Decomposition of added and native organic carbon from physically separated fractions of diverse soils

There have been increasing efforts to understand the dynamics of organic carbon (OC) associated with measurable fractions of bulk soil. We compared the decomposition of native OC (native C) with that of an added substrate (glucose) on physically separated fractions of a diverse suite of soils. Five soil orders were selected from four contrasting climate zones (Mollisol from temperate, Ultisol and Oxisol from tropics, Andisol from sub-arctic, and Gelisol from arctic region). Soils from the A horizon were fractionated into particulate OC (POC) and mineral-associated OC (MOC) by a size-based method. Fractions were incubated at 20 °C and 50 % water-holding capacity in the dark after the addition of unlabeled d-glucose (0.4 mg C g^?1 fraction) and U–¹⁴C glucose (296 Bq g^?1 fraction). Respiration of glucose ¹⁴C indicated 64 to 84 % of added glucose ¹⁴C which was respired from POC and 62 to 70 % from MOC within 150 days of incubation, with more than half of the cumulative respiration occurring within 4 days. Native C respiration varied widely across fractions: 12 to 46 % of native C was respired from POC and 3 to 10 % was respired from MOC fractions. This suggested that native C was more stabilized on the MOC than on the POC, but respiration from the added glucose was generally similar for MOC and POC fractions. Our study suggests a fundamental difference between the behavior of freshly added C and native C from MOC and POC fractions of soils.     

Distribution of Mercury and Monomethylmercury in Sediments of Vigo Ria, NW Iberian Peninsula

Fifty four samples of surface sediments (1-cm of thickness) and a gravity core of 154-cm long were collected in the Vigo Ria, NW of Iberian Peninsula. In the laboratory the sediments were oven dried at 40°C, desegregated, homogenised and analyzed for total Hg, monomethylmercury (MMHg), Al, and particulate organic carbon (POC). Mercury in sediments varied within a broad range: 0.09 to 8.9 nmol g^?1 the higher concentrations being found in the shipyards and docks areas of Vigo port (southern–middle Ria zone). No correlation was found between Hg and POC. The good exponential correlation between total Hg and Al levels suggests that Hg is closely associated with the fine fraction of sediments. Monomethylmercury concentrations in surface sediments ranged between <1.4 (DL) and 8.5 pmol g^?1 being the spatial distribution similar to that observed for total Hg. The lack of correlations MMHg–Al and MMHg–POC suggests that in situ processes of methylation/demethylation are responsible for MMHg distribution rather than the sediment characteristics. Additionally, these processes appear mercury-dependent only for Hg concentrations above 2.5 nmol g^?1. On the basis of these results it was estimated that 155 kg of Hg (0.1% MMHg) are present in the surface sediments of Vigo Ria, being 61% of anthropogenic origin.     

Landuse impacts on soil organic carbon fractions in different rainfall areas of a subtropical dryland

Landuse can alter soil organic carbon (SOC) fractions by affecting carbon inflows and outflows. This study evaluated changes in SOC fractions in response to different landuses under variable rainfalls. We compared cropland, grassland and forest soils in high rainfall (Islamabad ~1142 mm) and low rainfall (Chakwal ~667 mm) areas of Pothwar dryland, Pakistan. Forest soils in both rainfall areas had highest SOC (11.32 g kg^?1), particulate organic carbon (POC, 1.70 g kg^?1), mineral-associated organic carbon (MOC, 7.17 g kg^?1) and aggregate-associated organic carbon (AOC, 7.86 g kg^?1). However, in rangeland and cropland soils, these varied with rainfall. Under high rainfall, SOC and MOC were 12% and 17% higher in rangeland than in cropland while POC and AOC were equal. Under low rainfall, SOC and MOC were higher in rangeland than in cropland by 7.21 and 1.79 g kg^?1 at 0–15 cm and equal at 15–30 cm depth. POC and AOC were higher in rangeland than in cropland, in both depths. Averagely, SOC, POC, MOC and AOC were 26%, 68%, 76% and 30% higher in high rainfall than in low rainfall soils. Sensitivity of SOC fractions to landuses observed under different rainfalls could provide useful information for soil management in subtropical drylands.     

