Protocol to Quantify the Reactivity of Carbonate Limestone for Horticultural Substrates

Abstract

The current method for comparing the reactivity of different limestones used to correct pH in horticultural substrates is based on batch trials, where the limestones are incorporated into the substrate and the pH is measured over time (typically up to 28 days). The objective was to test a laboratory approach to provide a rapid analytical test on reactivity of various limestone sources. To a lime sample, 4M hydrochloric acid (HCl) was added, and the volume of carbon dioxide (CO₂) released into a burette was measured over time. Reagent‐grade calcium carbonate (CaCO₃) and two commercially available pulverized dolomitic limestones were tested. In addition, six particle‐size fractions derived from each of the limestone samples were also evaluated for reaction rate and the corresponding pH responses. In less than 1 min after acid addition, 100% of CaCO₃ reacted, whereas it took 3.9 and 11.5 min, respectively, for 50% of the limestone samples to react, and 14 and 52 min, respectively, for 90% neutralization. Reaction rate increased as the particle size decreased; however, a similar reaction rate was observed for the particle sizes larger than 150 µm (>100 U.S. mesh). Time to 90% reaction was negatively correlated with pH response when 6 g of each lime was incorporated per L of peat substrate. It may be possible to establish a lime reactivity index, for example based on the time required for 50% or 90% reaction, and thereby provide a rapid screening of different limestone sources.     

Liming effects on some chemical and biological parameters of soil (spodosols and histosols) in a hardwood forest watershed

Acidic lakes and streams can be restored with base application (usually limestone) provided that the base does not wash out before the benefits of alkalization can be realized; liming soils of the adjoining watershed may be an alternative approach. This study was conducted to provide a scientific basis for soil liming. Plots (50 m²) with different limestone dosages (e.g. 0, 5, 10 or 15 Mg CaCO₃ ha^?1) were established on each of two different soils (a Spodosol and a Histosol) in the Woods Lake watershed of the Adirondack Park Region of New York, USA. Six months after soil liming much of the added limestone was still present in both the Spodosol and in the Histosol. Ten months after soil liming results indicated that: (1) soil pH increased (>1 unit) but mostly in the top 1 cm; (2) net N mineralization increased from 9.6 to ca. 15 µg N g^?1 d^?1 and nitrification increased from 2.8 to ca. 8 µg N g^?1 d^?1; (3) denitrification was not affected (98 µg N g^?1 d^?1); (4) CO₂ production potential decreased in the surface soil and as a function of limestone dosage (60 to 6 µmol g^?1 d^?1); and (5) soluble SO ₄ ^2? concentrations in the Histosol were not affected (105 µmol L^?1). Liming acidic forest soils with >5 Mg CaCO₃ ha^?1 may increase the soil's acid neutralizing capacity, which could provide long-term benefits for surface water acidification.     

An Assessment of the Mobile Source Contribution to PM10 and PM2.5 in the United States

Mobile sources are significant contributors to ambient particulate matter (PM) in the United States. As the emphasis shifts from PM₁₀ to PM_2.5, it becomes particularly important to account for the mobile source contribution to observed particulate levels since these sources may be the major contributor to the fine particle fraction. This is due to the fact that most mobile source mass emissions have an aerodynamic diameter less than 2.5 µm, while the particles of geological origin that tend to dominate the PM₁₀ fraction generally have an aerodynamic diameter greater than 2.5 µm. A common approach to assess the relative contributions of sources to observed particulate mass concentrations is the application of source apportionment methods. These methods include material balance, chemical mass balance (CMB), and multivariate receptor models. This paper describes a number recent source attribution studies performed in the United States in order to evaluate the range of the mobile source contribution to observed PM. In addition, a review of the methods used to apportion source contributions to ambient particulate loadings is presented.     

