Soil DTPA-extractable Zn Research Articles

Dynamics of Zinc Fractions in Soil as Affected by Zinc Fertilization in a Maize-maize Cropping Sequence in Upper Brahmaputra Valley Zone of Assam, India

Zinc is considered as an important micronutrient for maize which is a promising emerging cash crop for the state of Assam, India. A field experiment was conducted at the experimental farm of Krishi Vigyan Kendra, Jorhat, Assam Agricultural University during 2018-19 and 2019-20 to study the dynamics of zinc fractions in soil in a maize-maize cropping sequence as affected by zinc fertilization. The experiment was laid down in a randomized block design (RBD) with twelve treatments combinations of basal and foliar application of zinc through zinc sulphate and zinc oxide nanoparticles (ZnO NPs). The results revealed that zinc fertilization significantlyinfluenced the studied zinc fractions in soil during both the years under investigation. The distribution of different zinc fractions in soils at harvest was found in the following order: water soluble plus exchangeable-Zn < complexed-Zn < crystalline sesquioxide bound-Zn < amorphous sesquioxide bound-Zn < residual-Zn. Among the zinc treatment combinations, soil application of Zn @ 3.75 kg ha-1 in combination with foliar application of 500 ppm ZnO NPs exhibited the highest concentration of water soluble plus exchangeable-Zn content (1.10 ppm) in soil. The highest concentration of complexed-Zn (2.95 ppm), amorphous sesquioxide-bound-Zn (4.11 mg kg-1), crystalline sesquioxide-bound-Zn (3.76 ppm), residual-Zn (125.65 ppm) and total-Zn (137.33 ppm) were recorded in the treatment receiving soil application of Zn @ 7.5 kg ha-1. Among the zinc fractions studied, the concentration and percent contribution of water soluble plus exchangeable-Zn to total-Zn was the lowest while residual-Zn fraction contributed the highest to the total soil zinc pool. Furthermore, path coefficient analysis revealed that the water soluble plus exchangeable-Zn had the highest contribution towards the plant available DTPA extractable-Zn in soil. Moreover, all the fractions of zinc were found to be significantly and positively correlated with each other indicating existence of dynamic equilibrium of zinc in soil.

Efficiency of MGDA and GLDA ligands in extracting plant-available Zn from calcareous soils: kinetics and optimization of extraction conditions

The selection of an appropriate soil nutrient-availability index, exhibiting high correlations with crop responses, is the first step in a soil-testing program. This study aimed to test if the quantity and rate of zinc (Zn) release from calcareous soils by two new extracting ligands provide suitable Zn availability indices for maize (Zea mays L.) or not. To this end, Zn extraction from diverse calcareous soils by three concentrations (0.005, 0.05, and 0.1 mol L−1) of glutamic acid N,N-diacetic acid (GLDA) and methylglycinediacetic acid (MGDA) ligands with different shaking times were studied. A greenhouse pot experiment was also conducted to determine how Zn absorption by maize plants is correlated to the quantity and rate of Zn release from the soils. The result showed that the initial Zn release rates from the soils were significantly (r = 0.77 to 0.94, P < 0.05) correlated to plant Zn uptake. The results of the greenhouse correlation study also revealed that Zn uptake by maize represented the highest correlations with the amount of Zn extracted from soils by 0.05 M GLDA for 2 h (r = 0.87, P < 0.05), 0.05 M MGDA for 1 h (r = 0.86, P < 0.05), and 0.005 M MGDA for 0.5 h (r = 0.84, P < 0.05). These correlations were stronger than those obtained between the DTPA-extractable soil Zn and plant Zn uptake (r = 0.77, P < 0.05). Based on the finding of this study, both quantity and rate of Zn release from the soil by MGDA and GLDA ligands could be satisfactorily considered as Zn availability indices for maize in calcareous soils.

Nutrient removal by rice\u2013wheat cropping system as influenced by crop establishment techniques and fertilization options in conjunction with microbial inoculation

