Control of hydraulic conductivity and chromium mobility in soil-drilling fluid mixtures by polyacrylamide

Land disposal of water-based oil and gas well drilling fluid is an cause of environmental concern due to the high salt concentration and potential chromium (Cr) contamination of groundwater. Safe land disposal of waste drilling fluid and remediation of drilling fluidaffected soils require an adequate hydraulic conductivity for the leaching of excessive salt accumulation and immobilization of Cr to prevent groundwater contamination. Anahuac and Crowley sandy loam surface soils sampled near the southern Louisiana-Texas state line were treated by a batch method with the drilling fluid and two cationic polyacrylamides (PAMs). The PAMs were used as amendments to increase the hydraulic conductivity and the adsorption capacity of the drilling fluid-affected soils for the Cr organic complex. Hydraulic conductivity of the soil-drilling fluid mixtures and light transmittance of the leachates increased, while the Cr mobility decreased by the PAM treatment. The larger PAM molecules were more effective in improving the hydraulic conductivity of the soil-drilling fluid mixtures than the smaller molecules. The Anahuac soil-drilling fluid mixtures showed a higher hydraulic conductivity and lower Cr mobility than the Crowley soil-drilling fluid mixtures apparently because of the higher organic matter content and lower sodium adsorption ratio (SAR) of the former. The hydraulic conductivity, light transmittance, and Cr mobility data indicated that the PAM treatment and soil organic matter enhanced the flocculation and aggregate stability of the soil-drilling fluid mixtures and contributed to the immobilization of the Cr added as lignosulfonate to the soils.     

Municipal Solid Waste Compost Improves Crop Productivity in Saline-Sodic Soil: A Multivariate Analysis of Soil Chemical Properties and Yield Response

A pot experiment was conducted in sandy clay loam saline-sodic soil to assess the effects of farm yard manure (FYM), municipal solid waste (MSW) composts and gypsum application on nitrate leaching, soil chemical properties and crop productivity under rice-wheat cropping system. It also aims at establishing the correlation between soil phsico-chemical properties and yield response using principle component analysis and Pearson correlation analysis. The MSW was decomposed aerobically, an-aerobically and co-composted. Maximum nitrate leaching was observed during rice (75.9 mg L^?1) and wheat (37.2 mg L^?1) with an-aerobically decomposed MSW as compared with control treatment. Results revealed a decrease in soil pH (?6.95% and ?8.77%), electrical conductivity (EC) (?48.13% and ?51.04%), calcium carbonate (CaCO₃) (?40.30% and ?48.96%), and sodium adsorption ratio (SAR) (?40.27% and ?45.98%) with an-aerobically decomposed MSW compost during rice and wheat, respectively. In this treatment, organic matter (OM) (93.55% and 121.51%) and cation exchange capacity (CEC) (19.31% and 31.79%) were the highest as compared with control treatment during rice and wheat, respectively. Rice and wheat growth were significantly (p≤ 0.05) increased by an-aerobically decomposed MSW followed by co-compost, aerobically decomposed MSW, FYM, gypsum and control. Furthermore, Pearson correlation coefficients predicted significant positive correlation of yield with soil OM, and CEC while inverse relationship was observed with EC, pH, CaCO₃, and nitrogen use efficiency. Soil amelioration with organic and gypsum amendments was further confirmed with principal component analysis. This study has proved an-aerobically decomposed MSW as an effective solution for MSW disposal, thereby improving soil chemical properties and crop productivity from sandy clay loam saline-sodic soil.     

