Cd Concentration In Rice Grains Research Articles

Effects of different potassium fertilizers on cadmium uptake by three crops.

Cadmium contamination of agricultural soils has aroused worldwide concern because of the threats posed to human health through accumulation in food chains. A greenhouse pot experiment was conducted with in situ Cd-contaminated soil to study the influence of different potassium fertilizers (KCl, K2SO4, and KNO3) on Cd accumulation in rice, wheat, and pak choi as well as the NH4NO3-extractable Cd (NEX-Cd) content in soils. In our study, rice and wheat biomass increased in the presence of K fertilizers, whereas pak choi biomass remained stable. Moreover, our experiment demonstrated that Cl- increased Cd uptake by crops more effectively than SO42- or NO3-. The KCl treatments increased the Cd content of all three crops; as the KCl dose was increased, the Cd content of rice grains, wheat grains, and pak choi shoots increased by 10.8-192.8%, 17.1-67.7%, and 15.1-40.4%, respectively. The KNO3 treatment also increased the Cd content of all three crops; however, the K2SO4 treatment only slightly increased the Cd content of wheat and pak choi and greatly decreased the Cd content of rice. In addition, both of the NEX-Cd content of wheat soil and pak choi soil were much higher than that of rice paddy soil. The KCl treatment resulted in a significant increase in the NEX-Cd content of rice paddy soil, but there were no significant differences in the NEX-Cd content of wheat soil or pak choi soil, regardless of which types or doses of K fertilizers were supplied. Based on these results, when K fertilizers are applied to Cd-contaminated soils, both types and doses should be carefully considered to mitigate Cd accumulation in crops, especially the edible part.

Agronomic Management and Rice Varieties Controlling Cd Bioaccumulation in Rice.

Selection of rice varieties and application of amendments are effective measures to ensure food safety. Here we report that in the non-Cd area, the grain quality of all rice varieties met the Chinese National Grain Safety Standards (CNGSS). In the high-Cd area, rice varieties showed significant different bioaccumulation of Cd with lower rice yields than those in non-Cd area with the average decrease of 31.1%. There was a negative correlation between grain Cd content and yields. A total of 19 rice varieties were selected as low Cd accumulating rice varieties and their Cd content met CNGSS in the low-Cd area. Six of them met CNGSS in the high-Cd area. The application of amendments significantly reduced Cd content in rice grains by 1.0–84.7% with an average of 52.6% and 13 of varieties met CNGSS. The amendments reduced available Cd content in soils by 1.1–75.8% but had no significant effects on rice yields. Therefore, the current study implied that proper agronomic management with selection of rice varieties and soil amendments was essential in controlling Cd accumulation in rice grains.

Mitigation of Cd accumulation in rice from Cd-contaminated paddy soil by foliar dressing of S and P

Cadmium (Cd)-contaminated paddy soil has become a global agricultural safety issue. The application of foliage dressing with mineral elements to alleviate Cd toxicity in rice might offer a cost-effective and practical strategy for safe food production. In this study, a pot experiment was conducted to optimize foliar composition and dosage. Field experiments in two consecutive rice seasons were performed to investigate the effectiveness and mechanisms of foliage dressing. Foliar spray of S, P, and a mixture of both were effective to reduce the Cd concentration in rice grain. The maximum decrease by leaf–grain translocation was achieved at 84%, and the maximum decrease of bio-concentration was 69% in the stem. The reduction of Cd concentration in rice decreased the direct damage to the photosynthetic system, and then increased the rice growth. Foliage dressing relieved the oxidative stress of Cd to rice by decreasing the MDA content, and increasing antioxidant enzyme activities. Foliar spray with S likely reduced Cd accumulation in rice by minimizing the production of reactive oxygen species, improving the activities of enzymatic and non-enzymatic antioxidant defense systems, and manipulating glutathione synthesis. The detoxification of foliar spray with P was originated from the decrease of Cd translocation and maintaining photosynthetic machinery. These results indicated that foliage dressing with S and P has great potential for the remediation of vast agricultural fields.

