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1.
Abstract. The worldwide occurrence of saline sodic and sodic soils on more than half a billion hectares warrants attention for their efficient, inexpensive and environmentally acceptable management. These soils can be ameliorated by providing a source of calcium (Ca2+) to replace excess sodium (Na+) from the cation exchange sites. Although chemical amendments have long been used to ameliorate such soils, the chemical process has become costly during the last two decades in several developing countries. As a low‐cost and environmentally acceptable strategy, the cultivation of certain salt tolerant forage species on calcareous sodic and saline sodic soils, i.e. phytoremediation, has gained interest among scientists and farmers in recent years. In a field study conducted at three calcareous saline sodic sites (pHs=8.1–8.8, ECe=7.8–12.5 dS m–1, SAR=30.6–76.1) in the Indus Plains of Pakistan, we compared chemical and phytoremediation methods. There were four treatments; two involved plants: Kallar grass (Leptochloa fusca (L.) Kunth), and sesbania (Sesbania bispinosa (Jacq.) W. Wight). The other two treatments were uncropped: soil application of gypsum and an untreated control. All treatments were irrigated with canal water (EC=0.22–0.28 dS m–1). The plant species were grown for one season (5–6 months). Sesbania produced more forage yield (34 t ha–1) than Kallar grass (23 t ha–1). Phytoremediation and chemical treatments resulted in similar decreases in soil salinity and sodicity, indicating that phytoremediation may replace or supplement the more costly chemical approach. The soil amelioration potential of sesbania was similar to that of the Kallar grass, which suggests that moderately saline sodic calcareous soils can be improved by growing a forage legume with market value.  相似文献   

2.
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 (pHs) = 7.2, electrical conductivity of the saturated paste extract (ECe) = 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.  相似文献   

3.
ABSTRACT

The objective of this study was to develop a Linear Regression Model for the prediction of soil bulk density based on organic matter content (OM) and textural fractions (% sand, silt and clay) as well as the soil exchangeable sodium percentage (ESP) based on soil sodium adsorption ratio (SAR) in some salt affected soils of Sahl El-Hossinia, El-Sharkia Governorate, Egypt. For this purpose, 160 samples were randomly taken from top of the surface soil (0–30 cm) from different locations and samples were subjected to various analyzes. XLSTAT Version 2016.02.27444 software was used to build and test conceptual and empirical models. The statistical results of the study indicated that to predict soil bulk density (BD) based on organic matter content and textural fractions the Multiple linear regression model BD = 1.817–0.730 × OM – 0.002 × Clay – 0.001 × Silt with R2 = 0.794. On the other hand, to predict soil ESP based on SAR the linear regression model ESP = 5.577 + 0.851 × SAR with R2 = 0.773. A Linear Regression Model for prediction of BD and ESP of Sahl El-Hossinia, El-Sharkia Governorate, Egypt, can be used with high prediction.  相似文献   

4.
This study was to evaluate the application effect of gypsum and rice straw on the saline–sodic soils of coastal reclaimed tidal lands during newly reclamation process by leaching method. Soil used in the lysimeter experiment is classified as Greyic Hydragric Anthrosols (Sodic Arenic). The experiment was carried out over a period of 1 year from May 2014 to July 2015 inside a plastic film house. Saturated electrical conductivity (ECe) and exchangeable sodium percentage (ESP) values of soils in gypsum treatment and gypsum with rice straw treatment then reached the desalinization criteria (ECe = 4.0 dS m?1, ESP = 15%) after the five or six pore volumes leaching cycles. However, in spite the 10 pore volumes leaching cycles in control and rice straw alone treatment, the values did not reach the desalinization criteria. The results showed that effectiveness of improvement of sodicity and salinity in coastal reclaimed tidal land soils was in the order of gypsum = gypsum + rice straw > rice straw = control. Our study has shown that gypsum alone treatment or gypsum with rice straw treatment in a coastal reclaimed tidal land soils improves their physicochemical characteristics.  相似文献   

