Soil Ca alters processes contributing to C and N retention in the Oa/A horizon of a northern hardwood forest

Recent studies on the effects of calcium (Ca) additions on soil carbon (C) cycling in organic soil horizons present conflicting results, with some studies showing an increase in soil C storage and others a decrease. We tested the legacy effects of soil Ca additions on C and nitrogen (N) retention in a long-term incubation of soils from a plot-scale field experiment at the Hubbard Brook Experimental Forest, NH, USA. Two levels of Ca (850 and 4250 kg Ca/ha) were surface applied to field plots as the mineral wollastonite (CaSiO₃) in summer of 2006. Two years after field Ca additions, Oa/A horizon soils were collected from field plots and incubated in the laboratory for 343 days to test Ca effects on C mineralization, dissolved organic carbon (DOC) export, and net N transformations. To distinguish mineralization of soil organic C (SOC) from that of more recent C inputs to soil, we incubated soils with and without added ¹³C-labeled sugar maple leaf litter. High Ca additions increased exchangeable Ca and pH compared to the control. While low Ca additions had little effect on mineralization of SOC or added litter C, high Ca additions reduced mineralization of SOC and enhanced mineralization of litter C. In litter-free incubations, δ¹³C of respired C was enriched in the high Ca treatment compared to the control, indicating that Ca suppressed mineralization of ¹³C-depleted SOC sources. Leaching of DOC and NH₄ ⁺ were reduced by Ca additions in litter-free and litter-amended soils. Our results suggest that Ca availability in these organic soils influences mineralization of SOC and N primarily by stabilization processes and only secondarily through pH effects on organic matter solubility, and that SOC binding processes become important only with relatively large alterations of Ca status.     

Transformation of iron and manganese in rice soils under different moisture regimes and organic matter applications

Summary Transformation of iron and manganese under three different moisture regimes,viz continuous waterlogged (W₁), continuous saturated (W₂) and alternate waterlogged and saturated (W₃) and three levels of organic matterviz 0, 0.5 and 1.0% in all possible combinations was studied in four soils. The results showed that under waterlogged moisture regime there was a sharp increase in the content of water soluble plus exchangeable manganese accompanied by significant decrease in the content of reducible manganese in all the soils excepting the acidic soil which was very poor in active manganese content. The increase in respect of iron in similar form was, however, very small. The increase in the content of water soluble plus exchangeable manganese as well as iron under the continuous saturated and alternate waterlogged and saturated moisture regimes was always much lower as compared to that under the continuous waterlogged condition. Application of organic matter brought about an increase in the content of water soluble plus exchangeable manganese in all the soils excepting the lateritic one irrespective of moisture regimes but did not cause any change in the content of iron and manganese in insoluble complex. The content of water soluble plus exchangeable iron and of insoluble ferrous iron although recorded some increase due to organic matter application, the increase was not so marked in any of the soils.     

Changes in the speciation,partitioning and phytoavailability of chromium induced by organic soil amendments

Abstract

This study investigated the effect of two organic amendments (compost of cattle ruminai content and Sphagnum-moss peat) on the reduction of hexavalent chromium and the distribution of this metal among the main solid phases of a soil with low organic matter content treated with different levels of Cr(VI) (0–2000 mg Cr kg^?1 soil). At the same level of added organic carbon, the peat reduced Cr(VI) added to the soil from 250 to 2000 mg kg^?1, with 100% efficiency. The reduction efficiency of the compost, however, decreased with the increasing dose of Cr(VI) soil. The distribution of Cr between the different soil components was evaluated by a sequential chemical extraction procedure. The concentration of water-soluble and exchangeable Cr decreased with the addition of organic amendments to the soil, whereas Cr increased in the organic fraction. The effect of added organic material on the Cr absorption was examined with two ornamental plants (Melissa officinalis and Begonia semperflorens). The increased Cr(VI) in the soil increased the Cr concentration in plant tissues. The addition of organic matter produced a greater aerial biomass for each level of added Cr in comparison with unamended soil. Sphagnum moss peat was more effective than the compost to decrease the total Cr and the Cr(VI) concentration in the water-soluble and exchangeable fraction of soil, thereby reducing the Cr accumulation in plants tissues and phytotoxic symptoms.     