Immobilization of Cadmium in Contaminated Soil Using Organic Amendments and Its Effects on Rice Growth Performance

Cadmium (Cd) contamination of rice is a serious public health concern in certain parts of the world. Amendment application based on local organic materials (e.g., manures, compost) is considered effective for reducing plant-available Cd in soil. In this study, two Thai rice (Oryza sativa L) varieties, Chorati and Mali Daeng, were grown in Cd-contaminated soil amended with cow manure, pig manure, organic fertilizer, and leonardite in a mesocosm system. Organic amendment treatments reduced Cd availability in soil. Specific effects of amendments were a function of amendment type and rice variety. Cow manure and leonardite substantially increased growth of the Mali Daeng variety in Cd-contaminated soils; however, there was no significant effect on total biomass of Chorati. Leonardite significantly enhanced grain production of Chorati (12.2 g plant−1) and reduced Cd content in rice grain to 0.14 mg kg−1 which is considered safe for consumption. Leonardite increased CEC in contaminated soil which helped reduce Cd bioavailability to plants. Both rice varieties had ‘excluder potential,’ as they accumulated Cd primarily in roots with translocation factor (TF) values < 1. Root anatomical analysis revealed that leonardite and pig manure treatments increased metaxylem vessel area, which could result in the enhancement of TF in the Chorati variety. However, any increase in TF was not associated with Cd content in rice grains. Our findings indicate that organic amendments immobilized Cd in soil and enhanced rice growth and production while reducing Cd content in rice grain. We emphasize here that the selection of cultivars and amendments plays a key role in the success of low-Cd rice production.

Use of soil amendments to reduce cadmium accumulation in rice by changing Cd distribution in soil aggregates

The objectives of this study were to investigate the response of cadmium (Cd) distribution and stability in soil aggregates as affected by applying different amendments and to understand the relationship between changes in soil aggregates and alleviation of Cd phytotoxicity to rice after amendment application. In the present study, rice (Oryza sativa L.) was cultivated on a Cd-polluted soil. Five soil amendments were applied, which are as follows: rice husk biochar (BC), Fe-added rice husk biochar (Fe-BC), attapulgite-based mixture (AM), zeolite-based mixture (ZM), and cow manure-based mixture (MM). The effect on Cd redistribution in soil and Cd accumulation in rice plant was evaluated. The results showed that the five amendments applied at the rate of 3% (w/w) significantly increased soil pH and decreased Cd mobility in soil and Cd accumulation in rice plants. The reduction rate of Cd content in rice grains ranged from 41 to 62% after amendment application. The remediation efficiency of the different amendments for decreasing Cd accumulation in rice tissues followed the order of Fe-BC > MM > BC > ZM > AM. Adding amendments promoted the formation of large aggregates (0.2-2.0mm) with more mass loading of Cd and enhanced aggregate stability. Comparatively, Fe-BC was more effective than others for remediation of acid Cd-polluted paddy soil, as a significantly decreased Cd concentration in rice grain after its application was observed. Structural equation modeling (SEM) analysis revealed that DTPA-extractable Cd in small aggregates was the main factor affecting Cd accumulation in rice grain; soil pH directly affected aggregate stability; and aggregate stability was closely related to Cd availability in different size soil particles. These results indicated that the applied amendments were effective in reducing Cd bioavailability, most likely through raising the soil pH, improving aggregate stability, and re-distributing Cd from smaller soil aggregates to larger ones.

Biochar significantly alters rhizobacterial communities and reduces Cd concentration in rice grains grown on Cd-contaminated soils

