Cd Concentrations In Brown Rice Research Articles

Effects of Different Organic Materials on Absorption and Translocation of Arsenic and Cadmium in Rice

A pot experiment was carried out to study the impacts of five organic materials (rape straw, broad bean stalk, peat, pig manure compost, and biochar) on the availability of arsenic (As) and cadmium (Cd) in soil, the amount of iron plaque on the root surface, as well as the uptake and translocation of As and Cd in rice grown in an As/Cd co-contaminated yellow paddy soil. The results indicated that the application of organic materials significantly increased the contents of the soil organic matter and the yield of rice. The application of broad bean stalk, peat, pig manure compost, and biochar remarkably increased the soil pH, while the application of rape straw exerted no significant influence. The addition of organic matter reduced the available Cd content by 34.77%-82.69%. However, the effects of organic materials on the availability of As varied with the organic materials. The soil-available As content was significantly increased by the application of pig manure compost and biochar, while it was significantly decreased by adding rape straw and peat. The application of organic materials increased As and Cd contents in the Fe plaques on rice root surface by 28.49%-94.86% and 17.73%-151.03%, respectively. It also reduced the As and Cd contents in brown rice by 27.04%-82.51% and 15.87%-79.45%, respectively. The largest decrease was observed in the biochar treatment. The application of organic materials also remarkably reduced the translocation efficiency of Cd from the root-stem-leaf-grain and that of As from the stem to grain. The correlation analysis revealed that the soil pH, available Cd, and Cd content in the Fe plaques are the major factors influencing the accumulation of Cd in the rice grain. Furthermore, the soil pH, soil organic matter, and As content in the Fe plaques are the major factors influencing the accumulation of As in the rice grain. Therefore, it has been concluded that organic materials could influence the uptake and translocation of As and Cd in rice through changing the soil pH, organic matter content, and As and Cd contents in the Fe plaques.

Combined amendment reduces soil Cd availability and rice Cd accumulation in three consecutive rice planting seasons

The scientific application of stabilized materials has been considered an effective method for the in situ remediation of Cd-contaminated soil. This study aimed to investigate the persistence of the effect of a combined amendment of limestone and sepiolite (LS) on soil Cd availability and accumulation in rice grown in a mildly Cd-contaminated paddy field (0.45 mg/kg of Cd) over three consecutive rice seasons. 1125–4500 kg/ha of LS was applied to the soil before the first rice planting season and 562.5–2250 kg/ha of LS was supplemented before the third rice planting season. The application of LS (1125–4500 kg/ha) increased the soil pH by 0.44–1.09, 0.18–0.53, and 0.42–0.68 in the first, second, and third season, respectively, and decreased the soil acid-extractable Cd content by 18.2–36.4%, 17.7–33.5%, and 9.6–17.6%. LS application significantly decreased the Cd contents in the rice tissues. The application of 4500 kg/ha of LS decreased the Cd content in brown rice to below the National Food Limit Standard of 0.2 mg/kg (GB 2762-2017) in the three consecutive rice seasons. However, the effect of LS on the soil-rice system was significantly weakened in the third season. The supplementary application of 562.5–2250 kg/ha of LS further decreased the Cd content in brown rice by 26.1–56.5% and decreased the health risk index by 23.7–43.8%. Therefore, it was recommended to apply 4500 kg/ha of LS in the first season and to supplement 2250 kg/ha of LS in the third season to effectively guarantee the clean production of rice in three consecutive rice seasons.

Remediation potential of spent mushroom substrate on Cd pollution in a paddy soil.