Particle size fractionation and metal distribution in sewage sludges

A sequential step filtration technique has been used to investigate the different particle size fractions of suspended solids in several raw, activated and digested sewage sludge samples. Liquid sludge was passed through filters with progressively smaller pore sizes, from 100 µm down to 0.2 µm. The concentrations of Cd, Cu, Ni, Pb, and Zn associated with each particle size fraction were also determined. The particle size distributions indicated that there was a greater proportion of larger particles in the raw and activated sludges than in the digested sludges. Generally in activated sludge the metals tended to be associated with the large particles of > 100 µm, whereas in raw and particularly digested sludges the metals were found in the smaller particle size fractions from 20 µm, down to 2.5 µm. Calculating specific associations in terms of mg kg^?1 the 8 to 20 µm range appears important in complexing metals. This was especially evident when comparing the sludges from the same treatment works. Generally distributions were more widespread when results were expressed as mg kg^?1 as opposed to mg L^?1.     

Pb/Ca in Thailand Coral Determined by LA-ICP-MS: Anthropogenic Pb Input of River Run-off into a Coral Reef from Urbanised Areas

In order to monitor lead pollution from urban areas to coral reefs in the Gulf of Thailand, linear and two-dimensional distributions of Pb in corals from Khang Khao Island, Thailand and Rukan-sho, Okinawa, were analysed with high resolution. Laser ablation inductively coupled plasma mass spectrometry was applied to measure Pb content in coral skeletons using synthetic Pb standards in a CaCO₃ matrix as calibration materials. Linear and two-dimensional ablation schemes were applied to determine the Pb content in corals collected from Khang Khao Island, Thailand and Rukan-sho, Okinawa. The coral skeleton was ablated by Nd:YAG laser (wavelength of 266 nm, beam diameter of 155 µm, scanning speed of 10 µm s^?1 and frequency of 10 Hz) along the growth axis, and ion counts for ²⁰⁸Pb were normalised to ⁴²Ca. Lead content in the corals was determined using a calibration curve obtained from the synthetic Pb standards (0–141 µg g^?1). The linear ablation track of the sample from Khang Khao showed over 30 peaks of Pb with an average value of 3.55 µg g^?1, while Pb content in the coral from Rukan-sho showed relatively small variation with an average value of 0.132 µg g^?1. Two-dimensional imaging of Pb in the coral skeletons was also carried out for an area of 7?×?20 mm on the sample from Khang Khao. The distribution patterns of Pb and Ba in the Thailand coral co-varied. These observations from the linear and imaging analyses suggest discontinuous inputs of anthropogenic Pb from rivers to the Gulf of Thailand.     

LIME-INDUCED CHLOROSIS

The following properties were measured on 22 soil samples from seven sites in the south east of England: total CaCO₃, active CaCO₃ apparent solubility product, particle size distribution of the CaCO₃, and pH. Active CaCO₃ was between one quarter and one half of the total for all sites except one. Apparent solubility products varied for each parent material, and increased with depth in each profile and ranged from 0.93 to 4.87 × 10^?9. Soil pH was directly related to apparent solubility product. Active CaCO₃ was closely related to the surface area. pH measured in 0.01 M CaCl₂ was the best index of yield of cauliflower, tomato, sweet white lupin and bitter blue lupin, with chlorotic symptoms increasing and yield decreasing as pH increased. The apparent solubility product of the soil carbonates and pH measured in water were also closely correlated with yield. Total and active CaCO₃ were only related to yield above limits of 20 and 10 per cent respectively and even then were poor indices of yield.     

A Module to Calculate Primary Particulate Matter Emissions and Abatement Measures in Europe

Primary particulate matter is emitted directly into the atmosphere from various anthropogenic and natural sources such as power plants (combustion of fossil fuels) or forest fires. Secondary particles are formed by transformation of SO₂, NO_x, NH₃, and VOC in the atmosphere. They both contribute to ambient particulate matter concentrations, which may have adverse effects on human health. Health hazards are caused by small particulate size, high number of especially fine (< 2.5 µm) and ultra-fine (< 0.1 µm) particles and/or their chemical composition. As part of an integrated assessment model developed at IIASA, a module on primary particulate matter (PM) emissions has been added to the existing SO₂, NO_x, NH₃ and VOC sections. The module considers so far primary emissions of total suspended particles (TSP), PM₁₀ and PM_2.5 from aggregated stationary and mobile sources. A primary PM emission database has been established. Country specific emission factors for stationary sources have been calculated within the module using the ash content of solid fuels.     

