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Despite some evidence in greenhouse experiments, the benefits of Bacillus subtilis and Trichoderma asperellum on nutrients uptake by plants under field conditions are unknown. This work aims to study the effect of these microbial inoculants on durum wheat nutrition and yield under Mediterranean conditions where soils may lead to micronutrients and phosphorus deficiencies and where drought may promote low use efficiencies of applied fertilizers. To this end, three experiments were performed in two growing seasons. B. subtilis increased the uptake of nitrogen, phosphorus, and manganese relative to other treatments in the experiment carried out in the first growing season involving two experimental sites. The increased phosphorus uptake was attributed to the increased activity of alkaline phosphatase. In this first season, T. asperellum increased acid phosphatase activity without effect on P uptake and decreased the P to Zn molar ratio in grains, thus improving grain quality for human consumption. In the second season, the effects of microbial inoculants were less evident possibly due to favourable environmental conditions for crops (higher water availability) or phosphate fertilization. Results evidenced that B. subtilis can be effective improving the development and nutrient uptake of durum wheat under more stressful conditions, such as drought stress. [ABSTRACT FROM AUTHOR]

Sulphur-oxidizing bacteria can alter the root environment by oxidizing sulphur and lowering pH to increase nutrient availability. A field experiment was conducted on calcareous soil to assess the impact of elemental sulfur and farmyard manure enriched with sulfur-oxidizing bacteria (named microbial soil conditioner; MSC) on P and micronutrient availability, as well as on wheat growth. Five treatments, CK (Control), NPK (recommended dose of NPK), MSC (microbial soil conditioner), ½ P + MSC (half recommended dose of P with a full recommended dose of NK + MSC) and NPK +MSC (recommended dose of NPK + MSC), were used. Data regarding plant physiological and yield parameters were analyzed. The results showed that MSC + NPK and ½ P significantly enhanced the nutrient availability, particularly phosphorus and micronutrients. The highest P concentrations in wheat grain, straw and yield were obtained by the recommended dose of NPK + MSC following half recommended dose of P with NK+ MSC. This work advocates that application of sulphur and farmyard manure enriched with sulphur-oxidizing bacteria could be a beneficial strategy for improving nutrient availability, mainly phosphorus and micronutrients ultimately with improved plant growth in calcareous soils. [ABSTRACT FROM AUTHOR]

Chlorosis caused by iron deficiency restricts the growth of plants on calcareous and alkaline soils. The aim of this study was to evaluate the effect of different application methods of FeSO4 on iron-deficient peach trees. The experiment was conducted for 2 years as a randomized complete blocks design with seven treatments including soil application (500 g tree−1), foliar spraying (0.5% solution, 21 liters tree−1) and trunk injection of 0%, 0.5%, 1%, 1.5% and 2% solutions of FeSO4 on eight-year-old trees. The application method had a significant effect on the characteristics of fruits and leaves. Injection of FeSO4 not only led to elimination of iron chlorosis by increasing chlorophyll and active iron contents of leaves but also increased fruit weight and volume, improved fruit yield and increased TSS content of fruits as compared to the control. On the other hand, soil and foliar application treatments did not have a significant effect on fruit weight, volume and yield. Foliar application increased the active iron content of the leaves but had no significant effect on their chlorophyll content. Based on the results, trunk-injection of FeSO4 is the most effective method for eliminating iron deficiency of peach trees on calcareous and alkaline soils. [ABSTRACT FROM AUTHOR]

The study was carried out to derive pedotransfer (PTFs) and spectrotransfer (STF) functions to estimate soil organic matter (SOM) content measured by time-consuming and expensive Walkley–Black wet combustion (W-B), using SOM content obtained from loss on ignition (LOI) and spectra reflectance bands at visible (Vis) and near infrared (NIR) regions. In total, 171 soil samples were collected from calcareous soils of southern Iran. The SOM content of the samples was determined using W–B wet combustion (SOMW-B) and LOI at temperatures of 360 °C during 2 h (LOI360-2); 550 °C during 3 h (LOI550-3); and 375°C during 16 h (LOI375-16). For the spectroscopy method, partial least squares regression (SpectPLSR) and forward stepwise multiple linear regression (SpectSMLR) approaches were used for function development. The LOI360-2 procedure with R2val of 0.9 for the validation dataset provided the best match with SOMW-B content. Furthermore, the SpectSMLR provided a STF using spectral reflectance bands at 495, 730, 970, 1906, 2262 and 2342 nm which predicted SOMW-B with R2val of 0.87. Results indicated both the SpectSMLR and LOI360-2, as easy and inexpensive approaches, could be recommended to accurately assess SOM content of calcareous soils. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effects of cypress cone biochar (RB) and its modifications (chitosan-coated biochar (CB), acid-modified biochar (AB), alkali-modified biochar (ALB), humic acid-coated biochar (HB), walnut shell residue extraction-coated biochar (WB), ball-milled biochar (BMB)) on the behavior of nickel (Ni) in Ni-spiked calcareous soil. The biochars were added separately to the soil at the rates of 1.5% and 3%, and the Ni behavior was investigated using methods of desorption kinetics and sequential extraction. The modification process significantly changed the specific area and functional groups of BMB, CB and HB compared to RB. Application of CB (26.3%), HB (28.7%), ALB (28.8%), BMB (30.7%), AB (31.9%) and RB (32.6%) showed the most effects on reduction of Ni mobility factor compared to control soil sample (38.8%). The results of Ni desorption showed high effectiveness of CB, BMB, ALB and HB, in reducing the Ni release compared to the control soil sample. Overall, our findings indicated that among the modified biochars, BMB, CB and HB showed a good performance in Ni stabilization, due to the simple and low-cost process of physical modification. BMB can be suggested as a suitable amendment for soil Ni immobilization. [ABSTRACT FROM AUTHOR]

Top soil burning may occur in shifting cultivation in hills, forest fire or burning of agricultural straw. It may affect the mechanisms of potassium (K) release by different extractants. Cumulative K release from six calcareous soils before and after heating (at 350°C) during 10 times extraction with 0.025 M CaCl2, HCl, oxalic and citric acids was determined. Initial K release was increased from 8–23 mg kg−1 to 13–47 mg kg−1 by heating the soils. Citric acid extracted more K than other solutions in the initial stage of K release. Cumulative K release ranged from 61 mg kg−1 for Torriorthents (containing high calcium carbonate and low clay) to 248 mg kg−1 for Haploxererts (containing low calcium carbonate and high illitic clay). Citric and oxalic acids extracted more K than CaCl2 and HCl. Heated soils released more K than unheated soils to the different extractants (62, 86, 112 and 105% increase for CaCl2, HCl, oxalic and citric acids, respectively). It is concluded that presence of calcium carbonate in soil affects the mechanisms of K release; in highly calcareous soils, exchange reactions were the main mechanism, while in slightly calcareous soils, exchange reactions and mineral dissolution were involved in the K release. [ABSTRACT FROM AUTHOR]

