Gypsum Amendment Research Articles

Gypsum addition to soils contaminated by red mud: implications for aluminium, arsenic, molybdenum and vanadium solubility

Red mud is highly alkaline (pH 13), saline and can contain elevated concentrations of several potentially toxic elements (e.g. Al, As, Mo and V). Release of up to 1 million m(3) of bauxite residue (red mud) suspension from the Ajka repository, western Hungary, caused large-scale contamination of downstream rivers and floodplains. There is now concern about the potential leaching of toxic metal(loid)s from the red mud as some have enhanced solubility at high pH. This study investigated the impact of red mud addition to three different Hungarian soils with respect to trace element solubility and soil geochemistry. The effectiveness of gypsum amendment for the rehabilitation of red mud-contaminated soils was also examined. Red mud addition to soils caused a pH increase, proportional to red mud addition, of up to 4 pH units (e.g. pH 7→11). Increasing red mud addition also led to significant increases in salinity, dissolved organic carbon and aqueous trace element concentrations. However, the response was highly soil specific and one of the soils tested buffered pH to around pH 8.5 even with the highest red mud loading tested (33% w/w); experiments using this soil also had much lower aqueous Al, As and V concentrations. Gypsum addition to soil/red mud mixtures, even at relatively low concentrations (1% w/w), was sufficient to buffer experimental pH to 7.5-8.5. This effect was attributed to the reaction of Ca(2+) supplied by the gypsum with OH(-) and carbonate from the red mud to precipitate calcite. The lowered pH enhanced trace element sorption and largely inhibited the release of Al, As and V. Mo concentrations, however, were largely unaffected by gypsum induced pH buffering due to the greater solubility of Mo (as molybdate) at circumneutral pH. Gypsum addition also leads to significantly higher porewater salinities, and column experiments demonstrated that this increase in total dissolved solids persisted even after 25 pore volume replacements. Gypsum addition could therefore provide a cheaper alternative to recovery (dig and dump) for the treatment of red mud-affected soils. The observed inhibition of trace metal release within red mud-affected soils was relatively insensitive to either the percentage of red mud or gypsum present, making the treatment easy to apply. However, there is risk that over-application of gypsum could lead to detrimental long-term increases in soil salinity.

Effect of different amendments on soil chemical characteristics, grain yield and elemental content of wheat plants grown on salt-affected soil irrigated with low quality water

A field trial experiment was carried out during the winter season of 2010/2011 to investigate the effect of different amendments i.e. gypsum, citric acid, farmyard manure, compost and the combination among them on heavy clay salt-affected soil irrigated with wastewater and also, their effects on wheat production. The experiment was conducted in north El-Hosinia plain, Sharkia Governorate that is irrigated with Bahr El-Baqar drain water. Obtained results showed that the chemical characteristics of the studied soil i.e. pH, ECe, soluble ions, SAR and ESP were improved by application of the amendments under irrigation with Bahr El-Baqar drain water. The better effect was shown by using 50%gypsum+50%FYM. Regarding to DTPA-extractable heavy metals i.e. Fe, Mn, Zn, Cu, Ni and Cd in soil, the applied amendments increased the downward movement of heavy metals as indicated by increasing their concentrations with increasing soil depth which means reducing such heavy metals concentration in plant root zone. Gypsum amendment was superior in reducing the chemically available heavy metals in the studied soil.The grain yield, weight of 1000 grains and NPK concentration of wheat plants were significantly increased due to the application of these amendments compared to the control, especially for 50%gypsum +50%FYM treatment. In addition, heavy metals concentrations under investigation in root parts of wheat plants were higher than shoot parts. It is worthy to mention that the heavy metals concentrations in grains were the lowest ones and within the normal range except for Cu and Ni. Regarding to whole plant parts the heavy metals concentrations were reduced by application of gypsum to the used soil.

The effects of gypsum on the transfer of phosphorus and other nutrients through clay soil monoliths

We applied gypsum (CaSO4×2 H2O) amendments to 100 m2 plots within two clay-textured fields, one under shallow cultivation to 10 cm depth and the other ploughed to 20 cm depth. Unamended plots and plots subjected to a CaCO3 (finely ground limestone) application served as controls. Separate soil monoliths (30 cm in diameter, 40 cm in depth) were collected for laboratory rainfall simulations from all plots 7, 19 and 31 months after the initial application of the amendments. Water passed through the monoliths during these simulations was analysed for turbidity, dissolved and particulate phosphorus (DRP and PP), nitrogen species, dissolved organic carbon (DOC), as well as dissolved Ca2+, Mg2+, K+ and S, pH, and electrical conductivity (EC). Over the three-year monitoring period, gypsum amended soils exhibited substantial decreases in turbidity (45%), PP (70%), DRP (50%) and DOC (35%) relative to control samples. The effects gradually decreased with time, and after 31 months gypsum effects on P species were detectible, but no longer statistically significant. We consider gypsum amendments as a potential tool for slowing P loss from agricultural areas with high P loss potential.

