Soluble Phosphorus Compounds Research Articles

Plant growth promotion of crops using phosphate solubilizing bacterial strains derived from insects

The aim of this study was to investigate insect derived bacteria for the ability to dissolve insoluble soil phosphate to release soluble phosphorus compounds, available to plants. Bacterial isolates were obtained from Diabrotica virgifera, Hermetia illucens, Oulema melanopus, and Ostrinia nubilalis. An in vitro evaluation of phosphate solubilization ability on Pikovskaya’s medium was done and the phosphate solubilizing index (PSI) was calculated for each isolate. Bacteria were tested in a greenhouse experiment on seeds of oats, wheat, triticale, barley and soybeans. After incubation, the weight and length of their aerial plant parts were measured. The highest increase in the weight of aerial parts was recorded for oats after using strain Om046 for inoculation (88.98%), then, wheat (Dv097, 31.43%), soybean (strain 96, 53.79%), and triticale (bacterial consortium, 36.9%). Bacteria used were identified as Lactococcus lactis (strains Om030 and Om046), Acinetobacter sp. (Dv123), Lactococcus garvieae (Dv097) and Rothia kristinae (strains 90 and 96). We showed that a successful application of insect derived bacteria for phosphate solubilization in soil, to promote plant growth, is possible. Innovative agriculture requires constant improvements in increasing crop growth. Thus, new sources of bacterial strains effectively promoting plant growth, are needed. We described a new source of plant growth-promoting bacteria that can be used in agriculture.

Bio-solubilization of Rock Phosphate Using Acidophilic Bacteria and Effect of Bio-Organic-Phosphate Composite on the Growth of Wheat

Acidophilic sulfur and iron oxidizing bacteria, such as Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, play a crucial role in releasing nutrients into the soil. This study utilized a mixture of these bacteria to solubilize phosphorus from phosphate rock. Acidophilic bacteria were enriched from soil samples taken from the collection pond of a coal heap constructed for biodesulfurization studies. Rock phosphate sample was supplemented with elemental sulfur (So) and pyrite (FeS2) as energy substrates for bioleaching of phosphorus. The effect of different pulp densities of the rock phosphate on biosolubilization of phosphorus elucidated that the pulp density and rock phosphate solubilization are negatively correlated. The mixture of acidophilic microorganisms solubilized 40.76% P2O5 at 10 g/L pulp density during 30 days of leaching. A comparative study showed that a two-step process is more effective for the phosphorus leaching from rock phosphate. In pot experiments under net house conditions, the acidophilic bacterial composite increased wheat grain yield by 2% and seed phosphorus content by 3%, while reducing the need for DAP fertilizer by 20%. Treating soil with BOP (a combination of phosphate rock and acidophilic bacteria) proves to be an efficient method for converting frugally soluble phosphorus compounds into readily available forms for plants.

From acidophilic to ornithogenic: microbial community dynamics in moss banks altered by gentoo penguins.

The study explores the indirect impact of climate change driven by gentoo's penguin colonization pressure on the microbial communities of moss banks formed by Tall moss turf subformation in central maritime Antarctica. Microbial communities and chemical composition of the differently affected moss banks (Unaffected, Impacted and Desolated) located on Galindez Island and Сape Tuxen on the mainland of Kyiv Peninsula were analyzed. The native microbiota of the moss banks' peat was analyzed for the first time, revealing a predominant presence of Acidobacteria (32.2 ± 14.4%), followed by Actinobacteria (15.1 ± 4.0%) and Alphaproteobacteria (9.7 ± 4.1%). Penguin colonization and subsequent desolation of moss banks resulted in an increase in peat pH (from 4.7 ± 0.05 to 7.2 ± 0.6) and elevated concentrations of soluble nitrogen (from 1.8 ± 0.4 to 46.9 ± 2.1 DIN, mg/kg) and soluble phosphorus compounds (from 3.6 ± 2.6 to 20.0 ± 1.8 DIP, mg/kg). The contrasting composition of peat and penguin feces led to the elimination of the initial peat microbiota, with an increase in Betaproteobacteria (from 1.3 ± 0.8% to 30.5 ± 23%) and Bacteroidota (from 5.5 ± 3.7% to 19.0 ± 3.7%) proportional to the intensity of penguins' impact, accompanied by a decrease in community diversity. Microbial taxa associated with birds' guts, such as Gottschalkia and Tissierella, emerged in Impacted and Desolated moss banks, along with bacteria likely benefiting from eutrophication. The changes in the functional capacity of the penguin-affected peat microbial communities were also detected. The nitrogen-cycling genes that regulate the conversion of urea into ammonia, nitrite oxide, and nitrate oxide (ureC, amoA, nirS, nosZ, nxrB) had elevated copy numbers in the affected peat. Desolated peat samples exhibit the highest nitrogen-cycle gene numbers, significantly differing from Unaffected peat (p < 0.05). The expansion of gentoo penguins induced by climate change led to the replacement of acidophilic microbiomes associated with moss banks, shaping a new microbial community influenced by penguin guano's chemical and microbial composition.

