Rates Of Gypsum Research Articles

The effect of pH on the formation of a gypsum scale in the presence of a phosphonate antiscalant

A massive gypsum scale in a discharge pipe of a desalination plant occurred despite the presence of an antiscalant (PermaTreat, PC-191). The scaling occurred following a sharp drop in the reject-brine pH when an acidic effluent (pH < 2) was introduced. Batch experiments revealed that the antiscalant is effective in postponing nucleation and hindering the crystal growth kinetics of gypsum in the supersaturated brine (Ω gypsum > 2) at neutral pH. However, as pH decreases both nucleation and crystal growth accelerate. A single general rate law that consistently described the crystal growth of gypsum as a function of pH in the batch experiments was found to be: R a t e S BET = k 1 ⋅ ( Ω 1 / 2 − 1 ) 10 + k 2 ⋅ ( Ω 1 / 2 − 1 ) 2 , where k i is the pH-dependant rate coefficient (mol m − 2 s − 1 ) and S BET is the BET surface area of gypsum (m 2). The dependence of the rate coefficients on pH is described quantitatively by an adsorption model which considers the protonation of the antiscalant functional groups. Finally, the precipitation rate of gypsum in the pipe was investigated with the laboratory rate law and adsorption model. It is shown that gypsum precipitation in the pipe occurs even in the absence of the acidic effluent and despite the fact that it could not be analytically detected.

α-calcium sulfate hemihydrate preparation from FGD gypsum in recycling mixed salt solutions

A pilot scale preparation of α-calcium sulfate hemihydrate (α-HH) from flue gas desulfurization (FGD) gypsum was conducted for the first time in mixed salt solutions under atmospheric pressure. The effects of salt solution recycling on the transition of α-HH from FGD gypsum were investigated by a comparison with that in laboratory scale, focusing on the dehydration rate of FGD gypsum, the crystal morphology, chemical composition and mechanical strength of the products. α-HH could be transformed from FGD gypsum in 3.5–6.0 h even though the salt solution was recycled seven times in laboratory tests and eight times in pilot tests. The product obtained in pilot scale has a purity of 95% and the α-HH crystals are mostly a prismatic morphology, with volume weighted mean diameter (D[3,4]) in the range of 52.9–84.0 μm, 2 h bending strength of 5.6–6.2 MPa and 3 d compressive strength of 15.7–25.3 MPa. The salt solution recycling achieves 56% recovery of salts in pilot scale and puts almost no negative impact on the product quality, which can be one of the best strategies to reduce the production cost. It is very likely that the process of salt solution recycling can be adopted in industry.

EFFECT OF CHICKEN MANURE AND GYPSUM ON SUGAR BEET (Beta vulgaris, VAR. SACCHARIFORA, L.) UNDER SALINE CONDITION

A plastic bags trial was conducted at the Agric. Experimental Station of Mansoura University using sandy soil to study the effect of chicken manure levels (0, 5, 10, 15 and 20 tons/fed) and gypsum rates (0, 2.5, 5, 7.5 and 10 tons/fed ) on nutrients uptake and yield of sugar beet plant irrigated with saline water. The experiment was conducted in a spilt plot design with three replicates during the two successive seasons 2007-2008 and 2008-2009 The Obtained results indicated that the yield of sugar beet roots increased significantly by adding chicken manure over the control. The highest level (20 tons/fed) gave 289.9 and 327.1 g/plant during first and second season, respectively. Also, the highest gypsum rate increased significantly root yield to be 307.15 and 341.77 g/plant during first and second season, respectively. Also, elements uptake such as N,P,K and Na were increased significantly over control due to supplying with either chicken manure or gypsum to a sandy soil. The same trend was found with the interaction effect of both treatments. Also, It could be recognized that chicken manure gave relatively higher increase in some characters than gypsum treatments. Data also revealed that root quality parameters such as SC%, TSS%, purity and sugar yield significantly increased with chicken manure over the control by 26.67% and 27.86 for TSS%, 18.96% and 18.74% for SC% and 77.39 and 79.98 g/plant for sugar yield in the 1st and 2nd season, respectively. Whereas, purity as a quality parameter significantly decreased with increasing chicken manure and gypsum treatments due to uneventually increasing for Sc% and TSS% which was not in a harmony which reflecting in decreasing purity. Generally, the interaction between chicken manure and gypsum revealed that the high rate of both chicken manure and gypsum treatments gave the highest root yield, elements uptake (N,P,K and Na) and sugar yield.

