Incorporation Of Gypsum Research Articles

Influence of Gypsum on the Residual Properties of Fly Ash-Slag-Based Alkali-Activated Concrete

High-temperature exposures of concrete lead to serious damage in concrete structures, resulting in the significant decay of mechanical properties and spalling of concrete. Alkali-activated concretes (AAC) of blended aluminosilicate precursors and activators have been proven to have higher thermal endurance than conventional portland cement concrete. Incorporation of gypsum (GY) in alkali-activated systems has proven to positively impact the mechanical properties when adopted in controlled amounts. GY releases SO42- to the binder system, which helps in the formation of ettringites, along with Ca2+, which leads to the formation of hydrates. This causes a reduction in porosity and improves strength gain. Incorporation of GY into the fly ash-slag-based alkali-activated system further improves thermal endurance by retaining considerable residual strengths even after 800°C exposure. In the present study, the influence of GY on the residual mechanical properties of fly ash-slag-based AAC is investigated to explore the thermal endurance of the ternary mix at elevated temperatures. The mechanical properties of fly ash (FA), Ground Granulated Blast Furnace Slag (GGBS), and gypsum (GY) ternary blended AAC subjected to elevated temperatures are studied in comparison with conventional portland cement concrete (control mix). AAC design mixes with varying proportions of GY as a replacement to FA-GGBS precursor are tested for mechanical properties to obtain the optimum mix. The residual mechanical properties of the FA-GGBS-GY optimum ternary AAC mix are obtained after exposure to elevated temperatures up to 800°C. The morphology and microstructural characteristics of AAC are studied by Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) analyses to investigate the influence of gypsum on the thermal endurance of concrete when exposed to elevated temperatures. Improved thermal endurance is observed for AAC when FA-GGBS precursors are replaced with 5% of GY as compared to the thermal endurance of conventional portland cement concrete (PCC) of the same compressive strength. Doi: 10.28991/CEJ-2024-010-03-017 Full Text: PDF

Effects of flue gas desulfurization gypsum incorporation and curing temperatures on magnesium oxysulfate cement

In this study, the industrial solid waste flue gas desulfurization gypsum (FGDG) was incorporated to the magnesium oxysulfate cement (MOSC). The study mainly focused on the effects of different dosages of FGDG and the initial curing temperature on characteristics of MOSC. The mechanical properties of MOSC were evaluated with compressive strength, softening coefficient and volumetric stability. The microstructure and hydration product composition of the cements were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that with the increase of FGDG dosing, MOSC showed a trend of decreasing compressive strength. However, 40 °C curing can improve the compressive strength of MOSC. The 28-day compressive strength of MOSC could reach up to 56.6 MPa under 40 °C curing, which was 12.5 % higher than that under 20 °C curing, and the softening coefficient could reach 0.99. Besides, it was confirmed by SEM and XRD that the curing at 40 °C curing contributed more to the generation of hydration product 5 Mg(OH)2·MgSO4·7H2O in MOSC, and the structure showed compactness. The microstructural analysis was consistent with the results of mechanical property tests.

Understanding the Influence of Gypsum upon a Hybrid Flame Retardant Coating on Expanded Polystyrene Beads.

A low-cost and effective flame retarding expanded polystyrene (EPS) foam was prepared herein by using a hybrid flame retardant (HFR) system, and the influence of gypsum was studied. The surface morphology and flame retardant properties of the synthesized flame retardant EPS were characterized using scanning electron microscopy (SEM) and cone calorimetry testing (CCT). The SEM micrographs revealed the uniform coating of the gypsum-based HFR on the EPS microspheres. The CCT and thermal conductivity study demonstrated that the incorporation of gypsum greatly decreases the peak heat release rate (PHRR) and total heat release (THR) of the flame retarding EPS samples with acceptable thermal insulation performance. The EPS/HFR with a uniform coating and the optimum amount of gypsum provides excellent flame retardant performance, with a THR of 8 MJ/m2, a PHRR of 53.1 kW/m2, and a fire growth rate (FIGRA) of 1682.95 W/m2s. However, an excessive amount of gypsum weakens the flame retardant performance. The CCT results demonstrate that a moderate gypsum content in the EPS/HFR sample provides appropriate flame retarding properties to meet the fire safety standards.

