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This study investigated the effect of different salinity (EC≈6 and 9 dS/m) and Ca/Mg ratios (≈0.95,0.50, and 0.25) in irrigation water on the chemical composition of soil solution and growth of pistachio (Pistacia vera L.). The physiological, biochemical, and yield-related responses of pistachio seedlings were measured within ≈30 weeks in a greenhouse pot experiment. The EC of the soil solutions rapidly approached the one in the irrigation waters while the Ca/Mg ratios slowly altered, as such the final ratios were ≈50-100% larger than the one in the irrigation waters. The slower change in the Ca/Mg ratio is due to the fact that Ca concentration is dominantly controlled by the calcite solubility but the Mg concentration by the ion-exchange reaction. With increasing EC of the soil solution from 5.8–10.4 dS/m, we found 4-fold reduction in shoot dry weight and 62% increase in electrolyte leakage. In each salinity level, the highest yield and membrane stability were achieved at the Ca/Mg ratio of ≈1 in the soil solution. Overall, a Ca/Mg ratio < 1 in the irrigation water shifted the ionic composition of the soil solution, even in calcareous soil, towards a ratio < 1 and negatively affected pistachio growth. [ABSTRACT FROM AUTHOR]

Extreme soils often have mineral nutrient imbalances compared to plant nutritional requirements and co‐occur in open areas where grazers thrive. Thus, plants must respond to both constraints, which can affect nutrient concentrations in all plant organs. Gypsum soil provides an excellent model system to study adaptations to extreme soils under current grazing practices as it harbours two groups of plant species that differ in their tolerance to gypsum soils and foliar composition. However, nutrient concentrations in organs other than leaves, and their individual responses to simulated herbivory, are still unknown in gypsum plants. We studied plant biomass, root mass ratio and nutrient partitioning among different organs (leaves, stems, coarse roots, fine roots) in five gypsum endemics and five generalists cultivated in gypsum and calcareous soils and subjected to different levels of simulated browsing. Gypsum endemics tended to have higher elemental concentration in leaves, stems and coarse roots than generalist species in both soil types, whereas both groups tended to show similar high concentrations in fine roots. This behaviour was especially clear with sulphur (S), which is found in excess in gypsum soils, and which endemics accumulated in leaves as sulphate (>50% of S). Moreover, plants subjected to clipping, regardless of their affinity to gypsum, were unable to compensate for biomass losses and showed similar elemental composition to unclipped plants. The accumulation of excess mineral nutrients by endemic species in aboveground organs may be a constitutive nutritional strategy in extreme soils and is potentially playing an anti‐herbivore role in grazed gypsum outcrops. [ABSTRACT FROM AUTHOR]

Calcareous soil is widely distributed throughout tropical areas. Due to its unique sedimentary environment and soil behaviors, severe engineering problems and disasters have occurred in many regions. To understand the differences in the mechanical properties of calcareous soils in different regions, material composition, physical and mechanical properties of calcareous soils, including specific gravity and void ratio, compression properties, shear properties, and strength properties, were analyzed. The relationship between the sedimentary environment, material composition, and mechanical properties of calcareous soil was examined based upon the results. Results show that the calcareous soil in the South China Sea has a high calcium carbonate content, large particle size, high compressibility, and low bearing capacity, while sand from the Kish Island in the Persian Gulf and Agami sand from Egypt have low compressibility and high bearing capacity. In the South China Sea, Calcareous soil is more difficult to crush than those from the Hormuz Island and Bushehr Port in the Persian Gulf, Dog's Bay in Ireland, and Quiou in France. Overall, calcareous soils from various locations exhibit significant differences in properties based upon their physical traits. It is suggested that the influence of sedimentary environment and geological conditions should be considered in engineering constructions. [ABSTRACT FROM AUTHOR]

An aerobic 15N microcosmic experiment was conducted to compare the inhibitory effects of the biological nitrification inhibitor (BNI), methyl 3-(4-hydroxyphenyl) propionate (MHPP) at rates of 500 and 1000 mg kg−1 with the synthetic nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) at 1% of applied NH4+, on the gross nitrification rate (n_gross) and on the abundance and community composition of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) of two contrasting soils (pH: 5.10 vs. 8.15, clay content 17.8 vs. 30.8). DMPP inhibited 56.6% of n_gross in the acidic soil and 50.3% in the calcareous soil, whereas MHPP inhibited 18.3–55.5% of n_gross in the acidic soil and 14.1–20.2% in the calcareous soil. MHPP used at the high rate showed the same inhibition on n_gross as DMPP in the acidic soil but not in the calcareous soil. DMPP and MHPP likely regulated n_gross by causing niche differentiation between AOA and AOB. Moreover, the community composition of AOB was more sensitive to nitrification inhibitor application than that of AOA, particularly in the acidic soil. However, the response of AOB community composition was less sensitive to the application of MHPP than to that of DMPP. MHPP mainly targeted Nitrosospira clusters 3a.2, 3b.2, and 9 of the AOB in the acidic soil. [ABSTRACT FROM AUTHOR]

Background: Saline and alkaline stresses damages the health of soil systems. Meanwhile, little is known about how saline or alkaline stress affects soil nitrifier and denitrifier communities. Therefore, we compared the responses of gene-based nitrifier and denitrifier communities to chloride (CS), sulfate (SS), and alkaline (AS) stresses with those in a no-stress control (CK) in pots with a calcareous desert soil. Results: Compared with CK, saline and alkaline stress decreased potential nitrification rate (PNR) and NO3-N; increased pH, salinity, water content, and NH4-N; and decreased copy numbers of amoA-AOA and amoA-AOB genes but increased those of denitrifier nirS and nosZ genes. Copies of nirK increased in SS and AS but decreased in CS. There were more copies of amoA-AOB than of amoA-AOA and of nirS than of nirK or nosZ. Compared with CK, SS and AS decreased operational taxonomic units (OTUs) of amoA-AOB but increased those of nirS and nosZ, whereas CS decreased nirK OTUs but increased those of nosZ. The numbers of OTUs and amoA-AOB genes were greater than those of amoA-AOA. There were positive linear relations between PNR and amoA-AOA and amoA-AOB copies. Compared with CK, the Chao 1 index of amoA-AOA and amoA-AOB decreased in AS, that of nirK increased in CS and SS, but that of nirS and nosZ increased in all treatments. The Shannon index of amoA-AOB decreased but that of nirS increased in CS and SS, whereas the index of nirK decreased in all treatments. Saline and alkaline stress greatly affected the structure of nitrifier and denitrifier communities and decreased potential biomarkers of nirS-type; however, AS increased those of nirK- and nosZ-type, and SS decreased those of nosZ-type. Soil water content, pH, and salinity were important in shaping amoA-AOA and denitrifier communities, whereas soil water and pH were important to amoA-AOB communities. Conclusion: These results indicate that the nitrifier and denitrifier communities respond to saline and alkaline stresses conditions. Communities of amoA-AOA and amoA-AOB contribute to nitrification in alluvial gray desert soil, and those of nirS are more important in denitrification than those of nirK or nosZ. [ABSTRACT FROM AUTHOR]