Endophytic bacteria for Cd remediation in rice: Unraveling the Cd tolerance mechanisms of Cupriavidus metallidurans CML2

The utility of endophytic bacteria in Cadmium (Cd) remediation has gained significant attention due to their ability to alleviate metal-induced stress and enhance plant growth. Here, we investigate C. metallidurans CML2, an endophytic bacterial strain prevalent in rice, showing resilience against 2400 mg/L of Cd(II). We conducted an in-depth integrated morphological and transcriptomic analysis illustrating the multifarious mechanisms CML2 employs to combat Cd, including the formation of biofilm and CdO nanoparticles, upregulation of genes involved in periplasmic immobilization, and the utilization of RND efflux pumps to extract excess Cd ions. Beyond Cd, CML2 exhibited robust tolerance to an array of heavy metals, including Mn2+, Se4+, Ni2+, Cu2+, and Hg2+, demonstrating effective Cd(II) removal capacity. Furthermore, CML2 has exhibited plant growth-promoting properties through the production of indole-3-acetic acid (IAA) at 0.93 mg/L, soluble phosphorus compounds at 1.11 mg/L, and siderophores at 22.67%. Supportively, pot experiments indicated an increase in root lengths and a decrease in Cd bioaccumulation in rice seedlings inoculated with CML2, consequently reducing Cd translocation rates from 43% to 31%. These findings not only contribute to the understanding of Cd resistance mechanisms in C. metallidurans, but also underscore CML2′s promising application in Cd remediation within rice farming ecosystems.

Phosphate and potash solubilizing bacteria from Moroccan phosphate mine showing antagonism to bacterial canker agent and inducing effective tomato growth promotion.

Most agricultural soils are facing limited phosphorus availability that challenges modern agriculture. Phosphate solubilizing microbia (PSM) has been explored extensively as potential biofertilizers for plant growth and nutrition, and harnessing phosphate rich areas could provide such beneficial microorganisms. Isolation of PSM from Moroccan rock phosphate led to the selection of two bacterial isolates, Bg22c and Bg32c, showing high solubilization potential. The two isolates were also tested for other in vitro PGPR effects and compared to a non-phosphate solubilizing bacterium Bg15d. In addition to phosphates, Bg22c and Bg32c were able to solubilize insoluble potassium and zinc forms (P, K, and Zn solubilizers) and produce indole-acetic acid (IAA). Mechanisms of solubilization involved production of organic acids as demonstrated by HPLC. In vitro, the isolates Bg22c and Bg15d were able to antagonize the phytopathogenic bacteria Clavibacter michiganensis subsp. michiganensis, causal agent of tomato bacterial canker disease. Phenotypic and molecular identification by 16S rDNA sequencing demonstrated delineation of Bg32c and Bg15d as members of the genus Pseudomonas and Bg22c as member of the genus Serratia. The two isolates Bg22c and Bg32c were further tested either alone or in a consortium and compared to the non-P, K, and Zn solubilizing Pseudomonas strain Bg15d for their efficacy to promote tomato growth and yield. They were also compared to treatment with a conventional NPK fertilizer. Under greenhouse conditions, Pseudomonas strain Bg32c remarkably improved the growth of whole plant height, root length, shoot and root weight, number of leaves and fruits, as well as fruit fresh weight. This strain also induced stomatal conductance enhancement. The strain also improved total soluble phenolic compounds, total sugars, protein, phosphorus and phenolic compounds contents compared to the negative control. All increases were more pronounced in plants inoculated with strain Bg32c in comparison with control and strain Bg15d. The strain Bg32c could be considered a potential candidate for formulation of a biofertilizer in order to improve tomato growth.