5.
Reforestation of saline sodic soil is increasingly undertaken as a means of reclaiming otherwise unproductive agricultural land. Currently, restoration of degraded land is limited to species with high tolerances of salinity. Biochar application has the potential to improve physical, biological and chemical properties of these soils to allow establishment of a wider range of plants. In a glasshouse trial, we applied biochar made from Acacia pycnantha (5 Mg ha−1) or no biochar to either a low (ECe 4·75 dS m−1, ESP 6·9), a moderate (ECe 27·6 dS m−1, ESP 29·3) or a high (ECe 49·4 dS m−1, ESP 45·1) saline sodic soil. The regional common reforestation species Eucalyptus viminalis and Acacia mearnsii were planted as tubestock in to the soils. Early establishment indicators, including growth, plant condition and nutrition, were assessed at the end of a simulated growing season, 108 days after biochar application. Application of biochar increased height, and decreased root : shoot and the concentration of Mn, N and S in plants of E. viminalis when grown in the highly saline sodic soil. Biochar application increased the concentration of B in leaves of E. viminalis and increased the concentration of P, K and S in leaves of A. mearnsii when grown in the low saline sodic soil. The results confirm that there is potential for biochar to assist in reforestation of saline sodic soils. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

6.
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 (ECe) 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 ECe and SAR levels. The infiltrated volume of water dropped with decrease in ECe : 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.  相似文献   

7.
Abstract

Soil salinization and sodication affect large areas of agricultural land in the world. Amelioration of these soils to make them suitable for agricultural production depends on understanding sodium dynamics and chemical interactions governing nutrient availability. Three locations in eastern Croatia were characterized to the 5‐m depth. The two solonetz‐solonchak soils were alkaline, whereas the solonetz soil had near‐neutral A/E horizon and alkaline deeper horizons. Electrical conductivity of the saturated extract (ECe) was greater than 4 dS m?1 in the top horizons in the solonetz‐solonchak soils. The solonetz soil had 2.8–4.7 dS m?1 in shallow A/E, CG, and G horizons and up to 6.3 dS m?1 below 1.5 m. Highly alkalinized sodic horizons (exchangeable sodium percentage, ESP >20) had 24–47% Ca2+ and 27–33% Mg2+ on the cation exchange complex. Sodium adsorption ratio (SAR) was high (18–26) in the P horizon and even more so in Bt,na horizon (35–36) of solonetz‐solonchak soils. A strong negative exponential relationship existed between soluble Ca2+ and SAR (SAR increased greatly when Ca2+ dropped to around 3 mg dm?3). An increase in pH to greater than 8.4 resulted in an exponential increase in SAR. Leaching of Na+ with successive volumes of water was similarly effective for the P and Bt,na horizons in the solonetz‐solonchak soils, but SAR remained greater than 15 even after six successive cycles of leaching. In conclusion, extensive amelioration of tested soils with gypsum and leaching will be required to overcome poor physical and chemical characteristics caused by various degrees of alkalization and sodication to bring these soils into production.  相似文献   

8.
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 (PCO2) 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 (pHs = 7.4, electrical conductivity of soil saturated paste extract (ECe) = 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.  相似文献   

9.
Abstract

Interrelations between soil pH and exchangeable sodium percentage (ESP) were examined using soils from the Burdekin River area in tropical Queensland. Highly significant correlations were found but the goodness of fit differed between groups of soil profile classes. In general, Typic Natrustalfs of the flood plains had better relationships (r2 = 0.85) between these soil properties than did the Chromusterts (r2 = 0.50). The regression ESP = 1.935 × 10‐5 pH6.205 (r2 = 0.61; n= 288) for all soils and depths underestimated ESP in Typic Natrustalfs groupings and overestimated this soil property in the Chromusterts.

By using the appropriate regression, pH levels associated with non‐sodic, sodic and strongly sodic horizons have been defined. Either laboratory or field determined estimates of pH may be used but the laboratory determined value is preferred. It is expected the predictive models will remain valid until soil ESP or pH levels are significantly modified as a consequence of agricultural development.  相似文献   

10.
For understanding the effects of soil salinity and nitrogen (N) fertilizer on the emergence rate, yield, and nitrogen-use efficiency (NUE) of sunflowers, complete block design studies were conducted in Hetao Irrigation District, China. Four levels of soil salinity (electrical conductivity [ECe] = 2.44–29.23 dS m?1) and three levels of N fertilization (90–180 kg ha?1) were applied to thirty-six microplots. Soil salinity significantly affected sunflower growth (P < 0.05). High salinity (ECe = 9.03–18.06 dS m?1) reduced emergence rate by 24.5 percent, seed yield by 31.0 percent, hundred-kernel weight by 15.2 percent, and biological yield by 27.4 percent, but it increased the harvest index by 0.9 percent relative to low salinity (ECe = 2.44–4.44 dS m?1). Application of N fertilizer alleviated some of the adverse effects of salinity, especially in highly saline soils. We suggest that moderate (135 kg ha?1) and high (180 kg ha?1) levels of N fertilization could provide the maximum benefit in low- to moderate-salinity and high- or severe-salinity fields, respectively, in Hetao Irrigation District and similar sunflower-growing areas.  相似文献   