Application of hydrochar and pyrochar to manure is not effective for mitigation of ammonia emissions from cattle slurry and poultry manure

Nitrogen (N) loss as ammonia (NH₃) from agricultural systems is one of the major sources of atmospheric pollutants and is responsible for more than 50% of global NH₃ emissions. Ammonia volatilization from animal manures may be altered by amendment with chars derived from pyrolysis (pyrochars) or hydrothermal carbonization (hydrochars) by providing exchange sites for ammonium (NH₄⁺) or changing the pH of manure. Pyrochar and hydrochar differ in chemical and structural composition, specific surface area, and pH and therefore may affect NH₃ volatilization differently. In a laboratory incubation experiment, we investigated the effect of pyrochar (pH 9.0) and hydrochar (pH 3.8) from Miscanthus on NH₃ emission after addition to poultry manure and cattle slurry. We analyzed manure treatments with and without char addition and acidification and determined the effect of char addition on immobilization of manure-derived NH₄⁺. Ammonia emission from pure poultry manure amounted 84% of the applied NH₄⁺-N, while 67% of the applied NH₄⁺-N was lost as NH₃ from cattle slurry. Addition of pyrochar or hydrochar had no or only marginal effects on NH₃ emissions except for a reduction in NH₃ emissions by 19% due to hydrochar application to CS (p?<?0.05), which seems to be primarily related to the char pH. Sorption of NH₄⁺ by admixture of chars to manure was generally small: between 0.1- and 0.5-mg NH₄⁺-N g^?1 chars were sorbed. This corresponds to between 0.1 and 3.5% of the NH₄⁺ applied, which obviously was not strong enough to reduce emissions of NH₃. Overall, our results do not provide evidence that addition of pyrochar or hydrochar to cattle slurry and poultry manure is an effective measure to reduce NH₃ volatilization.     

Cadmium Removal by Two Strains of Desmodesmus pleiomorphus Cells

The capacity of microalgae to accumulate heavy metals has been widely investigated for its potential applications in wastewater (bio)treatment. In this study, the ability of Desmodesmus pleiomorphus (strain L), a wild strain isolated from a polluted environment, to remove Cd from aqueous solutions was studied, by exposing its biomass to several Cd concentrations. Removal from solution reached a maximum of 61.2 mg Cd g^?1 biomass by 1 day, at the highest initial supernatant concentration used (i.e., 5.0 mg Cd L^?1), with most metal being adsorbed onto the cell surface. Metal removal by D. pleiomorphus (strain ACOI 561), a commercially available ecotype, was also assessed for comparative purposes; a removal of 76.4 mg Cd g^?1 biomass was attained by 1 day for the same initial metal concentration. Assays for metal removal using thermally inactivated cells were also performed; the maximum removal extent observed was 47.1 mg Cd g^?1 biomass, at the initial concentration of 5 mg Cd L^?1. In experiments conducted at various pH values, the highest removal was achieved at pH 4.0. Both microalga strains proved their feasibility as biotechnological tools to remove Cd from aqueous solution.     

Cadmium Phytoextraction Efficiency of Arum (Colocasia antiquorum), Radish (Raphanus sativus L.) and Water Spinach (Ipomoea aquatica) Grown in Hydroponics

Selection of a phytoextraction plant with high Cd accumulation potential based on compatibility with mechanized cultivation practice and local environmental conditions may provide more benefits than selection based mainly on high Cd tolerance plants. In this hydroponics study, the potential of Cd accumulation by three plant species; arum (Colocasia antiquorum), radish (Raphanus sativus L.) and water spinach (Ipomoea aquatica) were investigated. Arum (Colocasia antiquorum L.) plants were grown for 60 days in a nutrient solution with 0, 10 or 50 μM Cd, while radish and water spinach plants grew only 12 days in 0, 1.5, 2.5, 5 or 10 μM Cd. Growth of radish and water spinach plants decreased under all Cd treatments (1.5 to 10 μM), while arum growth decreased only at 50 μM Cd. At 10 μM Cd treatment, the growth of arum was similar to the control treatment indicating higher tolerance of arum for Cd than radish and water spinach. Cadmium concentrations in different plant parts of all plant species increased significantly with Cd application in the nutrient solution. Arum and water spinach retained greater proportions of Cd in their roots, while in radish, Cd concentration in leaves was higher than in other plant parts. Cadmium concentrations in arum increased from 158 to 1,060 in the dead leaves, 37 to 280 in the normal leaves, 108 to 715 in the stems, 42 to 290 in the bulbs and 1,195 to 3,840 mg kg^?1 in the roots, when the Cd level in the solution was raised from 10 μM Cd to 50 μM Cd. Arum accumulated (dry weight?×?concentration) 25 mg plant^?1 at 10 μM, while the corresponding values for radish and water spinach were 0.23 and 0.44 mg plant^?1, respectively. With no growth retardation at Cd concentrations as high as 166 mg kg^?1 measured in entire plant (including root) of arum at 10 μM Cd in the nutrient solution, arum could be a potential Cd accumulator plant species and could be used for phytoremediation.     

