Effect Of Soil pH Research Articles

Dynamics of phosphorus fractions in the rhizosphere of fababean (Vicia faba L.) and maize (Zea mays L.) grown in calcareous and acid soils

The dynamics of soil phosphorus (P) fractions were investigated, in the rhizosphere of fababean (Vicia faba L.) and maize (Zea mays L.) grown in calcareous and acid soils. Plants were grown in a mini-rhizotron with a thin (3 mm) soil layer, which was in contact with the root-mat, and considered as rhizosphere soil. Hedley sequential fractionation was used to evaluate the relationship between soil pH and P dynamics in the rhizosphere of fababean and maize. Soil pH influenced the dynamics of P fractions in both calcareous and acid soils. Fababean and maize roots decreased rhizosphere pH by 0.4 and 0.2 pH units in calcareous soil, and increased rhizosphere pH by 1.2 and 0.8 pH units in acid soil, respectively, compared with the no-plant control. The acid-soluble inorganic P fraction in the rhizosphere of calcareous soil was significantly depleted by fababean, which was probably due to strong rhizosphere acidification. In contrast, maize had little effect on this fraction. Both fababean and maize significantly depleted the alkali-soluble organic P fractions in calcareous soil, but not in acid soil. Fababean and maize utilised different P fractions in soil, which was partly due to their differing abilities to modify the rhizosphere. This study has decoupled successfully the effects of chemically induced pH change from plant growth effects (such as mineralisation and P uptake) on P dynamics. The effect of soil pH on plant exudation response in P-limited soils has been demonstrated in the present study.

Effect of soil pH and crop sequence on the response of wheat (Triticum aestivum) to phosphorus fertiliser

Changes in soil fertility following long periods of crop production in the south-west of Western Australia (WA) may have implications for phosphorus (P) fertiliser recommendations for wheat production. When the sandy soils of the region were first cleared for agricultural production, they were typically marginally acidic to neutral, with soil extractable-P levels inadequate for crop production. Recent surveys have shown that 87% of soils in south-west WA exceed the critical soil extractable-P level required for 90% of maximum grain yield, and ~70% of soils have a surface-soil pHCa <5.5. There has also been a shift towards a high frequency of wheat in the crop sequence. We conducted a field experiment to begin to quantify the importance of the interactions between soil pH and crop sequence on wheat response to P fertiliser. For grain yield, the magnitude of the response was greatest for rate of P applied, followed by lime treatment and then crop sequence. There were no interactions between these treatments. Our analysis of the grain-yield response to rates of P fertiliser showed no significant difference between the shape of the grain-yield response curve for treatments with and without lime. However, we did find a significant interaction between lime treatment and rate of P fertiliser applied for shoot P concentration and that soil P was more plant-available in the +lime than the –lime treatment. There is justification for making realistic adjustments to yield potential based on soil pH or crop sequence, although further work is required to determine whether the shape of the grain-yield response curve varies with these two factors.

The Effect of Soil pH on Bioremediation of Polycyclic Aromatic Hydrocarbons (PAHS)

Environmental fate of polycyclic aromatic hydrocarbons (PAHs) is a significant issue raising interest in bioremediation. Soil microorganism plays a vital role in degradation of PAHs and uses various metabolic pathways for degradation process. The effect of soil pH on degradation of PAH with a view to manipulating soil pH to enhance the bioremediation of PAH’s was studied. The degradation rate of key PAHs (phenanthrene, anthracene, flouranthene, and pyrene) was monitored in an Arthur Brower’s topsoil at range of soil pH (5-8). Isolation of microbes degrading PAHs was carried out. L-arginine ammonification was measured to estimate soil microbial biomass by ATPase, whilst soil enzyme associated with the degradation rate of each individual PAH was studied. It was observed that soil pH 7.5 was most suitable for the degradation of all the PAHs. 50% degradation was observed in soil pH 7.5 within first three days of time period which is a seventh of the time taken at pH 5 and pH 6.5 (21 days). Greater fungal populations were found at low (acidic) soil pH and also at high (basic) soil pH, in comparison with neutral pH 7. Pencillium species was found to be more prevalent at acidic pH whilst Aspergillus species was found to be more prevalent at pH 7.5-8. Greatest bacterial population was observed at soil pH 7.5. Moreover, the practical application to bioremediation process that natural detoxify PAHs and different organic compounds present at various contaminated sites is at slower rates and thus requires potential understanding in degradation improvement. However, amending the favorable soil pH as a result of its effect obtained in this study will fasten the rates of PAH degradation. Since, greatest degradation rates in this study were found at soil pH 7.5 suggesting that liming to increase soil pH, may significantly increase bioremediation rates.

