Increased Plant Uptake Research Articles

Light affects competition for inorganic and organic nitrogen between maize and rhizosphere microorganisms

Effects of light on the short term competition for organic and inorganic nitrogen between maize and rhizosphere microorganisms were investigated using a mixture of amino acid, ammonium and nitrate under controlled conditions. The amount and forms of N added in the three treatments was identical, but only one of the three N forms was labeled with 15N. Glycine was additionally labeled with 14C to prove its uptake by maize and incorporation into microbial biomass in an intact form. Maize out-competed microorganisms for $$^{15} {\text{NO}}_3^ - $$ during the whole experiment under low and high light intensity. Microbial uptake of 15N and 14C was not directly influenced by the light intensity, but was indirectly related to the impact the light intensity had on the plant. More $$^{15} {\text{NH}}_4^ + $$ was recovered in microbial biomass than in plants in the initial 4 h under the two light intensities, although more 15N-glycine was incorporated into microbial biomass than in plants in the initial 4 h under low light intensity. Light had a significant effect on $$^{15} {\text{NO}}_3^ - $$ uptake by maize, but no significant effects on the uptake of $$^{15} {\text{NH}}_4^ + $$ or 15N-glycine. High light intensity significantly increased plant uptake of $$^{15} {\text{NO}}_3^ - $$ and glycine 14C. Based on 14C to 15N recovery ratios of plants, intact glycine contributed at least 13% to glycine-derived nitrogen 4 h after tracer additions, but it contributed only 0.5% to total nitrogen uptake. These findings suggest that light intensity alters the competitive relationship between maize roots and rhizosphere microorganisms and that C4 cereals such as maize are able to access small amounts of intact glycine. We conclude that roots were stronger competitor than microorganisms for inorganic N, but microorganisms out competed plants during a short period for organic N, which was mineralized into inorganic N within a few hours of application to the soil and was thereafter available for root uptake.

Nitrogen mineralisation along a pH gradient of a silty loam UK soil

Most investigations into the effects of changing soil pH on microbial activity use, from necessity, soils taken from different sites so that soil physical and chemical properties are confounded. Studies along continuous gradients of soil pH within a single soil type are rare, simply because so few exist, in UK or even worldwide. Here we report measurements of mineralisation of native organic matter and added arginine along a continuous soil pH gradient (range about pH 3.7–8.3) of a UK silty clay loam soil (Chromic Luvisol or Typic Paleudalf). The soil has been maintained under constant management for more than 100 years, with winter wheat sown annually. The soil NH 4 +-N concentration was maximal at the lowest pH (pH 3.7), declining exponentially until pH 5.5 and remaining negligible thereafter. However, unexpectedly, soil NO 3 −-N concentration was also maximal at pH 3.7 and was significantly negatively correlated with increasing pH thereafter. To investigate these unexpected NO 3 −-N results, arginine was added as a labile source of organic N and its extent of ammonification and nitrification measured at soil pHs 3.79, 4.42, 6.08 and 7.82. While arginine ammonification was apparently greatest at pHs 3.79 and 4.42, similar to mineralisation of soil organic N, nitrification of this added N was greatest at soil pH 7.82 and least at pH 3.79, the reverse of the situation with soil organic N, but much more in line with what was expected. It was concluded that the decline in soil NO 3 −-N with increasing pH in the unamended soils was an artefact, caused by increasing plant uptake of NO 3 −-N as yield increased, rather than a true effect of low pH increasing nitrification of soil organic N. Our results differ from most previous studies, which showed poor correlations between soil pH and arginine mineralisation. This was attributed to our use of much longer incubation times (up to 50 days) than usually employed. Under our conditions, arginine was therefore shown to be a useful model for mineralisation of labile soil organic N.