Distribution of charred plant fragments in particle size fractions of Japanese volcanic ash soils

Abstract

To gain a better understanding of the distribution of charred plant fragment C (CPFC) and its contribution to organic C (OC) in the particle size fractions of Japanese volcanic ash soils, each of four soil samples was divided into six particle size fractions, namely three sand-sized aggregate (20–53, 53–212 and 212–2,000 µm) fractions, one silt-sized aggregate (2–20 µm) fraction, and two clay-sized aggregate (< 0.2 and 0.2–2 µm) fractions. Furthermore, after HCl–HF treatment of these aggregate fractions, sub-fractions of less than specific gravity (s.g.) 1.6 g cm^?3 (< 1.6 fraction) were isolated using s.g. 1.6 g cm^?3 sodium polytungstate solution. Microscopic observation indicated that the charred plant fragments, which are black or blackish brown, were the main components in the < 1.6 fractions. Therefore, the OC in this fraction was designated as CPFC. In all the soils studied, the quantitative distribution of the CPFC of the silt-sized aggregate fractions to total CPFC of whole soils, ranging from 59 to 84%, was greatest among the aggregate fractions. The sum of the distribution (%) values of the CPFC in the three sand-sized aggregate fractions varied from 6.9 to 33%, while that in the two clay-sized aggregate fractions ranged from 1.1 to 9.4%. Similar to the CPFC, in all soils, the quantitative distribution of the OC in the aggregate fractions was greater in the silt-sized aggregate fractions (52–76%) than in the other aggregate fractions (0.1–20%). In all soils, the quantitative contribution of total CPFC to total OC of whole soils ranged from 10 to 28%. The CPFC/OC values in the aggregate fractions were 21% or more in 10 samples from a total of 24 fractions, with a maximum value of 34%. On the basis of the findings obtained in the present study, it is assumed that in Japanese volcanic ash soils the silt-sized fraction is an important reservoir of CPFC and OC, and CPFC merits attention as one of the constituents of OC in particle size fractions.     

Soil properties related to phosphate buffering in calcareous soils

Abstract

In a group of 24 related calcareous soils, derived from Jurassic oolitic limestone, there was marked variability (13‐fold) in phosphate buffering when expressed as the maximum buffer capacity. This variability was most closely related to the iron content and pH of the soils, and these together accounted for 72% of the variance. This percentage was not increased by including CaC0₃ content or organic matter, which were also correlated with the maximum buffer capacity. A high correlation with specific surface area of CaCO₃ was probably an indirect effect due to the high correlation between this variable and the Fe and pH of the soils.

The equilibrium buffer capacity, which is the traditional measure of phosphate buffering, was less variable but quite unrelated to all the soil properties measured except the soil surface area. However the maximum buffer capacity and quantity of adsorbed P together accounted for 63% of the variance in this parameter.     

Sand-Sized Limestone Treatment of Streams Impacted by Acid Mine Drainage

Direct single point, instreamapplications of limestone sand were made in twostreams severely acidified by acid mine drainage. After high flows distributed the sand downstream,dissolution of the limestone significantly reduced theacid loads in both streams. Data from the treatedstream sections and laboratory experiments showed thatthe efficiency of treatment was more dependent onlimestone particle size than CaCO₃ content. Results from the stream treated with a narrow range oflimestone sand-sized particles showed a highutilization efficiency with nearly completedissolution of the limestone. The data indicated thatmonthly addition of limestone sand may be sufficientfor complete treatment of the streams studied. Ananalysis of such a treatment scheme indicated it to behighly cost efficient when compared to other activeand passive treatment systems.     

