Taolin Zhang

Effects of several amendments on rice growth and uptake of copper and cadmium from a contaminated soil

Heavy metals in variable charge soil are highly bioavailable and easy to transfer into plants. Since it is impossible to completely eliminate rice planting on contaminated soils, some remediation and mitigation techniques are necessary to reduce metal bioavailability and uptake by rice. This pot experiment investigated the effects of seven amendments on the growth of rice and uptake of heavy metals from a paddy soil that was contaminated by copper and cadmium. The best results were from the application of limestone that increased grain yield by 12.5-16.5 fold, and decreased Cu and Cd concentrations in grain by 23.0%-50.4%. Application of calcium magnesium phosphate, calcium silicate, pig manure, and peat also increased the grain yield by 0.3-15.3 fold, and effectively decreased the Cu and Cd concentrations in grain. Cd concentration in grain was slightly reduced in the treatments of Chinese milk vetch and zinc sulfate. Concentrations of Cu and Cd in grain and straw were dependent on the available Cu and Cd in the soils, and soil available Cu and Cd were significantly affected by the soil pH.

Carbon Dioxide Flux in a Subtropical Agricultural Soil of China

Red soils, one of the typical agricultural soils in subtropical China, play important roles in the global carbon budget due to their large potential to sequester C and replenish atmospheric C through soil CO2 flux. Soil CO2 emission was measured using a closed chamber method to quantify year-round soil flux and to determine the contribution of soil temperature, dissolved organic carbon (DOC) and soil moisture content to soil CO2 flux. Soil flux was determined every 10 d during the experiment from August 1999 to July 2000, at the Ecological Station of Red Soil (the Chinese Academy of Sciences). In addition, diurnal flux measurements for 24 hr were made on August 5 and November 5, 1999 during this experiment. The average soil fluxes from 2 hr measurements between 9:00 and 11:00 can be regarded as the representative of daily averages. Soil CO2 fluxes were generally higher in summer and autumn than in winter and spring, averaged 7.16 and 0.86 g CO2 m-2 d-1 for the former and latter two seasons, and had a seasonal pattern more similar to soil temperature and DOC than soil moisture. The annual soil CO2 flux was estimated as 1.65 kg CO2 m-2 yr-1. Regressed separately, the reasons for soil flux variability were 86.6% from soil temperature, 58.8% from DOC, and 26.3% from soil moisture, respectively. Regressed jointly, a multiple equation was developed by the above three variables that explained 85.2% of the flux variance, but only soil temperature was the dominant factor affectingsoil flux, with significant partial correlation coefficient (r2 = 0.804, p ≤ 0.05), through stepwise regression analysis. Based on the exponential equation using soil temperature, the predicted fluxes were calculated and were essentially equal to the measured ones throughout the experiment. No significant difference was detected between the predicted average and the measured one. The exponential relationship describing the response of soil CO2 flux to the changes in soil temperature should accurately predict soil CO2 flux from red soils in subtropical China.

The Composition of Root Exudates from Two Different Resistant Peanut Cultivars and Their Effects on the Growth of Soil-Borne Pathogen

The high incidence of various soil-borne diseases in the monoculture field of peanut is a major production constraint in the red soil regions of southern China. The peanut root exudates are generally thought to play an important role in regulating soil-borne pathogens. The responses of the soil-borne pathogens, Fusarium oxysporum and F. solani to the peanut root exudates were studied using one susceptible cultivar Ganhua-5 (GH) and one mid-resistant cultivar Quanhua-7 (QH) as the test materials. The components and contents of the amino acids, sugars and phenolic acids in the peanut root exudates were determined. The results demonstrated that the root exudates from both susceptible and mid-resistant cultivars significantly promoted the spore germination, sporulation and mycelial growth of soil-borne pathogens, F. oxysporum, F. solani compared with the control. The extent of the stimulation was depended on the strains of the Fusarium tested, and gradually increased with the increased concentrations of peanut root exudates. HPLC analysis showed that the contents of sugars, alanine, total amino acids in the root exudates of GH were significantly higher than that in QH, whereas the contents of p-hydroxybenzoic acid, benzoic acid, p-coumaric acid and total phenolic acids were significantly lower than that in QH. Results of the study suggested that the differences in the root exudates from the different peanut cultivars were considered to regulate the wilt-resistance mechanism in the rhizosphere of peanut. The results are therefore crucial important to illustrate the mechanism of peanut replanted obstacle, and to develop its control techniques in the red soil regions of southern China.