Biochar (BC) addition is widely used in agriculture to condition soils. However, the effects of BC addition on soil microbial community diversity and composition in karstic regions are unclear, especially after long-term application. To address this knowledge-gap, a field experiment was established to examine changes in soil physicochemical properties and microbial communities following six years of BC amendment. BC was applied to calcareous soils in a karstic region of southwestern China at four levels (w/w): 0%, 1.0%, 5.0%, and 10%. Bacterial community composition was then investigated in both the rhizosphere and bulk soils by 16S rRNA gene sequencing on the Illumina MiSeq Platform. BC addition increased soil pH, total carbon (TC), total nitrogen (TN), and total hydrogen (TH) contents in the rhizosphere and bulk soils. In addition, BC amendment was associated with changes in soil bacterial community compositions and diversities, especially at higher BC application levels. The relative abundances of Gemmatimonadetes increased in rhizosphere soils with increasing BC amendment, while those of the Bacteroidetes , Firmicutes , and Cyanobacteria decreased. The relative abundances of Proteobacteria and Chloroflexi increased in bulk soils with increasing BC application levels, while those of the Bacteroidetes and Verrucomicrobia decreased. Canonical correspondence analysis indicated that bacterial community composition was related to soil characteristics including pH, TC, TN, and TH contents in both rhizosphere and bulk soils. Importantly, variations in these soil parameters were closely associated with BC application rates. These results indicate that long-term BC application significantly impacts soil bacterial community characteristics in karstic regions via modulation of soil physiochemical properties. • Six years biochar addition altered rhizosphere and bulk soil properties. • Biochar changed the diversity and composition of soil bacterial communities. • Abundance of rhizosphere Gemmatimonadetes was increased by biochar addition. • Biochar increased the abundance of Proteobacteria and Chloroflexi in the bulk soil. • Long-term biochar application significantly affects the bacterial community. [ABSTRACT FROM AUTHOR]

Updating of the Soil Map of the Russian Federation (1 : 2.5 M scale, 1988) is planned on the basis of the new classification system of Russian soils. At the first stage, soil information for each polygon on the map is transformed into this system with due account for new factual data. In this paper, we consider problems in reclassification of legend unit "soddy-calcareous soils, including leached and podzolized soils." In dependence on the geographical position of particular polygons with these soils and the composition and properties of calcareous rocks, the soils of this legend unit are reclassified into different orders, types, and subtypes of the new classification system. The new soil names are introduced into the updated database to the vectorized version of the map. Thus, according to the thickness of the unconsolidated part of the profile, the former soddy-calcareous soils are specified into the orders of lithozems (<30 cm) and organo-accumulative soils (>30 cm). Within the latter order, the character of organic and humus horizons is taken into account in identification of the types of dark-humus, gray-humus, mucky–humus, raw-humus, and (probably) light-humus soil types with residual carbonates recorded at the subtype level. The types of raw-humus and light-humus carbolithozems are added to the classification system. An increased content of semidecomposed phytodetritus in the soils is reflected at the subtype level (the subtype of raw-humus soils). This level is also used to reflect the development of eluviation (eluviated soils), illuviation (clay-illuvial soils), and pedogenic transformation of middle-profile horizons (metamorphized, cryometamorphized, ferruginated, and gleyic subtypes) and the inheritance of some specific features of the parent material (red-profile soils). At the species level, the degree of leaching of carbonates from the upper part of the profile is indicated. Plowed soddy-calcareous soils are specified as agrohumus and agro-dark-humus soils. Geographical patterns of manifestation of these soil features and their "soil-ecological" logic are also discussed in the paper. [ABSTRACT FROM AUTHOR]

• Carbon in calcareous-rich soils was measured by six different methods. • The loss-on-ignition (LOI) analysis overestimated SOC compared to other methods. • The wet oxidation method did not overrate the result where SOC is<8.7% and allowed the analysis of soils containing up to 100% CaCO 3. • The LOI and volumetric methods gave identical SIC values. • Search for conversion factor is a necessary tool for data globalization on SOC. The pedosphere is an essential reservoir of carbon represented by organic (SOC) and inorganic (SIC) forms. Various methods are used worldwide to measure SOC and SIC. The trend towards globalization of data on soils requires having the accumulated information harmonized. Global soil databases are crucial for inventory and mapping, modeling and forecasting, monitoring and rational use of soil resources. This study compared the six most common methods for measuring carbon in soils on calcareous rocks. Standard soil samples and soils of the Polar Urals with a variation in CaCO 3 (0–100%) and SOC (0–40%) were selected as research targets. The loss-on-ignition (LOI) method (T = 550 °C) overestimates SOC. It is explained by the fact that the SOC to SOM conversion factor of 1.724 seems inadequate. The soils under study demand a coefficient of 2.326. The second reason is the presence of thermolabile mineral components in soils, as well as adsorbed and chemically bound water. For soils with a carbonate content of 0–100% and SOC < 8.7%, harmonized results of SOC measurements may be obtained on the analyzer and by the dichromatometric method (Walkley-Black) only with conversion factors applied (1.3). At a higher SOC (8.7–40%) content, soils in the area under study require a reduced coefficient of 1.18. The measurement results of SIC within the range of 3.2–12% (CaCO 3 27–100%) obtained by LOI methods (T = 800 °C) and with a calcimeter are identical with SOC < 16%. The presence of CaCO 3 does not inhibit the use of the dichromatometric method (Walkley-Black, Tyurin) to measure SOC. The reliability of carbon content measurement methods for soils was determined both by the specific composition of the soil and by the accuracy of the method itself. To facilitate future application of the methodology, guidelines were proposed to use methods for quantitative assessment of SOC and SIC. [ABSTRACT FROM AUTHOR]

The application of zinc (Zn) fertilizer to lentil is an agronomic strategy that has the potential to improve yield and enhance grain Zn concentration. A pot study was conducted to determine if Zn fertilizer applied to three popular Saskatchewan lentil cultivars could increase yield and concentration of Zn in the grain. The effects of soil and foliar applied Zn forms, including ZnSO4, Zn chelated with EDTA, Zn lignosulphonate, and a control were evaluated. Forms of Zn were not found to significantly increase yield (P = 0.828) or grain Zn concentration (P = 0.708) in any of the lentil cultivars tested. Fertilization with soil applied ZnSO4 resulted in significantly (P < 0.0001) higher amounts of residual available Zn in the soil relative to other Zn treatments. Soil fertilized with ZnSO4 had 1.13 mg kg−1 diethylenetriaminepentaacetic acid (DTPA)-extractable Zn compared to 0.84 mg Zn kg−1 and 0.77 mg Zn kg−1 in the soil and foliar applied chelated Zn, respectively. [ABSTRACT FROM AUTHOR]

Desorption of iron from soil is important for evaluating the availability and toxicity of soil Fe in agriculture. The aim of this investigation was to study the effect of organic substances (cow and sheep manures and vermicompost) on Fe release from a calcareous soil and determine the best models for the description of the Fe desorption kinetics. Organic substances were added to soils at the rate of 3 %. Basil (Ocimum basilicum L.) seeds were sown in each pot and pots were kept at 24-25 °C at about field capacity for 90 days. After 90 days, plants were harvested and soil samples were used for Fe desorption analysis. Seven kinetic models were evaluated to describe the rate of Fe desorption in soil extracted with diethylenetriaminepentaacetic acid (DTPA). Results showed that Fe release from soil samples increased with time. Release of Fe was rapid at first and then became slower. Iron release in the organic substances treatments was higher than in the unamended soil and the two-constant rate, parabolic diffusion and simple Elovich models were the best equations for the description of Fe release from soils. [ABSTRACT FROM AUTHOR]

Two typical Chinese soils including southern paddy soil and northern calcareous soils were used in a pot experiment to evaluate the effect of magnesium slag-based fertilizer on heavy metal accumulation and health risk in soil-plant system. The results indicated that magnesium slag-based fertilizer promoted the growth of maize plants. The concentrations of Cr, Cu, Pb and Zn in both soils amended with magnesium slag-based fertilizer were qualified for the second level criterion of Standard of Soil Environment (GB 15618-2009). Accumulation of HMs exhibited partitioning characteristics in maize plants, i.e. Cr and Cu were accumulated mainly in root and leaf parts while Pb was concentrated in roots. The order of transfer factors (TF) of HMs in different plant organs was ordered as follows: root > stem > leaf > grain. It indicated that less HMs were accumulated in the grain compared with that in other organs. The estimate daily intakes and total target hazard quotient of HMs including Cr, Cu, Pb, and Zn were less than 1, indicating that consumption of maize grain was at low risk and would not cause non-carcinogenic risks. From the above results, application of magnesium slag-based fertilizer at present level would not cause pollution risk for maize plants cultivated in two Chinese soils. [ABSTRACT FROM AUTHOR]