Gypsum amendment as a means to reduce agricultural phosphorus loading: an economic appraisal

This study analyzes the economic feasibility of gypsum amendment as a means to reduce particulate and dissolved phosphorus loads from arable areas. To this end, an optimization model is developed that includes gypsum amendment as well as matching phosphorus fertilization to crop need and the level of soil phosphorus reserves as phosphorus load mitigation measures, with soil phosphorus reserves measured by soil test phosphorus (STP). The optimal extent of gypsum amendment is then determined simultaneously with optimal fertilization use as a function of field STP level. The results indicate that whether or not gypsum amendment is economically feasible depends on field erosion susceptibility and STP level. When accounting for the costs and benefits to the society on the whole, gypsum treatment suits best to mitigation of phosphorus losses from soils with excessively high phosphorus reserves; once a threshold STP level is reached, gypsum amendment is optimally given up. This threshold level depends on field slope and on society’s willingness to pay for water quality.

Gypsum amendment of soils reduces phosphorus losses in an agricultural catchment

We estimated the changes in the losses of particulate and dissolved phosphorus (P) after treating 93 ha of agriculturalfields with gypsum (4 t ha–1) in a 245 ha catchment in southern Finland. Runoff was monitored using onlinesensors and manual sampling during one high-flow period before and six periods after the gypsum amendment.Turbidity recorded by the sensors correlated with particulate P analysed in the laboratory, which enabledthe evaluation of changes in particulate P from the online data. Using a covariance model, gypsum amendmentwas estimated to have reduced the loss of particulate P by 64%. The loss of dissolved reactive P appeared to decreaseby one third, but was estimated with less precision. No such changes were found during the same periodin a nearby ‘reference’ catchment, where gypsum was not used. Gypsum did not affect soil test values for P, K, Mgor Ca, but it did increase the ionic strength and soil test SO4. In clayey catchments discharging into the sea, gypsummay provide an efficient means to reduce P losses from field cultivation. The duration of the gypsum effect andimpact of SO4 associated with gypsum amendment on the ecology of rivers and lakes has yet to be determined.

Simulated effects of gypsum amendment on phosphorus losses from agricultural soils

Our objective was to incorporate the effects of gypsum on phosphorus (P) losses into the field-scale ICECREAM model and to simulate the treatment of 93 ha of clayey soil with gypsum in a catchment located in southern Finland. In addition to the gypsum effects, a macropore flow description was added to ICECREAM. First, a sensitivity analysis was performed for the new macropore parameters, retrieved from a literature survey. After this, the model was calibrated for a reference period by setting of the macropore parameters to correspond to the P losses observed in the catchment experiment. Next, the effect of gypsum was added to the model in line with laboratory and field experiments that suggested decreased P losses and changed hydraulic properties of the soil. Finally, the modified model was verified for four seasons after the gypsum amendment in the catchment experiment. The model was able to simulate the P losses in three out of the four seasons. According to the simulations, gypsum reduced total P losses by 44%. Although the effect of gypsum on P and erosion is a complex process, our relatively simple modifications to the ICECREAM model described the impact with reasonable accuracy. However, to increase confidence in the performance of the model, it should be tested under other environmental conditions.

Gypsum amendment of alkaline bauxite residue – Plant available aluminium and implications for grassland restoration

An inherent property of bauxite refining residue is high pH and associated elevated levels of solubilised aluminium. High solubilised Al content of the residue can inhibit plant growth and under natural conditions significant reduction of aluminium levels is extremely slow. Various procedures have been employed globally to reduce the alkaline properties of bauxite residue. At the Aughinish Alumina Ltd. refinery gypsum is applied as an amendment to reduce pH and sodicity of the residue for restoration. An additional benefit of this procedure is a significant decrease in plant available Al in the residue and low herbage concentrations. Furthermore, deficiencies of nutrients such as Ca, a symptom of Al toxicity, are not evident. To avoid excessive Al uptake in restored residue it is recommended that adequate calcium and other nutrients are added to the residue and nutrient cycling is encouraged as part of the restoration programme.