Cadmium (Cd) contamination poses a serious problem in paddy soils. Biochar is frequently reported to deactivate Cd in soils and reduce Cd accumulation in rice plants, but few studies have addressed whether and how biochar affected the microbial communities in rice rhizosphere, which was an important factor determining the metal bioavailability and plant growth. In this study, biochar was pyrolyzed from bamboo (Phyllostachys heterocycla) chips at 350 °C. By using ICP-MS analysis and 16S rRNA gene sequencing, the impact of the biochar on Cd uptake by rice and on rhizospheric bacterial communities was investigated in both high-accumulating (HA) and low-accumulating (LA) rice cultivars grown in soils artificially contaminated with different Cd levels. Applied biochar significantly reduced Cd contents in rice plants of both cultivars, with substantially lower grain Cd contents for LA grown in highly contaminated soil. Soil pH was slightly increased by the applied biochar. Cd bioavailability was somehow reduced in soils, but not as significant as the reduction of Cd contents in rice plants. More interestingly, biochar application significantly altered the rhizobacterial community: it stimulated growth-promoting bacteria, such as Kaistobacter, Sphingobium (order Sphingomonadales), and Rhizobiaceae (order Rhizobiales); improved natural barrier formation and the transformation of metal mobilization around the rhizosphere mediated by, e.g., Rhodocyclaceae (class Betaproteobacteria) and Geobacter (class Deltaproteobacteria); and enhanced colonization of the LA rhizosphere possibly by taxa involved in Cd immobilization (Desulfovibrionales and Desulfobacterales). These results indicate that biochar application significantly reduces Cd uptake and accumulation by altering the rhizosphere bacterial community in rice grown on Cd-contaminated soils. The baseline data generated in this study provide insights that pave the way toward safer rice production.

Effectiveness of simultaneous foliar application of Zn and Mn or P to reduce Cd concentration in rice grains: a field study.

Excess cadmium (Cd) in agricultural soils can be taken up by rice plants and concentrated in the grain, presenting a human health risk. In this study, we field tested the effects of three foliar treatments (zinc (Zn) alone, or combined with manganese (ZnMn) or phosphorus (ZnP)) on the Cd concentration and grain yield of six rice cultivars (C Liangyou 7, Fengyuanyou 272, Xiangwanxian 12, Tianyouhuazhan, Xiangwanxian 13, and Jinyou 284) at the grain filling stage. Our results showed that rice yield and Cd, Zn, Mn, P, and K concentrations were significantly different among the cultivars (p < 0.05); for example, Jinyou 284 recorded lower Cd levels than any other cultivar. Application of Zn, ZnMn, and ZnP had no significant effect on rice yield and Mn, P, and K concentrations for all cultivars. Compared with the control, Cd concentrations after treatment with Zn, ZnMn, and ZnP decreased by 19.03-32.55%, 36.63-55.78% (p < 0.05), and 25.72-49.10%, respectively, while Zn concentrations increased by 11.02-29.38%, 10.63-32.67%, and 11.97-36.82%, respectively. There was a significant negative correlation between Cd and Zn concentrations (p < 0.01). All three treatments increased Zn and reduced Cd concentration in rice grains, though ZnMn was most effective. Therefore, cultivar selection and Zn fertilizer application are effective strategies to minimize Cd concentration in rice grains. However, the lowest result still exceeded the Chinese Cd safety limit (0.2mg Cd kg-1) by a factor of 2.6, demonstrating that additional effective measures should be simultaneously used to further reduce the accumulation of Cd in rice grains.

Effect of sulfur and sulfur-iron modified biochar on cadmium availability and transfer in the soil–rice system

Cadmium (Cd) contamination in paddy soils has aroused global concern. Sulfur modified biochar (BC) could combine the benefits of BC and S for Cd remediation. However, no information is available on the impact of sulfur modified biochar on Cd phytoavailability in paddy soils. In this study, a pot experiment was conducted to investigate the effect of sulfur modified biochar (S-BC) and sulfur and iron (Fe) modified biochar (S-Fe BC) on Cd mobility and Cd transfer in the soil-rice system. The application of S-BC and S-Fe BC effectively reduced pore water Cd in the rhizosphere and non-rhizosphere pore water throughout the rice growth stages. S-BC and S-Fe BC addition increased the total chlorophyll content, as well as the root, shoot and grain biomasses of rice. Furthermore, S-BC and S-Fe BC amendments greatly increase the formation of Fe plaque on rice root surface, thus decreasing Cd accumulation in different rice tissues. In particular, S-Fe BC supplementation significantly reduced the Cd concentration in rice grains to 0.018 mg kg−1 in Cd-contaminated soil, which was lower than the China National standard for food contamination limit (0.2 mg kg−1 Cd). Sequential extraction results showed that S-BC and S-Fe BC can promote the transfer of exchangeable Cd to Fe-Mn oxide, organic and residual bound forms which reduce Cd in paddy soils. Thus, the amendment of S-Fe BC to Cd-contaminated paddy soil is an effective strategy to decrease Cd accumulation in rice grains and thereby protect public health.