Effect of Gypsum Waste Inclusion on Gasification of Municipal Solid Waste

Abstract Sustainable disposal techniques of municipal solid wastes (MSW) are essential for effective materials recovery and energy management. Synergistic incorporation of gypsum waste from the construction and demolition (C&D) sector is explored here for the low techno-economic viability of MSW in waste-to-energy facilities. Co-processing of MSW with this low-value gypsum can potentially provide improved product recovery and simultaneously furnish economic viability. To understand the impact of gypsum incorporation into MSW conversion, we tested synthetic MSW and a 1:1 mixture of MSW with gypsum from drywall wastes and compared their micro-scale mass loss kinetics along with macro-scale syngas evolution and conversion at different temperatures, and in pyrolytic and oxidizing environments. Gypsum incorporation led to increased syngas production and decreased char yields as the char was oxidized by CaSO4. Thermogravimetric analysis (TGA) revealed two different temperature zones of gypsum interaction with MSW depending on the oxidation concentration in the environment. Adding 50% gypsum only changed the final ash yield by 10% in pyrolysis conditions suggesting the viability of gypsum incorporation. While the addition of gypsum led to delayed evolution of H2 and CO, the cumulative yields of H2 and CO2 increased significantly and the yield of CO changed minimally. Additionally, hydrocarbon by-products such as CH4 decreased by gypsum addition. The results showed improved syngas yield and uniformity, as well as operational conditions from the gypsum interaction with MSW which can help in the further development of gypsum waste incorporation.

Improvement mechanism of water resistance and volume stability of magnesium oxychloride cement: A comparison study on the influences of various gypsum

The development of magnesium oxychloride cement can effectively utilize the waste of potash industry and reduce its harm to the environment. Although magnesium oxychloride cement paste (MOCP) has excellent performance in dry environment, its performance is greatly deteriorated in water or humid environment, which severely limits its practical application. In order to improve the water resistance of MOCP, MOCP was modified by various gypsum in this study, and the intrinsic mechanism was explored. Results showed that replacing MgO with gypsum delayed the setting time of MOCP and effectively improved its volume stability. Although the incorporation of gypsum reduced the 14-d air-cured compressive strength of MOCP, waste gypsum was able to significantly improve the water resistance of MOCP compared to natural gypsum. When 80% flue gas desulfurization gypsum and phosphogypsum (weight of magnesium oxide) were incorporated into MOCP, the 14-d air-cured compressive strength of MOCP was only decreased by 14.49% and 15.94% compared with the control group, but its 28-d water immersion strength retention coefficient (SRC) could still reach 61.02% and 46.55%, respectively. However, for the control group and MOCP with 80% natural gypsum, the 28-d SRC were only 28.99% and 8.41%. The incorporation of high-volume waste gypsum to MOCP not only reduced the relative content of MgO, but also improved the stability of the 5-phase in water, which was beneficial to improve the water resistance of MOCP. In addition, high-volume waste gypsum-modified MOCP had lower cost and carbon emissions, and exhibited superior water resistance and sustainability compared to existing MOCP compositions.