Nitrogen and Phosphorus Leaching as Affected by Gypsum Amendment and Exchangeable Calcium and Magnesium

The loss of N and P by leaching is an important issue, especially on agricultural fields with subsurface tile drainage. The objective of this study was to evaluate how gypsum amendment and soil exchangeable Ca2+ and Mg2+ could affect the movement of P, NH4-N, and NO3-N in infiltrated water and soil. A column experiment was performed using a Miami silt loam soil, and the treatments were (i) control, (ii) gypsum applied at the surface, (iii) gypsum mixed into the 2.5-cm depth, and (iv) alteration of five different target exchangeable Ca/Mg ratios. A clear Plexiglas cylinder was filled with a 15-cm layer of soil; N, P, and K were applied in solution at the surface after the soil had been wetted and drained. Deionized water at a flow of 0.5 mL min(-1) was applied and eight leachate fractions, totaling about five pore volumes, were collected. Gypsum (5000 kg ha(-1)) applied at the surface and mixed into the 2.5-cm depth significantly decreased P and increased NH4-N concentration but had no significant effect on NO3-N leaching. Exchangeable Ca/Mg ratio treatments did not affect soluble nutrient losses; however, leaching of particulate P was significantly less in the Ca-treated soil than the Mg-treated soil. The overall practical conclusion of this study is that to control P transport, it is necessary to add gypsum even with a high soil exchangeable Ca/Mg ratio. The application of gypsum to the soil could be recommended as a best management practice to avoid water pollution by P; on the other hand, this could cause environmental problems by increasing the NH4 soil mobility.

Relative Effectiveness of Various Amendments in Improving Yield and Nutrient Uptake under Organic Crop Production

In organic farming, artificial/synthetic inorganic fertilizers/chemicals are not applied to increase crop yields, but adequate amounts of nutrients are essential for sustainable high production from agricultural crops. Two 3-year (2008 - wheat, 2009 – pea, and 2010 - barley) field experiments were conducted on certified organic farms near Spalding (Dark Brown Chernozem – Typic Haploboroll) and Star City (Gray Luvisol – Typic Haplocryalf) in northeastern Saskatche-wan to determine the relative effectiveness of various organic amendments (compost, alfalfa pellets, wood ash, rock phosphate, Penicillium bilaiae, MykePro, or gypsum), and intercropping of non-legume (wheat, barley) and legume (pea) annual crops on seed yield, total biomass yield (TBY) and nutrient uptake in seed + straw of wheat, pea and barley. In 2008, seed yield, TBY and nutrient uptake of wheat increased (but small) with compost and alfalfa pellets. In 2010, seed yield, TBY and nutrient uptake of barley increased substantially with compost and alfalfa pellets and moderately with wood ash. Other amendments had little or no effect on crop yield and nutrient uptake. In 2009, there was no beneficial effect of any amendment on yield and nutrient uptake of pea, most likely due to fixation of N which is the most limiting nutrient in these soils. Intercropping of wheat or barley with pea produced greater seed yield and nutrient uptake per unit land area basis compared to wheat or barley grown as sole crops in most cases. In conclusion, our results suggest potential benefits in improving yield and nutrient uptake of wheat and barley from compost, alfalfa pellets and possibly wood ash, most likely by preventing deficiencies of some nutrients, especially N, lacking in these soils under organic farming. Our findings also suggest the need for future research to determine the feasibility of rock phosphate, Penicillium bilaiae, MykePro, gypsum or other amendments in preventing P and/or S deficiency in organic crops using soils extremely deficient in these nutrients.

Predictive hydrogeochemical modelling of bauxite residue sand in field conditions