To investigate the remediation potential of spent mushroom substrate (SMS) on Cd pollution in a paddy soil, a rice pot experiment was conducted to study the effects of SMS addition on the availability of Cd in soil and the uptake of Cd in rice tissues. Five percent of SMS from Pleurotus eryngii (SMS-A, treatment: A), SMS from Agaricus bisporus (SMS-B, treatment: B), or SMS-A plus SMS-B (1:1, treatment: A+B) were added into a Cd-contaminated paddy soil before planting, respectively. The treatment of no SMS amendment was set up as the control (CK). At the four main growth stages of rice, the soils and plant samples were collected to detect the soil properties, Cd concentration in soils and rice tissues, and Cd fractions in soils. Results indicated that the application of SMS-A, SMS-B, and A+B significantly increased soil pH by 14.0-22.9, 23.9-32.9, and 22.7-30%, organic matter (OM) contents by 12.9-31.5, 22.1-34.5, and 26.1-36.9% comparing with CK. While cation exchange capacities (CECs) were increased by 3.6-8.5, 4.9-13.1, and 0.4-10.0% in A, B, and A+B treatments, respectively, except those at the maturation stage in A and B treatments. However, the CaCl2-Cd concentrations in soils were significantly decreased by 64.8-77.9, 76.1-98.9, 73.2-98.9% in A, B, and A+B treatments, respectively, comparing with CK. The reduced availability of Cd was attributed to the changes of Cd from soluble to insoluble fractions in soils amended with SMS and resulted in the decreased Cd uptake in rice tissues. The Cd concentrations in roots significantly decreased by 22.8-36.9, 28.6-36.6, and 26.8-42.6%, while the Cd concentrations in straw decreased by 20.1-46.4, 9.3-41.6, and 16.0-49.1% in A, B, and A+B treatments, respectively. At the maturation stage, the Cd concentrations in brown rice were reduced by 17.7, 15.9, and 19.4% in A, B, and A+B treatments, respectively. Correlation analysis revealed that the Cd concentrations in rice roots, straws, and brown rice were all positively correlated with CaCl2-Cd concentrations of soils. Moreover, soil pH and OM were significantly negatively correlated with the Cd concentration in rice tissues, except that between soil pH and the Cd concentration in rice straws. Therefore, the reduced Cd availability in soil and uptake in rice plant tissues together with better soil nutrient conditions by SMS application improved the biomass of root and straw at heading, filling, and maturation stages and the rice production by 32.9-38.8% at the maturation stage. The combined application of SMS-A and SMS-B can be used as a potential method for remediation of Cd-contaminated paddy soil.

Phenotypic and genetic dissection of cadmium accumulation in roots, nodes and grains of rice hybrids

Rice accumulates higher levels of cadmium (Cd) in grain than other cereals, and hybrid rice varieties cover around half of the total rice area in China. Therefore, understanding the phenotypic and genetic characteristics of Cd accumulation in rice hybrids is vital for food safety. An incomplete diallel cross design was used to analyse the heritability and combining ability of Cd accumulation in rice hybrids growing in soil contaminated with Cd. The quantitative real-time PCR was used to detect the gene expressions that related to Cd uptake and transport. The Cd contents in brown rice, nodes and roots were detected by ICPOES, and the Cd contents in xylem sap were detected by ICPMS. Additive effects dominated the Cd accumulation in brown rice, upper nodes, and the Cd translocation efficiency from roots to nodes of hybrids. The Cd accumulation in brown rice was positively correlated with Cd accumulation in upper nodes and translocation efficiency from roots to nodes. Regarding the general combining ability, the restorer lines R2292 and R2265, and the male sterile lines KeBX58S, Ke20A, Ke76-1BS and Ke244-1BS were found to be potential elite parental lines for developing hybrid rice with low Cd accumulation. Hybrid rice with low Cd accumulation in brown rice can be derived from parental lines with low general combining ability for Cd content in brown rice.

DGT methodology is more sensitive than conventional extraction strategies in assessing amendment-induced soil cadmium availability to rice

Using diffusive gradients in thin films (DGT) is a recently developed alternative method of rapidly evaluating the bioavailability of metals in soil. However, the method has found only limited application in systematic assessment of the bioavailability of cadmium (Cd) in red limestone paddy soils treated with different soil amendments. Of the four methods compared for estimating Cd content of rice grains from plants grown in such soils of central China treated with eleven different soil amendments in pot culture, Cd content of DGT-labile soil was significantly correlated to Cd concentrations in brown rice (R = 0.447, p < 0.01). The other three methods involved CaCl2, diethylenetriaminepentaacetic acid (DTPA), or NH4NO3. Some other properties of soil, such as pH, redox potential, content of dissolved organic matter, and cation exchange capacity were also determined. A simple algorithm developed to evaluate the sensitivity of the four methods also confirmed DGT as the most efficient method to predict the bioavailability of Cd in red limestone paddy soils.