Dicyandiamide (DCD) has been extensively used to retard the nitrification process and decrease nitrogen (N) losses. However, its efficacy is variable and inconsistent depending upon the environmental conditions. The effects of temperature and moisture on DCD degradation and carbon dioxide (CO2) release from calcareous soil are not well-known. Therefore, an incubation experiment comprising three treatme ts (control, N fertilizer, and N fertilizer + DCD) was conducted for 67 d at different temperature (10 °C and 25 °C) and moisture (40% and 60% WFPS) levels. Results showed that nitrification activity and subsequent gaseous losses were increased with N addition and significantly affected by temperature and moisture levels. DCD effectively inhibited NH4+ oxidation, net NO3− production (31–59%), and N2O emissions (69%). CO2 emissions increased with N fertilization but reduced (18–161%) significantly with DCD application. DCD efficiency of inhibiting nitrification and controlling CO2 emission was related to its residence time in the soil. DCD degraded quickly at high temperature (25 °C) and moisture (60% WFPS), that is why it was least effective in inhibiting nitrification and controlling gaseous fluxes. Accordingly, DCD is not equally effective everywhere and is more suitable for regions with low temperature and low moisture. [ABSTRACT FROM AUTHOR]

Biochar due to its high K content may affect K forms and dynamics. The effect of biochars produced from licorice root pulp, municipal waste and cow manure at 300 °C and 600 °C on K forms, release and fixation in a loamy calcareous soil was investigated. The soil samples were analyzed after biochar application and incubation at field water-holding capacity or saturation conditions. The cow manure and municipal waste biochars increased all K forms, while licorice root pulp biochar only increased exchangeable K (10%). Cumulative K released to 0.01 M CaCl2 for the control soil was 101 mg kg−1, increasing to 108, 182 and 418 mg kg−1, with the application of licorice root pulp, municipal waste and cow manure biochars produced at 300 °C, and increased to 112, 200 and 486 mg kg−1 with the application of the biochars produced at 600 °C, respectively. Generally, 0.025 M CaCl2 extracted more K than 0.01 M CaCl2 (means of 250 vs. 230 mg kg−1). Saturation had a smaller effect on K forms and dynamics; increasing non-exchangeable K. Biochar increased soil K fixation. Biochar depending on its origin and pyrolysis conditions may be used as an amendment for increasing K supplying power of calcareous soils. [ABSTRACT FROM AUTHOR]

Deriving accurate pedo-transfer functions (PTFs) for predicting difficult-to-measure soil properties such as soil cumulative infiltration (CI) is an essential issue for saving time and cost. This study aimed to develop MLR (multiple-linear-regression), ANN (artificial-neural-network) and GMDH (group-method-of-data-handling) PTFs for predicting CI at different time intervals (i.e. 1, 2, 5, 15, 30, 60 and 120 min) and mapping in GIS in calcareous soils in northwest Iran. Soil infiltration measurements with a double-ring infiltrometer were carried out at 124 points with three replications. At each point, various easily measurable soil properties were measured. The results indicated that ANN-based PTFs provided the highest E (from 0.84 to 0.97) and the lowest RMSE (root mean square error) (from 0.19 to 8.91) compared to GMDH-based PTFs (E = 0.43–0.81 and RMSE = 0.34–19.59) and MLR-based PTFs (E = 0.41–0.83 and RMSE = 0.34–16.50). In addition, the map of soil CI at different time intervals was generated based on the best-derived PTFs (i.e. ANN-based PTFs) in GIS. We concluded that ANN-based PTFs provided an accurate prediction and a high-quality map to such costly studies by using easily measurable basic soil properties as input data in calcareous soils. [ABSTRACT FROM AUTHOR]

Novel adsorbents that remove P from contaminated waters can be potentially used as slow release P-fertilizers. In this study, Mg-Al layered double hydroxide (Mg-Al-LDH) and Mg-Al-LDH functionalized apple wood biochar and hydrochar were prepared to remove phosphate from aqueous solutions and then P-loaded LDH-biochar/hydrochar composites used as fertilizers for maize production in calcareous soils under controlled conditions. After five successive desorption cycles, the LDH, LDH-biochar, and LDH-hydrochar desorbed 18, 22, and 27% of adsorbed-P into a 0.03 M KCl solution, respectively, while, these adsorbents desorbed 52, 63, and 66% of adsorbed-P into a 0.1 M Na2CO3 solution, respectively. Additionally, increasing solution pH from 3.0 to 10 increased P desorption. The results revealed that the P-loaded LDH-biochar and LDH-hydrochar significantly increased available-P, maize shoot and root dry matters, and P uptake as compared with control. The integration of monocalcium phosphate fertilizer with ‎biochar, hydrochar, LDH-biochar, and LDH-hydrochar increased available-P, ‎maize shoot and root dry matters, and P uptake; while P integration with P-loaded LDH-biochar/hydrochar decreased shoot dry matter. Therefore, the P-loaded LDH-biochar/hydrochar can be added to soil as P-fertilizers without any chemical P-fertilizer. Application of biochar, hydrochar, and LDH-biochar/hydrochar accompany with chemical P-fertilizers is recommended to increase available-P and maize growth. [ABSTRACT FROM AUTHOR]

Adsorption and desorption rates play an important role in the availability and mobility of Lead (Pb2+) in soils treated with biochar. However, information is still limited about the effects of pyrolysis temperature, presence of Zn and incubation times on these processes. This study was performed to investigate the effects of 1% (w/w) walnut leaves biochars produced at different temperatures (200 °C (B200), 400 °C (B400) and 600 °C (B600)) on adsorption and desorption kinetics of Pb2+ in the presence of Zn2+ at two incubation times (30 and 90 d). Results explained that the adsorption rate of Pb2+ was decreased with increasing the pyrolysis temperature, whereas the desorption rate of Pb2+ was increased. In the presence of Zn2+, there was a decrease in the adsorption sites for Pb2+, while there was an increase in the available desorption sites for Pb2+. The rate of Pb2+ adsorption in 90 d of incubation was higher than 30 d of incubation, whereas the rate of Pb2+ desorption in 90 d of incubation was slower than 30 d of incubation. It can be concluded that 1% (w/w) walnut leaves biochar could not immobilize Pb2+ in the soil because more than 74% adsorbed Pb2+ desorbed in DTPA-TEA solution. [ABSTRACT FROM AUTHOR]

Zinc (Zn) deficiency is common on calcareous soils due to fixation with soil components and precipitation with other ions. ZnO nanoparticles (ZnO NPs) may serve a better source of Zn for improved growth and biofortification in maize grains. Pot and field experiments were conducted to evaluate the effect of ZnO nanoparticles in comparison with conventional Zn fertilizer (ZnSO4) on growth and grain Zn contents of maize. In both experiments, Zn application improved growth and physiological parameters of plants; however, maximum improvement was observed in treatments receiving ZnSO4 (soluble) or ZnO nanoparticles (insoluble source of Zn). Application of ZnO nanoparticles also improved Zn concentration in shoots as well as in grains in field experiment. In field experiment, Zn partitioning was also calculated and interestingly it is found that Zn concentration at maturity stages was reduced in stem and mature leaves. Maximum Zn concentration (~80 mg kg−1) was observed in young leaves at vegetative growth stage in treatments receiving ZnO nanoparticles. Foliar applied ZnO NPs showed maximum increase in grain Zn concentration (82%). It is concluded that ZnO NPs improved maize growth, yield and grain Zn contents. Being cheaper and efficient source, it can be used for Zn biofortification. [ABSTRACT FROM AUTHOR]

