Yellow Soil Research Articles

Pedogenic characteristics of soils distributed under Warm-temperate forest climate in Nyu mountains, Fukui Prefecture, Central Japan

The bioclimatic conditions, profile morphology and physico-chemical properties of five different soils under the Warm-temperate deciduous broad-leaved forest climate, Warm-temperate lucidophyllous forest climate, and Cool-temperate deciduous broad-leaved forest climate in the northern part of the Nyu mountains in Fukui Pref., Central Japan were examined. The outline of the results is as follows: 1) The Dark red soil, Kunimidake series, derived from pyroxene andesite may have been formed by the hydrothermal action of volcanism. 2) The Dry brown forest soil, Takasu-1 series, showed a brighter colour in the Bw horizon and a sudden decrease in the humus content below the AB horizon, suggesting that this soil was similar to Yellow-Brown Forest soils rather than to Brown Forest soils. 3) The Dry brown forest soil (reddish), Tega series, is likely to be a Yellow-Brown Forest soil derived from the loess which covered the underlying paleo-red soil. 4) The Red soil, Oshibayama series, was a paleo-red soil in which the upper part had been lost by erosion. 5) The Yellow soil, Yada series, on the Takasu coastal terrace was also considered to be a Yellow-Brown Forest soil affected by the seawater components from the neighboring coast. 6) It was suggested that zonal soils formed under the Warm-temperate deciduous broad-leaved forest climate in the northern part of the Nyu mountains, in the northwestern region of Fukui Pref. were Yellow-Brown Forest soils like those under the Warm-temperate lucidophyllous forest climate.

Effect of reduced air pressure on soil thermal conductivity over a wide range of water content and temperature

To clarify the role of air molecules in coupled heat and mass transfer in soil, we measured the thermal conductivity of three kinds of soil (Ando soil, Red Yellow soil, and Toyoura sand) under reduced air pressure over a wide range of water content and temperature (10–75°C). The thermal conductivity increased sharply under reduced air pressure above a critical water content of the soil, becoming several times larger than that under normal pressure (101 kPa). The maximum thermal conductivity for each soil was obtained below 75°C and was similar to the thermal conductivity of some metals such as Mn, Hg and stainless steel. When the soil was drier than its critical water content, the thermal conductivity did not increase under reduced air pressure. The hydraulic diffusivity at the critical water content for each soil was of the order of 10−8 m2 s−1. This suggests that the latent heat transfer is enhanced by the circulation of the condensed water. However, very little is known about the effect of circulating water on the latent heat transfer under reduced air pressure. To make this clear, the thermal conductivity would need to be measured in the steady state under reduced air pressure.

Adsorption–desorption processes of calcium on Brazilian soils

Thermodynamic data on ion-exchange equilibrium were obtained on the heterogeneous cationic red or red–yellow latosol soil/aqueous solution interface. The equilibrium with the attached acidic functional groups can be represented by a general equation: SH n+ M n+⇌ SM +n H + where SH is the soil surface containing H + ions available for exchanging and M n+ is the cation exchanged. After exchanging, the desorption process, which depends on the natural structure and properties of soil, presents reversibility expressed by: SM ⇌n S −+ M n+ . The thermodynamic data related to the coefficient of distribution, K d, equilibrium constant, K, and Gibbs free energy, Δ G, provide information about adsorbent–adsorbate interactions in the soil surface. K and Δ G values were calculated by the linearization of the Langmuir equation, to give a constant K L (Langmuir constant), with the values being compared with an absorption method, K R (adsorption constant). The equilibrium time for surface saturation was established as 2 h for both soils. The number of moles adsorbed, N f, on red latosol, (30.17±1.51)×10 −5 mol g −1, is five times higher than that found for red–yellow latosol, (6.07±0.30)×10 −5 mol g −1. N f for lead saturation and calcium/lead equilibrium were (7.09±0.35)×10 −5 and (4.59±0.23)×10 −5 mol g −1, respectively. The desorption process on red latosol soil occurred to the extent of 37.5% with nitric acid, after the soil surface was saturated with calcium as the index ion. The adsorption of the index cation caused a decrease in the adsorption curve of lead on the surface. The values obtained for red latosol and red–yellow soil for exchanging with calcium are: K d, (3.35±0.17 and 0.77±0.04)×10 −2 dm 3 g −1; K L, (1.04±0.05 and 7.10±0.36)×10 2; K R, (39.20±1.96 and 6.91±0.35)×10 2; −Δ G L, 11.51±0.58 and 16.27±0.81 kJ mol −1; and −Δ G R, 20.50±1.03 and 16.20±0.81 kJ mol −1, respectively. Based on Gibbs free energy values, a spontaneous exchange process for cations on soils is easily detected.

