1. This method can be used to estimate the size of microbial biomass N in volcanic or non-volcanic ash upland soils. For 20 microorganisms (10 bacterial strains and 10 fungal strains) the mean value of the K N nin factor was 0.255 for volcanic ash soils and 0.343 for the non-volcanic ash soils. 2. The newly proposed toluene treatment method enabled to extract a much larger quantity of ninhydrin-reactive nitrogen than the chlorofor...

Survival of inoculant Bradyrhizobium japonicum in an Andosol

The survival of an antibiotic-resistant mutant of a commercial inoculant Bradyrhizobium japonicum strain, A1017ks, was studied in a volcanic ash soil (Andosol) in comparison with a non-volcanic ash soil (Fluvisol) over a period of 84 days. In a non-sterile soil system, the population decline in the Andosol (15% or 1.2 log units) was larger than in the Fluvisol (6% or 0.54 log units). In both soils, however, the inoculant bradyrhizobium survived at fairly high population levels after the period of incubation [106 and 107 colony-forming units (CFU) g-1 dry soil in the Andosol and Fluvisol, respectively]. In sterile control soil, viable bradyrhizobium cells could not be detected after 1 week of incubation in the Andosol, whereas in the Fluvisol population of introduced bradyrhizobium was maintained throughout the period of incubation. Overall changes in the population of indigenous bacteria and fungi were also monitored. However, no clear pattern of interaction between the inoculant Bradyrhizobium japonicum and the indigenous microbes could be identified. The antibiotic-resistant mutant maintained its resistance in the Fluvisol throughout the 3-month period of incubation, making it a useful model for conducting ecological studies in the soil.