Zinc (Zn) deficiency is prevalent in human populations in developing countries. The present study compared two wheat (Triticum aestivum L.) cultivars [Jauhar-2016 (standard wheat) and Zincol-2016 (Zn-biofortified wheat)] for Zn biofortification with optimum soil Zn application. For this, Zn (at 0, 3, 6, 12 and 24 mg Zn kg−1) was applied to pots having an alkaline calcareous soil. Grain yield, grain Zn concentration and grain Zn bioavailability in both cultivars were significantly increased by Zn fertilization. However, Zn application decreased iron (Fe) and phytate concentration in grains of both cultivars. As compared to Jauhar-2016, Zincol-2016 had significantly higher grain Zn concentration and grain Zn bioavailability at all the respective soil Zn rates excepting only at control. At 6 mg Zn kg−1, Zincol-2016 attained in grains a desired concentration of Zn (53 mg Zn kg−1) and a desired level of human Zn bioavailability (2.8 mg d−1 for women and was 3.0 mg d−1 for men). Jauhar-2016 also attained such comparative levels but only at a plant toxic rate of Zn (24 mg Zn kg−1). Conclusively, soil Zn application (agronomic biofortification) to Zn-biofortified wheat (Zincol-2016) may be a promising approach to decrease human Zn deficiency in population groups dependent on wheat-based diets. [ABSTRACT FROM AUTHOR]

Increasing soil organic carbon (SOC) is a widely accepted strategy to offset greenhouse gases and improve soil quality. Straw return can modify SOC dynamics and increase its stock, which are also influenced by soil clay content and metals (i.e. Zn) availability. We conducted a short-term (42 d) incubation study to evaluate SOC dynamics in a calcareous loamy clay soil where available Zn (DTPA extractable) was modified by adding high-Zn straw (HZ-St), low-Zn straw alone (LZ-St) or combined with Zn fertilizer (LZ-St+ZF). Results showed that the DTPA-Zn concentration in soil with LZ-St was similar to the control receiving no straw return or Zn, but it increased by 24.3% in the soil receiving HZ-St and 1.46-fold in the soil receiving LZ-St+ZF. The increased Zn availability enhanced microbial biomass C and N, but did not increase SOC mineralization due to the higher microbial entropy and lower respiration entropy. Greater Zn availability enhanced SOC sequestration probably by promoting the organo-Zn-mineral interactions and thus chemical stabilization. Therefore, adding HZ-St or LZ-St+ZF increases both Zn availability and SOC sequestration in calcareous loamy clay soil. However, long-term and field-based research is necessary to confirm the practical effects of this approach. Abbreviations: DTPA-Zn: diethylenetriaminepentaacetic acid extractable Zn; SOC: soil organic carbon; MBC: microbial biomass carbon; MBN: microbial biomass nitrogen; ZnMB: storage of Zn in microbes; qMB: microbial entropy; qCO2,: respiration entropy; PCA: Principal component analysis, CCA: canonical correspondence analysis. [ABSTRACT FROM AUTHOR]

Utilization of biochars (BCs) surfaces as suitable substrates for placement of nanoscale zero-valent iron (nZVI) not only can increase the stability of nZVI, but also can improve biochar sorption mechanisms for various pollutants in the environment. In this research, pistachio-shell residues (R), pistachio-shell residues biochar (B), and pistachio-shell residues biochar coated by nZVI (BN) were applied to a Cd-spiked (200 mg Cd kg−1 soil) calcareous soil at three levels (0.5, 2, and 4%). After the incubation process (90 d), the soil cadmium (Cd) behavior was examined using desorption kinetic and sequential extraction experiments. The results showed that application of BN was more effective compared with the other two amendments in decreasing Cd desorption. Reduction of Cd mobility from 70.8% in the unamended sample to 60.2, 50.8 and 41.7% in the R, B, and BN treated samples, respectively, showed the high effectiveness of BN in Cd stabilization, as compared to B and R. The existence of ion exchange, surface complex formation, surface precipitation or co-precipitation processes as possible mechanisms by BCs, along with possible processes of adsorption and surface complex formation from nZVI, leads to higher efficiency in Cd stabilization using engineered BCs compared to pristine BCs. [ABSTRACT FROM AUTHOR]

Recently, the use of biochars for stabilization of soil heavy metals has been expanded due to their adsorption characteristics, low cost and carbon storage potential. A factorial experiment was performed to investigate the effects of two plant residue biochars (licorice root pulp and rice husk biochar each applied at 2.5% (w/w)) produced at two temperatures (350 and 550 °C), and three Ni application rates (0, 150 and 300 mg Ni kg−1) on bioavailability and chemical fractions of Ni in a calcareous soil after spinach cultivation. Application of all the biochars significantly reduced Ni bioavailability factor (5–15%) and spinach Ni concentration (54–77%) in Ni-treated soil. The biochars produced at 550 °C were more effective at reducing Ni mobility and Ni uptake by spinach than those produced at 350 °C, attributed to higher CaCO3 and lower acidic functional group content, which resulted in greater enhancement of soil pH. When comparing the biochars produced at the same temperature, the rice husk biochars were the most effective in reducing Ni bioavailability, likely due to their lower acidic functional group content and higher nano-silica content which resulted in higher soil pH values and potentially promoted the formation of Ni-silicates and hydroxides. Abbreviations : Ni: Nickel; RHB: rice husk biochar; LRB: licorice root pulp biochar; WsEx: water soluble and exchangeable; CARB: carbonate form; RES: residual; MnOx; manganese oxides bound; AFeOx; amorphous iron oxides bound; CFeOx: crystalline iron oxides bound; OM: organic bound. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The current research was done to investigate the effect of wetting-drying cycles, time, and clay mineralogy on K fixation capacity of highly calcareous soils. In order to conduct the study, eight soil samples were collected. The samples were treated with different concentrations of K including 200 (K1), 400 (K2) and 800 mg kg−1 (K3) and 8 different incubation time including 6 h (t1), 24 h (t2), 72 h (t3), one week (t4), two weeks (t5), one month (t6), two months (t7) and three months (t8). Also, a wetting-drying treatment was done (td) in order to simulate the effect of irrigation and soil drying on K fixation. The results showed that for all K levels addition, the percentage of fixed K was increased with time. The K fixation content was increased with the increase in the added K from K1 to K3, while K fixation percentage was decreased. The results also showed that there was a significant difference between soils with wetting-drying treatment (td) and soils with three-month incubation (t8) in K fixation capacity, so that the fixation of K by the soils was increased with wetting-drying cycles. [ABSTRACT FROM AUTHOR]

Little is known about the occurrence of phosphorus (P) acquisition processes in the field, especially for faba bean (Vicia faba L.) in calcareous soils. We sampled soil, rhizosphere and plant materials in 12 calcareous field sites in Algeria and performed physicochemical analysis during two growing seasons. Both proton exudation and root exploration increased in P-deficient soils as compared to P-sufficient soils. Inhibition of nitrogen (N) fixation and rhizosphere alkalization were observed in N-rich soils. We also found that calcium (Ca) concentrations in both shoots and roots significantly increased with P-deficiency. The same trend, although less significant, was observed with respect to Ca uptake. These field observations suggested that acidifying roots acquired P from dissolving Ca-P minerals. The concomitant increase of the ratio Ca/P uptake should further enhance their dissolution. Other rhizosphere processes such as the mineralization of organic P should control P acquisition as alkalization occurred in the root zone in response to the inhibition of N fixation. In conclusion, P-acquisition processes in the field were consistent with previous findings made at the laboratory. In addition, the variety of faba bean cultivated by local farmers appeared relatively well adapted to field conditions thanks to the deployment of rhizosphere processes. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the usefulness of physical and chemical fractionation in quantifying soil organic matter (SOM) in different stabilized fraction pools. Soil samples from three land use types in Lorestan province, Southwest Iran were examined to account for the amount of organic carbon and nitrogen in different SOM fractions. Size/density separation and chemical oxidation methods were applied to separate the SOM fractions including particulate organic matter (POM), Si + C (silt and clay), DOC (dissolved organic C), rSOM (oxidation-resistant organic carbon and nitrogen) and S + SA (sand and stable aggregates). The values obtained for TOC, TN, and HWC were highest in forest lands followed by the range and agricultural lands. Among the SOM fractions, S + SA showed the highest values (5.75, 5.77 and 20.6 g kg−1 for agriculture, range and forest lands respectively) followed by POM, Si + C, rSOM, and DOC. The concentrations of C and N in the labile fractions obtained the higher values than in the stabilized fractions. Forest lands had the highest amounts of organic C and N among all fractions whereas agricultural lands showed highest values for inorganic C content of soils in different fractions. [ABSTRACT FROM AUTHOR]

