Changes in soil nitrogen availability due to stand development and management practices on semi‐arid sandy lands,in northern China

Soil nitrogen (N) availability is one of the limiting factors for plant growth on sandy lands. Little is known about impacts of afforestation on soil N availability and its components in southeastern Keerqin sandy lands, China. In this study, we measured N transformation under sandy Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations of different ages (grassland, young, middle‐aged, close‐to‐mature) and management practices (non‐grazing and free‐grazing) during the growing seasons using the ion exchange resin bag method. Results showed that, for all plots and growing season, soil NH‐N, NO‐N, mineral N, and relative nitrification index, varied from 0·18 to 1·54, 0·96 to 22·05, 1·23 to 23·58 µg d⁻¹ g⁻¹ dry resin, and 0·76 to 0·97, respectively, and NO‐N dominated the available N amount due to intense nitrification in these ecosystems. In general, the four indices significantly increased in the oldest plantation, with corresponding values in non‐grazing sites lower than those in free‐grazing sites (p < 0·05). Our studies indicated that it is a slow, extended process to achieve improvement in soil quality after afforestation of Mongolian pine in the study area. Copyright © 2009 John Wiley & Sons, Ltd.     

Proton release by N2‐fixing plant roots: A possible contribution to phytoremediation of calcareous sodic soils

With a world‐wide occurrence on about 560 million hectares, sodic soils are characterized by the occurrence of excess sodium (Na⁺) to levels that can adversely affect crop growth and yield. Amelioration of such soils needs a source of calcium (Ca²⁺) to replace excess Na⁺ from the cation exchange sites. In addition, adequate levels of Ca²⁺ in ameliorated soils play a vital role in improving the structural and functional integrity of plant cell walls and membranes. As a low‐cost and environmentally feasible strategy, phytoremediation of sodic soils — a plant‐based amelioration — has gained increasing interest among scientists and farmers in recent years. Enhanced CO₂ partial pressure (P_CO2) in the root zone is considered as the principal mechanism contributing to phytoremediation of sodic soils. Aqueous CO₂ produces protons (H⁺) and bicarbonate (HCO₃^‐). In a subsequent reaction, H⁺ reacts with native soil calcite (CaCO₃) to provide Ca²⁺ for Na⁺ Ca²⁺ exchange at the cation exchange sites. Another source of H⁺ may occur in such soils if cropped with N₂‐fixing plant species because plants capable of fixing N₂ release H⁺ in the root zone. In a lysimeter experiment on a calcareous sodic soil (pH_s = 7.4, electrical conductivity of soil saturated paste extract (EC_e) = 3.1 dS m^‐1, sodium adsorption ratio (SAR) = 28.4, exchangeable sodium percentage (ESP) = 27.6, CaCO₃ = 50 g kg^‐1), we investigated the phytoremediation ability of alfalfa (Medicago sativa L.). There were two cropped treatments: Alfalfa relying on N₂ fixation and alfalfa receiving NH₄NO₃ as mineral N source, respectively. Other treatments were non‐cropped, including a control (without an amendment or crop), and soil application of gypsum or sulfuric acid. After two months of cropping, all lysimeters were leached by maintaining a water content at 130% waterholding capacity of the soil after every 24±1 h. The treatment efficiency for Na⁺ removal in drainage water was in the order: sulfuric acid > gypsum = N₂‐fixing alfalfa > NH4NO3‐fed alfalfa > control. Both the alfalfa treatments produced statistically similar root and shoot biomass. We attribute better Na+ removal by the N₂‐fixing alfalfa treatment to an additional source of H⁺ in the rhizosphere, which helped to dissolve additional CaCO₃ and soil sodicity amelioration.     