Effects of soil properties on the Cd threshold in typical paddy soils using BCR sequential extraction

Soil quality standards used for agricultural land do not fully consider the effect of soil properties on cadmium (Cd) uptake by crops. A pot experiment with six types of soil derived from two typical soil parent materials was conducted to determine the effect of soil properties on the soil Cd fractions and Cd concentration in rice grain. The results of soil Cd fractions obtained by the Community Bureau of Reference sequential extraction revealed significant differences among soil types. Redundancy analysis showed that soil pH was the most influential factor affecting soil Cd fractions for red paddy soil, but soil pH, soil organic matter, and clay content were significant for purple paddy soil. Stepwise multiple linear regression analysis showed that soil clay and soil organic matter were the two most significant variables contributing to soil Cd threshold, explaining 97.8% of the variance. These results suggest that soil clay and organic matter contents should be considered when evaluating the risk of Cd in paddy soil.

Impact of Alternate Wetting and Drying Irrigation on Arsenic Uptake and Speciation in Flooded Rice Systems

Alternate wetting and drying (AWD) irrigation can be used to promote oxic soil conditions and decrease arsenic (As) mobility and uptake into rice plants. However, scant information is available quantifying plant As speciation and uptake at the field scale for AWD with different soil drying severities. It is hypothesized that as the severity of soil drying increases, plant uptake and subsequent accumulation of both inorganic and organic As in the grain will decrease. However, since AWD can increase cadmium (Cd) bioavailability, Cd concentrations in rice grains should be evaluated concomitant to As. In this two-year field study, As and Cd uptake were examined, with routine plant and water sampling during the growing seasons, under three AWD practices varying in soil drying severity (from most to least severe: AWD25: drying to 25% volumetric water content at the root zone; AWD35: to 35%; AWDS: Safe AWD, drying to perched water table 15 cm below the soil surface), compared to a continuous flooding (CF) control. Arsenic speciation was also analyzed in grain and vegetative tissues. AWD25 and AWD35 decreased As accumulation in roots and straws by a similar amount compared to CF, leading to a 41-68% decrease in grain total As concentration. Speciation analysis revealed that AWD25 and AWD35 decreased grain concentration of organic As by 70-100% and inorganic As by 14-61% compared to CF. In contrast, AWDS did not decrease As uptake by rice compared to CF. Grain Cd levels were 6.5 μg kg−1 in CF, 16.6 μg kg−1 in AWD35, and 27.4 μg kg−1 in AWD25, suggesting AWD35 could serve as a mitigation option for As, while minimizing Cd accumulation.

Effect of Particulate Organic Matter on Cadmium Uptake and Transport in Rice

A pot experiment was carried out to investigate the effects and mechanism of particulate organic matter (POM) on cadmium uptake of rice on purple paddy soil. Organic carbon content in soil and POM and Cd content in POM and rice were analyzed. The results showed that the contents of total soil organic carbon (SOC), dissolved organic carbon (DOC), organic carbon in POM (POM-C), Cd in POM (POM-Cd), and the Cd enrichment factor in POM increased with the application of POM. When POM was applied at a rate of 2.5 g·kg-1, the proportion of POM-C and POM-Cd in soil significantly increased. Application of POM also increased rice plant biomass and enhanced the accumulation of Cd in rice. The Cd content was reduced by 24%-42% in rice roots and increased by 9%-30% in rice shoots with POM application, whereas it was reduced by 17% and 36% in rice grains when the application of POM was 0.5 g·kg-1 and 1.0 g·kg-1, respectively, but increased by 39% when the application of POM was 2.5 g·kg-1. Application of POM had no significant effect on the distribution of Cd in rice roots and shoots, but significantly affected the distribution of Cd in rice grains. The transportation of Cd from shoots to grains was inhibited at low rates of POM, but was promoted at high rates of POM, and consequently increased the Cd content in rice grains. Correlation analyses showed that the content of soil available Cd was the main factor affecting Cd accumulation in rice shoots, and the total content of POM-Cd in soil was the main factor affecting Cd accumulation in rice grains. Therefore, the addition of POM to soil could affect the Cd uptake of rice by changing the content of SOC, DOC, POM-C, POM-Cd, and available Cd in paddy soil.