This investigation was done to determine the release of potassium (K) from five calcareous soils of southern Iran using 0.025 M CaCl2, HCl and citric acid during six successive extractions and to study the K fixation capacity of the soils after K release experiment. Mineralogical study indicated that Vertisols and Mollisols were dominated with smectites; while other soils had illite, chlorite, palygorskite and smectite. Results indicated that citric acid extracted more K than CaCl2 and HCl (137 vs. 111 and 113 mg kg−1, respectively). The analysis of calcium (Ca), magnesium (Mg) and K concentrations in the solutions suggests that the exchange of K with soluble Ca and Mg (originated from dissolution of carbonates by acidic solutions) is the main mechanism of K release, but citrate is able to dissolve K-bearing minerals and release K in slightly calcareous soils. Soils with more illite released more K. Potassium fixation capacity of soils increased after extractions of soils with different extractants from 324 to 471 mg kg−1, with no significant difference. It is suggested to apply more K fertilizers in K-depleted calcareous soils and use of different solutions for extracting K from soil minerals may be a temporary and short term solution. [ABSTRACT FROM AUTHOR]

In an attempt to investigate variations in availability of native and applied phosphorus (P) with time, twenty five calcareous soil samples were treated with 0, 50 and 500 mg P kg−1 soil and incubated at 80–90% of field capacity moisture content in an open door glasshouse for a period of one year. Soil samples were taken out at certain intervals for P extraction with Olsen extractant under moist condition. Results indicated that following wetting the mean value of native Olsen-P decreased initially and then increased gradually with time of incubation. Generally, the short term (24 h) recoveries were not correlated with long term ones. The recovery of added P with time was described properly by the following new proposed model: R = 100/(1 + ktb), where R is percent recovery at time t, and k and b are empirical parameters. The values of k constant at 50 and 500 mg P kg−1 were in the ranges of 0.40 to 1.22 (0.84 ± 0.25, on average) and 0.04 to 0.52 (0.23 ± 0.14, on average), respectively. The corresponding respective values of b constant also ranged from 0.05 to 0.32 (0.15 ± 0.06, on average) and 0.12 to 0.92 (0.46 ± 0.23, on average). [ABSTRACT FROM AUTHOR]

This study investigated the adsorption behavior of selected heavy metals (Pb, Cu, and Ni) under single and multi-metal conditions by a light textured calcareous soil amended with plant residue biochars (corn straw, wheat straw, rice husk and licorice root pulp each at 3% w/w). The Freundlich isotherm best described the heavy metal adsorption suggesting multilayer adsorption. For all treatments under both adsorption conditions, the heavy metal adsorption capacity followed the order of Pb > Cu > Ni, which was associated with the hydrolysis constant, ionic radius, and electronegativity of these metals. Simultaneous presence of multiple metals decreased the adsorption capacity for each metal and the sequence was in the order of Ni > Pb > Cu. The corn straw biochar (CSB) had the highest adsorption capacity (Freundlich Kf (mg g−1) for Ni = 0.23, Cu = 1.41 and Pb = 2.73) and medium distribution coefficient (Kd medium(L kg−1) for Ni = 59.30, Cu = 1961.00 and Pb = 2602.00), indicating the CSB is the best treatment for stabilization of heavy metals in the soil. This was associated with the chemical characteristics of the CSB (high amounts of CaCO3 and P) and the greatest increase in soil pH value. [ABSTRACT FROM AUTHOR]

High levels of phosphorus (P) often induce zinc (Zn) deficiency in plants grown on Zn-poor soils. We investigated P-induced Zn deficiency in durum wheat (Triticum durum L. 'Carpio') grown on 16 noncalcareous and 31 calcareous soils differing in levels of available (Olsen) P and available (diethylenetriaminepentaacetic acid (DTPA)-extractable) Zn using micropots. A completely randomized factorial design with two levels of P (0 and 40 mg P kg−1 soil) and Zn (0 and 3 mg Zn kg−1 soil), i.e. four treatments ('control', + P, + Zn, and + PZn), were used. Grain yield of control plants depended mainly on the Olsen P level. Phosphorus had a negative effect on yield in 6 soils with Olsen P/ZnDTPA > 25, and Zn a positive one in 5 soils with Olsen P/ZnDTPA > 50; and the + PZn treatment generally resulted in the highest yield. Grain Zn concentration of control plants was negatively correlated with growth and Olsen P. Calcareous soils were less sensitive to P-induced Zn deficiency than noncalcareous soils because phosphate is sorbed by calcite rather than being co-adsorbed with Zn on the Fe oxides. Co-application of P and Zn to soil at low and application of Zn at high Olsen P ensured both maximum yield and grain Zn bioavailability. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate sorption, desorption, and immobilization of Pb in the clay and calcareous loamy sand soils treated with inorganic ligands (NO3−, Cl− and H2PO4−). Pb sorption was also determined in the presence of oxalate and citrate. The maximum Pb sorption capacities (q) ranged from 42.2 to 47.1 mmol kg−1 for the clay soil, and from 45.2 to 47.0 mmol kg−1 for loamy sand soil. It was observed that the binding energy constant (k) for Pb sorbed onto loamy sand soil (528-1061) is higher than that for clay soil (24.38-55.29). The loamy sand soil-sorbed greater quantities of Pb compared to the clay soil when initial pH was ≥ 3. However, it had lower sorption capacity at the lowest initial pH of 2. Additionally, the greatest Pb sorption and immobilization occurred in the soil treated with H2PO4. In the clay soil, the sorption of Pb was depressed at 0.1 mol kg−1 of Cl−, as compared with other ligands. Concerning organic acids, citrate ligand showed the highest decrease in Pb sorption. It could be concluded that the nature of Pb sorption can depend on the type and quantity of ligands present, as well as the soil type. [ABSTRACT FROM AUTHOR]

Sensor-based strategies for nitrogen (N) management are promising to achieve high N fertilizer use efficiency and to reduce the amount of wasted N reaching the environment. A need-based N management strategy using an active optical sensor was evaluated for maize grown in a calcareous soil, western of Nile Delta, Egypt. Field experiments were conducted at two locations during 2015 and 2016 to develop and validate an algorithm for refining N fertilizer application. An increasing rate of N fertilizer was applied in the experiment conducted in 2015 year at two different locations to establish plots with different yield potentials. The experiment conducted in 2016 year aimed at validating the established sensor algorithms. It was demonstrated that growth stage V9 (9th leaf collar fully unfolded) is the appropriate stage for applying a corrective N fertilizer dose. Application of a prescriptive dose of 150 kg N ha−1 in two equal split doses, followed by a corrective dose guided by the optical sensor resulted in similar yield as general recommendation, but with lower total fertilizer application. This study revealed that N fertilizer in maize could be managed more efficiently using sensor-guided management than the current general recommendation in calcareous soils of Egypt. [ABSTRACT FROM AUTHOR]