Characterization of water soluble organic matter in soils by size exclusion chromatography and fractionation with polyvinylpyrrolidone

Water extracts were obtained from four types of soils (Brown Lowland soil, Yellow soil with manure application for 6 years, non-allophanic Andosol, and allophanic Andosol), and the organic matter in the water extracts was fractionated according to the solubility in acid and adsorption onto polyvinylpyrrolidone (PVP). For the water extracts and their fractions, the amounts of organic C, total N, and anthrone-reactive C (ARC) were analyzed, and high performance size exclusion chromatography (HPSEC) was carried out. The PVP-non-adsorbed fulvic acid (FA) fraction accounted for the largest proportion of the total water-soluble organic C, ranging from 52% for the Yellow soil to 96% for the allophanic Amdosol, followed by the PVP-adsorbed FA and humic acid (HA) fractions. The water extract of the allophanic Andosol was characterized by the lack of HA fraction and a small proportion of PVP-adsorbed FA fraction. For all the water extract samples, more than 90% of the ARC was recovered in the PVP-non-adsorbed FA fraction. The proportion of ARC in the total organic C in the fraction was also highest in the PVP-non-adsorbed FA fraction. The molecular weight (MW) of the humic substances (HS) at peak maximum was estimated at 1,300 Da for the water extracts and their fractions from the Brown Lowland soil and non-allophanic Andosol samples by HPSEC using polyethylene glycols as MW standards. Manure application increased the MW of HS in the HA and PVP-adsorbed FA fractions. On the other hand, only a small amount of HS was found in the water extract of the allophanic Andosol by HPSEC.

Comparison of fate of nitrogen applied to 4 different kinds of soils with particular reference to denitrification

We determined the in situ denitrification rate of four different kinds of soils during the growing season of maize by the combination of an intact core method and an acetylene inhibition technique. The soils used were Low-humic Andosols, Cumulic Andosols, Gray Lowland Soils, and Yellow Soils to which 20 Mg ha−1 of manure was applied every year. In addition, we simultaneously investigated the N balance sheet of the same maize fields using 15N-labelled fertilizer. The average denitrification rate during the growing season of maize (from May 21 to August 24, depth: 0–20 cm) was 2.0 g N ha−1 d−1 for Low-humic Andosols, 16.1 g N ha−1 d−1 for Cumulic Andosols, 20.3 g N ha−1 d−1 for Gray Lowland Soils, and 192.4 g N ha−1 d−1 for Yellow Soils, respectively. The denitrification rates in the subsurface layer (10–20 cm) were higher than those in the surface layer (0–10 cm) irrespective of the soils. Logarithm to the average denitrification rate throughout the growing season was highly correlated with the solid-phase ratio of the soils. Total amount of denitrified N from Yellow Soils during the growing season of maize was estimated to be 12% of applied N, whereas the amount from the other soils was lower than 2%. A considerable amount of nitrate remained in the subsurface layer (30–45 cm) of the Low-humic Andosols and Cumulic Andosols at harvest time. The major part of the remaining 15N-labelled fertilizer in the Gray Lowland Soils and Yellow Soils was distributed in the surface layer, which mainly occurred in an immobilized form. At harvest time, the ratio of 15N-labelled fertilizer which was unaccounted for was 19.2 ± 11.1% of the total for Low-humic Andosols, 44.4 ± 10.6% for Cumulic Andosols, 47.4 ± 9.8% for Gray Lowland Soils, 65.8 ± 12.0% for Yellow Soils, respectively. The discrepancy between the amount of denitrification and unaccounted loss indicates that leaching of nitrate was mainly responsible for the loss of N fertilizer. However, in the Yellow Soils, denitrification was considered to be a significant cause of N loss as well as leaching of nitrate.