Long term field trials demonstrate sustainable nutrient supply and uptake in rehabilitated bauxite residue

Establishing a sustainable vegetation cover is one of the most important steps in progressive rehabilitation and final closure of ore-processing residues and tailings facilities. Sustainable rehabilitation partly depends on establishing and maintaining a supply of plant-available nutrients, but few long term field studies demonstrating the success or failure of rehabilitation of degraded land such as mineral processing tailings have been reported. Bauxite-processing residues are a highly sodic, highly alkaline, nutrient-poor by-product generated from alumina extraction, and pose many challenges for successful rehabilitation. This study investigated long term performance of rehabilitation established on bauxite-processing residue storage areas (RSAs) by comparing the nutrient content of the vegetation cover with nutrient concentrations in the underlying residue sand. Five plant species having diverse physiology were selected from rehabilitation varying in age from 1 to 10 years old; these being: Hardenbergia comptoniana – a vigorous growing legume ground cover/creeper), Acacia cochlearis and A. rostellifera - legume shrubs tolerant of sandy, alkaline conditions, Grevillea crithmifolia - a drought-tolerant proteaceous shrub tolerant of alkaline soil, and Spyridium globulosum - a robust, fast-growing shrub, commonly found on alkaline coastal soils. Gypsum incorporation reduced the pH and soluble aluminium levels in residue sand, but also acted as a long-term source of nutrients for the vegetation cover. Legume species contained more nitrogen than non-legumes (2.5% N and 1.5% N, respectively), and decomposition of surface litter increased organic carbon and total and mineral nitrogen contents of the residue sand over time. Nutrient cycling maintained a supply of macro- and micro- nutrients for the vegetation cover, and 10-year old rehabilitation exhibited characteristics similar to an analogue site. This study highlighted the importance of organic matter accumulation, developing a functional microbial community, and a diverse plant species mix on transforming the residue sand characteristics and encouraging nutrient cycling as key mechanisms for establishing a sustainable vegetation cover and functional ecosystem on residue sand embankments.

Secondary enrichment of soil by alkaline emissions: The specific form of anthropo‐geogenic soil degradation near magnesite processing factories and possibilities of land management

AbstractOver the past 90 years, anthropogenic degradation of soil caused by alkaline, magnesium‐rich dust deposition has presented a serious problem near magnesite processing factories in Jelšava and in Lubeník (Slovakia). The objective of this study was to investigate the chemical and biological soil properties in 14 sampling sites at different distances from factories, and based on the results, to propose further use of affected land. Results revealed that the available Mg was 3‐ to 68‐fold that of medium‐textured soils at all grassland sampling sites, and areas close to the factories contained up to 14,366–17,394 mg kg−1. Higher amounts of available Mg caused significant increase of soil pH (up to 9.39) and worsened the conditions for the growth of vegetation. As a result, a lower stock of labile soil organic carbon (501–961 mg kg−1) with consequently weaker enzymatic activity occurred. Enrichment by organic matter provides a means to support the biological activity of soil. The content of monitored heavy metals (Zn, Cu, Pb, and Ni) was not related to Mg and did not influence the enzymatic activity of soil. Because alkaline emissions have decreased by 99.8% since 1970, the application of established measures (mechanical removal of the Mg‐rich crust, incorporation of gypsum and manure into the soil), or newer methods (growing of Mg hyper‐accumulating plants) can offer more lasting positive effects than could be achieved 50 years ago. This study concluded alkaline dust was the main factor affecting soil degradation. Nevertheless, the natural origin of Mg from Mg‐parent rocks should be allowed for.

Growth of Rhodes grass and leaching of ions from seawater neutralized bauxite residues after amendment with gypsum and organic wastes