The field experiments on calcareous sodic Vertisols were conducted on farmer’s fields in Purna valley of Vidarbha region of Maharashtra. The treatments comprised of different green manures (GMs); crop residues (CRs); gypsum. The chemical and biological properties after 2 years experiment showed that the application of gypsum recorded significant drop in pH and exchangeable sodium percentage (ESP) as compared to organic amendments. But later has outperformed with respect to biological activities viz., dehydrogenase activity (DHA) and microbial respiration and carbon sequestration by enhancing soil organic carbon (SOC), soil organic carbon (SOC) stock, soil microbial biomass carbon (SMBC) and labile carbon pool (POXC). Among the different organic amendments the application of dhaincha improved SMBC by 90%, microbial respiration by 104%, POXC by 59% and DHA by 265% as compare to control. High ESP of these soils showed negative relationship with microbial respiration and POXC (r = 0.48 and r = 0.43, p = < 0.05). While addition of biomass showed positive relationship with SMBC, microbial respiration, POXC and DHA (r = 0.93, r = 0.81, r = 0.83 and r = 0.91 p = < 0.01). The results of study showed green manuring in sodic black soil found to be alternative choice to gypsum, which besides gradual reclamation also enhance biological properties and carbon sequestration. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the effect of different biochar on alkaline calcareous soil, inherently low in soil organic carbon and fertility. Experiments were conducted in laboratory and greenhouse. Biochar was produced from wheat and rice straws at pyrolysis temperatures of 300°C, 400°C and 500°C (denoted as WSB300, WSB400, WSB500, RSB300, RSB400 and RSB500, respectively). In the first experiment, soil was incubated with biochar (1.0 % w/w) for up to 50 weeks. The results indicate that, WSB300 caused a significant decrease in soil pH and increased the CEC and nutrients (N, P and K) after 50 weeks of incubation. In the second experiment, maize plants were grown in pots containing calcareous soil amended with WSB and RSB for 60 days the results revealed that the application of WSB300 caused a significant increase in shoot (36%) and root (38%) dry matters over the respective control. Moreover, the highest nutrient concentrations (N and P) in shoot and root were observed with the WSB300 compared to other treatments. Therefore, it is concluded that application of wheat straw biochar produced at low temperature (WSB300) could be successfully used to improve soil properties and growth of plants in calcareous soils. [ABSTRACT FROM PUBLISHER]

A large proportion of phosphate fertilizer applied to calcareous soils reacts with calcium. Changes in soil phosphorus (P) availability after single application of biochar and phosphate-solubilizing bacteria have been reported. However, interaction of biochar (increasing soil pH) and phosphate-solubilizing bacteria (decreasing soil pH) on P availability in calcareous soil is not well known. An incubation experiment was conducted to study how the interactive effects of biochars (produced from wheat straw and cow manure at 300°C and 500°C with residence time of 1, 3 and 6 h) at different rates (0, 5 and 10 t ha−1) and phosphate-solubilizingPseudomonassp. IS8b2 affected on content of soil available P after 0, 60, 120 and 180 days of incubation (DOI) in a calcareous soil. After 60 DOI, the maximum value of available P (50.31 mg kg−1) was observed in the compound treatment ofPseudomonassp. IS8b2 and wheat straw biochar (10 t ha−1) produced at 500°C with residence time of 3 h. We conclude that the combination use of wheat straw biochar and phosphate-solubilizing bacterium is promising to potentially improve soil P availability in calcareous soil, but further research at field scale is needed to confirm this. [ABSTRACT FROM AUTHOR]

Soil factors such as pH, calcium, carbonate, and bicarbonate precipitation products in calcareous soils reduce iron (Fe) availability to crops and limit grain Fe concentrations. In the present greenhouse study, we evaluated the potential of Fe fertilizer amendments combined with organic amendments, like biochar (BC) and poultry manure, in sulfur (S)-treated low pH calcareous soils (pHS1) to assess Fe biofortification of maize. Elemental sulfur (S) was used both for lowering soil pH and Fe solubilization. Soil pH was successfully lowered down from 7.8 to 6.5 by S application at the rate of 2.5 g kg−1soil. Pot experiment results revealed that Fe fertilizer combined with BC and S (pHS1) significantly increased root and shoot dry weight, grain weight, photosynthetic rate, transpiration rate, and stomatal conductance by 69%, 86%, 28%, 74%, 57%, and 33%, respectively, relative to the control. Similarly, combined application of Fe + BC in S-amended (pHS1) soil increased starch (34%), protein (64%), and fat (1 fold) while antinutrient phytate and polyphenols were decreased up to 29% and 40%, respectively, over control. Regarding the maize nutrients profiles, application of Fe with BC gave the maximum increase of Fe and ferritin was increased 1.7 fold at pHS1. The results of this study showed that Fe fertilization with BC at pHS1soil is beneficial for crop growth and Fe bioavailability. [ABSTRACT FROM AUTHOR]

Field-applied salicylic acid (SA) could provide a potential protection against drought stress in onion large-scale production. Two-season field experiments were consecutively conducted in 2013/2014 and 2014/2015 to study the effect of 1 and 2 mM SA on growth, yield, plant water relations, chlorophyllafluorescence, osmoprotectants, and water-use efficiency (WUE) in onion plants under four levels of irrigation (I120 = 120%, I100 = 100%, I80 = 80%, and I60 = 60% of crop evapotranspiration). Foliar application of SA enhanced drought stress tolerance in onion plants by improving photosynthetic efficiency and plant water status as evaluated by membrane stability index and relative water content. These results were positively reflected by improving plant growth, productivity, and WUE under drought stress conditions. Therefore, SA application may, in future, find application as a potential growth regulator for improving plant growth and yield under deficit irrigation by 20–40%. [ABSTRACT FROM AUTHOR]

Understanding the role of organic acids on phosphorus (P) sorption capacity of soils is very important for its economic and friendly management. Combining P application with low-molecular weight organic acids could result in its higher plant availability for prolonged time. Therefore, citric and oxalic acid (at the rate of 1.0 mM kg−1soil) were evaluated for their effect on P sorption capacity and its plant availability in two different textured calcareous soils. Organic acids decreased P sorption capacity and organic carbon partition coefficient (Koc) whereas increased Gibbs free energy (ΔG) of P. Organic-acid-treated soils required lesser quantity of P fertilizer to produce soil solution P concentration optimum for plant growth (external P requirement [EPR0.2]), that is, 0.2 mg L−1. Citric acid was efficient than oxalic acid in the above effects. P sorption parameters of Freundlich model were negatively correlated with lime potential and ΔGwhereas had positive correlation (P < 0.05) with EPR0.2andKoc. Incubation with oxalic acid increased available P in loamy sand and loam soil by 20% and 30%, respectively. Thus, organic acids could help reduce application rate of P fertilizer through lowering its adsorption in highly P-fixing soils without compromise on yield. [ABSTRACT FROM AUTHOR]

