Abstract:Effects of soil type and type of first-class land use on spatial distribution of SOC at the depth of 0~20 cm in Hebei Province were explored based on the data of Hebei Province of the Second National Soil Survey and using variance analysis and regression analysis. It was found that they were the major factors controlling SOC spatial distribution. The effect of soil type was related with soil classification. Soils in lower soil categories of the soil classification were more capable of reflecting SOC spatial distribution. Land use explained SOC spatial distribution better than soil type at the soil group level, but not at the soil subgroup and soil family levels. Therefore, it is advisable to use soil type and land use in combination as main controlling factors in predicting or assessing SOC spatial distribution at the provincial scale, giving prior consideration to land use, then to soil type in the lower categories of soil classification under the same land use.

Abstract:Conservation tillage of farmlands is very important to soil building, guarantee of food security and mitigation of global warming. A total of 303 sets of field experiment data was collected from 157 long-term (1980 – 2012) conservation tillage experiment sites for meta-analysis to characterize quantitatively changes of SOC (soil organic carbon) in the topsoil (0~15cm for paddy and 0~20cm for upland) of farmlands under conservation tillage. Results show that the practices of conventional tillage plus straw incorporation (CTS), no tillage (NT), and no tillage plus straw incorporation (NTS) significantly increased SOC content in the topsoil with a relative change rate (RC) being 0.22, 0.35, and 0.52 g kg^-1 a^-1, respectively, as compared with the practice of conventional tillage (CT). The effect was more significant in paddy fields than in uplands and in farmlands under the double cropping system than in those under the single cropping system. It seems, however, that SOC accumulation and its amplitude is not fully related to the initial content of organic carbon in the soil. The SOC increase rate in short-term field experiments (≤5a) is about 1.75 times as high as that in long-term ones (>5a). It is, therefore, possible to overestimate SOC sequestrating potential of the conservation tillage practices just based on short-term field experiments.

Abstract:Soil apparent electrical conductivity (ECa) acquired by proximal sensor EM38, normalized difference vegetation (NDVI) extracted from high resolution remote sensing images and backscattering coefficient obtained from radar images were selected as the source data for farm field soil management zoning with the clustering method of the coastal saline soil for precision agriculture. So, based on spatial variability analysis of the data and the law for spatial variation of soil salinity in the area, zoning was done using the unsupervised classification method—fuzzy k-means cluster algorithm. Results show that the optimal number of zones was 3. In light of the characteristics of each zone, corresponding management practices should be adopted to ameliorate the soil and implement precision farmland management. The zoning in useful not only to guiding soil sampling, but also to recommendation of variable input and precision fertilization, and moreover, provides scientific basis for decision making in large-scale soil management.

Abstract:Soil classification in China is still at its developing stage where the soil genetic classification system remains to be in dominance, while the Soil Taxonomy Systerm is developing rapidly in China. In order to know how the typical soils on the Bashang Plateau in Chengde are classified in the Soil Taxonomy System, 8 typical soil profiles were collected in genetic soil regions, such as chestnut soil, grey forest soil, black soil, et al, and their soil forming environments were investigated, and then soil samples were taken from various soil layers of the soil profiles for analysis of physical and chemical properties. Results showed that (1) the diagnostic surface horizons of 8 soil profiles are Histic epipedon, Mollic epipedon and Ochric epipedon; the diagnostic subsurfaces are Calcic horizon and Cambic horizon; the diagnostic characteristics are Ustic soil moisture regime, Udic soil moisture regime, Stagnic soil moisture regime, Aquic soil moisture regime, Frigid soil temperature regime, Fibric soil materials, Hemic soil materials, Gleyic features, Redox features and Base saturation. (2) Based on the “Key to the Chinese Soil Taxonomy (Third edition)”, the 8 soil profiles could be sorted into three Orders (Isohumosols, Histosols and Primosols), four Suborders, five Groups, and six Subgroups. However, based on the Genetic Soil Classification System, they fell into 5Orders,6Suborders,7Groups and 8Subgroups. (3) The differentiations of the classification of the 8 profiles between the two classification systems varied significantly with classification level, and the relationships between the various classification levels of CSGC and CST are complicated ones rather than the simple one-to-one type.

