matichenkof - siicon fertilizer sandy soil usa.pdf

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FINAL REPORT

For

Of Project entitled

MINIMIZING NUTRIENT LEACHING FROM

SANDY AGRICULTURAL SOILS

South Florida Water Management District.

Submitted by

University of Florida, Institute of Food and Agricultural Science.

The Principal Investigators:

Dr. V.V. Matichenkov,

Professor D. V. Calvert,

Professor G.H.Snyder

December 1, 1999

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1.0 Executive Summary

During 6 months, laboratory, column and greenhouse experiments were conducted to demonstrate the potential for using Si-rich materials to reduce P, K and N leaching from sandy soils of south Florida (native and cultivated Spodosols, cultivated Entisols and Alfisols). The Si-rich materials tested included amorphous SiO2, CaSiO3, Slag and Recmix. The experiments showed that application of Si-rich materials reduced P leaching from 40 to 70% and leaching of K, NH4+ and NO31- from 10 to 50%. The main mechanism of this process is adsorption. The adsorbed P remained in the plant-available forms. Therefore, soil treatment with Si-rich materials both reduces P leaching, and improves P nutrition of plants. Amorphous silica has specific adsorption for K. Recmix has specific adsorption for P. The data demonstrated the mechanisms of interaction among P, Si substances (soluble and solid), soil microorganisms and plants. Soluble polysilicic acids firmly adsorbed by microorganisms. By this means the soil adsorption surface may be increased. On the other hand, microorganisms blocked surfaces applied silicon-rich materials. The applied silicon-rich material had high effect on growth of Bahiagrass. The project showed the importance of using silicon substances in south Florida to prevent P pollution. Certainly, these results indicate that future field investigation of Si rich material for south Florida is both important and needed.

2.0 INTRODUCTION

The lack of phosphorus (P), nitrogen (N) and potassium (K) is a major factor limiting plant growth on sandy soils in Florida. Sandy soils often have low P retention due to (i) the essential lack of alumino-silicates and metal-oxide clay in the albic E horizon (Harris et al., 1996), and (ii) the presence of a seasonal shallow water table promoting lateral P transport within the E horizon (Mansell et al., 1991). Frequent, heavy rainfall and widespread use of irrigation and drainage lead to leaching of 20 to 80% of added nutrients and chemicals (Campbell et al., 1985; Humphreys and Pritchett, 1971; Sims et al, 1998). The biotic integrity of the Florida ecosystem has been endangered by the alterations of hydrological and nutrient regimes due to urban and agricultural development. Reduction of phosphorus in runoff from south Florida agriculture is a prerequisite to restoring and protecting the remaining natural resources. The 1994 Everglades Forever Act (EFA, Section 373.4592, Florida Status) requires that water released from the Everglades Agriculture Area into the Everglades Protection Area (EPA) meet a threshold discharge limit for P. Devepoping Best Management Practices (BMPs) to control nutrient leaching from agricultural soils is of critical importance for preserving the Everglades environment.

2.1 Silicon

2.1.1 Silicon in the soil

Si is one of the most widely distributed elements in the Earths crust. The soil layer is the most silica enriched layer of the Earths crust 40 to 70 % of SiO2 in the clay soils and from 90 to 98% in sandy soils. Silicon plays a significant role in soil formation processes. The transformation of rock and formation of secondary or sediment minerals in low temperature processes are controlled by mobile (soluble) silicon compounds (Lindsay, 1979; Perelman, 1989). In the classification of elements on the basis of mobility, Si is defined as mobile element (together with P) and an

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inert element (Perelman, 1989). The dual purposes of Si are determined by its chemical properties and possibility to create and biogeochemical active substances like monosilicic acids or fine amorphous dioxide of silicon and high-strength mineralogical structures (glass, quartz).

It is known that about 200-800 kg of Si ha-1 is removed from soil annually (Bazilevich, 1993). This occurs by leaching, horizontal migration of Si, and adsorption by plants. Probably the main silicon transport flows between soil and plants. Plants assimilate silicon as monosilicic acids (Yoshida, 1975). Various authors calculated that plants can adsorb from 70 to 700 kg of Si ha-1 (Anderson, 1990; Bazilevich, 1976). In tropical regions, plants adsorbed silicon much more than in boreal regions (Bazilevich, 1993). Most of adsorbed monomers are polymerized and transformed into amorphous silica in epidemical tissue. Plant debris is returned to soil where phytholiths serves as the source of monosilicic acids. In turn, the content of monosilicic acids control the concentration and formation polysilicic acids, organo-silicon compounds, and silicon-rich complexes (Landsay, 1979; Fotiev, 1971). The main biogeochemical cycle of silicon occurs by this means in the soil-plant system.

Most monosilicic acid in the soil is weakly adsorbed (Matichenkov, 1990). Monosilicic acid migrates very slowly in the soil profile (Khalid, Silva, 1980). Increasing monosilicic acid concentration in the soil solution results in transformation of plant-unavailable phosphates into plant-available phosphates (Matichenkov, Ammosova, 1996).

Monosilicic acids can react with Al, Fe, Mn, forming slightly soluble silicate substances (Horigushi, 1988; Lumsdon, Farmer, 1995):

Al2Si2O5 + 2H+ + 3H2O = 2Al3+ + 2H4SiO4 log Ko=15.12

Al2Si2O5(OH)4 + 6H+ = 2Al3+ + 2H4SiO4 + H2O log Ko=5.45

Fe2SiO4 + 4H+ = 2Fe2+ + 2H4SiO4 log Ko=19.76

MnSiO3 + 2H+ + H2O = Mn2+ + 2H4SiO4 log Ko=10.25

Mn2SiO4 + 4H+ = 2Mn2+ + H4SiO4 log Ko=24.45

Monosilicic acids are able to react with heavy metals (Cd, Pb, Zn, Hg and others), and form two types of substances - soluble complex compounds (Schindler et. al., 1976) and slightly soluble heavy metal silicates (Lidsay, 1979). Slight increase in monosilicic acid concentration in the solution leads to formation of complex substances of heavy metal with silicic acid anion.

At the same time, high concentration of monosilicic acids may cause full precipitation of heavy metals with formation of slightly soluble silicates (Cherepanov et al., 1994; Lindsay, 1979).

ZnSiO4 + 4H+ = 2Zn 2+ + H4SiO4 log Ko=13.15

PbSiO4 + 4H+ = 2Pb 2+ + H4SiO4 log Ko=18.45

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Polysilicic acids are an integral component of the soil solution. They affect essentially on soil density and structure (Matichenkov et.al., 1995). The mechanism of polysilicic acid formation is not clearly understood. Silicic acid polymerization is assigned to the type of condensable polymerization (Dracheva, 1975; Iler, 1979).

n(Si(OH)4) (SiO2) + 2n (H2O) Unlike monosilicic acids, polysilicic acids are chemically inert and basically act as adsorbents and form colloidal particles (Jacinin, 1994). They are sorb by minerals and form the siloxane bridges (Chadwik et al., 1987). Considering that polysilicic acids are highly saturation by water, they probably affect water holding capacity. Polysilicic acid is important for formation of soil structure (Matichenkov et al., 1995).

The above-listed properties of silicon compounds demonstrate that for describe soil processes necessary to consider information about the concentration of biogeochemically active silicon-rich substances.

We suggested that two main types silicon cycles occur in terrestrial ecosystems with predominance of accumulation of Si in the soil (accumulative type) or with predominance of removal Si from the soil (eluvial type). The accumulative type is characterized by accumulation of silicon substances in the upper soil horizon, which mainly occurs of phytholith development. Ecosystems with Mollisols, Vertisols, Ultisols usually are exemplified by this type of silicic cycle.

The eluvial type of the biogeochemical silicon cycle is inherent in the ecosysytems with clearly defined leaching or lessivage processes which occur in soils of humid tropic and subtopic regions on highly weathered parent material. 80-90% of SiO2 can be removed from ancient crust by weathering in the humid tropics (Kovda, 1973). Ecosystems with Oxisols, Spodosols, sandy Entisols are characterized by eluvial type of silicic cycle. Florida ecosystems are typical eluvial type of silicic cycle.