Effects of Ferrous Sulfate and Ferric Nitrate on Cadmium Transportation in the Rhizosphere Soil-Rice System

Cadmium (Cd) contamination in the agricultural soils of China is a serious and growing environmental problem that urgently needs to be controlled and completely remediated. The biogeochemical cycles of nitrogen (N), sulfur (S), and iron (Fe), and the coupled cycles of Fe-N and Fe-S have been reported to control Cd transportation in the soil-rice system. Exploring practical remediation strategies for Cd from the perspective of the application of nutrients such as N, S, and Fe for rice growth is expected to obtain farm-specific and state-of-the-art technologies and products to reduce the accumulation of Cd in rice grains. Using our earlier study as a basis, the rhizosphere bag-pot experiment with ferrous sulfate (FeSO4) and ferric nitrate[Fe(NO3)3] treatments was conducted to investigate Cd bioavailability in rhizosphere soil and Cd translocation in rice plants, and to highlight some possible factors and mechanisms controlling Cd accumulation in rice grains. The results showed that both FeSO4 and Fe(NO3)3 treatments reduced the bioavailable Cd (NH4Ac-Cd) content in rhizosphere soil, with the decreasing extent being significantly lower in the former (55.6%) than in the latter (76.0%). Both FeSO4 and Fe(NO3)3 treatments changed the distribution characteristics of Cd in rice tissues, and the FeSO4 treatment increased the Cd content in brown rice (0.6 mg·kg-1), but the Fe(NO3)3 treatment decreased the Cd content in brown rice (0.1 mg·kg-1). Adsorption or co-precipitation of Cd by iron plaque, increased accumulations of Cd in root, stem, and leaf, and enhanced translocations of Cd from root, stem, and nodule to brown rice occurred with the increased Cd content in brown rice of the FeSO4 treatment. However, the decreased Cd content in brown rice with the Fe(NO3)3 treatment was ascribed to adsorption or co-precipitation of Cd by poorly crystalline Fe oxides and solid Fe sulfides, decreased accumulations of Cd in stem and nodule, and weakened translocations of Cd from root, leaf, and nodule to brown rice. These findings provide a scientific basis for the exploration and application of nutritive soil amendment, and will have significance in regards to the remediation of Cd-contaminated agricultural soils in China.

Upland rice intercropping with Solanum nigrum inoculated with arbuscular mycorrhizal fungi reduces grain Cd while promoting phytoremediation of Cd-contaminated soil

Intercropping of hyperaccumulators with crops is a promising measure to enhance phytoremediation without impeding agricultural production. A Cd-hyperaccumulator, Solanum nigrum L. (S. nigrum), was intercropped with upland rice in a pot and rhizo-box experiment with Cd-contaminated soil to evaluate the combined effects of intercropping and arbuscular mycorrhizal fungi on plant growth and Cd accumulation. The results showed that, compared with monoculture, the combined treatments markedly decreased Cd concentration in rice parts, with the lowest Cd concentration in brown rice (reducing by 64.5%). The spatial distribution of root surface area and DTPA-Cd in the rhizo-box indicated competitive Cd uptake by neighbouring S. nigrum. Moreover, the combined treatments reduced Nramp5 expression but increased HMA3 levels in rice roots, leading to lower bioaccumulation and transfer coefficients. Additionally, fewer secreted organic acids and a higher rhizosphere pH were observed in rice. Conversely, the combined treatments promoted biomass, root length, root surface area, and decreased the rhizosphere pH in S. nigrum, thus increasing the Cd accumulation. Although the intercropping system with AMF inoculation notably reduced rice yield, the land-use efficiency was higher. These results provided insights into the role of AMF in the upland rice/S. nigrum system and demonstrated an alternative system for Cd phytoremediation.

Application of different foliar iron fertilizers for enhancing the growth and antioxidant capacity of rice and minimizing cadmium accumulation.