Calcite and gypsum solubility products in water‐saturated salt‐affected soil samples at 25°C and at least up to 14 dS m−1

Calcite and gypsum are salts of major ions characterized by poor solubility compared with other salts that may precipitate in soils. Knowledge of calcite and gypsum solubility products in water‐saturated soil samples substantially contributes to a better assessment of processes involved in soil salinity. The new SALSOLCHEMIS code for chemical equilibrium assessment was parameterized with published analytical data for aqueous synthetic calcite and gypsum‐saturated solutions. Once parameterized, SALSOLCHEMIS was applied to calculations of the ionic activity products of calcium carbonate and calcium sulphate in 133 water‐saturated soil samples from an irrigated salt‐affected agricultural area in a semi‐arid Mediterranean climate. During parameterization, sufficiently constant values for the ionic activity products of calcium carbonate and calcium sulphate were obtained only when the following were used in SALSOLCHEMIS: (i) the equations of Sposito & Traina for the free ion activity coefficient calculation, (ii) the assumption of the non‐existence of the Ca (HCO ₃)⁺ and CaCO₃^o ion pairs and (iii) a paradigm of total ion activity coefficients. The value of 4.62 can be assumed to be a reliable gypsum solubility product (pKs) in simple aqueous and soil solutions, while a value of 8.43 can only be assumed as a reliable calcite solubility product (pKs) in simple aqueous solutions. The saturated pastes and saturation extracts were found to be calcite over‐saturated, with the former significantly being less so (p IAP = 8.29) than the latter (p IAP = 8.22). The calcite over‐saturation of saturated pastes increased with the soil organic matter content. Nevertheless, the inhibition of calcite precipitation is caused by the soluble organic matter from a dissolved organic carbon threshold value that lies between 7 and 12 mm . The hypothesis of thermodynamic equilibrium is more adequate for the saturated pastes than for the saturation extracts.     

Gypsic pedofeatures and elementary pedogenetic processes of their formation

Elementary pedogenetic processes forming gypsic pedofeatures in gypsiferous soils are discussed. Several groups of such processes are distinguished: (1) weathering of gypsum-bearing rocks; (2) gypsum formation associated with weathering of sulfuric (pyritic) rocks; (3) precipitation of gypsum owing to the inflow of soil solutions saturated with Ca and SO₄ and their evaporative concentration; (4) gypsum formation owing to exchange reactions in soils between calcium in the exchange complex and sodium sulfate solutions; (5) gypsum formation upon interaction of calcium carbonates with sodium sulfate water resulting in the loss of CaCO₃ and gypsum accumulation (decalcification process); (6) colluvial and alluvial redeposition of gypsum in the landscape with its accumulation in the subordinate positions, where gypsiferous soils are formed; and (7) eolian deposition of gypsum on the soil surface with the formation of gypsum-bearing horizons. The micromorphological specificity of the gypsic pedofeatures reflects the processes of their destruction and/or accumulation in the soil profiles. It is shown that gypsum accumulation in soils is a pedogeochemical process that manifests itself in different natural zones upon the presence of gypsum sources.     

Influence of Increasing Soil Copper Concentration on the Susceptibility of Phosphomonoesterase and Urease to Heat Disturbance

The sorption of chromium (Cr) species to soil has become the focus of research as it dictates the bioavailability and also the magnitude of toxicity of Cr. The sorption of two environmentally important Cr species [Cr(III) and Cr(VI)] was examined using batch sorption, and the data were fitted to Langmuir and Freundlich adsorption isotherms. The effects of soil properties such as pH, CEC, organic matter (OM), clay, water-extractable SO₄ ^2– and PO₄ ^3–, surface charge, and different iron (Fe) fractions of 12 different Australian representative soils on the sorption, and mobility of Cr(III) and Cr(VI) were examined. The amount of sorption as shown by K _f was higher for Cr(III) than Cr(VI) in all tested soils. Further, the amount of Cr(III) sorbed increased with an increase in pH, CEC, clay, and OM of soils. Conversely, the chemical properties of soil such as positive charge and Fe (crystalline) had a noticeable influence on the sorption of Cr(VI). Desorption of Cr(VI) occurred rapidly and was greater than desorption of Cr(III) in soils. The mobility of Cr species as estimated by the retardation factor was higher for Cr(VI) than for Cr(III) in all tested soils. These results concurred with the results from leaching experiments which showed higher leaching of Cr(VI) than Cr(III) in both acidic and alkaline soils indicating the higher mobility of Cr(VI) in a wide range of soils. This study demonstrated that Cr(VI) is more mobile and will be bioavailable in soils regardless of soil properties and if not remediated may eventually pose a severe threat to biota.     