34S/32S Fractionation during Sulfate Reduction in Groundwater Treatment Systems: Reactive Transport Modeling

Isotope ratio measurements provide a tool for indicating the relative significance of biogeochemical reactions and for constraining estimates of the extent and rate of reactions in passive treatment systems. In this paper, the reactive transport model MIN3P is used to evaluate sulfur isotope fractionation in column experiments designed to simulate treatment of contaminated water by microbially mediated sulfate reduction occurring within organic carbon-based and iron and carbon-based permeable reactive barriers. A mass dependent fractionation model was used to determine reaction rates for 32S and 34S compounds during reduction, precipitation, and dissolution reactions and to track isotope-dependent mass transfer during SO4 removal. The δ34S values obtained from the MIN3P model were similar to those obtained from the Rayleigh equation, indicating that there was not a significant difference between the conceptual models. Differences between the MIN3P derived α value and the Rayleigh equation derived value were attributed to minor changes in the dissolution and precipitation rate of gypsum and mathematical differences in the fitting models. The results indicated that the prediction of δ34S was fairly insensitive to differences in the fractionation factor at the concentration ranges measured in the current study. However, more significant differences would be expected at low sulfate conditions.

Kinetics of gypsum crystal growth from high ionic strength solutions: A case study of Dead Sea – seawater mixtures

Gypsum precipitation kinetics were examined from a wide range of chemical compositions ( 11 < Ca 2 + / SO 4 2 - < 115 ) , ionic strengths (4.75–10 m) and saturation state with respect to gypsum (1.16–1.74) in seeded batch experiments of mixtures of Ca 2+-rich Dead Sea brine and SO 4 2 - -rich seawater. Despite the variability in the experimental solutions, a single general rate law was formulated to describe the heterogeneous precipitation rate of gypsum from these mixtures: Rate het = k 1 · ( Ω 0.5 - 1 ) 10 + k 2 · ( Ω 0.5 - 1 ) 2 mol m - 2 s - 1 , where k 1 and k 2 are heterogeneous rate coefficients (mol s −1 m −2) that vary as a function of the solution compositions, and is the saturation state with respect to gypsum. It is suggested that two parallel mechanisms control the heterogeneous precipitation rate. Under closer-to-equilibrium conditions, the reaction is dominated by a mechanism best described as a 2nd order reaction with respect to Ω 0.5 − 1, which fits to the predictions of both the Burton Cabrera and Frank (BCF) crystal growth theory ( Burton et al., 1951) and other layer-by-layer growth mechanisms ( Goto and Ridge, 1967; Van Rosmalen et al., 1981; Bosbach and Rammensee, 1994). Under further-away-from-equilibrium conditions, the reaction is dominated by an apparent 10th order reaction. A conceptual model for gypsum growth kinetics is presented. The model is based on the 2nd order kinetic coefficients determined in the present study and data from the literature and is valid under a wide range of ionic strengths and Ca 2 + / SO 4 2 - ratios. According to this model, the integration of SO 4 2 - to kinks on the surface of the growing crystals is the rate-limiting step in the precipitation reaction. At ionic strengths above 8.5 m the precipitation rate of gypsum is enhanced, possibly due to the formation of CaSO 4 ° ion pairs and/or a decrease in hydration frequencies.

Land application of spent gypsum from ditch filters: phosphorus source or sink?