2.1.2 Silicon fertilizers

Silicon fertilizers are used in commercial rice and sugar cane production in the Everglades Agriculture Area (Datnoff et al., 1997; Raid et. al., 1992). Our data showed that the content of plant available silicon (monosilicic acids) and sources of biogeochemical active silicon in sandy soil are smaller then in Histosols (Matichenkov, Snyder, 1996; Matichenkov et al., 1999a). Consequently, cultivated plants (sugar cane, citrus, corn, vegetables) grown in sand soils may have a need for silicon fertilization. Silicon nutrition influences plant viability, disease- and insect-resistance (Datnoff et al., 1997). In addition, application of silicon fertilizers can increase soil adsorption capacity, and optimize physical properties and soil structure (Matichenkov et al., 1996; Jacinin, 1994).

2.1.3 P-Si interactions

Si-rich biogeochemically active substances (silicon fertilizers) usually exhibit very good adsorption properties (Rochev et al., 1980). Owing to that, leaching of potassium and other mobile nutrients from the surface soil horizon was demonstrated to be reduced by silicon fertilization (Matichenkov, 1990; Tokunaga, 1991). Solid silicon-rich substances with high surface area adsorb mobile phosphates, keeping

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them in a plant-available form (Matichenkov, 1990, Matichenkov et al, 1997; Olivera et al., 1986).

The application of silicon fertilizers results in increasing concentrations of monosilicic acids in the soil solution and their adsorption on slightly soluble phosphates of calcium, aluminium, iron, and magnesium. The next phase is the exchange of phosphate-anion by silicate-anion:

CaHPO4 + Si(OH)4 = CaSiO3 + H2O + H3PO4

2Al(H2PO4)3 + 2Si(OH)4 + H+ = Al2Si2O5 + 5H3PO4 + 3H2O

2FePO4 + Si(OH)4 + H+ = Fe2SiO4 + 2H3PO4

These reactions are followed by desorption of phosphate-anion leading to increasing content of phosphorus in the soil solution. A new equilibrium between silicate and phosphate-anions is established. Part of the newly formed mobile phosphates can be adsorbed on new mineral surfaces.

By this means, silicon fertilization can initiate two processes transformation of slightly soluble phosphates into mobile forms and physical adsorption of mobile phosphates by silicon-rich surfaces.

In addition, Si is a major mineral forming, non-toxic and non-carcinogenic element. Si is very important for both crop plants and microorganisms (Epstein, 1999). The element decreases the toxic effect of heavy metals present in mineral fertilizers and pesticides (Bocharnikova et al., 1999). Silicon-rich materials have a liming effect (Myhr and Erstad, 1996).

All there facts suggest, that Si-rich materials can be used for reducing P leaching and for keeping applied nutrients in plant-available forms

The supply of silicon-rich materials is inexhaustible in the world. They are industrial by-products from energy production, Fe, Al, and color metal industries, the chemical industry, the agriculture, and forest industry.

It has been demonstrated that the use of Al2O3 in columns for purification of natural waters can result in the concentration of P being reduced to about 0.01 mg L-1 (Cherepanov et al., 1994). But the use of Al2O3 as an alkaline or acids. Toxic solid and soluble wastes will be accumulated after each columns regeneration.

Using lime material or Si-rich material in this technology would produce a P fertilizer in the column. The columns material after saturation with P can be used in agriculture. By this means all process of water purification will be recycled.

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3.0 OBJECTIVE

The overall objective of the research was to demonstrate the effectiveness of reducing nutrient leaching through the use of silicon-rich substances, and to determine the underlying mechanisms of this process.

3.1 Hypotheses

The investigators hypothesize that biogeochemically active Si-rich materials applied to soil initiate the following processes:

1. adsorption of nutrients and pollutants on Si-rich surface , 2. mineral formation resulting in reduced nutrient leaching and in the

transformation of heavy metals into inert forms, 3. activation of the microbial population contributing to nutrient retention and

organic pollutant decomposition.

4.0 MATERIALS AND METHODS

Demonstrative experiments were conducted with Spodosols (virgin and cultivated), a cultivated Alfisol, cultivated Entisols, and quartz sand. Soil samples (0-20 cm) were taken at the Indian River Research and Education Center (Fort Pierce) and in Hendry county (near road 832 and canal C-139, and near Zipperer Farms II). Selected properties of investigated soils were presented in Table 1. Soil samples, air-dried and ground to pass a 1 mm sieve .

Table 1. Selected properties of investigated soils.

Soil Organic matter,

%

pH

(H2O)

Water extractable P, mg

kg-1

Acid extractable P, mg

kg-1

Sand, %

Virgin Spodosol 0.6.-0.8 5.0 0.2-0.7 5-12 95-97

Cultivated Spodosol 0.7-0.8 7.0-7.4 28-32 128-135 90-93

Cultivated Alfisol 0.8-1.2 8.0-8.2 5-8 135-145 85-90

Cultivated Entisol (Fort Pierce)

0.6-0.7 7.5-7.8 8-14 95-105 95-97

Cultivated Entisol (near road 832)

0.6-0.7 7.4-7.6 0.8-2.4 46-55 95-97

Cultivated Entisol (near Zipperer Farms II)

0.7-0.8 7.5-7.8 20-25 257-267 93-95

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The following Si-rich materials were studied:

1. Amorphous fine silica.

2. Calcium silicate (Wollastonite).

3. Slag (by-product from the electric production of phosphorus, Calcium Silicate Corp., TN).

4. Recmix (product of processing steel slag, PRO-CHEM Chemical Company, FL).

Lime (CaCO3) was used as well.

The chemical compositions of all materials are present in Appendix 1. Selected properties of investigated materials are presented in Table 2.

Table 2 Selected properties of investigated materials.

Material pH (H2O) Ca,% Fe, % Al,% Si, %

Amorphous fine silica (SiO2)

7.0 0 0 0 46.5

CaSiO3 8.0 34.5 0 0 24.1

Slag 7.5 27-30 0.3-0.9 4.3-14.3 18-20

Recmix 7.6 27-31 0.08-0.4 0.2-0.3 13-14

CaCO3 8.4 40 0 0 0

4.1 P adsorption by Si-rich materials.

Four replicate 0.5-g material samples were mixed with 20 mL P-bearing solutions (prepared from dissolving KH2PO4) and shaken for 24 hours. The following concentrations of P were used: 0.5, 2, and 10 mg P L-1. The samples were centrifuged and orthophosphate was determined in supernatant solution by standard method using a spectrophotometer at a wavelength of 880 nm (Eaton et al., 1995).

4.2 Nutrient adsorption by soils treated with Si-rich materials

Triplicate soil and sand samples were thoroughly mixed with the Si-rich compounds and lime treatments. The amount of the applied materials was equal to 10 t ha-1. The changes in the phosphate retention characteristic of soils treated with silicon-rich compounds and lime were tested were by standard procedure for determination P sorption (Nair, et al., 1984).

Phosphate sorption of soils mixed with various materials were measured under aerobic conditions using 2 g of air-dried, thoroughly mixed soils or sand, treated with

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20 mL of 0.01 M KCl solution containing various levels of P (10, 15, 20, 25, 30, 50, and 65 mg P L-1) in 50 mL centrifuge tubes. The tubes were placed on a shaker for a 24-h equilibration period. At the end of this period, the soil samples were centrifuged. Orthophosphate was determined in the supernatant solution by standard method using a spectrophotometer at a wavelength of 880 nm. All extractions and determinations were conducted at room temperature (24oC 5). The potassium, ammonium and nitrate sorption of soils mixed with various materials under aerobic condition was determined by using 2 g of air-dried, thoroughly mixed soils or sand, treated with 20 mL solutions containing 55 mg L-1 K, 25 mg L-1 NO3- and 20 mg L-1 NH4+ in 50 mL centrifuge tubes. The tubes were placed on a shaker for a 24-h equilibration period. At the end of this period, the soil samples were centrifuged. The K in the supernatant solution was determined by standard method on AA spectrophotometer (Spectr AA-20). NO3- and NH4+ were determined in the supernatant solution with specific-ion electrodes (Bartels, 1996; Eaton et al., 1995). All extractions and determinations were conducted at room temperature (24oC 5). 4.3. Column experiments.