RESEARCH OF THE PROPERTIES OF PHOSPHATMOBILIZING BACTERIA PERSPECTIVE FOR INCREASING THE PRODUCTIVITY OF AGRICULTURAL GRAINS

Phosphorus is one of the main nutrients that ensure the formation of high and sustainable crop yields with a favorable quality of marketable products. One of the perspective directions for improving the phosphorus nutrition of agricultural crops is biological phosphate mobilization with the help of soil microorganisms, which promotes the transfer of sparingly soluble phosphorus compounds from soil and fertilizers into a form accessible to agricultural plants. Aboriginal soil phosphate-mobilizing bacteria were isolated from the rhizosphere soil of the northern region of the Republic of Kazakhstan. From 5 strains of phosphate-mobilizing bacteria 3 cultures with a high activity of soil phosphate mobilization were selected. Selected strains of phosphate-mobilizing bacteria are perspective as a basis for creating a complex biofertilizer for a wide range of agricultural crops. &nbsp;

Bacillus Strains as an Effective Treatment of Mobile Forms of Phosphorus in Bulgarian Soils

Strains of genus Bacillus have the potential to increase the availability of phosphorus to plants by the dissolution of inorganic phosphate, which favours the growth of plant species and that has an important economic and agricultural impact. Soils with low phosphate intensity (Lеаched chernozem) were enriched with poorly soluble phosphorus compounds and inoculated with the tested newly isolated strains from genus Bacillus (Bacillus subtilis T 2, Bacillus amyloliquefaciens T 3, Bacillus subtilis T 4, Bacillus subtilis T 10, Bacillus thuringiensis T 17 and Bacillus cereus Т 18). Six newly isolated strains from different regions in Bulgaria were identified by classical phenotypic techniques and 16S rDNA sequence analysis. Tested strains were inoculated (2 ml and 15 ml) in the soil and incubated for 25 days at 28oC. After the incubation period, the degradation of phosphorite flour to available phosphorus was examined by the classical method of Egner-Riehm and by extraction with CaCl2. A vegetation experiment was conducted with a test plant Pelargonium zonale, characterized by its ability to absorb large amounts of phosphorus. A peat substrate enriched with all macro-and microelements was used, and phosphorus was added to the medium in the form of phosphorite flour. The amounts of phosphorus absorbed by one plant Pelargonium zonale treated with newly isolated strains Bacillus subtilis T 10 and Bacillus cereus T 18 absorbed 23% more phosphorus than the control variant. As a result of the experiments, it was found that the studied strains have a positive impact on the increase of phosphorus mobility in soils with low phosphate intensity treated with hardly degradable phosphors.