A contemporary overview of silicon availability in agricultural soils

AbstractOur current understanding of silicon (Si) availability in agricultural soils is reviewed and knowledge gaps are highlighted. Silicon is a beneficial rather than essential plant nutrient and yield responses to its application have been frequently demonstrated in Si‐accumulator crops such as rice and sugarcane. These crops are typically grown on highly weathered (desilicated) soils where soil solution Si concentrations are low. Increased yields are the result of simultaneous increases in plant tolerance to a wide range of biotic (plant pathogens, insect pests) and abiotic (water shortage, excess salts, metal toxicities) stresses. Traditionally, soil solution Si is viewed as being supplied by dissolution of primary and secondary minerals and buffered by adsorption/desorption of silicate onto Al and Fe hydrous oxide surfaces. In recent years it has become recognized that phytogenic cycling of Si [uptake of Si by plants, formation of phytogenic silica (SiO2 · nH2O) mainly in leaves and subsequent return of this silica to soils in plant litter] is the main determinant of soil solution Si concentrations in natural forests and grasslands. Considerable diminution of the phytogenic Si pool in agricultural soils is likely due to regular removal of Si in harvested products. A range of extractants (unbuffered salts, acetate‐based solutions, and acids) can provide valuable information on the Si status of soils and the likelihood of a yield response in rice and sugarcane. The most common Si fertilizers used are industrial byproducts (e.g., blast furnace slag, steel slag, ferromanganous slag, Ca slag). Since agriculture promotes soil desilication and Si is presently being promoted as a broad spectrum plant prophylactic, the future use of Si in agriculture is likely to increase.Aspects that require future research include the role of specific adsorption of silicate onto hydrous oxides, the significance of phytogenic Si in agricultural soils, the extent of loss of phytogenic Si due to crop harvest, the role of hydroxyaluminosilicate formation in fertilized soils, and the effect of soil pH on Si availability.

Effects of soil pH on the Vicia-micronucleus genotoxicity assay

In the field of contaminated sites and soil management, chemical analyses only bring typological data about pollution. As far as bioavailability and effects on organisms are concerned, we need ecotoxicology tools. In this domain, among many existing tests, we chose to study genotoxicity because it is a short-term endpoint with long-term consequences. The aim of this study is to assess the effects of soil pH on the results of the Vicia faba root tip micronucleus test for the two following reasons: (i) to define the pH range within which the test can be performed without modifying the soil to be tested, within the framework of the ISO standard of the test and (ii) to provides information about the effects of the pH on the genotoxic potential of soils. In this context, we modified the pH of a standard soil with HCl or NaOH and we spiked the matrix with copper (2, 4 and 8mmolkg−1 dry soil) or with maleic hydrazide, an antigerminative chemical (5, 10 and 20μmolkg−1 dry soil). We concluded that the pH had no effect on the mitotic index or micronucleus frequency in the root cells of the negative controls: extreme pH values did not induce micronucleus formation in root cells. Moreover, according to our results, the Vicia-micronucleus test can be performed with pH values ranging between 3.2 and 9.0, but in the ISO 29200 “Soil quality – assessment of genotoxic effects on higher plants – V. faba micronucleus test” we recommended to use a control soil with a pH value ranging between 5 and 8 for a more accurate assessment of chemical genotoxicity. We also found that acid pH could increase the genotoxic potential of pollutants, especially heavy metals. With hydrazide maleic spiked soil, plants were placed in a situation of double stress, i.e. toxicity caused by extreme pH values and toxicity induced by the pollutant.