The suitability of residue sand (the coarse fraction remaining from Bayer's process of bauxite refining) for constructing the surface cover of closed bauxite residue storage areas was investigated. Specifically, its properties as a medium for plant growth are of interest to ensure residue sand can support a sustainable ecosystem following site closure. The geochemical evolution of the residue sand under field conditions, its plant nutrient status and soil moisture retention were studied by integrated modelling of geochemical and hydrological processes. For the parameterization of mineral reactions, amounts and reaction kinetics of the mineral phases natron, calcite, tricalcium aluminate, sodalite, muscovite and analcime were derived from measured acid neutralization curves. The effective exchange capacity for ion adsorption was measured using three independent exchange methods. The geochemical model, which accounts for mineral reactions, cation exchange and activity corrected solution speciation, was formulated in the geochemical modelling framework PHREEQC, and partially validated in a saturated-flow column experiment. For the integration of variably saturated flow with multi-component solute transport in heterogeneous 2D domains, a coupling of PHREEQC with the multi-purpose finite-element solver COMSOL was established. The integrated hydrogeochemical model was applied to predict water availability and quality in a vertical flow lysimeter and a cover design for a storage facility using measured time series of rainfall and evaporation from southwest Western Australia. In both scenarios the sand was fertigated and gypsum-amended. Results show poor long-term retention of fertilizer ions and buffering of the pH around 10 for more than 5 y of leaching. It was concluded that fertigation, gypsum amendment and rainfall leaching alone were insufficient to render the geochemical conditions of residue sand suitable for optimal plant growth within the given timeframe. The surface cover simulation demonstrates that the soil moisture status in the residue sand can be ameliorated by an appropriate design of the cover layer with respect to thickness, slope and distance between lateral drains.

Bauxite Processing Residue: A Critical Review of Its Formation, Properties, Storage, and Revegetation

Bauxite is processed in alumina refineries by the Bayer process in which Al-containing minerals are dissolved in hot NaOH. The insoluble solids (bauxite processing residue mud and sand) are washed, sometimes partially neutralized (using CO2 or seawater treatment), and deposited in impoundments surrounding the refinery using either wet (15–30% solids) or dry (50–65% solids) disposal techniques. Revegetation strategies for impoundments include constructing a soil cap over the mud deposit, amending the mud with residue sand and other materials or revegetating the sand fraction that surrounds and covers the mud deposit. Major limitations to plant growth in residues include salinity, sodicity, alkalinity, Al toxicity, and deficiencies of macro- and micronutrients. Physical properties are also problematic since residue mud consolidates to form a solid mass that waterlogs easily or dries to form a massive structure, while sand has a very low water holding capacity. Gypsum amendment reduces pH, displaces Na with Ca and tends to improve porosity. Organic amendments supply nutrients, increase CEC, and improve physical conditions while inorganic fertilizers supply essential nutrients. An integrated approach using all of the previously mentioned amendments as well as saline sodic-tolerant plant species is likely to increase the success of revegetation compared to use of only 1 or 2 techniques. There are very few reports on microbial activity in residue but since it is heat and chemically treated, activity is likely to be initially very low. Organic residue addition provides a substrate for heterotrophic microbes and provide the beginnings for a below-ground living ecosystem. Inoculation of plants with appropriate mycorrhiza and legumes with Rhizobium might also increase plant establishment and growth. These aspects deserve future examination. Although much research has concentrated on the establishment phase of revegetation, little consideration has been given to the subsequent growth and self-propagation of the introduced species, changes in residue properties during weathering and leaching of alkalinity from residue over time. These facets need careful study before definitive statements can be made regarding the sustainability of various revegetation strategies.

Calcium sulfate ameliorates the effect of aluminum toxicity differentially in genotypes of highbush blueberry (Vaccinium corymbosum L.)

Abstract The effect of gypsum (CaSO 4 ) amendment in the reduction of Al phytotoxicity of blueberry cultivars differing in Al resistance (Legacy and Brigitta, Al-resistant and Bluegold, Al-sensitive) was studied in a Hoagland’s nutrient solution under acidic conditions for 2 weeks. Treatments were: Control (Hoagland solution), 2.5 mM CaSO 4 , 5 mM CaSO 4 , 100 µM Al (AlCl 3 ), 100 µM Al + 2.5 mM CaSO 4 , 100 µM Al + 5 mM CaSO 4 . Physiological, biochemical and chemical features of leaves and roots were determined to establish the amendment efficiency in the reduction of Al toxicity in these cultivars. Results showed that under Al toxicity the three investi-gated cultivars accumulated high Al concentrations in leaves and roots. These con-centrations decreased with CaSO 4 application. Statistically significant interactions among Al in leaves but not in roots ( p =0.719) and cultivars ( p <0.001), were found. The lowest Ca concentration was found in the most Al-sensitive cultivar (Bluegold) and the highest in the more Al-resistant cultivars (Legacy and Brigitta). Among the underlying processes affected by Al stress in these blueberry cultivars the most evident changes were exhibited by the Al-sensitive cultivar Bluegold, where the photosynthetic performance decreased showing a slight recovery in presence of gyp -sum amendment at the end of experiment. Instead, the more Al-resistant cultivar (Legacy) did not change its photosynthetic parameters in presence of the gypsum amendments during the treatment, whereas in Brigitta, only a slight recovery at the end of treatment was evidenced by the gypsum application. Thus, in relation to these parameters the gypsum amendment was efficient in complete recovery from the toxic Al effect in the Al-resistant cultivar Brigitta and a slight recovery of the toxic Al effect in the Al-sensitive cultivar Bluegold. Nonetheless, this amendment is a good alternative to ameliorate Al toxicity in Al-sensitive cultivars and additionally provides a good source of Ca and S.