外源水溶性有机物及温度对红壤铜形态的影响

利用模拟培养试验研究了外源水溶性有机物（DOM）添加量和培养温度对红壤中Cu形态的影响. 结果表明: 与不添加DOM比较, 添加不同量的DOM均可提高土壤中交换态Cu的含量、降低铁锰结合态Cu含量; 随着培养时间的延长,不同DOM添加量下土壤交换态Cu含量呈逐渐下降趋势;至试验结束时,DOM添加量为250 mg·L^-1时土壤交换态和碳酸盐结合态Cu含量最高, 添加量为500 mg·L^-1时铁锰结合态Cu含量最高;不同DOM添加量下, 土壤中有机结合态Cu含量较CK增加10.67%～23.66%. 在25 ℃和45 ℃温度条件下, 添加DOM后土壤交换态和铁锰结合态Cu含量均随培养时间的延长呈下降趋势, 但在5 ℃下变化趋势相反; 3种温度下添加DOM后土壤碳酸盐结合态Cu含量有随培养时间延长而增加的趋势. 随着培养温度的升高,土壤有机结合态Cu含量增加, 但在温度较低(5 ℃)时土壤残渣态Cu含量下降.     

Nitrogen mineralization and its controlling factors in various kinds of temperate humid-zone soils

The N mineralization capacity of 41 temperate humid-zone soils of NW Spain was measured by aerobic incubation for 15 days at 28°C and 75% of field capacity. The main soil factors affecting organic N dynamics were identified by principal components analysis. Ammonification predominated over nitrification in almost all soils. The mean net N mineralization rate was 1.63% of the organic N content, and varied according to soil parent materials as follows: soils on basic and ultrabasic rocks < soils over acid metamorphic rocks < soils developed over sediments < soils over acid igneous rocks < soils on limestone. The N mineralization capacity was lower in natural soils than in cropped soils or pastures. The accumulation of organic matter (C and N) seems to be due to poor mineralization which was caused, in decreasing order of importance, by high exchangeable H-ion levels, high Al and Fe gel contents and, to a lesser extent (though more markedly in cropped soils), by silty clay texture and exchangeable Al ions.     

Gains and losses in soil nutrients associated with harvesting and burning eucalypt rainforest

In mixed eucalypt/rainforest in southern Tasmania, samples of surface soil 0 to 2 cm, 2 to 5 cm, and 5 to 10 cm were taken from a clear-felled coupe before and after burning in 1982, from a similar coupe after burning in 1979, and from an uncut area adjacent to each coupe. Factors compared were bulk density; total organic C, N, P, Ca, Mg, and K; pH; exchangeable Ca, Mg, and K; cation exchange capacity; extractable P; and N-mineralisation rates. The effect of burning was found to be restricted mainly to the upper 2 cm of soil. The combustion of organic matter caused losses of 7360 kg organic C and 211 kg N/ha; 348 kg Ca and 282 kg Mg and 151 kg K/ha were added to the soil in ash. Burning caused significant increases in pH, exchangeable Ca, Mg, and K, and in extractable P; cation exchange capacity was reduced. In the 6 months after burning only K was leached from the upper 2 cm of soil. Equilibrium levels of NH₄?N increased initially after the fire, but between 6 and 18 months, equilibrium levels and rate of production of NH₄?N during anaerobic incubation in soil of burned coupes differed little from that in adjacent uncut forest. Rates of production of NO₃?N during aerobic incubation were very low throughout the period of study. It is concluded that for soils developed on dolerite in mixed eucalypt/rainforest, a single regeneration burn probably improves the nutritional status of the soil. Nutrients lost from the area as particulate ash are in quantities that will probably be replaced in rainfall in 15 to 20 years.     