ФОСФАТМОБИЛИЗУЮЩИЕ МИКРООРГАНИЗМЫ: 1. БИОРАЗНООБРАЗИЕ, ВЛИЯНИЕ НА МИНЕРАЛЬНОЕ ПИТАНИЕ РАСТЕНИЙ И ИХ ПРОДУКТИВНОСТЬ

Phosphorus is an essential plant nutrient involved in plants’ growth and development, accelerated formation of reproductive organs and other important factors for obtaining high and stable crop yields and, therefore, high-quality products. Easily absorbed phosphorus compounds obtained from soil or fertilizers are the most valuable for plants. One of the promising directions for improving the phosphorus nutrition of agricultural crops is biological phosphate mobilization that is carried out by soil microorganisms – bacteria and filamentous fungi (micromycetes). They contribute to the conversion of poorly soluble phosphorus compounds into forms accessible to higher plants. The effect of microorganisms on plants in terms of improving their mineral nutrition, in particular phosphorus, was reviewed in this article. We analysed domestic and foreign literature sources (over the last 15 years) focused on the biodiversity of soil phosphate-mobilizing microorganisms and their influence on converting insoluble phosphate to soluble forms. The features of the mechanisms of biotransformation of organic and mineral phosphates by soil microorganisms and the main criteria for screening effective isolates able to convert poorly soluble phosphorus compounds into forms available for plants were described in detail. This review also demonstrates that several microorganisms belonging to different taxonomic groups (bacteria and micromycetes) are recognized as powerful phosphate solubilizers or bioconverters of poorly soluble phosphorus compounds into water-soluble forms. We also surveyed scientific works, in which the practical application of effective strains of microorganisms that transform unavailable phosphorus compounds into available for plants was studied; and those, in which the role of microorganisms in increasing the availability of phosphorus for agricultural plants and their productivity improvement was demonstrated. A comprehensive description of microbial preparations “Agrofil”, “Biovays”, “Ekophosphorin”, “Ekovital”, “Biophosphorin”, “Albobacterin”, “Polymiksobacterin”, “Agrobacterin”, “Phosphostim”, “Fitostimophos”, “Agromik”, “Baktopin” based on phosphate-mobilizing microorganisms, developed and used in various countries to optimize mineral nutrition of cultivated plants, is given.

DYNAMICS OF THE DEVELOPMENT OF PHOSPHATE MOBILIZATION MICROORGANISMS IN COMPOSTS BASED ON SEWAGE SLUDGE IN ODESSA

To increase crop yields and soil fertility, organic fertilizers play an important role. This is because they not only enrich the soil with all the nutrients, but also improve its properties. The current state of use of organic fertilizers encourages the search for new types of local fertilizer resources. Phosphorus is directly involved in many processes of plant life, and ensuring a normal level of phosphorus nutrition — one of the main conditions for the formation of high crop yields. The soil microbiota is actively involved in the mobilization of sparingly soluble phosphates, which has a positive effect on plants, improving their phosphorus nutrition, growth, development and productivity. Therefore, phosphate-mobilizing microorganisms can become one of the components of bioorganic fertilizers. The dynamics of development of phosphate-mobilizing microorganisms in the composting of sewage sludge (ERU) of biological treatment plants (SBU) — «Northern» and «Southern» Odessa with fillers (winter wheat straw and sunflower seed husk) to increase biofertilizers with water fertilizers. Research methods: microbiological, statistical. Analysis of the dynamics of phosphate-mobilizing microorganisms during 3 months of research showed that at the beginning of composting there is a rapid development of microorganisms that dissolve organophosphates, and as the mineralization of organophosphates, the number of bacteria in this group decreases. After 60 days of composting, the development of bacteria is dissolved, which dissolve the mineral forms of phosphates. The gradual transformation of highly soluble phosphorus compounds into labile helps to reduce the number of microorganisms that dissolve both organic and mineral forms of phosphorus. The results of research indicate the possibility of obtaining bioorganic fertilizers with the participation of phosphate-mobilizing microorganisms.

Physical and chemical properties of bentonite and its influence on acid and alkaline indicators and fertility of sod-podsolic sandy loamy soil (Retisols)

The article presents data on how bentonite clay (applied at reclamation rates) affects acid-alkaline characteristics and fertility indicators of soil (sod-podsolic sandy loamy soil - retisols). The experiment was conducted in the Nizhny Novgorod region. Physical and chemical properties of the used bentonite clay were preliminary studied. It is characterized by alkaline reaction of aqueous solution (pH 10.9) and of salt extract as well (pH 9.8) and undergoes electrolytic dissociation. The micro-plot field experiment which lasted over 3 years revealed some positive effect of bentonite application. As a result, the lowering of exchangeable soil acidity (by 0.31. pHKci units) and hydrolytic soil acidity (by 0.20 mg-eqv./100 g) was recorded, substantial reduction of aluminium soluble forms content (up to 48 %) was noticed as well, meanwhile the content of exchangeable Ca 2+ and Mg 2+ increased by 0.70 and 0.24 mg-eqv./100 g correspondingly. Bentonite application contributed to humus preservation in the soil and humus content was maintained at 1.221.28 % level. Moreover, this practice helped to increase the content of soluble (available) phosphorus and potassium compounds (on average by 27-30 % depending on experiment trial). The studied bentonite clay was proved to have stabilizing effect on acid-alkaline and nutrition balances in the soil. Some interaction between mineral soil part and bentonite clay is supposed to take place which results in the reconstruction of chemically-active fine particles (so-called active mineral centers) in soil adsorption complex.