Agricultural drainage ditches can provide a direct connection between fields and surface waters, and some have been shown to deliver high loads of phosphorus (P) to sensitive water bodies. A potential way to reduce nutrient loads in drainage ditches is to install filter structures containing P sorbing materials (PSMs) such as gypsum to remove P from ditch flow. The objective of this study was to determine the effect of land-application of gypsum removed from such filters on soil P forms and concentrations. Gypsum was saturated at two levels on a mass basis of P and applied to two soils of contrasting texture, a silt loam and a sandy loam and applied at both a high and low rate. The treated soils were incubated in the laboratory at 25˚C, and samples were collected at 1, 7 and 119 days after initiation. Soil type, time after application, gypsum rate, and P saturation level all had a significant impact on soil P forms and concentrations. However, it appears that land application of spent filter gypsum at realistic rates would have little effect on soluble P concentrations in amended soils.

RESPONSE OF PEANUT CROP CULTIVATED ON A NEWLY RECLAIMED SANDY SOIL TO BIO-INOCULATION, GYPSUM ADDITION AND FOLIAR SPRAY WITH IRON

A field experiment was carried out on a newly reclaimed sandy soil atSouth-Tahrir Sector, Al-Behira Governorate, Egypt during the twosuccessive summer seasons of 2008 and 2009, under sprinkler irrigationsystem. This study was conducted to identify the effect of bio-inoculation byRhizobium leguminosarum in combination with applied gypsum at the ratesof 0, 0.5 and 1.0 ton fed-1 and iron foliar spray at the rates of 0, 0.3 and 0.6 gL-1 on improving some soil properties as well as peanut pod or seed yield andits contents of oil, protein and nutrients.The obtained data showed that application of gypsum led to improvesome soil properties, i.e., soil bulk density, total porosity, pH and ECe, wherean increased was occurred in soil total porosity. On the contrary, soil bulkdensity and pH were decreased, and such favorable effects were achieved atthe highest rate of gypsum. The data revealed also that the available contentsof NPK as macro and Fe, Zn, Mn and Cu as micronutrients in soil afterpeanut harvesting increased as a result of bio-inoculation with rhizobium andgypsum addition, however, the combined treatment of (gypsum at a rate of 1ton fed-1 with bio-inoculation) gave the best results.In addition, the applied triple treatment of (bio-inoculation + gypsum +iron foliar spray) significantly increased the number and dry weight ofnodules plant-1 as well as dry weight of shoot and root of peanut plants at 75days from sowing. A pronounced increase was achieved in each peanut podor seed yield and its contents of oil, protein and nutrients (i.e., N, P, K, Fe,Zn, Mn and Cu). The greatest values for the abovementioned traits wererecorded with bio-inoculation. Application of gypsum resulted in asignificantly increase for each of the previous peanut parameters, except ofpotassium content in seed that tended to decrease with increasing the appliedrates of gypsum.Iron foliar spray resulted in a significantly increase for each of theprevious peanut parameters in both studied seasons as compared to thecontrol. The greatest values were attained by iron foliar spray at the appliedrate of 0.6 g L-1, except for P, Zn and Cu contents and uptake that weresignificantly decreased with increasing the applied rates of Fe as foliar spray.Therefore, under the condition of the studied newly reclaimed sandy soil, theapplied gypsum with bio-inoculation plays an effective role for improvingsoil characters, increasing the available nutrient contents and raising theefficiency of iron foliar spray. This of course positively reflected on peanutyield and improved its seed quality.

EFFECT OF APPLYING GYPSUM ON SOME PHYSICO-CHEMICAL AND HYDROLOGICAL PROPERTIES OF A SALINE-SODIC CLAY SOIL PROVIDED WITH A TILE DRAINAGE SYSTEM