The pure quartz sand, Entisols from C-139 basin, soils from Fort Pierce without incubation and soils after a two month incubation with various Si-rich materials were used in this experiment. Leaching of nutrients was modeled in a column experiment. For the quartz sand the following doses of Si-rich materials were used 10, 20 and 40 ton ha-1. For all unincubated soils the rate was 10 ton ha-1. The incubated soils were amended with 10 and 20 ton ha-1 of silicon materials. The plastic column had a volume of 60 cm3 and a diameter of 2.5 cm. The solution was added to the column at 6-8 ml h-1 using a peristaltic pump. The percolate was collected at 20 ml interval. A drop of chloroform was added to the collected solution, which was stored in a refrigerator at 4oC. A total of 300 ml or more solution was applied to each column. A minimum of 2 replications of columns and triplicate analyses of each liquid samples were conducted. Distilled water or P-bearing solutions were used for irrigation of columns. Orthophosphoric, total P and Si were analyzed in the percolate by colorimetric methods. NH4+ and NO31- were analyzed with specific ion electrodes, K was analyzed by atomic-adsorption method (Bartels, 1996; Eaton et al., 1995).

At the conclusion of the leaching period, the soils were air-dried and ground. Triplicate soil and sand samples were analyzed for mobile (water extractable) and plant-available (acid extractable, 0.1 M HCl) P by standard colorimetric methods (Bartels, 1996; Eaton et al., 1995).

In addition, the columns experiments with only Si-rich materials and/or Al2O3 or CaCO3 without soil were conducted as well. The size of the columns was a same as in column experiments with soil and sand. The rate of solutions was controlled with peristaltic pump. The column experiments without soil were conducted in 2 stages. Firstly, it was conducted an experiment: Al2O3, Al2O3: Recmix (1:1), SiO2, SiO2:Lime (1:1), SiO2:Recmix (1:1), and Lime:Recmix (1:1) in columns. When two types of materials were used in the same columns, the materials were not mixed together. The first ingredient was located in the bottom. The columns were irrigated with P bearing solution (dissolved KH2PO4) at concentration 100 g L-1 during 24 hours with rate of solution 10 ml h-1. Percolated solutions were sampled at the beginning and end of the experiment.

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The second experiment was conducted with original Recmix (Fresh Recmix) and condensed Recmix (Rock Recmix). The condensed Recmix was ground, and passed through a 3, 2 and 1 mm sieves. The fractions 1-2 and 2-3 mm in diameters were selected. The columns with the following compositions were made: fresh Recmix mixed with quartz sand (1:1), Rock Recmix 1-2 mm, Rock Recmix 2-3 mm. These columns were irrigated with solutions containing 10 and 2.5 mg L-1 of P. The columns with Rock Recmix 1-2 mm, Rock Recmix 1-2 mm with CaCO3 in button (10:1) and Rock Recmix 1-2 mm mixed with Fresh Recmix (1:1) were irrigated with distilled water, P bearing solution (100 g L-1) and canal water (100 g L-1). The rate of addition was 15 ml h-1. The percolates were sampled after 20, 40, 100, 200, 300, 400, 500 and 600 ml of irrigation. Orthophosphoric was analyzed by colorimetric methods (Eaton et al., 1995).

4.4. Incubation experiment.

Four types of soil (virgin and cultivated Spodosols, Alfisols and sandy Entisols from Fort Pierce) were treated with various doses of amorphous fine SiO2, CaSiO3, Slag, Recmix and Lime under sterile conditions (addition 2-3 ml of Glutaraldehyte 50% with distilled water), normal conditions (addition of only distilled water) and supporting microbial activity (addition of 50 mg kg-1 of tryptic soy broth (Difco Laboratories) supplemented with distilled water). During the experiment (2 months) the moisture was about 30-40% by weight, which was maintained with additions of distilled water. After 2 months, the content of monosilicic acids, polysilicic acids and acid extractable silicon were examined by elaborated and standard methods (Matichenkov et al., 1999 a). At the conclusion of the incubation the soil samples were dried and ground. The soil samples were used in the P leaching column experiment. The clay fractions from composted soils were separated by standard methods. The clay fractions were analyzed by IR-spectroscopy method with "Bohem" MB-100 with computer software "Win-Bohem Easy" at the University of Guelph.

4.5. Greenhouse experiment

The greenhouse experiment was conducted with the cultivated Entisol collected from basin C-139 near road 832. 1 kg of soil mixed with SiO2, CaSiO3, CaCO3, Slag or Recmix were added to plastic pots. The phosphate fertilizer (ground Superphosphate) was applied in the doses of 0, 50 and 100 kg P ha-1. The rates of applied Si-rich materials and lime were 10 t ha-1 for 0, 50 and 100 kg P ha-1 of superphosphate and 20 t ha-1 for 100 kg P ha-1. Bahiagrass was used as the test plant (120 seeds per pot). Each variant had 2 replications.

After seeding, the initial samples of percolate were collected from the bottom of the pot. Then each week after irrigation percolate was collected and filtered. Orthophosphate was measured in percolate by standard method using spectrophotometer at a wavelength of 880 nm with 3 replications for each pot (Eaton et al., 1995).

After 3 months, the plants were harvested. One hundred plants from each variant were examined. The weight of fresh and dried (65oC) shoots and roots were separately measured for each 10 plants. After that the dried shoots and roots were ground and the content of total P was determined by standard method (Walsh, Beaton, 1973).

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4.6. Microbial experiment

The mechanisms of microbial mineral formation and interaction between microorganisms and silicon were studied in the University of Guelph. Pseudomonas aeruginosa (PA) was used to grow biomass (Makin, Beveridge, 1996). Silicon-rich solution was prepared from amorphous silica in distilled water.

The biomass of PA was grown at 36oC in typical soy broth (Difco Laboratories) supplemented during 24 hours. After that the biomass was separated and washed in Hepes solution. The concentrated biomass was added to a Si-bearing solution with or without Al (2 mg L-1) or Fe (6 mg L-1). The final concentration of biomass was 0.6 g L-1. The initial solution contained 28.6 mg Si L-1 monosilicic acids, 2.6 mg Si L-1 low molecular polysilicic acids and 10.2 mg Si L-1 high molecular polysilicic acids. Periodically, the pH were determined with a standard electrode (Orion) in sterile and unsterile solutions.

The mixtures were sampled at 1 hour, and at 1, 3, 6, 14, and 30 days of the experiment. The content of the following forms of silicon compounds were determined: soluble monosilicic acids, low molecular polysilicic acids, high molecular polysilicic acids; weakly adsorbed on microorganisms monosilicic acids, low molecular polysilicic acids, high molecular polysilicic acids; firmly adsorbed monosilicic acids, low molecular polysilicic acids and high molecular polysilicic acids.

Triplicate 20 mL of solution were centrifuged. In supernatant solution the soluble silicic acids were tested. Monosilicic acids were examined by standard colorimetric method (Iler. 1979). Low molecular polysilicic and high molecular polysilicic acids were tested in the solution after 2 hours and 1-week of depolymerization, respectively. Depolymerization of high molecular polysilicic acids was conducted by addition of 0.5 mL of 10% NaOH solution in 20 mL of tested solution.

Depolymerizated low and high molecular polysilicic acids were measured by the molybdate method (Iler, 1979).

20 mL of distilled water was added to precipitated biomass and shaking for 1 hour. The solution was centrifuged and monosilicic acids was determined in the supernatant solution. Low molecular polysilicic acids and high molecular polysilicic acids were determined separately. These forms of silicic acids were defined as weakly adsorbed.

20 mL of distilled water was added to precipitated biomass and shaking for 24 hours. The solution was centrifuged and monosilicic acids was determined in the supernatant solution. Low molecular polysilicic acids and high molecular polysilicic acids were determined separately. These forms of silicic acids were defined as firmly adsorbed.

The content of fixed monosilicic acids were determined by calculation.

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4.7. Statistical calculation.

All data were subjected to analysis of variance. The standard deviations were calculated. Fishers coefficients was used for determining LTD05. Excel Microsoft from Office 97 was used for all calculations.

5.0 Results and Discussion.

5.1 Equilibrium system investigation.

5.1.1 Adsorption capacity of Si-rich materials and lime.

The silicon rich materials varied in their capacity to adsorb P from solution (Table 3). Amorphous silica significantly adsorbed P from the solution only at P concentration of 10 mg L-1. There was no significant adsorption from the solutions with concentration 0.5 and 2 P mg L-1 (Table 3). Other types of silicon-rich materials adsorbed P from all of the P-bearing solutions. The most effective adsorption of P was observed by Recmix (Table 3). CaCO3 adsorbed P from solutions with 2 and 10 P mg L-1 as well.

Table 3. Phosphorus in supernatant after shaking with silicon materials and centrifugation.