Lithofacies and palaeosol analysis of the Middle and Upper Siwalik Groups (Plio–Pleistocene), Haripur-Kolar section, Himachal Pradesh, India

The Middle–Upper Siwalik Groups (Plio–Pleistocene) are exposed at Haripur-Kolar, Himachal Pradesh, India. The succession is 2800-m thick and has been subdivided into Unit M1 of the Middle Siwalik and four units U1–U4 of the Upper Siwalik Group, on the basis of facies associations, and type and degree of development of palaeosols. The available magnetostratigraphic ages for bases of Units U1, U3 and U4 are 5.5, 2.6 and 1.77 Ma, respectively. The top of the section has been dated as 19 ka. Lithofacies association and palaeocurrent analysis indicates that the Middle and Upper Siwalik Groups were formed mainly by a basin transverse fluvial system. Two types of river systems, which differ in their size, can be documented in Unit-M1, Unit U1 and Unit-U2: one trunk river system similar to the modern Kosi and the other smaller river system, which formed tributaries to the former. The large rivers were mainly braided in nature. The Unit U3 and lower part of Unit U4 were deposited in the piedmont depositional system mainly by small braided streams and the upper part of the Unit U4 was deposited during a period of arid climate by sediment gravity-flows. Integration of fluvial lithofacies and pedofacies helps to identify two fluvial depositional systems from the modern Indo-Gangetic Plains. The Lowland System involved deposition on alluvial megafans and interfan areas, which resulted in sand-rich and mud-rich sequences with weekly developed soils. The Upland System allowed large tracts to act as high ground for thousands of years, thereby giving rise to sandstone poor intervals with moderately to strongly developed soils. Occurrence of moderately to strongly developed soils was controlled by uplifting and tilting of large tectonic blocks, without any relation to distance from the main channels. Rate of subsidence apparently controlled the occurrence of Lowland and Upland systems. Deposition of the Unit M1, Unit U1 and Unit U2 took place under Upland and Lowland systems, very similar to those identified from the modern Indo-Gangetic Plains. The warm and humid climate between 5.3 and 2.6 Ma led to the formation of red Alfisols with calcrete nodules at places. Slightly cooler and drier climate starting at about 2.6 Ma and approximately coinciding with the onset of global-scale glaciation, produced poorly developed yellow soil with common development of nodular calcretic horizon and calcitc material disseminated in the groundmass. At ca. 0.9 Ma, a probable significant change to still drier and cooler climate produced typical sediment gravity-flows in the piedmont system, that continued until at least up to 19 ka.

Organic Carbon Storage in Soils of Tropical and Subtropical China

Tropical and subtropical China occupies a total area of about215 Mha, but the contents and storage of soil organic carbon (C)on this land have not been well studied. This research wasconducted in this concern by jointly using soil survey data andthe regional soil map. It was estimated that the 0–20 cm Cdensity of the soil subgroups in the region varied from 1.2 to9.7 kg C m-2. In the major zonal soils, soil subgroup`young ∼' had generally a C density about 1.2–4.4 timeslower than its other natural counterparts. Furthermore, subgroups of thecultivated soil gave a C density about 20–63% lower than theirnatural counterparts (except subgroup `young ∼'), showingremarkable C losses caused by cultivation. For soil groups inthe east, brown soil had the highest C density (6.8 and 21.4 kgC m-2, for the upper 20 and 100 cm soil, respectively),followed by yellow soil, yellow brown soil and limestone soil (4.6–5.5 and 12.3–14.5 kg C m-2, idem). Torrid red soil, purplishsoil and fluvo-aquic soil had the lowest C density (2.0–2.2 and5.8–7.5 kg C m-2, idem) with the others ranking at amedium level. In the west, podzolic soil ranked the highest(17.9 and 55.8 kg C m-2, idem), followed by dark brownsoil, brown soil and limestone soil (6.9–11.6 and 21–29 kg Cm-2, idem), and again torrid red soil, purplish soiland fluvo-aquic soil ranked the lowest (3.9–5.1 and 11.4–14.1 kg C m-2, idem). Finally, a total of about 26.8±7.4 Pg organic C was estimated being stored in soils of the entire region.