Nutrient Availability Response to Sulfur Amendment in Histosols having Variable Calcium Carbonates

High soil pH and excessive calcium carbonate (CaCO₃) in the Everglades Agricultural Area of south Florida reduce the availability of phosphorus and micronutrients to crops. Sulfur (S) amendment is recommended to reduce soil pH and enhance nutrient supply. The study’s objective was to determine the sulfur amendment effectiveness on soil pH and nutrient availability in organic soil as CaCO₃ content increases in soil. An experiment of four S rates (0, 90,224, and 448 kg ha^?1) and three added CaCO₃ (0%, 12.5%, and 50% by volume) in organic soil was established. Sulfur application had limited effects on soil pH reduction as CaCO₃ level increased and therefore failed to enhance nutrient availability; however, it increased sulfate concentration in soils, which could be at risk for export from the field. Unexpected increases in manganese concentration with added CaCO₃ was associated with reducing conditions due to increased soil bulk density, which changed the soil physical properties.     

LIMESTONE PARTICLE SIZE AND RESIDUAL LIME CONCENTRATION AFFECT PH BUFFERING IN CONTAINER SUBSTRATES

The objective was to quantify how the concentration and particle size of unreacted “residual” limestone affected pH buffering capacity for ten commercial and nine research container substrates that varied in residual calcium carbonate equivalents (CCE) from 0.3 to 4.9 g CCE·L^?1. The nine research substrates contained 70% peat:30% perlite (by volume) with dolomitic hydrated lime at 2.1 g·L^?1, followed by incorporation of one of four particle size fractions [850 to 2000 μm (10 to 20 US mesh), 250 to 850 μm (20 to 60 US mesh), 150 to 250 μm (60 to 100 US mesh), or 75 to 150 μm (100 to 200 US mesh)] of a dolomitic carbonate limestone at 0, 1.5 or 3.0 g·L^?1. Substrate-pH buffering was quantified by measuring the pH change following either (a) mineral acid drenches without plants, or (b) a greenhouse experiment where an ammonium-based (acidic) or nitrate-based (basic) fertilizer was applied to Impatiens wallerana Hook. F. Increasing residual CCE in commercial substrates was correlated with greater pH buffering following either the hydrochloric acid (HCl) drench or impatiens growth with an ammonium-based fertilizer. Research substrates with high applied lime rate (3.0 kg·m^?3) had greater pH buffering than at 0 or 1.5 g·L^?1. At 3 g·L^?1, the intermediate limestone particle size fractions of 250 to 850 μm and 150 to 250 (20 to 60 or 60 to 100 US mesh) provided the greatest pH-buffering with impatiens. Particle fractions finer than 150 μm reacted quickly over time, whereas buffering by particles coarser than 850 μm was limited because of the excessively slow reaction rate during the experimental periods. Addition of acid from either an ammonium-based fertilizer or HCl reduced residual CCE over time. Dosage with 40 meq acid from HCl per liter of substrate or titration with HCl acid to substrate-pH of 4.5 were well-correlated with pH buffering in the greenhouse trials and may be useful laboratory protocols to compare pH buffering of substrates. With nitrate fertilizer application, residual CCE did not affect buffering against increasing pH. Residual limestone is an important substrate property that should be considered for pH management in greenhouse crop production under acidic conditions.     