Original Solution 0.50 2.00 10.00

Amorphous SiO2 0.48 1.92 4.82

CaSiO3 0.24 0.48 0.94

Slag 0.39 0.43 0.67

Recmix 0.02 0.02 0.11

CaCO3 0.43 1.60 3.02

LSD05 0.06 0.08 0.10

5.1.2 Adsorption capacity of soil and sand treated with various materials

The adsorption capacity of pure quartz sand without application of any Si-rich materials or Lime (Control) was very low (Fig 1). All silicon substances and lime resulted in increasing P adsorbed from solutions as solution concentration increased. Recmix enhanced P adsorption to the greatest degree, with the content of adsorbed P varying from 10 to 200 mg P kg-1 over P solution concentrations ranging from 10 to 65 mg P L-1. Two zones of Recmix saturation by P can be distinguished (Fig. 1). A similar effect was observed for lime. Probably, Recmix and Lime has as minimum two different mechanisms of P adsorption, which define two various levels of saturation of P adsorption. Slag and SiO2 had another regularity of P adsorption in comparison with Recmix and Lime (Fig 1). Lime, Slag and SiO2 increased the adsorption capacity of

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pure quartz sand from the solution of 65 mg P L-1 from 10 to 100, 95 and 85 mg kg-1, respectively.

The determination of P adsorption in Entisols and Spodosols demonstrated that the effects of silicon-rich materials and lime applied were similar to that observed for pure quartz sand (Fig. 2, 3, 4).

Some silicon rich materials, alone, or incorporated into soil, increased adsorption of K, NO3--N and NH4+ N (Table 4). The greatest increase in K adsorption occurred with soils treated with SiO2. Probably, SiO2 has specific adsorption capacity for K like Recmix has specific adsorption for P. Other materials may lack specific adsorption, but their application can reduce the leaching of tested nutrients.

Usually it was observed the statistically significant increase of K adsorption in treated soils. The increasing NO3--N and NH4+ N adsorption was usually not significant between control and treated variations (Table 4).

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Table 4. Potassium, nitrates and ammonium in supernatant after shaking with soil treated with various materials.

Variant K, mg L-1 NO3-N, mg L-1 NH4+ N, mg L-1

Original Solution 55.0 25.0 20.0

Alfisol

Control 52.3 22.7 15.2

SiO2 40.7 21.1 13.3

CaSiO3 45.1 18.4 12.7

CaCO3 49.4 23.6 14.3

Slag 44.3 22.8 15.3

Recmix 53.0 15.4 13.8

LSD05 2.3 1.9 3.0

Entisols (Fort Pierce)

Control 54.1 24.1 20.1

SiO2 40.0 22.4 18.2

CaSiO3 45.1 20.1 16.9

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CaCO3 40.9 23.2 17.5

Slag 52.2 22.7 14.4

Recmix 51.4 21.5 14.8

LSD05 2.4 2.8 3.0

Native Spodosols

Control 53.7 23.9 19.2

SiO2 39.4 22.2 17.3

CaSiO3 47.8 21.7 18.0

CaCO3 45.5 23.1 16.4

Slag 51.8 22.7 18.2

Recmix 52.3 21.5 14.4

LSD05 2.3 2.8 2.8

Cultivated Spodosols

Control 52.1 22.4 17.9

SiO2 34.5 21.0 16.6

CaSiO3 44.1 20.3 15.7

CaCO3 47.2 24.1 14.3

Slag 51.8 23.3 13.8

Recmix 50.3 20.4 13.5

LSD05 2.5 3.0 3.0

Significant difference

No significant difference

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5.1.3 Incubating.

The content of monosilicic acids, polysilicic acids and acid extractable silicon will presented in Table 5. Lower acid extractable Si can indicate a new mineral formation (Rochev et al., 1980). The data obtained showed that in the soils where microbial population was activated and Si-rich material was added the formation of minerals started. The IR-spectroscopy analysis data did not clearly concluded formation of new minerals (Appendix 2). Therefore we cannot conduct an X-ray analysis. Perhaps more than 2 months is required to obtain information on the formation of new minerals or it is necessary more aggressive activation of microbial population.

Table 5. The content of silicon compounds in the composting experiment.

Variant Monosilicic acids,

mg Si kg-1

Polysilicic acids,

mg Si kg-1

Acid extractable mg Si kg-1

Entisol - control

Soil before any treatment

5.6 11.4 124

Sterile condition 13.2 10.0 108

Low microbial activity

14.6 8.9 103

High microbial activity

17.0 25.9 106

LSD05 1.4 1.9 25

Entisol treatment with amorphous silica, 10 t ha-1



14.1 14.5 154


29.6 10.5 163

LSD05 1.8 1.9 25

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Entisol treatment with Recmix, 10 t ha-1



56.9 4.2 663


19.5 15.2 500

LSD05 1.8 1.7 21

Entisol treatment with Recmix, 20 t ha-1



67.0 0.1 988


47.8 - 969

LSD05 1.5 1.3 24

Alfisol - control


12.4 13.6 476



13.0 7.0 411


14.6 0.3 394

LSD05 1.5 1.3 21

Alfisol treatment with Recmix, 10 t ha-1



30.1 2.4 919


32.3 - 753

LSD05 1.5 1.5 24

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31.2 6.4 1412


40.3 - 952

LSD05 1.4 1.9 24




55.4 - 1456


63.6 - 1095

LSD05 1.3 1.0 18.7

Virgin Spodosol control


8.6 6.4 88



20.2 22.6 54


26.6 6.2 52

LSD05 1.3 1.8 20

Virgin Spodosol treatment with lime, 10 t ha-1



21.6 19.2 82


23.5 27.9 83

LSD05 1.5 1.7 13

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Virgin Spodosol treatment with Recmix, 10 t ha-1



56.6 8.2 354


43.2 2.4 261

LSD05 1.4 0.6 19.3

Virgin Spodosol treatment with Recmix, 20 t ha-1



- - 531


55.8 - 373

LSD05 1.4 0.24 24

Cultivated Spodosol control


14.1 15.4 288



20.2 21.6 248


28.6 17.4 269

LSD05 1.3 1.8 24

Cultivated Spodosol treatment with amorphous silica, 10 t ha-1



33.2 24.7 380


39.2 6.3 242

LSD05 0.9 1.1 22

20

Cultivated Spodosol treatment with Lime, 10 t ha-1



13.9 4.9 216


48.9 5.8 235

LSD05 1.5 2.0 22

Cultivated Spodosol treatment with Recmix, 10 t ha-1



45.9 3.5 636


48.5 - 706

LSD05 1.4 1.2 18

Cultivated Spodosol treatment with Recmix, 20 t ha-1



60.3 5.2 905


47.2 1.9 916

LSD05 0.9 2.0 21

5.1.4 Interaction between microorganisms and soluble silicon substances

The laboratory experiments with microorganisms were used to obtain theoretical information about mechanisms of mineral formation on the microbial walls. The presence of Al or Fe simulated soil conditions; because soil solutions contain not only Si, but also numerous elements (Ca, Al, Fe, Mg, et al). All these elements affect microbial interaction with Si.

The initial solution contained 28.6 mg Si/l monosilicic acids, 2.6 mg Si L-1 low molecular polysilicic acids and 10.2 mg Si L-1 high molecular polysilicic acids and 2 mg Fe L-1 or 0.5 Al mg L-1. After 30 days of the experiment, the solution contained 37.0 mg Si L-1 of monosilicic acids, 0 mg Si L-1 of low molecular polysilicic acids and 4.4 mg Si L-1 of high molecular polysilicic acids under sterile conditions in the absence of Fe and Al; 35.7 mg Si L-1 of monosilicic acids, 2.0 mg Si L-1 of low molecular polysilicic acids and 3.2 mg Si L-1 of high molecular polysilicic acids under sterile conditions in the presence of Fe; 35.9 mg Si L-1 of monosilicic acids, 2.1 mg Si L-1 of low molecular

21

polysilicic acids and 2.3 mg Si L-1 of high molecular polysilicic acids under sterile conditions in the presence of Al. pH level was tested as 7.0 0.5 during all the experiment.

The dynamic change over time of silicic substance adsorption by Pseudomonas aeruginosa (PA) was similar in all variants (Fig. 5, 6, 7). But the equilibrium concentration of silicic acids in the solution varied among the different materials. The content of monosilicic acids in the solution in all variants increased in the first stage of interaction between solution and PA (Fig. 5). The presence of PA, or Al or Fe, increased the stability of low molecular polysilicic acids in the solution (Fig. 6).