Amelioration of an acid ultisol by agricultural by‐products

Ultisols are widely distributed in the subtropical regions of China as well as in the world. High acidity of Ultisols limits plant growth and reduces crop yields. Amelioration of an acid Ultisol was investigated by incorporating the residues of canola (Brassica campestris L.), wheat (Triticum aestivum L.), rice (Oryza sativa), corn (Zea mays), soybean (Glycine max), peanut (Arachis hypogaea), faba bean (Vicia faba L.) and pea (Pisum sativum) and Chinese milk vetch (Astragalus sinicus L.) shoots after incubation of the agricultural by‐products for a maximum of 75 days, soil pH was increased by each of the plant materials. The degree of amelioration of the soil acidity by the plant materials was found to depend on the ash alkalinity and N content of the materials; the legumes of higher ash alkalinities and lower N contents, such as peanut straw and faba bean straw, led to the largest increases in soil pH, while the legumes of higher N contents showed less amelioration of the acidity to a certain degree, because of the release of protons during nitrification of NH from mineralisation of organic N. The non‐leguminous materials have medium amelioration effects and increased soil pH by 0·42–0·56 units at the end of incubation. The incorporation of the plant materials also increased exchangeable base status and reduced exchangeable Al, and thus decreased the toxicity of Al in the soil. This study demonstrates that plant materials, especially crop residues, can be used as amendments for acidic soils to restore degraded land in subtropical regions. Copyright © 2010 John Wiley & Sons, Ltd.     

Implication of Gypsum Rates to Optimize Hydraulic Conductivity for Variable‐Texture Saline–Sodic Soils Reclamation

Sodium (Na⁺) dominated soils reduce saturated hydraulic conductivity (K_s) by clay dispersion and plugging pores, while gypsum (CaSO₄•2H₂O) application counters these properties. However, variable retrieval of texturally different saline–sodic soils with gypsum at soil gypsum requirement (SGR) devised to define its quantity best suited to improve K_s, leach Na⁺ and salts. This study comprised loamy‐sand (LS), sandy loam (SL), and clay loam (CL) soils with electrical conductivity of saturation extract (EC_e) of ~8 dS m⁻¹, sodium adsorption ratio (SAR) of ~44 (mmol L⁻¹)^1/2 and exchangeable sodium of ~41%, receiving no gypsum (G₀), gypsum at 25% (G₂₅), 50% (G₅₀) and 75% (G₇₅) of SGR. Soils packed in lysimeters were leached with low‐carbonate water [EC at 0·39 dS m⁻¹, SAR at 0·56 (mmol L⁻¹)^1/2 and residual sodium carbonate at 0·15 mmol_c L⁻¹]. It proved that a rise in gypsum rate amplified K_s of LS ≫ SL > CL. However, K_s of LS soil at G₂₅ and others at G₇₅ remained efficient for salts and Na⁺ removal. Retention of calcium with magnesium (Ca²⁺ + Mg²⁺) by LS and SL soils increased by G₅₀ and decreased in G₇₅, while in CL, it also increased with G₇₅. The enhanced Na⁺ leaching efficiency in LS soil with G₂₅ was envisaged by water stay for sufficient time to dissolve gypsum and exchange and leach out Na⁺. Overall, the superiority of gypsum for LS at G₂₅, SL at G₅₀ and CL at G₇₅ predicted cost‐effective soil reclamation with a decrease in EC_e and SAR below 0·97 dS m⁻¹ and 5·92 (mmol L⁻¹)^1/2, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Multivariate analyses and spatial distribution of Manganese minerals in soils close to an abandoned Manganese mine

Four hundred soil samples were obtained from a 4 km² area close to the abandoned Kgwakgwe Mn oxide ore mine in order to investigate the environmental association of Mn minerals and concentrations in the soils. Manganese minerals and Mn concentrations in samples were identified by X‐ray diffractometry and atomic absorption spectrometry, respectively, and results statistically analysed. Bixbyte, Mn₂O₃; braunite, Mn⁺²MnSiO₁₂; ramsdellite, MnO₂; pyrolusite, β‐MnO₂ and cryptomelane, K_{2 − x}Mn₈O₁₆ were identified in soil samples at the study site but none of these minerals found in soil samples from the control site. Manganese concentrations in samples from the study area were significantly higher than those from the control site. Statistical data yielded seven clusters with distribution of the Mn minerals and concentrations as follows: cluster 1 dominated by Mn concentrations in soil, cluster 2 by none of the seven Mn minerals, cluster 3 by pyrolusite, cluster 4 by braunite, cluster 5 by cryptomelane, cluster 6 by bixbyite and cluster 7 by ramsdellite. Very weak associations of these minerals were depicted from their correlations. The clusters had a bearing on the spatial distribution of the different minerals. Comparing results obtained from the control site, and geological materials, to the soils from the study area, it is certain that Mn minerals and high Mn concentrations in soils originated from the surrounding geological materials. The mining activities most possibly have affected Mn concentrations' and minerals' occurrences in the soils at the study area. Copyright © 2009 John Wiley & Sons, Ltd.     