Ameliorating the saline-sodic soil process represents an important target inthe agricultural security program of Egypt. In this concern, field trial wasconducted for improving salt-affected clay soil provided with tile drainagesystem at Mehallet Mousa, Kafr El-Shiekh Governorate, Egypt. The main target ofthis work was at identifying the effective role of applied gypsum, as soil chemicalamendment, with different rates on physico-chemical and hydrological propertiesof such soil as well as maximizing its productivity from maize and wheat crops.The applied gypsum treatments were categorized into: i. control without appliedgypsum, ii. 3.75 ton gypsum/fed ≈ 75 % of gypsum requirements (GR) for theuppermost 15 cm, iii. 5 ton gypsum/fed ≈ 100 % GR and iv. 6.25 ton gypsum/fed ≈125 % GR. The applied gypsum rates were uniformly spread on surface andthoroughly mixed with the soil top 15 cm, and then followed by recycle ofwetting and drying was repeated four times through period of about two months..A recycle of wetting and drying was repeated four times through period of abouttwo months. Soil samples at depths of 0-15, 15-30, 30-45 and 45-60 cm wereperiodically collected after 3, 6, 9 and 12 months from starting the experiment todetermine soil physico-chemical, i.e., ECe, ESP, salt leaching index, bulk density,infiltration rate, aggregation index and quickly drainable pores. Moreover, theshape of water table between drains, water table depth were monitored as well asthe drainage intensity factor a and the rate of water drawdown were calculated.The obtained results revealed that the reduction percentages of soil salinityafter 3, 6, 9 and 12 months from starting the experiment reached 30.3, 33.1, 35.4and 45.0 % for the applied gypsum rates 75 % GR vs 34.6, 36.9, 45.6 and 53.3 %for 100 % GR and 35.0, 66.6, 69.9 and 75.7 % for 125 % GR, respectively. Thatwas true, since additional gypsum in excess of the requirement helped speedily soilamelioration process. In general, the soil salinity reached the safe limits of soilsalinity (ECe= in water table level differs from one day to another as well as the applied gypsumrates, probably due to the nature of the stratified layering of such Nile alluvial soil.The average rate of water table drawdown after one year of gypsum applicationmounted 35.2, 44.8 and 95.0 % for soils treated with 75 %, 100 % and 125 % GRas compared with the initial state, respectively. In general, lowering the water tablehas given the top soil chance to dry, shrink and creating water passageways. Itwas also noticed that the drainage intensity factor (a) tended to increase withincreasing the applied gypsum rate, where its greatest value was achieved at 125 %GR, may be due to the increase of released Ca2+ and its positive action to link clayparticles, and in turn enhance soil internal drainage and water movement to drains.In addition, parallel pronounced decrease in the total water resistance wasassociated with increasing the applied gypsum rate, i.e., 7.69, 23.07 and 30.77 % at75, 100 and 125 % GR, respectively. This means that applied gypsum led toimprove the soil structure which helped in creating more permeable soil mediumwith less resistance to water flow towards tile drains.The achieved amelioration in physico-chemical and hydrological propertiesof the studied soil positively reflected on the increases of grain yields of bothsummer maize and winter wheat, which were approached 27.8, 50.0 and 61.1 % formaize vs 25.7, 42.9 and 57.1 % over the control for wheat at 75, 100 and 125 %GR, respectively. Finally, the obtained results suggest that this work is consideredas scientific and logic fundamental base for successful agricultural developmentof such salt affected area as well as possible to increase unite area income

Reclamation of a calcareous saline-sodic soil using phosphoric acid and by-product gypsum

Phosphoric acid is increasingly used as a source of water-soluble P, but it has not been widely tested for its effectiveness in reclaiming calcareous sodic and saline-sodic soils relative to chemically equivalent rates of gypsum. In lysimeters experiments, we showed that a calcareous saline-sodic soil can be ‘reclaimed’ using phosphoric acid and leaching with moderately saline irrigation water (sodium adsorption ratio = 4.1 and electrical conductivity = 2.2 dS/m). Phosphoric acid (50% pure) was dissolved directly in the leaching water at application rates of 450, 600 and 900 kg/ha, and phosphogypsum (80% pure) was mixed with soil prior to leaching at application rates of 15, 20, 30 and 40 t/ha. Phosphoric acid was more efficient than the chemical equivalent of phosphogypsum in improving soil hydraulic conductivity, and in reducing the exchangeable sodium percentage (ESP). The ESPs after leaching were: 10 (water only), 5.5–5.3 (phosphoric acid) and 8.2–5.9 (phosphogypsum).