Nutrient uptake by the rice–wheat cropping system (RWCS) is an important indicator of soil fertility and plant nutrient status. The hypothesis of this investigation was that the rate and sources of nutrient application can differentially influence nutrient removal and soil nutrient status in different crop establishment techniques (CETs). Cropping system yield was on par in all the CETs evaluated, however, there were significant changes in soil nutrient availability and microbiological aspects. The system nitrogen (N), phosphorus (P), potassium (K) and zinc (Zn) uptake in aerobic rice system followed by zero tillage wheat (ARS-ZTW) was 15.7–17.6 kg ha−1, 0.7–0.9 kg ha−1, 7–9.8 kg ha−1 and 13.5–23.1 g ha−1 and higher than other CETs. The formulations of Anabaena sp. (CR1) + Providencia sp. (PR3) consortium (MC1) and Anabaena–Pseudomonas biofilm (MC2) recorded significantly higher values of soil chlorophyll and microbial biomass carbon and positively affected cropping system nutrient uptake and soil nutrient balance, illustrating the beneficial effect of microbial inoculation through increased supply of biologically fixed N and solubilised P. Zinc fertilization (5 kg Zn ha−1 through ZnSO4·7H2O as soil application) increased soil DTPA-extractable Zn by 4.025–4.836 g ha–1, with enhancement to the tune of 20–24% after two cropping cycles of RWCS. Our investigation recommends the need for change in the present CETs to ARS–ZTW, along with the use of microbial inoculation as a means of significantly enhancing cropping system nutrient uptake and soil nutrient status improvement.

Zinc fractions in soils and uptake in winter wheat as affected by repeated applications of zinc fertilizer

This field study was conducted to determine the effect of repeated zinc (Zn) applications at different rates on the concentrations and availability of different forms of Zn in the calcareous soil, in relationship to their contributions to Zn uptake by wheat. Plot-based field experiment was established in 2009 in a winter wheat-summer maize rotation. In each growing season of wheat and maize, six levels of Zn (0, 2.3, 5.7, 11.4, 22.7 and 34.1 kg Zn ha−1) as ZnSO4·7H2O were applied at planting. Following the harvest of the winter wheat in 2010, 2012, 2014 and 2016, soil samples (0−30 cm) from 5 selected Zn levels except 2.3 kg Zn ha-1 were collected and subjected to a sequential extraction to examine the concentrations of Zn fractions including water soluble plus exchangeable Zn (Ex-Zn) and Zn as bounded to carbonate (Car-Zn), manganese oxide (MnO-Zn), iron oxide (FeO-Zn), or organic matter (OM-Zn), and residual (Res-Zn). Stepwise multiple regression was used to identify the contributions of each soil Zn fraction to variation in crop Zn uptake. The results showed that repeated Zn fertilization over the multiple years increased concentrations of all soil Zn fractions. However, the percentage of each Zn fraction to total Zn varied with Zn inputs. Increasing Zn input increased the percentages of Ex-, Carb-, MnO- and FeO-Zn to soil total Zn, whereas reduced that of OM- and Res-Zn. The FeO-, Ex-, and Res-Zn were selected by the stepwise regression procedure as the significant variables explaining the variation in wheat Zn uptake, with partial adjusted coefficient (R2) of 0.81, 0.03 and 0.04, respectively. Crop Zn uptake also increased linearly with soil DTPA-extractable Zn and reached a maximum at DTPA-extractable Zn concentration of 12 mg kg−1. In conclusion, repeated Zn fertilization increased the concentrations of Zn in exchangeable and adsorption forms, which in turn resulted in higher uptake of Zn by winter wheat. DTPA-extractable Zn is a good indicator of Zn availability for wheat. Fraction of FeO-Zn is an important Zn retention pool for determining crop uptake on the calcareous soil. These results emphasize the importance of Zn retention capacity in response to repeated application of Zn fertilizer.

Residual effect of zinc applied to rice on zinc nutrition of succeeding wheat crop inoculated with zinc solubilizing microbial consortium

Large scale deficiency of Zn results in low crops yields and the problem of Zn malnutrition in humans and livestock. To economize crop production on Zn deficient soils, two-year field experiments were undertaken with two wheat varieties to evaluate the performance of seed inoculation with a consortium of three bacterial strains in combination with varying doses of Zn fertilizer applied to 1 year rice crop on yields, Zn concentration and Zn uptake of wheat. Seed coating of wheat with bacterial consortium significantly increased grain yields, Zn concentration and uptake in grains and straw and total Zn uptake over the control. It also helped to increase the apparent recoveries of soil applied Zn fertilizer to 1 year rice by succeeding wheat crops and DTPA extractable Zn in soil after 2 year wheat in comparison to the control. Seed inoculation in combination with low dosage of Zn also significantly decreased phytic acid: Zn ratio but increased methionine concentration in wheat grains.