Abstract:From the fields of a long-term (since 2005) experiment on integrated water and nitrogen management in Fengqiu National Agro-ecological Experiment Station, samples were taken of the soils in the cultivated layers (0~10 cm, 10~20 cm and 0~20 cm) of fields under different patterns of integrated water and nitrogen management after the harvest of summer maize in September, 2011 for analysis of six forms of nitrogen, i.e. inorganic nitrogen (IN), organic nitrogen (ON), dissolved organic nitrogen (DON), acidolytic organic nitrogen (AON), acidolytic ammonium nitrogen (AAN), microbial biomass nitrogen (MBN), and three biological indices that are closely related to N turnover, i.e. urease activity (URE), protease activity (PRO) and nitrification potential (NP). Three-way ANOVA of the analytic results indicate that both nitrogen fertilization and topsoil depth had significant effects on the six forms of nitrogen, but irrigation had none. One-way ANOVA shows that nitrogen fertilization significantly increased soil IN, ON, URE and NP in the 0~20 cm topsoil, but had no such effect on soil AON and AAN and volume of irrigation had nothing to do with the six forms of nitrogen, PRO and NP. Regardless of patterns of integrated water and nitrogen management, the six forms of nitrogen, URE, PRO and NP were almost all considerably higher in the 0~10 cm topsoil than in the 10~20 cm topsoil. Through the experiment, it is found that irrigation to meet the field water-holding capacity in the 0~20 cm soil layer and nitrogen fertilization at a rate of 190 kg hm^-2 per crop season is the optimal patterns of integrated water and nitrogen management.

Abstract:In situ measurements with a Guelph Permeator were performed to investigate the saturated hydraulic conductivity of soils (Kfs) at various desertified sand lands, such as grassland, fixed sand dune and mobile sand dune of Horqin Sand Land. Based on analyzing the relationships of Kfs with the sand land types, soil depths, slope position of sand dunes and soil physical and chemical properties, the results indicated that: (1) The average Kfs increased in the order: grassland (potential desertification), fixed sand dune (light desertification) and mobile sand dune (serve desertification), and the value was 2.15, 4.79 and 5.89 mm min^-1, respectively. That was, the more serious desertified, the higher infiltration capacity. A statistically significant differences (p<0.05) in Kfs were found among the three sites and between the slope positions of the two dunes. So, the Kfs at Horqin Sand Land has showed a higher heterogeneity; (2) The changes of Kfs was considerably with the increase of soil profile depths. The changes of Kfs with soil depths at grassland could be fitted with parabola models, and for fixed sand dune by exponential models; (3) The stepwise regression revealed that the soil organic matter content, the fine sand fraction (0.1~0.05 mm) and the clay and silt content (<0.05 mm) were some key factors affecting Kfs with a significantly negative relationship, but there was a significantly positive correlation with the coarse sand fraction (2~0.1 mm).

Abstract:Movement of Cd in soil profiles different in texture was simulated with the advection-dispersion equation for solute transport in an indoor experiment using soil columns. Results show that the chemical nonequilibrium one-site model (OSM) can be used to simulate Cd transport better in silty loam (R²=0.810) and loamy sand (R²=0.901) than in sandy loam (R²=0.542). The OSM can predict accurately the time for Cd to transport through the soil column, but not fit so well the trailing of the breakthrough curve of Cd. The retarding effect of the soil on Cd transport was related to soil physical and chemical properties, however, its mechanism needs to be studied further in depth. At the end, the parameters obtained from fitting with the aforementioned model were used to simulate transport of Cd in soil profiles consisting of soil layers. The simulated breakthrough curves didn’t reveal the heterogeneity of the soil profiles. As a result of the strong sorption of Cd by the upper sandy loam layer, it took a long time (10 pv) for Cd to pass through the profile. And moreover, the variation of Cd concentration and adsorption quantity at the interface of two soil layers different in texture was obvious.

Abstract:It is the key to numerical modeling of water and solute transportation in unsaturated soil to identify parameters of the transportation. Based on the vertical one-dimensional equation for transportation of water-solute in unsaturated adsorptive soil, a multi-target optimized model for identification of parameters of water-solute transportation was established, using KBr as infiltration solution and the minimum standard deviations between measured and observed values of water content and solute concentration as targets of optimization. The multi-target optimization issue was converted into a single-target one, with the weight coefficient method. The particle swarm optimization (PSO) algorithm of dynamic weight and asynchronous time-varying learning factors was used to solve the model. A soil column experiment was conducted in lab to determine water content and spatial distribution of K+ at the time of 220,380 and 780 minutes, separately. The data of the first two time groups were used for identification of parameters, and those of the third group for validation. Results show that the correlation coefficient between measured and calculated values of water content and K+ concentration was 0.977 and 0.952, when the weight coefficient of the treatment of 780 min infiltration was 0.5, demonstrating that they are well dovetailed and that it is feasible to use PSO to identify soil transportation parameters of water and solute in the soil. The numerical simulation indicates that the higher the weight, the higher the correlation coefficient between measured and calculated values of water content and the lower the correlation coefficient between measured and calculated values of K+ concentration.