A 2-year field experiment (2013 and 2014) was conducted in calcareous soil (CaCO319.2%), on soybean grown under three irrigation regimes 100%, 85% and 70% of crop evapotranspiration combined with three potassium (K2O) levels (90, 120 and 150 kg ha−1). The objective was to investigate the complementary properties of potassium fertilizer in improving soybean physiological response under water deficit. Plant water status (relative water content RWC, chlorophyll fluorescenceFv/F0andFv/Fm), had been significantly affected by irrigation or/and potassium application. Potassium improved growth characteristics (i.e. shoot length, number, leaf area and dry weight of leaves) as well as physiochemical attributes (total soluble sugars, free proline and contents of N, P, K, Ca and Na). Yield and yield water use efficiency (Y-WUE) were significantly affected by irrigation and potassium treatments. Results indicated that potassium application of 150 and 120 kg ha−1significantly increased seed yield by 29.6% and 13.89%, respectively, compared with 90 kg ha−1as average for two seasons. It was concluded that application of higher levels of potassium fertilizer in arid environment improves plant water status as well as growth and yield of soybean under water stress. [ABSTRACT FROM AUTHOR]

Nanoscale zero-valent iron particles (nZVIs) have been used as the stabilizing materials for remediation of heavy metals (HMs). The usage of nZVIs in the presence of oxygen is a challenging task. When this material comes in contact to air, immediately oxide formation takes place. Thus, preparation of air-stable nZVIs is necessary for successful remediation process. Therefore, the present study has attempted to evaluate the effects of three kinds of synthesized nZVIs, including nZVIEDTA(stabilized by ethylenediaminetetraacetic acid), nZVIDTPA(stabilized by diethylenetriamine pentacetic acid) and nZVI (without chelating agent), to determine their ability to stabilize lead (Pb) in two Pb-spiked soils. Pb-spiked soils were separately incubated with additives at the rates of 0.5% and 2% (W/W) for 90 days. The efficacy of nZVIs was evaluated by desorption kinetic and chemical fractionation experiments. According to the results, addition of nZVIEDTA, nZVIDTPAand nZVI significantly decreased Pb release by 70.1–86.4%, 56.5–70.6% and 24.3–49.2%, respectively. Among the three kinds of nZVIs, nZVIEDTAwas the most effective treatment in decreasing desorption and mobility factor of Pb. In practice, all three kinds of nZVIs are effective in Pb immobilization, while application of nZVIEDTAat the rate of 2% was the best treatment to immobilize Pb in polluted soils. [ABSTRACT FROM AUTHOR]

Little information is available regarding the effect of sewage sludge biochar on soil properties and crop yield. Thus, our objective was to evaluate the effect of sewage sludge (S) and its biochar (B) on maize shoot yield, nutrients and heavy metals uptake in two calcareous soils. The amendments were applied at the rates of 0, 10, 20 and 40 Mg ha−1. Moreover, NK treatment was included to compare the effects of S and B with conventional fertilization. At harvest time, plant shoots and soil samples were collected for yield, nutrients uptake and chemical analyses. The highest shoot dry matter was obtained in the S treatment. The B application in the clay loam and loam soils resulted in 5.2% increment and 17.7% decrement of shoot dry matter relative to the control, respectively. Shoot dry matter in the NK treatment was significantly higher than in the control. B application decreased Fe, Zn, Mn, Cu and Pb uptake by maize shoot. DTPA-extractable Pb in B-amended soils was lower than in control, while an inverse trend was obtained for available Fe, Zn, Mn and Cu. Biochar application at the rate of 7.3 Mg ha−1might be suggested for maize cultivation in clay loam soils. [ABSTRACT FROM AUTHOR]

A laboratory column experiment was conducted to investigate the effects of 400°C biochar at application rate of 15 g kg−1(21.9 t ha−1) with different particle sizes (<0.5 mm (S1), 0.5–1 mm (S2) and 1–2 mm (S3)) and application depths (0–2 cm depth (D0), 4–6 cm depth (D5) and 8–10 cm depth (D10)) on hydro-physical properties of sandy loam soil. The results indicated that applying biochar decreased the waterfront and saturated hydraulic conductivity of sandy loam soil. The cumulative evaporation was the highest and amounted to 40.9 mm in the non-treated soil, but it recorded the lowest amount of 32.2–35.5 mm in the biochar-treated soil. Applying biochar caused significant increases in the amount of conserved and retained water with the highest amount of water conserved in soil treated with S2biochar at D5. Moreover, the cumulative water infiltration through the soil was significantly reduced by S1and S2biochars at D0. The values of saturated hydraulic conductivity for biochar treatments were significantly lower than those for the control, with the lowest values for S1at D0and D5. These results suggest positive improvement for the hydro-properties of coarse-textured soils following biochar addition, especially with finer particles of biochar. [ABSTRACT FROM AUTHOR]

Continuous application of sewage sludge (SS) as a source of organic matter, may increase available heavy metals (HMs) up to their critical levels. As a consequence their uptake by plants, risks of accumulation in food chain and groundwater pollution increases. To evaluate the effects of perlite and SS on total content and available fraction of iron (Fe), manganese (Mn), lead (Pb), copper (Cu), nickel (Ni), cadmium (Cd) and zinc (Zn) over 45 and 90 days a completely randomized pot experiment was conducted. Treatments consisted of SS (0, 2 and 4%) and combined SS and perlite levels (1:1, 1.5:0.5 and 0.5:1.5% SS:perlite). Mean available Fe, Ni, Cd, Mn and Zn fractions decreased over time by 7–27%, whereas, total contents did not change. Available HMs in SS-treated soils increased by 0.5–25%; whereas, only total Zn, Cu and Pb concentrations increased with SS application (although concentrations fall in the range of critical levels). The lowest (1.6 fold) and highest (22.1 fold) increases obtained for available Cu and Zn, respectively. Perlite could mitigate the adverse effect of high rate application of SS on amplification of HMs extractability. Therefore, their concomitant applications can be suggested considering the perlite durability and its positive effects on soil physical properties. [ABSTRACT FROM AUTHOR]

A greenhouse pot experiment was conducted with peanuts (Arachis hypogaeaL., Fabceae) to evaluate iron compound fertilizers for improving within-plant iron content and correcting chlorosis caused by iron deficiency. Peanuts were planted in containers with calcareous soil fertilized with three different granular iron nitrogen, phosphorus and potassium (NPK) fertilizers (ferrous sulphate (FeSO4)–NPK, Fe–ethylendiamine di (o-hydroxyphenylacetic) (EDDHA)–NPK and Fe–citrate–NPK). Iron nutrition, plant biomass, seed yield and quality of peanuts were significantly affected by the application of Fe–citrate–NPK and Fe–EDDHA–NPK to the soil. Iron concentrations in tissues were significantly greater for plants grown with Fe–citrate–NPK and Fe–EDDHA–NPK. The active iron concentration in the youngest leaves of peanuts was linearly related to the leaf chlorophyll (via soil and plant analyzer development measurements) recorded 50 and 80 days after planting. However, no significant differences between Fe–citrate–NPK and Fe–EDDHA–NPK were observed. Despite the large amount of total iron bound and dry matter, FeSO4–NPK was less effective than Fe–citrate–NPK and Fe–EDDHA–NPK to improve iron uptake. The results showed that application of Fe–citrate–NPK was as effective as application of Fe–EDDHA–NPK in remediating leaf iron chlorosis in peanut pot-grown in calcareous soil. The study suggested that Fe–citrate–NPK should be considered as a potential tool for correcting peanut iron deficiency in calcareous soil. [ABSTRACT FROM AUTHOR]