Soil moisture and pH control relative contributions of fungi and bacteria to N2O production.

Fungal N(2)O production has been progressively recognized, but its controlling factors remain unclear. This study examined the impacts of soil moisture and pH on fungal and bacterial N(2)O production in two ecosystems, conventional farming and plantation forestry. Four treatments, antibiotic-free soil and soil amended with streptomycin, cycloheximide, or both were used to determine N(2)O production of fungi versus bacteria. Soil moisture and pH effects were assessed under 65-90 % water-filled pore space (WFPS) and pH 4.0-9.0, respectively. Irrespective of antibiotic treatments, soil N(2)O fluxes peaked at 85-90 % WFPS and pH 7.0 or 8.0, indicating that both fungi and bacteria preferred more anoxic and neutral or slightly alkaline conditions in producing N(2)O. However, compared with bacteria, fungi contributed more to N(2)O production under sub-anoxic and acidic conditions. Real-time polymerase chain reaction of 16S, ITS rDNA, and denitrifying genes for quantifications of bacteria, fungi, and denitrifying bacteria, respectively, showed that fungi were more abundant at acidic pH, whereas total and denitrifying bacteria favored neutral conditions. Such variations in the abundance appeared to be related to the pH effects on the relative fungal and bacterial contribution to N(2)O production.

Effect of soil organic matter content and pH on the toxicity of ZnO nanoparticles to Folsomia candida

Organic matter (OM) and pH may influence nanoparticle fate and effects in soil. This study investigated the influence of soil organic matter content and pH on the toxicity of ZnO–NP and ZnCl2 to Folsomia candida in four natural soils, having between 2.37% and 14.7% OM and pHCaCl2 levels between 5.0 and 6.8. Porewater Zn concentrations were much lower in ZnO–NP than in ZnCl2 spiked soils, resulting in higher Freundlich sorption constants for ZnO–NP. For ZnCl2 the porewater Zn concentrations were significantly higher in less organic soils, while for ZnO–NP the highest soluble Zn level (23mgZn/l) was measured in the most organic soil, which had the lowest pH. Free Zn2+ ion concentrations were higher for ZnCl2 than for ZnO–NP and were greatly dependent on pH (pHpw) and dissolved organic carbon content of the pore water. The 28-d EC50 values for the effect of ZnCl2 on the reproduction of F. candida increased with increasing OM content from 356 to 1592mgZn/kg d.w. For ZnO–NP no correlation between EC50 values and OM content was found and EC50 values ranged from 1695 in the most organic soil to 4446mgZn/kg d.w. in the higher pH soil. When based on porewater and free Zn2+ concentrations, EC50 values were higher for ZnCl2 than for ZnO–NP, and consistently decreased with increasing pHpw. This study shows that ZnO–NP toxicity is dependent on soil properties, but is mainly driven by soil pH.

Effect of Soil pH on Immobilization of Lead by Phosphate-Solubilizing Bacteria

Two phosphate-solubilizing bacteria were used to immobilize the lead in contaminated soil using the selective sequential extraction methods to detect the chemical forms of lead. The results showed that PSB 3-5-1-1 had higher ability of Pb immobilization compared with ID-a .The beat remediation efficiency could be obtained when pH is 6.

Soil pH Effect on Phosphate Induced Cadmium Precipitation in Arable Soil

The objective of this study was to determine soil pH conditions that allow cadmium (Cd) to precipitate as Cd minerals in phosphate (P) amended soil. Cadmium immobilization could be attributed primarily to Cd adsorption due to increase in pH and negative charge. Soil pH might not affect Cd precipitation as Cd3(PO4)2 by direct reaction of Cd and P in the studied soil, even when soil pH increased up to 9.0. However, Cd might precipitate as CdCO3 with increasing pH up to 9.0 in P untreated soil and up to 8.0 in P treated soil depending on CO2 level.