Application of mineral magnetism to describe profile development of toposequences of a sedimentary soil in south-eastern Australia

Mineral magnetism and chemical properties of soil profiles across a valley with an erosion gully in a Yellow Dermosol sedimentary soil suggest that the magnetic profile resulted from a combination of alluviation and pedogenesis. The concentration of soil magnetic minerals in a range of particle sizes (3.36–2 mm to <2 μm) diminished from the surface downwards to a minimum (referred to as layer P), then increased to high values (layer H), after which it decreased to bed rock level at the base layer. It is proposed that the H layer was the surface of a buried soil, and that the ferrimagnetic mineral through the profiles was dominantly maghemite, formed by fire enhancement. The magnetic pattern of the profiles compressed as the soil became shallower up-slope, from 3 m in depth at the lowest site to 0.7 m at a site 40 m up-slope. Above this site the high susceptibility H layer was absent, which is consistent with the H layer being an earlier soil surface. Except for the profile at the very top of the slope (depth of 0.63 m), the magnetic grain size did not vary with depth. In the P layers, there was a greater proportion of paramagnetic minerals than in the other layers. The changes in magnetic susceptibility through the profiles were influenced by ferrimagnetic, paramagnetic, and canted anti-ferromagnetic material. For all depths in all profiles the magnetic susceptibility changed consistently through the particle size range, decreasing from the larger sizes to the 10–20 m size then increasing slightly to the smallest size (<2 μm). The mean magnetic grain size also decreased through the particle size range. Magnetic particles of 3 concentration levels were extracted by a hand magnet from the 4 largest particle sizes and showed the same magnetic-particle size relationships, for both mass susceptibility and magnetic grain size, as the other particle sizes. This showed that the proportion of highly magnetic particles effectively determined the susceptibility and magnetic grain size features of the bulk samples of each particle size class. The particle size/magnetic susceptibility pattern described in this paper occurs in all sedimentary soils and derived river sediments studied in this part of Australia. However, soils and sediments of granitic origin have an inverse pattern. These differences are attributed to pedogenic and geomorphological process. The difficulties in using mineral magnetic properties as a means of sourcing mobile sediments in catchments are discussed.

Effects of Pot Size, Soil Type, and Sodium Alginate Application on the Soil Prevention Rate at the Transplanting of Tea Cuttings Grown in Paper Pots.

チャのペーパーポット(無底)を用いた育苗では,挿し木苗の移植時におけるポットからの挿し土の崩壊・脱落を防ぎ,ポット内に残る挿し土の割合(挿し上保持率)を高める必要がある.本報では,ポットの大きさ,アルギン酸ナトリウム処理及び挿し土の種類が挿し土保持率に及ぼす影響を検討した.その結果,内径の小さなポットで挿し土保持率が高かった.アルギン酸ナトリウム0.3%溶液をポット(内径6cm,深さ15cm)当たり80mL以上処理することで挿し土の固着化が進み,保持率を80～90%以上に高めることができ,その効果は,処理後無潅水で育苗することにより持続した.また,挿し土の種類ごとに挿し上保持率は異なり,砂質土あるいは赤黄色土にピートモスやもみがらくん炭を混合したもので高かった.これら9種類の挿し土にアルギン酸ナトリウムを処理した結果,いずれの挿し土でも保持率は高まったが,その効果の程度は挿し土の種類により異なった.

Extraction of Selenium from a Contaminated Forest Soil Using Phosphate

Laboratory batch experiments were conducted to develop an environment-friendly and cost-effective technique for the treatment of selenium contaminated soils. A yellow brown forest soil was artificially contaminated with sodium selenite (Na2SeO3) and used as a model contaminated soil sample. Among various potassium and sodium salts, potassium phosphate exhibited a pronounced effect in extracting selenium, attaining more than 55% extraction in the pH range of 4 to 6, with minimum damage to the soil properties. Based on the sorption selectivity between phosphate and selenite, an exchange mechanism is proposed for the extraction of selenium from soil by phosphate. The results of sequential extraction show that phosphate is effective in extracting selenium, NH4F-extractable and NaOH-extractable fractions. The CH3COOH-extractable and residual fractions were poorly extracted by phosphate. Selenium was most efficiently extracted at 40°C with a 300 mM (pH 6) phosphate solution.