Nitrification mediated nitrogen immobilization in soils

Summary The influence of nitrification on the status of soil organic nitrogen is examined by applying NH ₄ ⁺ -¹⁵N to the soil in the absence and the presence of a selective inhibitori.e. nitrapyrin. Parallel with nitrification, formation of organic nitrogen from the added fertilizer was followed. In the soil examined (pH 6.5, 4% organic carbon),ca. 55% of the fertilizer-N was immobilized during the 60 days incubation period, as a consequence of the nitrification process. Nitrification not only appeared to contribute to the binding of added mineral nitrogen onto soil organic matter, but also to re-immobilization of mineralised soil nitrogen.     

The Fate and Retention of Organic and Inorganic <Superscript>15</Superscript>N-Nitrogen in an Old-Growth Forest Soil in Western Oregon

Forests in the American Pacific Northwest receive very little nitrogen (N) through atmospheric deposition; therefore, they can provide insights into how the N cycle functioned in other regions before heavy atmospheric deposition of inorganic N began. Our objectives were to determine (a) if the fate of organic N differed from the fate of inorganic N, (b) the effect that polyphenols have on the fate of organic N, and (c) the effect of season of addition on the fate of N inputs. We traced N added to in situ soil cores as ammonium, organic N, tannin-complexed organic N, and the N₂-fixing lichen Lobaria oregana. Total ¹⁵N recovery was between 74% and 109% for all N additions. Total ¹⁵N recovery did not vary significantly from the first sampling date to the last date. The litter/organic horizon, as a bulk pool, was the largest N retention pool for all forms of N addition. Within the litter/organic horizon, the chloroform-extractable microbial biomass initially accounted for nearly all of the added N from the ammonium additions. On a different time scale, microbial biomass also played a noteworthy role in the retention of N from organic N, tannin-complexed organic N, and Lobaria. Complexing organic matter with tannin appeared to slow N cycling, but it did not significantly change the ultimate distribution of added organic N. Season of N addition had little effect on the retention of added N; however, where differences did occur, spring additions had lower recoveries than autumn additions.     

Changes in the microbial community in a forest soil amended with aluminium in situ

Considerable knowledge exists about the effect of aluminium (Al) on root vitality, but whether elevated levels of Al affect soil microorganisms is largely unknown. We thus compared soils from Al-treated and control plots of a field experiment with respect to microbial and chemical parameters, as well as root growth and vitality. The field experiment was established in a 50-year-old Norway spruce (Picea abies L.) stand where no Al or low concentrations of Al had been added every 7–10 days during the growth season for 7 years. Analysis of soil solutions collected using zero tension lysimeters and porous suction cups showed that Al treatment lead to increased concentrations of Al, Ca and Mg and lower pH and [Ca + Mg + K/Al] molar ratio. Corresponding soil analyses showed that soil pH remained unaffected (pH 3.8), that exchangeable Al increased, while exchangeable Ca and Mg decreased due to the Al treatment. Root in-growth into cores placed in the upper 20 cm of the soil during three growth seasons was not affected by Al additions, neither was nutrient concentration or mortality of these roots. The biomass of some taxonomic groups of soil microorganisms, analyzed using specific membrane components (phospholipid fatty acids; PLFAs), was clearly affected by the imposed Al treatment, both in the organic soil horizon and in the underlying mineral soil. Microbial community structure in both horizons was also clearly modified by the Al treatment. Shifts in PLFA trans/cis ratios indicative of short term physiological stress were not observed. Yet, aluminium stress was indicated both by changes in community structure and in ratios of single PLFAs for treated/untreated plots. Thus, soil microorganisms were more sensitive indicators of subtle chemical changes in soil than chemical composition and vitality of roots.     

Influence of organic matter and flooding on the chemical and electrochemical properties of sodic soil and rice growth

The influence of organic matter, added in the form ofCasuarina equisetifolia andAcacia nilotica leaves, on the chemical and electrochemical kinetics of a flooded sodic soil and rice growth, was studied in a pot experiment. With the addition of organic matter, not only the peaks of CO₂ production and maximum concentrations of extractable Fe and Mn and other cations occurred earlier, but their concentrations were also significantly higher as compared to the control (no organic matter). The high concentrations of CO₂ and reduced redox potential (Eh) appeared to influence the soil pH, exchangeable sodium percentage (ESP) and the accumulation of cations and to be chiefly responsible for better rice growth. Acacia proved more effective than Casuarina in improving rice yield and the sodic soil.     