Iron (Fe) fertilizer can reduce cadmium (Cd) uptake and toxicity in rice, but the underlying mechanisms of Cd mitigation by different fertilizers are poorly understood. Here, pot experiments in rice were conducted to characterize the effects of four types of foliar-applied Fe fertilizer (chelated ferrous Fe, ferric Fe, ionic ferrous Fe, and ferric Fe) at three doses (20, 50, and 100mgL-1) on photosynthetic capacity, antioxidant ability, yield, and Cd accumulation in Cd-contaminated soil. The results showed that foliar Fe application increased the net photosynthesis rate by 19.3%, peroxidase (POD) by 18.2%, superoxide dismutase (SOD) by 26.9%, and catalase (CAT) by 19.6%, and led to a 7.2% increase in grain yield compared with the control. Moreover, foliar Fe application significantly reduced Cd accumulation by 15.9% in brown rice and decreased the translocation of Cd from roots to other plant tissues. Overall, application of moderate doses (50mgL-1) of chelated ferrous Fe was the most effective method for reducing Cd uptake (decreasing the Cd concentration in brown rice by 29.0%) and toxicity in rice (decreasing malondialdehyde by 23.2% and increasing POD, SOD, and CAT by 54.4%, 51.6%, and 45.7%, respectively), which may stem from the fact that chelated ferrous Fe was a more stable and bioavailable source of Fe for rice. The Cd concentration in rice had negative relationship with Fe concentration, and the translocation of Cd from root to the other tissues was reduced by the higher Fe nutrition status in leaf, suggesting that a high Fe supply may decrease Cd content by inhibiting the expression of the Fe transport system. These results indicate that foliar application of chelated ferrous Fe provides a promising alternative approach for enhancing growth and controlling Cd accumulation in rice plants. Furthermore, these results advance our understanding of the associations between plant Fe nutrition status and Cd accumulation.

Effects of Exogenous Phosphorus on Rice Growth and Cadmium Accumulation and Transportation Under Cadmium Stress

In this study, we investigated the effects of exogenous phosphorus on the accumulation and transportation of cadmium in rice plants through a hydroponic experiment. In the experiment, the rice variety was Huanghuazhan, P solution concentrations were 10.0-45.0 mg ·L-1 that was made using NaH2PO4, and Cd solution concentrations were 0.1 mg ·L-1 and 0.2 mg ·L-1. The results showed that: ① the biomass in all parts of rice plants and contents of photosynthetic pigment (chlorophyll a, chlorophyll b, and carotenoid) increased gradually with an increase in exogenous P. ② Content of Cd in rice stems, leaves, husk, and brown rice increased gradually with an increase in the amounts of exogenous P. The content of Cd in brown rice increased by 2.8%-22.8% and 40.9%-61.8% when treated with Cd concentrations of 0.1 mg ·L-1 and 0.2 mg ·L-1 in hydroponic solutions, respectively. ③ Cd accumulation in rice plants was accelerated due to the application of exogenous P. Cd accumulating amounts increased from 395.1 μg ·plant-1 to 542.6 μg ·plant-1 and 639.6 μg ·plant-1 to 1082.0 μg ·plant-1 when treated with Cd concentrations of 0.1 and 0.2 mg ·L-1 in hydroponic solutions, respectively. ④ With an increase in the applied amounts of exogenous P, the P/Cd quality ratio in rice roots increased, while those in rice stems, leaves, husks, and brown rice decreased; meanwhile, the Cd transfer coefficients from root to stem (TFroot-stem) and stem to leaf (TFstem-leaf) increased. This showed that there was a certain synergistic effect between P and Cd in the rice parts. Finally, the application of exogenous P promoted the transfer of Cd from the rice root to other rice tissues, resulting in a synergistic effect on Cd accumulation and transportation in various rice tissues and increased Cd contents in brown rice.

Role of passivators for Cd alleviation in rice-water spinach intercropping system

Soil pollution with cadmium (Cd) has posed a threat to our food safety. And rice consumption is the main source of Cd intake in China. Rice intercropping with water spinach is an efficient way for crop production and phytoremediation in Cd-contaminated soil. However, few people work on the Cd remediation by a combination of the passivation and intercropping. In this study, two passivators (the Si–Ca–Mg ameliorant and the Fe-modified biochar with microbial inoculants) were used in the monoculture and intercropping systems to evaluate the potential of co-effect of passivators and cropping systems on the plant growth and Cd phytoremediation. Results showed that the highest rice biomass and rice yield were presented in the intercropping system with the passivator additions, however, relatively lower biomass was showed in water spinach due to the competition with rice. And more Cd accumulated in water spinach while lower Cd in that of different rice parts. The intercropping system with the addition of the Si–Ca–Mg ameliorant and the microbial Fe-modified biochar significantly reduced the Cd contents in brown rice by 58.86% and 63.83%, while notably enhanced the Cd accumulation of water spinach by 32.0% and 22.0%, compared with the monoculture without passivation, respectively. This probably due to the increased pH, the lowered Cd availability in soil, and the reduced TF and BCF values in rice plants with passivator applications. Collectively, this study indicated that rice-water spinach intercropping, especially with the passivator additions, may function as an effective way for Cd remediation and guarantee rice grain safety.