Zinc (Zn) is an essential micronutrient for crop growth. This metal can be found in chemical forms or fractions in the soil. The objective of this study was to investigate the distribution of Zn in special chemical forms using the sequential extraction method after treating eight calcareous soils by zinc sulfate and municipal solid waste (MSW) compost. Zn was separated in seven defined forms as exchangeable (Ex), carbonate (Car), organic (Om), manganese oxide bound (MnOX), amorphous iron oxide bound (FeAOX), crystalline iron oxide bound (FeCOX), and residual (Res). According to the results, the mean concentrations of Zn in chemical forms in untreated soils from higher to lower were 31.84, 8.13, 2.64, 2.57, 0.45, 0.39, and 0.16 mg kg−1for the Res, FeCOX, Car, FeAOX, Om, MnOX, and Ex forms, respectively. The total applied Zn to the studied soils from both the sources of zinc sulfate and MSW compost after incubation for 30 days was converted to chemical forms in the following order: Car > Res > FeCOX > Om > FeAOX > MnOX > Ex. On average, 30.3% of total Zn from zinc sulfate and 28.8% of total Zn in the MSW compost were converted into the Car form. The high content of calcium carbonate (CaCO3) in the studied soils is an important factor affecting the conversion of Zn forms, mostly in the Car form through the application of both the inorganic and the organic sources of Zn. [ABSTRACT FROM AUTHOR]

Natural concentrations of trace elements are necessary for assessing trace elements contamination affected by anthropogenic activities in soils. This study was conducted to establish background concentrations of cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn) in 50 unpolluted native soils with a total of 100 soil samples (surface and subsurface soil layers) in Hamedan province of Iran. Different methods have been used for the evaluation of background limits, and the relationships between soil properties and trace elements concentrations and among trace element concentrations have been analyzed. Values from Geometric Mean (GM) procedure had the lowest background limit, while the GM × GSD 2 (geometric standard deviation) method produces the highest background limits. The percentage of outliers in Median + 2MAD (median absolute deviation) ranged from 4.0 to 16.0% for natural data and from 0.0 to 12% for log-transformed data. The smallest outlier percentage was for Cd and Cr, and it was higher for Co, Cu, and Zn. The obtained geochemical baseline concentrations (mg kg −1 ) based on Median + 2MAD were (log-transformed data) Cd 1.36, Co 15.42, Cr (natural data) 36.69, Cu 29.99, Fe 25.79 (g kg −1 ), Mn 368.68, Ni (natural data) 53.59, Pb 39.60, Zn 103.80. Carbonate calcium had significant negative correlations with Co, Cr, Cu, Fe, and Mn, indicating that trace elements are not included in the crystal structure of secondary carbonate minerals; consequently, accumulation of CaCO 3 causes a dilution effect in the soils. The content of clay, silt and organic matter had significant role in the accumulation of Mn, Ni, and Pb in the soils of the studied area. Significant correlation was found among Co, Cr, Cu, Fe, Mn, and Ni and between Zn with Cd, Cr, Cu, Mn, and Ni. Factor analysis of trace elements explored six factors attributing 64.1% of the total variability. According to the results found by upper whisker method, correlation analysis and factor analysis, studied trace elements contaminated none of the soil samples, natural accumulation processes influenced their contents in soils and origin of trace elements may be lithogenic, but their sources may be different. [ABSTRACT FROM AUTHOR]

Biochar (BC) was produced by pyrolyzing the date palm leaf waste at 600 °C and then loaded with phosphorus (P) via sorption process. Greenhouse pot experiment was conducted to investigate the application effects of BC and P-loaded biochar (BCP) on growth and availability of P and heavy metals to maize ( Zea mays L.) plants grown in contaminated mining soil. The treatments consisted of BC and BCP (at application rates of 5, 10, 20, and 30 g kg −1 of soil), recommended NK and NPK, and a control (no amendment). Sorption experiment showed that Langmuir predicted maximum P sorption capacity of BC was 13.71 mg g −1 . Applying BCP increased the soil available P, while BC and BCP significantly decreased the soil labile heavy metals compared to control. Likewise, heavy metals in exchangeable and reducible fractions were transformed to more stable fraction with BC and BCP applications. The highest application rate of BCP (3%) was most effective treatment in enhancing plant growth parameters (shoot and root lengths and dry matter) and uptake of P and heavy metals by 2–3 folds. However, based on metal uptake and phytoextraction indices, total heavy metals extraction by maize plants was very small for practical application. It could be concluded that using P-loaded biochar as a soil additive may be considered a promising tool to immobilize heavy metals in contaminated mining areas, while positive effects on the biomass growth of plants may assist the stabilization of contaminated areas affected by wind and water erosion. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) which does not have a biological role is one of the most toxic heavy metals for organisms. This metal enters environment through industrial processes and fertilizers. The main objective of this study was to determine the relationships between absorbed Cd by pistachio kernel and some of soil physical and chemical characteristics using modeling by stepwise regression and Artificial Neural Network (ANN), in calcareous soils in Rafsanjan region, southeast of Iran. For these purposes, 220 pistachio orchards were selected, and soil samples were taken from two depths of 0–40 and 40–80 cm. Besides, fruit and leaf samples from branches with and without fruit were taken in each sampling point. The results showed that affecting factors on absorbed Cd by pistachio kernel which were obtained by regression method (pH and clay percent) were not interpretable, and considering unsuitable vales of determinant coefficient (R 2 ) and Root Mean Squares Error (RMSE), the model did not have sufficient validity. However, ANN modeling was highly accurate and reliable. Based on its results, soil available P and Zn and soil salinity were the most important factors affecting the concentration of Cd in pistachio kernel in pistachio growing areas of Rafsanjan. [ABSTRACT FROM AUTHOR]

A two-year experiment was conducted in an iron(Fe)-deficient orchard with calcareous soil to find out an alternate method for soil application of Fe ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid) (Fe-EDDHA) in orange trees. Foliar sprays of Fe-EDDHA (5 g l−1, pH = 7.8), sulfuric acid (pH = 3), citric acid (5 g l−1, pH = 2.4), Fe (II) sulfate solutions (250, 500, and 750 mg Fe l−1) with their initial pH (6.5, 6.35, and 6.12) and reduced ones to pH of 3 were compared with soil applied (75 g tree−1) Fe-EDDHA and a control test. Although optimum chlorophyll content, leaf Fe concentration, fruit quantitative and qualitative attributes were resulted from soil application of Fe-EDDHA, repeated sprays of Fe-EDDHA or acidified Fe solutions created suitable results. Acidification of Fe solutions made them more effective in alleviation of leaf Fe concentration and Fe chlorosis, probably due to remobilization of inactive Fe within the plant and prevention of Fe oxidation and precipitation in foliar solutions. [ABSTRACT FROM AUTHOR]