The content of high molecular polysilicic acids in the presence of PA quickly decreased during first few days (Fig. 7).

Polysilicic acids are adsorbed by microorganisms and transformed much more intensively than monosilicic acids. Probably for the natural mineral formatting process polysilicic acids are more important component of the soil solution. By this means, the content of polysilicic acids is an important parameter for elaboration of technology and monitoring of sandy soil.

The results pioneered in demonstrating the importance of polysilicic acids in the interaction between microorganisms and soluble silicon compounds. The processes of modern mineral formation processes has been poorly investigated (Sokolova, 1975). Therefore, our data are very important and this work will be continued.

23

The data obtained are important for understanding method for reducing nutrient leaching. The application of silicon-rich material has resulted in increases both of monosilicic acids and polysilicic acids in the soil solution (Matichenkov, Ammosova 1996; Matichenkov, Snyder, 1996). Consequently, formatted polysilicic acids can be adsorbed by microorganisms. Polysilicic acids have very high surface area and can adsorbed nutrients (Iler, 1979). Without adsorption by microorganisms, polysilicic acids leached together with nutrients. Therefore, the interaction between microorganisms and polysilicic acids may increase a total mineral surface area in the soil and reduce of nutrient leaching.

5.2 Column experiments.

5.2.1 Column experiments with pure quartz.

Irrigation of quartz sand by solutions containing 2.5 mg P L-1 showed that Recmix works as filter for P. Recmix applied at 10, 20 and 40 t ha-1 reduced content of P in percolated solution from 2.5 mg P L-1 to 0.065, 0.040 and 0.035 mg P L-1 respectively (Fig 8). These data are in agreement with increasing P adsorption capacity of soil treated with Recmix. Other silicon-rich compounds had much smaller effect (Fig. 8).

The treatment of sand with amorphous silica decreased K leaching better than other tested materials (Fig. 9). Probably amorphous silica has a specific adsorption capacity by K. CaSiO3 and Recmix increased NH4+ adsorption of quartz sand (Fig. 10). Recmix was determined to be the most effective silicon-rich material for increasing NO31- adsorption (Fig. 11).

25

5.2.2 Column experiments with soil.

The irrigation by distilled water imitated heavy rain (150-300 mm/cm2). Both Entisols from basin 139 were characterized by rapid P leaching followed by stabilization of P concentration in percolated solution at the end of the experiment (Fig. 12, 13). The application of amorphous silica resulted in increasing P leaching at the start. The treatment with Lime and Slag had no effect on P leaching from the two Entisols. Chemically pure CaSiO3 reduced P leaching at the beginning of column experiments with Entisols (Fig 12, 13). The application of Recmix most dramatically decreased P leaching (Fig 12, 13).

The Spodosol was characterized by very low content of leachable P (Fig. 14). The increase in P in percolated water from 0.43 to 0.68 mg L-1 was observed at the beginning of Spodosols irrigation by distilled water. Then, the P concentration in percolated water stabilized. The application of amorphous silica resulted in a similar increase of P in percolated water and than the concentration of P in percolated solution decreased to 0.3 mg L-1 P (Fig 14). Treatment with other materials resulted in only decreasing P in percolated water. Recmix had the greatest effect on reducing P leaching (Fig 14).

Irrigation with P-bearing solution simulated P fertilization of tested soils. The content of P in percolate from Entisols near road 832 was lower than that from Zip. Farm field (Fig 15, 16). During the course of the experiment, the P concentration in percolated solution increased for soil from the area near 832 road and decreased for soil from Zip. Farm. The application of all investigated materials decreased P leaching in soil from area near 832-road field (Fig 15). Amorphous silica increased P leaching at the

26

beginning of irrigation of soil from Zip. Farm field (Fig 16). Other materials reduced P leaching. In both experiments. Recmix had the greatest effect on reducing P leaching (Fig 15, 16).

The irrigation of the Spodosol with the P-bearing solution resulted in gradually increasing P concentration in percolated solution except in soil amended with Remix (Fig. 17). The application of amorphous silica, wollastonite, Slag and Lime slightly reduced P leaching but less than in Entisols. The reduction in P leaching by Recmix was observed in the study with pure quartz sand and Entisol near 832-road field.

29

The content of mobile (water-extractable) and plant-available (acid-extractable) forms of P in pure quartz increased after irrigation by P-bearing solution (Table 6). The application of all investigated substances also resulted in an increase in both forms of P in sand. Amorphous silica had the greatest effect on water-extractable P and Recmix had the greatest effect on acid-extractable P (Table 6).

The other investigated materials (other than Lime and Recmix) applied in Entisols and Spodosols had no significant effect on the content of mobile and plant available P. Lime and Recmix slightly decreased water-extractable P and increased acid-extractable P (Table 6).

Following irrigation by distilled water, the content of water-extractable P in the soil from area near road 832 and native Spodosols treated with Si materials did not significantly change (Table 6). The content of acid-extractable P in all soils treated with Recmix and Lime changed little after irrigation with distilled water. Other variants and the control were characterized by decreasing acid-extractable P (Table 6).

The irrigation of the unamended soils by the P-bearing solution slightly increased acid-extractable P (Table 6). The content of water-extractable P increased in the soil from area near road 832 and Spodosols and decreased in the soil from Zip. Farm field (Table 6). The application of silicon-rich materials or Lime resulted in increasing acid-extractable P. In all soils, Recmix was more efficient in increasing acid-extractable P than other materials (Table 6). Amorphous silica had the least influence on this form of P. On the other hand, Recmix reduced the content of mobile P in the soils.

30

5.2.3 Column experiments after incubation of soils.

The column experiment with incubated agricultural and native Spodosols, Alfisols and Entisols (Fort Pierce) demonstrated that Si-rich materials retained their capacity for adsorption of P (Table 7, 8, 9). The experiment with incubated Spodosols demonstrated that Recmix more reduced P leaching that Lime after 2 months incubating under sterile, low microbial activity and high microbial activity (Table 6 a, 6 b). In all variations and with both types of irrigation (distilled water and P-bearing solution), Recmix decreased the leaching of P. Lime had an effect in all conditions except incubation under high microbial activity and irrigation with distilled water (Table 7 a).

The Recmix retained high adsorption capacity for P during incubation (Table 8 a, 8 b). In the first volume of percolated solution the content of P in the treatment with 20 t ha-1 of Recmix was greater than in control (Table 8 a and 8 b). But the analysis for P in the second volume of sampled percolate demonstrated that Recmix again reduce P leaching. Probably this phenomenon is connected with reaction transformation of slightly soluble P into mobile forms by monosilicic acids (Matichenkov, Ammosova, 1996).

The comparison between treatment with amorphous silica and Recmix demonstrated that amorphous silica initiated the process of transformation of slightly soluble P into mobile phosphates without adsorption (Table 9a, 9b). The increase of microbial activity in treatments whizzing amorphous silica increased P leaching. The application of Recmix reduced P leaching under all tested conditions (Table 9 a, 9 b). The low microbial activity did not decrease the adsorption properties of Recmix.

It is very important to note that the Recmix retained unique adsorption properties after 2 month incubation in all investigated soils and under sterile, low and high microbial activities (Tables 7, 8, 9).

The presence of microorganisms reduces the effect of Recmix and Lime for decreasing the leaching of P (Table 7, 9). Probably microorganisms blocked surface adsorption sites. On the other hand, the microorganism activity resulted in increased plant-available P (Table 10, 11, 12).

Most of the microorganisms are present in surface soil horizon (0-5 cm) (Ehrlich, 1990). But fertilizers are applied in soil at depths of 0-20 cm. The study suggested that the silicon-rich material application will operate in an ideal spatial arrangement. Plant-available P will increase in the surface soil level, whereas the reduction of P leaching will be realized in sub-surface horizon.

Table 6. The content of water and acid extractable P in soil and pure quartz sand before and after column experiments,

mg P kg-1.