Responses of a Non–N‐Limited Forest Plantation to the Application of Alkaline‐Stabilized Dewatered Dairy Factory Sludge

Amendment of forest soils with dewatered dairy factory sludge (DDFS), characterized by low heavy metal contents and high amounts of degradable C, can prevent the depletion of soil nutrients that results from intensive harvesting in forest plantations. However, this practice involves environmental risks when N supplies exceed the demand of plants or when the strong acidity of the soil favors the mobility of trace metals. These aspects were assessed in a young radiata pine plantation growing in a sandy, acidic, and organic N-rich soil for the 7 yr after application of a DDFS. The supply of limiting nutrients (mainly P, Mg, and Ca) provided by application of the DDFS, along with control of the ground vegetation, improved the nutritional status of the stand and led to increases in timber volume of more than 60 to 100%. Increases in soil inorganic N were observed during the first months after amendment. Data from soil incubation experiments revealed that some of the additional N was immobilized and, to a lesser extent, denitrified due to the readily available organic C content of the DDFS. Leaching and increased plant uptake of N were prevented by a combination of the latter processes and the low rate of nitrification. The strong acidity of the soil enhanced the availability of Mn and Zn to plants, although the maximum concentrations did not reach levels harmful to organisms. We conclude that although application of DDFS has positive effects on tree nutrition and growth and the environmental risks are low, repeated application may favor mobility of N and availability of heavy metals.

Effect of chelating agents and solubility of cadmium complexes on uptake from soil by Brassica juncea

Brassica juncea, or Indian mustard, was grown in soil artificially contaminated with either a soluble salt, CdCl(2), at 186mg Cdkg(-1), or alternately an insoluble, basic salt, CdCO(3), at 90mg Cdkg(-1). These experiments study the range of Cd uptake by Indian mustard from conditions of very high Cd concentration in a soluble form to the other extreme with an insoluble Cd salt. After plants were established, four different chelating agents were applied. Chelating agents increased plant uptake of Cd from the CdCl(2) soil but did not significantly increase plant uptake of Cd from the CdCO(3) contaminated soil. Addition of ethylenediaminetetraacetic acid (EDTA) increased the plant concentration of Cd by almost 10-fold in soils contaminated with CdCl(2), with a concentration of 1283mg Cdkg(-1) in the dried EDTA-treated plants over a concentration of 131mg Cdkg(-1) in plants without added chelate. However, EDTA increased the aqueous solubility of Cd by 36 times over the soil matrix without added chelator, and thereby, increased the possibility of leaching. Other chelators used in both experiments were ethylenebis(oxyethylenenitrilo)tetraacetic acid, trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, and diethylenetriaminepentaacetic acid (DTPA) increasing Cd in plants to 1240, 962, and 437mg Cdkg(-1), respectively. The other chelating agents increased the solubility of Cd in the leachate but not to the extent of EDTA. Comparing all chelating agents studied, DTPA increased plant uptake in terms of Cd in dried plant concentration most relative to the solubility of complexed Cd in runoff water.

Leaching of nitrate from temperate forests – effects of air pollution and forest management

We compiled regional and continental data on inorganic nitrogen (N) in seepage and surface water from temperate forests. Currently, N concentrations in forest waters are usually well below water quality standards. But elevated concentrations are frequently found in regions with chronic N input from deposition (>8–10 kg ha–1a–1). We synthesized the current understanding of factors controlling N leaching in relation to three primary causes of N cycle disruption: (i) Increased N input (air pollution, fertilization, N2fixing plants). In European forests, elevated N deposition explains approximately half of the variability in N leaching, some of the remaining variability could be explained by differences in N availability or "N status". For coniferous forests, needle N content above 1.4% and (or) forest floor C:N ratio lower than 25 were thresholds for elevated nitrate leaching. At adjacent sites conifer forests receive higher N deposition and exhibit higher nitrate loss than deciduous forests; an exception is alder that shows substantial nitrate leaching through N fixation input. Fertilization with N poses limited risk to water quality, when applied to N-limited forests. (ii) Reduced plant uptake (clear-cut, thinning, weed control). The N cycle responses to plant cover disturbance by clear-cut are well studied. Nitrate losses peak after 2–3 years and are back to pre-cut levels after 3–5 years. Nitrogen losses increase with deposition and are higher at N rich sites. The extent and duration of the nitrate response is especially connected to the recovery of the vegetation sink. Less intensive disturbances like thinning have only minor effects on N loss. (iii) Enhanced mineralization of soil N (liming, ditching, climate change). Responses in nitrate leaching after liming may increase with N deposition and in older stands. However data on these types of N cycle disruption are too sparse to allow general conclusions on controlling factors. Nitrate leaching occurs when N deposition (input) and net mineralization (N status) exceed plant demand. A combined N flux to the soil of 50 to 60 kg ha–1a–1from N deposition and litterfall may be a threshold for nitrate leaching in undisturbed forests. This threshold also indicates risk of increasing losses in case of a disturbance (e.g., clear-cut). We conclude by discussing forest management options for water quality protection. These options focus on decreasing input, increasing plant uptake, increasing biomass removal, and (re)establishing immobilization and denitrification processes at the catchment scale.Key words: clear-cut, disturbance, forest management, nitrate, nitrogen cycling, nitrogen saturation.