Zinc (Zn) deficiency is a widespread problem in wheat-cultivated lands, and understanding important mechanisms determining Zn phytoavailability is of high importance. Accordingly, a two-year field experiment was conducted to investigate the effects of two Zn-deficiency tolerant wheat cultivars on Zn binding forms in a calcareous saline soil. Changes in soil Zn fractions were also found to be related to Zn uptake by wheat. Rhizosphere and bulk soil samples and the above-ground biomass were collected at grain maturity and analyzed for Zn. By using a sequential extraction procedure, soil Zn was divided into the following operationally defined fractions which are conceptually designated: ‘exchangeable Zn’ (EXCH-Zn), ‘Zn bound to carbonates’ (CAR-Zn), ‘organically bound Zn’ (ORG-Zn), ‘Zn bound to iron and manganese oxides’ (FeMnOX-Zn), and ‘residual Zn’ (RES-Zn). EXCH-Zn and ORG-Zn in the rhizosphere soil were found to be positively correlated with Zn uptake into the aboveground biomass of both wheat cultivars, thereby indicating that these fractions could be considered as labile pools. Higher EXCH-Zn and ORG-Zn fractions were determined in the rhizosphere, not in the bulk soil, whereas the non-labile Zn pools was decreased, suggesting strong Zn solubilization due to the input of acidity and organic compounds by root and the associated microbial activity. The differences between rhizosphere and bulk soil in EXCH-Zn and ORG-Zn were associated with the lower pH and the higher concentrations of the total (TOC) and dissolved organic carbon (DOC) in the rhizosphere. The fact, these effects (lower pH and higher DOC in the rhizosphere, rather than in the bulk soil) were stronger for Back Cross Rushan than were for Kavir; this was in line with the higher Zn uptake of Zn-deficiency tolerant Back Cross Rushan. [ABSTRACT FROM AUTHOR]

Soil salinity is a serious abiotic factor affecting the production of crops by reducing potassium (K) uptake due to strong competition with sodium (Na) cations in the root regions. In calcareous soils, most of the nutrients precipitate in unavailable forms for plants. This study investigated the physiological and biochemical response of two wheat genotypes salt tolerant Abadghar and salt sensitive Pari-73 supplemented with K and zinc (Zn) nutrition. A factorial experiment with three levels of K (0, 50 and 100 kg ha−1) and three levels of Zn (0, 25 and 50 kg ha−1) based on a complete randomized design was employed. The results showed significant effect of treatments on chlorophyll (Chl) contents, water relations, nitrogen metabolism and yield attributes. The treatment K+Zn (100, 25 kg ha−1) was the most effective in increasing grain yield. The results achieved highlight the importance of K and Zn nutrition in salt-stress conditions. [ABSTRACT FROM AUTHOR]

The high potassium (K)-fixing capacity of calcareous soils with homogeneous K supply limits crop K concentration. The objective of this study was to determine the increase in the leaf K concentration of tobacco ( Nicotiana tabaccum L.) with a heterogeneous K supply. Two field experiments were conducted from 2013 to 2015 with five K rates applied in homogeneous environments and one K rate applied in varying fractions of soil volume (from 0% to 100%) in heterogeneous environments. Under ridge culture, leaf biomass was not significantly affected by homogeneous (K rate) or heterogeneous (patch size) K management. Under homogeneous conditions, increasing the K supply to three times the standard rate used by farmers (249 kg K ha−1) increased leaf K concentration significantly, but the effect was limited and not cost-effective. Heterogeneous supply of K fertilizer at the standard K rate in patches of 0-40% of soil volume outperformed homogeneous K supply in terms of leaf K concentrations. Furthermore, K fertilizer mixed in intermediate soil volume fractions of 1-20% resulted in higher leaf K concentrations than the smallest (0%) and larger (30-40%) soil fractions. However, such K-rich patch application should be managed precisely with specific placement due to the sharp reduction in available K with increasing distance from the fertilizer. To maximize the sorption of immobile K, the match between the uptake volume of the rhizosphere and the area available for K diffusion is important. [ABSTRACT FROM AUTHOR]

The application of organic fertilizers in soils not only increases soil organic matter but also introduces essential nutrients to soil. Therefore, applying these fertilizers can affect the availability and desorption characteristics of nutrients. The main objective of this research is to study the effects of cow manure (CM) and vermicompost (VC) on availability and desorption characteristics of zinc (Zn) in a loamy calcareous soil. In this study, concentration of available Zn (using DTPA-TEA, AB-DTPA, and Mehlich 3) and desorption characteristics of Zn (using successive extraction with DTPA-TEA For 1–504 h at 25 ± 1°C) in amended soil with 0, 0.5, and 1% (w/w) of CM and VC were investigated in a completely randomized design. Results of this research showed that concentration of Zn extracted by using three methods was higher in amended soils with 1% CM and VC than those with 0.5% of these fertilizers. Furthermore, the difference between concentration of available Zn in amended soils with CM and VC was not found to be significant (p > 0.05). The results of kinetics study illustrated that the effect of organic fertilizers on Zn desorbed after 504 h was found to be significant (p < 0.01). Amount of cumulative of Zn desorbed in amended soils was significantly (p < 0.05) higher than unamended soil. Concentration of Zn desorbed after 504 h in 0.5 and 1% of CM and VC compared with unamended soil increased 26, 54, 12, and 46%, respectively. In addition, Zn desorption rate in amended soils with CM was higher than those with VC. It can be concluded that organic fertilizers applied to loamy calcareous soils enhance source of available Zn for the plant. Moreover, the results of this study showed that the ability of amended soils with VC to supplying Zn for plants was lower than those with CM. [ABSTRACT FROM AUTHOR]

This paper reports the results of desorption experiments of cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) from some contaminated calcareous soils under four electrolyte types (CaCl2, MgCl2, NaCl and Na2SO4) with different electrolyte concentrations (0.5, 4 and 10 mM). Among electrolytes, CaCl2significantly released more metals from soils. There was a negative relationship between total Cu and Zn content and percentage of Cu and Zn released (average of electrolyte concentrations) using CaCl2solution, indicating a higher Cu and Zn released when their total content was low. Generally, Cd, Cu, and Zn speciation was affected by both type of electrolytes and their concentrations, whereas Ni speciation stayed mostly stable and was almost unaffected by applied solutions. It can be suggested that beside competition with cations, chloro-complexation is important parameter in Cd release, while CuOH+, and to some extent ZnOH+are important species affecting release of Cu and Zn. The distribution coefficient (Kd) values for each metals greatly varied with the types of electrolytes and electrolyte concentration. On the basis of average percentage of metal released under different electrolytes and concentrations the following sequences was found: Cd > Cu > Ni > Zn. The results are important in understanding the mobility of metals under different solutions and indicating that, Cd and Zn soils may pose a higher and lower mobility and ecological risk in contaminated calcareous soils, respectively. [ABSTRACT FROM AUTHOR]

Background and aims: Iron (Fe) is an essential micronutrient for all higher organisms. Fe is sparingly available in calcareous soils and Fe deficiency is a major agricultural problem worldwide. Nicotianamine (NA) is a metal chelator involved in metal translocation in plants. Sweet potato is an attractive crop that can grow in poor soil and thus is useful for planting in uncultivated soil. In addition, the sweet potato has recently been suggested as a source of bioethanol. Our aim is to increase NA concentration in sweet potato to ameliorate Fe deficiency. Method: Sweet potato plants expressing the barley NA synthase 1 ( HvNAS1) gene under the control of CaMV 35S promoter were produced by Agrobacterium-mediated transformation. Results: The transgenic sweet potato exhibited tolerance to low Fe availability when grown in calcareous soil. The level of tolerance to low Fe availability was positively correlated with the HvNAS1 expression level. The NA concentration of the transgenic sweet potato leaves was up to 7.9-fold greater than that of the non-transgenic (NT) plant leaves. Furthermore, the Fe and zinc concentrations were 3- and 2.9-fold greater, respectively, in transgenic sweet potato than in NT plant leaves. Conclusions: Our results suggest that increasing the NA concentration of sweet potato by overexpression of HvNAS1 could significantly improve agricultural productivity and energy source. [ABSTRACT FROM AUTHOR]