31

Variant Before irrigation After irrigation by distilled water

After irrigation by

P-bearing solution

P water extractabl

e

P acid extractable

P water extractable

P acid extractable

P water extractabl

e

P acid extractable

Pure quartz sand

Control 0 0 - - 5.7 3

SiO2 0 0 - - 6.7 10

CaSiO3 0 0 - - 6.6 19

Slag 1.2 4 - - 5.7 22

Recmix 0.02 0.1 - - 4.5 54

Lime 0 0 - - 2.2 24

LSD05 0.7 1.8 1.5 5

32

Entisols, Basin 139, near 832 road

Control 1.9 51 2.9 25 5.4 102

SiO2 2.0 52 2.4 29 6.4 104

CaSiO3 2.1 51 2.0 31 5.2 110

Slag 2.0 50 2.1 35 4.8 107

Recmix 1.5 52 1.4 47 3.0 145

Lime 1.4 51 1.6 32 3.1 130

LSD05 1.5 14.8 1.7 8.9 1.7 10.8

33

Entisols Basin 139, Zipp. Farm

Control 23.2 262 18.3 235 19.9 281

SiO2 23.4 259 17.4 245 18.5 301

CaSiO3 24.1 258 15.5 250 14.2 294

Slag 23.1 259 14.4 241 15.6 312

Recmix 20.4 260 10.1 261 5.9 324

Lime 20.7 262 12.4 257 4.3 300

LSD05 0.9 15.1 2.1 17.9 1.2

34

Spodosols

Control 0.3 7 0.7 6 4.6 59

SiO2 0.3 8 0.6 6 4.4 64

CaSiO3 0.4 8 0.4 5 5.1 70

Slag 0.5 9 0.6 4 5.0 64

Recmix 0.2 8 0.2 7 2.4 94

Lime 0.3 9 0.2 5 3.1 65

LSD05 1.5 5 1.5 5 1.5 5

35

Table 7 a. The content of P in percolated solution after irrigation incubated native Spodosol by distilled water, mg P L-1.

Variant Volume of solution, ml/cm2

10 20 50 100 125 150

Unamended soil

Sterile condition

4.4 2.9 1.9 1.0 0.6 0.6


4.6 3.1 1.8 1.3 0.7 0.6


7.4 6.7 2.1 1.3 1.0 0.8

LSD05 0.4 0.43 0.49 0.49 0.24 0.43

36

Soil treated with Recmix 10 t ha-1

Sterile condition

0.5 0.5 0.6 0.5 0.5 0.4


0.7 0.6 0.7 0.5 0.6 0.7


3.1 2.3 1.5 1.0 0.5 0.5

LSD05 0.49 0.6 0.7 0.49 0.24 2.4

Soil treated with Lime 10 t ha-1

Sterile condition

0.8 0.7 1.0 0.7 0.7 0.9


0.6 0.9 0.8 0.5 0.5 0.4


6.5 5.8 3.9 2.9 2.5 1.6

LSD05 2.4 7.4 8.6 4.9 0.7 0.7

37

Table 7 b. The content of P in percolated solution after irrigation incubated native Spodosol by solution with 10 mg P L-1 , mg P L-1.


10 20 50 100 125 150

Unamended soil

Sterile condition

8.1 8.6 8.5 9.5 10.0 10.1


13.2 9.5 10.5 10.2 10.3 10.4


15.4 12.3 11.0 10.5 10.5 10.7

LSD05 0.8 0.7 0.5 0.7 0.7 0.5

38


Sterile condition

0.9 0.8 2.4 6.1 6.0 7.0


0.9 1.2 3.3 6.6 6.4 7.0


6.9 6.1 7.2 7.2 7.3 7.2

LSD05 0.7 0.7 0.2 0.4 0.5 0.6


Sterile condition

1.3 3.9 6.1 6.4 6.8 8.2


2.0 5.1 6.8 8.5 8.9 9.5


7.7 7.3 7.8 7.6 8.5 9.2

LSD05 0.5 0.5 0.5 0.5 0.5 0.5

39

Table 8 a. The content of P in percolated solution after irrigation incubated Alfisol by distilled water, mg P L -1.


10 20 50 100 125 150

Unamended soil

Sterile condition

0.4 1.0 0.9 0.9 0.8 0.9


0.9 1.5 1.0 1.4 1.1 1.0


3.0 4.0 2.6 3.6 3.4 3.6

LSD05 0.24 0.5 0.5 0.5 0.5 0.5

40


Sterile condition

0.2 0.8 1.3 1.5 1.5 1.7


0.5 0.8 0.7 0.8 0.8 0.8


0.8 1.8 1.9 2.0 1.3 2.0

LSD05 0.5 0.5 0.5 0.5 0.5 0.5


Sterile condition

1.2 0.9 0.8 1.3 1.0 0.8


0.3 0.4 0.5 0.6 0.6 0.6


0.2 0.3 0.3 0.4 0.3 0.3

LSD05 0.5 0.5 0.5 0.5 0.5 0.5

41

Table 8 b. The content of P in percolated solution after irrigation incubated Alfisol by solution with 10 mg P L-1, mg P L-1.


10 20 50 100 125 150

Unamended soil

Sterile condition

0.5 1.0 2.0 2.5 2.6 3.7


2.3 0.9 1.1 1.2 1.1 1.8


4.4 5.5 6.1 4.6 6.3 8.3

LSD05 0.5 0.5 0.5 0.5 0.5 0.5

42


Sterile condition

0.2 1.0 1.9 2.2 2.2 2.9


1.2 0.6 0.9 0.9 1.2 1.2


1.4 1.9 2.2 2.9 2.9 5.9

LSD05 0.5 0.5 0.5 0.5 0.5 0.5


Sterile condition

1.7 1.6 1.4 0.9 1.0 1.1


0.3 0.6 0.7 0.7 0.7 0.6


0.4 0.5 0.5 0.6 0.7 0.7

LSD05 0.5 0.5 0.5 0.5 0.5 0.5

43

Table 9 a. The content of P in percolated solution after irrigation incubated Entisol (Fort Pierce) by distilled water, mg P L-1.


10 20 50 100 125 150

Unamended soil

Sterile condition

7.1 5.9 5.3 3.5 3.6 2.1


5.6 4.9 4.0 2.9 2.5 1.7


5.3 5.2 4.5 3.1 3.4 2.3

LSD05 0.5 0.5 0.24 0.24 0.8 0.5

44


Sterile condition

0.6 1.0 1.1 1.1 1.3 1.9


0.8 0.8 0.9 1.1 0.8 1.1


1.9 2.7 3.1 3.2 3.1 2.8

LSD05 0.25 0.37 0.5 0.5 0.25 0.5

Soil treated with SiO2 10 t ha-1

Sterile condition

6.9 5.4 4.5 3.0 2.3 1.7


1.2 8.7 7.5 4.4 3.1 2.3


6.2 6.4 6.5 6.5 5.6 4.3

LSD05 0.5 0.5 0.5 0.5 0.5 0.5

45

Table 9 b. The content of P in percolated solution after irrigation incubated Entisol (Fort Pierce) by solution with 10 mg P L-1 ,

mg P L-1.


10 20 50 100 125 150

Unamended soil

Sterile condition

7.4 7.8 8.5 9.5 10.0 10.4


4.2 5.9 6.6 7.5 8.9 10.1


7.0 7.7 8.2 9.2 10.2 10.5

LSD05 0.5 0.25 0.7 0.5 0.5 0.25


46

Sterile condition

0.9 1.1 1.3 2.8 3.4 5.7


0.7 0.9 1.2 2.3 2.0 3.1


1.5 3.4 4.4 6.6 6.8 7.1

LSD05 0.5 0.7 0.4 0.5 0.9 0.9


Sterile condition

7.4 7.2 8.5 8.6 9.5 9.8


7.6 7.3 8.5 8.9 9.9 10.0


9.1 9.5 9.6 11.6 10.5 10.8

LSD05 0.5 0.5 0.5 0.5 0.5 0.5

Table 10. The content of water extractable and acid extractable P in incubated native Spodosol after and before irrigation, mg P kg-1.

47


After irrigation by P-bearing solution

Water extractable P

Acid extractable P

Water extractable P

Acid extractable P

Water extractable P

Acid extractable P

Unamended soil

Sterile condition

5.3 61 7.6 59 11.4 78


7.7 48 9.2 55 11.7 88


9.6 52 10.4 61 12.4 97

LSD05 0.9 13 1.6 10.8 1.3 17.4


48

Sterile condition

7.0 70 7.8 89 15.3 112


10.5 88 7.8 78 16.4 104


14.4 124 14.3 112 13.0 125

LSD05 1.4 20 0.4 16.2 1.4 15.5


Sterile condition

3.6 51 7.5 51 13.8 83


5.3 54 6.9 50 15.6 65


17.5 110 13.6 74 17.7 83

LSD05 1.5 20 1.5 20 1.5 20

Table 11. The content of water extractable and acid extractable P in incubated Alfisol after and before irrigation, mg P kg-1.