Improvement of wheat (Triticum aestivum) drought tolerance by seed priming with silicon

Silicon has the potential to improve drought tolerance in crops. Seeds primed with silicon were used in the present study to explore its potential benefit to withstand water stress. Seeds of two wheat varieties, NARC-2009 and Chakwal-50, were sown in pots after priming with distilled water and different concentrations (0.5%, 1.0% and 1.5%) of silicon sources (silicic acid, sodium silicate and silica gel) at PMAS, Arid Agriculture University, Rawalpindi. Maximum silicon uptake at three-leaf stage (0.028 µg g^?1 dry weight (DW)), anthesis (0.072 µg g^?1 DW) and maturity (0.103 µg g^?1 DW) was recorded for silica gel. Silicon uptake increased significantly in response to increase in Si concentration from 0.5% to 1.5%. Leaf membrane stability index, epicuticular wax, relative water content and proline remained maximum – 78.90%, 2.6 mg g^?1 DW, 83.88% and 54.90 µg g^?1 – for silica gel treatments compared with others. Silica gel with 1.5% silicon concentration resulted in maximum spike length (14.3 cm), biological yield (7.63 g pot^?1), hundred-grain weight (3.97 g pot^?1) and grain yield (2.46 g pot^?1). Based on the study outcomes, it is concluded that silica gel might be a good priming option with 1.5% silicon concentration to establish plant under drought stress.     

Effect of organic and inorganic sources of nutrients on soil microbial activity and soil organic carbon build-up under rice in west coast of India

The effect of medium-term (5 years) application of organic and inorganic sources of nutrients (as mineral or inorganic fertilizers) on soil organic carbon (SOC), SOC stock, carbon (C) build-up rate, microbial and enzyme activities in flooded rice soils was tested in west coast of India. Compared to the application of vermicompost, glyricidia (Glyricidia maculate) (fresh) and eupatorium (Chromolaena adenophorum) (fresh) and dhaincha (Sesbania rostrata) (fresh), the application of farmyard manure (FYM) and combined application of paddy straw (dry) and water hyacinth (PsWh) (fresh) improved the SOC content significantly (p < 0.05). The lowest (p < 0.05) SOC content (0.81%) was observed in untreated control. The highest (p < 0.05) SOC stock (23.7 Mg C ha^?1) was observed in FYM-treated plots followed by recommended dose of mineral fertilizer (RDF) (23.2 Mg C ha^?1) and it was lowest (16.5 Mg C ha^?1) in untreated control. Soil microbial biomass carbon (C_mb) (246 µg g^?1 soil) and C_mb/SOC (1.92%) were highest (p < 0.05) in FYM-treated plot. The highest (p < 0.05) value of metabolic quotient (qCO₂) was recorded under RDF (19.7 µg CO₂-C g^?1 C_mb h^?1) and untreated control (19.6 µg CO₂-C g^?1 C_mb h^?1). Application of organic and inorganic sources of nutrients impacted soil enzyme activities significantly (p < 0.05) with FYM causing highest dehydrogenase (20.5 µg TPF g^?1 day^?1), phosphatase (659 µg PNP g^?1 h^?1) and urease (0.29 µg urea g^?1 h^?1) activities. Application of organic source of nutrients especially FYM improved the microbial and enzyme activities in flooded and transplanted rice soils. Although the grain yield was higher with the application of RDF, but the use of FYM as an organic agricultural practice is more useful when efforts are intended to conserve more SOC and improved microbial activity.     