Degradation of Lindane (γ-HCH) in a Mollisol as Effected by Different Soil Amendments

Soil amendments play an important role in management of pesticide residues. In this study, incubation experiment was conducted using the surface (0 - 15 cm) sample of a mollisol supplied with different soil amendments (farmyard manure, cow-dung slurry, pyrite and gypsum) to investigate the effect of amendments on the dissipation of lindane in mollisols. Dissipation of lindane in soil was studied at eight consecutive samplings (0, 1, 3, 5, 7, 10, 15 and 30 d). The results indicated that soil amendments could promote the degradation of lindane in soil. After 30 d of incubation 79% degradation was observed in the untreated soil (without any amendment) whereas, in the case of farmyard manure and cow-dung slurry amended soils, 83% and 91% degradation was observed, respectively. The pyrite and gypsum amendments also enhanced the degradation of lindane in soils, but the effect was less pronounced as compared to the organic amendments. Enhanced degradation in soil treated with organic amendments could be attributed to stimulated microbial activity after the addition of organic amendments. These addition, under different soil management conditions, minimize the persistence of lindane and consequently the risk of leaching and seepage into aquifers.

EXAFS speciation and phytoavailability of Pb in a contaminated soil amended with compost and gypsum

Due to unregulated uses of lead pellets for hunting purposes in Japan, soils and sediments in some river basins and wetlands have become highly contaminated with Pb. Deterioration of natural vegetation has occurred sporadically in these areas, and therefore revegetation is needed for ecological restoration. The objectives of the present study were to assess the effects of surface applications of compost and gypsum amendments on Pb availability to a watercress plant ( Nasturtium officinale W.T. Aiton) and molecular-scale speciation of Pb in soil solid phases. The compost and gypsum amendments significantly decreased dissolved Pb and Sb in pore water. The concentration of Pb in aboveground plant tissues was 190 mg kg − 1 in the control soil and was reduced to < 20 mg kg − 1 in the compost and gypsum-amended soils. The concentration of Sb in plants grown in the control soil was 13 mg kg − 1 , whereas that in the soils receiving compost and gypsum decreased below detectable levels. Redox potential was higher in vegetated soils (ave. 349 mV) than in the unvegetated soils (ave. 99 mV) due to oxygen introduced by plant roots. Extended X-ray absorption fine structure (EXAFS) spectroscopy illustrated that Pb occurred as Pb sorbed on birnessite and/or ferrihydrite (Pb–Mn/Fe, ~ 60%) and Pb sorbed on organic matter (Pb-org, ~ 15%), and galena (PbS, ~ 10%) in the vegetated and unvegetated control soils. The compost amendment increased the proportion of Pb-org by 2-fold than in the control soils. The amended soils with plant growth decreased the proportion of Pb–Mn/Fe phases by half of that without plant growth. Galena and anglesite (PbSO 4) were not detected in compost-amended soils and even in gypsum-amended soils since a significant soil reduction to anoxic levels did not occur in the entire soil. The present study indicated that, under flooded conditions, surface applications of compost and gypsum amendments reduced plant Pb uptake from the Pb contaminated soil.