A 32-week leaching column study was carried out in the greenhouse to investigate the effects of incorporation of gypsum, cattle manure, biosolids, gypsum plus cattle manure and gypsum plus biosolids into the topsoil layer (0–10 cm) on growth of Rhodes grass, and on root distribution and chemical and microbial properties in the topsoil and subsoil (10–30 cm) layers of seawater neutralized bauxite residues. The columns were leached for a period of 8 weeks prior to sowing Rhodes grass and during that time the bulk of the salts accumulated during seawater neutralization were leached out. The main cation leached was Na+ and the main balancing anions were Cl− and SO42−. During this period the pH of leachates rose from 7 to 8 up to 9–10. At the end of the study, exchangeable Na and pH were lowered in the surface horizon by all treatments with a combination of gypsum plus organic amendments having the greatest effect. The latter treatments also caused a significant decrease in pH, extractable Al and exchangeable Na in the subsoil. Rhodes grass dry matter production followed the order Control < gypsum < cattle manure = gypsum plus cattle manure < biosolids = gypsum plus biosolids. Growth of roots into the subsoil layer was inhibited in the Control and gypsum treatments but when organic amendments were applied, 50% or more of root dry matter was recovered in the subsoil layer. It was concluded that incorporating a combination of gypsum and organic matter into the surface soil is an effective strategy for revegetation of bauxite residue.

Techno-economic impact assessment of recycled gypsum usage in plasterboard manufacturing

Recycled gypsum derived from post-consumer sources is a promising resource that can be reincorporated in the production chain, offering opportunities to decrease manufacturing costs given its significantly lower price compared to conventional gypsum. The systematic usage of post-consumer recycled gypsum is a relatively new practice in the plasterboard industry and there is lack of extensive literature references on the potential effects on the manufacturig process, since the available related studies are limited to more holistic approaches. The current work is, to our knowledge, the first study to assess the practice of gypsum recycling from an economical and technical point of view within the boundaries of the plasterboard manufacturing process. The paper provides a detailed techno-economic impact assessment of the usage of recycled gypsum up to 30% by weight in feedstock in the manufacturing of Type A plasterboard, based on data collected from full-scale industrial production trials carried out in five representative European plants located in four different countries. The potential impacts are analyzed in relation to each affected process parameter. A series of options for process adjustments, modifications and corrective measures in order to amortize the effects on product quality and/or cost are also reported. The analysis indicates high dependence of the cost impacts on process-specific characteristics. A limited reduction of 0.6% in the average total manufacturing cost per m2 of plasterboard was calculated, which can be associated to the considerable decrease, by 9.5%, of raw material costs. The latter fully compensates the increases to other process costs, and mainly to chemical additives which increased by 8%. The overall analysis allows quantification of the process parameters and costs that are affected when the percentage of recycled gypsum incorporated in plasterboard production is significantly increased. The results and the methodology proposed in the study can serve as a basis for a representative cost impact assessment of high-percentage recycled gypsum incorporation in any typical plasterboard production line plant. The methodology can serve as a guideline for techno-economic assessment of industrial production lines where the input datasets originate from different plants and can be characterized as “non-homogeneous” due to case-specific differences.

Mineralogical, Chemical, and Thermal Characterizations of Historic Lime Plasters of Thirteenth–Sixteenth-century Daulatabad Fort, India

ABSTRACTIron ore as pozzolanic filler is an uncommon constituent of historic plaster rarely reported in any research. This paper presents one such study from western India where hematite instead of crushed bricks was identified as admixture in thirteenth–sixteenth-century CE Mughal masonry lime works of Daulatabad Fort. The outer/inner coat plasters from different locations of the fort were examined for morphological, mineralogical, chemical, and basic physical properties. The analytical investigative study was performed by optical microscopy, sieve analysis, X-ray fluorescence, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, SEM-EDX, and thermal analyzer. Although the plaster is dominantly made of micritic calcite and aggregate, incorporation of gypsum in the outer and inner coats has been detected and probably acted as a second binder. Cannabis sativa was mixed in the plaster, pointing to the knowledge of hempcrete technology by the makers of Daulatabad Fort. This investigation has now provided essential information with enough precision about this historic plaster for formulation of compatible repair materials essential for the site restoration.