Abstract:Based on the CBERS images in 2000, CBERS images in 2005 and TM images in 2010, dynamic change in cultivated land and landscape pattern along the mainstream of the Tarim River from 2000 to 2010 were studied using the 3S technology and the analytical method of combining the mathematical statistics and landscape pattern quantity analysis. Results show that the area of the cultivated land along the mainstream of the Tarim River varied significantly, increasing from 1.61 × 105 hm² or 3.89% of the total land area in 2000 to 3.27 × 105 hm² or 7.88% in 2010, that is, by 1.66×104 hm² a^-1; spatial variation of the cultivated land was also significant between sections of the river. At Sections A, B, C and D cultivated land spread as wide as 21~23 kilometer, 11~16 kilometer, 6~17 kilometer, and 4~9 kilometer, respectively and the spread was the fastest at Sections C and D on north bank of the river and Sections D and E on the south bank. During the period from 2000 to 2010, the cultivated land increased steadily in number of patches with its area weight shape index rising; and its patches becoming more irregular in shape. On the whole, the landscape aggregation degree was moderate; the distribution uniformity of patches various in size within a landscape and landscape diversity declined; and the proportions the various types of landscapes account for became less harmonious.

Abstract:Effects of elevated atmospheric ozone (pO₃) (50% higher than the ambient pO₃ in concentration) on root respiration and biomass accumulation and distribution of rice (Oryza sativa L. cv. Xiandao 63) at the jointing stage were investigated in fully open-air field conditions, and effect of alternation of anaerobic and aerobic conditions on root respiration was analyzed using special gas-collecting installations. Results show that under elevated pO₃ canopy and total biomass of the crop decreased slightly, while its root dry matter weight and ratio of root/canopy dropped significantly by 14.7% and 10.4%, respectively. The mixture of N₂ and O₂ at a ratio of 9:1 or 9.5:0.5 was the most propitious for root respiration, whereas in pure N₂, natural air and CO₂-saturated distilled water root respiration rate was lowered to a varying degree. The treatment of elevated pO₃ coupled with measurement inn CO₂-saturated distilled water and the treatment of ambient air coupled with measurement in pure N₂ was the least in root respiration rate, indicating that although the condition in which root respiration was measured affected root respiration rate, the impact was restricted in degree by the atmospheric environment in which the plant grew. The root respiration rate of rice growing under elevated ozone was 23.6%~52.7% higher than that under natural atmosphere when measured in pure gas condition, and the difference between the two was insignificant when the measurement was done in CO₂-saturated distilled water, showing that the influence of ozone pollution on root respiration obviously decreased. Under elevated and ambient pO₃ environments, root respiration of the rice displayed a curve of convex quadratic function with increasing oxygen supply in the gaseous environment for measurement. The oxygen concentration of 5%~10% in the environment promoted rice root respiration, while stronge anaerobic condition (i.e., pure N₂) and aerobic conditions (i.e., air) both affected root respiration of rice reversely.

Abstract:During the period from May to November, 2011, a survey was carried out to investigate variation of soil nematode communities in different soil layers varying from 0~30 cm as affected by plant community in alpine meadows in North Tibet. The shallow dish method was adopted for nematode extraction. In order to analyze composition, distribution and diversity of nematode communities in an extremely cold condition, indices, such as individual density, genus number and diversity, were applied in the research. A total of 33 038 nematodes were extracted and sorted into 93 genus, 51 families, 6 orders and 2 phylums. The average individual density of the nematodes was 847 idv 100 g^-1 dry soil. They were found mainly in the top soil. Differences in nematode community were found existing between meadows different in plant community. In terms of population of nematodes, the three alpine meadows followed an increasing order of Potentilla < Kobresia littledalei < K. pygmaea , and the differences are distinctive (p<0.05); while in terms of genus number, an reverse order went like Potentilla > Kobresia littledalei > K. pygmaea . Quantity and genus number of nematodes were fluctuated sharply during the period. The plant reviving period was the highest and followed by the flourishing period and the withering period. Dominant species varied with plant community. In terms of biodiversity, the three meadows follow an order of Potentilla > K. pygmaea > Kobresia littledalei . This might be explained by disturbance of grazing, as well as soil properties as affected by different plant communities. Therefore, nematodes can be used as a potential indicator for analyzing impacts of environmental factors on soil ecosystems.