여러 안정화제가 산성 및 알칼리 토양에서 중금속 안정화에 미치는 영향

BACKGROUND: Recent studies using many amendments for heavy metal stabilization in soil were conducted in order to find out new materials. But, the studies accounting for the use of appropriate amendments considering soil pH remain incomplete. The aim of this study was to investigate the effects of initial soil pH on the efficiency of various amendments. METHODS AND RESULTS: Acid soil and alkali soil contaminated with heavy metals were collected from the agricultural soils affected by the abandoned mine sites nearby. Three different types of amendments were selected with hypothesis being different in stabilization mechanisms; organic matter, lime stone and iron, and added with different combination. For determining the changes in the extractable heavy metals, water soluble, Mehlich-3, Toxicity Characteristic Leaching Procedure, Simple Bioavailability Extraction Test method were applied as chemical assessments for metal stabilization. For biological assessments, soil respiration and root elongation of bok choy (Brassica campestris ssp. Chinensis Jusl.) were determined. CONCLUSION: It was revealed that lime stone reduced heavy metal mobility in acid soil by increasing soil pH and iron was good at stabilizing heavy metals by supplying adsorption sites in alkali soil. Organic matter was a good source in terms of supplying nutrients, but it was concerning when accounting for increasing metal availability.

The assessment of common mugwort (Artemisia vulgaris L.) and cup plant (Silphium perfoliatum L.) productivity and technological preparation for solid biofuel

The research was carried out to determine the effects of soil pH (or liming) and nitrogen (N) fertilization on the common mugwort (Artemisia vulgaris L.) and cup plant (Silphium perfoliatium L.) dry mass (DM) yield, calorific value and mechanical properties. Field experiments were set up in 2008 in Western Lithuania on a naturally acid (pH 4.2–4.4) moraine loam. According to the averaged data of four experimental years, the highest DM yield 4100 kg ha-1 of common mugwort was established in 2009, which significantly decreased in the subsequent years. And, conversely, the highest cup plant DM yield 17980 kg ha-1 was obtained in 2011. An increase in soil pH from 4.2–4.4 up to 5.6–5.7, resulting from 6.0 t ha-1 CaCO3 application, increased cup plant DM yield by 27.4%. Fertilization with 120 kg ha -1 N significantly increased common mugwort and cup plant DM yield by 34.5% and 26.7% respectively, compared with the treatment without N fertilization. We also studied the chopping quality of common mugwort and cup plant and chaff fractional composition using sieves with different mesh sizes. The chaff of cup plant was finer and more even, and thus more suitable for use for energy purposes. Plant milling quality showed cup plant particles to be smaller and more even too, and thus better suited for pressing and combustion. The highest calorific value of common mugwort (17.97 MJ kg-1) was obtained in 2010 and that of cup plant (17.48 MJ kg-1) in 2012. The calorific values of common mugwort and cup plant were influenced most by the year of cultivation and 120 kg ha-1 N application.

The effect of soil pH and dicyandiamide (DCD) on N2O emissions and ammonia oxidiser abundance in a stimulated grazed pasture soil