Zinc nutrition of rice as influenced by crop establishment methods, rates of nitrogen and phosphorus fertilization and inoculation with microbial consortia

Zinc (Zn) fertilization in rice is important to enhance productivity and increase Zn concentration in rice grain to improve its nutritional status. A field experiment was conducted in wet seasons of 2013 and 2014 to study Zn nutrition of rice in three different crop establishment methods (CEMs) viz. puddled transplanted rice (PTR), system of rice intensification (SRI) and aerobic rice system (ARS), under three different rates of nitrogen (N) and phosphorus (P) viz. 0, 75 and 100% of recommended dose of fertilizer (RDF) (120 kg N ha−1 and 25.8 kg P ha−1) and two different sources of N and P viz. chemical fertilizer and microbial inoculation (MI). Concentration and uptake of Zn at different growth stages and in straw and milled rice was significantly higher in PTR and SRI than ARS. Soil DTPA–extractable Zn content of soil was increased by 1142.4, 1140.3 and 755.8 g ha−1 in PTR, SRI and ARS after two year of Zn fertilization (soil application of 5 kg Zn ha−1). Zinc nutrition increase its Zn concentration in straw and milled rice and improvement in total uptake was 38.1, 40.3 and 40.8 g ha−1 when Zn was applied with RDF, 75% RDF + Anabaena sp. (CR1) + Providencia sp (PR3) consortia (MI1) and 75% RDF + Anabaena-Pseudomonas biofilmed bio-fertilizer (MI2), respectively. Positive correlation between milled rice yield and Zn concentration (R2= 0.95 and 0.97) showed the importance of Zn nutrition in improving rice yield. Zinc concentration at 70 days after sowing (DAS) and 100 DAS was also found positively correlated with dehydrogenase activity and microbial biomass carbon in soil.

Fertilizer management and soil type influence grain zinc and iron concentration under contrasting smallholder cropping systems in Zimbabwe

Micronutrient deficiencies remain prevalent in food systems of southern Africa, although advances in biofortification through crop breeding and agronomy provide opportunities to address these. We determined baseline soil availability of zinc (Zn) and iron (Fe) and the effects of soil type and farmer management on extractable soil Zn and Fe and subsequent concentration in cereal and legume grains under two contrasting agro-ecologies in Zimbabwe. Soil and crop surveys were conducted in Hwedza and Mutasa Districts of Zimbabwe in 2015–16 on 350 locations over different soil types. Fields with different levels of productivity (designated as “most” and “least” productive fields) were sampled using an inherited hierarchical randomized sampling design. Grain Zn and Fe concentration in maize (Zea mays), sorghum (Sorghum bicolor), finger millet (Eleusine coracana) and cowpea (Vigna unguiculata) were generally insufficient for adequate human nutrition. A Linear Mixed Effects (LME) model revealed that diethylene triamine penta-acetic acid- (DTPA) extractable soil Zn concentration and grain Zn concentration were affected primarily by field productivity level. DTPA-extractable soil Zn concentration was more than two-fold greater on the most productive fields (mean 0.8 mg kg−1) than on the least productive fields, with mean grain Zn concentration of 25.2 mg grain Zn kg−1 which was 13% greater than seen on the least productive fields. An interaction effect of field productivity level and total soil Zn concentration on DTPA-extractable soil Zn concentration suggests potential contribution of organic matter management to unlocking unavailable forms of soil Zn. DTPA-extractable soil Fe and grain Fe concentration were primarily affected by soil type and crop type, respectively. The LME modelling approach revealed additional soil geochemical covariates affected DTPA-extractable soil Zn and Fe concentration and grain Zn and Fe concentration within Districts. Future studies can therefore be powered to detect their roles at wider spatial scales for sustainable management of crop Zn and Fe nutrition.

Ability of sulfur-oxidising bacteria to hasten degradation of ground rubber particles in soil for release of zinc as a fertiliser to correct deficiency in wheat

Previous research has shown that ground rubber from tyres can be used to supply fertiliser zinc (Zn) for prevention of Zn-deficiency in crops, and that inoculation of the ground rubber with several bacterial species hastens the release of Zn to the soil. We evaluated the ability of several microbial combinations to speed the release of Zn from ground rubber and to decrease soil pH to favour phytoavailability of Zn to crops. In a batch experiment, treatment combinations of two rates of ground crumb rubber (nil or 300mg kg–1, equal to 0 or 3.4mg Zn kg–1) and 24 bacterial inoculants were incorporated into a Zn-deficient calcareous soil. In a pot experiment, two wheat cultivars were grown on the soil without or with ground rubber amendment or with equivalent Zn from ZnSO4 (15mg kg–1) in combination with two selected microbial treatments. All microbial treatments significantly decreased soil pH at week 3, most notably the inoculant comprising Rhodococcus erythropolis and Acinetobacter calcoaceticus (RA)+Pseudomonas putida P41 (P1)+mixed Thiobacillus spp. (Mt). In the presence of tyre rubber, soil pH at week 10 was still significantly lower than the initial value, and soil DTPA-extractable Zn concentration increased until week 6 and then remained unchanged or slightly reduced at week 10. The greatest increase in DTPA-Zn concentration occurred with the RA inoculation. Microbial inoculation treatments were classified by cluster analysis into eight groups based on soil pH and concentrations of iron (Fe) and Zn. Group 8 produced the lowest pH and highest concentrations of DTPA-Fe ( average 6.92mg kg–1) and DTPA-Zn (average 2.67mg kg–1). Inoculations with RA and with RA+P1+T. thioparus were the most effective in hastening an increase in DTPA-extractable Zn and significantly enhanced Zn uptake by wheat plants, whereas inoculations with P. putida P168 and with RA+P2+Mt were most effective in decreasing soil pH and increasing plant Fe concentration.