Abstract:To explore spectral characteristics of soil organic matter (SOM) and their effects and hence to lay down theoretical basis for quantitative reversion of organic matter and soil iron oxides, effects of soil organic matter on soil reflection rate, soil line parameters and quantitative inversion of soil iron oxides were studied in this paper by making use of spectral data of the soil before and after organic matter was removed. Results show that removal of organic matter significantly raised soil reflection rate and the change was the most obvious in the visible orange light band of 570~630 nm. And correlation analysis also shows that the correlation coefficient of removal of soil organic matter with the relative variation or difference in the orange light band was higher than that in the other light bands. The highest correlation coefficient was found at 600 nm. It is, therefore, suggested that the spectral data in light band of 570~630 nm be used for inversion of soil organic matter. Removal of SOM also lowered soil line slope and significantly increased intercept. The changes in thse two aspects were significantly related to SOM remval rate. Hence, soil line parameters can be used to predict content of SOM. The effect of SOM on quantitative inversion of soil iron oxides was significant, especially in soils with SOM content being above 2%. So in performing the inversion, it is essential to take into account effect of SOM on accuracy of the inversion and adopt some effective technologies to mitigate these effects. Only by so doing, can quantitative inversion of soil iron oxide content achieve better results.

Abstract:Contents and distributions of nutrients (total N, total P, total K and OM) and organic carbon of different forms (ready-to-oxidize and hard-to-oxidize) in water-stable aggregates (>0.25 mm) in ultisols different in erosion degree (slight, medium and severe) were studied. Results show that with erosion aggravating, the contents of nutrients (OM, total N and total P) in water-stable aggregates (>0.25 mm) gradually decreased. In terms of contribution to the total of soil nutrients, various fractions of water-stable aggregated a sequence of [>4 mm] > [0.5～1 mm] > [1～2 mm] > [2～4 mm] > [0.25～0.5 mm]. The contents of total N, total P and OM were significantly and positively related to the content of >0.25 mm water-stable aggregates. The contents of soil total organic carbon, readily-oxidation and hard-oxidation organic carbon took on a falling trend with the enhancing of erosion degree and had the marked positive correlation with >0.25 mm water-stable aggregates, OM, total N and total P, while oxidation stability coefficient of organic matter was negatively related to the contents of water-stable aggregates of various fractions, OM, total N and total P.

Abstract:Using the stable carbon isotope (δ¹³C) technique, an indoor incubation experiment was carried out to study distribution of fresh carbon in soil aggregate fractions of red soil (Ferrisols), yellowish red soil (Luvisol) and mountain meadow soil (Cambisols). To trace dynamics of fresh carbon in soil aggregates ¹³C-labelled rice straw was applied to the soils, which were then put under incubation at 25℃for 360 days. Results show that the quantity of the fresh carbon found in soil aggregates followed a decreasing order of 250 ~ 2 000 μm > 50 ~ 250 μm > <50 μm in all these soils, accounting for 56.8% ~ 59.6%, 25.9% ~ 28.7% and 11.7% ~ 17.3%, respectively, of the total applied into the soil, which further indicates that the added fresh carbon was mainly accumulated in large-sized soil aggregates.