Maximizing phosphorus and potassium recycling by supplementation of lignin combustion ash from dry biorefining of lignocellulose

Lignocellulose biorefinery produces fuel ethanol and lignin residue byproduct. The combustion ash of lignin residue after electricity generation contains high amount of phosphorous and potassium elements and the recycling to farmland provides a sustainable nutrients supply. This study demonstrated a maximum scenario of water- soluble phosphorous and potassium recycling through a dry biorefining process by reduction of wastewater generation to an extremely low level, in which the soluble phosphorus and potassium compounds were preserved. For biorefining one metric ton of five different lignocellulose biomass, averagely 51–87 kg of lignin combustion ash, 0.75–1.12 kg of phosphorous or equivalent 1.75–2.57 kg of P2O5, and 1.03–2.26 kg of potassium or equivalent 1.24–2.73 kg of K2O were obtained. The recycling of the ash to farmland covered 78–90% and 100% (with surplus) of the world average phosphate and potash fertilizer use, respectively. Even for the need of farmland in China with the heavily overused phosphate and potash fertilizers, the lignin combustion replaced 17–19% of phosphate fertilizer and 30–70% of potash fertilizer. The minimum ethanol selling price was also reduced by 2.1–3.3% by the fertilizer replacement.

DISTRIBUTION AND VARIABILITY OF PHOSPHATE-MOBILIZING BACTERIA AND PHOSPHOROUS COMPOUNDS IN THE DANUBE COASTAL WATERS

In 2010-2012 on the coastal waters of theDanubeRiverthe character of the distribution and variability of phosphorus compounds, as well as the phosphate and heterotrophic bacteria were analyzed.There is lacks of bioavailable phosphorus compounds in the ecosystem of the coastal waters, which is due to excessive intake of nitrogen compounds from the Danube River basin. The number of heterotrophic and the phosphatemobilising bacteria in the surface layer of the seaside exceeds the value in the bottom layer and increases with distance from the edge of the delta. In the bottom layer at various depths the distribution of the bacteria are mainly homogenous. The number of bacteria, mobilizing phosphate from sparingly soluble compounds made 29-78% of the number of heterotrophic bacteria in the surface layer, and 44-85% in the bottom layer. The content of phosphorus compounds generally positively correlated with quantitative indices of the phosphate and heterotrophic bacteria, due to the leading role of "microbial loop" in the biological cycle of phosphorus in the coastal water ecosystem. Negative correlation of the coefficients between the number of bacteria and soluble inorganic compounds and organic phosphorus compounds (p &lt;0.05) were registered only for the bottom layer in November 2012, which is probably due to the full utilization of phosphorus by bacteria and its accumulation in cells.Abiotic environmental factors - temperature and salinity - have no significant impact on the abundance of bacteria. Microbial degradation of organic matter is related to the saturation of water with oxygen and is characterized by an inverse relationship with the number of bacteria in the warm season, and direct - in the cold. Revealed correlations enhance understanding of the ways of phosphorus transformation in water column and the role of bacteria in these processes.