Microbial community composition differs between soil aggregate sizes, which markedly affects phosphorus cycling in agroecosystems. The genes phoD and pqqC regulate phosphorus mobilization and act as molecular markers of phosphate-mobilizing bacteria, but differences in phoD - and pqqC -harbouring bacterial communities between different-sized aggregates remain unclear. The abundance and community composition of phoD - and pqqC -harbouring bacteria were determined in three aggregate size classes (> 250, 63–250, and < 63 µm) in calcareous soil from northwest China in a 38-year experiment. The > 250 and < 63 µm aggregates showed the lowest and highest cumulative relative abundance, respectively, of operational taxonomic units in phoD - and pqqC -harbouring bacterial communities. Simpler co-occurrence networks (fewer nodes, links, and shorter network diameter) were found in > 250 and < 63 µm aggregates, compared to 63–250 µm aggregates. For phoD and pqqC gene networks, > 250 and < 63 µm aggregates (phoD : α-Proteobacteria and Actinomycetia; pqqC : Actinomycetia) contained keystone taxa distinct from 63 to 250 µm aggregates (phoD : Rubrobacteria and γ-Proteobacteria; pqqC : β-Proteobacteria). Total nitrogen (TN) and Olsen-P significantly affected the abundance and community richness of phoD - and pqqC -harbouring bacteria. phoD and pqqC gene abundance was determined by TN in > 250 µm aggregates, whereas they were indirectly determined by Olsen-P in < 63 µm aggregates. Our results emphasized the distinct distribution characteristics of phosphate-mobilizing bacterial communities in different-sized aggregates and identified the main factors regulating phoD and pqqC gene abundance. • phoD and pqqC bacterial communities differed among soil aggregate sizes. • Different keystone taxa of phoD and pqqC were found between soil aggregate sizes. • TN regulate the gene abundances of phoD and pqqC in >250 µm aggregates. • Olsen-P regulate the gene abundances of phoD and pqqC in < 63 µm aggregates. [ABSTRACT FROM AUTHOR]

Biochar may affect nitrogen (N) cycling processes and, therefore, plant-available forms of soil N by modifying the activity and composition of the soil microbial community. However, it is unclear how biochar addition can influence microbial N cycling and availability in saline polluted soils. The present study investigated the impact of sugarcane bagasse biochars (SBBs) produced at 400 and 600 °C on potential net ammonification, nitrification and N mineralization, microbial biomass N (MBN), and urease activity in a calcareous soil polluted with lead (Pb) under different levels of NaCl salinity (6 and 10 dS m-1) during a 120-day incubation period. NaCl salinity increased soil available Pb concentration, with a greater increase at high than low salinity level. The application of SBBs increased soil organic carbon (SOC, 96–101 % relative to controls), dissolved organic carbon (DOC, 14–110 %), total nitrogen (TN, 6–25 %), cation exchange capacity (CEC, 12–20 %), and immobilized soil Pb (10–25 %). Lead immobilization, which largely resulted from increased soil CEC, was greater with addition of 600 °C (20–25 %) than 400 °C (15–20 %) biochar in saline soils. Addition of SBBs decreased the availability of soil Pb that was enhanced by salinity. Biochar application stimulated potential net ammonification (177–218 %), nitrification (70–83 %) and N mineralization (92–110 %), MBN (114–221 %) and urease activity (66–79 %) in saline Pb-polluted soils. Redundancy analysis revealed that increased DOC, increased TN and Pb immobilization were the most significant factors contributing to the enhanced N bio-transformations, MBN, and urease activity in saline polluted soils amended with SBBs. Our highlights the potential benefits of low-temperature SBBs as an amendment to minimize the impact of metal toxicity associated with salinity on microbial N cycling processes in Pb-polluted soils. In conclusion, biochar application could be a useful practice for enhancing the N turnover rate in saline Pb-polluted soils by increasing substrate availability and decreasing Pb mobility. • Salinity increased lead (Pb) mobility and slowed nitrogen (N) processes. • Biochar reduced Pb mobility and consequently accelerated soil N transformations. • Lower-temperature biochar has greater impact on N cycling. • Biochar is a useful amendment to enhance N turnover in saline Pb-polluted soils. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) loss due to intensive cultivation is the focus of studies on climate change and food security. Dropping tillage intensity has been widely reported as a potential tool for SOM increase; however, the chemical composition, storage mechanisms, and vertical distribution of SOM gain are not fully understood, especially in calcareous soils. This study aimed to analyze the increased SOM conditions among pools and depths in an eighteen-year-long field experiment comparing SOM under conventional moldboard plowing (PT), deep cultivation (DC), and no tillage (NT) systems on a base-saturated Endocalcic Chernozem (Loamic). Soil samples were collected from the 0–10 cm and 30–40 cm soil layers and divided into mineral phase-associated organic matter (<63 µm, stable pool; MPAOM) and aggregate related organic matter (>63 µm, labile pool). The aggregate related organic matter was further divided into particulate organic matter (POM, <1.0 g cm-3) and aggregates-associated organic matter (AAOM, >1.0 g cm-3). Results indicated an overall increase in soil organic carbon (SOC) concentration in the topsoil in the order of PT

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]

Iron (Fe) deficiency is a critical agricultural problem, especially in calcareous soil, which is distributed worldwide. Rice plants take up Fe(II) from soil through a OsIRT1 transporter (Strategy I-related system) and also take up Fe(III) via a phytosiderophore-based system (Strategy II system). However, rice plants are susceptible to low-Fe conditions because they have low Fe(III) reduction activity and low-level phytosiderophore secretion. Previously, we produced transgenic rice plants expressing a mutationally reconstructed yeast ferric chelate reductase, refre1/372, under the control of the OsIRT1 promoter. This transgenic rice line exhibited higher Fe(III) chelate reductase activity and tolerance to Fe deficiency. In addition, we produced transgenic rice overexpressing the Fe deficiency-inducible transcription factor, OsIRO2, which regulates the expression of various genes involved in the strategy II Fe(III) uptake system, including OsNAS1, OsNAAT1, OsDMAS1, OsYSL15, and TOM1. This transgenic rice exhibited improved phytosiderophore secretion ability and tolerance to Fe deficiency. In the present research, transgenic rice plants that possess both the OsIRT1 promoter-refre1/372 and the 35S promoter-OsIRO2 (RI lines) were produced to enhance both Strategy I Fe(II) reductase ability and Strategy II phytosiderophore productivity. RI lines exhibited enhanced tolerance to Fe-deficient conditions at the early and middle-late stages of growth in calcareous soil, compared to both the non-transgenic line and lines harboring either OsIRT1 promoter-refre1/372 or 35S promoter-OsIRO2 alone. RI lines also exhibited a 9-fold higher yield than the non-transgenic line. Moreover, we successfully produced Fe-deficiency-tolerant Tachisugata rice, which is a high-biomass variety used as fodder. Collectively, our results demonstrate that combined enhancement of two Fe uptake systems in rice is highly effective in conferring tolerance to low Fe availability in calcareous soil. [ABSTRACT FROM AUTHOR]

Thirty-five yeast strains were isolated from soil samples that were collected from different locations in Upper Egypt. The purified isolates were screened for the release potassium from mica on Aleksandrov agar medium. Two yeast isolates (KSY-29 and KSY-33) showed an ability to solubilize potassium by inducing clear zones around their colonies. They were identified asPichia anomalaandRhodotorula glutinis, respectively, based on PCR analysis of the ITSI-26S region that was amplified by NL1/NL4 species-specific primers. The amount of K released from muscovite mica in the broth culture of the yeast isolates was measured after 5, 10, 15 and 20 days of the incubation at 25°C. Both yeast isolates were very effective in releasing K of muscovite in broth culture, recording 8.11–13.21 μg/ml that were released from muscovite mica after 20 days of incubation. The inoculation of maize (Zea maize) plants with these yeast isolates under different K levels (25, 50 and 100% of recommended dose of potassium, RDK) as potassium sulfate was tested on growth and K uptake by these plants in the greenhouse. Significant increases (p< 0.05) in plant height, root and shoot dry weights as well as K uptakes by shoots and roots maize plants occurred through the inoculation with KSY-29 or KSY-33 isolates. [ABSTRACT FROM PUBLISHER]