Effects of Different Treatments with Water Management Combined with Leaf Spraying Silicon Fertilizer on Cd Accumulation in Rice

A field experiment involving eight treatments with water management combined with leaf spraying silicon fertilizer was conducted in a paddy field heavily contaminated with Cd (2.83 mg·kg-1) to study the effects of these treatments on rice growth and Cd accumulation in different rice tissues. The results showed that:① the treatments had no significant effects on rice plant height or number of tillers, but increased the biomass of brown rice by 1.7% to 25.0%. Among the eight treatments, that of water flooding during the rice maturation period plus leaf spraying silicon fertilizer (CY) resulted in the highest amount of brown rice yield. ② The treatment of conventional water management plus leaf spraying silicon fertilizer (Si) had no significant effect on the exchangeable Cd content and TCLP extractable Cd content in soil, whereas the other treatments reduced the exchangeable Cd content by 7.8%-42.6% and the TCLP extractable Cd content by 20.0%-40.8%. ③ The Si treatment could reduce the Cd content in various rice tissues, with an overall decrease of 19.0% in brown rice. The other treatments significantly reduced the Cd content in various rice tissues. The treatment of moisture during the rice maturation period plus leaf spraying silicon fertilizer (CS) resulted in the highest reduction in the Cd content in brown rice (44.0%), and was followed by the treatments of batch-type water flooding during the entire rice growth period plus leaf spraying silicon fertilizer (JX; 36.4%), and moisture during the rice pustulation period plus leaf spraying silicon fertilizer (GS; 31.8%). ④ For paddy-fields that are contaminated with Cd to medium and heavy levels, the CS and JX treatments are recommended to manage rice production in order to significantly reduce the Cd content of brown rice whilst having little effect on the rice yield.

Watering techniques and zero-valent iron biochar pH effects on As and Cd concentrations in rice rhizosphere soils, tissues and yield

Zero-valent iron amended biochar (ZVIB) has been proposed as a promising material in immobilizing heavy metals in paddy fields. In this study, the impacts of pH of ZVIB (pH 6.3 and pH 9.7) and watering management techniques (watering amount in the order of CON (control, 5/72)>3/72>1–3/72>3/100>1/72, with 5/72, for example, representing irrigation given to 5 cm above soil surface in 72 hr regular interval) on As and Cd bioavailability for rice and its grain yield (YieldBR) were investigated in a pot experiment. Brown rice As (AsBR) content was irrelative to the watering treatments, while significantly decreased (>50%) with the addition of both ZVIB materials. The diminutions of brown rice Cd (CdBR) content as well as the YieldBR were highly dependent on both the soil amendment materials’ pH and watering amount. Among all the watering treatments, 3/72 treatment (15% less irrigation water than the CON) with ZVIB 6.3 amendment was the optimum fit for simultaneous reduction of AsBR (50%) and CdBR contents (19%) as well as for significant increment (12%) of the YieldBR. Although high pH (9.7) ZVIB application could also efficiently decrease As and Cd contents in brown rice, it might risk grain yield lost if appropriate (e.g. 3/72 in our study) watering management technique was not chosen. Therefore, ZVIB would be an environmentally friendly option as an amendment material with proper selection of watering management technique to utilize As and Cd co-contaminated arable soils safely for paddy cultivation.

Effects and Mechanism of Continuous Liming on Cadmium Immobilization and Uptake by Rice Grown on Acid Paddy Soils

Lime application is the most effective agricultural practice for the reduction of cadmium (Cd) bioavailability in acid soils. This study was conducted to investigate the impact of continuous liming across five consecutive growing seasons on the remediation of Cd in acid paddy soils, as well as rice yield. Two rice cultivars, i.e., Zhuliangyou 819 and Xiangwanxian 12, were cultivated in Cd-contaminated paddy soil for five consecutive growing seasons from 2014 to 2018. The investigated lime levels were 0, 450, 900, 1350, 1800, 2250, 3000, and 3750 kg ha−1. Lime application significantly increased rice yield, soil pH, exchangeable soil Ca2+, and rice calcium (Ca) contents; besides, it reduced soil and rice Cd contents. The application of lime at the rate of 1350–2250 kg ha−1 significantly increased rice yield. Under continuous liming, rice yield obviously increased first and then decreased with the cumulative application of lime. The application of a cumulative lime amount of 18,000 kg ha−1 was identified as the critical transition point of soil pH, soil Cd, and rice Cd content. Application of lime up to or above 3000 kg ha−1 per season reduced Cd content in brown rice below 0.20 mg kg−1. The results suggest that the reduction in effective Cd content might be a result of the combined action of exchangeable soil Ca2+ and soil pH rather than being a direct effect of Ca2+. Therefore, acid Cd-contaminated paddy fields can realize the safe production of rice by the continuous application of an appropriate amount of lime.