A rapid method to determine cation exchange capacity and exchangeable bases in calcareous,gypsiferous, saline and sodic soils

Summary

A simple, single‐step extraction with LiEDTA for the estimation of CEC and exchangeable bases in soils has been developed. Multivalent cations are stripped from the soil adsorption sites by the strongly chelating agent EDTA, and are replaced by Li. In soils without CaCO₃ or water soluble salts, exchangeable divalent cations (Ca, Mg) are chelated by EDTA and exchangeable monovalent cations (Na, K) are replaced in a single extraction step using 0.25–2.5 g of soil and 10.0 ml of extractant.

In calcareous soils the CEC can be determined in the same way, but for the extraction of exchangeable Ca and Mg, another separate extraction is needed because dissolution of calcite by EDTA is unavoidable. This extraction is done with as much NaEDTA as needed to extract only exchangeable Ca and Mg in a 1:2 (m/V) soil/alkaline‐50% (V/V) aethanolic solution to minimize dissolution of calcite.

In gypsiferous soils gypsum is transformed into insoluble BaSO₄ and soluble CaEDTA by LiBaEDTA thus avoiding interference of Ca from dissolution of gypsum, which renders the traditional methods for determining CEC unsuitable for such soils. To determine exchangeable Ca and Mg, Na₄EDTA is used as for calcareous soils.

In saline/sodic soils replacement of Na by Li is incomplete but the Na/Li‐ratio at the complex after extraction is proportional to the molar Na/Li‐ratio in the extracts, so that the CEC and original exchangeable sodium (ESP) content can be calculated. Additional analysis of Cl and, if necessary, SO₄ in the extracts of saline soils can be used to correct for the effect of dissolution of the salts on the sum of exchangeable cations.

This new method is as convenient as the recently developed AgTU (silverthiourea), but is better suitable for calcareous and gypsiferous soils.     

Effect of Primary Treated Biomethanated Spentwash on Soil Properties and Yield of Sunflower (Helianthus annuus L.) on Sodic Soil

The field experiment on effect of primary treated biomethanated spentwash (PBSW) on physiochemical and biological properties of soil and yield of sunflower (Helianthus annuus L.) on sodic soil was conducted at the Postgraduate Farm, Mahatma Phule Agricultural University, Ahmednagar, India, during 2008–9. The experiment was laid out in a randomized block design (RBD) with nine treatments [control, varying doses of PBSW (30, 60, 90, 120, 150, and 180 m³ ha^?1), farmyard manure (FYM) + recommended dose of fertilizer (RDF), and FYM + gypsum at 50% gypsum requirement (GR) + RDF] with three replications. The FYM dose was 5 Mg ha^?1. The experimental soil was sodic calcareous, being of the Sawargaon series of isohyperthermic family of Vertic haplustepts with high exchangeable sodium percentage (ESP), low available nitrogen (N) and phosphorus (P), and high available potassium (K). The results revealed that the physical properties [bulk density, mean weight diameter (MWD) of water-stable aggregates, and hydraulic conductivity] of soil were improved in both layers of sodic soil (0–30 and 30–60 cm) as a result of the addition of increased doses of PBSW. The significant reduction in pH, calcium carbonate (CaCO₃), ESP and increase in organic carbon, cation exchange capacity (CEC) and electrical conductivity (EC) were observed in both soil layers as a result of the addition of PBSW at 180 m³ ha^?1. The changes in chemical properties were also seen in the treatment of FYM + GR + RDF, but it was at par with lower doses of PBSW (30 to 90 m³ ha^?1). The microbial populations [bacteria, fungi, actinomycetes, azotobacter, and phosphate-solubilizing bacteria] increased with an increase in the levels of application of PBSW. However, it was maximum in FYM + GR + RDF treatment, and it showed an overall increase up to the flowering stage and thereafter reduced at harvest. The soil basal respiration as mg carbon dioxide (CO₂) increased with the increase in levels of PBSW application but it was the greatest in the FYM + gypsum + RDF treatment. Among the PBSW treatments, the greatest activities of soil enzymes (urease, dehydrogenase, and acid phosphatase) under the treatment of 180 m³ ha^?1 PBSW were observed at the flowering stage. The available N, P, and K after harvest of sunflower crop were significantly greater in the PBSW treatment applied at 180 m³ ha^?1; however, N, P, and K uptake and yield of sunflower were significantly greater in FYM + RDF + gypsum treatment followed by FYM + RDF and 180 m³ ha^?1 of PBSW.     