PHOSPHATE-MOBILIZING BACTERIA IN WATER COLUMN AND SEDIMENTS OF ESTUARIES OF NORTH-WESTERN BLACK SEA REGION

Number of phosphate-mobilizing bacteria has been investigated in the water column and in the sediments of the estuaries of North-Western Black Sea Region.The aim was to determine the number of phosphate-mobilizing bacteria in the water column and bottom sediments of estuaries17 samples of water and bottom substrates from coastal area in each estuary in July-August 2012.The highest abundance of soluble inorganic compounds and organic phosphorus compounds in the sediments was observed in Khadzhibey (an average 85.8 thousand CFU/g) and Dofinovskiy Limans (331.6 thousand CFU/g) respectively; the lowest – in the Tiligul Liman (9.5 and 40.3 thousand CFU/g). The greatest number of microorganisms in the water column observed in Dofinovskiy (17.0 thousand CFU/g) and Grigorievskiy Limans (13.8 thousand CFU/g), respectively, the lowest – in Tiligul Liman (1.6 and 1.4 thousand CFU/g). A significant part of phosphate-mobilizing bacteriaaccumulates in sediments of estuaries, where their abundance is 10-100 times more than in the samples ofOdessaregion shelf of North-Western Black Sea Region. In the water column the difference in these water bodies is 2.0-2.5 times. The data on the number of phosphate-mobilizing bacteria in the limans of North-Western Black Sea Region may be one of indicators of eutrophication of aquatic ecosystems.

On Pretreatment Experimental Study of Yunnan Phosphorus Building Gypsum

This paper studied effect of different pretreatment process on Yunnan phosphorus building gypsum strength and crystal morphology such as washing method, lime neutralization method, flotation method and Hans method. A lots experiment result indicated that basic properties of phosphorus building gypsum of different pretreatment methods could satisfy related building materials products technology requirements. While inorganic impurities could be effectively removed by lime neutralization method and washing method, as well as organics could be better removed by flotation method, however, compared with other methods, the Hans method possessed the best effect about removing soluble phosphorus, fluorine and organic compounds in phosphogypsum , and had other benefit such as low cost, easy operated and high strength.

Trend and mechanisms of transformation of natural sorption barriers in acid soils under phosphate loading

The current status of studies on chemisorption of phosphate anions on soil aluminum(iron)-bearing sorbents has been analyzed. The theoretical possibility of the formation of soluble phosphorus compounds during chemisorption was supported by experiments. It was shown that a decrease in efficiency of aluminum (iron)-bearing mineral and humus-mineral sorbents is related to the peculiar transformation of their phosphatized surfaces with formation of soluble metallophosphate anionic complexes. Mechanisms of the decrease in the efficiency of soil sorbents and their destruction are considered.

PECULIARITIES OF PHOSPHOROUS NUTRITION OF WINTER WHEAT UNDER THE INFLUENCE OF MINERAL FERTILIZERS AND BACTERIZATION

The paper describes peculiarities of formation of microorganisms associations, capable of hydrolysis of hardly soluble phosphorus compounds as well as content dynamics of labile phosphorus in rhizosphere soil, winter wheat productivity and phosphorus carry-over with yield in field experiments without bacterization and at presowing seeds inoculation with microbial preparation Polymyxobacterin on meadow chernozem soils on different agricultural backgrounds. Microbial preparation was shown to be an active optimization element of phosphorus nutrition of winter wheat plants especially on mineral backgrounds.

Early response of plant cell to carbon deprivation: in vivo31P‐NMR spectroscopy shows a quasi‐instantaneous disruption on cytosolic sugars, phosphorylated intermediates of energy metabolism, phosphate partitioning, and intracellular pHs

• In plant cells, sugar starvation triggers a cascade of effects at the scale of 1-2 days. However, very early metabolic response has not yet been investigated. • Soluble phosphorus (P) compounds and intracellular pHs were analysed each 2.5 min intervals in heterotrophic sycamore (Acer pseudoplatanus) cells using in vivo phosphorus nuclear magnetic resonance ((31)P-NMR). • Upon external-sugar withdrawal, the glucose 6-P concentration dropped in the cytosol, but not in plastids. The released inorganic phosphate (Pi) accumulated transiently in the cytosol before influx into the vacuole; nucleotide triphosphate concentration doubled, intracellular pH increased and cell respiration decreased. It was deduced that the cytosolic free-sugar concentration was low, corresponding to only 0.5 mM sucrose in sugar-supplied cells. • The release of sugar from the vacuole and from plastids is insufficient to fully sustain the cell metabolism during starvation, particularly in the very short term. Similarly to Pi-starvation, the cell's first response to sugar starvation occurs in the cytosol and is of a metabolic nature. Unlike the cytoplasm, cytosolic homeostasis is not maintained during starvation. The important metabolic changes following cytosolic sugar exhaustion deliver early endogenous signals that may contribute to trigger rescue metabolism.