Organic matter plays a key role in availability and transformation of soil Zn (zinc), which greatly controls Zn concentrations in cereal grains and human Zn nutrition level. Accordingly, soils homogenized with the wheat straw (0, 12 g straw kg-1) and Zn fertilizer (0, 7 mg Zn kg-1) were buried and incubated in the field over 210 days to explore the response of soil Zn availability and the ageing of exogenous Zn to straw addition. Results indicated that adding straw alone scarcely affected soil DTPA-Zn concentration and Zn fractions because of the low Zn concentration of wheat straw and the high soil pH, and large clay and calcium carbonate contents. However, adding exogenous Zn plus straw increased the DTPA-Zn abundance by about 5-fold and had the similar results to adding exogenous Zn alone, corresponding to the increased Zn fraction loosely bounded to organic matter, which had a more dominant presence in Zn reaction than soil other constituents such as carbonate and minerals in calcareous soil. The higher relative amount of ineffective Zn (~50%) after water soluble Zn addition also occurred, and at the days of 120–165 and 180–210when the natural temperature and rainfall changed mildly, the ageing process of exogenous Zn over time was well evaluated by the diffusion equation, respectively. Consequently, combining crop residues with exogenous water soluble Zn application is promising strategy to maximize the availability of Zn in calcareous soil, but the higher ageing rate of Zn caused by the higher Zn mobility should be considered. [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]

Rate of zinc (Zn) release from solid to solution phase by organic acids can influence Zn availability in calcareous soils. The objective of the present study was to investigate the effect of different concentrations (1.1, 2.2, and 3.3 mM) of oxalic acid and citric acid on the kinetic release of Zn from two calcareous soils from Eastern Iran. The two organic acids showed significant difference in Zn release from studied soils. Cumulative Zn release during 72 h ranged from 5.85 to 10.4 mg kg−1in soil 1 and ranged from 8.7 to 16.9 mg kg−1in soil 2 using different concentrations of oxalic acid. The amount of cumulative Zn release after 72 h in soil 1 ranged from 13.65 to 28.77 mg kg−1and from 17.63 to 23.13 mg kg−1when different concentrations of citric acid was used. In general, Citric acid released 38% more Zn from soils than oxalic acid. The release of Zn from soils increased with citric acid concentration but decreased with increasing of oxalic acid concentrations in the solution. The simplified Elovich equation best described Zn release as a function of time (r2 = 0.93 and SE = 0.78). From the present study, Zn release from soils can be limited by the higher concentration of oxalic acid, while citric acid is suitable for enhancing soil lability of Zn. [ABSTRACT FROM AUTHOR]

Kinetic batch and saturated column experiments were performed to study the oxidation, adsorption and transport of Sb(III) in two soils with contrasting properties. Kinetic and column experiment results clearly demonstrated the extensive oxidation of Sb(III) in soils, and this can in return influence the adsorption and transport of Sb. Both sorption capacity and kinetic oxidation rate were much higher in calcareous Huanjiang soil than in acid red Yingtan soil. The results indicate that soil serve as a catalyst in promoting oxidation of Sb(III) even under anaerobic conditions. A PHREEQC model with kinetic formulations was developed to simulate the oxidation, sorption and transport of Sb(III) in soils. The model successfully described Sb(III) oxidation and sorption data in kinetic batch experiment. It was less successful in simulating the reactive transport of Sb(III) in soil columns. Additional processes such as colloid facilitated transport need to be quantified and considered in the model. [ABSTRACT FROM AUTHOR]

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 status of soil K forms and its relationship with K content in wheat grain at harvest period may be important for nutrient fertility management. For this purpose, 40 surface (0-20 cm) and subsurface (20-40 cm) soil samples and also grain samples from wheat fields of Darab region were randomly sampled in 2014. Then physicochemical properties of the soils and the contents of soluble, exchangeable and non-exchangeable K and contents of K in wheat grains were determined. Results indicated that content of soluble, exchangeable and non-exchangeable K in the studied soils ranged 15-70, 91-443 and 396-1182 mg kg-1, respectively. Significant relationships were obtained between soil K forms and clay, calcium carbonate and CEC. Although it is expected that content of easily available K (soluble and exchangeable K) was low at late stage of wheat growth, most soils had sufficient K content. The positive and significant relationship among different K forms was indicative of the K forms equilibration at the time of wheat harvesting. Although there is not a relationship between K content in wheat grain and soil K forms, it was shown that K content of wheat grain was correlated with soil exchangeable K and clay content in fine-textured soils (clay > 30%). It means that ammonium acetate may be a suitable extractant for estimation of soil K status and plant available K of heavy-textured soils in the studied region. [ABSTRACT FROM AUTHOR]

We combined lab experiments, a 2-year pot experiment, light microscopy and X-ray photoelectron spectroscopic measurements to understand the fate of Fe in biochar-amended soils with, and without, three sustainable Fe-fertilization strategies (siderite, aqueous extract of Amaranthus retroflexus either alone or enriched with FeSO 4 ). In addition, we examined biochar effects on plant-available micronutrients using metal Fe. We also assessed nonlinear interactions between biochar and Fe management strategies, evaluating the effectiveness of sustainable fertilization strategies in improving Fe-nutrition of kiwifruit vines under Fe-stressed conditions. Fe chlorosis symptoms of pot-cropped kiwifruit vines were pronounced in the biochar-amended soils, especially during the first season. However, the biochar rate adopted in this study was relatively high (5 g kg − 1 w/w) while the real impact of this strategy may change at lower rates. In the lab, increasing biochar rates progressively removed dissolved micronutrients from solution. Light microscopy revealed rust-colored patches on the biochar surface exposed to a Fe source in solution and XPS analyses confirmed that the biochar surface had become coated with Fe and O in ratios consistent with the formation of Fe-(hydr)oxides. Although we investigated one specific biochar, our results suggest that some redox reactions can act to form a micronutrient sink on the biochar surface. This mechanism likely contributed to binding soil Fe (through reactive functional groups on its surface) into plant-unavailable forms, promoting the occurrence of Fe chlorosis symptoms of kiwifruit vines grown in soils amended with biochar. We also confirmed the effectiveness of siderite and A. retroflexus extract enriched with FeSO 4 in alleviating the occurrence of Fe-deficiency symptoms in kiwifruit vines. [ABSTRACT FROM AUTHOR]

Greenhouse experiment was conducted to assess the iron (Fe) and zinc (Zn) fractionation patterns in soils of arbuscular mycorrhizal (AM) fungus-inoculated and uninoculated maize plants fertilized with varying levels of Fe and Zn. Soil samples were collected for Fe and Zn fractions and available Fe, Zn and phosphorus (P) contents besides organic and biomass carbon (BMC), soil enzymes and glomalin. Major portion of Fe and Zn fractionations was found to occur in the residual form. Mycorrhizal symbiosis increased the organically bound forms of Fe and Zn while reducing the crystalline oxide, residual Fe and Zn fractions, indicating the transformation of unavailable forms into available forms. Soil enzymes, viz. dehydrogenase and acid phosphatase activities in M+ soils, were significantly higher than M− soil consistently. Overall, the data suggest that mycorrhizal symbiosis enhanced the availability of Fe and Zn as a result of preferential fractionation and biochemical changes that may alleviate micronutrient deficiencies in calcareous soil. Abbreviations: AM: arbuscular mycorrhiza; Fe: Iron; Zn: Zinc; P: Phosphorous; Amox-Zn: amorphous oxide bound zinc; Cryox-Zn: crystalline oxide bound zinc; DAS: days after sowing; DTPA: diethylene Triamine Penta Acetic Acid; MnO2-Zn: manganese oxide bound zinc; OC-Zn: organically bound zinc; WSEX: water soluble plus exchangeable zinc; MnO2Fe: manganese oxide bound iron; OC-Fe: Organically bound iron; WSEX Fe: water soluble plus exchangeable iron. [ABSTRACT FROM AUTHOR]