11.
ABSTRACT

We studied (i) the pH buffer capacity (pHBC) of calcareous soils varied widely in calcite and texture, (ii) the contribution of soil properties to pHBC and (iii) the significance of using a model based on calcite dissolution to estimate the pHBC of calcareous soils. The pHBC of soils was measured by adding several rates of HCl to soils (100–6500 mM H+ kg–1), in a 0.01 M CaCl2 background and an equilibration time of 24 h. The pHBC (mM H+ kg–1 pH?1) varied from 55 to 3383, with the mean of 1073. The pHBC of the soils was strongly correlated with soil CaCO3 equivalent (calcite) (r = 0.94), sand (r = ?0.72), silt (r = 0.60), EC (r = 0.63), pH (r = 0.55), and weakly (r = 0.37) but significantly with clay content. The attained pHBC values indicated that calcite was probably the main buffer system in these soils. The chemical equilibrium model successfully predicted pH titration curves based on calcite dissolution, indicating buffering of acid inputs in the calcareous soils is dominated by calcite dissolution. The model can be used to simulate acidification of calcareous soils and to provide information for making environmental management decisions.  相似文献   

12.
Soil degradation affects soil properties such as structure, water retention, porosity, electrical conductivity (EC), sodium adsorption ratio (SAR), and soil flora and fauna. This study was conducted to evaluate the response of contrasting textured soils irrigated with water having different EC:SAR ratios along with amendments: gypsum (G), farm manure (FM), and mulch (M). Water of different qualities viz. EC 0.6 + SAR 6, EC 1.0 + SAR 12, EC 2.0 + SAR 18, and EC 4.0 + SAR 30 was used in different textured soils with G at 100% soil gypsum requirement, FM at 10 Mg ha?1, and M as wheat straw was added on surface soil at 10 Mg ha?1. Results revealed that the applied amendments in soils significantly decreased pHs and electrical conductivity (ECe) of saturated paste and SAR. Four pore volumes of applied water with leaching fraction 0.75, 0.77, and 0.78 removed salts 3008, 4965, and 5048 kg ha?1 in loamy sand, silty clay loam, and sandy clay loam soils, respectively. First four irrigations with LF of 0.82, 0.79, 0.75, and 0.71, removed 5682, 5000, 3967, and 2941 kg ha?1 salts, respectively. The decreasing order for salt removal with amendments was FM > G > M > C with LF = 0.85, 0.84, 0.71, and 0.68, respectively. This study highlights a potential role of soil textures to initiate any mega program for reclamation of saline-sodic soils in the perspective of national development strategies.  相似文献   

13.
Corn (Zea mays L.) is planted in two seasons per year in northern Iran (mid-April as a main crop and mid-June as a second crop). The main objective of this study was to determine whether corn yield response would differ between these two seasons and different plant populations. Two field experiments were conducted at the Agricultural Research Center of Golestan – Iran in 2007 and 2008 at different planting densities. The results showed that the values of grain yield and most traits were significantly lower in the second season. Maximum grain yield was observed at planting densities of 6.5 plants m?2 in the first season, whereas in the second season grain yield was the same for planting densities between 2.5 and 12.5 plants m?2. Based on the second-year experimental results, the following functions were fitted to show the relationship between yield ha?1 (Y) and planting densities (X) for the first and second seasons, respectively: (Y = ?167.6X 2 + 2672.2X + 511.77; R 2 = 0.992) and (Y = 1200.1 ln(X) + 2924.4; R 2 = 0.935). This study found that the optimum plant population was 6.5 plants m?2 under low heat stress, and should be reduced to 2.5–4.5 plants m?2 under heat stress conditions.  相似文献   

