Content In Rice Grain Research Articles

Comparison of 2-Acetyl-1-Pyrroline (2AP) in Rice Leaf at Different Growth Stages Using Gas Chromatography

Aromatic rice lines were examined for 2-Acetyl-1-Pyrroline (2AP) content in leaf tissue at five different growth stages (tillering, panicle initiation, 50% heading, booting, and maturity). A small plot trial with plot size of 1.42 m × 4.88 m (7 row-plots) was arranged in completely randomize design with three replications. Dry-seeded, delayed flood cultural practice was used in this study. The experiment was conducted at three locations. The average 2AP concentrations in leaf tissue at tillering stages were higher than the other four growth stages. 2AP levels were declined when rice plant reached booting. AP levels decreased slightly at heading stage and decreased significantly at maturity. There was no significant different between 2AP in leaf at 50% heading from three locations as well as the 2AP content in rice grain. Correlations between 2AP in leaf and 2AP in grain were significantly in all five growth stages. The highest correlation coefficient was found between 2AP in leaf at booting and grain (r = 0.811**) and lowest was in the leaf at harvest (r = 0.564**). Results indicated that 2AP could be determined in leaf tissue at early growth stage.

Rice organs concentrate cadmium by chelation of amino acids containing dicarboxyl groups and enhance risks to human and environmental health in Cd-contaminated areas

When rice plants grown in paddy fields with Cd content of 0.3–1.5 mg kg−1, Cd quantities in roots and straws were 2–7 times higher than that in topsoil. Return of these vegetative organs to topsoil aggravated the ecological risk of Cd pollution. Cd content in rice grains was 0.1–1.3 mg kg−1, and hazard quotients for local consumers by intake of these rice were 0.7–8.8. Planting low-Cd-accumulating (LCA) cultivar reduced hazard quotients for consumers by intake of rice, but had similar ecological risks as high-accumulating (HCA) cultivars. LCA cultivar had lower Cd content in grains as well as higher efficiency of altering Cd into insoluble forms in flag leaves and upmost nodes than HCA cultivars. Insoluble Cd content in nodes was linearly increased with soil Cd content, companied by significant decline of 4 amino acids with dicarboxyl groups. Glu or Asp can form a cyclic complex with Cd by two O atoms from α-COO- and side chain-COO-. These results indicate that roots and straws have high potential to concentrate Cd by forming complexes between amino acids and Cd ions, and Cd-enriched straw return to topsoil may aggravate the ecological risk of Cd contamination.

Genetic Approaches for Iron and Zinc Biofortification and Arsenic Decrease in Oryza sativa L. Grains.

Rice is the staple diet to half of the world's population, being a major source of carbohydrates, vitamins, and some essential elements. However, rice naturally contains low amounts of essential minerals such as iron (Fe) and zinc (Zn), which are drastically decreased after milling. Thus, populations that consume mostly rice may have micronutrient deficiency, which is associated with different diseases. On the other hand, rice irrigated by flooding has a high ability to accumulate arsenic (As) in the grain. Therefore, when rice is grown in areas with contaminated soil or irrigation water, it represents a risk factor for consumers, since As is associated with cancer and other diseases. Different strategies have been used to mitigate micronutrient deficiencies such as Fe and Zn and to prevent As from entering the food chain. Each strategy has its positive and its negative sides. The development of genetically biofortified rice plants with Fe and Zn and with low As accumulation is one of the most promising strategies, since it does not represent an additional cost for farmers, and gives benefits to consumers as well. Considering the importance of genetic improvement (traditional or molecular) to decrease the impact of micronutrient deficiencies such as Fe and Zn and contamination with As, this review aimed to summarize the major efforts, advances, and challenges for genetic biofortification of Fe and Zn and decrease in As content in rice grains.