Occurrence of pharmaceutical and personal care products (PPCPs) in marine sediments in the Todos os Santos Bay and the north coast of Salvador,Bahia, Brazil

Purpose

The Todos os Santos Bay is the largest bay in Brazil and receives drainage from various watersheds. For more than 450 years, it was the main destination for the domestic and hospital sewage from the city of Salvador, Bahia. With the growing concern regarding the presence of pharmaceutical and personal care products (PPCPs) in the environment, an investigation was undertaken to determine the presence and levels of some commonly used drugs (i.e., atenolol, caffeine, carbamazepine, diazepam, diclofenac, erythromycin, ibuprofen) and personal care products (i.e., galaxolide, tonalide), using sediments as an indicator of their presence in the water column.

Material and methods

Surficial sediment samples from 17 stations located in the intertidal zone of the Todos os Santos Bay and infralittoral zone along the north coast of Salvador were tested for the presence of some PPCPs using LC-MS/MS (for drugs) and GC-MS/MS (for fragrances).

Results and discussion

The PPCPs examined were present in all sediment samples at levels of parts per billion of dry sediment. The highest concentrations were found for the fragrances galaxolide (52.5 ng g^?1) and tonalide (27.9 ng g^?1), followed by caffeine (23.4 ng g^?1) and pharmaceuticals ibuprofen (14.3 ng g^?1), atenolol (9.84 ng g^?1), carbamazepine (4.81 ng g^?1), erythromycin (2.29 ng g^?1), diclofenac (1.06 ng g^?1), and diazepam (0.71 ng g^?1).

Conclusions

Pharmaceuticals were found to be ubiquitous in the sediments of the study areas. The texture of the sediment was an important factor in PPCPs fixation and deposition. The concentrations of all PPCPs had statistically significant positive correlations with the percentage of clay in the sediments.     

Response of Mycorrhiza,Organic Sources,Secondary and Micro Nutrients on Soil Microbial Activities and Yield Performance of Colocasia (Colocasia esculenta L.) in Alfisols

Response of the integrated use of mycorrhiza, inorganic and organic manures on microbial variables and yield performance of colocasia (Colocasia esculenta L.) was studied in an acid Alfisol. Significantly highest mean cormel yield (14.13 t ha^?1) was recorded due to application of super optimal doses of nitrogen, phosphorus, and potassium (NPK). Integrated application of lime + farmyard manure (FYM) + ½ NPK + zinc sulfate (ZnSO₄) has recorded the highest dehydrogenase activity (2.048 µg TPF hr^?1 g^?1) and Fluorescein Diacetate Hydrolysis assay (1.855 µg g^?1 hr^?1). The highest acid and alkaline phosphatase activities (77.67 and 51.18 µg PNP g^?1 h^?1, respectively) were observed due to Vesicular Arbuscular Mycorrhiza (VAM) inoculation in combination with lime + FYM + ½ NPK. Dehydrogenase and phosphatase activities had a highly significant relationship with cormel yield and the biochemical constituents of colocasia. The study emphasized the conjunctive use of balanced inorganic fertilizers and organic manures to enhance the enzymatic activities and to realize higher crop yields of colocasia in acid Alfisols.     

Effects of Bt-cotton on biological properties of Vertisols in central India

Growing areas under transgenic crops have created a concern over their possible adverse impact on the soil ecosystem. This study evaluated the effect of Bt-cotton based cropping systems on soil microbial and biochemical activities and their functional relationships with active soil carbon pools in Vertisols of central India (Nagpur, Maharastra, during 2012–2013). Culturable groups of soil microflora, enzymatic activities and active pools of soil carbon were measured under different Bt-cotton based cropping systems (e.g. cotton-soybean, cotton-redgram, cotton-wheat, cotton-vegetables and cotton-fallow). Significantly higher counts of soil heterotrophs (5.7–7.9 log cfu g^?1 soil), aerobic N-fixer (3.9–5.4 log cfu g^?1 soil) and P-solubilizer (2.5?3.0 log cfu g^?1 soil) were recorded in Bt-cotton soils. Similarly, soil enzymatic activities, viz. dehydrogenase (16.6–22.67 µg TPF g^?1 h^?1), alkaline phosphatase (240–253 µg PNP g^?1 h^?1) and fluorescein di-acetate hydrolysis (14.6–18.0 µg fluorescein g^?1 h^?1), were significantly higher under Bt-cotton-soybean system than other Bt- and non-Bt-cotton based systems in all crop growth stages. The growth stage-wise order of soil microbiological activities were: boll development > harvest > vegetative stage. Significant correlations were observed between microbiological activities and active carbon pools in the rhizosphere soil. The findings indicated no adverse effect of Bt-cotton on soil biological properties.     