Polyacrylamide and gypsum amendments for erosion and runoff control on two soil series

Application of polyacrylamide (PAM), gypsum, or their combination generally decreases erosion and runoff. However, their benefits are uncertain for soils with varying properties. The objectives of this study were to evaluate the effects of 5 Mg ha⁻¹ (2 tn ac⁻¹) gypsum (5G), 20 kg ha⁻¹ (18 lb ac⁻¹) PAM (20P), 40 kg ha⁻¹ (36 lb ac⁻¹) PAM (40P), and 20 kg ha⁻¹ (18 lb ac⁻¹) PAM with 5 Mg ha⁻¹ gypsum (20P+5G) for increasing time to initial runoff (TRO), decreasing cumulative runoff (RO), and decreasing cumulative sediment loss (SL) after 1 hour of a simulated rainfall on soil samples from two soil series (Hoberg and Brussels). Soils were packed to a bulk density of 1.3 Mg m⁻³ (81 lb ft⁻³) in test beds 0.3 × 0.3 × 0.15 m (12 × 12 × 6 in) set to a slope of 20% and subjected to a 61 mm h⁻¹ (2.4 in hr⁻¹) simulated rainfall with a kinetic energy of 1.5 kJ m⁻² h⁻¹ (103 ft lb ft⁻² hr⁻¹). Differences in TRO, RO, and SL for four soil samples (two sample depths per soil series) and four amendments plus an unamended check were all significantly different (<i>p</i> &lt; 0.01). Amendments of 20P, 40P, and 20P+5G increased TRO for soil samples with ≤0.5% organic matter (OM). The 5G amendment increased TRO for an acid soil sample (pH 4.1) with low OM (0.2%). The 20P+5G amendment produced an average 25% reduction in RO. Other amendments reduced RO by an average of 9% to 10%. The 40P amendment did not reduce RO, except for a Brussels silt loam surface soil that showed a 41% decrease. The 20P+5G amendment reduced SL by an average of 47% for soil samples, except for a high OM (3.7%) soil sample where OM likely interfered with soil-PAM bonding. The order of the amendment effectiveness for increasing TRO, and reducing RO and SL was 20P+5G &gt; 40P &gt; 20P &gt; 5G. Generally, the 20P+5G amendment was the best, irrespective of soil calcium (Ca⁺⁺) content. On average, this amendment increased TRO by 69%, decreased RO by 25%, and decreased SL by 36%. When this amendment was used on an acid soil sample with low OM (0.2%) and low cation exchange capacity (9.2 cmol_c kg⁻¹), it increased TRO by 71% and reduced RO and SL by 45% and 74%. The amendment effectiveness was influenced by soil properties, including texture, clay mineralogy, cation exchange capacity, and OM.

Changes in water quality following gypsum application to catchment soils of the Mount Lofty Ranges, South Australia

The impacts of gypsum application to pasture on the concentration and character of dissolved organic carbon (DOC) and on the inorganic profile of surface and subsurface water were investigated in the Mount Lofty Ranges of South Australia. Two adjacent sub-catchments of the Mount Bold reservoir were selected for study, where gypsum was applied at a rate of 15,000 kg ha −1 to one and the other left untreated, as a control. Gypsum amendment led to reductions in DOC concentrations in surface and subsurface flows of about 50%, significant increases in aqueous Ca, Mg, Mn and Na and lower concentrations of other metals (Al, Fe) due to Ca 2+ exchange. Natural organic matter (NOM) in water from the gypsum-treated site was found to have a lower relative aromaticity compared with the control. Alum treatment of control and gypsum-treated waters by a jar test procedure led to 73% and 48% removal of DOC, respectively, resulting in similar residual concentrations. This indicates that DOC removed by traditional alum treatment of drinking water supplies is also susceptible to in situ gypsum treatment, probably via a similar metal-catalysed aggregation mechanism. We conclude that gypsum application to soils of medium to heavy texture has potential to enhance their capacity to bind NOM, thereby lowering DOC concentrations in surface and subsurface flows.

Evaluation of amendments used to prevent sodification of irrigated fields

Gypsum and S are applied to soils being irrigated with Na–HCO3 dominated coalbed natural gas (CBNG) produced water to protect soil structure and fertility. Wyoming law requires beneficial use of produced water and irrigation with CBNG produced water in the semi-arid Powder River Basin is becoming more common. Strontium isotopes were used to evaluate the effectiveness of the gypsum and S applications in preventing sodification of these irrigated soils. The isotope ratio of Sr on the cation exchange complex of irrigated soil falls between that of the gypsum amendment (0.7074) and that of local soil (0.712–0.713). Strontium isotopes indicate that, to a depth of 30 cm, as much as 50% of the Sr on the irrigated soil cation exchange sites originated from the applied gypsum amendment on a field irrigated for 3 a. This was also true to a depth of 5 cm on a field irrigated less than 1 a. Strontium isotope ratio measurements of vegetation illustrate plant utilization of Sr from gypsum amendments, thereby reinforcing the conclusions about the presence of Sr from gypsum on the soil’s exchange sites. This Sr tracing technique may be useful in a wide variety of settings where monitoring soil health is necessary, especially in settings where poor quality water is used for irrigation: a more common occurrence as demand for fresh water increases.