Dynamics and distribution pattern of trace metals in agricultural lands are an increasing concern due to potential risks to the environment and human health. To ascertain more knowledge of this aspect, the fractions of total and available Fe, Mn, Zn, Cu, and Cd belonging to Vertisols under intensive cultivation and adjoining uncultivated soils were investigated. The order of abundance of metals in both cultivated and uncultivated soils was Fe > Mn > Cu > Zn > Cd and Fe > Mn > Zn > Cu > Cd for both available and total fraction, respectively. A relative enrichment was observed in the value of diethylene-triamine pentaacetic acid-extractable Fe (1.2–201%), Mn (2–31%), Cu (1–40%), and Cd (21–45%) as well as total fraction of Zn (3–17%), Cu (12–32%), and Cd (42–108%) after intensive cropping, which can be contributed to repeated application of agrochemical inputs and manure over long time. The values of RI (potential ecological risk) showed that cultivation caused a low potential ecological risk (33.3% of the soil samples) to moderate potential ecological risk (66.7% of the soil samples) in the study region and that cadmium made up 88%, on average, of the RI value. [ABSTRACT FROM AUTHOR]

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]

Higher grain Zn concentration is desirable to combat human Zn deficiency. A total of 58 farmers' fields were surveyed from districts of Multan and Lodhran to represent cotton-wheat rotation zone of Punjab. Soils were sampled separately from the surface (0–15 cm depth) and subsurface (15–30 cm depth) layers. Within 5 m2 of soil sample, about 100 spikes from mature tillers of wheat were also collected. Nearly all subsurface and 76% of the collected surface soil samples were deficient in plant available Zn resulting in grain Zn concentration of 20 µg g–1, on average. The inherent capacity of subsurface soil layer to supply Zn positively correlated with grain Zn concentration (r=0.33, n=58; P=0.01). Organic matter content (r=0.32, n=58; P=0.02) in subsurface layer and soil salinity (ECe) of both layers (r=–0.53, n=58; P<0.01 for ECe of both layers) were the other major soil characteristics that significantly correlated with grain Zn concentration. Zinc bioavailability in wheat grains, estimated by [phytate]:[Zn] ratios and trivariate model of Zn absorption, was low. Present study indicated a need to reduce current grain [phytate]:[Zn] ratio (46, on average) and to increase the current trivariate model based estimated Zn bioavailability (1.5 mg Zn for 300 g flour, on average) by about 2-folds. Conclusively, Zn fertilization strategy for southern Punjab was suggested as a solution to human Zn deficiency and low grain yields. [ABSTRACT FROM AUTHOR]

Global nitrogen fertilizer consumption is expected to continue to increase. To explore effective mitigation strategies, a deeper understanding of the responses of nitrogen use efficiency, nitric oxide (NO) emission and the NO direct emission factor (EF d ) to increasing fertilization rates is needed. A gradient of fertilization rates (0, 135, 270, 430, 650 and 850 kg N ha −1 yr −1 in the form of urea, hereafter referred to as N0, N135, N270, N430, N650 and N850, respectively) was used to fully represent the nitrogen application levels in the wheat–maize rotational cropping system that has been widely adopted in China. The annual NO emissions ranged from 0.43 ± 0.04 (N0) to 2.64 ± 0.35 kg N ha −1 yr −1 (N850) and linearly increased with increasing fertilization rates ( P < 0.01). The high pH and low carbon availability in the calcareous soil limited NO production; thus, low EF d values (0.26–0.36%) were observed. The partial factor productivity of applied nitrogen (PFP N ) rapidly decreased with increasing fertilization rates; the relationship could be characterized by a rectangular hyperbolic function ( P < 0.01). The expected trade-off between EF d and PFP N was not observed. The on-farm PFP N was only 33 ± 3 kg grain kg −1 N (N430), highlighting the necessity of optimizing current management strategies. Based on a review of previous studies, a comprehensive optimized management strategy is recommended to obtain the maximum benefits for multiple goals of a wheat–maize cropping system. However, consecutive field observations and model studies are still needed to validate the long-term effects of this management strategy. [ABSTRACT FROM AUTHOR]

The short-term effectiveness of soil-applied humic acid–like substances [naturally complexed or uncomplexed with iron (Fe)] extracted from composted poultry (HLSP) and sheep (HLSS) manures in preventing lime-induced Fe chlorosis in Eureka lemon (Citrus lemonL.) cuttings grafted on sour orange (Citrus aurantiumL.) was investigated and compared with the commonly applied ethylenediamine di-2-hydroxyphenyl acetate ferric (FeEDDHA). Treatments were untreated plants and plants fertilized with FeEDDHA, HLSP, and HLSS injected into the soil at a total rate of 25 mg Fe per plant each. Chlorophyll concentration index (CCI) of the youngest fully expanded leaves, growth vigor, and leaf Fe concentration were measured. HLSP and HLSS, similar to FeEDDHA, resulted in significantly greater CCI values, growth vigor, and leaf Fe concentration compared to untreated plants. HLSP and HLSS offer potential alternative to FeEDDHA to prevent lime-induced Fe deficiency in Eureka lemon. Concentrates of HLSP and HLSS can be commercially prepared to offer an inexpensive and environmentally safe product. [ABSTRACT FROM AUTHOR]

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 field experiment was carried out to investigate effects of phosphorus (P) fertilizer type and rate on plant growth and toxic heavy metals contents (Cd, Pb and As) in head lettuce plant on calcareous soil. Four P fertilizer types {single super phosphate (SSP), di ammonium phosphate (DAP), mono ammonium phosphate (MAP) and a local phosphate rock (PR)} were applied as main plot treatments and five rates of each fertilizer (0, 125, 250, 375, and 500 kg P2O5/ha) as subplot treatments. P fertilizer type, rate and their interaction showed a significant effect on the fresh plant yield and dry matter production. Both P fertilizer type and rate didn't induce significant differences in heavy metals contents of the plant and soil, as they were within tolerable limits. The examined P fertilizers constitute no potential risks for heavy metals accumulation in the soil-plant system over short-term. [ABSTRACT FROM AUTHOR]

This experiment was conducted to establish how earthworms and arbuscular mycorrhizal fungi (AMF) interactively impact cadmium (Cd) chemical fractions in a calcareous soil artificially contaminated with Cd. The chemical forms of Cd using the Sposito's sequential extraction procedure were determined in a soil spiked with Cd (10 and 20 mg Cd kg−1), inoculated or un-inoculated with earthworm (Lumbricus rubellus L. species) and AMF (Glomus intraradices and Glomus mosseae species) under greenhouse conditions for two months. Results showed that Cd concentrations of the non-residual fraction (i.e., soluble/exchangeable, organic bound and inorganic bound forms) increased with earthworm addition and the residual Cd fraction tended to decrease. Arbuscular mycorrhizal inoculation decreased the inorganic bound Cd fraction with a concurrent increase in the residual Cd fraction. However, no significant interactions between earthworm and AMF were observed for the non-residual Cd fraction, suggesting the combined influence of both soil organisms on the easily and potentially available Cd was largely independent or additive. While the presence of both earthworms and AMF resulted in an antagonistic interaction on the residual Cd fraction at high Cd level, this interaction was additive at low Cd level. Cadmium addition increased its uptake into the body of earthworms, which was significantly greater at high than low Cd levels. However, bioaccumulation factor for Cd accumulation in the earthworm body was lower at high than low Cd levels, indicating the low transfer of Cd from the soil environment to earthworm tissues at higher exposure levels. It is concluded that earthworms affects the chemical Cd fractions more than AMF. [ABSTRACT FROM AUTHOR]