Land Application of Domestic Effluent onto Four Soil Types: Plant Uptake and Nutrient Leaching

Land application has become a widely applied method for treating wastewater. However, it is not always clear which soil-plant systems should be used, or why. The objectives of our study were to determine if four contrasting soils, from which the pasture is regularly cut and removed, varied in their ability to assimilate nutrients from secondary-treated domestic effluent under high hydraulic loadings, in comparison with unirrigated, fertilized pasture. Grassed intact soil cores (500 mm in diameter by 700 mm in depth) were irrigated (50 mm wk(-1)) with secondary-treated domestic effluent for two years. Soils included a well-drained Allophanic Soil (Typic Hapludand), a poorly drained Gley Soil (Typic Endoaquept), a well-drained Pumice Soil formed from rhyolitic tephra (Typic Udivitrand), and a well-drained Recent Soil formed in a sand dune (Typic Udipsamment). Effluent-irrigated soils received between 746 and 815 kg N ha(-1) and 283 and 331 kg P ha(-1) over two years of irrigation, and unirrigated treatments received 200 kg N ha(-1) and 100 kg P ha(-1) of dissolved inorganic fertilizer over the same period. Applying effluent significantly increased plant uptake of N and P from all soil types. For the effluent-irrigated soils plant N uptake ranged from 186 to 437 kg N ha(-1) yr(-1), while plant P uptake ranged from 40 to 88 kg P ha(-1) yr(-1) for the effluent-irrigated soils. Applying effluent significantly increased N leaching losses from Gley and Recent Soils, and after two years ranged from 17 to 184 kg N ha(-1) depending on soil type. Effluent irrigation only increased P leaching from the Gley Soil. All P leaching losses were less than 49 kg P ha(-1) after two years. The N and P leached from effluent treatments were mainly in organic form (69-87% organic N and 35-65% unreactive P). Greater N and P leaching losses from the irrigated Gley Soil were attributed to preferential flow that reduced contact between the effluent and the soil matrix. Increased N leaching from the Recent Soil was the result of increased leaching of native soil organic N due to the higher hydraulic loading from the effluent irrigation.

Soil microbial responses to experimental warming and clipping in a tallgrass prairie

AbstractGlobal surface temperature is predicted to increase by 1.4–5.8°C by the end of this century. However, the impacts of this projected warming on soil C balance and the C budget of terrestrial ecosystems are not clear. One major source of uncertainty stems from warming effects on soil microbes, which exert a dominant influence on the net C balance of terrestrial ecosystems by controlling organic matter decomposition and plant nutrient availability. We, therefore, conducted an experiment in a tallgrass prairie ecosystem at the Great Plain Apiaries (near Norman, OK) to study soil microbial responses to temperature elevation of about 2°C through artificial heating in clipped and unclipped field plots. While warming did not induce significant changes in net N mineralization, soil microbial biomass and respiration rate, it tended to reduce extractable inorganic N during the second and third warming years, likely through increasing plant uptake. In addition, microbial substrate utilization patterns and the profiles of microbial phospholipid fatty acids (PLFAs) showed that warming caused a shift in the soil microbial community structure in unclipped subplots, leading to the relative dominance of fungi as evidenced by the increased ratio of fungal to bacterial PLFAs. However, no warming effect on soil microbial community structure was found in clipped subplots where a similar scale of temperature increase occurred. Clipping also significantly reduced soil microbial biomass and respiration rate in both warmed and unwarmed plots. These results indicated that warming‐led enhancement of plant growth rather than the temperature increase itself may primarily regulate soil microbial response. Our observations show that warming may increase the relative contribution of fungi to the soil microbial community, suggesting that shifts in the microbial community structure may constitute a major mechanism underlying warming acclimatization of soil respiration.