The influence of organic soil amendments on sulfate adsorption and sulfur availability in a Brazilian Oxisol

Soil management practices that involve additions of organic materials may influence plant sulfur availability in highly-weathered, acid soils. This study evaluated the effects of organic additions on sulfate adsorption and sulfur availability in a limed (3,4 t ha^-1) and unlimed Typic Haplustox soil of the Cerrado Region of Brazil. In unlimed soil, the proportion of applied sulfate (600 kg S ha^-1 as gypsum) that was adsorbed temporarily decreased over two cropping seasons by incorporation of 10 t dry matter ha^-1 crop^-1 of guinea grass (Panicum maximum Jacq.) but not when a similar quantity of a tropical legume, feijâo de porco (Canavalia ensiformis L.), was added. Liming reduced sulfate adsorption and resulted in sulfate leaching to a depth of 30 to 45 cm. Both plant materials temporarily reduced sulfate adsorption in laboratory studies when added to an unlimed soil at a rate equivalent to 40 t ha^-1. Analysis of soil properties affected by organic additions and liming showed significant correlations between sulfate adsorption and soil pH, extractable aluminum, calcium and magnesium, and surface charge. Maize dry matter yields increased by 1.3 to 3.5 t ha^-1 with addition of both organic materials. However, only the feijâo de porco treatment resulted in increases in sulfur uptake for the years in which organic materials were applied. Determining the effects of organic material additions on plant sulfur availability is complicated by the combined effects of sulfur mineralization, sulfate adsorption, and the plant's ability to utilize adsorbed subsoil sulfate.Joint contribution of Cornell University and CPAC-EM- BRAPA. This research was supported by USAID through the Title XII CRSP subgrant SM-CRSP-10 from North Carolina State University     

The effects of water content of the topsoil on micronutrient availability and uptake in a siliceous sandy soil

Summary Effects of water content of the topsoil on the supply of manganese, zinc and copper to plants from an acid, siliceous sandy soil were investigated. The experiment was designed to provide a good supply of water and of nutrients other than those mentioned above at all times.Water content of the topsoil affected the root growth in that layer significantly. However, drying of the topsoil for as long as 42 days did not significantly affect the concentration of micronutrients in the shoots of oats, provided the plants did not experience water stress.Despite the acidic, siliceous sandy nature of the topsoil it showed a surprisingly high ability to render added manganese, zinc and copper unavailable. This phenomenon, probably mediated by organic matter, had a dominant effect on the exchangeable micronutrients in comparison to the effects due to fluctuations in soil water content.     

Effect of algal growth on the availability of phosphorus,iron and manganese in rice soils

Summary Laboratory experiments were conducted to study the effect of algal growth on the change of (I) pH, (II) available phosphorus and (III) solubility of iron and manganese content in five waterlogged alluvial rice soils of West Bengal, India. The results showed that the algal growth initially caused an increase in the soil pH, which later declined to the original value in some of the soils. The available phosphorus content decreased upto 90 days of their growth and began to increase towards the later period of incubation. The drastic fall of water soluble plus exchaneable manganese content of the soils due to algal growth was accompanied by similar increase in reducible manganese content. No appreciable change in water soluble plus exchangeable ferrous iron content was encountered but theN-NH₄OAC(pH 3) extractable iron due to algal growth progressively decreased with the progress of the incubation period.     