Mineralogical composition of iron oxides in red- and yellow-colored soils from Southern Japan and Yunnan, China

Six soil samples from the Bt2 horizon of red- and yellow-colored soils collected in Southern Japan and Yunnan, China, were used in this study. Detailed mineralogical studies by differential X-ray diffraction analysis showed the presence of hematite in association with goethite in the red-colored soils, whereas no hematite was detected in the yellow-colored soils. Among the samples studied, the increase in the hematite contents was as follows: Terra rossa-like/Red-Yellow soil in Kikai Island, Red soil in Toyota City, Lateritic Red soil in Minami-Daito Island and Lateritic Red soil in Yunnan, China. Since Lateritic Red soil and Lateritic Yellow soil are distributed adjacently on the Pleistocene raised coral reef terrace in Minami-Daito Island, having a fairly similar soil temperature regime, soil pH, soil organic matter and iron oxide contents, the difference in the soil color between the two soils may be caused by the difference in the hydrologic conditions.

Three-year determination of trace metals and the lead isotope ratio in rain and snow depositions collected in Higashi–Hiroshima, Japan

The concentrations of 14 elements (Al, Ba, Ca, Cd, Cu, K, Mg, Mn, Na, Ni, Pb, Sr, V and Zn) and five ions (Cl −, NO 3 −, SO 4 2−, NH 4 + and H +) in wet depositions are reported. Samples were collected in Higashi–Hiroshima in western Japan for 3 years (1995–1997). The characteristic variations of these species were investigated in terms of the source of atmospheric heavy metals. The elements were classified into three categories by principal component analysis; constituents from an anthropogenic source (Cd, Cu, Pb, V, Zn, NO 3 −, SO 4 2−, NH 4 + and H +), elements associated with crustal source (Al, Ba, Ca, and Mn) and elements from sea salts (Na, Mg and Cl −). The depositions and concentrations of the elements associated with soil dust were peculiarly enhanced in the spring. The Kosa phenomenon, in which yellow soil dust was transported from Asian deserts by strong westerly winds in spring, is a possible reason of increased deposition and concentration of the elements. Soil-derived elements were washed out at the early stage of a precipitation event, and their concentrations were mostly controlled by dilution. For the anthropogenic elements, such as Cd, Pb and Zn, no systematic seasonal variation in wet deposition was observed. Log–log plots of precipitation volume and the concentration of anthropogenic elements suggested that the concentrations of these elements were controlled not only by dilution but also by other factors. Lead isotope ratios changed in winter. The changes must be associated with pollutant-enriched aerosols and snow particles transported from the Asian continent by strong northwest monsoons, since lead isotope ratios in aerosols transported from Asian continent are different from those in Japanese aerosol. The chemical species in snow depositions collected between the Sea of Japan and the Seto Inland Sea were also determined to evaluate the long-range transport of pollutants from the Asian continent in winter.

Soil-released carbon dioxide from microbial biomass carbon in the cultivated soils of karst areas of southwest China

Soil microbial biomass and the emission of CO2 from the soil surface were measured in yellow soils (Ultisols) of the karst areas of southwest China. The soils are relatively weathered, leached and impoverished, and have a low input of plant residues. The measurements were made for a 1-year period and show a reciprocal relationship between microbial biomass and surface CO2 efflux. The highest (42.6±2.8 mg CO2-C m–2 h–1) and lowest (15.6±0.6 mg CO2-C m–2 h–1) CO2 effluxes are found in the summer and winter, respectively. The cumulative CO2 efflux is 0.24 kg CO2-C m–2 year–1. There is also a marked seasonal variation in the amount of soil microbial biomass carbon, but with the highest (644±71 μg C g–1 soil) and lowest (270±24 μg C g–1 soil) values occurring in the winter and summer, respectively. The cumulative loss of soil microbial biomass carbon in the top 10 cm of the soil was 608 μg C g–1 year–1 soil over 17 sampling times. The mean residence time of microbial biomass is estimated at 105 days, suggesting that the carbon in soil microbial biomass may act as a source of the CO2 released from soils.