14.
Reclamation of sodic soils is proving increasingly vital as greater land area becomes salt-affected in the northern Great Plains of the United States. Flue gas desulfurization gypsum (FGDG) can be an agriculturally important resource for increasing land productivity through the amelioration of sodic soils. Biochar is also considered as an aid in reclaiming degraded soils. In this incubation study, two rates of FGDG (33.6 Mg ha?1 and 66.2 Mg ha?1), two rates of biochar made from sugar beet (Beta vulgaris L.) pulp (16.8 Mg ha?1), and one rate of FGDG combined with one rate of biochar (33.6 Mg ha?1 ea.) were applied to a sodic soil. Soil physicochemical properties, including cationic exchange, pH, electrical conductivity (ECe), sodium adsorption ratio (SARe), total organic carbon (TOC), water retention, and soil respiration rate, were assessed during and at the end of the incubation period. Addition of FGDG to sodic soil increased ECe from 3.5 to 8.4 dS m?1 and decreased SARe from 16 to 9. Biochar addition to sodic soil increased TOC from 62.2 to 99.5 μg g?1 and increased soil respiration rate (mg C kg?1 soil day?1) on every measurement period. When FGDG and biochar were both added to the sodic soil, TOC did not significantly improve; however, ECe increased from 3.5 to 7.7 dS m?1, SARe decreased from 16 to 9, and soil respiration rate increased for all measurements. The results confirm there is potential for FGDG and biochar to reclaim sodic soils alone, and applied in combination.  相似文献   

15.
The effects of wheat, potato, sunflower, and rape residues and calcite were evaluated in soil that received sodic water. These materials were added to a sandy‐loam soil at a rate of 5%, after which the treated soils were incubated for 1 month at field‐capacity moisture and a temperature of 25°C–30°C. Column leaching experiments using treated soils were then conducted under saturated conditions using water with three sodium‐adsorption ratios (SAR) (0, 10, 40) with a constant ionic strength (50 mmol L–1). The results indicated that the application of plant residues to soils caused an increase in cation‐exchange capacity and exchangeable cations. Leaching experiments indicated that the addition of plant amendments led to increased Na+ leaching and decrease in exchangeable‐sodium percentage (ESP). The ESP of the control soil, after leaching with solutions with an SAR of 10 and 40, increased significantly, but the level of sodification in soils treated with plant residue was lower. Such decreases of soil ESP were greatly affected by the type of plant residues, with the order of: potato‐treated soil > sunflower‐treated soil > rape‐treated soil > wheat‐treated soil > calcite‐treated soil > control soil.  相似文献   

16.
Sodium (Na+) dominated soils reduce saturated hydraulic conductivity (Ks) 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 Ks, leach Na+ and salts. This study comprised loamy‐sand (LS), sandy loam (SL), and clay loam (CL) soils with electrical conductivity of saturation extract (ECe) 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 mmolc L−1]. It proved that a rise in gypsum rate amplified Ks of LS ≫ SL > CL. However, Ks 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 ECe and SAR below 0·97 dS m−1 and 5·92 (mmol L−1)1/2, respectively. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

17.
Organics, biological, and inorganic fertilizers play a crucial role for improving crop yield and soil properties. Accordingly, we assessed their impact on yield, microbial activities, and transformations of carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) in soils under a 12-year-old intensively cultivated rice (Oriza sativa L.), mustard (Brassica juncea L.), sesame (Sesamum indicum L.) system with sole inorganic (NPK); NPK + farmyard manure (NPKF); NPK + green manure (NPKG) (Sesbania sesban L.), and NPK + green manure + bio-fertilizer (NPKGB) (Azotobacter chroococcum+ pseudomonas putida) treatments in sub-tropical India. The system yield was much higher with NPKF (23%) and NPKGB (18%) than that with NPK. Organic supplementation had a favorable influence on soil microbial biomass C (Cmic), N (Nmic), and activities of extracellular enzymes. Results of principal component and multiple regression analyses showed significant influence of Cmic on system yield (R2 = 91, p = 0.001) and S availability (R2 = 62, p = 0.001). Similarly, mineralizable N and acid phosphatase could predict significantly soil available N (R2 = 85, p = 0.001) and P (R2 = 51; p = 0.001), respectively. Results thus indicated that integrated nutrient management (NPKF/G) improved system yield, nutrient accumulation, and microbial activities in soils.  相似文献   