Incorporation of Np(V) and U(VI) in carbonate and sulfate minerals crystallized from aqueous solution

The neptunyl Np(V)O2+ and uranyl U(VI)O22+ ions are soluble in groundwater, although their interaction with minerals in the subsurface may impact their mobility. One mechanism for the immobilization of actinyl ions in the subsurface is co-precipitation in low-temperature minerals that form naturally, or that are induced to form as part of a remediation strategy. Important differences in the crystal-chemical behavior of the Np(V) neptunyl and U(VI) uranyl ions suggest their behavior towards incorporation into growing crystals may differ significantly. Using a selection of low-temperature minerals synthesized in aqueous systems under ambient conditions, this study examines the factors that impact the structural incorporation of the Np(V) neptunyl and U(VI) uranyl ions in carbonate and sulfate minerals.Calcite (CaCO3), aragonite (CaCO3), gypsum (CaSO4·2H2O), strontianite (SrCO3), cerussite (PbCO3), celestine (SrSO4), and anglesite (PbSO4) were synthesized from aqueous solutions containing either 400–1000ppm of U(VI) or Np(V) relative to the divalent cation present in the system. The synthetic products were investigated by inductively coupled plasma mass spectrometry, luminescence and time resolved luminescence spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. Amongst the carbonate minerals, calcite significantly favors Np(V) incorporation over U(VI). U(VI) and Np(V) are incorporated in aragonite and strontianite in similar amounts, whereas cerussite did not incorporate either U(VI) or Np(V) under the synthesis conditions. The sulfate minerals weakly interact with the actinyl ions, relative to the carbonate minerals. Incorporation of U(VI) and Np(V) in celestine was observed at the level of a few tens of ppm; anglesite and gypsum did not incorporate detectable U(VI) or Np(V). Luminescence spectra of the uranyl incorporated in aragonite and strontianite are consistent with a uranyl unit coordinated by three bidentate CO32− groups. The time-resolved spectra of calcite indicate multiple coordination environments about the uranyl unit, with the spectra of the longer-lived components displaying similarities with uranyl-incorporated aragonite. The luminescence spectrum of uranyl-bearing celestine is consistent with a uranyl unit coordinated by monodentate sulfate groups. Anglesite synthesized in the presence of uranyl shows no luminescence, whereas the spectra of gypsum and cerussite suggest uranyl surface adsorption or precipitation of secondary uranyl minerals on the mineral surfaces.Our findings indicate that geometrical constraints of the Np(V) and U(VI) species in solution, together with the crystallographic steric constraints of the host material, affect preferential uptake in the mineral structures studied. Calcium and strontium appear to be favorable incorporation sites for both U(VI) and Np(V) in aragonite and strontianite. In calcite, Np(V) incorporation is strongly favored over U(VI), whereas in gypsum incorporation of neither actinyl ion occurs. Substitution of actinyl ions was also not observed for lead, in either the carbonate or sulfate minerals studied.

Effect of Brackish Ice on Salt and Nutrient Contents of Saline Soil in Flue‐Gas Desulfurization Gypsum Amended, Raised Bed Agroecosystem