Co-utilizing milk vetch, rice straw, and lime reduces the Cd accumulation of rice grain in two paddy soils in south China

The danger posed by cadmium (Cd) pollution to rice production is continuously increasing. Co-utilizing milk vetch (Astragalus sinicus L.) and rice straw is a good practice for rice yield and soil fertility in south China. However, its effects on Cd availability in soil–rice systems remain unclear. A micro-plot trial of two typical paddy soils (alluvial sandy soil and reddish clayey soil) in south China was conducted to investigate the effects of milk vetch, rice straw, lime, and their combined application on Cd availability and the related mechanisms. Soil chemical properties, CaCl2-extractable Cd (CaCl2-Cd), total content of Cd (Total-Cd), Cd fractionation (BCR sequential-extraction method), and Cd accumulation in rice were measured. Results showed that the co-utilization of milk vetch, rice straw, and lime (GRFL) decreased the Cd content in rice grain by 91.43% and 15.63% in early rice of two soils, respectively. Cd was not detected in late rice grains. CaCl2-Cd decreased by 0.025 mg kg−1 in late rice of alluvial sandy soil, 0.057 and 0.044 mg kg−1 decreased in early and late rice of reddish clayey soil, and Total-Cd decreased by 19.4% and 9.1% for early rice of two soils, respectively. Co-utilizing milk vetch, rice straw, and lime changed the distribution of different chemical forms of Cd, decreased the content of bioavailable Cd in soil by reducing the Aci-Cd and RedCd, and benefited the formation of more stable residual fraction (ResCd). Redundancy analysis showed that the improvement in soil pH, dissolved organic matter (DOM), and other soil properties was the main cause of the transformation of Cd form. Among the soil properties, pH and DOM had the greatest impacts on Cd availability. In conclusion, co-utilizing milk vetch and rice straw can alleviate the danger of soil Cd in rice production, and this effect could be strengthened by applying lime.

Risk Assessment of Arsenic Toxicity Through Groundwater-Soil-Rice System in Maldah District, Bengal Delta Basin, India.

Arsenic (As), a toxic trace element, is of great environmental concern due to its presence in soil, water, plant, animal and human continuum. Its high toxicity and increased appearance in the biosphere have triggered public concern. The present study measured As concentrations in soil, groundwater and rice plant samples of five selected blocks of Maldah district, West Bengal, India. Soil, irrigation water and rice plant samples were collected from the fields of the selected study areas. The results revealed the presence of As in higher concentrations than the maximum permissible limit of As in irrigation water (0.1mg L-1 by FAO, 2010) in groundwater of Manikchak (0.553 ± 0.17mg L-1), Kaliachak III (0.528 ± 0.20mg L-1), and Kaliachak II (0.449 ± 0.15mg L-1), Kaliachak I (0.207 ± 0.19mg L-1). The soil As was also found higher in those four blocks. The As content in rice grain of the study area was positively correlated (r = 0.896**, p < 0.001) with As content in irrigation water. The data of consumption of rice per day in the survey were used for the measurement of average daily intake, Hazard quotient (HQ) and Incremental Life time Cancer Risk. Kaliachak III, Manikchak and Kaliachak II showed HQ greater than 1, indicating the possibility of non-carcinogenic health hazard due to As exposure to the local residents. The study emphasized the severity of As problem in remote areas of West Bengal where people consume As tainted rice due to lack of awareness about the As associated health issues.

Effects of combined soil amendments on Cd accumulation, translocation and food safety in rice: a field study in southern China.

Excessive Cd content and high Cd/Zn ratio in rice grains threaten human health. To study the reduction effects of combined soil amendments on Cd content and Cd/Zn ratio in rice planting in soils with different Cd contamination levels, we conducted field trials in three regions of Hunan province, China. Six field treatments were designed in each study area, including control (CK), lime alone (L), lime combined with sepiolite (LS), phosphate fertilizer (LP), organic fertilizer (LO) and phosphate fertilizer + organic fertilizer (LPO). The application of the combined amendments reduced the Cd content in rice grains to less than the Food Health Standard of China (0.2mg/kg) and the Cd/Zn ratio to less than the safety threshold of 0.015. The average reduction rates of grain Cd content under the combined treatments among the three regions increased with the increase in Cd content in the soil. Meanwhile, the amendments also decreased the soil available Cd and Zn concentration significantly. The LO had the highest efficiency on decreasing Cd content in rice grains among these amendments, which is ranged from 44.6% to 52.8% in the three regions compared with CK. Similarly, high reduction rates of Cd/Zn ratio were found in the LO treatment, with an average value of 57.3% among the three regions. The grain Cd contents and Cd/Zn ratios were significantly correlated with the soil available Cd concentrations, plant uptake factor and the straw to rice grain translocation factor (TFgs) (P < 0.05). The results indicated that the combined soil amendments, especially lime combined with organic fertilizer, would be an effective way to control Cd content in rice.