Role of zinc, nitrogen and phosphorus fertilization, and use of microbial inoculation in zinc nutrition of wheat (Triticum aestivum) under different crop establishment methods

A field experiment was conducted during rabi season of 2013-14 and 2014-15 at the Research Farm of ICAR-Indian Agricultural Research Institute, New Delhi to study the role of N, P and Zn fertilization, and microbial inoculation on concentration and uptake of zinc (Zn) in wheat plant ('HD 2967') at different growth stages, and DTPA-extractable Zn content in soil under three different crop establishment methods (CEMs), viz. conventional drill-sown wheat (CDW), system of wheat intensification (SWI) and zero tillage wheat (ZTW). Experiment was conducted in split-plot design with three CEMs as main plot, viz. CDW, SWI and ZTW. In subplot, two rate of N and P application [100% recommended dose of nutrients (N120P25.8) (RDN) and 75% RDN] and two microbial inoculations (MI), viz. Anabaenasp. (CR1) + Providencia sp. (PR3) (MI1) and Anabaena-Pseudomonas biofilmed formulation (MI2) was applied with 75% RDN making total four combination which were applied with and without Zn (5 kg Zn/ha through zinc sulphate heptahydrate) along with absolute control. Zinc fertilization increased Zn concentration in wheat grain by 3 and 2.9- 3.2 mg/kg when Zn was applied with 100% RDN and 75% RDN + MI1 and 75% RDN + MI2, respectively which showed the role of Zn fertilization in Zn nutrition of wheat. Application of 100% RDN increased total Zn uptake by 78 and 180 g/ha over 75% RDN and control in Zn applied treatments which showed the role of N and P application on Zn nutrition of wheat. Application of MI1 and MI2 with 75% RDN increased grain Zn concentration by 2.3 and2.5 mg/kg indicating their role in Zn nutrition of wheat. Among CEMs, ZTW was found superior and increased Zn concentration in wheat grain by 4.7 and 4.5 mg/kg over CDW and SWI, respectively. Soil DTPA-extractable Zn content was increased in all Zn applied treatments at harvest over initial level which indicates the positive effect of Zn fertilization on soil Zn status. Our study showed that application of recommended dose of Zn alone was not good enough to have proper Zn nutrition of wheat and to increase concentration and uptake of Zn in wheat plant and grain, but application of N and P at recommended rate and selecting suitable CEM is equally important.

Effect of arbuscular mycorrhizal (AM) fungi inoculation on enzymatic activity and zinc uptake under direct seeded rice system

The application of treatment T3 (Glomus mosseae + 100 % RDF NK) produced significantly more root volume by 72.60 %, 17.80 %, 12.25 %, 14.13 % over the application of treatment T1 (Control), treatment T5 (Glomus coronatum+ 100 % RDF NK), T6 (Gigasporadecipein + 100 % RDF NK) and T7 (BAU AM-1(Glomus sp + 100 % RDF NK), respectively. Similar trend shows at harvesting stage, here the maximum root volume (23c.c) was recorded by the application of T3 (Glomus mosseae + 100 % RDF NK). Maximum AM colonization and spore count was observed at panicle initiation stage with the application of treatment T3 (Glomus mosseae + 100 % RDF NK). This treatment also gave maximum dehydrogenase activity (55.86 µg TPF g-1 24 hr-1), acid phosphatase activity (0.299 mg PNP g-1 hr-1) and alkaline phosphatase activity (0.54 mg PNP g-1 hr-1) at panicle initiation stage. Application of treatment T3 (Glomus mosseae + 100 % RDF NK) significantly increased DTPA extractable Zn in soil and Zn content in plant when compared with all the treatments except treatment T6 (Gigasporadecipien+ 100 % RDF NK). The maximum zinc uptake (0.056 mg pot-1) by grain was recorded under treatment T3 (Glomus mosseae + 100 % RDF NK) followed by application of treatment T6 (Gigasporadecipien + 100 % N and K). Highest grain yield (14.08 g pot-1) was found with the treatment T3 (Glomus mosseae + 100 % RDF NK). As evident from the results, the AM fungal inoculation can effectively modify the soil microbe population and community structure by increasing the soil enzymatic activities and significantly increased the zinc uptake by grain in direct seeded rice (DSR).