Driving forces for sodium removal during phytoremediation of calcareous sodic and saline–sodic soils: a review

Abstract. Sodic and saline–sodic soils are characterized by the occurrence of sodium (Na⁺) at levels that result in poor physical properties and fertility problems, adversely affecting the growth and yield of most crops. These soils can be brought back to a highly productive state by providing a soluble source of calcium (Ca²⁺) to replace excess Na⁺ on the cation exchange complex. Many sodic and saline–sodic soils contain inherent or precipitated sources of Ca²⁺, typically calcite (CaCO₃), at varying depths within the profile. Unlike other Ca²⁺ sources used in the amelioration of sodic and saline‐sodic soils, calcite is not sufficiently soluble to effect the displacement of Na⁺ from the cation exchange complex. In recent years, phytoremediation has shown promise for the amelioration of calcareous sodic and saline–sodic soils. It also provides financial or other benefits to the farmer from the crops grown during the amelioration process. In contrast to phytoremediation of soils contaminated by heavy metals, phytoremediation of sodic and saline–sodic soils is achieved by the ability of plant roots to increase the dissolution rate of calcite, resulting in enhanced levels of Ca²⁺ in soil solution to replace Na⁺ from the cation exchange complex. Research has shown that this process is driven by the partial pressure of CO₂ (P_CO2) within the root zone, the generation of protons (H⁺) released by roots of certain plant species, and to a much smaller extent the enhanced Na⁺ uptake by plants and its subsequent removal from the field at harvest. Enhanced levels of P_CO2 and H⁺ assist in increasing the dissolution rate of calcite. This results in the added benefit of improved physical properties within the root zone, enhancing the hydraulic conductivity and allowing the leaching of Na⁺ below the effective rooting depth. This review explores these driving forces and evaluates their relative contribution to the phytoremediation process. This will assist researchers and farm advisors in choosing appropriate crops and management practices to achieve maximum benefit during the amelioration process.     

运东近滨海地区燕麦秸秆盐分积累与改良盐碱地潜力分析

为探明燕麦在运东滨海盐碱地区秸秆盐分积累特点以及改良盐碱地的潜力,选用"坝莜1号"、"白燕2号"和"花早2号"燕麦,采用单因素随机区组试验,以品种和土壤含盐量作为因素,进行了2组田间试验,测得燕麦的生物量、秸秆离子浓度和积累量及秸秆与土壤离子浓度比值。研究结果显示,"坝莜1号"燕麦开花-灌浆至成熟期整株生物量从2.9 t·hm-2增加至3.8 t·hm-2,延迟20 d收获则减少至2.5 t·hm-2。"白燕2号"在低土壤盐分浓度(1.0 g·kg-1左右)下的生物量(3.1 t·hm-2)显著大于中浓度(2.0 g·kg-1左右,1.7 t·hm-2)和高浓度(3.0 g·kg-1左右,0.4 t·hm-2)下的生物量。中等土壤盐分浓度下"坝莜1号"的生物量(3.8 t·hm-2)显著高于"白燕2号"(3.1t·hm-2)和"花早2号"(2.2 t·hm-2)。"坝莜1号"秸秆中Na+、K+浓度从开花到成熟均显著增加,而Mg2+、Ca2+和Cl-则显著降低。延迟20 d收获,除Ca2+外,其他离子浓度均显著降低。随着土壤盐分的升高,"白燕2号"秸秆Na+、Mg2+、Ca2+和Cl-浓度显著升高,而K+显著下降。3个品种的Na+、K+和Mg2+之间存在显著差异,而Cl-和Ca2+浓度无显著差异。燕麦秸秆中Cl-浓度最高,K+和Na+基本相当,均高于Mg2+和Ca2+。"坝莜1号"秸秆中Na+、K+、Mg2+、Cl-积累量成熟期最高,延迟收获20 d后积累量均显著降低。"白燕2号"秸秆Na+、K+、Mg2+、Ca2+、Cl-积累量随土壤盐分升高显著下降。除Ca2+外,Na+、K+、Mg2+、Cl-积累量品种之间差异显著。"坝莜1号"秸秆与土壤离子浓度比值中,Na++K+最大(46~63),其次是Cl-(30~46)、Mg2+(24~30)和Ca2+(3~15);延迟收获后Na++K+和Cl-秸秆与土壤浓度比值显著下降,Mg2+比值无显著变化,Ca2+比值显著升高。随着土壤盐分升高"白燕2号"秸秆与土壤Na++K+和Cl-浓度比值显著下降,Ca2+无显著变化。秸秆与土壤离子浓度比值在品种之间存在显著差异。燕麦理论上具有改良盐碱地的潜力,但收获时间和土壤盐分均会显著地影响燕麦生物量、离子浓度和积累量,从而影响燕麦改良盐碱地的效果。     