Abstract:Dissimilatory iron reduction, an important microbial process of the degradation of organic matter in anaerobic environment, is closely related to mineralization of organic carbon. Samples of cinnamon soil were prepared into slurry and then incubated anaerobically in dark or under illumination, to study effect of illumination on iron oxides reduction. Water soluble inorganic carbon and total water soluble carbon were analyzed simultaneously to explore relationship between anaerobic redox of iron oxides and carbon transformation under illumination in cinnamon soil. Results show that 55.31% of the free iron oxides in the soil could be reduced anaerobically under dark regime, and only 38.90% could under illumination. As Fe(II) produced anaerobically could be oxidized by oxygen generated by photosynthesis of cyanobacteria, the reduction rate of free iron oxides was found to be lowered to 7.95% after 40 days of anaerobic incubation under illumination. The content of soluble total carbon and soluble inorganic carbon increased by 69% and 246%, respectively, after 40 days of anaerobic incubation in dark, while they both displayed a rising-and-then-declining trend during anaerobic incubation under illumination. When the 40 days of incubation ended soluble total carbon and inorganic carbon was found only 47% and 70% higher, respectively, than it was at the beginning of the incubation The content of soluble total carbon was closely related to the content of 0.5 mol L^-1 HCl extractable iron, while the content of soluble inorganic carbon was to the content of Fe(II) in the soil under the incubation.

Abstract:In a pot experiment rice seedlings were planted in mesh bags that were filled with vermiculite to simulate rhizosphere and the bags were imbedded separately in submerged red, paddy and saline soils for cultivation for 13days. Results show that during the rice cultivation period, pH in the red, paddy and saline soils varied in the range of 6.05~6.78, 6.47~7.33 and 6.47~7.44, respectively. In the OM (organic matter) treatments, all the soils, regardless of rhizospheric or nonrhizospheric, decreased in pH, except for rhizospheric red soil, which increased significantly. Eh in all the rhizospheric soils of the control treatments lingered within 233~385 mV, and treatment with OM reduced rhizospheric Eh, but increased nonrhizospheric Eh of the red and paddy soils. Oxide-Fe fraction accounted for more than 90% of the reductively dissolved Fe and vermiculite-absorbed Fe, which was significantly correlated with soil solution Eh and pe+pH, indicating that Fe redox reactions occurred simultaneously on the surfaces of the soils and the vermiculites, but in opposite directions. The formation of iron plaque on root surface of the rice seedlings was related to redox conditions in rhizosphere. In the rhizospheres of CK (higher in Eh), Fe content on the root surface decreased with increasing pH, whereas in the rhizospheres of OM treatment (lower in Eh), Fe increased with increasing pH. In the red soil, iron plaques on the root surface retarded Fe absorption, while in the paddy and saline soils it acted reversely. Cd content on the root surface was significantly and positively related to Cd in root and in shoot. In the red soil iron plagued on the root surface retarded adsorption and uptake of Cd by rice, whereas in paddy and saline soils, it acted reversely too.

Abstract:To build up a fertilization index system for winter wheat in Guanzhong irrigation area of Shaanxi, the data of 95 “3414” field experiments on winter wheat carried out in 2008 were analyzed; relative yields of the fields, i.e. 70%, 80%, 90% and 95%, were set as indices for grading abundance of soil nutrients; relationship between fertilization rate and yield of each field experiment site was simulated with a linear quadratic model; and an optimal economical fertilization rate was determined for each experiment site. In the end, a model for recommendation of N, P₂O₅ and K₂O application rates for winter wheat in this area was established based on the measurements of alkalytic N (AN), available P (AP) and available K (AK) in the soils and fertilization rates were recommended for fields different in soil fertility level. In wheat fields with the content of AN being very low (＜50 mg kg^-1), low (50~80 mg kg^-1), medium (80~120 mg kg^-1) or high (＞120 mg kg^-1), the application rate of N 190~230, 150~190, 110~150 and 0~110 kg hm^-2 was recommended, respectively; in fields with the content of AP being ＜10, 10~20, 20~35 and ＞35 mg kg^-1, the application rate of P₂O₅ 130~160, 110~130, 90~110 and 0~90 kg hm^-2 was, respectively; and in fields with the content of AK being ＜90, 90~150, 150~190 and ＞190 mg kg^-1, the application rate of K₂O 120~150, 90~120, 70~90 and 0~70 kg hm^-2 was, respectively. Demonstration trials showed that compared with farmer’s practice, recommended fertilization increased the yield and profit of winter wheat on average by 789 kg hm^-2 and 1 227 yuan hm^-2, and fertilizer contribution rate and agronomic efficiency by 8.2% and 1.7 kg kg ^-1, respectively.