Green manure and long-term fertilization effects on soil zinc and cadmium availability and uptake by wheat (Triticum aestivum L.) at different growth stages

Zinc (Zn) deficiency in human populations depending on cereals as a main source of Zn is a global malnutrition problem. In this field study, we investigated the potential of green manure application to increase soil Zn availability and wheat grain Zn concentrations (biofortification) on a Luvisol with different long-term fertilizer management. We also studied cadmium (Cd), as wheat is a major contributor of this undesired non-essential element to human diets. Clover (Trifolium alexandrinum L.), mustard (Sinapis alba L.) or no green manure was grown on field plots which had been managed with farmyard manure or mineral fertilizers for 65years in Switzerland. After green manure incorporation into the soil, spring wheat (Triticum aestivum L.) was grown on all plots. The “diffusive gradients in thin films” (DGT) method and DTPA extraction were used to compare soil Zn and Cd availability among the treatments. In contrast to mustard, clover increased soil mineral nitrogen concentrations and wheat biomass; however, neither increased grain Zn concentrations. DGT-available Zn and Cd increased temporarily after both farmyard manure and mineral nitrogen fertilizer application. Higher DTPA-extractable soil Zn and Cd, lower wheat grain yields, but higher grain Zn concentrations were obtained with farmyard manure compared to mineral fertilizers, independent of the green manure treatment. Farmyard manure added Zn, Cd and organic matter that increased the soil binding capacity for Zn and Cd. The decomposition of clover residues caused higher wheat grain yields, but only marginally lower grain Zn concentrations. The absence of a stronger dilution of grain Zn was probably due to organic acid and nitrogen release from decomposing clover, which facilitated Zn uptake by wheat. The study revealed that both long- and short-term field management with organic matter alters soil Zn and Cd concentrations but that the long-term effects dominate their uptake by wheat, in Zn sufficient soil.

Organic Wheat Farming Improves Grain Zinc Concentration.

Zinc (Zn) nutrition is of key relevance in India, as a large fraction of the population suffers from Zn malnutrition and many soils contain little plant available Zn. In this study we compared organic and conventional wheat cropping systems with respect to DTPA (diethylene triamine pentaacetic acid)-extractable Zn as a proxy for plant available Zn, yield, and grain Zn concentration. We analyzed soil and wheat grain samples from 30 organic and 30 conventional farms in Madhya Pradesh (central India), and conducted farmer interviews to elucidate sociological and management variables. Total and DTPA-extractable soil Zn concentrations and grain yield (3400 kg ha-1) did not differ between the two farming systems, but with 32 and 28 mg kg-1 respectively, grain Zn concentrations were higher on organic than conventional farms (t = -2.2, p = 0.03). Furthermore, multiple linear regression analyses revealed that (a) total soil zinc and sulfur concentrations were the best predictors of DTPA-extractable soil Zn, (b) Olsen phosphate taken as a proxy for available soil phosphorus, exchangeable soil potassium, harvest date, training of farmers in nutrient management, and soil silt content were the best predictors of yield, and (c) yield, Olsen phosphate, grain nitrogen, farmyard manure availability, and the type of cropping system were the best predictors of grain Zn concentration. Results suggested that organic wheat contained more Zn despite same yield level due to higher nutrient efficiency. Higher nutrient efficiency was also seen in organic wheat for P, N and S. The study thus suggests that appropriate farm management can lead to competitive yield and improved Zn concentration in wheat grains on organic farms.

Arbuscular mycorrhizae alleviate negative effects of zinc oxide nanoparticle and zinc accumulation in maize plants--A soil microcosm experiment.