Soil Acidification and Solute Budgets for Forested Lysimeters in Nordrhein-Westfalen

Solute budgets and nitrogen use were quantified in two 400 m² forested lysimeters in St. Arnold, Nordrhein-Westfalen. The lysimeters are covered by a mixture of oak-beech and Weymouth pine, respectively. The average bulk deposition between May 1985 and May 1987 of NH, SO and NO₃ was 1.1, 1.7, and 0.4 kmol_c ha^?1 yr^?1 in the deciduous stand and 2.1, 2.1, and 0.8 kmol_c ha^?1 yr^?1 in the coniferous stand. The input of N is almost completely retained in the deciduous stand. In the coniferous stand about 30% of this N-input is leached as NO₃. Due to N-transformations, total proton turnover is 4.4 kmol_c ha^?1 yr^?1 in the coniferous stand and only 2.5 kmol_c ha^?1 yr^?1 in the deciduous stand. Ca-mobilization is the major acid buffering process in both lysimeters. Only the deciduous stand was limed in 1980 (90 kmol_c/ha). Mobilization of Al is only relevant down to a soil depth of 30 cm. Below a 30 cm depth, Al is immobilized. The amounts of exchangeable and silicate-bound Ca in the soil underlying the coniferous stand are very small, but no evidence was found for explanation of the observed high Ca-mobilization by artificial Ca-sources.     

Nitrous oxide emissions and dynamics of soil nitrogen under 15N‐labeled cow urine and dung patches on a sandy grassland soil

Grazing animals highly influence the nutrient cycle by a direct return of 80% of the consumed N in form of dung and urine. In the autumn‐winter period, N uptake by the sward is low and rates of seepage water in sandy soils are high, hence high mineral‐N contents in soil and in seepage water as well as large losses of N₂O are expected after cattle grazing in autumn. The objective of this study was the quanitfication of N loss deriving from urine and dung leaching and by N₂O emission. Therefore the deposition of urine and dung patches was simulated in maximum rates excreted by cows by application of ¹⁵N‐labeled cow urine and dung (equivalent to 1030 kg N ha^–1 and 1052 kg N ha^–1, respectively) on a sandy pasture soil in N Germany. Leachate was collected in weekly intervals from free‐draining lysimeters, and ¹⁵N‐NO , ¹⁵N‐NH , and ¹⁵N‐DON (dissolved organic N) were monitored over 171 d. Furthermore, the ¹⁵N‐N₂O emission rates and the dynamics of inorganic ¹⁵N in the upper soil layer were monitored in a field trial, adjacent to the lysimeters. After 10 d following the urine application, the urea was completely hydrolyzed, shown by a 100% recovery of urine‐N in the soil NH . The following decrease of ¹⁵N‐NH in the soil was higher than the increase of ¹⁵N‐NO , and some N loss was explained by leaching. Amounts of 51% and 2.5% of the applied ¹⁵N were found in leachate as inorganic N, 2.4% and 0.7% as DON derived from urine and dung, respectively. Release of N₂O from urine and dung patches applied to the pasture was low, with losses of 0.05% and 0.33% of the applied ¹⁵N, respectively. Overall loss of dung‐derived N was very low, but as the bulk dung N remained in the soil, N loss after mineralization of the dung needs to be investigated.     