Combined Effects on Nitrogen Fertilization and Soil of CaCO3 Contents on Corn Performance in Al-Marj Soil,Libya

A two-year field trial was conducted at Al-Marj Research Center, northeast Libya, during the summers of 1996 and 1997 to examine the effect of nitrogen (N) fertilizers on corn (Zea mays L.) growth in a Libyan soil (fine mixed thermic, Typic Haploxerolls) amended with different calcium carbonate (CaCO₃) levels. Two N fertilizer sources (urea and diammonium phosphate, or DAP) were used at three application rates (0, 80, and 160 kg N/ha). The CaCO₃ treatments were 1%, 6%, and 12% based on the soil weight of a 15 cm furrow slice. A basal phosphorus (P) dose of 46 kg P₂O₅/ha as triple superphosphate was applied to all experimental plots before planting. The experimental plots were arranged in a randomized split-split plot design with three replications. The parameters measured included corn grain weight, plant dry-matter content, leaf contents of N, P, potassium (K), calcium (Ca), and magnesium (Mg). The plant dry matter and corn-grain yield were significantly decreased by CaCO₃, but were significantly increased by N fertilizer rates. Average grain yield dropped from 8 to 3 Mg/ha at 1% and 12% soil CaCO₃ content, respectively. Generally, the N source did not have a significant effect on dry matter or on grain yield. The negative effect of CaCO₃ on yield was associated with concomitant significant reduction in leaf N, P, K, and Mg contents, and an increase in Ca content. However, the leaf levels of these nutrients were considered sufficient for corn growth. Therefore, the reduction of leaf-N by CaCO₃ in fertilized soils might have been the major cause of corn dry-matter and grain-yield reductions.     

Sodium removal from a calcareous saline–sodic soil through leaching and plant uptake during phytoremediation

Saline–sodic and sodic soils are characterized by the occurrence of sodium (Na⁺) to levels that can adversely affect several soil properties and growth of most crops. As a potential substitute of cost‐intensive chemical amelioration, phytoremediation of such soils has emerged as an efficient and low‐cost strategy. This plant‐assisted amelioration involves cultivation of certain plant species that can withstand ambient soil salinity and sodicity levels. It relies on enhanced dissolution of native calcite within the root zone to provide adequate Ca²⁺ for the Na⁺ Ca²⁺ exchange at the cation exchange sites. There is a lack of information for the Na⁺ balance in terms of removal from saline–sodic soils through plant uptake and leaching during the phytoremediation process. We carried out a lysimeter experiment on a calcareous saline–sodic soil [pH of saturated soil paste (pH_s) = 7.2, electrical conductivity of the saturated paste extract (EC_e) = 4.9 dS m⁻¹, sodium adsorption ratio (SAR) = 15.9, CaCO₃ = 50 g kg⁻¹]. There were three treatments: (1) control (without application of a chemical amendment or crop cultivation), (2) soil application of gypsum according to the gypsum requirement of the soil and (3) planting of alfalfa (Medicago sativa L.) as a phytoremediation crop. The efficiency of treatments for soluble salt and Na⁺ removal from the soil was in the order: gypsum ≈ alfalfa > control. In the phytoremediation treatment, the amount of Na⁺ removed from the soil through leaching was found to be the principal cause of reduction in salinity and sodicity. Copyright © 2003 John Wiley & Sons, Ltd.     