ZnO nanoparticles (NPs) are considered an emerging contaminant when in high concentration, and their effects on crops and soil microorganisms pose new concerns and challenges. Arbuscular mycorrhizal (AM) fungi (AMF) form mutualistic symbioses with most vascular plants, and putatively contribute to reducing nanotoxicity in plants. Here, we studied the interactions between ZnO NPs and maize plants inoculated with or without AMF in ZnO NPs-spiked soil. ZnO NPs had no significant adverse effects at 400 mg/kg, but inhibited both maize growth and AM colonization at concentrations at and above 800 mg/kg. Sufficient addition of ZnO NPs decreased plant mineral nutrient acquisition, photosynthetic pigment concentrations, and root activity. Furthermore, ZnO NPs caused Zn concentrations in plants to increase in a dose-dependent pattern. As the ZnO NPs dose increased, we also found a positive correlation with soil diethylenetriaminepentaacetic acid (DTPA)-extractable Zn. However, AM inoculation significantly alleviated the negative effects induced by ZnO NPs: inoculated-plants experienced increased growth, nutrient uptake, photosynthetic pigment content, and SOD activity in leaves. Mycorrhizal plants also exhibited decreased ROS accumulation, Zn concentrations and bioconcentration factor (BCF), and lower soil DTPA-extractable Zn concentrations at high ZnO NPs doses. Our results demonstrate that, at high contamination levels, ZnO NPs cause toxicity to AM symbiosis, but AMF help alleviate ZnO NPs-induced phytotoxicity by decreasing Zn bioavailability and accumulation, Zn partitioning to shoots, and ROS production, and by increasing mineral nutrients and antioxidant capacity. AMF may play beneficial roles in alleviating the negative effects and environmental risks posed by ZnO NPs in agroecosystems.

Bioavailability of Zn in ZnO nanoparticle-spiked soil and the implications to maize plants

Little is known about the relationships between Zn bioavailability in ZnO nanoparticle (NP)-spiked soil and the implications to crops. The present pot culture experiment studied Zn bioavailability in soil spiked with different doses of ZnO NPs, using the diethylenetriaminepentaacetic acid (DTPA) extraction method, as well as the toxicity and Zn accumulation in maize plants. Results showed that ZnO NPs exerted dose-dependent effects on maize growth and nutrition, photosynthetic pigments, and root activity (dehydrogenase), ranging from stimulatory (100–200 mg/kg) through to neutral (400 mg/kg) and toxic effect (800–3200 mg/kg). Both Zn concentration in shoots and roots correlated positively (P < 0.01) with ZnO NPs dose and soil DTPA-extractable Zn concentration. The BCF of Zn in shoots and roots ranged from 1.02 to 3.83 when ZnO NPs were added. In most cases, the toxic effects on plants elicited by ZnO NPs were overall similar to those caused by bulk ZnO and soluble Zn (ZnSO4) at the same doses, irrespective of some significant differences suggesting a higher toxicity of ZnO NPs. Oxidative stress in plants via superoxide free radical production was induced by ZnO NPs at 800 mg/kg and above, and was more severe than the same doses of bulk ZnO and ZnSO4. Although significantly lower compared to bulk ZnO and ZnSO4, at least 16 % of the Zn from ZnO NPs was converted into DTPA-extractable (bioavailable) forms. The dissolved Zn2+ from ZnO NPs may make a dominant contribution to their phytotoxicity. Although low amounts of ZnO NPs exhibited some beneficial effects, the accumulation of Zn from ZnO NPs into maize tissues could pose potential health risks for both plants and human.

Green manure addition to soil increases grain zinc concentration in bread wheat.

Zinc (Zn) deficiency is a major problem for many people living on wheat-based diets. Here, we explored whether addition of green manure of red clover and sunflower to a calcareous soil or inoculating a non-indigenous arbuscular mycorrhizal fungal (AMF) strain may increase grain Zn concentration in bread wheat. For this purpose we performed a multifactorial pot experiment, in which the effects of two green manures (red clover, sunflower), ZnSO4 application, soil γ-irradiation (elimination of naturally occurring AMF), and AMF inoculation were tested. Both green manures were labeled with 65Zn radiotracer to record the Zn recoveries in the aboveground plant biomass. Application of ZnSO4 fertilizer increased grain Zn concentration from 20 to 39 mg Zn kg−1 and sole addition of green manure of sunflower to soil raised grain Zn concentration to 31 mg Zn kg−1. Adding the two together to soil increased grain Zn concentration even further to 54 mg Zn kg−1. Mixing green manure of sunflower to soil mobilized additional 48 µg Zn (kg soil)−1 for transfer to the aboveground plant biomass, compared to the total of 132 µg Zn (kg soil)−1 taken up from plain soil when neither green manure nor ZnSO4 were applied. Green manure amendments to soil also raised the DTPA-extractable Zn in soil. Inoculating a non-indigenous AMF did not increase plant Zn uptake. The study thus showed that organic matter amendments to soil can contribute to a better utilization of naturally stocked soil micronutrients, and thereby reduce any need for major external inputs.