Soil and nutrient losses due to root crops harvesting: a case study from southwestern Iran

Although root crops are widely cultivated in Iran, little is known about soil loss due to crop harvesting (SLCH). We assessed the annual exported soil, soil organic matter (SOM) and nutrients from 47 farms under root crops in southwestern Iran. Soil losses for garlic, potato, sugar beet, radish and beetroot were estimated as 6.27, 2.52, 2.26, 4.10 and 6.95, Mg ha^?1, respectively, which on average was of the order of soil losses by water erosion in the watershed basins of Iran. Total N, P₂O₅ and K₂O losses were estimated as 36.61, 1.10 and 31.50 kg ha^?1 and their costs as 18.24, 0.74 and 19.93 USAlthough root crops are widely cultivated in Iran, little is known about soil loss due to crop harvesting (SLCH). We assessed the annual exported soil, soil organic matter (SOM) and nutrients from 47 farms under root crops in southwestern Iran. Soil losses for garlic, potato, sugar beet, radish and beetroot were estimated as 6.27, 2.52, 2.26, 4.10 and 6.95, Mg ha^?1, respectively, which on average was of the order of soil losses by water erosion in the watershed basins of Iran. Total N, P₂O₅ and K₂O losses were estimated as 36.61, 1.10 and 31.50 kg ha^?1 and their costs as 18.24, 0.74 and 19.93 US$ ha^?1, respectively. For the whole country, total soil, N, P₂O₅, K₂O and SOM losses for garlic, potato and sugar beet were estimated as 731.7 × 10³, 836, 27, 476 and 14.5 × 10³ Mg, respectively (radish and beetroot were excluded due to no reliable data on their planted areas). Correlation analysis showed no significant relationship between soil properties and SLCH (except soil moisture content for radish and clay content for beetroot). The findings indicated that the exported soil, SOM and nutrients were at such levels that SLCH should be considered in soil erosion studies.     

Substrate‐Induced Respiration of a Sandy Soil Treated with Different Types of Organic Waste

A sandy soil was amended with different types of sewage sludge (digested, dried, and composted) and pig slurry. The composted sludges displayed higher organic‐matter stability (39–45%) than only digested sludge (26–39%) or digested + dried sludge (23–32%). The microbial biomass of the dried sludge was undetectable. Digested and composted sludges and pig slurry displayed microbial biomasses (12492–13887 µg g^?1, 1221–2050 µg g^?1, and 5511 µg g^?1, respectively) greater than the soil (108 µg g^?1). The wastes were applied at seven doses, ranging from 10 to 900 g kg^?1. Soils were incubated for 28 days. Substrate‐induced respiration (SIR) was measured for 12 consecutive hours on day 1 and on day 28. The results showed that SIR increased with the dose of organic amendment. However, SIR decreased when moderate doses of pig slurry or high doses of digested + dried sludge were tested. The possibility of using this inhibition as an ecotoxicological indicator is discussed.     

A Survey of Organotin Compounds in the Northern Adriatic Sea

The extent of pollution with organotin compounds was investigated in water, sediment and bivalve mussels (Mytilus galloprovincialis) from the Northern Adriatic Sea. Butyl-, phenyl- and octyltin species were quantified after extraction and derivatisation by gas chromatography–mass spectrometry in a total of 99 samples from the period from 2000 to 2006. The accuracies of the analytical procedures were checked by spiking of unpolluted water samples and by the analysis of standard reference materials (harbour sediment PACS-2 and mussel tissue ERM-CE 477). Among organotin species analysed in samples butyltins were the predominant. Tributyltin was found to be present in the highest concentrations, suggesting its recent input into the marine environment. Butyltins were detected at all sites surveyed (sum of butyltins was up to 718 ng Sn L^?1, 3,552 ng Sn g^?1 d.w. and 9,991 ng Sn g^?1 d.w. in water, sediment and mussel samples, respectively), phenytins in much lower concentrations (up to 31 ng Sn L^?1, 326 ng Sn g^?1 d.w. and 442 ng Sn g^?1 d.w. in water, sediment and mussel samples) and to a much smaller extent, while octyltins were not detected at any location. The spatial distribution of tributyltin was closely related to boating, with the highest concentrations found in marinas (up to 586 ng Sn L^?1 for water samples, 1,995 ng Sn g^?1 d.w. for sediment and 6,434 ng Sn g^?1 d.w. for mussel samples). The temporal distribution clearly indicates a decrease of organotin pollution at all sites.     