Physico‐chemical changes in bauxite residue following application of spent mushroom compost and gypsum

AbstractPhysical properties exhibited by unvegetated mine wastes pose limitations to vegetation establishment and growth. In an attempt to promote vegetation cover on bauxite residue, a field trial was established to determine the effect of spent mushroom compost (SMC) and gypsum amendment on enhancing the physical properties of the residue. SMC was incorporated at rates of 0, 60, 80 and 120 t ha−1 with gypsum at 0, 40 and 90 t ha−1 and Holcus lanatus sown at a rate of 80 kg ha−1.The addition of SMC and gypsum was beneficial in improving the physical properties of the residue and promoting growth. Principally increasing organic content of the residue decreased bulk density and particle density whilst improving substrate porosity. Residue pH, EC and sodicity of the residue were also affected by the amendments, which positively impacted on microaggregate stability and preventing clay dispersion. Pearson correlations demonstrate that the most significant parameters in determining clay dispersion potential are the pH and the exchangeable sodium percentage (ESP) of the residue. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Soil Solarization as a Component of an Integrated Program for Control of Raspberry Root Rot.

Field and growth chamber studies were conducted during 2000 to 2005 to determine the efficacy of soil solarization for the control of Phytophthora root rot of raspberry (PRR). The exposure time that was lethal to Phytophthora rubi cultures on V8 juice agar plates was evaluated at intervals up to 240 h and at a range of temperatures from 20 to 35°C. Colonies incubated at 20 and 25°C nearly covered the plates in 240 h, while radial growth slowed at 27°C and ceased at temperatures ≥29°C. The exposure times required to kill P. rubi were estimated to be 222 h at 29°C, 168 h at 31°C, 108 h at 33°C, and 52 h at 35°C. Previous exposure to shorter durations at temperature ≥29°C slowed growth of colonies when they later were incubated at 20°C. Field trials were established in 2000 and 2003 at three locations in Washington State to evaluate soil solarization for the management of PRR. Cumulative hours with soil temperatures >29°C at 30 cm soil depth in solarized plots exceeded 200 h in each trial. In the 2000 trial, combinations of solarization, bed shape, and amendments of gypsum were evaluated. Over the 3 years after planting PRR-susceptible raspberry 'Malahat' and 'Willamette', primocane growth and survival were greater (P < 0.05) in raised bed plots that were solarized than in solarized and nonsolarized flat bed plots or hilled bed plots with gypsum. In 2003, trials were initiated to evaluate solarization in combination with applications of mefenoxam and fosetyl-Al. In 2004, solarization increased (P < 0.05) primocane growth of 'Malahat' and 'Qualicum' raspberries at both locations compared to application of fungicides alone and nontreated control plots. At both locations in 2005, density and growth of 'Qualicum' primocanes were greatest in solarized plots, while canes in solarized and fungicide only plots of 'Malahat' were similar. Incidence of diseased canes was lowest in plots that received fungicides. Primocane survival and fruit yields were very low at both locations in the third season because of favorable conditions for PRR and plant stress in late spring. These results indicate that soil solarization can be an effective component of integrated management of PRR in the Pacific Northwest, especially when combined with raised beds and gypsum amendments.

Soil amendments and cultivar selection can improve rice yield in salt-influenced (tsunami-affected) paddy fields in Sri Lanka

The tsunami disaster in the Indian Ocean in December 2004 caused devastation of agricultural soils by salt water over wide areas. Many rice fields located close to the coast were affected by the flood of seawater. Electric conductivity (EC) of soils in tsunami-affected rice fields was found to be higher compared to unaffected fields 2 years after the tsunami. Four soil amendments (gypsum, dolomite, cinnamon ash and rice-husk-charcoal) were tested for their influence on improving the yield parameters of rice grown in a tsunami-affected and a non-affected area. Yield parameters were compared with an untreated control of the same cultivar (AT362) and with a salt resistant rice variety (AT354). The salt resistant variety had the highest grain yield. The two amendments gypsum and rice-husk-charcoal led to an increase in grain yield compared to the untreated control, whereas dolomite and cinnamon ash had no significant effect on grain yield.