The effect of brackish ice application on the salt content and nutrient levels of a saline soil was determined in a flue‐gas desulfurization (FGD) gypsum amended, raised bed agroecosystem. Experimental plots in the raised bed were exposed to six treatments: 0, 4000, and 8000 m3 ha−1 brackish ice mulch, with or without the use of FGD gypsum. The applied brackish ice significantly decreased (P &lt; 0.05) the electrical conductivity of a saturated soil paste extract (ECe) to 4.22 (4000 m3 ha−1) and 3.85 dS m−1 (8000 m3 ha−1) from 7.20 dS m−1 (non‐brackish ice mulch) in the 0‐ to 20‐cm soil layers in the absence of FGD gypsum. Electrical conductivity was also significantly decreased in the 0‐ to 40‐cm soil layers following incorporation of FGD gypsum. The application of brackish ice significantly reduced (P &lt; 0.05) soil Na adsorption ratio (SAR) to &lt;11 and exchangeable Na percentage (ESP) in the 0‐ to 20‐cm soil layer, compared with the control treatment to which brackish ice had not been applied, regardless of FGD gypsum incorporation. The incorporation of FGD gypsum increased soil ECe to 12.89, 7.72, and 7.03 dS m−1 (P &lt; 0.01) but gave a lower soil SAR (P &lt; 0.05) in the 0‐ to 20‐cm soil layer following zero, low, and high volumes of brackish ice application compared with the same treatments without FGD gypsum. The incorporation of FGD gypsum significantly decreased soil pH in the 0‐ to 20‐cm soil layer compared with the treatment without FGD gypsum, regardless of brackish ice volume. The application of brackish ice significantly decreased the available P of the 0‐ to 20‐cm soil layer (P &lt; 0.05) and NO3–N content of the 0‐ to 40‐cm soil layer (P &lt; 0.05) compared with the control treatment without brackish ice when FGD gypsum was not incorporated. These results indicated that mulching of raised beds of saline soil by brackish ice seems to be a promising technology for growing spring crops on soils that would normally be unproductive.

Gypsum effects on plant growth, nutrients, ginsenosides, and their relationship in American ginseng

Wild American ginseng is typically found in the shade of deciduous forests, in slightly acidic soils with a relatively high Ca content. Wood-cultivated ginseng is often grown using forest farming agroforestry systems under similar conditions. Supplementing Ca by soil incorporation of gypsum (CaSO4·2H2O) is often recommended for wood-cultivated ginseng. The objective of this study was to determine the effects of gypsum application on ginseng growth, tissue nutrients, and ginsenoside contents in American ginseng. Three-year-old rootlets were grown for 120 days with 0, 2, 4, 8, or 16 Mt·ha−1 gypsum in greenhouse containers. Gypsum application reduced the soil pH slightly and elevated soil electrical conductivity (EC) and available soil Ca and S contents. While the Ca content in the ginseng increased with increasing levels of applied gypsum, shoot and root growth decreased. Root fresh weight prior to transplanting primarily affected the contents of ginsenoside Re, Rb1, Rc, and Rd and total ginsenosides. Gypsum treatment increased ginsenoside Rb1, Rc, and Rd and total ginsenoside contents. Furthermore, soil Ca, Mn, Cu, and Al contents positively correlated with total ginsenoside, but Mg was negatively correlated. HPLC analysis of root ginsenosides revealed that, although the concentrations of ginsenoside Rb1, Rc, and Rd increased with gypsum treatment, the contents of total ginsenosides were reduced. Changes in concentration may result from reduced root growth. Therefore, the results suggest that excess gypsum application (over 2 Mt·ha−1) is not beneficial for American ginseng production due to reduced plant growth.

Utilization of Raw Gypsum as Hydrated Filler in Bagasse Particleboard Bonded with a Formaldehyde-Free Epoxidized Natural Rubber Adhesive

The present study described the feasibility of using raw gypsum as filler to improve the flame retardant and mechanical properties of particleboard (PB) prepared from bagasse. The PB was made with a formaldehyde-free adhesive based on epoxidized natural rubber (ENR) latex via a hot pressing process. The effect of gypsum loading on the mechanical properties of the PB was initially investigated. Both the tensile strength and modulus of rupture (MOR) of the PB tended to increase with increasing gypsum loading and reached the maximum values at 150 phr. The incorporation of gypsum into the PB beyond this loading level brought about a decrease in the corresponding properties. A horizontal burning test was conducted to determine the flame retardant properties of the PB (i.e., elapsed time and burning rate). The PB containing 150 phr of gypsum (PB-150G) was found to have a much shorter elapsed time and a lower burning rate than the PB with no gypsum added. The lower values of the corresponding properties indicated the better flame retardancy of PB. It was also found that the PB-150G exhibited a comparable level of flame retardancy to the PB containing 8 wt% of total flame retardants (i.e., 5 wt% magnesium chloride in combination with 3 wt% antimony trioxide) based on the combined weight of bagasse and ENR contained in the PB. These results revealed that the use of an appropriate amount of gypsum as filler could significantly enhance the flame retardancy with considerable improvement in the mechanical properties of BP.