Phytoremediation is a cleanup technology for the removal of contaminants from polluted soils. The influences of humic acid (HA) and four plant growth regulators, i.e. gibberellic acid, salicylic acid, 3-indoleacetic acid, and 6-benzylaminopurine on the phytoremediation of Pb by maize were investigated in a pot trial on a Pb-contaminated soil. Foliar spray of 6-benzylaminopurine and salicylic acid significantly increased mean root dry matter but none of growth regulators had a significant effect on that of shoot. Addition of HA decreased root dry matter and had no significant effect on that of shoots. Application of all growth regulators except gibberellic acid significantly increased root Pb uptake. Application of salicylic acid significantly increased mean uptake efficiency and shoot Pb concentration and uptake. Although addition of HA significantly increased mean phytoextraction and translocation efficiencies, these responses were mainly attributed to the role of HA in the reduction of both root dry weight and Pb uptake, meaning that HA is not promising in Pb phytoremediation by maize. Among the four plant growth regulators evaluated, salicylic acid was the most effective in enhancing phytoremediation through phytostabilization of Pb. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the effects of poultry manure (PM) and its derived biochars on chemical properties of a calcareous soil. PM and biochars prepared at 200°C (B200), 300°C (B300) and 400°C (B400) were applied to a calcareous soil at 2% level (w/w) and incubated for 150 days. Selected soil chemical properties and phosphorous, potassium, iron, manganese, zinc and copper availability and recovery were determined at 1, 15, 45 and 150 days of incubation. Soil nutrients availability, organic carbon (OC), electrical conductivity (EC) and cation exchange capacity (CEC) increased by addition of all organic substances. Biochars prepared at higher temperatures were more effective in increasing soil OC with higher durability compared to other treatments. The addition of PM and B200 decreased soil pH, whereas B400 increased it. Although the highest soil EC was observed in B300- and B400-treated samples in the early stages of incubation, the rate of increase in soil EC was higher for PM- and B200-treated soils compared to other treatments. It was concluded that biochar prepared at 300°C had the highest positive effect on nutrients availability and lasts longer in calcareous soil compared to the other produced biochars and PM. [ABSTRACT FROM PUBLISHER]

Recently, application of sewage sludge or effluents resulted in raising the concentrations of some heavy metals in some agricultural soils of Iran. Experiments were conducted to evaluate the competitive adsorption of lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) on six calcareous soils. Adsorption characteristics were evaluated by equilibration of 1 g of each soil sample with 20 ml of 0, 10, 20, 30, 40, 50, 100, or 200 mg L−1of their nitrate solutions and 0.01 M NaNO3as background electrolyte. Furthermore, solid/liquid distribution coefficients (Kd) of studied metals, as an index of soil capacity to resist a change of the soil solution concentration, were calculated. Results indicated that amounts of adsorbed Pb, Cu, Zn, and Cd increased with increase in their concentrations in the contact solutions, but this trend was more pronounced for Pb and Cu than the others. For all studied soils and metals, Langmuir equation described the adsorption behavior fairly well. Furthermore, Langmuir and Freundlich equation parameters were positively correlated to cation exchange capacity (CEC) and smectite contents; whereas, they were negatively correlated to sand content. Considering Kdvalues, the selectivity sequence of the metal adsorption was Pb > Cu > Zn > Cd. Therefore, the risk of leaching and also plant uptake of Zn and Cd will be higher as compared to those of the other elements. [ABSTRACT FROM AUTHOR]

The effect of different kinds of amendments including coal fly ash (CFA), municipal solid waste compost (MSWC), rice husk biochars prepared at 300°C (B300) and 600°C (B600), zero valent iron (Fe°) and zero valent manganese (Mn°) were evaluated to determine their ability to stabilize lead (Pb) in Pb-spiked soil. The Pb-spiked soils were separately incubated with amendments at the rates of 2 and 5% (W/W) for 45 and 90 days at 25°C. The efficacy of amendments treatment was evaluated by desorption kinetic experiment and sequential extraction producer. According to the results, with increasing time, considerable changes in distribution of chemical forms of Pb occurred and carbonate-bound fraction significantly decreased, while amorphous Fe-bound fraction significantly increased. The applied treatments efficiently decreased the mobility factor of Pb compared to control treatment. Application of Mn°, Fe°, CFA, MSWC, and B600 in soils significantly decreased Pb desorption rate with respect to control treatment. Biphasic pattern of Pb desorption kinetic was fitted well by the model of two first-order reactions. In general, present study showed that from the practical point of view, all applied amendments (except for B300) were effective in Pb immobilization; however, application of Mn° at 5% (W/W) rate was the best treatment to immobilize Pb, so it can be recommended for the immobilization of Pb in calcareous polluted soil. [ABSTRACT FROM PUBLISHER]

Reactions of elements with the water mineral interface are important and affect their bioavailability and transportation within soil. Effects of metal sorption on X-ray-diffraction (XRD-photographs) of clay minerals have been not studied. Therefore, sorption experiments were done on clay fractions of two calcareous soils using 12 concentrations of 0–2000 mg L−1Zn(NO3)2and Cu(NO3)2. Langmuir and Freundlich isotherms’ coefficients were determined. After sorption, XRD-diffraction were prepared and compared with those of initial samples. Langmuir (R2 = 0.996–0.999 and SE = 0.001–0.002) and Freundlich equation were the best-model for Zn and Cu-sorption, respectively. Sorption energy was higher for Zn than Cu, whereas the maximum concentration of sorbed-Cu was higher than that of Zn. Distribution coefficient (Kd) of Cu were more (threefold) than that of Zn. TheKdvalues representing the slope of Freundlich isotherms decreased according to linear regression equations (R2= 0.72–0.91) as the equilibrium concentrations of metals increased. No significant differences were observed among XRD-photographs of applied concentrations (some negligible differences were found in position/sharpness of peaks). Dry-XRD-method resulted in omission of intensity peaks at 2θ which may interfere in recognition of clays that show a maximum intensity >1.4 nm in the mentioned 2θ. Zinc can become more leachable especially in Shekarbani-soil-series, whereas, Cu highly adsorb on clay minerals and can show less tendency to transportation. [ABSTRACT FROM PUBLISHER]

Iron (Fe) deficiency is common in calcareous soils of southern Iran. Chemical forms of Fe in a calcareous soil were studied in the beneath and the interspace soils of five common range plant species. Results showed that electrical conductivity (EC) and organic matter (OM) content was significantly higher in the soil beneath canopies as compared to interspace soil. The reverse was true for pH of the soil except in case ofSalvia compressa. Among different forms of Fe, soluble and exchangeable Fe (SolEx-Fe) form was higher in the soil beneath canopy of all plant species as compared to interspaces. Similar results were recorded for Fe bound to organic materials (Om-Fe) but only in the case ofConvolvulus argyracanthus, Echinops glanduloso-punctatus, andCentaurea intricata. In the soil beneathConvolvulus argyracanthusandCentaurea intricatacanopies Fe bound to manganese (Mn) oxides (Mnox-Fe) was significantly higher but the amount of residual Fe (Res-Fe) was lower compared to the interspace soil. A reverse trend was, however, observed in the case ofTeucrium polium, demonstrating differential distribution of Fe forms at the two locations. The summation of reactive Fe forms [SolEx-Fe, Fe bound to carbonates (Car-Fe), and Om-Fe] known as readily or potentially available Fe was higher in the soil under canopies than in interspace soils. It is assumed that the higher contents of OM and lower values of pH enhanced Fe availability in the soil under plant canopies in comparison with interspace soil. [ABSTRACT FROM AUTHOR]