Thirty-year amendment of horse manure and chemical fertilizer on the availability of micronutrients at the aggregate scale in black soil

This study evaluates manure and chemical fertilizer effects on micronutrient (Fe, Mn, Cu, and Zn) content and availability in crops. Seven treatments were selected, including three conventional fertilization treatments (NP, horse manure (M), and NP plus M (NPM)), three corresponding double rate fertilization (N2P2, M2, and N2P2M2), and a CK. Soil samples were collected and separated into four aggregates by wet-sieving in September 2009. Corn samples were collected and analyzed simultaneously. Treatment N2P2 increased DTPA extractable Fe, Mn, and Cu in soil by 732%, 388%, and 42%, whereas M2 decreased the corresponding values by 26%, 22%, and 10%, respectively, compared to CK. DTPA extractable Zn in soil and Zn in corn grain were higher in the M and M2 treatments than in the other treatments, and DTPA Zn was significantly correlated with soil organic carbon (SOC) in large macroaggregate, microaggregate, and silt + clay fractions. The Mn concentrations in corn stalks and grain were significantly correlated with DTPA extractable Mn in bulk soil and microaggregates, and Zn in stalks were significantly correlated with DTPA Zn in bulk soil, microaggregates, and large macroaggregates. Long-term application of horse manure could increase soil Zn availability and uptake by corn, possibly due to its activation by SOC. In contrast, chemical fertilizer application increased DTPA extractable Fe, Mn, and Cu in soil by reducing soil pH. Our results also suggest that Mn uptake by corn originated mainly in microaggregates, whereas Zn in crops was primarily sourced from large macroaggregates and microaggregates.

Kinetics of zinc release from ground tire rubber and rubber ash in a calcareous soil as alternatives to Zn fertilizers

Ground rubber contains 15–20 g Zn kg−1 but very low levels of Cd and could serve as an inexpensive byproduct Zn fertilizer. The aim of this investigation was to test Zn release in a soil treated with ground tire rubber and rubber ash compared with commercial Zn fertilizer and a laboratory grade zinc sulfate. A Zn-deficient soil was chosen from wheat fields in Isfahan province, central Iran, and the ground rubber, rubber ash and fertilizer-Zn and laboratory ZnSO4 were added at 0.5 and 2 mg Zn kg−1; 0.5 kg ha−1 would usually correct Zn deficiency in such pot tests. The soil DTPA-extractable Zn was then measured with time and the results were described examining first order, Elovich, power function and parabolic diffusion kinetics models. In the pot experiment, corn (Zea mays L.) plants were exposed to three rates of Zn (0, 20, 40 mg Zn kg−1) from two different sources (ZnSO4 and ground rubber). Ground rubber was applied as 2–3 mm and <1 mm diameter particles. Zinc treatments were mixed with the soils before planting. At harvest, concentrations of Zn, Pb, and Cd in roots and shoots of corn were measured. Results showed that ground rubber and rubber ash significantly increased the concentration of DTPA-Zn in the soil and this increase was higher than achieved with the commercial Zn fertilizer. At the lower Zn application rate, Zn release followed parabolic diffusion, while at the higher rate the kinetics of release followed power function and Elovich models. There was an increase in Zn concentration of corn shoot and roots by adding of Zn regardless the source of applied Zn. With increase in the rate of rubber used, the shoot Zn uptake increased. The Pb concentration of shoot and Cd concentrations of shoot and roots were low (less than 0.02 mg kg−1) in all treatments. The results showed that the soil DTPA Zn decreases over time if the soil is amended with a soluble form of Zn whereas the reverse was observed if the Zn is added as ground rubber which only gradually transforms. Thus ground rubber and rubber ash offer strong value as Zn fertilizer for Zn deficient soils.