Modelling evaluation of key cadmium transformation processes in acid paddy soil under alternating redox conditions

The intermittent flooding conditions in acid paddy field can substantially affect the phytoavailability of cadmium (Cd), but the underlying mechanisms controlling Cd transformation are still poorly understood, and furthermore the corresponding models for predict the Cd phytoavailability during pre-harvest drainage phase are still lacked. In this study, Cd-spiked paddy soil was incubated under anaerobic condition for 40 days and then aerobic condition for 15 days. The transformation of Cd speciation and the redox cycling of Fe/N/S was investigated. During anaerobic incubation, the dissolved and exchangeable Cd rapidly decreased, which were mainly attributed to enhanced adsorption on the surface of organic matter with the increasing soil pH. Moreover, the reductive dissolution of Fe oxides induced the release of soil colloids, which result in increasing the surface sites to immobilize Cd. In addition, the formation of Cd sulfide contributed to slight decrease the availability of Cd. However, when oxygen was re-introduced into the system, the rapid decrease of soil pH and surface sites resulted in the release of adsorption on soil surfaces, and oxidative dissolution of Cd sulfide also contributed to the increase of Cd availability. The kinetic models were established based on the key elementary reactions for soil biogeochemical processes on the transformation of Cd fractions. The kinetic models were applied to calculate the potential available Cd in acid paddy soils samples (pH ≤ 6.0) from the field, and moreover, the dissolved Cd was estimated from the surface complexation model (SCM) by incorporating the changes of soil pH. The concentration of model-predicted dissolved Cd during drainage phase had a stronger correlation with the Cd content in rice grain than that of chemical extraction methods. Our results demonstrated that it was feasible to use the kinetic models and SCM to predict Cd phytoavailability during drainage phase of acid paddy field.

Dark septate endophyte Falciphora oryzae-assisted alleviation of cadmium in rice

Dark septate endophytes (DSEs) are the typical representatives of root endophytic fungi in heavy metal (HM)-contaminated environments. However, little is known about their roles in the HMs tolerance of hosts and the underlying mechanism. Here, we investigated the biological roles and molecular mechanisms of a DSE strain Falciphora oryzae in alleviating cadmium (Cd) toxicities in rice. It was found that F. oryzae possessed a capacity of accumulating Cd in its vacuoles and chlamydospores. During symbiosis, F. oryzae conferred improved Cd tolerance to rice, decreasing Cd accumulation in roots and translocation to shoots. F. oryzae alleviated Cd toxicity to rice by sequestering Cd in its vacuoles. Further application of F. oryzae as fertilizer in the field could reduce Cd content in rice grains. We identified a SNARE Syntaxin 1 gene through proteomics, which participated in Cd tolerance of F. oryzae by regulating chlamydospore formation and vacuole enlargement. This study provided novel insights into how the DSEs and their host plants combat Cd stress.