Short‐Term Effect of Lime,Phosphorus, and Iron Amendments on Water‐Extractable Lead and Arsenic in Orchard Soils

Abstract

Lead arsenate was extensively used to control insects in apple and plum orchards in the 1900s. Continuous use of lead arsenate resulted in elevated soil levels of lead (Pb) and arsenic (As). There are concerns that As and Pb will become solubilized upon a change in land use. In situ chemical stabilization practices, such as the use of phosphate‐phosphorus (P), have been investigated as a possible method for reducing the solubility, mobility, and potential toxicity of Pb and As in these soils. The objective of this study was to determine the effectiveness of calcium carbonate (lime), P, and iron (Fe) amendments in reducing the solubility of As and Pb in lead‐arsenate‐treated soils over time. Under controlled conditions, two orchard soils, Thurmont loam (Hapludults) and Burch loam (Haploxerolls), were amended with reagent‐grade calcium carbonate (CaCO₃), iron hydroxide [Fe(OH)₃], and potassium phosphate (KH₂PO₄) and incubated for 16 weeks at 26°C. The experimental results suggested that the inorganic P increased competitive sorption between H₂PO₄ ^? and dihydrogen arsenate (H₂AsO₄ ^?), resulting in greater desorption of As in both Thurmont and Burch soils. Therefore, addition of lime, potassium phosphate, and Fe to lead‐arsenate‐contaminated soils could increase the risk of loss of soluble As and Pb from surface soil and potentially increase these metal species in runoff and movement to groundwater.     

Sugarcane yield and plant nutrient response to sulfur-amended Everglades histosols

High soil pH causes leaf nutrient deficiencies and reduces sugarcane yield. Soil pH in Florida histosols has been increasing as these soils subside and depth to limestone is decreased. A factorial experiment of four sulfur (S) rates and three added calcium carbonate (CaCO₃) levels in soil was designed to determine S-amendment effectiveness in reducing pH and increasing nutrient availability in sugarcane as calcium (Ca) carbonate levels were increased. Sulfur-amendment and increased CaCO₃ level had limited effects on yield and leaf nutrient concentrations during the growing season. Most leaf nutrients were within optimum range except nitrogen (N), phosphorus (P), iron (Fe), and manganese (Mn). Unexpected increases in Mn concentrations with added CaCO₃ were associated with reducing conditions due to increased soil bulk density. High soil pH caused Mn deficiencies in the plants. Soil pH, P and Mn concentrations were important factors in predicting sugarcane yield.     

ON THE POSSIBILITY OF CHARACTERIZING CALCIUM PHOSPHATES IN CALCAREOUS SOILS BY ISOTOPIC EXCHANGE

Characterization of calcium phosphates depended upon the nature and the amount of phosphate used to react with reagent-grade CaCO₃. Formation of octa-calcium phosphate (OCP) was inferred from the solubility equilibria after reacting CaCO₃ with KH₂PO₄ solutions. Isotopic exchange measurements confirmed the presence of OCP, when the amount of P retained exceeded 44 μrnoles/g CaCO₃. The determined surface-Ca to surface-P molar ratios were close to the theoretical Ca/P ratio of 1.33 in OCP. As P retained on CaCO₃ decreased the surface Ca/P ratio markedly increased because of interference from surface Ca of the CaCO₃. When CaCO₃ was reacted with monocalcium phosphate (MCP), solubility equilibria indicated the formation of dicalcium phosphate dihydrate (DCPD). Isotopic exchange measurements, however, showed an average Ca/P ratio of only 0.375. This value corresponds to the composition of the metastable triple point solution (MTPS) formed on MCP dissolution rather than to the Ca/P ratio in DCPD. MCP application decreased the measured surface-Ca (exchangeable Ca) either for soil or Ca-resin, because of blocking of the exchange sites by the MCP reaction products and, consequently, a lower rate of isotopic exchange. Surface phosphorus of the two investigated calcareous soils proved to be proportional to the lowering in pH initiated by MCP application. Characterization of MCP reaction products in calcareous soils may thus prove infeasible, in view of the unexpected reduction in surface-Ca and the pH dependency of surface P.     