Verteilung von Stickstoff auf Sproß und Wurzel bei jungen Bohnenpflanzen nach der Aufnahme von NO und NH

Translocation of nitrogen to the shoot of young bean plants after uptake of NO and NH by the root Phaseolus vulgaris plants (var. nana, cv. Saxa) at the primary leaf stage (without nodules) were fed during 6 hours with ¹⁵NO and ¹⁵NH, respectively. 24 hours after the absorption period more ₁₅N from the absorbed NO was translocated from the root to the shoot. The presence of NH in the nutrient solution enhanced the translocation of ¹⁵NON, probably by an inhibition of nitrate reductase. NH_4-⁺¹⁵N is mainly retained in the root by a high incorporation into the root protein. It can be concluded that nitrogen from newly absorbed NO is not retained and used for protein synthesis in the root according to the root's potential to synthesize protein. Nitrate reduction in the root is considered to be the limiting factor. This is supported by the fact that withdrawal of NO in the nutrient solution prior to the ¹⁵N-experiment increased NOtranslocation to the shoot as a consequence of a lowered level of nitrate reductase. In an experiment with ¹⁴NOsupply to the roots and ¹⁵NOapplication to the primary leaves (infiltration method) a considerable amount of ¹⁵N was translocated from the leaves to the roots. This indicates that an insufficient NOreduction in the root can be substituted by a retranslocation of reduced N-compounds from leaves to the roots. The proportion of NO reduced in the root influences also the pattern of primary distribution of nitrogen in the shoot of plants at the 4 leaf stage. At a concentration of 0,2 meq/l NO in the nutrient solution as compared to 20 meq/l NO during 10 hours a relative higher amount of ₁₅N was transported from the root to the younger, growing leaves i.e. via the phloem to metabolic sinks.     

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.     

Limits imposed by salt to the growth of the halophyte Sesuvium portulacastrum

The growth of the halophyte Sesuvium portulacastrum, commonly known as sea purslane, is impeded by NaCl only at high (600–1000 mM) concentration. Therefore, the goal of this investigation was to identify the mechanisms which set the limit of the salt resistance of S. portulacastrum. 21‐day‐old cuttings were grown for 45–50 d under split‐root conditions in which one half of the root system was immersed in complete nutrient solution supplemented with 800 mM NaCl, while the other half was immersed in a NaCl‐free medium, containing all nutrients or being deprived of potassium or calcium or nitrogen. Using this approach, we demonstrate that K⁺ and N uptake was impaired in roots exposed to NaCl. Concerning Ca²⁺, there was no indication of uptake inhibition by NaCl. However, restriction of K⁺ uptake by roots was compensated by an increase in the K⁺‐use efficiency, so that growth was not inhibited. Concerning N, our analysis shows that NO and/or NH uptake, but not their assimilation, was limited by salt treatment. Thus, we conclude that at high salinity levels, the growth of S. portulacastrum is limited by the restrictions imposed by NaCl on N uptake, perhaps in addition to inhibiting effects of excessive Na⁺ accumulation in shoot.     

Enhancing the productivity of high‐magnesium soil and water resources in Central Asia through the application of phosphogypsum

Recent evidences from some irrigated areas worldwide, such as Central Asia, suggest that water used for irrigation contains magnesium (Mg²⁺) at levels higher than calcium (Ca²⁺). Excess levels of Mg²⁺ in irrigation water and/or in soil, in combination with sodium (Na⁺) or alone, result in soil degradation because of Mg²⁺ effects on the soil's physical properties. More than 30 per cent of irrigated lands in Southern Kazakhstan having excess levels of Mg²⁺ are characterized by low infiltration rates and hydraulic conductivities. The consequence has been a gradual decline in the yield of cotton (Gossypium hirsutum L.), which is commonly grown in the region. These soils require adequate quantities of Ca²⁺ to mitigate the effects of excess Mg²⁺. As a source of Ca²⁺, phosphogypsum—a byproduct of the phosphorous fertilizer industry—is available in some parts of Central Asia. In participation with the local farming community, we carried out a 4‐year field experiment in Southern Kazakhstan to evaluate the effects of soil application of phosphogypsum—0, 4·5, and 8·0 metric ton per hectare (t ha⁻¹)—on chemical changes in a soil containing excess levels of Mg²⁺, and on cotton yield and economics. The canal water had Mg²⁺ to Ca²⁺ ratio ranging from 1·30 to 1·66 during irrigation period. The application of phosphogypsum increased Ca²⁺ concentration in the soil and triggered the replacement of excess Mg²⁺ from the cation exchange complex. After harvesting the first crop, there was 18 per cent decrease in exchangeable magnesium percentage (EMP) of the surface 0·2 m soil over the pre‐experiment EMP level in the plots where phosphogypsum was applied at 4·5 t ha⁻¹, and a 31 per cent decrease in EMP in plots treated with phosphogypsum at 8 t ha⁻¹. Additional beneficial effect of the amendment was an increase in the soil phosphorus content. The 4‐year average cotton yields were 2·6 t ha⁻¹ with 8 t ha⁻¹ phosphogypsum, 2·4 t ha⁻¹ with 4·5 t ha⁻¹ phosphogypsum, and 1·4 t ha⁻¹ with the control. Since the amendment was applied once at the beginning, exchangeable Mg²⁺ levels tended to increase 4 years after its application, particularly in the treatment with 4·5 t ha⁻¹ phosphogypsum. Thus, there would be a need for phosphogypsum application to such soils after every 4–5 years to optimize the ionic balance and sustain higher levels of cotton production. The economic benefits from the phosphogypsum treatments were almost twice those from the control. Copyright © 2007 John Wiley & Sons, Ltd.     