Influences of application of sewage sludge compost on N2O production in soils

Laboratory incubation was conducted to determine the controlling factors affecting the production of N2O in soil taken from short- and long-term experimental sites continuously amended with SS in three types of soil samples. Soil types and sludge application rates significantly affected the production of N2O from soil amended with sludge compost. The yellow soil, with low organic matter content, resulted in higher production of N2O with sewage sludge application probably due to ammonium oxidation in the soil. While andosol soil, with high organic matter content and heavy metal (Zn), resulted in lower N2O production when amended with SS. Uncultivated brown forest soil amended with sewage sludge plus sawdust compost (SSS) at the rate of 20 ton ha−1 showed a peak of N2O production, while no N2O was observed in the same soil at 10 ton ha−1 application rate. These results help us to explain that N2O production from soil amended with SS is greatly affected by soil types, types and application rate of the composts. It should be considered carefully to reduce N2O emission from the recycling of nutrient between soil/agriculture and urban/water treatments in future.

Temperature dependence of thermal conductivity of soil over a wide range of temperature (5–75°C)

SummaryThe coupled heat and mass transfer in soil can be analysed by examining the temperature dependence of thermal conductivity. We have measured the thermal conductivity of two kinds of soil (Ando soil and Red Yellow soil) as a function of both temperature (5–75°C) and water content by the twin heat probe method. From our results we concluded that the thermal conductivity resulting from the latent heat transfer can be separated from the apparent thermal conductivity by subtracting the thermal conductivity at a temperature near 0°C from that at a higher temperature. The relation between the phenomenological enhancement factor (β) and the volumetric air‐filled porosity was divided into two parts: β increases linearly as the volumetric air‐filled porosity increases from zero (that is, water saturation), to the point at which soil water potential corresponds to −320 J kg−1; from that point to oven‐dry condition, β decreased logistically with the volumetric air‐filled porosity. From these results, we could generalize the behaviour of β.

Effects of salts and moisture content on N 2 O emission and nitrogen dynamics in Yellow soil and Andosol in model experiments

The effects of salt type and its concentration on nitrification, N mineralization and N2O emission were examined under two levels of moisture content in Yellow soil and Andosol samples as simulated to agriculture under arid/semi-arid conditions and under heavy application of fertilizer in a glass-house, respectively. The salt mixtures were composed of chlorides (NaCl and NH4Cl) or sulphates [Na2SO4 and (NH4)2SO4] and were added at various concentrations (0, 0.1, 0.2, 0.4 and 0.6 M as in the soil solution). These salts were added to non-saline Yellow soil at different moisture contents (45 or 40 and 65% of maximum water-holding capacity; WHC) and their effects on the changes in mineral N (NH4 +-N and NO3 –-N) concentration as well as N2O emission were examined periodically during laboratory incubation. We also measured urease activities to know the effect of salts on N mineralization. Furthermore, Ca(NO3)2 solution was added at various concentrations (0, 0.1, 0.3, 0.5 and 0.8 M as in the soil solution) to a non-saline Andosol taken from the subsurface layer in a glass-house and incubated at different moisture contents (50% and 70% of WHC) to examine their effects on changes in mineral N. Nitrification was inhibited by high, but remained unaffected by low, salt concentrations. These phenomena were shown in both the model experiments. It was considered that the salinity level for inhibition of nitrification was an electric conductivity (1 : 5) of 1 dS m–1. This level was independent of the type of salts or soil, and was not affected by soil moisture content. The critical level of salts for urease activities was about 2 dS m–1. The emission rate of N2O was maximum at the beginning of the incubation period and stabilized at a low level after an initial peak. There was no significant difference in N2O emission among the treatments at different salt concentrations, while higher moisture level enhanced N2O emission remarkably.