Reduction of Cd accumulation in Se-biofortified rice by using fermented manure and fly ash.

Large areas of soils in China are contaminated with Cd and are deficient in Se. Therefore, here, we aimed to reduce Cd accumulation while increasing Se content in rice grain, and to elucidate the mechanisms associated. A greenhouse pot experiment was conducted to determine grain concentrations of Se and Cd upon foliar spraying of Se combined with the application of horse manure and/or fly ash to different contaminated soils containing Cd 0.51 (T1), 1.46 (T2), and 4.59mg Cd kg-1 (T3). The amount of Fe, Si, and Cd in root iron plaque, and concentrations of Cd and Si in rice tissues were also determined. Foliar spray of Se increased Se concentration in brown rice from approximately 0.04 to 0.15mgkg-1. Fly ash significantly reduced Cd concentration in brown rice from 0.07 to 0.05, 0.15 to 0.09, and 1.00 to 0.55mgkg-1 at the T1, T2, and T3 treatment levels, respectively, and soil Cd bioavailability (by at least 33.3%), while it increased Si content in rice roots and shoots by at least 34%. The increase of Si concentration in rice tissues inhibited Cd translocation to brown rice by at least 17%. Horse manure increased the formation of root Fe plaque by approximately 2.3-fold, which resulted in the significant reduction of Cd accumulation in brown rice, shoots, and roots by 36-56%. Thus, foliar spray of Se in combination with the application of fly ash and horse manure proved an effective method to produce Cd-low and Se-rich rice.

Application of inorganic passivators reduced Cd contents in brown rice in oilseed rape-rice rotation under Cd contaminated soil

Immobilization of heavy metals by the application of chemical amendments is an eco-friendly, economical and effective method to remediate cadmium (Cd) -contaminated soils. Field experiments were conducted during 2016–2018 following oilseed rape-rice rotation with the application of inorganic passivators i.e., slaked lime (CaOH2>95%) and sepiolite (SiO2>50%, MgO>20%). The experimental treatments were comprised of: rice planting in winter fallow and without passivator (F-PA0); fallow with slaked lime (F-PA1); fallow with sepiolite (F-PA2); oilseed rape–rice rotation without passivator (R-PA0); rotation with slaked lime (R-PA1); and rotation with sepiolite (R-PA2). The slaked lime and sepiolite were applied after the harvest of rape at 2000 and 5000 kg ha−1, respectively. Results revealed that the Cd contents were reduced by 47.44–49.03% in brown rice for F-PA2 and 9.54–42.66% in soil for R-PA2. The superoxide dismutase (SOD) activity was decreased by 10.65–17.98%, the malondialdehyde (MDA) contents were reduced by 28.57% whereas the proline content was decreased by 32.61% under R-PA2. In addition, the filled grain percentage was improved by 6.87% (F-PA2) and 3.70% (R-PA1), respectively. Overall, rice sown after oilseed rape gave better yields than sown after fallow fields while application of slaked lime and sepiolite as passivator could be a potential management option to grow crops in metal polluted soils.

Reducing Cd accumulation in rice grain with foliar application of glycerol and its mechanisms of Cd transport inhibition

Excessive cadmium (Cd) in rice grain has become a major global public health problem. Here, the effect of foliar glycerol application on Cd accumulation in brown rice was examined. Various spraying concentrations of glycerol between 0.4mM and 50mM were investigated and the results showed that 0.8 mM was the best application concentration for decreasing Cd content in brown rice. After different application period experiment, filling stage was considered as the optimal spraying time. 0.4mM–5mM glycerol application one time at the filling stage could significantly reduce Cd concentration in brown rice by 28.5%–60.4%. Cd transport factors (the ratio of brown rice and flag leaf/node) were decreased by 48.5% and 27.3%, respectively, with glycerol application. Glycerol application also significantly increased Cd concentration in soluble fraction in flag leaf while reduced inorganic Cd and water-soluble Cd in both flag leaf and stem. Our results showed foliar spraying glycerol inhibited Cd transport to brown rice through Cd compartmentalisation in the vacuole and transformation of cadmium chemical form. This study may provide a new method to effectively alleviate the problem of excessive Cd in rice.