Soil Properties and Maize Growth in Saline and Nonsaline Soils using Cassava‐Industrial Waste Compost and Vermicompost with or Without Earthworms

The aim of this study was to investigate the effectiveness of compost and vermicompost as soil conditioners in alleviating salt‐affected soils and increasing maize productivity. A greenhouse trial, consisting of seven soil amendment treatments in a completely randomized design with three replications, was carried out at Khon Kaen University, Thailand, during the rainy season of 2011. Plant height and total dry matter of maize increased in treatments with compost and vermicompost application when compared with the control (no fertilizer) in two types of soils (saline and nonsaline) during the growing season. Soil pH and electrical conductivity in saturation paste extracts were decreased by compost and vermicompost amendments with or without earthworms when compared with unamended treatments in the saline soil. Compost and vermicompost amendments improved cation exchange capacity, soil organic carbon, total nitrogen and extractable phosphorus in both soils. These amendments also increased exchangeable K⁺, Ca²⁺ and Mg²⁺ while decreasing exchangeable Na⁺ in the saline soil, which suggested that Ca²⁺ was exchanged for Na⁺, exchangeable Na⁺, then leached out, and soil salinity reduced as a result. Soil microbial activities including microbial C and N and basal soil respiration were improved by the application of compost and vermicompost amendments with or without earthworms when compared with the control in both soils. This experiment showed that the compost and vermicompost were effective in alleviating salinity and improving crop growth. Copyright © 2013 John Wiley & Sons, Ltd.     

Amelioration strategies for sodic soils: a review

Sodic soils are characterized by the occurrence of excess sodium (Na⁺) to levels that can adversely affect soil structure and disturb availability of some nutrients to plants. Such changes ultimately affect crop growth and yield. There are large areas of the world that exist under sodic soils and need attention for efficient, inexpensive and environmentally feasible amelioration. Sodic soil amelioration involves increase in calcium (Ca²⁺) on the cation exchange sites at the expense of Na⁺. The replaced Na⁺ together with excess soluble salts, if present, is removed from the root zone through infiltrating water as a result of excessive irrigations. Records nearly a century old reveal the use of water, crop, chemical amendment, electric current, and tillage as amelioration tools for such soils. Among the amelioration strategies, chemical amendments have an extensive usage. Owing to gradual increases in amendment cost in some parts of the world during the last two decades, this amelioration strategy has become cost‐intensive, particularly for the subsistence farmers in developing countries. In the meantime, phytoremediation with low initial investment has emerged as a potential substitute of chemical amelioration. Phytoremediation works through plant root action that helps dissolve native soil calcite (CaCO₃) of low solubility to supply adequate levels of Ca²⁺ for an effective Na⁺−Ca²⁺ exchange without the application of an amendment. Although significant progress has been achieved in improving amelioration methods, a great deal of work remains to analyse the economics of such methods with focus on (1) the long‐term sustainability of the amelioration projects and (2) the consequences of amelioration for the farmer himself, other growers and society as a whole. Computer modelling may help assess economic viability of different soil amelioration methods to extend results broadly to other similar locations. In addition, computer modelling to stimulate movement and reactions of salts in sodic soils has been a potentially useful complement to experimental data. However, such models need evaluation under field conditions. Copyright © 2001 John Wiley & Sons, Ltd.     