成县土壤数值分类的初步研究

本文应用标准化数据—斜交距离—误差平方和聚类分析法对甘肃成县34个土壤剖面进行了数值分析研究。研究结果表明,供试34个剖面可分为五个土壤类型。对五类土壤的pH值、有机质、代换量、SiO₂、Al₂O₃、Fe₂O₃、CaCO₃及粘粒含量八项主要指标进行方差分析的结果表明,除pH、代换量和SiO₂含量未达类型间F测验显著水平外,其他各项指标均达显著或极显著水平。各类土壤在地理分布、植被类型、田间石灰反应等特性上也有明显的差异,并且每一类土壤都具有一定的发生学意义。并分别对应于棕壤、淋溶褐土、褐土、碳酸盐褐土和潮土五种发生学类型。     

Determination of gypsum and cation exchange capacity in arid soils by a resin method

A simple and direct method for the quantitative determination and removal of gypsum in gypsiferous soil samples was developed. This procedure incorporates a combination of Na- and Cl-resins to aid in the dissolution of the gypsum. The primary effect of the exchange resins is to buffer the composition of the solution and thereby keep the rate of gypsum dissolution high. The dissolved calcium and sulfate exchange with the sodium and chloride on the resins, resulting in a solution containing primarily Na and Cl. The electrical conductivity of the supernatant is directly related to the amount of gypsum dissolved. This method was used on samples of artificially prepared mixtures and naturally gypsiferous soils. Compared with results obtained by other methods, the resin method gave identical results, while requiring much less time and fewer calculations. The resin method was also used to remove gypsum from gypsiferous soil samples prior to CEC determinations to see if the presence of gypsum effects the CEC as determined by the Bower method. No significant effect was noted for soil samples containing less than 20% gypsum.     

Estimation of Saturated Paste Extracts’ Electrical Conductivity from 1:5 Soil/Water Suspension and Gypsum

Texture and salt type influence the relationships between saturated paste electrical conductivity (EC_e) and EC of other soil/water ratios. The objectives of this study were to develop and validate relationships between EC_e and EC_1:5 suspension for soils in Yazd Province and evaluate the effects of soil texture and gypsum on those relationships. Three hundred twenty-two soil samples were collected, of which 272 (all data) were used to develop the models and 50 were used to validate them. The soils were divided into two general textural categories of coarse and fine and two categories of with (G) and without gypsum (NG). Gypsum content had a stronger impact on the accuracy of the suspension method in predicting EC_e than texture. The EC_e = 5.60 EC_1:5 ? 4.37 and EC_e = 5.37 EC_1:5 + 0.57 models are recommended for soils with and without gypsum, respectively. The methodology can be implemented in other regions, particularly if gypsum is present.     

Zinc Sorption in Selected Soils

Abstract

The adsorption of nutrient elements is one of the most important solid‐ and liquid‐phase interactions determining the retention and release of applied plant nutrients and the efficiency of fertilization. The study showed that the soils with high cation exchange capacity (CEC), CaCO₃, organic matter contents, and heavy texture adsorbed more zinc (Zn). The alkaline soils from Pakistan adsorbed more Zn than English acidic soils. Langmuir and Freundlich isotherm fit was excellent, and r² values for the Langmuir isotherm were highly significant (r²=0.84 to 0.99). The Langmuir b values, representing the adsorptive capacity of a soil, increased as the texture fineness increased in the soil, with increases in the concentration of adsorptive material (such as organic matter and CaCO₃) and with increases in CEC and pH. The alkaline soils from Pakistan had higher bonding energy constant and higher log Kf values than the acidic English soils. Sequential extraction of Zn in these soils showed that most of the Zn was held in CaCO₃ pool in the alkaline soils, whereas in acidic soils adsorbed Zn was in exchangeable form.     