Solubilization of Morocco phosphorite by Aspergillus niger

Phosphorus containing fertilizers have an important role in agriculture. Conventionally phosphate fertilizers are obtained by rock phosphate (RP) dissolution using mineral acids. Biotechnological methods can be a promising alternative in RP processing. The influence of Aspergillus niger strain, the composition of a nutritive medium, Morocco phosphorite (MP) concentration in the liquid medium, the time of bioconversion and the preliminary mechanical activation (PMA) of MP on the phosphorite microbial solubilization has been presented. The phosphorus concentration (as P2O5), citric acid production, glucose concentration and pH in the cultural medium were monitored. The phosphate concentration was expressed as water soluble – α1 (in the native cultural liquid), citrate soluble – α2 (after treating the biomass and remaining mineral mass with citric acid) and biomass available phosphorus – α3. Phosphate dissolution was not strongly correlated both with the citric acid production and the incubation period. When the fungi were grown without water soluble phosphorus compounds the MP solubilization had higher values. A maximum of 94.80% total P2O5 extraction was achieved. The PMA activity does not facilitate MP dissolution during the bioconversion.

Bio-decomposition of rock phosphate containing pyrites by Acidithiobacillus ferrooxidans

Leaching soluble phosphorus from rock phosphate containing pyrites by Acidithiobacillus ferrooxidans (A. f.) is feasible, and the reaction mechanism is as follows. Pyrites are oxidized by A. f. to produce H2SO4 and FeSO4; the rock phosphate is decomposed by H2SO4, forming soluble phosphorus compounds; and Fe2+ from FeSO4 is oxidized to Fe3+, providing energy for the growth of A. f.. In this process, as H2SO4 is produced in the reaction, an acidic condition in the culture medium is formed, which benefits the growth of A. f. and aids both continuous oxidation of pyrites and leaching of soluble phosphorus from rock phosphate. The fraction of phosphorous leached can reach the largest in the presence of 1.0 g/L Fe3+, 200 mg/L Mg2+ and 400 mg/L NH4 +. The optimal technological parameters on the fraction of phosphorous leached are as follows: the volume fraction of inocula of A. f., the mass ratio of pyrites to rock phosphate and the pH value are in ranges of 5%–25%, 3:1–5:1 and 1.8–2.2, respectively.

The Use of Grassed Buffer Strips to Remove Pesticides, Nitrate and Soluble Phosphorus Compounds from Runoff Water

Experiments on grassed buffer strips have been conducted since 1993 by ITCF (Institut Technique des Cereales et des Fourrages) at three research farms (La Jailliere, Bignan and Plelo). Literature data and conclusions drawn from previous work with isoproturon and diflufenican were confirmed in a range of soil and cropping conditions: grassed buffer strips are effective in restricting pollutant transfer in runoff; those with widths of 6, 12 and 18 m reduced runoff volume by 43 to 99·9%, suspended solids by 87 to 100%, lindane losses by 72 to 100% and loss of atrazine and its metabolites by 44 to 100%. More than 99% of isoproturon and 97% of diflufenican residues in runoff were removed by buffer strips. Nitrate and soluble phosphorus in runoff were reduced by 47 to 100% and by 22 to 89%, respectively. At La Jailliere, a rainfall simulator was used in 1995 to verify that buffer strips are still effective in conditions of intense runoff. Investigation of the influence of sowing direction during the 1994–95 cropping period at Bignan showed that sowing perpendicular to the slope seemed to be beneficial in reducing pesticide content in runoff. © 1997 SCI.