Zinc sorption–desorption by sand,silt and clay fractions in calcareous soils of Iran

Zinc sorption–desorption by sand, silt and clay fractions of six representative calcareous soils of Iran were measured. Sand, silt and clay particles were fractionated after dispersion of soils with an ultrasonic probe. Zinc sorption analysis was performed by adding eight rates of Zn from 6 to 120 μmol g^?1. For the desorption experiment, samples retained after the measurement of Zn sorption were resuspended sequentially in 0.01 M NaNO₃ solution and shaken for 24 h. Results indicated that Zn sorption by soil fractions increased in the order clay > silt > sand, and correlated negatively with CaCO₃ content and positively with cation exchange capacity (CEC) and smectite content. Results indicated that for all fractions, the Langmuir equation described the sorption rates fairly well. In contrast to sorption, Zn desorption from soil fractions increased in the order sand > silt > clay, and correlated positively with CaCO₃ content, CEC and smectite content. Results showed that parabolic diffusion and two constant equations adequately described the reaction rates of Zn desorption. In general, for all soils studied, the coarser the particle size, the less Zn sorption and more Zn desorption, and this reflects much higher risk of Zn leaching into groundwater or plant uptake in contaminated soils.     

Size Characterization by Laser Granulometry of Colloids Extracted from Compost at Different Temperatures

The objective of this work was to characterize colloids extracted from composts and their potential retention in soils. Compost made of sludge and green wastes was sampled (i) during the fermentation phase and (ii) after maturation. The same kind of compost was used in a long-term field experiment at Feucherolles (France), near Paris where amended and nonamended soils were sampled. The colloidal fraction was extracted from composts in water at room temperature (20°C) and compared to the colloidal fraction extracted from the soil. Composts were also extracted by pressurized hot liquid water at 50, 125 and 175°C. The total organic carbon of the extracts was measured and the particle size distribution (PSD) of colloidal extracts was analyzed by laser granulometry. The diameters of the colloids extracted from the soil ranged between 0.040 and 0.300 μm, independently of the temperature. For composts, it varied from 0.040 to 3.200 μm when extraction was done at 20°C, while at higher temperatures, much more organic matter was extracted, and colloid diameters ranged from 0.040 μm to 0.200 μm. The water-soluble C decreased and the size of colloids recovered in water at temperatures below 50°C increased when compost maturity increased. The adsorption on soils of colloidal particles extracted from composts was characterized. The largest adsorption (up to 30% of the initial soluble C) occurred with the extracts recovered at high temperature, in relation to the more hydrophobic properties of the colloids extracted with hot water maintained in subcritical conditions. After adsorption, the particle size distribution in the colloidal fraction extracted at 20°C moved towards finer fractions; by contrast, the colloidal fraction extracted at 175°C moved towards coarser fractions. The coarsest colloids coming from the soil disappeared during the adsorption experiment, probably because of the coprecipitation with the finest colloids coming from compost.     

RETRACTED ARTICLE: Distribution of carbon,nitrogen, carbohydrate and calcium carbonate in aggregates of histosols in Shahrekord,Iran

Soil organic matter and its components play a key role in the stabilization of soil aggregates. This study aimed to investigate the distribution of organic carbon (OC), total nitrogen (TN), hot-water extractable (HWE) and dilute acid extractable (DAE) carbohydrates and CaCO₃ in water-stable aggregates in histosols of Shahrekord, Iran. Additionally, correlations between aggregate stability (mean weight diameter (MWD) values) and mentioned characters were also examined. Results showed that at all depths in all 18 profiles, larger aggregates contained more OC, TN and carbohydrate content than the smaller aggregates, whilst CaCO₃ had the opposite trend. OC, TN and carbohydrate fractions followed a consistent similar trend by aggregate size. The positive correlation between OC and TN within the aggregates was considerable. OC, TN, carbohydrate fractions and MWD significantly (P < 0.01) decreased with depth. Average concentration of CaCO₃ was almost the same in aggregates <4 mm at all depths. We observed very low values of ratios HWE:OC and DAE:OC in the study site. OC, TN and carbohydrate fractions each gave highly or very highly significant correlations with aggregate stability. We obtained significant, but weak negative correlation of CaCO₃ with aggregate stability (P = 0.05; r = ?0.23), implying that CaCO₃ is a disaggregating agent in these histosols.     