Efeitos da calagem em semedura direta de milho

As conseqüências das alterações químicas do solo, decorrentes da calagem na superfície, sobre o crescimento radicular e a nutrição do milho cultivado em semeadura direta são pouco conhecidas. Com o objetivo de avaliar os efeitos da aplicação superficial de calcário nos atributos químicos do solo, no crescimento de raízes e na nutrição da planta de milho, e seus reflexos sobre o rendimento de grãos, foi realizado um experimento em Latossolo Vermelho distrófico textura muito argilosa, manejado há seis anos em semeadura direta, em Tibagi (PR). Os tratamentos, aplicados em parcelas de 44,8 m², foram dispostos em blocos completos ao acaso com quatro repetições e constaram da aplicação de quatro doses de calcário dolomítico na superfície: 0, 1, 2 e 3 t.ha-1 (PRNT = 100%). As doses de calcário (27% de CaO, 20% de MgO e 85% de PRNT) foram baseadas no requerimento de 1/3, 2/3 e na quantidade total calculada para elevar a saturação por bases do solo, na camada de 0-20 cm, a 70%. A calagem, após 22 meses, aumentou o pH em CaCl2 0,01 mol.L-1, os teores de Ca e Mg trocáveis e a saturação por bases, e reduziu os teores de H + Al e de Al trocável, na camada superficial do solo (0-10 cm), e ocasionou aumento de Ca trocável e redução de Al trocável no subsolo (20-40 cm). A aplicação superficial de doses de calcário não alterou o comprimento e a distribuição relativa de raízes de milho até a profundidade de 40 cm, reduziu o raio médio de raízes e aumentou a absorção de P, Ca, Mg e S pelas plantas, sem causar reflexos sobre o rendimento de grãos. Os teores de Cu, Fe, Mn e Zn no solo e no tecido foliar do milho, bem como sua absorção pelas plantas, não foram alterados com a aplicação de calcário na superfície.

Plant availability and leaching of (heavy) metals from ammonium‐, calcium‐, carbohydrate‐, and citric acid‐treated uranium‐mine‐dump soil

AbstractRemediation of an uranium‐mine soil from Settendorf (East Germany) includes phytoextraction under conditions which make its heavy metals more plant‐available but less leachable. A second way is active inhibition of heavy metal uptake by the plant. In a pot trial with Chinese cabbage (Brassica chinensis L.), planted and unplanted soil samples were daily irrigated with deionized water or aqueous solutions with a total of (g (kg soil)–1) CaCl2 (0.26 Ca), NH4Cl (1.39), casein, sucrose, citric acid (13), and an extract of rape (B. napus L.) shoots (13 DW) in a phytotron for 26 d. Water‐irrigated plants were also treated with a 50 mM citric acid solution (10.5 g (kg soil)–1) 6 and 7 d prior to harvesting. Total elements in plant tissue and soluble elements in aqueous extracts from control and postharvest soils were determined by ICP‐AES. Supplements of NH$_4^+$, and the NH$_4^+$‐generating casein and rape extract reduced soil pH during nitrification, and increased plant uptake of Cd, Cu, Ni, and Zn. Citric acid at 50 mM adjusted soil to pH 4.5–6.0 and enhanced uptake of all elements. Long‐term application of sucrose and citric acid increased pH and inhibited uptake of Cd, Cr, Cu, Ni, and Zn. Contemporarily, leaching of heavy metals and humic substances was lowest with Ca and NH$_4^+$ and highest with sucrose and citric acid amendments. It is concluded that Chinese cabbage grown for chelate‐assisted phytoextraction should be supplied with Ca and NH$_4^+$ to obtain a high plant biomass on soil with a low hazard of leaching. Metal uptake should be stimulated by application of chelator 7 d prior to harvesting. Undesired uptake of heavy metals by Chinese cabbage determined as food should be inhibited with carbohydrate amendments. Long‐term application of NH$_4^+$ or chelator, which reduces the solubility of certain elements but increases their uptake moderately, is recommended as a tool for continuous phytoextraction technologies.