Effect of Potassium Sodium Tartrate and Sodium Citrate on the Preparation of α‐Calcium Sulfate Hemihydrate from Flue Gas Desulfurization Gypsum in a Concentrated Electrolyte Solution

Flue gas desulfurization (FGD) gypsum mainly composed of calcium sulfate dihydrate (DH) was used as a raw material to obtain α‐calcium sulfate hemihydrate (α‐HH) through dehydration in a Ca–Mg–K–Cl‐solution medium at 95°C under atmospheric pressure. The effects of potassium sodium tartrate and sodium citrate on the preparation of α‐HH in the electrolyte solution were investigated. The results revealed that the addition of potassium sodium tartrate (1.0 × 10−2–2.5 × 10−2M) decreased the dehydration rate of FGD gypsum and increased the length/width (l/w) ratio of α‐HH crystals, which could yield unfavorable strength properties. Addition of sodium citrate (1.0 × 10−5– 2.0 × 10−5M) slightly increased the dehydration rate of FGD gypsum and decreased the l/w ratio of α‐HH crystals, which could be beneficial to increase strength. However, it also led to a partial formation of anhydrite (AH) crystals. AH was also the only dehydration product when the concentration of sodium citrate increased to 1.0 × 10−4M. Therefore, sodium citrate rather than potassium sodium tartrate could be used as an additive in Ca–Mg–K–Cl electrolyte solutions if α‐HH with a shorter l/w ratio is the desired product from FGD gypsum dehydration. The concentration of sodium citrate should be properly controlled to reduce the formation of AH.

Impact of Gypsum Applied to Grass Buffer Strips on Reducing Soluble P in Surface Water Runoff

The threat of P transport from land applied manure has resulted in water quality concerns. Research was conducted to evaluate gypsum as a soil amendment applied to grass buffer strips for reducing soluble P in surface runoff. A simulated concentrated flow was created in an established tall fescue (Festuca arundinacea Schreb.) pasture. Poultry litter (PL) was applied at a rate of 250 kg N ha(-1) to the upper 3.05 m of each plot, while gypsum was applied at rates of 0, 1, 3.2, and 5.6 Mg ha-1to the lower 1.52 m of the plot functioning as a grass buffer strip. Two 30-min runoff events ( approximately 4 L min(-1)) were conducted, immediately after PL application and 4 wk later to determined soluble P concentration in the surface water samples. The greatest concentration of soluble P was in the runoff event occurring immediately after the PL application. Gypsum applied to grass buffer strips was effective in reducing soluble P concentrations (32-40%) in surface runoff, while the untreated buffer strip was somewhat effective in reducing soluble P (18%). No significant differences were observed between gypsum rates, suggesting that land managers would achieve the greatest benefit from the lowest application rate (1Mgha(-1)). In the second runoff event, although concentrations of soluble P in the surface water runoff were greatly reduced, the effect of gypsum had disappeared. Thus, these results show that gypsum is most effective in reducing the initial P losses from PL application when applied to grass buffer strips. The information obtained from this study may be useful in aiding land managers in developing management practices that reduce soluble P loss at the edge of a field.

Origin of terrestrial gypsum dunes—Implications for Martian gypsum-rich dunes of Olympia Undae