A novel method for predicting cadmium concentration in rice grain using genetic algorithm and back-propagation neural network based on soil properties

Heavy metal pollution is a global ecological safety issue, especially in crops, where it directly threatens regional ecological security and human health. In this study, the back-propagation (BP) neural network optimized by the genetic algorithm (GA) was used to predict the concentration of cadmium (Cd) in rice grain based on influencing factors. As an intelligent information processing system, the GA-BP neural network could learn the laws of Cd movement in the soil-crop system through its own training and use the soil properties to predict the concentration of Cd in grain with high accuracy. The total soil Cd concentration, clay content, Ni concentration, cation exchange capacity (CEC), organic matter (OM), and pH have important impacts and interactions on Cd concentration in rice grain were selected as input factors of the prediction model based on Pearson's correlation analysis and GeoDetector. By using GA to optimize the initial weight, the prediction accuracy of the GA-BP neural network model was optimal compared with the BP neural network model and multiple regression analysis. Based on the Cd concentration predicted in grain by the model, human exposure and health risk can be assessed quickly, enabling measures to be taken in time to reduce the transfer of Cd from soil to the food chain.

Long-term effects of biochar on rice production and stabilisation of cadmium and arsenic levels in contaminated paddy soils

ABSTRACTHeavy metal contamination in the paddy soils of China is a serious concern because of its health risk through transfer in food chains. A field experiment was conducted in 2014–2015 to investigate the long-term effects of different biochar amendments on cadmium (Cd) and arsenic (As) immobilisation in a contaminated paddy field in southern China. Two types of biochar, a rice-straw-derived biochar (RB) and a coconut-by-product-derived biochar (CB), were amended separately to determine their impacts on rice yield and their efficacy in reducing Cd and As in rice. The two-year field experiment showed that biochar amendments significantly improved the rice yields and that CB is superior to RB, especially in the first growth season. Using a large amount of biochar amendment (22.5tha–1) significantly increased soil pH and total organic carbon, and concomitantly decreased the Cd content in rice grains over the four growth seasons, regardless of biochar type and application rate. Arsenic levels in rice were similar to the control, and results from this study suggest that there was a sustainable effect of biochar on Cd sequestration in soil and reduction of Cd accumulation in rice for at least two years. Biochar amendment in soil could be considered as a sustainable, reliable and cost-effective option to remediate heavy metal contamination in paddy fields for long periods.

Strategic use of water: a step toward cadmium-free basmati rice (Oryza sativa L.)

Sewage contains several trace elements of environmental concern, and cadmium (Cd) is one of the most mobile elements in soil–plant system that can pose drastic effects on plants and human health due to its long persistence and non-biodegradability nature in environment. It is necessary to prevent its entry into food chain for better food quality and human health. Present study was designed to evaluate the effectiveness of different water management practices, viz. W1: flooding throughout the growing season, W2: flooding after 4 days of disappearance of standing water (DAD), W3: flooding till heading and after that flooding of soil after 4 days of DAD, W4: Aerobic condition throughout growing season (flooding after 8 days) for reducing Cd concentration in rice grain grown under varying levels of Cd (0, 20, 40 mg kg−1) spiked soil. Results revealed that grain yield declined with increasing Cd levels but maximum plant height (89.3 cm), straw yield (16.9 g) and grain yield (22.5 g pot−1) was observed where pots were flooded till heading and thereafter flooding. Cadmium concentration increased with increasing concentration of Cd in soil. Further, it is added that the lowest Cd concentration in shoot, grain and husk and translocation factor were observed under W3 when the soil was spiked with 40 mg kg−1. In crux, continuous flooding till heading and thereafter flooding after 4 DAD can significantly decrease the grain Cd concentration without compromise on yield.