Stabilization of lead in waste water and farmland soil using modified coal fly ash

As a by-product of coal-fired power plants, fly ash has attracted widespread attention because of its heavy metal adsorption potential. In this study, two fly ashes from different power plants were re-used through modification to adsorb Pb(Ⅱ) from aqueous solution and field soil. The physicochemical properties of adsorbents were characterized by X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), the X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), as well as the X-ray photoelectron spectroscopy (XPS). In addition, batch sorption experiments and field study were conducted to investigate their adsorption capacity on Pb(Ⅱ). The results demonstrated that, the surface area of modified fly ash-2 (MFA-2) has increased 25 times. The kinetic study illustrated that the adsorption process on both modified fly ash-1 (MFA-1) and MFA-2 were more suitable for pseudo-second-order model. Nevertheless, MFA-2 took less time to reach adsorption equilibrium. Compared with the raw fly ashes, the prepared MFAs had stronger affinities to Pb(II). When used as adsorbents, more than 146 and 165 mg of Pb(II) could be adsorptively stabilized by per gram of MFA-1 and MFA-2 at 318 K from waste water, respectively; when employed as amendments, the addition of MFA-1 and MFA-2 into soil could reduce Pb accumulation in rice, with the total Pb content in rice grains is lower than the level of natural standard. The investigation declared that the MFAs were promising materials which had great potentials on adsorptive stabilization of Pb(II) from waste water and contaminated soil, which also realizes the recycling of resources and cleaner production.

Mechanism of S-allyl-L-cysteine Alleviating Cadmium Stress in Seedling Roots and Buds of Rice Seedlings

Cd has toxic effects on rice seed germination and plant growth, which may eventually lead to decreased yield and excessive Cd content in rice grains. The potential mechanism of S-allyl-L-cysteine (SAC), a natural sulfur compound derived from garlic extract, in alleviating Cd2+ stress in young roots and buds of rice seedlings was studied by a seed germination experiment. "Zhong zao 35", one of the main rice varieties in Southern China, was selected as the test material. Firstly, the alleviating effect of SAC on Cd2+ stress in rice seedling roots and buds was studied. Following this, the physiological mechanism of Cd2+ stress alleviation by SAC was examined based on the expression of the Cd transporter coding gene using real-time fluorescent quantitative PCR. The results showed that when the Cd2+ stress concentration reached 50 μmol·L-1, the young roots and buds of rice seedlings were significantly inhibited, and when the SAC concentration reached 200 μmol·L-1, Cd2+ stress was significantly alleviated. Compared to a Cd2+ stress treatment group, the total root length, surface area, and volume of young roots was increased by 173.5%, 65.52%, and 37.04%, respectively; CAT and SOD activity in young roots and buds was increased by 212.42% and 110.76%, and 31.41% and 47.31%, respectively; MDA and GSH content was decreased by 43.09% and 34.12%, and 33.97% and 35.74%, respectively; and Cd content was decreased by 35.91% and 28.86%, respectively. The results of quantitative real-time PCR showed that the relative expression levels of OsNramp5 and OsHMA2 were significantly reduced by 33.38% and 34.99% compared with the Cd2+ stress group, respectively. However, the relative expression level of OsHMA3 was significantly increased by 33.96%. From the above experimental results, the main mechanism by which SAC reduces Cd2+ stress in the young roots and buds of rice is via the regulation of Cd transporter-encoding genes, reducing Cd2+ transport to young roots and buds, and increasing transport to vacuoles.

Determination of Suitable Extractant for Estimating Plant Available Arsenic in Relation to Soil Properties and Predictability by Solubility-FIAM

Extractant for estimating plant available arsenic (As) in soil has not been universally established. Moreover, to assess and monitor the complex chemical behaviour of arsenic (As) in soil and subsequently its transfer in crops, a suitable extraction protocol considering the soil properties in relation to crop uptake is required. For this purpose, a pot experiment was conducted to evaluate the suitability of the extractants for determination of extractable As in soil and risk assessment by solubility-free ion activity model (FIAM) with rice (variety: Sushk Samrat) as the test crop. Soil in bulk was collected from six locations of Indo-Gangetic Plain of Bihar, India, varying in physicochemical properties to conduct the pot experiment using five doses of As (0, 10, 20, 40 and 80 mg kg−1). Six extractants namely 0.2 (M) NH4-oxalate, 0.05 (N) HCl + 0.025 (N) H2SO4, 0.5 (M) KH2PO4, 0.5 (N) NH4F, 0.5 (M) NaHCO3 and 0.5 (M) EDTA were used. The results revealed that 0.5 (M) KH2PO4 gave the best correlation with the soil properties and crop uptake and can be considered a suitable extractant of As. Regardless of the As dose and the soil type used, in rice tissue, concentration of As followed the order root > straw > leaf and grain. As high as 94% variation in As content in rice grain could be explained, when 0.5 (M) KH2PO4 extractable As is being used as input for solubility-FIAM. Extractable As cannot be determined by atomic absorption spectrophotometer (AAS) coupled with vapour generation accessory (VGA) when 0.5 (M) EDTA was used as an extractant.