Phosphate fertilizer enhancing soil erosion: effects and mechanisms in a variably charged soil

Purpose

The extensive application of phosphate fertilizers could produce a series of environmental problems by adsorbing on the surface of soil particle and migrating into water during soil erosion. Therefore, this study is to explore the effects of phosphate on soil aggregate stability and soil erosion and to analyze the mechanisms of phosphate enhancing soil erosion from the scope of soil charge density, electric field, and particle interaction.

Materials and methods

A variable charged soil (0–20 cm) was pre-treated firstly by KCl, K₂HPO₄, and KH₂PO₄, respectively. Under the conditions of KCl, K₂HPO₄, and KH₂PO₄ solutions with concentrations of 0.0001, 0.001, 0.01, 0.1, and 1 mol L^?1, (1) the amounts of soil particle transport and erosion intensities were measured using rainfall simulation with electrolyte solutions instead of rainwater; (2) the aggregate stabilities were measured by weighing the particles and micro-aggregates of <2, 5, and 10 μm after soil aggregate breakdown in electrolyte solutions; and (3) the zeta potentials of soil particles were measured in electrolyte solutions.

Results and discussion

The application of K₂HPO₄ and KH₂PO₄ in soil strongly enhanced soil aggregate breakdown and soil erosion, while in KCl application, soil aggregates were stable and erosion did not occur. Moreover, the intensities of soil aggregate breakdown and soil erosion for K₂HPO₄ application were much stronger than that for KH₂PO₄ application. Phosphate, especially K₂HPO₄, strongly increased surface negative charge density of soil particles and thus increased the electrostatic repulsive pressure between adjacent soil particles in aggregates, and as a result, the soil erosion intensity increased. However, the surface charge density was not increased by the increased pH, specific adsorption, and dispersion force adsorption but possibly attributed to a non-classic induction force adsorption arising from the anionic non-classic polarization in the strong electric field around soil particle surface.

Conclusions

The application of phosphate decreased aggregate stability and stimulated soil erosion through increasing charge density of particle surface by a new non-classic induction adsorption of phosphate.

     

The significance of various sediment magnetic mineral fractions for tracing sediment sources in Killimicat Creek

The mineral magnetic properties of sediment are increasingly being used to determine the sources of sediment, and associated nutrients and contaminants in drainage basins. This study was undertaken to measure the relative contributions of the magnetic mineral components in sediment (i.e., components associated with surface bound Fe, the heavy mineral fraction, and as inclusions in particles) to determine the extent to which they represent the bulk of the sediment. Deposited channel sediment samples from the tributaries and downstream reach at the first major confluence in the headwaters of Killimicat Creek, New South Wales, were sieved to separate 6 particle size fractions, and the mineral magnetic properties measured to determine the relative contribution of sediment from the smaller tributary basin. The finest sand component (63–125 μm) was then separated into light and heavy mineral fractions, and magnetic measurements made on each fraction. Magnetic parameter data from the 63–125 μm fraction, measured before density separation, show a dominance of sediment (70±12%) derived from the smaller tributary basin. Measurements of the light sediment fraction give a similar result (73±13%). The proportion of the heavy mineral fraction delivered from the smaller tributary is 78±38%. The light mineral fraction of all of the samples were treated with HCl to remove surface bound Fe, and subsequent magnetic measurements show that 41–94% of the mass specific magnetic susceptibility is attributable to magnetic minerals associated with surface bound Fe. The heavy mineral component, while <4% by weight of the 63–125 μm fraction, contributes 5–40% of the total magnetic susceptibility. The results show that most of the magnetic mineral component (>60%) is associated with sediment particles, rather than the discrete heavy mineral component.     