Recovery of fertilizer-derived inorganic-15N in a vegetable field soil as affected by application of an organic amendment

To examine the effect of organic amendment application on the fate of inorganic-N accumulated in a vegetable field soil during conversion from inorganic to organic input, a pot experiment using 15N-labeled soil was conducted. The soil was labeled with 15N through addition of urea-15N (98 atom % 15N) and was then incubated for 1 year resulting in inorganic soil-N concentration and 15N abundance of 211 mg kg−1 soil and 4.950 atom %, respectively. Chinese cabbage [Brassica campestris (L.) Samjin] plants were grown in the labeled soil for 30 and 60 days after application of organic amendment at the rates of 0 (control), 200, 400, and 600 mg N kg−1 soil. Although organic amendment application did not show any significant effect on the uptake efficiency of inorganic-N by Chinese cabbage during the first 30 days, it significantly (P<0.05) increased inorganic-N uptake efficiency as well as total-N uptake and dry matter yield at the end of the 60-day growth period. Application of the organic amendment also increased microbial immobilization of inorganic-N in both growth periods. Between 30 and 60 days of growth, however, the amount of immobilized N from the inorganic-15N pool decreased, indicating re-mineralization of previously immobilized N. Although the amount of inorganic-15N lost was virtually the same among treatments at day 30, increased immobilization of inorganic-15N caused by organic amendment application led to the higher retention of inorganic-N in the soil and less loss of N at day 60 as compared to the control. These results indicate that increased immobilization by organic amendment application in the early growth season and the subsequent gradual re-mineralization may play an important role in increasing plant uptake of inorganic-15N, while minimizing N loss.

Effects of compost and phosphate amendments on arsenic mobility in soils and arsenic uptake by the hyperaccumulator, Pteris vittata L.

Chinese brake fern (Pteris vittata L.), an arsenic (As) hyperaccumulator, has shown the potential to remediate As-contaminated soils. This study investigated the effects of soil amendments on the leachability of As from soils and As uptake by Chinese brake fern. The ferns were grown for 12 weeks in a chromated–copper–arsenate (CCA) contaminated soil or in As spiked contaminated (ASC) soil. Soils were treated with phosphate rock, municipal solid waste, or biosolid compost. Phosphate amendments significantly enhanced plant As uptake from the two tested soils with frond As concentrations increasing up to 265% relative to the control. After 12 weeks, plants grown in phosphate-amended soil removed >8% of soil As. Replacement of As by P from the soil binding sites was responsible for the enhanced mobility of As and subsequent increased plant uptake. Compost additions facilitated As uptake from the CCA soil, but decreased As uptake from the ASC soil. Elevated As uptake in the compost-treated CCA soil was related to the increase of soil water-soluble As and As(V) transformation into As(III). Reduced As uptake in the ASC soil may be attributed to As adsorption to the compost. Chinese brake fern took up As mainly from the iron-bound fraction in the CCA soil and from the water-soluble/exchangeable As in the ASC soil. Without ferns for As adsorption, compost and phosphate amendments increased As leaching from the CCA soil, but had decreased leaching with ferns when compared to the control. For the ASC soil, treatments reduced As leaching regardless of fern presence. This study suggest that growing Chinese brake fern in conjunction with phosphate amendments increases the effectiveness of remediating As-contaminated soils, by increasing As uptake and decreasing As leaching.