Prediction Model for Cadmium Transfer from Soil to Carrot (Daucus carota L.) and Its Application To Derive Soil Thresholds for Food Safety

At present, soil quality standards used for agriculture do not fully consider the influence of soil properties on cadmium (Cd) uptake by crops. This study aimed to develop prediction models for Cd transfer from a wide range of Chinese soils to carrot (Daucus carota L.) using soil properties and the total or available soil Cd content. Path analysis showed soil pH and organic carbon (OC) content were the two most significant properties exhibiting direct effects on Cd uptake factor (ratio of Cd concentration in carrot to that in soil). Stepwise multiple linear regression analysis also showed that total soil Cd, pH, and OC were significant variables contributing to carrot Cd concentration, explaining 90% of the variance across the 21 soils. Soil thresholds for carrot (cultivar New Kuroda) cropping based on added or total Cd were then derived from the food safety standard and were presented as continuous or scenario criteria.

Optimization of RP-HPLC Analysis of Low Molecular Weight Organic Acids in Soil

Abstract RP‐HPLC analysis for low molecular weight organic acids in soil solution has been optimized. An Atlantis™ C18 column was used for the analyses. An optimal determination for eleven organic acids in soil solution was found at room temperature (25°C) and 220 nm detection wavelength, with a mobile phase of 10 mM KH2PO4–CH3OH (95∶5, pH 2.7), a flow rate of 0.8 mL/min and 10 µL sample size. The detection limits ranged 3.2–619 ng/mL, the coefficients of variation ranged 1.3–4.6%, and the recoveries ranged 95.6–106.3% for soil solution with standard addition on the optimal conditions proposed.

Changes in Organic Carbon and Nutrient Contents of Highly Productive Paddy Soils in Yujiang County of Jiangxi Province, China and Their Environmental Application

Abstract Paddy field is an important land use in subtropical China. Development of high soil fertility and productivity is the management goal of paddy field. Fertilization and management practices have not only influenced the status of organic matter and nutrients in the soil but also affected the environmental quality. This article investigates the contents of organic carbon and the nutrients, and the change over the last 20 years in highly productive paddy soils and their environmental application. Field soils were sampled and the analytical results were compared with the corresponding values in the Second Soil Survey in Yujiang County of Jiangxi Province, China. The results showed that surface soils at a depth of 0-10 cm in highly productive paddy fields in Yujiang County of Jiangxi Province had contents of organic carbon (20.2±3.88) g kg −1 , total nitrogen (2.09±0.55) g kg −1 , and available phosphorus (42.7±32.7) mg kg −1 , respectively, which were all at very rich levels. Over the last 20 years, the organic carbon pool of the highly productive paddy soils reached a steady state. Total N and available P significantly increased, whereas available K changed a little. The amount and percentage of P immobilization in the surface soil (0-10 cm) of highly productive paddy fields were (142.7±41.1) mg kg −1 and (36.2±10.4)% of added P, and CEC (7.93±1.32) cmol kg −1 . These two parameters were not higher than the mean values of paddy soils and upland red soils in the areas. Results also showed that fertilizer P in highly productive paddy soils had a high mobility and was prone to move toward a water body, which is the main source of nutrients causing eutrophication. Because of a weak K-fixing capacity, the available K content was not high in highly productive paddy soils. This suggests that attention should be paid to the K balance and the increase of soil K pool.

Discrepancy in Response of Rice Yield and Soil Fertility to Long-Term Chemical Fertilization and Organic Amendments in Paddy Soils Cultivated from Infertile Upland in Subtropical China

Abstract From 1990, over 17 years field experiment was carried out in paddy field cultivated from infertile upland to evaluate the response of rice productivity, soil organic carbon (SOC), and total N to long-term NPK fertilization or NPK combined with organic amendments. The field trials included NPK (N, P, K fertilizer), NPKRS (NPK combined with rice straw), NPK2RS (NPK combined with double amount of rice straw), NPKPM (NPK combined with pig manure) and NPKGM (NPK combined with green manure) and the cropping system was rice-rice ( Oryza sativa L.) rotation. Annual rice yield, straw biomass, and harvesting index increased steadily with cultivation time in all treatments. Average annual rice yield from 1991 to 2006 was ranged from 7 795 to 8 572 kg ha −1 among treatments. Rice yields in treatments with organic amendments were usually higher than that in treatment with NPK. Contents of SOC and total N also increased gradually in the cultivation years and reached the level of 7.82 to 9.45 and 0.85 to 1.03 g kg −1 , respectively, in 2006. Soil fertilities in treatments with chemical fertilization combined with organic amendments were relatively appropriate than those in treatment with NPK. There was obvious discrepancy between cumulative characters of rice yield and soil organic fertility in newly formed paddy field. Compared with relatively high rate of crop productivity improvement, cumulative rates of SOC and total N were much lower in our study. SOC and total N contents were still less than half of those in local highly productive paddy soils after 17 years cultivation in subtropical China. Present work helps to better understand the development of infertile paddy soils and to estimate the potential of yield improvement in this region.