Predicting spatial and temporal variation of Cd concentration in rice grains in the Lower Changjiang Plain during 2004–2014 based on soil geochemical survey data with GIS

The Lower Changjiang Plain (LCP) is one of the most important regions for rice production in China. A significant increase of soil Cd concentration (Cdsoil) with the decrease of soil pH has been found during the recent decade (2004–2014) on the regional scale. In order to evaluate the effects of the changing soil parameters on Cd concentrations in rice products, a linear mixed model was built to relate the carefully selected soil parameters to Cd concentration in rice grains (Cdrice) with the random component modelled as a spatially correlated random variable. With the 2004 soil geochemical survey data, and the 2014 soil monitoring data, spatial and temporal variation of Cdrice was predicted in Geographical Information System (GIS) with the model. It was found that although the predicted Cdrice in 2014 is still under the food standard limitation of 200 μg/kg, it has increased significantly (p < 0.001) over this decade, with the median increased from 19.06 μg/kg in 2004 to 24.11 μg/kg (in dry weight basis) in 2014. The result also showed that the spatial patterns of Cdrice did not coincide with those of the soil pollution levels calculated from the environmental quality standard of China (GB15618-1995), which implies that the traditional soil Cd pollution assessment needs to be improved with more consideration of its bio-availability.

Biochar reduces cadmium accumulation in rice grains in a tungsten mining area-field experiment: effects of biochar type and dosage, rice variety, and pollution level.

Cadmium (Cd)-contaminated rice (Oryza sativa) in Southern China is a great threat to food security, and the paddy soil remediation is urgently needed to reduce Cd accumulation in rice. Application of biochar could effectively immobilize soil Cd and reduce Cd uptake by rice. Fields that were applied with soil treatments including control and 15 and 30tha-1 each hickory nut shell-derived biochar (KC) or maize straw-derived biochar (MC), and grown with two rice varieties (hybrid rice and late japonica rice) were selected for this study. The long-term effect of biochars on decreasing Cd bioavailability in paddy soils was evaluated. The results showed when MC was applied at 15tha-1, DTPA-Cd (soil cadmium extracted by diethylenetriamine pentaacetic acid) was reduced by 20.0 and 34.5% in Field A (slightly Cd pollution) and B (moderately Cd pollution), respectively. In Field B, soil DTPA-Cd concentrations with application of 30 t ha-1 biochars were all lower than that of 15tha-1 biochar, but there were no significant differences between the two types of biochars. Cd concentration in rice grains and straws of hybrid rice are two times more than those of late japonica rice. Cd bio-concentration factor both of grains and straw was significantly increased by biochar application, which in Field A was higher than that in Field B. Our results suggest that biochars reduce Cd accumulation in rice grains by immobilizing soil Cd. KC has a higher potential in lowering Cd bioavailability than MC. Hybrid rice should be prohibited to cultivate in these areas.

Attenuation of inorganic arsenic and cadmium in rice grains using by-product iron materials from the casting industry combined with different water management practices

ABSTRACTWe examined the effect of two types of iron (Fe) material produced by the casting industry (spent steel shot [SSS] and residual iron material from steel shot production) on the mobility of arsenic (As) and cadmium (Cd) in soils. We also examined the uptake of these elements by rice plants (Oryza Sativa L.) under continuously flooded (CF) and water-saving (WS) cultivation. The application of both Fe materials (at 10 and 30 t ha‒1) strictly limited As mobilization in soils under CF cultivation. As a result, As uptake by rice plants declined, along with the total and inorganic As (iAs) concentration in rice grains. In comparison, As immobilization caused by the application of Fe material was less clear under WS cultivation. The rate of Fe material application was negatively correlated with As uptake by rice plants. It was also negatively correlated with total and iAs concentration in rice grains under both water management practices. The combination of applying Fe materials and WS cultivation decreased iAs concentration in rice grains to approximately one-fifth of that in rice grains produced from plants grown on soils without Fe material application under CF cultivation. CF cultivation strictly decreased dissolved Cd in soils, as well as Cd in rice grains with and without Fe material application. The application of Fe materials decreased Cd mobility and, hence, Cd uptake in rice plants, ultimately reducing the accumulation of Cd in rice grains under WS cultivation. Residual Fe material had a statistically greater effect at attenuating Cd accumulation in rice grains than SSS. The present study demonstrated the potential of combining by-product Fe material application and water management practices to attenuate iAs and/or Cd concentrations in rice grains. Practical countermeasures should be carefully adopted that consider the existing risks of iAs and Cd on each paddy field, and the combined effect of Fe material application and water management practices.