Nitrous oxide (N2O) is a potent greenhouse gas which is mainly produced from agricultural soils through the processes of nitrification and denitrification. Although denitrification is usually the major process responsible for N2O emissions, N2O production from nitrification can increase under some soil conditions. Soil pH can affect N2O emissions by altering N transformations and microbial communities. Bacterial (AOB) and archaeal (AOA) ammonia oxidisers are important for N2O production as they carry out the rate-limiting step of the nitrification process. A field study was conducted to investigate the effect of soil pH changes on N2O emissions, AOB and AOA community abundance, and the efficacy of a nitrification inhibitor, dicyandiamide (DCD), at reducing N2O emissions from animal urine applied to soil. The effect of three pH treatments, namely alkaline treatment (CaO/NaOH), acid treatment (HCl) and native (water) and four urine and DCD treatments as control (no urine or DCD), urine-only, DCD-only and urine + DCD were assessed in terms of their effect on N2O emissions and ammonia oxidiser community growth. Results showed that total N2O emissions were increased when the soil was acidified by the acid treatment. This was probably due to incomplete denitrification caused by the inhibition of the assembly of the N2O reductase enzyme under acidic conditions. AOB population abundance increased when the pH was increased in the alkaline treatment, particularly when animal urine was applied. In contrast, AOA grew in the acid treatment, once the initial inhibitory effect of the urine had subsided. The addition of DCD decreased total N2O emissions significantly in the acid treatment and decreased peak N2O emissions in all pH treatments. DCD also inhibited AOB growth in both the alkaline and native pH treatments and inhibited AOA growth in the acid treatment. These results show that N2O emissions increase when soil pH decreases. AOB and AOA prefer different soil pH environments to grow: AOB growth is favoured in an alkaline pH and AOA growth favoured in more acidic soils. DCD was effective in inhibiting AOB and AOA when they were actively growing under the different soil pH conditions.

Effects of Soil pH on Wheat Grain Yield and Quality

The effects of planting wheat in permanent beds with fertilization on grain yield and quality need to be better understood. An experiment was conducted at five sites during 2008 and 2009. The objective was to estimate the effects on wheat (Triticum aestivum L.) grain yield and quality of two granular forms of nitrogen (N) (urea and ammonium sulfate, AS) split applied at planting and tillering, and three sprays (urea, AS, and a fungicide) at anthesis. The granular N source affected yield, spike number, and rheological parameters depending upon the soil reaction. Dough resistance/extensibility ratio (P/L) was associated with the normalized difference vegetative index (NDVI) readings collected during tillering before the granular N application. Fungicide spray at anthesis improved yield and grain physical quality evaluated as thousand-grain weight (TGW), test weight, and hardness. Grain protein concentration (GPC) appeared to be mainly affected by environmental factors rather than fertilization practices.

Major controlling factors and prediction models for mercury transfer from soil to carrot

Soil-plant transfer models are needed to predict levels of mercury (Hg) in vegetables when evaluating food chain risks of Hg contamination in agricultural soils. A total of 21 soils covering a wide range of soil properties were spiked with HgCl2 to investigate the transfer characteristics of Hg from soil to carrot in a greenhouse experiment. The major controlling factors and prediction models were identified and developed using path analysis and stepwise multiple linear regression analysis. Carrot Hg concentration was positively correlated with soil total Hg concentration (R 2 = 0.54, P < 0.001), and the log-transformation greatly improved the correlation (R 2 = 0.76, P < 0.001). Acidic soil exhibited the highest bioconcentration factor (BCF) (ratio of Hg concentration in carrot to that in soil), while calcareous soil showed the lowest BCF among the 21 soil types. The significant direct effects of soil total Hg (Hgsoil), pH, and free Al oxide (AlOX) on the carrot Hg concentration (Hgcarrot) as revealed by path analysis were consistent with the result from stepwise multiple linear regression that yielded a three-term regression model: log [Hgcarrot] = 0.52log [Hgsoil] − 0.06pH − 0.64log [AlOX] − 1.05 (R 2 = 0.81, P < 0.001). Soil Hg concentration, pH, and AlOX content were the three most important variables associated with carrot Hg concentration. The extended Freundlich-type function could well describe Hg transfer from soil to carrot.