Analysis of airborne particles sampled in the southern Appalachian mountains

Over 3 yr of particulate measurements were made at two high elevation sites in the southern Appalachian Mountains of Tennessee and Virginia. Both dichotomous samplers and filter packs were used to obtain day and night, week-long samples for subsequent elemental and ionic analysis. Total No _inf3 ^sup? (HNO₃ + No _in3 ^sup? ) and SO _inf4 ^sup2? averaged, respectively, 1.1 and 5.0 µg m^?3 at Look Rock, Tennessee and 2.0 and 6.4 µg m^?3 at Whitetop Mountain, Virginia. At Whitetop Mountain, the spring and summer seasons had the highest average SO _inf4 ^sup2? concentrations. Seasonally, total N03 varied little. The diurnal variation of elements and SO _inf4 ^sup2? was small. Only total NO _inf3 ^sup? varied substantially with highest values during the day. The fine fraction (particle diameter < 2.5 µm) accounted for about 67% of the total mass. Fine mass and elemental concentrations were generally higher at Look Rock. The elements comprising the principal mass fraction of the coarse samples (2.5 gm < particle diameter < 10 to 15 µm) were of crustal origin (e.g., Al, Si, Ca, Fe) while the element comprising the principal mass fraction of the fine samples (i.e., S) was of manmade origin. Cluster analysis identified two groups of elements at Whitetop Mountain. These groups, in both the coarse and fine fraction, were associate with a soil and an automobile emission component. At Look Rock, only a soil component was obvious.     

Effect of magnesium on crop yields within maize–green manure–T. aman rice cropping pattern on acid soil

An experiment was conducted to study the response of maize to magnesium (Mg) and to find out the residual effect of Mg and green manure (GM) on transplanted aman (T. aman) rice in the maize–GM–T. aman cropping pattern. There were six treatments: T₁ (recommended dose of fertilizer (RDF) + 0 kg Mg + 2 t CaCO₃ ha^?1), T₂ (RDF + 10 kg Mg + 2 t CaCO₃ ha^?1), T₃ (RDF + 20 kg Mg +2 t CaCO₃ ha^?1), T₄ (RDF + 30 kg Mg + 2 t CaCO₃ ha^?1), T₅ (RDF) and T₆ (2 t CaCO₃ ha^?1). The response of maize to Mg was quadratic and the optimum dose of Mg was found to be 19 kg ha^?1, which resulted in maximum yield of 10,507 kg ha^?1. The residual effect of Mg along with GM and reduced dose of chemical fertilizer resulted in significant increase of grain yield of rice. Thus, N₂₅₀P₆₀K₁₀₀Mg₁₉S₄₀Zn₅B₂ kg ha^?1 for maize, only 20 kg N ha^?1 for GM (Sesbania) and N₆₀P₉K₃₃S₁₀Zn₁B₁ kg ha^?1 for T. aman appeared as the best combination for maximizing the productivity and may be recommended for this pattern at non-calcareous light-textured soils of Bangladesh. Application of lime increased soil pH, and this together with fertilizer and GM tended to improve soil fertility and thus may be recommended for soil amelioration.     

Preferential Attachment of Escherichia coli to Different Particle Size Fractions of an Agricultural Grassland Soil

This study reports on the attachment preference of a faecally derived bacterium, Escherichia coli, to soil particles of defined size fractions. In a batch sorption experiment using a clay loam soil it was found that 35% of introduced E. coli cells were associated with soil particulates >2 μm diameter. Of this 35%, most of the E. coli (14%) were found to be associated with the size fraction 15–4 μm. This was attributed to the larger number of particles within this size range and its consequently greater surface area available for attachment. When results were normalised with respect to estimates of the surface area available for bacterial cell attachment to each size fraction, it was found that E. coli preferentially attached to those soil particles within the size range 30–16 μm. For soil particles >2 μm, E. coli showed at least 3.9 times more preference to associate with the 30–16 μm than any other fraction. We report that E. coli can associate with different soil particle size fractions in varying proportions and that this is likely to impact on the hydrological transfer of cells through soil and have clear implications for our wider understanding of the attachment dynamics of faecally derived bacteria in soils of different compositions.