Expansion of mortars with gypsum contaminated fine recycled aggregates

This study evaluates the expansivity of fine recycled aggregates mortars depending on the type of Portland cement, the consistency and the equivalent of acid soluble sulphates (SO3) content. For that, an experimental campaign divided in two phases was performed. In the first phase, the cement pastes were produced and tested by means of X-rays diffractions in order to analyze the hydrated compounds formed over time. In the second phase mortars samples were cast in order to assess the physical and mechanical properties as well as the expansion over time. The results showed that incorporation of gypsum contaminated fine recycled aggregates with SO3 contents up to 2.9% by weight does not compromise the durability in mortars, regardless of the cement types studied in this study, the consistency and the contaminant present.

Cation and anion leaching and growth of Acacia saligna in bauxite residue sand amended with residue mud, poultry manure and phosphogypsum

To examine (1) the effect of organic (poultry manure) and inorganic (residue mud and phosphogypsum) amendments on nutrient leaching losses from residue sand and (2) whether amendments improve the growth of plants in residue sand. Leaching columns were established using residue sand. The phosphogypsum-treated surface layer (0-15 cm) was amended with poultry manure and/or bauxite residue mud and the subsurface layer (15-45 cm) was either left untreated or amended with phosphogypsum. Much of the Na⁺, K⁺, Cl⁻ and SO₄²⁻ was lost during the first four leachings. Additions of phosphogypsum to both surface and subsurface layers resulted in partial neutralization of soluble alkalinity. Mean pH of leachates ranged from 8.0 to 8.4, the major cation leached was Na⁺ and the major balancing anion was SO₄²⁻ . Where gypsum was not applied to the subsurface, mean pH of leachates was 10.0-10.9, the main cation leached was still Na⁺ and the main balancing anions were a combination of SO₄²⁻ and HCO₃⁻/CO₃²⁻. At the end of the experiment, concentrations of exchangeable Na⁺ in the subsurface layers were similar regardless of whether gypsum had been applied to that layer or not. Yields of Acacia saligna were promoted by additions of poultry manure to the surface layer but unaffected by gypsum incorporation into the subsurface layer. Lack of reaction of phosphogypsum with the subsurface layer is unlikely to be a major factor limiting revegetation of residue sand since in the absence of phosphogypsum the excess Na⁺ leaches with the residual alkalinity (HCO₃⁻/CO₃²⁻) rather than SO₄²⁻.

GYPSUM AFFECTS AMERICAN GINSENG'S GROWTH, NUTRITION, AND GINSENOSIDES

In the Northeast, wild American ginseng (Panax quinquefolium L.) is typically found growing in the dense shade provided by deciduous hardwood tree species such as a sugar maple, in slightly acidic soils with relatively high calcium content. Woods cultivated ginseng is often grown in forest farming agroforestry systems under similar conditions. Supplemental calcium by soil incorporation of gypsum (CaSO4·2H2O) is often recommended for woods cultivated ginseng. The objective of this study was to investigate the effects of this practice on soil chemical properties, plant growth and quality of American ginseng. In a greenhouse pot culture experiment, 2-year-old seedlings were treated with 0, 2, 4, 8, or 16 Mt·ha–1 gypsum and grown for 12 weeks. Gypsum application decreased soil pH slightly, elevated soil electrical conductivity and increased available soil Ca and sulfate concentrations. Tissue calcium concentration was increased with by gypsum treatment, but shoot and root growth was reduced. HPLC analysis of root ginsenosides revealed that Re, Rb1, Rc, and Rb2, PT ginsenoside (sum of ginsenoside Rb1, Rc, Rb2, and Rd) and total ginsenoside concentration increased by gypsum soil amendment.