DOM对米槠次生林不同土层土壤微生物呼吸及其熵值的影响

可溶性有机质(Dissolved organic matter,DOM)作为土壤可溶性有机碳的重要来源,进入土壤之后通过改变土壤微生物数量和活性影响土壤矿化。DOM输入对土壤微生物呼吸和熵值的研究多集中在表层土壤,但对深层土壤微生物呼吸和熵值的影响关注较少。通过室内培养实验(120 d)研究米槠(Castanopsis carlesii)鲜叶DOM添加对表层土壤(0—10 cm)和深层土壤(40—60 cm)微生物呼吸及其土壤代谢熵和微生物熵的影响,为揭示DOM输入对亚热带森林土壤碳过程的影响提供理论依据。结果表明,在培养第1天,添加DOM的表层和深层土壤CO_2瞬时排放速率均显著高于对照(P0.001),分别是对照(不添加DOM)的3.58倍和6.93倍,之后显著下降。就累积排放量而言,无论是DOM添加处理还是对照,表层土壤显著大于深层土壤;在米槠鲜叶DOM添加后,表层土壤累积排放量显著大于对照的表层土壤(P0.001),但DOM添加处理深层土壤累积排放量与对照的深层土壤无明显差异。就微生物生物量碳而言,表层土壤微生物生物量碳含量在培养期间显著大于深层土壤。在整个添加DOM培养期间,表层土壤微生物生物量碳含量显著大于表层对照土壤,深层土壤微生物生物量碳含量显著大于深层对照土壤(第3天除外)。培养结束时(120 d),米槠鲜叶DOM添加处理下,表层土壤和深层土壤有机碳含量与第3天相比分别减少26%和19%。米槠鲜叶DOM添加处理后的深层土壤代谢熵(qCO_2)显著低于对照的深层土壤和DOM添加处理的表层土壤qCO_2(P0.001),说明外源DOM进入深层土壤后提高了土壤微生物对碳的利用效率。米槠鲜叶DOM添加处理后的深层土壤微生物熵是培养第3天的1.58倍,显著大于培养初期(P0.05),而DOM添加处理的表层土壤、对照的表层土壤与深层土壤的微生物熵分别是培养第3天的68%、79%和21%,说明DOM添加提高了深层土壤质量。     

Manganese studies in some soils with a high organic matter content

Summary The total and available forms of manganese in high organic matter content soils are reported. Most of the manganese is retained in an unavailable form either by organic matterper se or by some components of organic matter and, as a result, the available forms are extremely low and fall below the critical limits. Retention studies indicate that, exchange processes in the soil are more responsible for the retention of added manganese than redox processes. Organic matter as such does not quantitatively represent the component or components that influence the manganese retentive capacity of the soil. There is an indication to suggest that, if most of the total manganese is in organic form then fixation of added manganese various inversely with total manganese content.     

Factors affecting the microbial degradation of phenanthrene in soil

Summary Because phenanthrene was mineralized more slowly in soils than in liquid media, a study was conducted to determine the environmental factors that may account for the slow biodegradation in soil. Mineralization was enhanced by additions of phosphate but not potassium, and it was reduced by additions of nitrate. Aeration or amending the soil with glucose affected the rate of mineralization, although not markedly. Phenanthrene was sorbed to soil constituents, the extent of sorption being directly related to the percentage of organic matter in the soil. Soluble phenanthrene was not detected after addition of the compound to a muck soil. The rate of mineralization was slow in the organic soil and higher in mineral soils with lower percentages of organic matter. We suggest that sorption by soil organic matter slows the biodegradation of polycyclic aromatic hydrocarbons that are otherwise readily metabolized. Offprint requests to: M. Alexander     

Growth characteristics and seasonal allocation patterns of biomass and nutrients in Carex species growing in floating fens