Enhanced Heavy Metal Phytoextraction from Marine Dredged Sediments Comparing Conventional Chelating Agents (Citric Acid and EDTA) with Humic Substances

Metal (Cu, Mn, Ni, Zn, Fe) concentrations in marine sediment and zooplankton were investigated in Izmir Bay of the Eastern Aegean Sea, Turkey. The study aimed to assess the levels of metal in different environmental compartments of the Izmir Bay. Metal concentrations in the sediment (dry weight) ranged between 4.26–70.8 μg g^?1 for Cu, 233–923 μg g^?1 for Mn, 14.9–127 μg g^?1 for Ni, 25.6–295 μg g^?1 for Zn, 12,404–76,899 μg g^?1 for Fe and 38,226–91,532 μg g^?1 for Al in the Izmir Bay. Maximum metal concentrations in zooplankton were observed during summer season in the inner bay. Significant relationships existed between the concentrations of certain metals (Al, Fe, Mn and Ni) in sediment, suggesting similar sources and/or similar geochemical processes controlling such metals. Higher concentrations of Cu, Zn and percent organic matter contents were found in the middle-inner bays sediments. Based on the correlation matrix obtained for metal data, organic matter was found to be the dominant factor controlling Cu and Zn distributions in the sediment. In general, mean Cu and Zn levels in the bay were above background concentrations in Mediterranean sediments. Zooplankton metal concentrations were similar to sediment distributions.     

Crop production impacts on soil phosphorus removal and soil test levels

An 8-year field study documented the impact of tillage, crop rotations, and crop residue management on agronomic and soil parameters at Brookings, South Dakota. The greatest annual proportion of above-ground biomass phosphorus (P) removed was from the grain (78–87% of total) although crop residue removed some P as well. Greater above-ground total biomass P (grain P + crop residue P) was removed from corn than from soybean and spring wheat crops mainly due to the greater corn grain biomass harvested. Cumulative above-ground biomass P removal was greatest for the corn-soybean rotation (214 kg P ha^?1), while it was lowest for the soybean-wheat rotation (157 kg P ha^?1). Tillage treatments within crop rotation or residue management treatments did not influence annual or cumulative P removal rates. Olsen extractable soil orthophosphate-P levels declined consistently through time from a mean of 40 µg g^?1 (2004) to 26 µg g^?1 (2011). Biomass P removal was calculated to be 15.7 ha^?1 yr^?1 to decrease Olsen extractable soil orthophosphate-P levels by 1 µg g^?1 yr^?1 over 8 years of the study.     

Hg, Cu, Pb, Cd, and Zn Accumulation in Macrophytes Growing in Tropical Wetlands

The concentrations of Hg, Cu, Pb, Cd, and Zn accumulated by regional macrophytes were investigated in three tropical wetlands in Colombia. The studied wetlands presented different degrees of metal contamination. Cu and Zn presented the highest concentrations in sediment. Metal accumulation by plants differed among species, sites, and tissues. Metals accumulated in macrophytes were mostly accumulated in root tissues, suggesting an exclusion strategy for metal tolerance. An exception was Hg, which was accumulated mainly in leaves. The ranges of mean metal concentrations were 0.035?C0.953 mg g^?1 Hg, 6.5?C250.3 mg g^?1 Cu, 0.059?C0.245 mg g^?1 Pb, 0.004?C0.066 mg g^?1 Cd, and 31.8?363.1 mg g^?1 Zn in roots and 0.033?C0.888 mg g^?1 Hg, 2.2?C70.7 mg g^?1 Cu, 0.005?C0.086 mg g^?1 Pb, 0.001?C0.03 mg g^?1 Cd, and 12.6?C140.4 mg g^?1 Zn in leaves. The scarce correlations registered between metal concentration in sediment and plant tissues indicate that metal concentrations in plants depend on several factors rather than on sediment concentration only. However, when Cu and Zn sediment concentrations increased, these metal concentrations in tissues also increased in Eichhornia crassipes, Ludwigia helminthorriza, and Polygonum punctatum. These species could be proposed as Cu and Zn phytoremediators. Even though macrophytes are important metal accumulators in wetlands, sediment is the main metal compartment due to the fact that its total mass is greater than the corresponding plant biomass in a given area.     