The Estancia, White Sands, Guadalupe and Cuatrociénegas Dune Fields are among the largest known aeolian gypsum sand-dune accumulations on Earth and occupy closed-drainage basins within the Rio Grande Rift. High sedimentation rates of lacustrine gypsum occur in topographic depressions within the closed basins. The gypsum accumulations result from long-term, complex, interaction between tectonism, climate, and a hydrologic cycle that involves geochemical recycling of sulfur from older sedimentary rocks flanking and underlying the basins. Gypsum precipitation in lacustrine environments is strongly controlled by local groundwater/bedrock interaction. The ranges of δ 34S values (per mil, vs. VCDT) for gypsum sand in the White Sands Dune Field (12.1 to 13.9‰), Guadalupe Dune Field (10.2 to 12.5‰) and Cuatrociénegas Dune Field (14.6 to 15.9‰) indicate that the main sources of dissolved sulfate are evaporite strata of Lower Permian, Middle Permian and Cretaceous ages, respectively. A spatial increase of δ 34S values across the White Sands Dune Field, in the direction of prevailing winds, matches well with a stratigraphically upward increase of δ 34S values recorded in Lake Otero (an ancient lake in the basin) strata. This finding supports previous suggestions that White Sands Dune Field evolved as a result of the step-wise deflation of previously stored sediments in Lake Otero. The modern gypsum dune fields are primarily wet eolian systems in which dune accumulation is controlled by a near-surface groundwater table, which promotes early cementation of the dune accumulations. Early cementation in the interdune surfaces and, to a lesser degree, on the dune surfaces reduces the amount of sand available for transport and slows rates of dune migration. Based on an average migration rate of 2 m/year, the time needed for a dune at White Sands to migrate the downwind distance of the dune field is approximately 6500 years, which matches well with other estimates of the initiation of the dune field at approximately 7000 years ago and indicates that White Sands likely evolved as a wet aeolian system. As on Earth, gypsum-rich dune fields apparently are rare on Mars. Gypsum has been identified only within the Olympia Undae Dune Field which encircles a portion of the Martian north polar residual ice cap. Analogous to terrestrial gypsum dunes, the gypsum within the Olympia Undae gypsum-rich dunes might have originated from transport and deposition via aeolian processes. In this model, gypsum-rich source sediment could have been formed by confined groundwater or surface water activity and later transported by the wind. Any subsequent gypsum precipitation in the source area could have been initiated by episodic melting of the Martian polar ice cap. It is likely that the gypsum was deposited in the Olympia Undae dunes after the main deflation events that led to formation of the siliciclastic components of the dune field.

N2 fixation by faba bean (Vicia faba L.) in a gypsum-amended sodic soil

The response of faba bean to the application of four rates of gypsum (0, 2.5, 5.0, 10.0 t ha−1) to a non-saline, alkaline sodic soil was measured in terms of grain yield, dry matter (DM) production, N accumulation and the proportional dependence of the legume on symbiotic N2 fixation (Patm). A yield-independent, time-integrated 15N-dilution model was used to estimate symbiotic dependence. A significant decrease in the exchangeable sodium percentage and significant increases in exchangeable Ca++ and the Ca++:Mg++ ratio in the 0–10-cm soil layer were measured 30 months after application of 10 t ha−1 gypsum. Despite low and erratic rainfall during crop growth, faba bean DM and N uptake responded positively to gypsum application. The symbiotic dependence of the legume at physiological maturity was little affected by sodicity (Patm = 0.74 at zero gypsum and 0.81–0.82 at 2.5–10 t ha−1 gypsum). The increase in fixed N due to gypsum application was mainly due to increases in legume DM and total N uptake. At 10 t ha−1 of gypsum, faba bean fixed more than 200 kg N ha−1 in above-ground biomass.

Pod Yield and Mineral Concentration of Four Peanut Cultivars Following Gypsum Application With Subsurface Drip Irrigation

Abstract A 2-year study (2004 and 2005) was conducted where gypsum was applied to four peanut (Arachis hypogaea L.) cultivars and irrigated with subsurface drip to determine pod yield and mineral concentration of peanut plants and kernels. Gypsum rates were none, 560 and 1120 kg/ha. Peanut cultivars were C99R, Georgia Green (GG), NCV-11 (NCV), and GA-O2C (O2C). Irrigation was applied daily with subsurface drip irrigation except when precipitation exceeded the estimated daily water requirement. Average soil Ca and S concentrations increased as gypsum was applied, 5% and 20%, respectively, compared with the non-treated control. The average soil calcium to potassium (Ca∶K) ratio increased to 9.8∶1 compared with 7.6∶1 prior to applying calcium. When averaged across calcium rates, peanut leaves had 3 and 14 times higher calcium and 1.4 times higher S concentrations compared with pegs and pods, respectively. The cultivars GG and NCV had the same pod yield. Cultivars C99R and O2C had the same yield as NCV but were less than GG. Germination rates were higher when gypsum was added compared to the non-treated control and with cultivars C99R and O2C. There was no difference in vigor by gypsum application rate. Kernel Ca concentration was higher with the addition of gypsum compared to the non-treated control. Cold test germination seed vigor increased with C99R and O2C compared with GG and NCV.