To reduce Cd phytoavailability in calcareous soils, the effects of soil amendments of red mud, rape straw, and corn straw in combination with zinc fertilization on Cd extractability and phytoavailability to spinach, tomato, Chinese cabbage and radish were investigated in a calcareous soil with added Cd at 1.5 mg kg−1. The results showed that water soluble and exchangeable Cd in soils was significantly decreased by the amendments themselves from 26% to 70%, which resulted in marked decrease by approximately from 34% to 77% in Cd concentration in vegetables. The amendments plus Zn fertilization further decreased the Cd concentration in vegetables. Also cruciferous rape straw was more effective than gramineous corn straw. In all treatments, rape straw plus red mud combined with Zn fertilization was most effective in decreasing Cd phytoavailability in soils, and it is potential to be an efficient and cost-effective measure to ensure food safety for vegetable production in mildly Cd-contaminated calcareous soils. [ABSTRACT FROM AUTHOR]

BACKGROUND The concentration of Zn and phytic acid in wheat grain has important implications for human health. We conducted field and greenhouse experiments to compare the efficacy of soil and foliar Zn fertilisation in improving grain Zn concentration and bioavailability in wheat ( Triticum aestivum L.) grain grown on potentially Zn-deficient calcareous soil. RESULTS Results from the 2-year field experiment indicated that soil Zn application increased soil DTPA-Zn by an average of 174%, but had no significant effect on grain Zn concentration. In contrast, foliar Zn application increased grain Zn concentration by an average of 61%, and Zn bioavailability by an average of 36%. Soil DTPA-Zn concentrations varied depending on wheat cultivars. There were also significant differences in grain phytic acid concentration among the cultivars. A laboratory experiment indicated that Zn (from ZnSO4) had a low diffusion coefficient in this calcareous soil. CONCLUSION Compared to soil Zn application, foliar Zn application is more effective in improving grain Zn content of wheat grown in potentially Zn-deficient calcareous soils. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Diazotrophs and arbuscular mycorrhizal fungi (AMF) are important functional microbes that provide and transport nutrients to plants. Diazotroph and AMF diversity and community composition were investigated in karst mature forests (MFs) and non-karst forests, as well as in croplands (CRs) as a reference. Diazotroph diversity and community composition significantly shifted in MFs between karst and non-karst soils, with a higher diazotroph richness and Shannon index in karst MFs than in non-karst soils. Similar levels of AMF diversity and community composition were observed between karst and non-karst CRs and MFs. According to the co-occurrence network analysis results, the pairs of correlation links within the diazotroph and AMF groups were higher in karst MFs than in non-karst MFs, whereas this interaction was lower in karst CRs than in non-karst CRs. The diazotroph genera Bradyrhizobium and Anabaena and the AMF genera Glomus and Rhizophagus were mostly correlated with other species in both karst and non-karst soils. Diazotrophs and AMF communities were mainly affected available nutrients (e.g., nitrogen and phosphorus) and environmental factors (e.g., temperature and precipitation), respectively. Soil calcium content was an important factor that affected the distributions of diazotrophs and AMF between karst and non-karst soils. Overall, our study suggested that the increased interactions between diazotrophs and AMF in karst forests, as compared with those in non-karst soil, led to the stability of the diazotrophs and AMF co-occurrence patterns for maintaining nutrients that are effectively absorbed and utilized. Thus, strengthening the cooperative relationships between diazotrophs and AMF are important and necessary in calcareous soils during natural vegetation restoration. [Display omitted] • Diazotroph diversity increased in karst mature forest compared with that in non-karst soil. • Arbuscular mycorrhizal fungal (AMF) diversity was similar in karst and non-karst soil. • Karst mature forest strengthened interactions among diazotroph and AMF. • AMF were more sensitive to climate; diazotrophs were more sensitive to nutrients. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate citrus tissue's response to varying applications of Fe-EDDHA, zinc (Zn) and manganese (Mn) combinations and the resulting effects on citrus fruit yield and quality in calcareous soil. A field experiment was conducted for three years with satsuma mandarin trees planted in calcareous soil. Four treatments were conducted: (i) control; (ii) soil Fe application; (iii) soil Fe+Zn application; and (iv) soil Fe+Zn+Mn application. Soil available Fe and Zn concentrations were raised through the application of Fe-EDDHA and Zn, whereas the soil available Mn concentration was not increased through the application of Mn. Applying Fe-EDDHA raised the leaf active Fe content significantly without influencing the leaf and fruit Fe concentrations. The Zn concentrations in leaf and fruit decreased when Fe-EDDHA was applied exclusively, but increased when Fe+Zn and Fe+Zn+Mn were applied in the third year. There was no significant difference in leaf and fruit Mn concentrations among all treatments between 2010 and 2012. Soil Fe, Fe+Zn and Fe+Zn+Mn application increased fruit number by 23.5%, 26.7% and 24.9%, respectively, and soil Fe+Zn application increased the yield in 2012. Fruit TSS, TA and Vc content were higher through the application of Fe+Zn and Fe+Zn+Mn in 2012. The results revealed that Fe and Zn play different roles that affect fruit yield and quality in calcareous soil. The citrus yield was mainly affected by Fe, whereas fruit quality was improved by Zn. The application of Fe-EDDHA alone could induce Zn deficiency, so the co-application of Fe-EDDHA and Zn fertilizer was useful for obtaining higher yield and quality in satsuma mandarin in calcareous soil. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a combination of column experiments and micro-analytical techniques exploiting synchrotron generated X-rays was used to assess the effect of aging time on Zn retention and mobility in the specific case of calcareous soils (high pH value, ≈8). The samples were subjected to aging for 2, 6, 17, and 63days. Freshly added Zn mainly existed as an exchangeable form, and this metal fraction decreased over time due to Zn redistribution to stronger binding sites. Thus, after aging for 63days, 45% of Zn is remobilized from exchangeable sites to stronger binding sites. μ-XRF maps were used to find correlations among elements in the sample, and μ-XANES spectra were recorded to precise Zn speciation. These analyses evidenced an increasing partitioning of Zn from organic matter to iron oxy(hydr)oxides over time. The occurrence of hydrozincite is evidenced in all samples. [Copyright &y& Elsevier]

Iron availability in alkaline and calcareous soils is limited because of high pH and calcium carbonate contents. Various sources may have different solubilities within soil and may result in varying degrees of Fe availability. An incubation study was conducted to evaluate effectiveness of different sources of Fe to maintain water soluble Fe in different soils over passage of time. For this purpose, three different soils were incubated with various organic (Fe-EDDHA, Fe-DTPA, FYM) and inorganic (ferrous sulphate, vivianite) Fe sources for the period of four weeks. All amendments were adjusted to maintain 20 mg kg-1 of soil Fe except FYM. Iron sources showed significantly different behavior in maintaining soil Fe in different soils. The chelates of Fe proved very effective in maintaining soil solution Fe throughout the incubation period. Fe-EDDHA maintained 12 mg kg-1 with 56% recovery of total Fe added Followed by Fe-DTPA (with 30% recovery). Recovery of ferrous suphate was negligible on the first day of incubation. Vivianite which was prepared by mixing DAP fertilizer with FeSO4.7H2O also rapidly converted in to insoluble fractions on first contact to soils but maintained slightly more amount of soluble Fe as compared ferrous sulphate. [ABSTRACT FROM AUTHOR]