18.
ABSTRACT

The performance of DNDC (DeNitrification-DeComposition) and RothC (Rothamsted Carbon model) in simulating soil organic carbon (SOC) storage in soils under rice (Oryza sativa L.) – wheat (Triticum aestivum L.), maize (Zea mays L.) – wheat and cotton (Gossypium hirsutum L.) – wheat cropping systems was evaluated on field and regional scale. Field experiments consisted of N, NP, NK, PK, NPK, FYM, N + FYM, NPK + FYM, and control (UF) treatments. DNDC and RothC over-estimated SOC storage by 0.35–1.16 Mg C ha?1 (6–21%) in surface layer with manure application, compared with inorganic fertilizer treatments by 1.01–1.16 Mg C ha?1 (14–18%). Although RothC only slightly over-estimated SOC stocks, DNDC provided a better match for measured versus simulated SOC stocks (R 2 = 0.783*, DNDC; 0.669*, RothC, p < .05). Model validation on independent datasets from long-term studies on rice–wheat (R 2 = 0.935**, DNDC; R 2 = 0.920**, RothC, p < .01) and maize–wheat (R 2 = 0.895** for DNDC and R 2 = 0.967** for RothC, p < .01) systems showed excellent agreement between measured and simulated SOC stocks. On a regional scale, change in SOC storage under Scenario 1 (NPK) was significant up to 8 years of simulation, with no change thereafter. In Scenario 2 (NPK + FYM), DNDC simulated SOC storage after 10 years was 2.0, 0.4, and 1.4 Mg C ha?1 in three systems, respectively. Amount of C sequestered in silt + clay fraction varied between 0.31 and 0.97 kg C 10 years?1 (Mg silt + clay)?1 under Scenario 1, and between 0.78 and 2.67 kg C 10 years?1 (Mg silt + clay)?1 under Scenario 2.  相似文献   

19.
This study examined zinc (Zn) fixation pattern and kinetics in three semiarid alkaline soils of the Southern High Plains, USA. Soil chemical data obtained from Zn-extraction experiments conducted at different depths were fitted to various kinetic models to examine Zn fixation patterns. Within the experimental period of 90 days, approximately 57% of the total plant-available Zn fixed occurred in the first 14 days when averaged across all soils and depths. Zinc fixation over the experimental period (90 days) was better described by the power function (pfxn) model (R2 = 0.87–0.92, standard error [SE] = 0.130–0.154), but poorly described by the zero-, first- and second-order models (R2 = 0.55–0.76, SE = 0.038–0.267). Average reaction rate constant (from the pfxn model) was higher in the subsurface soils (0.323), suggesting a more rapid Zn fixation, compared to the surface soils (0.293). Zinc fixation within the first 35 days was also more rapid and better described by both the second-order (R2 = 0.91, SE = 0.018) and pfxn (R2 = 0.92, SE = 0.119) models. Findings are applicable to field settings and kinetic parameters obtained will help to advance Zn studies and management in these semiarid soils.  相似文献   

20.
Water dispersible clay (WDC) can influence soil erosion by water. Therefore, in highly erodible soils such as the ones in eastern Nigeria, there is a need to monitor the clay dispersion characteristics to direct and modify soil conservation strategies. Twenty‐five soil samples (0–20 cm in depth) varying in texture, chemical properties and mineralogy were collected from various locations in central eastern Nigeria. The objective was to determine the WDC of the soils and relate this to selected soil physical and chemical attributes. The soils were analysed for their total clay (TC), water‐dispersible clay (WDC), clay dispersion ratio (CDR), dispersion ratio (DR), dithionite extractable iron (Fed), soil organic matter (SOM), exchangeable cations, exhangeable sodium percentage (ESP) and sodium adsorption ratio (SAR). Total clay contents of the soil varied from 80–560 g kg−1. The USLE erodibility K ranges from 0·02 to 0·1 Mg h MJ−1 mm and WEPP K fall between 1·2 × 10−6–1·7 × 10−6 kg s m−4. The RUSLE erodibility K correlated significantly with CDR and DR (r = 0·44; 0·39). Also, a positive significant correlation (r = 0·71) existed between WEPP K and RUSLE K. Soils with high clay dispersion ratio (CDR) are highly erodibile and positively correlates (p < 0·51) with Fed, CEC and SOM. Also, DR positively correlates with Mg2+ and SOM and negatively correlate with ESP and SAR. Principal component analysis showed that SAR, Na+ and percent base saturation play significant role in the clay dispersion of these soils. The implication of this result is that these elements may pose potential problem to these soils if not properly managed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

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