The effect of phosphorus split application on use efficiency and dynamic of phosphorus and zinc at the soil, aerial parts, and grain, and Zinc biofortification of two rice varieties (Oryza sativa L.) (Hashemi and Guilaneh)

Introduction: Despite the P vitality for rice cultivation, its recovery index in paddy soils is very low and less than 25% of added P, and the rest goes out of reach of rice plant through the P fixation by soil particles at different fractions. Also, despite abundant studies on the effect of basal soil P application, we face a lack of knowledge on research findings of the P splitting application and its effect on soil Zn concentration and tissues Zn content. Thus, the current research project was done to explore the effect of P splitting application at flooded conditions on the soil and rice plant tissues P and Zn variation trend at the different rice growth stages of two more common varieties (Hashemi and Guilaneh varieties). Materials and methods: The outdoor pot experiment was conducted on a three factors factorial experiment in a randomized complete block design with three replications in 2017 at the research farm of the rice research institute of Iran, Rasht. The experimental treatments were: phosphorus fertilizer split application at five levels, soil at two levels, and rice varieties at two levels (Hashemi (local variety) and Guilaneh(improved variety)), The P application treatments were: control (no added P), 100% basal, P split application at 50% basal and 50% at 20 days after transplanting (DAT), P split application at 50% basal and 50% at 60 days after transplanting (DAT), P split application at 50% basal, 25% at 20 days after transplanting, and 25% at 60 days after transplanting. Results: The results indicated that the highest soil available P and Zn concentrations were recorded at the flowering stage about 95.3 and 90.10, and 8.6 and 8.7 mgkg-1by two and three P split for Hashemi and Guilaneh, respectively. Also, the maximum P of rice grain was obtained about 0.17 and 0.20 mgkg-1 for Hashemi and Guilaneh, respectively. The Zn content of rice grain at P split pots was significantly more than control and 100% basal application. The highest agricultural recovery (13.31 and 12.72), physiological (693.19 and 740.10) and physiological-agricultural efficiency (482.00 and 753.00), P use efficiency (5.34 and 5.66), and apparent recovery (1998 and 1272.22 kg kg-1) were found for Hashemi and Guilaneh, respectively, in the two and three P split application. Furthermore, stepwise multiple regression analysis revealed that the soil available P concentration at ripening stage, Zn content of the grain, and Zn concentration at rice aerial parts can explain 52% of grain yield variations for studied rice cultivars. Conclusion: The three-stage P splitting (50% soil basal, 25% 20 DAT, and 25% 60 DAT) increased the Zn content of the Hashemi variety by about 54.72% at slit loam soil, whereas the Guilaneh rice variety was received a 37.5% increase in Zn content of grain in silty clay through two-stage P splitting (50% soil basal and 50% 20 DAT) compare to control (100 % basal). It can be concluded both three and two-stage P splitting might be positively significantly effective on rice grain nutritional quality.