Reduction of Soil Cadmium Activity and Rice Cadmium Content by 4-year-consecutive Application of Organic Fertilizer

Because commercial organic fertilizers may contain cadmium (Cd) and may cause the dual effect of "inhibition" and "activation" on Cd availability in paddy soil with organic fertilizer input, the reduction of rice Cd following organic fertilizer application is still uncertain. Herewith, typical purple mud paddy fields were selected in the eastern Hunan Province. The effect of commercial organic fertilizer input on Cd reduction of double-rice paddy ecosystem was monitored for four consecutive years. The relationships between brown rice Cd content, soil available Cd, and soil factors (pH, soil labile organic carbon fractions, and iron oxide) at different growth stages in double-rice paddy fields were investigated. Results showed that the input of organic fertilizer reduced the Cd content in brown rice by 28%-56%. Meanwhile, the decrease of Cd content in brown rice of late rice (43%-56%) was higher than that of early rice (28%-45%), and the inter-annual fluctuation of the decrease was relatively small. On the one hand, soil available Cd content decreased by 6%-7% during several growth stages of double-rice (from tillering peak stage to full heading stage) with organic fertilizer input. Additionally, the content of soil exchangeable Cd was decreased by 11%, whereas the content of organic bound Cd was increased by 14%. This directly reflects the decrease of soil Cd availability. On the other hand, the soil pH value was steadily increased by 0.1-0.3 units following organic fertilizer input, which promoted the development of soil from acidity to slight acidity. Besides, the content of soil active organic carbon (light fraction organic carbon, coarse particulate organic carbon, and fine particulate organic carbon) was increased significantly (53%, 77%, and 107%, respectively). This indirectly reflects the decrease in soil Cd availability. This study implies that the decrease of soil Cd availability may be the primary driving force for the reduction of rice Cd content with consecutive organic fertilizer input in purple mud paddy fields.

Silicon application improved the yield and nutritional quality while reduced cadmium concentration in rice.

Silicon (Si) is an essential nutrient for rice, but its effects on the yield and quality of rice under heavy metal stress remain uncertain. In this study, two typical paddy soils (acidic and calcareous purple soils) in the western region of Chongqing were selected for field plot experiment, with the purpose of understanding the effects of Si implementation methods on grain yields and cadmium (Cd) uptake, transport, and accumulation in the grain of a hybrid rice (Oryza sativa L, Changliangyou 772). Four treatments were set for the purposes including soil-based Si application, foliar spray of Si alone, foliar spray of selenium (Se)-containing Si fertilizer, and a control without Si application, respectively. The results indicated that the Si applications reduced Cd contents in brown rice by 11.45~51.85% in the slightly Cd-contaminated acidic purple soil (pH = 4.77, soil total Cd content 0.413 mg kg-1) and 26.93~43.77% in the purple calcareous paddy soil (pH = 7.77) with similar Cd-polluting levels. It is worth noting that the Cd content of conventional fertilized rice exceeds the Chinese National Food Safety Standard limit (0.2 mg kg-1, GB2762-2017) in the slightly Cd-contaminated acidic purple soil, and foliar spray treatments showed most effective effects that meets the safety threshold standard. Soil-based Si application reduced Cd accumulation in rice grains mainly by inhibiting the translocation of Cd from stem to the rice grain or root to stem, while foliar sprays of Si mainly by inhibiting the translocation of Cd from stem to brown rice. Si applications increased the rice yield by 17.15 to 25.45% in calcareous paddy soil with foliar spray being the best, while no significant yield increase was found in acidic paddy soil. Si and Se-containing Si fertilizer improved the nutritional quality of rice grain as indicated by the increases of Se, Si, and protein contents and the significant decreases of Cd contents in the rice grains. The comprehensive effects in improving the rice quality follow the order of foliar spray of Se-containing Si fertilizer > foliar spray of Si alone > soil-based Si application. Thus, foliar spray Si-containing fertilizer could be helpful in increasing rice yield while reducing the Cd uptake in rice grains, which might be a feasible approach in controlling Cd entry into the human body via crops.