49



Water extractable P

Acid extractable P

Water extractable P

Water extractable P

Acid extractable P

Water extractable P

Unamended soil

Sterile condition

6.6 140 7.6 125 7.5 150


7.3 141 8.5 130 8.2 159


7.3 170 9.2 142 9.2 189

LSD05 1.2 21 0.7 24 0.7 19

50


Sterile condition

5.8 120 8.7 120 9.4 134


7.5 162 9.8 173 10.2 189


11.2 158 12.5 154 12.7 198

LSD05 0.9 19.3 1.7 17.3 1.2 13.8


Sterile condition

6.4 214 8.6 225 8.3 224


4.8 199 8.5 200 8.2 240


12.0 181 14.4 202 15.4 242

LSD05 1.5 20 1.5 20 1.5 20

Table 12. The content of water extractable and acid extractable P in incubated Entisols (Fort Piers) after and before irrigation,

mg P kg-1.

51



Water extractable P

Acid extractable P

Water extractable P

Water extractable P

Acid extractable P

Water extractable P

Unamended soil

Sterile condition

11.5 100 11.2 91 11.4 116


9.1 120 10.5 89 10.9 123


15.2 131 9.1 116 11.5 159

LSD05 0.8 19 2 7.4 1.3 20

52


Sterile condition

9.2 104 12.3 100 12.2 117


8.7 140 12.0 123 13.0 159


9.2 145 16.2 135 18.9 159

LSD05 0.7 13 1.3 18 1.5


Sterile condition

10.5 118 11.5 110 10.5 110


14.2 128 8.4 120 12.5 132


18.0 142 12.5 124 16.5 145

LSD05 1.3 20 1.5 20 1.5 20

53

5.2.4 Column experiments with Si-rich materials.

Considering that silicon-rich material have good adsorption capacity for P, additional column experiments were conducted only with silicon-rich substances in comparison with Al2O3 for purification of canal water in columns. But Al2O3-rich saturated columns will have to be restored by strong acids or alkaline. Therefore Al2O3 is not profitable for practical implication. It is hypothesized that are using Si-rich material in column for purification of the canal water will permit use of saturated material from the columns as an effective fertilizer.

P-bearing solution as Al2O3 (Table 13).

Table 13. The adsorption of P by various materials from solution with 100 g P L-1.

Column Content of P in percolated solution,

g P L-1

Start Final

Al2O3 50 65

Al2O3 : Recmix (1:1) 64 52

SiO2 61 58

SiO2 :Lime (1:1) 42 48

SiO2: Recmix (1:1) 45 51

Lime: Recmix (1:1) 45 45

LSD05 30 30

54

Recmix had unique adsorption capacity for P. Probably; this material will be very successful for column technology of natural water purification. The fresh Recmix material is mixture of dust and small particles. Using only this material in a column is impossible because of slow percolation. But fresh Recmix can be transformed into a rock consistence material. This is a strong particle. The following data demonstrated that mixture of fresh and rock Recmix cleaned solution with low concentration of P (Table 14).

Table 14. The content of P in percolated solution, g P L-1.

Variant Volume of solution (ml/cm2)

20 40 100 200 300 400 500 600

10.000 g P L-1

Fresh Recmix:sand 1:1

580 80 20 20 20 20 50 40

Rock Recmix 1-2 mm

710 420 70 70 50 100 150 200

Rock Recmix 2-3 mm

670 480 80 80 60 40 50 110

2500 g P L-1b

Fresh Recmix:sand 1:1

800 50 60 30 30 30 20 40

Rock Recmix 1-2 mm

850 460 90 80 70 60 70 70

Rock Recmix 2-3 mm

860 500 80 60 60 60 50 100

55

100 g P L-1

Rock Recmix 1-2 mm

150 70 50 50 60 30 40 50

Rock Recmix 1-2 mm + CaCO3

130 120 60 40 20 30 30 10

Rock Recmix 1-2 mm + fresh Recmix

70 50 20 10 20 20 10 20

Canal water (100 g P L-1)

Rock Recmix 1-2 mm

150 80 70 60 50 40 40 30

Rock Recmix 1-2 mm + CaCO3

120 80 50 60 40 40 30 20

Rock Recmix 1-2 mm + fresh Recmix

60 50 20 20 10 20 20 20

0

Rock Recmix 1-2 mm

100 50 70 20 10 20 20 10

56

5.3. Greenhouse experiments.

5.3.1. P in percolates solution.

The concentration of P in percolate from pots without superphosphate applied decreased gradually from 1.8-2.4 to 0.64-0.7 mg P L-1 (Fig. 18). The application of Slag and Recmix reduced P concentration by 25-40%. The application of CaCO3 did not affect on P leaching (Fig. 18).

The application of P fertilizer resulted in sharp increase of P in percolate solution associated with the dose of superphosphate (Fig. 19, 20). High P concentration in percolated solution occurred most intensively during the first month. After that, the concentration of P in percolate became stable. The application of both amorphous silica (10 t ha-1) and superphosphate resulted in increasing P in percolate during the first week (Fig. 19, 20). Amorphous silica at a high dose reduced concentration of P in percolate (Fig. 21). Probably, amorphous silica at low dose initiated transformation of plant-unavailable P into mobile form to a greater degree than adsorption of orthophosphates.

The application of other Si-rich materials resulted in reduction of P in percolate (Fig. 18, 19,20, 21). Slag and Recmix adsorbed P more than other materials and an especially great effect was observed for Recmix, which decreased P concentration in percolated water from 15.2 to 5.1 mg P L-1 and from 31.0 to 9 mg P L-1 under application of 50 kg P ha-1 with 10 t ha-1 of Recmix and 100 kg P ha-1 with 20 t ha-1 Recmix, respectively (Fig. 20, 21).

59

5.3.2 Effect of P and Si fertilizers on Bahiagrass growth.

Treatment with both phosphate and silicon resulted in increasing mass of shoots and roots (Table 15, 16). The effect of silicon fertilization was greater than that of P fertilization. This probably occurs because of several mechanisms. Firstly, P leaching decreased under application of Si-rich materials (Fig 19, 20, 21). This thesis is supported by the content of P adsorbed by Bahiagrass (Table 17). Secondly, silicon substances accelerate the growth and development of the root system (Matichenkov, 1990; Matichenkov et al., 1999 b). We suggest that silicon is accumulated in the cap cells of roots. A deficiency of Si results in reduced cap cell formation. Finally, silicon accelerates plant growth (Matichenkov 1990). An increase in biomass of shoots and roots resulted in reduced P concentration in plant tissue (Table 16).

Table 15. The weight of fresh shoots and roots of Bahiagrass after 3 month of greenhouse experiment (average for 10 plants).

Table 15. The weight of fresh shoots and roots of Bahiagrass after 3 month of greenhouse experiment (average for 10 plants).

Variant

Without P fertilizer 50 kg P ha-1 as superphosphate

100 kg P ha-1 as superphosphate

100 kg P ha-1 as superphosphate + 2 doses of tested materials

Shoots Roots Shoots Roots Shoots Roots Shoots Roots

g % g % g % g % g % g % g % g %

Control 0,57 100 0,17 100 0,84 100 0,29 100 0,89 100 0,37 100 0,89 100 0,37 100

Amorphous SiO2 0,58 102,2 0,22 133,1 0,85 100,4 0,27 91,9 0,861 96,7 0,45 123,7 1,11 124,7 0,72 194,5

CaCO3 0,47 82,6 0,14 81,9 0,59 69,6 0,31 106,6 0,92 103,6 0,38 102,7 0,99 111,2 0,64 172,9

CaSiO3 0,59 103,5 0,23 134,3 0,63 74,3 0,21 70,2 0,88 99,3 0,35 96,7 1,04 116,8 0,73 197,3

Slag 0,56 98,4 0,35 205,2 0,73 86,6 0,52 175,9 1,12 126,4 0,66 179,2 1,12 125,8 0,77 208,1

Recmix 1,12 197,5 0,97 569,1 1,14 135,2 1,14 383,2 1,48 166,7 1,37 370,2 1,63 183,1 1,07 289,3

LSD05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05

60

Table 16. The weight of dry shoots and roots of Bahiagrass after 3 month of greenhouse experiment (average for 10 plants).