Quantitative Relationship Between Paddy Soil Properties and Cadmium Content in Rice Grains

Rice is a crop with the potential for high accumulation of Cd, which can be affected by many factors. Sixty pairs of soil and rice samples from different plots were collected and analyzed, in order to understand the quantitative relationships between the Cd content in soil and the properties of soil and the Cd content in rice grains under field conditions, by simple and multiple regression analyses. The results showed that the Cd contents in soil and rice grains ranged from 0.15-2.54 mg·kg-1 and 0.02-2.00 mg·kg-1, respectively. According to the result of simple regression analysis, there were significantly positive correlations (P<0.01) between the Cd contents in soil and rice grains (r=0.392); the pH, SOM, and CEC in soil also had certain effects on Cd accumulation in rice grains, which were not significant, however. When the soil pH was<6.5, the Cd content in rice grains increased with increasing soil pH, but decreased with increasing soil pH when the soil pH was>6.5. The Cd content, pH, SOM, and CEC in the soil and the Cd content in rice grains were analyzed by multiple regression analysis, and five equations, which all reached extremely significant levels (P<0.01), were obtained. The equation that included the four variables (Cd content, pH, SOM, and CEC in soil) had the most r, and it could predict the Cd content in rice grains better, given the conditions of the present study.

Influence of different sewage sludges and composts on growth, yield, and trace elements accumulation in rice and wheat

AbstractThe use of sewage sludge (SS) and solid waste composts in agriculture is considered as one of the best disposal options. In this study, impact of different composts and SS was evaluated on the soil quality, growth, and yield performance of rice and wheat crops. Four types of composts and SS were collected from different sources and applied in soil at 0.5% (5 g kg−1 soil) and 1.0% (10 g kg−1 soil) in comparison with chemical fertilizer (no SS/compost). The application of all types of composts at all the tested rates increased the straw and grain yields of both the crops compared with control. Nevertheless, application of Lahore compost and all SS (1.0%) resulted in a significant increase in the concentration of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) in plant parts. The Cd concentration in rice grains with Lahore compost and Kasur SS applied at the rate of 1.0% was above the safe limit. The trace elements in wheat grains with all composts and SS at all the tested rates remained within safe limits. The release of amendment bound trace elements in soil solution was highly dependent upon dissolved organic carbon and concentration of these trace elements especially for Cu and Zn. Application of SS at low level (0.5%) and compost (except Lahore compost) at both levels could be a better strategy to exploit their benefits in terms of crop performance and soil quality. However, application of SS and compost at high rates may lead to accumulation of trace elements in rice grains limiting its suitability for human consumption.

Manganese, Zinc, and pH Affect Cadmium Accumulation in Rice Grain under Field Conditions in Southern China.

Very little has been reported on the effects of pH, Zn, and Mn on Cd uptake in rice ( L.) and their levels under field conditions. Rice accumulates a high concentration of Cd in acid soils, even at low soil Cd levels. Lime (CaO) was spread at 1200 kg ha on the topsoil of a rice field during the tillering stage. Effects of liming on rice Cd, soil pH, and amorphous Mn (MnO-AM) were then investigated. Slight increases in pH from 5.17 to 5.45 and MnO-AM from 66.3 to 82.1 mg kg were observed after liming. The proportion of rice samples with a Cd concentration greater than the Chinese rice Cd standard (0.2 mg kg dry wt. in grain) decreased by ∼15%. The pH, which varied from 4.8 to 5.8, did not significantly affect rice Cd, whereas soil Cd and Zn had a significantly positive effect, together accounting for ∼14% of the variance. Soil Mn had significantly negative effects on rice Cd, accounting for >18% of the variance. For a Cd concentration <0.2 mg kg dry wt. in rice grain, the critical pH value in paddy soil was ∼5.7, and that for Mn at pH 4.8 to 5.8 was ∼300 mg kg. Our findings showed that Cd concentration in rice grain in an acid paddy soil increased with an increase of Zn and a decrease of Mn when these metals were at sufficient levels.