Abstract:A four-year stationary field experiment, using the lysimeter method, was conducted to investigate effects of application of nitrogen fertilizer and incorporation of straws on nitrate leaching in the soil layer, 90 cm in depth, in a field under wheat and maize rotation in Guanzhong Plain of Shaanxi Province. Results show that nitrate leaching varied sharply in a year and occurred mainly in July, August and September, the rainy season of the year, and could be observed after flood irrigation, too. The nitrate concentration in the leachate and nitrate leaching loss in the whole monitored period was 0~103.5 mg L^-1 and 0~21.8 kg hm^-2, respectively, and both displayed an increasing trend along with nitrogen application rate. The crops gained relatively high yields (14.4 t hm^-2 on average) in all the 4 years, when 330 kg hm^-2 N (150 kg hm^-2 N for wheat and 180 kg hm^-2 N for corn) was applied for the wheat/maize rotation system. Any further increase in nitrogen application rate did not bring about increase in crop yield, but enhanced accordingly nitrate accumulation in the soil profile and nitrate leaching loss monitored at the depth of 90 cm of the profile. Straw incorporation showed some yield increasing effect only two years later. Compared with Treatment N330, Treatment N330+S increased yield of the crops by 15.1% and 14.2% in 2010 and 2011, respectively. However, no significant effects were observed on nitrate accumulation and leaching. Regression analysis of the data exposed an positive exponential relationship of nitrate accumulation in the 0～100 cm soil layer and nitrate leaching loss with annual nitrogen application rate, which means that the higher the nitrogen application rate, the higher the nitrate accumulation, the higher the nitrate leaching loss, and the higher the proportions of the two to the total nitrate applied.

Abstract:To provide scientific basis for management and efficient utilization of nitrogen in fields, effects of combined application of organic and inorganic fertilizers plus DMPP (3,4-dimethypyrazole phosphate) on nitrogen transformation in soils as affected by to various factors were studied. For that end, an aerobic thermostat pot experiment was designed to have various affecting factors, like fertilization rate, soil moisture, environmental temperature, soil type, etc., and carried out. After 60 days of incubation, it was found that NH₄⁺-N concentration was 89 times higher and NO₃^--N concentration 57.8% lower in the pots higher in fertilization rate than in the pots conventional in fertilization rate (no DMPP was added in either pots); in the pots subjected to flooding and combined application of organic and inorganic fertilizers plus DMPP, NH₄⁺-N concentration kept on rising and nitrification process was more significantly inhibited; NH₄⁺-N concentration was 56 times higher and NO₃^--N concentration 18 times lower in the pots incubated under 15℃ than in the pots under 25℃, and NH₄⁺-N concentration was 30 and 31 times higher and NO₃^--N concentration was 44.3% and 66.4% lower in the pots of red soil than in the pots of silt paddy soil and blue clayey paddy soil, respectively. The optimal nitrification inhibitory effect was observed during the period from day 30 to day 40 in the pots of blue clayey paddy soil, silt paddy soil and red soil subjected to combined application of organic and inorganic fertilizers plus DMPP under 25℃, and inhibitory effect of the treatment may last throughout the experiment period of 60 days. Obviously the addition of DMPP could increase NH₄⁺-N concentration in the pots subjected to combined application of organic and inorganic fertilizers, and effectively extend residence of the NH₄⁺-N in the soils, and keep NO₃^--N concentration at a lower level for a longer period. The inhibitory effect of DMPP was more outstanding in the pots subjected to high rates of combined fertilization. Low temperature is benefit to the inhibitory effect of DMPP. It is, therefore, worthwhile to do some further studies on mechanisms of different factors affecting effects of combined application of organic and inorganic fertilizers plus DMPP on nitrogen transformation.

Abstract:Using the recovery (standard addition) method, analysis for comparison was done of the silver nitrate titration method, the ultraviolet spectrophotometry method and the automatic potentiometric titration method, used in determining chloride contents in sweet potato seedlings of six different cultivars, and chloride absorption and distribution in shoots and roots of these sweet potatoes explored. Results show that the silver nitrate titration method was low in reproducibility and it was also hard to determine when to end the titration; the ultraviolet spectrophotometry was low in chloride recovery, ranging from 52.9% to 81.4%, and analysis of samples was influenced by the color of sample extraction solvent; whilst the automatic potentiometric titration method was high in chloride recovery rate, reaching high in the range from 93.9% to 105.5% with relative standard deviation being 0.6%~6.0%, and moreover, the method was simple to use, good in reproducibility and high in accuracy. Therefore, the automatic potentiometric titration method is the best one in determination of chloride in sweet potato. Chloride accumulation and distribution were determined of these sweet potato samples, using the automatic potentiometric titration method. Results show that chloride contents ranged from 0.067 to 0.096 mmol g^-1DW in shoot and 0.038 to 0.087 mmol g^-1DW in root. Significant differences were found between different cultivars in chloride contents in shoot and in root. The selectivity ratios of Cl^-1 translocation from root to shoot of the sweet potatoes were all above 1.0 regardless of cultivars, indicating that chloride tends to accumulate in shoot. The cultivar of leafy vegetable sweet potato (Fushu No.7-6) was the highest in selectivity ratio, and followed by Xuzi No.20-1 and Zhezi No.1, and the cultivar of starchy sweet potato (Quanshu No.9) the lowest.