A LIQUID MANURE INJECTION TOOL ADAPTED TO DIFFERENT SOIL CONDITIONS

Injection of liquid manure into soil can reduce nutrient loss through volatilization, reduce odor emission, reduce surface runoff pollution, and increase plant uptake of nutrients. A liquid manure injection tool was developed based on the following design criteria: easy adaptation, low draft force and surface exposure of injected manure, and suitability for different soil conditions and for variable manure application rates. The tool featured a chisel with a sweep and a shank. The first prototype was tested using swine manure in a field with clay soil and wheat stubble to examine the draft forces and the resultant manure exposure indices under different injection depths and manure application rates. Based on the field test results of the first prototype, a second prototype was designed with a narrower tool cutting width and a smaller rake angle, and was compared with the first prototype in an indoor soil bin (loamy sand soil and no residue cover). The tool geometry and features implemented in the design met the proposed design criteria. The second prototype required lower draft force and caused less soil disturbance when compared with existing injection tools reported in the literature.

Species specific effects of ants on microbial activity and N-availability in the soil of an old-field

Microbial biomass and activity as well as N-availability were measured in the mounds of three ant species strongly differing in foraging strategy and mound architecture: Myrmica scabrinodis, Lasius niger and L. flavus. Soil microbial biomass (C mic) was significantly increased in the mounds of all three ant species. This positive effect was due to the accumulation of organic matter (C org) within the mounds. Microbial activity was increased in M. scabrinodis mounds only. Available N min was accumulated in all mound types, independent of the feeding mode of the ants, with Lasius mounds having significantly higher N min content than M. scabrinodis mounds. It is hypothesised that the differences between the mound types are due to differences in nest architecture, especially the integration of grassy vegetation. Higher microbial activity in M. scabrinodis mounds may be a consequence of supplementary energy provided by root exudates. The amount of N min in M. scabrinodis mounds may be reduced by increased plant uptake and by immobilisation within the microbial biomass.

Feasibility of Phytoextraction to Clean Up Low-Level Uranium-Contaminated Soil

ABSTRACT The potential to phytoextract uranium (U) from a sandy soil contaminated at low levels was tested in the greenhouse. Two soils were tested: a control soil (317 Bq 238U kg-1) and the same soil washed with bicarbonate (69 Bq 238U kg-1). Ryegrass (Lolium perenne cv. Melvina), Indian mustard (Brassica juncea cv. Vitasso), and Redroot Pigweed (Amarathus retroflexus) were used as test plants. The annual removal of the soil activity with the biomass was less than 0.1%. The addition of citric acid (25 mmol kg-1) 1 week before the harvest increased U uptake up to 500-fold. With a ryegrass and mustard yield of 15000 kg ha-1 and 10000 kg ha-1, respectively, up to 3.5% and 4.6% of the soil activity could annually be removed with the biomass. With a desired activity reduction level of 1.5 and 5 for the bicarbonate washed and control soil, respectively, it would take 10 to 50 years to attain the release limit. A linear relationship between the plant 238U concentration and the 238U concentration in the soil solution of the control, bicarbonate-washed, or citric acid-treated soil points to the importance of the soil solution activity concentration in determining U uptake and hence to the importance of solubilising agents to increase plant uptake. However, citric acid addition resulted in a decreased dry weight production (all plants tested) and crop regrowth (in case of ryegrass).

Use of Isotopic Dilution Techniques To Assess the Mobilization of Nonlabile Cd by Chelating Agents in Phytoremediation

Metals are unavailable to plants when fixed within relatively inert mineral matrices in soil. The success of phytoremediation may be limited by restricted bioavailability of metals in such nonlabile forms. We conducted a pot trial with EDTA added at rates of 0, 0.1, 1.0, 5.0, and 10 mmol kg-1, to soil historically contaminated with sewage sludge to increase the availability of metals to a test crop, Indian Mustard (Brassica juncea). The soil was found to have large total concentrations (mg kg-1) of Cd (59.3), Cu (664), Pb (605), Ni (489), and Zn (1780); the EDTA-extractable metal contents (mg kg-1) were Cd (36.2), Cu (483), Pb (302), Ni (372), and Zn (1280). Isotopic dilution of 109Cd was used to measure labile Cd both (i) chemically (the E value: 28.3 mg Cd kg-1) and (ii) biologically (the L value). Comparison of E and L values was then used to determine whether nonlabile Cd was mobilized by the chelate treatment. Addition of EDTA increased plant uptake of Cd, Zn, Pb, Ni, and Cu from sludge-amended soil...