Micronutrient status of calcareous paddy soils and rice products: implication for human health

Modern agricultural systems have to provide enough micronutrient output to meet all the nutritional needs of people. Accordingly, knowledge on micronutrient status in soil and crop edible tissues is necessary. This study was carried out to investigate zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu) concentration of calcareous paddy soil and the relative rice grain. Rice crops (straw, hull, and grain) and associated surface soils (0–25 cm) were collected from 136 fields and analyzed for total and diethylene triamine pentaacetic acid (DTPA) available Zn, Fe, Mn, and Cu. The DTPA-Zn concentration in more than 50% of paddy soils was less than its critical deficiency concentration (2 mg kg−1), while the concentrations of DTPA Fe, Mn, and Cu were sufficient. The grain Zn concentration of more than 54% of the rice samples was less than 20 mg kg−1. About 55% and 49% of the rice samples were deficient in Mn and Cu, respectively, while the Fe concentration in rice grains was sufficient. A significant negative correlation was found between the CaCO3 content and soil DTPA-extractable Zn, Fe, Mn, and Cu. There were significant relationships between the total soil phosphorus and DTPA-extractable micronutrient concentrations. By considering the average daily rice consumption of 110 g per capita, the Zn, Fe, Mn, and Cu intake from rice consumption was estimated to be 2.4, 7.7, 1.6, and 0.7 mg for adults, respectively.

Comparative study of a Zn-enriched post-methanation bio-sludge and Zn sulfate as Zn sources for a rice–wheat crop rotation

A field experiment was carried out during 2005–2007 to compare the efficacy of Zn-enriched post-methanation bio-sludge (ZEMB, 4.4% Zn) and ZnSO4 (ZSH, 22% Zn) as Zn source to rice (Oryza sativa L.)—wheat (Triticum aestivum L.) rotation. A new Zn source (ZEMB) contained most of the Zn (98.4% of total Zn) in citrate-soluble form as compared to ZSH which had all Zn in water-soluble form. Chemical speciation of Zn in the aqueous solution of both fertilizers revealed that 85.8% of water-soluble Zn present in ZEMB existed as complexes of dissolved organic matter. In the field experiment, application of ZEMB at 5 kg Zn ha−1 to I-year rice increased the grain yields of rice and wheat in both years significantly over the control while application of ZSH at 5 kg Zn ha−1 to I-year rice increased only grain yields of I- and II-year rice (first year and second year, respectively). The magnitude of increase in grain yields was also higher with ZEMB than with ZSH. Application of ZEMB at 5 kg Zn ha−1 to I-year rice maintained significantly higher concentrations of Zn in the flag leaves of rice and wheat in both years, in the grains of I- and II-year rice, and also in the straw of I-year rice than ZSH applied at an equivalent dose. Total Zn uptake values for I-year rice and wheat and II-year rice, apparent recovery of applied Zn and also DTPA-extractable Zn in soil were significantly higher with ZEMB at 5 kg Zn ha−1 than with ZSH at an equivalent dose.

Soil micronutrient availability to crops as affected by long-term inorganic and organic fertilizer applications

Micronutrient status in soils and crops can be affected by different fertilization practices during a long-term field experiment. This paper investigated the effects of different fertilization treatments on total and DTPA-extractable micronutrients in soils and micronutrients in crops after 16 year fertilization experiments in Fengqiu County, Henan Province, China. The treatments of the long-term experiment included combinations of various rates of N, P and K in addition to two rates of organic fertilizer (OF) treatments. Winter wheat and summer maize were planted annually. Soil macro- and micronutrients along with pH and organic matter (OM) were analyzed. Grains and above ground parts of both crops in the final year were harvested and analyzed for Cu, Zn, Fe and Mn. The results showed that soil Cu, Zn, Fe and Mn concentrations did not change among the different treatments to a significant level, except for a slight decrease of soil Zn in the CK (no fertilizer application) compared to the OF treatment. The DTPA-extractable soil Zn, Fe and Mn concentrations increased from 0.41 to 1.08 mg kg −1, from 10.3 to 17.7 mg kg −1, and from 9.7 to 11.8 mg kg −1, respectively, with increasing soil OM content, thus showing the importance of soil OM in micronutrient availability for crops. The NPK treatment also had higher DTPA-extractable micronutrient concentrations in soil. Deficiency of N or P resulted in a low yield but high micronutrient concentrations in crops except Cu in maize stalks. Higher available soil P significantly decreased crop micronutrients, possibly because of their precipitation as metal phosphates. Maize stalks contained higher concentrations of micronutrients than those of wheat straw, whereas wheat grain had higher micronutrients than those of corn grain. The transfer coefficients (TCs) of micronutrients from straw to grain were significantly different between winter wheat (1.63–2.52 for Cu; 2.31–3.82 for Zn; no change for Fe; 0.55–0.84 for Mn) and summer maize (0.24–0.50 for Cu; 0.50–1.21 for Zn; 0.02–0.04 for Fe; 0.07–0.10 for Mn). In conclusion, application of organic matter significantly increased the DTPA-extractable concentrations of Zn, Fe and Mn compared to the CK, grain and vegetative tissue in the CK and NK had higher micronutrient concentrations than those in other treatments.