Effect of Calcium Magnesium Phosphate on Remediation Paddy Soil Contaminated with Cadmium Using Lime and Sepiolite

The combined application of amendments, such as hydroxyhistidine and zeolite, can effectively reduce both the bioavailability of heavy metals in soil and the bioaccumulation of heavy metals by rice, thus improving the safety of agricultural products. In this work, the effect of calcium magnesium phosphorus fertilizer on the content of available Cd in paddy soil and Cd accumulation in various parts of rice by lime combined with sepiolite was studied using a plot experiment. The results show that calcium magnesium phosphorus fertilizer can significantly promote the remediation effect of lime combined with sepiolite. Compared with the treatment with lime combined with sepiolite, the application of calcium magnesium phosphorus fertilizer significantly decreases the available Cd content in the soil and the Cd accumulation in the brown rice. With calcium magnesium phosphorus fertilizer of 2250 kg·hm-2, Cd2+ in soil formed less soluble cadmium phosphate, the content of extractable, reducible and oxidizable Cd was reduced, and the percentage of available Cd content in the soil was significantly (P<0.05) reduced by 46.97%. Meanwhile, the Cd content in brown rice was decreased to 0.04 mg·kg-1, which is far lower than the level required by the National Standard for Food Safety (GB 2762-2017) (0.2 mg·kg-1). In addition, the production of brown rice was increased by 28.34%. Correlation analysis shows that the Cd content in rice roots, straw, and brown rice was positively correlated with the available Cd content in soil (P<0.01), and between the Cd content in brown rice and in roots and straw (P<0.01). In general, the results indicate that the available Cd content in soil was the key factor affecting the Cd content in brown rice. The application of calcium magnesium phosphorus fertilizer can improve the amendment of lime combined with sepiolite for available Cd in soil and reduce the Cd absorption of rice roots and straw so that the Cd content in brown rice is reduced. The results show that the application of calcium magnesium phosphorus fertilizer enhances the effect of reducing the Cd content in brown rice by lime combined with sepiolite. Finally, it can both meet the safety requirements of brown rice quality and increase the yield of brown rice in Cd-contaminated paddy soil.

Cadmium accumulation in rice (Oryza sativa L.) alleviated by basal alkaline fertilizers followed by topdressing of manganese fertilizer

Rice is a main source of dietary cadmium (Cd), thus, how to reduce the Cd concentration in brown rice has received extensive attention worldwide. In three acidic paddy soils slightly to moderately contaminated with Cd, a series of field experiments were conducted to evaluate the effects of different proportions of nitrogen-phosphorus-potassium (N-P-K) fertilizer (urea, calcium magnesium phosphate, and potassium carbonate, respectively) alone or coupled with a topdressing of manganese (Mn) fertilizer at the tillering stage on reducing Cd bioavailability in soil and uptake in rice. The rational application of N-P-K fertilizer not only provided the basic nutrients to promote the normal growth of rice but also increased soil pH and thereby reduced the Cd bioavailability in soil. The Mg(NO3)2-extracted Cd concentrations in the three soils were reduced by 26.46–56.53%, while TCLP-extracted Cd were reduced by 19.87–45.41%, with little influence on soil cation exchange capacity (CEC) and organic matter (OM). The application of Mn fertilizer at the tillering stage increased Mn and Cd sequestration in the iron plaque. The Mn content in iron plaque increased by 15.71–58.67% and a significant positive correlation between Cd and Mn was observed at the three sites. Collectively, this combined method of fertilization significantly reduced Cd accumulation in rice tissues, the Cd concentrations in roots of treated plants decreased by 11.18–37.78%, whereas the concentrations in straw decreased by 13.16–41.03%. Particularly to brown rice, in which accumulation decreased by 25.19–44.70%, 37.35–47.84%, and 38.00–60.88% in three typical paddy fields, but no significant effect was observed for the Cd translocation factors (TF) among rice tissues. Thus, the basal application of combined urea and alkaline inorganic fertilizers followed by topdressing of Mn fertilizer may be a promising and cost-effective tactics for the remediation of Cd-contaminated paddy soils.