Dissolution Rate of Gypsum Under Different Environments

Dissolution Rate of Gypsum Under Different Environments

Physics and Chemistry of Dissolution on Subaerialy Exposed Soluble Rocks by Flowing Water Films

The basic process active in the formation of subaerial features on karst rocks is chemical dissolution of limestone or gypsum by water films flowing on the rock surface. The dissolution rates of limestone and gypsum into thin films of water in laminar flow are given by F = α(ceq-c), where (ceq-c) is the difference of the actual concentration c in the water film and the equilibrium concentration ceq with respect to the corresponding mineral. Whereas for gypsum α is determined by molecular diffusion the situation is more complex for limestone. Experiments are presented, which show that for high undersaturation, c 0.3ceq. These rate laws are used to calculate denudation rates on bare rock surfaces exposed to rainfall with differing intensity. The estimations are in reasonable agreement to field data. Starting from the experiments on the formation of Rillenkarren on gypsum performed by Glew and Ford (1980), we suggest a new relation between their length from the crest to the “Ausgleichsflache” and the inclination of the rock surface. This is also applied to field data of Rillenkarren on limestone provided by J. Lundberg and A. Gines. In view of the many parameters influencing the formation of Rillenkarren these correlations can be considered as satisfactory.

Soybean yield and quality a function oflime and gypsum applications

Effects of lime and gypsum applications on the quality of soybeans grown under no-till (NT) are not well defined yet. A field trial established in 1998 on a dystrophic clayey Rhodic Hapludox, at Ponta Grossa, State of Paraná, Brazil, evaluated grain yield and soybean quality based on oil, protein and nutrient content, after lime and gypsum applications under NT, in a randomized complete block design (n = 3), split-plot experiment. In the main plots, the treatments with dolomitic lime were: control (no lime), split application of lime on the surface (three yearly applications of 1.5 Mg ha¹), surface lime (4.5 Mg ha¹), and incorporated lime (4.5 Mg ha¹). Subplots received four different rates of gypsum: 0, 3, 6, and 9 Mg ha-1. The soybean crop was evaluated in the agricultural years of 20022003 and 20032004. After 58 months, the correction of acidity through surface liming, with full or split rates, was more pronounced in the top layer (00.05 m) and there was greater reaction at the depths of 0.050.10 and 0.100.20 m when lime was incorporated. Surface or incorporated liming had no effect on grain yield, soybean oil and protein content. Gypsum improved chemical subsoil conditions, raising pH (0.01 mol L-1 CaCl2) as well as Ca2+ and S-SO4(2-) contents; it also caused exchangeable Mg2+ leaching in the soil profile. The application of gypsum did not affect grain yield, yet it improved soybean quality through an increase in protein and S contents, in 20032004, and in grain P, K and Ca, in the two cropping years. The use of gypsum in NT soybeans can be especially important for fields of seeds production.

Resorbable Gypsum Coating on Calcium Metaphosphate for Controlled Degradation Rate