Determining Critical Soil pH for Sunflower Production

Soil acidity has become a major yield-limiting factor in cropping systems of the Southern Great Plains, in which winter wheat (Triticum aestivumL.) is the predominant crop. Sunflower (Helianthus annuusL.) is a strong rotational crop with winter wheat due to its draught and heat tolerance. However, the effects of low soil pH on sunflower productivity have not been explored. The objective of this study was to determine the critical soil pH and aluminum concentration (AlKCl) for sunflower. Sunflower was grown in a randomized complete block design with three replications of a pH gradient ranging from 4.0 to 7.0 at three locations with varying soil types. Soil pH was altered using aluminum sulfate (Al2(SO4)3) and hydrated lime (Ca(OH)2). Plant height, vigor, and survivability were all negatively affected by soil acidity. Sunflower yield was reduced by 10% at or below soil pH 4.7 to 5.3 dependent upon location and soil type. Levels ofAlKClabove 6.35 mg kg−1reduced seed yield by 10% or greater. We concluded that sunflower may serve as a better rotational crop with winter wheat under acidic conditions when compared to other adaptable crops.

Urease activity and its relationships to soil physiochemical properties in a highly saline-sodic soil

To ascertain the levels of urease activities (UA) and their relationships with soil physicochemical properties in salt-affected soils during reclamation, soil transects of a saline-sodic soil with different planting years under drip irrigation were intensively sampled. An enhanced soil UA in root zone (0-40 cm beneath drip emitter) was found as the planting years increased. In all transects, soil UA ranged from 0.38 to 8.53 mu g NH4+-N released g(-1) dry soil h(-1) at 37 degrees C, and showed a large spatial variability within transect. R-2 of multiple regressions increased gradually with planting years, indicating that variations in UA could be better predicted after amelioration. Path analysis showed that the negative direct effects of soil pH on UA were clearly dominant, with the direct path coefficients of -0.357 similar to -0.666 (p < 0.05). Soil organic matter yielded greater positive indirect path coefficients through pH and total nitrogen. An exponential relationship was found between soil UA and pH values (p < 0.01). Our findings demonstrate that after the cultivation under drip irrigation for 3 years, soil biological activities and fertility level increased, with the decrease of soil salinity and sodicity.

High throughput sequencing analysis of biogeographical distribution of bacterial communities in the black soils of northeast China

Black soils (Mollisols) are one of the most important soil resources for maintaining food security of China and are mainly distributed in northeast China. To understand which environmental factors influence the microbial communities and how the communities are distributed in the black soils, we collected 26 soil samples with different soil carbon contents across the black soil zone in northeast China, and the soil bacterial community compositions were estimated using high resolution bar-coded pyrosequencing. A total of 355,813 bacterial 16S rDNA sequences were obtained, which were classified into at least 35 bacterial groups. The dominant groups across all samples (>5% of all sequences) were Acidobacteria, Actinobacteria, Proteobacteria, Bacteroidetes, Chloroflexi, Gemmatimonadetes and Planctomycetes. The composition and diversity of the soil bacterial community were dominantly affected by both soil pH and soil total carbon content, and the effect of soil pH was stronger than that of soil carbon content. Variance partitioning analysis showed that geographic distance contributed 14.75% of the bacterial community variation, and soil environmental factors explained approximately 37.52% of the variation. Pairwise analysis showed that a relatively higher diversity of the bacterial community was observed at lower latitudes, suggesting that a latitudinal diversity gradient of the bacterial community might be present in the black soil zone. In general, our results indicated that contemporary factors, such as soil pH and soil carbon content, were more important than the historical factor of geographic distance in shaping the bacterial community in the black soil zone in northeast China.