SOIL PROPERTY CHANGES FOLLOWING IRRIGATION WITH COALBED NATURAL GAS WATER: ROLE OF WATER TREATMENTS,SOIL AMENDMENTS AND LAND SUITABILITY

Saline‐sodic water is a by‐product of coalbed natural gas (CBNG) production in the Powder River Basin of Wyoming, USA and is being beneficially used in places as irrigation water. This study evaluated effects of 2 years of natural precipitation on soil properties of a hay field after the cessation of managed irrigation with CBNG water. The hay field had been irrigated with only CBNG water [CBNG(NT)], CBNG water amended with gypsum [CBNG(G)] or gypsum plus sulfur via a sulfur burner [CBNG(GSB)] in combination with soil amendments—gypsum ( +G ), elemental sulfur ( +S ), and both ( +GS ). Results indicated that infiltration rates were the lowest on fields irrigated with CBNG(NT), followed by CBNG(G) and CBNG(NT) +G treatments (12·2, 13·2, and 13·5 cm h⁻¹, respectively). The CBNG(GSB) +GS treatment had the highest infiltration rates (33·5 cm h⁻¹). By the second year, salinity and sodicity of treated soils had decreased in the A‐horizon of most CBNG‐water irrigated plots, whereas in Bt₁‐ and Bt₂‐horizons salinity generally decreased but sodicity increased; S and GS soil amended plots had higher profile salinities compared with NT and G soil treatments. Although Na⁺ leaching was observed in all fields that received soil and/or water amendments, CBNG(GSB) +GS plots had the lowest sodicity in the A‐ and Bt₁‐horizons. Effective managed irrigation requires knowledge of site‐specific soil properties, plant suitability, water chemistry, and amendments that would be needed to treat the CBNG waters and soils. This study indicates the greatest success was realized when using both soil and water amendments. Copyright © 2011 John Wiley & Sons, Ltd.     

Cation treatment and drying‐temperature effects on nonylphenol and phenanthrene sorption to a sandy soil

The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na⁺, Ca²⁺, or Al³⁺ and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na⁺ led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca²⁺ and Al³⁺ decreased it. The ¹H‐NMR relaxometry analyses showed that Al³⁺ restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca²⁺ or Na⁺. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.     

IONIC DISPLACEMENT AND RECLAMATION OF SALINE‐SODIC SOILS USING CHEMICAL AMENDMENTS AND CROP ROTATION

Biological, chemical and bio‐chemical strategies have been tested in the past for reclamation of saline‐sodic and sodic soils. The efficiency of two crop rotations (rice‐wheat and Sesbania‐wheat) alone or in combination with either gypsum (CaSO₄.2H₂O) or sulfuric acid (H₂SO₄) was tested for ionic displacement from four saline‐sodic soils. Pure gypsum was applied at 50 per cent of soil gypsum requirement at the time of planting rice and Sesbania, whereas 95 per cent pure sulfuric acid was added at 50 per cent soil gypsum requirement as one‐third applications by mixing with the first three irrigations. The rice crop biomass decreased at a soil saturation extract electrical conductivity (EC_e) of 8 dS m⁻¹, whereas wheat and Sesbania were influenced at a sodium adsorption ratio (SAR) of ≥40. Gypsum treatment helped the crops flourish well at these EC_e and SAR levels. The infiltrated volume of water dropped with decrease in EC_e : SAR ratio of soils and increase in crop biomass production. Crops rotation treatments alone helped leach sodium (Na⁺) and other ions successfully at SAR ≤ 21 but were less effective at SAR ≥ 40 at which point plants growth was also curtailed. Gypsum and H₂SO₄ treatments significantly aided leaching of Na⁺ and other ions with water at SAR ≥ 40 under both the crop rotations. Hence, crops effectively reclaimed soil at low sodicity level, whereas at high SAR, chemical amendments are obligatory in order to reclaim soils. This study also suggests that the required dose of H₂SO₄ should be applied with pre‐planting irrigation for better yield of the first crop. Copyright © 2011 John Wiley & Sons, Ltd.