Seasonal change in precipitation, snowpack, snowmelt, soil water and streamwater chemistry, northern Michigan

We have studied weekly precipitation, snowpack, snowmelt, soil water and streamwater chemistry throughout winter for over a decade in a small (176 ha) northern Michigan watershed with high snowfall and vegetated by 60 to 80 year-old northern hardwoods. In this paper, we examine physical, chemical, and biological processes responsible for observed seasonal change in streamwater chemistry based upon intensive study during winter 1996-1997. The objective was to define the contributions made to winter and spring streamwater chemical concentration and flux by processes as snowmelt, over-winter forest floor and surface soil mineralization. immobilization, and exchange, and subsurface flowpath. The forest floor and soils were unfrozen beneath the snowpack which permitted most snowmelt to enter. Over-winter soil mineralization and other biological processes maintain shallow subsurface ion and dissolved organic carbon (DOC) reservoirs. Small, but steady, snowmelt throughout winter removed readily mobilized soil NO 3 - which resulted in high over-winter streamwater concentrations but little flux. Winter soil water levels and flowpaths were generally deep which increased soil water and streamwater base cation (C B ), HCO 3 - , and Si concentrations. Spring snowmelt increased soil water levels and removal of ions and DOC from the biologically active forest floor and shallow soils. The snowpack solute content was a minor component in determining streamwater ion concentration or flux during and following peak snowmelt. Exchangeable ions, weakly adsorbed anions, and DOC in the forest floor and surface soils dominated the chemical concentration and flux in soil water and streamwater. Following peak snowmelt, soil microbial immobilization and rapidly increased plant uptake of limiting nutrients removed nearly all available nitrogen from soil water and streamwater. During the growing season high evapotranspiration increased subsurface flowpath depth which in turn removed weathering products, especially C B , HCO 3 - , and Si, from deeper soils. Soil water was a major component in the hydrologic and chemical budgets.

Factors affecting soil acidification under legumes I. Effect of potassium supply

This study examined the effect of K (as K2SO4) supply on acid production under N2-fixing plants of lupin (Lupinus angustifolius L. cv. Gungurru) and clover (Trifolium subterraneum L. cv. Dalkeith) grown in a K-deficient soil with a low pH buffer capacity for 55 days in the glasshouse at 20/12 °C (day/night). Increasing K supply up to 240 mg K kg-1 soil markedly increased plant growth of both species but clover growth was more responsive than lupin. Growing plants for 55 days decreased soil pH by 0.65–0.85 units under lupin and 0.45–0.83 units under clover. The amounts of H+ produced per kg biomass (specific acid production) were the highest at the nil K supply, generally decreased with increasing K level up to 30 mg K kg-1 under lupin and up to 120 mg K kg-1 soil under clover and only slightly increased with further increasing K under lupin. Increasing K2SO4 supply proportionally increased plant uptake of K and SO 4 2- but generally decreased concentrations of Ca, Mg, Na, P and Cl. Specific acid production correlated well with concentrations of excess cations and ash alkalinity, and total acid production was strongly correlated with total excess cations and total ash alkalinity in plants. These relationships were not affected by K treatment and species. Specific acid production also correlated with plant Ca concentration but not with K concentration. In addition, lupin and clover extruded similar amounts of H+ per kg biomass produced. It is suggested that application of K2SO4 does not have a significant impact on acid production by lupin and clover.