Effects of Water Management on Cadmium Accumulation by Rice (Oryza sativa L.) Growing in Typical Paddy Soil

In order to explore the effects of water management on the Cd accumulation of rice in paddy soils with different parent materials, a pot experiment with three paddy soils with different parent materials from Hunan Province (granite sandy soil, plate shale soil, and purple sandy shale soil) with different water management treatments ［flooding and alternate wetting and drying (AWD)］ was performed. The soil pH, DTPA-Cd, Fe plaque in the rice roots, and heavy metal concentration in the rice were determined. The results showed that the soil pH of the three paddy soils under the flooding treatment was increased by 0.17-1.33 units. During the filling and maturity periods, compared with that under AWD, the DTPA-Cd concentration in the three paddy soils was reduced by 14.39%-36.56% under the flooding treatment, but the DTPA-Fe concentration was increased by 35.35%-347.25%. In the three growth stages, the Cd and Mn concentrations in the Fe plaque (except for DCB-Fe) were in the order of tillering stage < filling stage < mature stage. Compared with that under AWD, the brown rice Cd concentration in the three soils was reduced by 57.84%-93.79% under flooding treatment. The Cd accumulation in rice was reduced under flooding treatment by reducing the DTPA-Cd via increasing the soil pH and DTPA-Fe and by decreasing the formation of Fe plaque. According to the results of the correlation and SEM analysis, the soil pH and DCB-Cd were the main factors affecting the Cd accumulation in rice grains, although the changes in the DTPA-Cd and DTPA-Fe also impacted the Cd in rice grains. In summary, our study demonstrated that water management had a significant impact on the Cd content in rice, and there were significant differences among the three paddy soils with different parent materials. In conclusion, the Cd content in rice grains was affected by the soil parent material, soil physicochemical properties, and Fe plaque on the surface of the rice roots. The granite sandy soil and plate shale soil with different water management treatments had significant impacts on the contents of heavy metals in rice. Continuous flooding is a valuable strategy for improving soil acidity and alkalinity and minimizing soil available Cd, but the soil parent materials must be considered.

Zerovalent Iron Modulates the Influence of Arsenic-Contaminated Soil on Growth, Yield and Grain Quality of Rice

This study aimed to investigate the effects of zerovalent iron (ZVI/Fe0) on growth, yield and grain quality of rice (Oryza sativa L.) cv. BRRI dhan49 in arsenic (As)-contaminated soils. The pot experiment was arranged in a complete randomized design (CRD). The treatments on rice applied were As in soils at As0 (0 mg kg−1), As20 (20 mg kg−1), and As40 (40 mg kg−1) with a combination of ZVI at ZVI0 (0%), ZVI0.5 (0.5%), ZVI1.0 (1.0%), and ZVI1.5 (1.5%) with three replications. Contents of phosphorus (P), potassium (K), manganese (Mn), zinc (Zn), iron (Fe), and As in grains of rice; and Fe and As content in cultivated soils were determined. The application of ZVI had negative or no effect on shoot weight, tiller number, and grain yield. Although application of ZVI had little or no effect on thousand grain weight, P, K, Zn, and Mn of rice grains, Fe content in rice grains was increased by ZVI treatments in a dose-dependent manner. The grain As content was non-significantly reduced by the ZVI application. Soil bacterial population was negatively influenced by the ZVI in a dose-dependent manner which might be linked with As content in the soils. Therefore, a further elaborative study is needed to elucidate the mechanisms of the effects of ZVI and soil As on rice and rhizosphere soil microorganisms.

Zinc and nitrogen synergistic act on root-to-shoot translocation and preferential distribution in rice