Declined soil suppressiveness to Fusarium oxysporum by rhizosphere microflora of cotton in soil sickness

Cotton yield and quality have been severely compromised by soil sickness throughout the primary cotton-growing regions of China. The aim of this study was to gain insight into the role of rhizosphere microbial community in governing soil sickness of cotton. Plant growth, disease resistance, root exudates, and the composition of the rhizosphere microbial community of cotton were analyzed in two different (4- and 15-year) monocropped soils and in a fallow agricultural soil (control). The monocropped soils significantly influenced cotton growth and root exudates and reduced soil suppressiveness to Fusarium wilt in bioassay experiments. Additionally, pyrosequencing of the whole internal transcribed spacers (ITS1 and ITS2) and 16S rRNA gene amplicons demonstrated clear variations in the microbial composition of cotton rhizosphere between monocropped rhizosphere soils and control soil. Specifically, monocropped soils were characterized by an increase in the abundance of fungal pathogens, including Fusarium oxysporum f. sp. vasinfectum and Verticillium dahliae, relative to the rhizosphere of control soil. Some plant-beneficial and disease-suppressive bacterial taxa, including Xanthomonadaceae, Comamonadaceae, Oxalobacteraceae, and Opitutaceae, were associated with healthy cotton. A significant correlation existed between the presence of certain amino acids (e.g., glutamic acid and alanine) and the above identified taxa, indicating that some constituents in root exudates influenced the microbial compositions of the cotton rhizosphere to manage the disease status of plant in monocropped soils. Collectively, these results suggest that pathogenic fungal build-up and a reduction in the abundance of beneficial rhizobacteria in the rhizosphere contribute to changes in soil suppressiveness to soil-borne pathogens in monocropped soils, resulting in an aggravated level of soil sickness.

Effects of soil type and genotype on lead concentration in rootstalk vegetables and the selection of cultivars for food safety

Lead (Pb) contamination of soil poses severe health risks to humans through vegetable consumption. The variations of Pb concentration in different parts of rootstalk vegetables (radish, carrot and potato) were investigated by using twelve cultivars grown in acidic Ferralsols and neutral Cambisols under two Pb treatments (125 mg kg(-1) and 250 mg kg(-1) for Ferralsols; 150 mg kg(-1) and 300 mg kg(-1) for Cambisols) in a pot experiment. The Pb concentration in edible parts was higher in Ferralsols under two Pb treatments, with range from 0.28 to 4.14, 0.42-10.66 mg kg(-1) (fresh weight) respectively, and all of them exceeded the food safety standard (0.1 mg kg(-1)) recommended by the Codex Alimentarius Commission of FAO and WHO. The Pb concentration in edible parts was significantly affected by genotype, soil type and the interaction between these two factors. The variation of Pb concentration in different cultivars was partially governed by Pb absorption and the transfer of Pb from aerial to edible part. The results revealed that caution should be paid to the cultivation of rootstalk vegetables in Pb-contaminated Ferralsols without any agronomic management to reduce Pb availability and plant uptake. For Cambisols with slight to moderate Pb contamination, growing potato cultivar Shandong No.1 and Chongqing No.1 was effective in reducing the risk of Pb entering human food chain. The results suggest the possibility of developing cultivar- and soil-specific planting and monitoring guidelines for the cultivation of rootstalk vegetables on slight to moderate Pb-contaminated soils.

Major controlling factors and prediction models for mercury transfer from soil to carrot

PurposeSoil-plant transfer models are needed to predict levels of mercury (Hg) in vegetables when evaluating food chain risks of Hg contamination in agricultural soils.Materials and methodsA total of 21 soils covering a wide range of soil properties were spiked with HgCl2 to investigate the transfer characteristics of Hg from soil to carrot in a greenhouse experiment. The major controlling factors and prediction models were identified and developed using path analysis and stepwise multiple linear regression analysis.Results and discussionCarrot Hg concentration was positively correlated with soil total Hg concentration (R2 = 0.54, P < 0.001), and the log-transformation greatly improved the correlation (R2 = 0.76, P < 0.001). Acidic soil exhibited the highest bioconcentration factor (BCF) (ratio of Hg concentration in carrot to that in soil), while calcareous soil showed the lowest BCF among the 21 soil types. The significant direct effects of soil total Hg (Hgsoil), pH, and free Al oxide (AlOX) on the carrot Hg concentration (Hgcarrot) as revealed by path analysis were consistent with the result from stepwise multiple linear regression that yielded a three-term regression model: log [Hgcarrot] = 0.52log [Hgsoil] − 0.06pH − 0.64log [AlOX] − 1.05 (R2 = 0.81, P < 0.001).ConclusionsSoil Hg concentration, pH, and AlOX content were the three most important variables associated with carrot Hg concentration. The extended Freundlich-type function could well describe Hg transfer from soil to carrot.