Occlusive effect of soil aggregates on increased soil DTPA-extractable zinc under low soil pH causedby long-term fertilization

To investigate the effect of low soil pH caused by fertilization on soil available zinc in calcareous soil, this study was conducted based on a long-term experiment consisting of: (a) no fertilization (CT); (b) mineral fertilizer application coupled with 7500 kg/ha of wheat straw (WS-NPK); (c) mineral fertilizer application coupled with 3750 kg/ha of wheat straw (1/2WS-NPK); (d) mineral fertilizer application alone (NPK). Long-term fertilization results in a significant increase in soil DTPA-extractable zinc. However, the increased soil DTPA-extractable zinc is unavailable to crops and mainly confined to 0.25 mm &amp;gt; and 0.25 mm to 1 mm aggregates. Compared to CT, soil DTPA-extractable zinc under fertilization is more than 9.67% and 122.36% higher in 0.25 mm &amp;gt; and 0.25 mm to 1 mm aggregates, respectively. Furthermore, plant-available zinc in the 0&amp;ndash;15 cm soil layer and wheat grain zinc are both significantly positive related to soil DTPA-extractable zinc in &amp;gt; 2 mm aggregates. Therefore, plant-available zinc in the 0&amp;ndash;15 cm layer is closely associated with DTPA-extractable zinc in &amp;gt; 2 mm aggregates, and the low soil pH caused by long-term fertilization could not enhance plant-available zinc in the surface soil layer nor elevate wheat grain zinc concentration because of the occlusive effect of soil aggregates.

Influence of soil pH on the toxicity of zinc oxide nanoparticles to the terrestrial isopod Porcellionides pruinosus

The effects of soil pH on the toxicity of ZnO nanoparticles (NPs) to the terrestrial isopod Porcellionides pruinosus were evaluated. Isopods were exposed to a natural soil amended with CaCO3 to reach 3 different pH(CaCl2) levels (4.5, 6.2, and 7.3) and to standard LUFA 2.2 soil (pH 5.5) spiked with ZnO NPs (30 nm), non-nano ZnO (200 nm), and ionic Zn as ZnCl₂. Toxicity was expressed based on total Zn concentration in soil, as well as total Zn and free Zn²⁺ ion concentrations in porewater. Compared with ZnO-spiked soils, the ZnCl₂-spiked soils had lower pH and higher porewater Ca²⁺ and Zn levels. Isopod survival did not differ between Zn forms and soils, but survival was higher for isopods exposed to ZnO NPs at pH 4.5. Median effect concentrations (EC50s) for biomass change showed similar trends for all Zn forms in all soils, with higher values at intermediate pH. Median lethal concentration (LC50) and EC50 values based on porewater Zn or free Zn ion concentrations were much lower for ZnO than for ionic zinc. Zn body concentrations increased in a dose-related manner, but no effect of soil pH was found. It is suggested not only that dissolved or free Zn in porewater contributed to uptake and toxicity, but also that oral uptake (i.e., ingestion of soil particles) could be an important additional route of exposure.

The Effects of Soil pH on Elymus Repens Growth and Tissue Nutrients

The perennial, graminaceous, plant quackgrass (Elymus repens (L.) Gould) is a serious weed problem. When corn is grown continuously, the high amounts of nitrogen fertilizer applied can alter the pH of the soil, and this decrease in soil pH with time may change the weed spectrum present in corn fields. Studies were conducted to determine the effect of four different pH soils (3.7, 4.3, 5.5, 6.2) on the growth of quackgrass rhizome fragments in terms of biomass accumulation and tissue nutrient content. As the soil pH decreased from 6.2 to 3.7, quackgrass plants accumulated less shoot, rhizome and root biomass, as well as less shoot height and numbers of main axis shoots, leaves and rhizome buds. This inhibitory effect of soil pH on quackgrass growth was most apparent in the later six weeks of development, until seedhead anthesis was apparent. In the first four weeks after planting the rhizomes, the reductions in quackgrass growth were best indicated by numbers of leaves and main axis shoots, as well as by shoot height. This reduction in growth associated with lower pH soils probably was due to two mechanisms. The first mechanism could be interference with uptake and incorporation of magnesium and phosphorus into both above and below ground plant parts, as well as with copper and calcium in shoots, and zinc in rhizome and root tissue. A second mechanism could be due to toxicity caused by excessive amounts of manga- nese in all plant parts, as well as excessive boron in shoot plant parts.