IntroductionMultiple studies have shown strong relationships between different nutrients in plants, and the important role of N in Zn acquisition and translocation has been recognized. ObjectivesThe aim of this study was to estimate the effect of Zn on N uptake, translocation, and distribution in rice as well as the corresponding molecular mechanisms. We also aimed to evaluate the impact of N on the Zn content in rice grains which is closely related to the Zn nutrition in humans with rice-based diets. MethodsWe conducted both field trials and hydroponic cultures of two rice cultivars to analyze the growth and yield, the uptake, translocation, and distribution of N and Zn, as well as the expression of N transport and assimilation genes, and the Zn transporter genes under different combined applications of N and Zn. ResultsZn supply promoted the root-to-shoot translocation (12–70% increasing) and distribution of N into the leaves (19–49% increasing) and brown rice (6–9% increasing) and increased the rice biomass (by 14–35%) and yield (by 13–63%). Zn supply induced the expression of OsNRTs and OsAMTs in both roots and shoots, but repressed the expression of OsNiR2, OsGS1;2, and OsFd-GOGAT in roots, whereas it activated the expression of OsNiR2, OsGS1;1, OsGS2, and OsFd-GOGAT in the shoots. Moreover, the enzyme activities of nitrite reductase, nitrate reductase, and glutamine synthetase increased and the free NO3– concentration decreased, but the soluble protein concentration increased significantly in the shoots after Zn supply. Synergistically, N significantly facilitated the root-to-shoot translocation (1.68–11.66 fold) and distribution of Zn into the leaves (1.68–6.37 fold) and brown rice (7–12% increasing) and upregulated the expression levels of Zn transporter genes in both the roots and shoots. ConclusionsWe propose a working model of the cross-talk between Zn and N in rice plants, which will aid in the appropriate combined application of Zn and N fertilizers in the field to improve both N utilization in plants and Zn nutrition in humans with rice-based diets.

RETRACTED: Inhibition effects of long-term calcium-magnesia phosphate fertilizer application on Cd uptake in rice: Regulation of the iron-nitrogen coupling cycle driven by the soil microbial community

Cadmium (Cd) pollution in paddy soil seriously endangers food safety production. To investigate the effects and microbiological mechanisms of calcium-magnesium-phosphate (CMP) fertilizer application on Cd reduction in rice, field experiments were conducted in Cd-contaminated paddy soil. Compared with conventional compound fertilizer, CMP fertilizer treatments inhibited Cd uptake through plant roots, significantly decreasing Cd content in rice grains from 0.340 to 0.062 mg/kg. Soil pH and total Ca, Mg and P contents increased after CMP fertilizer application, resulting in a further decrease in soil available Cd content from 0.246 to 0.181 mg/kg. Specific extraction analysis recorded a decrease in both available Fe content and the ratio of nitrate to ammonium nitrogen, indicating that the soil Fe-N cycle was affected by the addition of CMP fertilizer. This finding was also recorded using soil bacterial community sequencing, with CMP fertilizer promoting the progress of nitrate-dependent Fe-oxidation driven by Thiobacillus (1.60–2.83%) and subsequent dissimilatory nitrate reduction to ammonium (DNRA) driven by Ignavibacteriae (1.01–1.92%); Fe-reduction driven by Anaeromyxobacter (3.09–2.23%) was also inhibited. Our results indicate that CMP fertilizer application regulates the Fe-N coupling cycle driven by the soil microbial community to benefit remediation of Cd contaminated paddy soil.

Fe and Zn content of various genetic background of released rice varieties in Indonesia

Fe and Zinc deficiency is one of the most prevalence micro nutrient disorder in Indonesia. Increasing of Fe and Zn content in rice grain is expected to be useful to reduce the micronutrient deficiency. This research was aimed to identify rice varieties containing high Fe and Zn content and initially study the correlation among some related traits. The experiment was conducted in October – December 2016 by testing 176 released varieties and 4 elite rice lines. The samples were prepared as brown rice. Fe and Zn contents were measured using XRF Oxford machine which is validated by ICP method. The results showed that Fe content of the tested genotypes is normally distributed ranged from 9.70 ppm to 17.40 ppm with the mean of 13.03 ppm and the Zn content is not normally distributed ranged from 15.80 ppm to 31.10 ppm with the mean of 22.41 ppm. Majority of the released rice varieties in Indonesia had lower Fe and Zn content compared to the most popular variety, Ciherang (12.20 ppm and 24.70 ppm). Kalimutu had the highest both for Fe and Zn content (17.40 ppm and 31,10 ppm). Fe and Zn content are positively correlated and breeding effort for both traits is prospective.