A soil incubation and short-term root growth experiment was conducted to investigate the effects of organic matter application on Al toxicity alleviation in a highly weathered acid soil. Ground leaves of a tree legume (Calliandra calothyrsus Meissn.), ground barley (Hordeum vulgare L.) straw, or CaCO₃ were mixed at various rates with A-horizon soil of a red podzolic soil (Epiaquic Haplustult) and incubated at 90% of field capacity for 4 or 10 weeks. After the incubation, a short term (48 h) root growth test was conducted using mung bean (Vigna radiata (L.) Wilczek), followed by the analysis of the solution and solid phases of the post-harvest soil. Adding either CaCO₃ or organic matter increased root length in mung bean largely by decreasing the activity of monomeric Al in the soil solution. With organic matter, the major mechanisms of this decrease were presumed to be precipitation of soluble Al and the formation of Al-organic matter complexes. The former effect was predicted from the pH increase accompanying the organic matter addition, the increase being larger with legume leaves which had the higher exchangeable and soluble Ca and Mg contents. The concentration of Al complexed with soluble organic matter also was shown to increase with increasing rate of organic matter addition, the effect again being larger with legume leaves. The sum of monomeric Al species activity and Al³⁺ activity was negatively correlated with relative root length for the organic matter and CaCO₃ treatments. However, indices which took into account the possible alleviation effects of basic cations in soil solution on Al toxicity provided an improvement in correlation with relative root length. The efficiency of the two organic amendments relative to CaCO₃ in decreasing Al toxicity was assessed by comparing the rates required to reduce Al³⁺ activity below 10 μ M, the value found to be associated with 90% relative root length for mung bean. The rates of CaCO₃, legume leaf and barley straw required to reach this critical value were 0.75, 14, and 42 t ha⁻¹ respectively.     

Effect of organic matter on availability of nickel

Summary Additions of organic matter to a red soil resulted in the solubilization of the native and added nickel during the early days of its decomposition due to the production of various organic acids. It has been observed that as the incubation period advanced, more and more nickel was transformed into less soluble form so that after 80 days, only 8.1–8.8 and 14.1 ppm nickel could be recovered with berseem and glucose respectively when added along with 100 ppm nickel. The berseem has been found to have a tendency to fix greater amount of nickel in the soil than glucose. The available phosphate in the soil was also found to increase initially and then decrease. A greater content of organic carbon in the berseem-treated soil was closely related to the fixation of nickel in the soil. Formation of a complex between nickel and organic matter has been envisaged. re]19730806     

Uptake of six heavy metals by oat as influenced by soil type and additions of cadmium,lead, zinc and copper

Summary The influence of heavy metal additions on availability and uptake of cadmium, lead, zinc, copper, manganese and iron by oat was studied. The experiments were carried out as pot experiments using sandy loam, sandy soil and organic soil. Selective extractants were used to remove metals held in different soil fractions.Lead and copper were preferently bound by organics and oxides, zinc by oxides and inorganics, and cadmium by inorganics and organics.Addition of cadmium to the soils resulted in higher cadmium concentrations in all plant parts but lower concentrations of lead, zinc, copper, manganese and iron, and the accumulation indexes of these metals were also lower when cadmium was added to the soil.Addition of cadmium plus lead, zinc and copper resulted in higher cadmium concentrations in leaves and straw of plants grown in sandy loam and sandy soil, but lower concentrations when plants were grown in organic soil as compared with the results when cadmium was added separately. The transfer of cadmium, lead, zinc and copper from soil to plant was greatest from sandy soil, and zinc and cadmium were more mobile in the plant than were lead and copper.Cadmium concentrations in leaves correlated significantly with CaCl₂ and CH₃COOH extractions in sandy loam and sandy soil and with CH₃COOH extractions in organic soil.Generally, the total metal uptake was lowest from organic soil.     

Root biomass distribution in a moist tropical montane forest

Effects of N sources (ammonium, nitrate and ammonitrate) and VA mycorrhizae (Glomus intraradices) on rhizosphere soil characteristics (pH, exchangeable acidity, exchangeable cations, inorganic N concentrations) growth and nutrient acquisition of coffee seedlings (Coffea arabica L. cv guatemala) were investigated in a pot study with an acid soil (Red Bluff Loam) sterilized by autoclaving. Ammonium addition decreased rhizosphere pH while nitrate and ammonitrate additions both increased rhizosphere pH. Mycorrhizae induced a higher pH, a lower exchangeable acidity and higher values of exchangeable cations in the rhizosphere. Ammonium addition resulted in a lower mycorrhizal infection than the two other N sources. Mycorrhizal plants grew better and accumulated more N, Ca and Mg than non-mycorrhizal plants.