The effect of gypsum and other salts on the growth of narrow‐leafed lupins

Abstract

Glasshouse experiments were conducted to establish the cause of poor lupin growth in the presence of gypsum in field trials which had been conducted in Western Australia. In the first experiment, Bradyrhizobium‐inoculated lupins were grown in nutrient solutions with varying concentrations (1, 3, 5, and 10 mM) of calcium (Ca) and sulfate (SO₄) added as either CaSO₄, K₂SO₄, or CaCl₂ to establish whether gypsum caused Ca or SO₄ toxicity to the plants. Although a general decrease in lupin plant growth was observed as the concentration of each salt increased, there was no evidence that either Ca or SO₄ directly caused toxicity to the plants. Two soil experiments were therefore conducted to investigate lupin growth responses to the salts in a soil environment. The first soil experiment was conducted in a yellow earth— the same soil in which lupins had been adversely affected by gypsum in the field. The second soil experiment was conducted in the topsoil of a siliceous sand. Basal nutrients and different rates of CaSO₄, K₂SO₄, and CaCl₂ were added so that similar amounts of Ca and SO₄ were present for each treatment at a given application rate. In both soils, lupin growth generally decreased as the application rate of treatments increased, although the magnitude of the decrease in growth was higher in the yellow earth than the siliceous sand. The strongest correlation between lupin growth and a soil solution chemical property was a log‐linear relationship between the shoot or root dry weight and the electrical conductivity (EC) of the soil solution. Plant nutrition was affected by different treatments, particularly with respect to nutrient balances. It is suggested that a high ionic strength in the soil, which results when gypsum is applied in the field, may contribute to the lupin yield decline. Possible reasons for the effect are discussed.     

黄土性土壤在连续液流条件下吸附、解吸磷酸根的动力学研究

采用连续液流法研究了黄土性土壤吸附,解吸磷酸根的动力学性质。结果表明：（１）供试土壤对磷酸根的吸附,解吸扫速率可分为快,中,慢三种反应类型;（２）描述吸附,解吸反应的最优模型均为Ｅｌｏｖｉｃｈ方程,最差模型分别为一级反应方程及双常数方程,拟合差的模型对反应速率变化“敏感”,可用于反应类型划分和机理研究;（３）粘粒含量及代换量对吸附速率有著影响,游离铁对吸附速率,ＣａＣＯ３对较低温度下的吸附及较高温     

Calcium Sulphate versus Lime as Fertilizer Filler: Effects on Ammonium and Nitrate Uptake by Perennial Ryegrass

Abstract

The recovery of ¹⁵N‐labelled nitrogen (N) by perennial ryegrass can be significantly increased by mixing gypsum (CaSO₄ · 2H₂O) into soil rooting medium at rates equivalent to 0.7 t ha^?1. Similar improvements in fertilizer N efficiency might be achieved, at less cost and more conveniently, by applying smaller amounts of CaSO₄ anhydrite more strategically to fertilizer microsites as a fertilizer filler or diluting agent, in calcium ammonium nitrate (CAN), in place of CaCO₃. With this in mind, two complementary pot experiments were conducted under simulated spring conditions in a controlled environment chamber. Use of CaSO₄ as diluting agent, in place of CaCO₃, appreciably enhanced (>30%) the uptake of labeled N by perennial ryegrass plants within the second week of regrowth, but thereafter, because losses of ¹⁵N‐labeled NO₃ ^?‐N from pots by denitrification or leaching had been minimal, plants in both treatments eventually recovered equal amounts of this N form from the soil.     

Gypsum and Texture Effects on the Estimation of Saturated Paste Electrical Conductivity by Two Extraction Methods

Abstract

Texture and salt type can influence the relationships between saturated paste electrical conductivity (EC_e) and EC of other soil/water ratios. The objectives of this study were to develop and validate relationships among EC_e, EC_1∶2, and EC_1∶5 for soils in Yazd Province, and evaluate the effects of texture and gypsum on those relationships. Two hundred thirty‐six soil samples were collected, of which 200 were used to develop and 36 were used to validate the models. The soils were divided into two textural categories, coarse and fine, and two categories, with and without gypsum. The 1∶2 procedure predicted EC_e of slightly more than 1∶5. Gypsum content had stronger impact on the accuracy of models in predicting EC_e than texture. The EC_e=4.0723EC_1∶2?5.7135 and EC_e=3.5142EC_1∶2+0.7615 models are recommended for soil with and without gypsum, respectively. The methodology can be implemented in any other region, particularly if gypsum is present.