Extraction of organic phosphorus in Andosols by various methods

The amounts of inorganic (Pi) and organic (Po) phosphorus extracted by the Truog, Bray II, Olsen, and Citrate methods, in upland soils consisting of three Andosols and a Yellow soil, with different levels of fertilization were determined. In the soils subjected to the application of both chemical fertilizers and organic matter, the amount of Po extracted by the respective extraction methods was much smaller than that of Pi. Especially, in the Andosol with yearly addition of manure for 28 y, the amount of extractable Po did not increase with the increase of the amount of manure applied even though the contents of total carbon, total phosphorus, and extractable Pi linearly increased. In the uncultivated high humic Andosols, on the other hand, Po was the dominant form extracted by the Olsen and Citrate methods. In order to determine the Po status, Pain each extract was further hydrolyzed by phosphatases (acid phosphatase, phytase, and alkaline phosphatase), and the amount of Pi released was measured. Citrate-Po was hydrolyzed to a certain extent (30–40% by phytase, and 12–13% by acid phosphatase), whereas Olsen-Po was not hydrolyzed by these phosphatases. These results suggest that the chemical structure or molecular size of the Po extracted by these methods is different. Citrate-Po may enable to evaluate plant available P to a certain extent, which is particularly important in Andosols with a low fertility.

Comportamento físico-hídrico de um podzólico vermelho-amarelo câmbico fase terraço sob diferentes sistemas de manejo

O estudo foi desenvolvido no município de Viçosa, MG, na fazenda Fundão, pertencente ao câmpus da Universidade Federal de Viçosa (UFV), com o fim de verificar o comportamento físico- hídrico de um Podzólico Vermelho-Amarelo câmbico fase terraço, sob diferentes sistemas de manejo. Foi utilizado delineamento experimental em blocos ao acaso, com cinco tratamentos e quatro repetições. Os tratamentos foram: 1 - arado de aiveca; 2 - arado de discos; 3 - grade pesada; 4 - plantio direto; 5 - testemunha, com as parcelas mantidas em pousio. Os parâmetros avaliados foram: teores de matéria orgânica; granulometria; densidade do solo; densidade de partículas; porosidade total, macroporosidade, microporosidade, agregados e curva de retenção da água no solo. Pode-se concluir que: o uso da grade pesada reduz os teores de matéria orgânica na camada de 0-15 cm; a utilização da grade pesada acarreta adensamento da camada superficial; o revolvimento do solo ocasiona maior macroporosidade; o sistema plantio direto proporciona menor desagregação do solo; o sistema plantio direto garante maior retenção de água.

USING CHARACTERISTICS OF BURROWING ANIMALS TO REDUCE SOIL-TOOL ADHESION

Reduction of soil adhesion and resistance of soil engaging parts is an important area of investigation. In this article, consideration is given to mechanisms by which soil animals reduce adhesion and resistance when moving through moist soil. It is suggested that the rough surface of soil animals is the main reason for reduced adhesion and resistance. A bulldozing plate was prepared with various kinds of rough surfaces that simulate the cuticle of typical soil animals. Tests were carried out in dry sand, wet sand, loose yellow soil, and compact yellow soil to verify the proposed mechanism for reducing adhesion and resistance. The results show that, when bulldozing a compact soil, macro-rough surfaces such as convex, wavy and scaly surfaces can reduce soil resistance and soil adhesion when compared with a smooth surface.

INFLUÊNCIA DO CULTIVO CONSORCIADO DE AVEIA PRETA (AVENA STRIGOSA SCHIEB.) E ERVILHACA COMUM (VICIA SATIVA L.) NA PRODUÇÃO DE FITOMASSA E NO APORTE DE NITROGÊNIO

Em um Podzólico Vermelho Amarelo e sob preparo convencional, foi avaliada a influência de proporções de sementes de ervilhaca (Vicia sativa L.) e de aveia preta (Avena strigosa Schieb.) cultivadas em consórcio, na produção de fitomassa e no aporte de nitrogênio no sistema. O experimento foi implantado em solo podzolico vermelho amarelo, de Santa Maria, RS. Os tratamentos foram casualizados em quatro blocos, constituindo-se de: 1- 100% Ervilhaca comum (E); 2- 90% E + 10% Aveia preta (A); 3- 75% E + 25% A; 4- 50% E + 50% A; 5- 25% E + 75% A; 6- 100% A; 7- pousio de inverno. A amostragem da fitomassa das coberturas verdes foi efetuada na ocasião do pleno florescimento em área de 0,8m2 por parcela. Os resultados evidenciaram que a aveia preta e a ervilhaca comum podem ser consorciadas, beneficiando assim, a produção de fitomassa e acúmulo de nitrogênio.