Influence of acidity and potassium saturation on plant uptake of indigenous soil rubidium

Rubidium is frequently used as a tracer of K + in plants and soils. However, uptake of Rb + from soils by plants, fungi, and even animals is greatly influenced by soil properties. Field biomass concentrations of Rb + usually vary by one-two orders of magnitude, largely according to soil acidity. A growth experiment was conducted using a sedge, Carex pilulifera, transplanted in 50 natural and semi-natural unfertilized soils representing a wide range of chemical properties. It is suggested that pH-dependent reactions regulating the Rb + solubility in soils and an increased plant uptake of Rb +, when K + is deficient, are major conditions accounting for differences in plant uptake of Rb + from contrasting soils. The pool size of exchangeable, indigenous soil Rb +, within the ranges usually encountered, seems to be of less importance.

Developmental toxicity of Exell, a surfactant mixture, in rats and rabbits.

A surfactant mixture (C.A.S No. 104559-06-2), is used in combination with foliar-acting herbicides to improve herbicidal performance by increasing plant uptake. It was administered by gavage as an aqueous solution to groups of 25 assumed pregnant Crl:CD BR rats from days 7-16 of gestation at daily dosage levels of 0, 3, 8, 20 or 50 mg/kg body weight. The dams were euthanized on Day 22 of gestation and the offspring were weighed and examined for external, visceral, and skeletal alterations. The surfactant mixture was maternally toxic at levels of 20 mg/kg/day and above as evidenced by reduced maternal weight gain and by an increased incidence of lung noise (wheezing and/or rattling) and sneezing. In addition, maternal food consumption was reduced in the high dosage group. There was no evidence of developmental toxicity at any dosage level. In the rabbit study, groups of 20 artificially inseminated adult Hra:(NZW)SPF rabbits were similarly dosed from Days 6-18 of gestation at daily dosage levels of 0, 12, 35, or 100 mg/kg body weight. The dose were euthanized on Day 29 of gestation and the offspring were weighed and examined for external, visceral, and skeletal alterations. Dosages of 35 and 100 mg/kg/day resulted in reduced maternal body weight gain, food consumption and fetal body weight. Thus, in the rat, the maternal and developmental no-observed-adverse-effect levels (NOAELs) were 8 mg/kg/day and greater than 50 mg/kg/day, respectively. In the rabbit, the maternal and developmental NOAELs were 12 mg/kg/day. This surfactant mixture was, therefore, not demonstrated to be uniquely toxic to either the rat or rabbit conceptus.

Cadmium status of soils and plants from a long-term fertility experiment in southeast Norway

To determine whether the use of phosphate fertilizer resulted in measurable cadmium accumulation in soils and crops harvested, soil and plant samples were collected from some selected treatments of a seventy year-old fertilizer experiment at Moystad, southeast Norway. Soil samples after extraction with Aqua Regia or 1M NH4NO3 and plant samples after digestion were analyzed for Cd. Cadmium balance based on fertilizer and atmospheric inputs and crop removal and leaching losses was worked out. Neither the total nor the available (NH4NO3-extractable) Cd in the soil was significantly affected by Cd added through fertilizer, though a tendency of higher Cd in soils from the plots receiving higher amounts of fertilizer was seen. The same trend was also observed for the Cd concentration in plants. Annual Cd input rates (fertilizer and atmosphere) varied from 1.20 to 2.57 g Cd ha-1 y-1 and the Cd removal (crops and leaching) rates varied from 1.16 to 1.79 g Cd ha-1 y-1. The balance calculations based on the seventy years data indicated Cd accumulation in the soil was <1 g Cd ha-1 y-1, but that increasing the doses of either commercial fertilizer or farm yard manure would likely result in increased accumulation of the element. This may have a negative impact because the available soil Cd content would be increased at a faster rate, resulting in increased plant uptake. Although Cd tended to accumulate as a result of P fertilization, the rate of increase was slow. The annual increase in the total Cd content of fertilized plots varied from 0.04 to 0.12% indicating that it may take from 800 to 2000 years, depending upon the fertilizer input, to accumulate Cd equivalent to that currently present in the soil.