Abstract:A pot experiment was carried out using different types of soils to study their potassium (K) supply capacities and K dynamics under a ryegrass-rice rotation system, with a view to providing scientific basis for the research on mechanism of soil supplying K and reasonable K control. Results show that both aboveground biomass and K uptake of the crops in the group without K treatment (NP) were the highest in fluvo-aquic soil (FS), which was followed by yellow cinnamon soil (YCS), then red soil (RS), while in the group with K, fertilization, no significant difference (p>0.05) between the soils was observed in aboveground biomass and a decreasing order of YCS > FS > RS was in terms of K uptake. Treatment NPK was 55.6%, 45.2% and 23.2% higher than treatment NP for red soil, yellow cinnamon soil and fluvo-aquic soil, respectively, in biomass and 368.8%, 166.8% and 74.5%, higher, respectively in K uptake. In the ryegrass growth season, the concentrations of water soluble K and exchangeable K in treatment NP decreased in all the soils. The concentration of non-exchangeable K decreased significantly in fluvo-aquic, but remained almost unchanged in the early season, rose in the middle season and dropped in the late season in yellow cinnamon soil and red soil. Soil K was much higher in treatment NPK than in treatment NP, but varied in a similar pattern in all the three soils, regardless of treatments and K forms. During the rice growing period, in treatment NP, water soluble K in all the soils did not change much soil exchangeable K declined first and then rose, but non-exchangeable K showed a reverse trend, while in treatment NPK, soil exchangeable K rose significantly in the early, and declined in the middle and then turned slightly back again in the late period, whereas soil water soluble K and non-exchangeable K showed a rising and then falling trend. To sum up, In treatment NP, K consumption was higher in all the soils and in all the periods of the rotation, thus decreasing both soil water soluble K and exchangeable K and in turn triggering release of non-exchangeable K. Application of K fertilizer increases the concentrations of water soluble K and exchangeable K and the ratio of K transformed into non-exchangeable K, thus effectively improving K supply capacity of the soil, and eventually increasing the yield of ryegrass and rice significantly.

Abstract:In a field experiment, where two successive crops of soybeans, including 2 P-efficient transgenic soybeans AP15-1 and AP15-3, and their receptors YC03-3 and YC04-5, were planted. Samples of rhizosphere soils were collected at the seedling, florescence, and mature stages for analyses of pH, total P, available P, organic P, total N, alkali N, total K, available K and eight trace elements, and the activities of four soil enzymes, including sucrase, phosphatase, hydrogen peroxidase and urease, in the rhizosphere soils of AP15-1 and YC03-3 at the full bloom stage, to explore effects of planting of the transgenic soybeans on soil nutrients and enzyme activities in the rhizosphere soil. Results showed that the significant differences were found at certain stages between AP15-1 and YC03-3 and between AP15-3 and YC04-5 in nutrient content, except for total K and trace elements. However, the differences were observed mostly at the seedling stage, and at the mature stage, the difference existed only in content of organic P between AP15-1 and YC03-3, and in content of available K between AP15-3 and YC04-5. Moreover, such differences were no longer detected any time of the two seasons. The determination of activities of the four soil enzymes indicated that there was no significant difference between the transgenic varieties and their respective receptors in the same season. To sum up, the findings demonstrate that planting P-efficient transgenic soybeans is likely to have no significant effects on contents of the main soil nutrients or activities of the four soil enzymes in rhizosphere.

Abstract:This paper reviews the current applications of molecular and systematic biological technologies in polluted soil microbial ecology researches. These approaches include nucleic acid hybridization, DNA fingerprints, metagenomics, metaproteome and metabolomics. The mechanisms, applications, advantages and limitations of these approaches were discussed respectively, and the potential applications of these biological technologies were also discussed.

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