Five kinds of gypsums, (1) CaSO4•2H2O (caldium sulfate dihydrate; CSD), (2) CaSO4•1/2H2O (calcium sulfate hemihydrate; CSH), (3) CaSO4 (calcium sulfate anhydrite; CSA), (4) CSH200 (CSH heat-treated at 200°C after self-hardening), and (5) CSH600 (CSH heat-treated at 600°C after self-hardening) were used as candidates for coating materials on calcium metaphosphate (CMP) scaffod to control degradation rate of CMP and to extend degradation limit. The disks of CSD, CSH, CSA, CSH 200, and CSH600 were prepared by self-hardening after mixing with water, where CSH200 and CSH600 were heat-treated at 200°C and 600°C, respectively. In order to control fast resorption rate of gypsum, CMP-CSA composites were prepared with different CSA contents such as 0, 5, 10, 20, 30, 50, and 70 vol% and heat-treated at 900°C for 4 hours. The degradation rates of various gypsums were evaluated in revised simulated body fluid (r-SBF) for 1, 3, 7, and 21 days, respectively. Degradation rate of each specimen was measured in terms of weight loss change with time and degraded surface morphology was examined by SEM. All kinds of gypsums were transformd into CSD after self-hardening with water. Most of gypsums were degraded by 35~60 wt% at 7 days and by 70~99 wt% at 21 days of soaking in SBF. In the group of CMP-CSA composites, the degree of degradation of them was considerably retarded compared to that of five pure gypsums. The surface morphology showed elongated needle-like crystals during the degradation with time.

Downward Movement of Soil Cations in Highly Weathered Soils Caused by Addition of Gypsum

Besides supplying calcium (Ca) and sulfur (S) to plants, gypsum has recently been used in agriculture to ameliorate some soil physical and chemical properties, especially to alleviate aluminum phytotoxicity in subsoils. When applied in large quantities, however, gypsum may leach significant amounts of nutrients from the plow layer. This study was conducted to assess the effect of gypsum addition to the soil on the magnitude of cation leaching as well as the relationship of leaching with some soil properties in a group of seven Brazilian soils. Rates of gypsum equivalents to 0, 5.0, 10, and 20 t ha−1 (0, 2.5, 5.0, and 10 g kg−1) were mixed with triplicate soil samples consisting of 3.0 kg of dry base soil. After 60 days of incubation at room temperature (15–25°C), the experimental units were packed into polyvinyl chloride leaching columns (32‐cm‐high×10 -cm-diameter) at a density of 0.9 g cm−3. Thereafter, they were percolated once a week with a volume of distilled water equivalent to 1.5 times the total soil porosity over 11 weeks. Soil samples were collected before the first and after the last percolation, for chemical analysis. Averaged across soils, 11 percolation events leached about 26% of each Ca, magnesium (Mg), and potassium (K) from the treatment without gypsum. Averaged across soils and rates, addition of gypsum leached 41–94% of added Ca, 13–90% of exchangeable Mg, and 13–58% of exchangeable K, and the highest losses occurred on the sandiest soils. The relationship between soil parameters and Ca leaching varied with gypsum rate: in the treatments that received gypsum, leaching was negatively related to cation exchange capacity (CEC), clay, and organic matter, and positively correlated with sand; in the treatment with no gypsum, leaching correlated with the same parameters above, nevertheless, all coefficients presented opposite signs. Leaching of K caused by gypsum was negatively associated with clay and positively with sand, whereas leaching of Mg was poorly correlated with any soil parameter. Gypsum is a good source to promote high and fast downward movement of Ca in the soil profile, but rates must be cautiously chosen because of excessive leaching of Mg especially on soils with low CEC.

Effect of gypsum and polyacrylamides on water turbidity and infiltration in a sodic soil

Water ponded on sodic soils can develop turbidity problems which seriously affect rice crop establishment. A total of 19 polyacrylamide products were assessed for their effectiveness to control water turbidity in a sodic soil under laboratory conditions. Anionic polyacrylamides were more effective than cationic or non-ionic polyacrylamides. When combined with gypsum, polyacrylamides were found to be more effective than when applied alone. A split application strategy was more efficient than continuous application of polyacrylamide treatments. Different rates of polyacrylamides at 2.5, 5, and 10 kg/ha did not show significant difference in controlling water turbidity. Selected polyacrylamides were also tested on soil columns to study their effect on infiltration and percolation of water through the soil. Results showed that polyacrylamides combined with low rates of gypsum did not modify the infiltration pattern to a greater extent. This study demonstrated that anionic polyacrylamides applied with small quantities of gypsum through a split application strategy would be an appropriate technique to overcome water turbidity problems in sodic soils.