Variant

Without P fertilizer 50 kg P ha-1 as superphosphate 100 kg P ha-1 as superphosphate 100 kg P ha-1 as superphosphate + 2 doses of

tested materials


g % g % g % g % g % g % g % g %

Control 0,113 100 0,037 100 0,195 100

0,0562 100 0,183 100 0,087 100 0,183 100 0,087 100

Amorphous SiO2 0,119 105,3 0,054 147,9 0,169 86,5 0,058 103,1 0,163 89,3 0,080 91,1 0,159 87,1 0,105 119,6

CaCO3 0,094 83,0 0,035 95,9 0,116 59,3 0,058 103,1 0,238 130,3 0,070 80,6 0,233 127,4 0,087 100

CaSiO3 0,109 96,4 0,058 157,4 0,138 70,5 0,056 100,4 0,149 81,5 0,051 58,6 0,217 118,7 0,094 107,1

Slag 0,101 88,5 0,066 178,3 0,116 59,3 0,068 120,8 0,205 112,1 0,097 110,8 0,246 134,8 0,133 151,5

Recmix 0,244 215,4 0,171 462,8 0,264 135,0 0,221 392,8 0,351 191,5 0,230 262,6 0,276 150,9 0,186 211,9

LSD05 0,01 0,007 0,005 0,005 0.006 0.007 0.015 0.01

61

Table 17. The content of P in shoots and roots of Bahia grass after 3 month of greenhouse experiment (mg P 100g-1).

Variant



100 kg P ha-1 as superphosphate + 2 doses

of tested materials


Control 404 346 422 306 481 388 481 388

Amorphous SiO2 367 304 464 353 522 364 520 381

CaCO3 418 450 360 362 432 378 457 348

CaSiO3 441 309 367 325 339 285 478 355

Slag 343 288 278 288 353 306 281 211

Recmix 309 246 239 211 339 239 362 381

LSD05 25 25 25 25 25 25 25 25

62

Table 18. The calculated content of total P uptake by shoots and roots of Bahiagrass after 3 month of greenhouse experiment (mg P 100-1 plants).

Variant




of tested materials


Control 2,30 0,59 3,57 0,91 4,28 1,43 4,77 1,83

Amorphous SiO2 2,14 0,69 3,94 0,97 4,49 1,66 5,78 2,74

CaCO3 1,97 0,63 2,12 1,15 3,98 1,43 4,52 2,23

CaSiO3 2,60 0,71 2,31 0,68 2,99 1,02 5,00 2,59

Slag 1,92 1,01 2,04 1,51 3,97 2,02 3,16 1,64

Recmix 3,48 2,40 2,73 2,41 5,03 3,27 5,90 4,07

63

Table 19. The content of mobile (water extract) and plant-available P (acid extract) in Entisols after greenhouse experiment (mg P kg-1 of soil).

Variant




of tested materials

Mobile P Plant-available P




Original soil 6.9 106 - - - - - -

Control 2.8 63 7.1 95 14.8 123 14.8 123

Amorphous SiO2 2.4 68 10.4 113 14.7 126 11.7 106

CaCO3 3.6 51 7.8 85 13.5 114 15.4 129

CaSiO3 3.5 67 13.1 126 12.5 128 15.6 125

Slag 4.6 65 12.6 112 12.6 129 16.2 142

Recmix 6.8 64 12.9 115 14.8 128 20.6 134

LSD05 1.0 10 1.0 10 1.0 10 1.5 15

.

65

5.3.3. Content of mobile and plant-available P in soil.

The original Entisols had 6.9 mg P kg-1 of water-extractable P and 106 mg P kg-1 of acid-extractable P (Table 19). The irrigation and Bahiagrass production decreased both forms of P. The application of Si-rich material increased both forms of plant-available P. CaCO3 reduced acid-extractable P and tended to increase water-extractable P (Table 19). Probably, silicon substances transform plant-unavailable P into plant-available form.

The application of superphosphate increased water-extractable and acid-extractable P in the soil (Table 19). The application of phosphate and silicon fertilizers also increased plant-available P.

5.4 Hypotheses.

The main parts of our hypothesis have been experimentally confirmed.

The investigation demonstrated that biogeochemically active Si-rich materials applied to soil initiate the adsorption of nutrients on Si-rich surfaces. The studies with pollutants were not included in this project.

The mineralogical investigation showed that there is a tendency to increase the amount of some secondary minerals, which were present in soil before. But new minerals did not form. The investigation of this process requires more sensitive methods of investigation (special methods for separation of clay fractions).

Our hypothesis about retention of nutrients by activation of the microbial population was supported only partially.. In actuality, interaction between microorganisms and silicon-rich material was more complicated. On one hand, microorganisms can adsorb polysilicic acids and create new mineral surfaces (Fig 7). But, on the other hand, microorganisms probably blocked the silicon-rich surface area. By this means two different processes were initiated in the soil under application of silicon-rich material and activation of microbial population. These are very important for practical implication conclusions. Soil microorganisms are concentrated in the surface soil horizon. Silicon-rich material is applied in the soil at a depth of 0-20 cm. Consequently, an increase of plant-available P will be occur in the surface soil level. A reduction of P leaching will be realized in sub-surface horizon.

5.5 Reduction of P by Lime

At present, Lime is usually used for reduction of P leaching (Haynes, 1983; Sims et al., 1998). The Ca carbonate transforms mobile P to slightly soluble form:

CaCO3 + H3PO4 = CaHPO4 + H2CO3

By this means it is possible to reduce the P leaching. But this way is not profitable for agriculture. The plant available P is converted into plant-unavailable P. This presents a conflict between environmental and agricultural organizations. Farmers must pay

66

both: for phosphate fertilizers and for Lime. In addition, the crop remains under P nutrition deficiency.

Using Si-rich material will improve this situation. Firstly, monosilicic acids formed from silicon fertilizers can transform plant-unavailable P to available forms:

CaHPO4 + Si(OH)4 = CaSiO3 + H2O + H3PO4

Secondly the mobile P adsorbed on Si-rich surface remains as plant-available P as is demonstrated by the data obtained in this project.

5.5. OVERAL conclusions.

The investigated Si-rich material have good adsorption capacity for P. The sandy soils and sand treated with amorphous silica, Calcium silicate, Slag and Recmix increased soil adsorption capacity for P, K , NO3-, and NH4+. During incubation, Si-rich material retained their adsorption properties.

The interaction between microorganisms and silicon substances has a dual effect on nutrient leaching. In one side, polysilicic acids can firmly adsorb on microbial walls and form a new surface for adsorption of nutrients. On the other hand, microorganisms can block surfaces of silicon-rich substances.

The investigation conducted demonstrated that application of Si-rich substances could initiate both processes: reduce P leaching and transform slightly soluble P into plant-available forms with adsorb mobile P. The new equilibrium between mobile, adsorbed and slightly soluble P in the soil depends on adsorption capacity and solubility of applied silicon substances. The substances with physical-chemical characteristics like Recmix can sharply reduce P leaching from sandy soils and keep P in a plant-available form. By this means, it is possible to fertilize agricultural soils with P and still protect natural waters from P contamination.

The data obtained showed that only by applying Si-fertilizers in sandy soils can P leaching be reduced from 40 to 70% and provide an increase in crop production. Leaching other nutrients (K, NO3- NH4+) was decreased under application of Si-fertilizers as well.

The greenhouse experiment demonstrated the great effect of silicon fertilizers on Bahiagrass. The greatest effect was for Recmix. The application of Recmix was more effective than application of P fertilizers. The silicon fertilizers had more effect on the evolution of the root system than on shoots of grass.

Various Si-rich materials have different capability to adsorb nutrients. Recmix has very high adsorption capacity for P. Amorphous SiO2 has specific adsorption capacity for K.

67

6.1. Future investigations.

6.1.1. Field experiments.

The next step for investigating the use of silicon to prevent P contamination of natural water is to conduct field experiments. The field demonstration will provide complete information about technology for reducing P and other agrochemical leaching and possibility to increase agriculture production in south Florida thorough the use of silicon-rich substances.

6.1.2. Column experiments.

Using a column adsorption technology for reducing P in water will be very practical if the adsorbent is cheap and recyclable. The preliminary column experiments showed that Recmix (fresh and rock) is a promising source for columns. It is possible that practical implementation of both field and column technologies will result in synergetic effects and will reduce the P content of water to the necessary level (20-10 g P L-1).

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