Zinc Tolerance in Wheat Cultivars as Affected by Varying Levels of Phosphorus

Abstract

The effect of zinc–phosphorus (Zn‐P) interaction on Zn efficiency of six wheat cultivars was studied. The higher dry matter yields were observed when Zn was applied at 5 µg g^?1 soil than with no Zn application. Phosphorus applications also increased dry matter yield up to the application of 25 µg P g^?1 soil. The dry matter yield was significantly lower at the P rate of 250 µg g^?1 soil. At the Zn‐deficient level, the Zn‐efficient cultivars had higher Zn concentrations in the shoots. Zinc concentrations in all cultivars increased when the P level in the soil was increased from 0 to 25 µg P g^?1 soil except for the cv. Durati, in which Zn concentrations decreased with increases in P levels. However, when Zn×P interactions were investigated, it was observed that at a Zn‐deficient level, Zn concentrations in the plant shoot decreased with each higher level of P, and more severe Zn deficiency was observed at P level of 250 µg g^?1 soil.     

Nitrogen Management for Sustainable Soil Organic Carbon Increase in Inceptisols Under Wheat Cultivation

Application of nitrogen (N) fertilizers to increase crop yield is a worldwide practice, which also has a positive influence on the soil organic carbon (SOC) increase. This study was carried out to investigate the dynamics of SOC and its fractions under different levels of N fertilization in wheat grown inceptisols of Northeast India over a period of 2 years. For the purpose of this study, fertilizer treatments with five N levels (40, 60, 72, 80, and 100 kg N ha^?1) were applied in randomized block design. Increased SOC particulate organic carbon (POC), humic acid carbon, and fulvic acid carbon were recorded under application of higher N. Stability of SOC as indicated by E4/E6 ratio and microbial biomass carbon (MBC) was higher on application of 72 kg N ha^?1. Among the SOC fractions, POC and MBC respond rapidly to different N fertilization rates. Available N and phosphatase activity increased while pH and urease activity (UA) decreased as a function of applied N fertilizer levels. Nitrogen fertilization increased wheat yield and biomass with insignificant differences among 100, 80, and 72 kg N ha^?1. Thus, under the present experimental conditions, application of 72 kg N ha^?1 can sustain SOC and soil health without compromising wheat yield in the inceptisols of Northeast India.     

Effects of microbial inoculations on soil chemical,biochemical and microbial biomass carbon of cassava (Manihot esculenta Crantz) growing Vertisols

Cassava is an important subsidiary food in the tropics. In Tamil Nadu, India, microbial cultures were used to eradicate the tuberous root rot of cassava. Hence, an experiment was conducted for two consecutive years to test the effects of coinoculation of microbes on soil properties. The surface soil from the experimental site was analysed for soil available nutrients, soil enzyme activities and microbial biomass carbon. The treatment of Azospirillum with Trichoderma at the 50% recommended N:P₂O₅:K₂O (NPK) rate (50:25:50 kg ha^?1) significantly increased soil available nitrogen (142.81 kg ha^?1) by 72.66% over uninoculated control. There was a significant increase in available phosphorus in soil by the inoculation of AM (arbuscular mycorrhizal) fungi with Trichoderma at the 50% recommended NPK rate (41.04 kg ha^?1) compared to other treatments. The application of Pseudomonas fluorescens with Trichoderma at the 50% recommended NPK rate significantly increased available iron (19.34 µg g^?1) in soil. The treatment of Azospirillum with Trichoderma increased urease enzyme activity at the recommended NPK rate (816.32 μg urea hydrolyzed g^?1 soil h^?1). Soil application of all cultures at the 50% recommended NPK rate significantly increased dehydrogenase activity (88.63 μg TPF g^?1 soil) and β-glucosidase activity (48.82 μg PNP g^?1 soil) in soil. Inoculation of Trichoderma alone at the 50% recommended NPK rate significantly increased microbial biomass carbon (3748.85 μg g^?1 soil). Thus, the microbial inoculations significantly increased soil available nutrient contents, enzyme activities such as urease, dehydrogenase and β-glucosidase activity and microbial biomass carbon by reducing the amount of the required fertilizer.