A greenhouse experiment (5 × 2 × 2 factorial arranged in randomized-complete-design with three replicates) was conducted to assess the combined effects of nickel (Ni) and drought stress on growth and yield parameters of canola (Brassica napusL. var. Talaye) grown on two calcareous soils of loamy and sandy clay textures. Treatments consisted of five Ni levels (0, 0.05, 0.1, 0.5 and 1 mg Ni kg−1soil) and two levels of water status 100% and 60% field capacity (FC and 0.6FC, respectively). Growth parameters and yield components of plants decreased at drought-stress conditions. Almost all of the studied growth/yield parameters of canola grown on loamy soil were significantly more than those of the sandy clay soil, probably due to the increased capability of loamy soil for supplying the plant water/nutrient requirements. Nickel could positively affect some of the mean growth and yield parameters (e.g., grain yield) over both of the water status conditions. Nevertheless, some of the traits not only increased by Ni fertilization but also decreased compared to that of the control. The positive responses of canola was observed with higher amounts of applied Ni in the sandy clay soil than in loamy soil, e.g., the maximum grain yields of canola grown on loamy and sandy clay soils were obtained with applications of 0.5 and 1 mg Ni kg−1, respectively. Generally, results demonstrated that Ni could not mitigate the negative effects of drought stress on canola growth or yield components. [ABSTRACT FROM AUTHOR]

Rhizosphere processes have a major impact on Zn desorption and Zn uptake by plant. However, information about Zn desorption characteristics in the rhizosphere of wheat is limited. Therefore, a greenhouse experiment was performed to determine Zn desorption characteristics in the bulk and rhizosphere soil of wheat (Triticum aestivumL.) of 10 soils amended and un-amended with municipal sewage sludge using rhizoboxes. The kinetics of Zn desorption was determined by successive extraction with 10 mM citric acid in a period of 1–504 h at 25 ± 1°C in the bulk and rhizosphere of un-amended and amended soils. The results showed that the Zn amount extracted after 504 h in the rhizosphere soils was significantly (p < 0.01) higher than the bulk soils. The mean of Zn desorption in the bulk and rhizosphere of un-amended soils were 10.4 ± 0.34 and 11.4 ± 0.43 mg kg−1, respectively, while the mean of Zn desorption in the bulk and the rhizosphere of amended soils were 13.2 ± 0.48 and 14.8 ± 0.67 mg kg−1, respectively. Desorption kinetics of Zn conformed fairly well to the first-order, parabolic diffusion, power function, and zero-order equations. The results of Zn fractionation indicated that exchangeable Zn and Zn associated with organic matter decreased and Zn associated with iron-manganese oxides and residual Zn increased in the rhizosphere soils compared to the bulk soils. Zinc desorption after 504 h and residual Zn in the bulk and rhizosphere of un-amended and amended soils were significantly positively correlated (p < 0.05). Therefore, residual Zn was the main Zn pool that controlled Zn desorption after 504 h in the bulk and rhizosphere soils studied. [ABSTRACT FROM PUBLISHER]

A laboratory study was performed to investigate the influence of soil texture (sandy loam vs. clay loam), Pb supply (as Pb(NO3)2without or with compost) and Pb levels on the extraction of available Pb by diethylene triamine pentaacetic acid (DTPA) and its desorption patterns at ten shaking periods. The soils were polluted with five Pb levels without or with compost and incubated for 1 month. Kinetic models commonly used to study the release of the nutrients were used in this study. Results showed that Power function model described the pattern of Pb desorption better than other models. The amount of extracted Pb increased as the Pb levels increased and was found to be higher in sandy loam soil treated with Pb without compost than that of clay loam soil treated with Pb with compost. Theavalue (Pb desorption constant) was the highest in sandy loam soil amended with Pb without compost. The lowest value ofa, however, was observed in clay loam soil amended with Pb with compost. Theabcoefficient (initial desorption rate of Pb) was higher in sandy loam than clay loam soil, demonstrating higher initial release rates of Pb in the coarser-textured soil. Addition of Pb without compost resulted in a higher increase inabvalue in comparison with Pb with compost, in both the soils. [ABSTRACT FROM AUTHOR]

The objective of the investigation was to evaluate the effect of applied phosphorus (P) and cadmium (Cd) on Cd chemical forms determined by sequential extraction and the relationship between these forms and plant responses, i.e., dry weights, concentration, and total uptake of Cd and P in a greenhouse experiment. Treatments consisted of five levels of Cd (5, 10, 20, 40 and 80 mg kg−1 soil as cadmium sulfate) and four levels of P (0, 15, 30 and 60 mg kg−1 soil as monocalcium phosphate), which were added to the soil and left to equilibrate for 1 month under greenhouse conditions. Spinach seeds (Spinacea oleracea L., cv Viroflay) were sown and then grown for 8 weeks. The chemical composition in the aerial part of the pant and soil was determined. Application of Cd decreased plant dry matter and increased Cd concentration in the plant, whereas at each level of applied Cd, P increased plant dry matter and decreased plant Cd concentration. All chemical forms of Cd in soil, as determined by a fractionation method, were increased following Cd application, the highest being the carbonatic form. Phosphorous application decreased exchangeable and carbonatic forms of Cd, whereas it increased other forms. [ABSTRACT FROM PUBLISHER]

This study was conducted to investigate the effect of time on chemical forms of P in 10 calcareous soils of western Iran. Phosphorus was added to soils at the rate of 200 mg kg−1as KH2PO4. The samples were incubated for 1, 7, 15, 30, 60, 90 and 120 days at 25°C and constant moisture. After incubation, P was fractionated by the sequential extraction procedure: soluble and exchangeable P (NaHCO3-P) Al + Fe-P (NaOH-P), Ca-P (HCl-P) and residual P (Res-P). The distribution of added P into different fractions consisted of two phases involving initial rapid retention followed by a slow continuous retention. In general, the majority of the P applied entered mostly in the HCl-P and Res-P fractions. After 120 days incubation, the HCl-P fraction remained the most dominant in all soils. A combination of silt and sand content of the soils together explained between 88.5 and 83.3% of the variance inNaHCO3-P and HCl-P transformation rates, respectively, 76.6 and 72.8% of which is explained by silt alone. CaCl2-P and electrical conductivity (EC) together accounted for 66.3% of the variation in the rate constant of NaOH-P. The release rate of Res-P was not significantly related to soil properties. [ABSTRACT FROM PUBLISHER]

Vegetative bioremediation of saline calcareous soil (EC1:111.01 dS m?1) was practised through growing fodder beet (Beta Beta vulgarisvar. magnum) and millet (Panicumspp.) in soil columns. Beet was grown at a planting density of 4427 plants m?2, whereas millet was grown at two planting densities: 5202 (M1) and 8928 (M2) plants m?2. Some plants were irrigated with 233 ? S cm?1water throughout the experiment (70 days), while for others non-saline water was replaced with saline water (2.52 dS m?1) at the middle of the experiment. The control was leaching of uncropped soil. Beet had higher ash content and efficiently extracted higher amount of salts (particularly Na and Cl) along with their aboveground biomass than millet under the two irrigation regimes. Millet grown at high planting density had higher ash content and extracted higher amount of salts (particularly Cl) than those at low planting density. Bioremediation, particularly in the case of millet (M1), considerably enhanced soil hydraulic conductivity as compared with leaching treatment; thus, facilitating the removal of some soluble salts beyond the root zone. Accordingly, soil electrical conductivity was considerably decreased by 54–69% compared with the untreated soil. It is concluded that mainly fodder beet is a potential candidate for efficient bioremediation of saline calcareous soils. [ABSTRACT FROM PUBLISHER]