The Influence of Preharvest Calcium Applications on Postharvest Quality and Yield of `Sweet Charlie' Strawberry

Strawberries are a high value commodity with a short shelf life. Florida is the largest producer of winter strawberries in the United States with 2,790 hectares of production, 90% are located in Hillsborough County. Many Florida growers apply additional calcium (Ca) as a foliar spray despite the lack of conclusive evidence of an increase in fruit quality or yield. It is believed that additional Ca will improve cell wall integrity through Ca linkages with pectins with in the cell wall and increase fruit firmness. Preharvest applications of calcium chloride have shown to delay the ripening of strawberry fruit and mold development. The objectives of this two year study were to determine the effects of Ca on yield, growth, and postharvest quality of strawberry when applied to the soil or as a foliar spray. `Sweet Charlie' strawberry plants were grown on a Seffner fine sand in Dover, Fla. The experimental design was a split-block replicated four times with soil and foliar Ca applications. Main plots consisted of a broadcast preplant incorporation of gypsum (calcium sulfate) 0 kg·ha-1, 36.7 kg·ha-1, and 73.4 kg·ha-1. Sub-plots consisted of foliar applications of 400 mg·L-1 Ca from calcium sulfate, 400 and 800 mg·L-1 Ca from calcium chloride and a water control applied weekly throughout the 2002-03 and 2003-04 growing season. Yield data was collected twice weekly through out the growing season. Fruits were graded for quality based upon size, visual appearance of pathogens degradation, frost/water damage, and misshapen form. Calcium content was determined for leaves, fruit, and calyxes in January and March. Postharvest quality evaluations of pH, titratable acidy, soluble solids, and firmness (Instron 4411) were determined in January and March.

Effect of saline-sodic sewage on the growth, yield and quality of cotton

Field experiment was conducted during 1999 to exploit the possibilities of recycling the open drain sewage by an integrated management approach. The sewage used was saline-sodic in nature and six treatments were employed. Apart from well water and raw sewage controls, treatments involving application of gypsum, alternating with well water and raw sewage were also included for the test crop of cotton (MCU 5). The results revealed that the attempt to neutralize the undesirable RSC of sewage by soil incorporation of gypsum was effective. This management practice produced high total dry matter and seed cotton yield of 4687 and 1847 kg ha¹ during winter representing 25.2 and 58.6 per cent increase in yield and 4612 and 1748 kg ha¹ during summer representing 47.9 and 55.2 per cent increase in yield over the control respectively. Similar effect was also recorded in the treatment that involved sewage cum well water irrigation supplemented by gypsum. This treatments during both winter and summer,. produced the total dry matter yield of 4636 and 4590 kg ha and cotton yield of 1934 and 1828 kg ha respectively.

Ammonia volatilization from nitrogen fertilizers with and without gypsum

Abstract. Ammonia volatilization with and without gypsum incorporation was measured in Gujranwala soil (Udic Haplustalf) in an incubation study using different nitrogen fertilizers e.g. urea, ammonium sulphate (AS), calcium ammonium nitrate (CAN), and urea nitrophos (UNP). Nitrogen from different fertilizers was applied at the rate of 200 mg N kg−1 to two sets of soils in plastic bags (1.0 kg soil) and plastic jars (0.5 kg soil). Soil moisture was maintained at field capacity. Application of urea increased soil pH to 9, three hours after its addition. Ammonium sulphate and calcium ammonium nitrate had little effect on soil pH. Ammonium volatilization losses from fertilizers were related to the increase in soil pH caused by the fertilizers. Consequently maximum losses were recorded due to application of urea. Losses through ammonia volatilization were significantly lower with AS, CAN and UNP in descending order. Gypsum incorporation significantly reduced the losses. Therefore, application of gypsum to soil before urea may substantially improve N use efficiency for crop production by reducing N losses.