Effectiveness of Water Management in Producing Cadmium-Safe Rice in Soils of Different Contamination Levels and Physicochemical Properties

The effectiveness of water management in reducing cadmium (Cd) accumulation in rice grain has mainly been investigated in slightly and moderately contaminated soils but seldom in heavily contaminated soils. In addition, how soil physicochemical properties influence the effectiveness of water management merits investigation. In this study, a pot experiment was performed using six soils of slight (S1), moderate (S2–S5), and heavy (S6) Cd contamination levels and of different properties. Three water managements, flooding until full tillering (W1), flooding until full tillering and reflooding after 7–10-day drying (W2), and continuous flooding without drying (W3), were implemented for each soil. Cadmium content in rice grain was significantly decreased (by 60% on average) in W2 and further decreased (by 82% on average) in W3 as compared with W1 in all the six soils. Grain Cd contents in the W3 treatments were decreased to below the Chinese food safety standard of 0.2 mg kg−1 in all the six soils except in S6 (0.36 mg kg−1). For all the three water management regimes, the lowest grain Cd content was observed in S3 which had high contents of organic matter, sulfur, and iron. The results indicate that extended flooding can effectively decrease rice grain Cd accumulation in soils of various contamination levels especially those rich in organic matter, sulfur, and iron. But for heavily contaminated soils, water management may need to combine with other approaches to further decrease grain Cd content to meet food safety standard.

Assessing mineral and toxic elements content in rice grains grown in southern Brazil

The development of rice genotypes with higher mineral content and less accumulation of toxic elements can help to mitigate problems related to mineral deficiency and insure consumption of safe foods. However, genetic improvement depends on the presence of genetic diversity. Therefore, here we characterize a rice panel, grown in southern Brazil, regarding iron (Fe), zinc (Zn), selenium (Se), manganese (Mn), copper (Cu), arsenic (As), cadmium (Cd) and lead (Pb) content in irrigated system with permanent flooding. The environment of each harvest season significantly influenced Cu, Zn, Se, Fe and Mn content in rice grains. None of the analyzed rice genotypes can meet the daily recommendation of Fe and Zn, being the highest contents detected for these mineral of ∼17 and ∼27 mg kg−1, respectively. We detected genotypes able to supply Mn, Cu and Se demand, and genotypes accumulating ∼37, ∼5, ∼0.200 mg kg−1 were detected, respectively. None of the analyzed genotypes showed Cd and Pb accumulation above the Brazilian allowed limits. However, As content was above of the allowed limit for most of the studied accessions, and some genotypes reached 1 mg kg−1of As in their grains. Among the genotypes, low genetic diversity was detected for the evaluated elements.

Effect of water and fertilization management on Cd immobilization and bioavailability in Cd-polluted paddy soil

The field trial was conducted to investigate remediation effects of two alkaline fertilizers and three water management techniques on Cd contaminated paddy soil. The results revealed downward trend of soil pH and EC during growth period of rice. The treatment of organic fertilizer has indicated high pH and organic matter than treatment of calcium magnesium phosphate fertilizer. The integrated effect of organic fertilizer and continuous flooding (COF) has significantly (p < 0.05) reduced soil Eh to −180 mv at booting stage. The exchangeable Cd of soil decreased with growth of rice in all treatments. The continuous flooding has showed lowest content of soil exchangeable Cd at every stage of rice growth than other treatments. The organic fertilizer, calcium magnesium and phosphorus have promoted growth of rice. The treatments of continuous flooding were most effective in reducing Cd content in rice grain by 12.6–51.9%. The treatments of continuous flooding have lowest TFhusk-rice, and TFshoot-husk. The BCF of continuous flooding was 0.13, 0.35 and 0.13. According to Pearson correlation coefficients, soil exchangeable Cd concentration has significantly (P < 0.05) negative correlation with soil pH and EC, but has significantly (P < 0.05) positive correlation with soil Eh. The Cd concentration of rice grain has significantly (P < 0.05) positive correlation with Cd of leaf, and negative correlation with Cd of husk. It is concluded that organic fertilizer combined with continuous flooding was most effective management strategy for Cd remediation in paddy soil.