AbstractA series of 9 soil samples were taken at a timber treatment site in SW France where Cu sulphate and chromated copper arsenate (CCA) have been used as wood preservatives (Sites P1 to P9) and one soil sample was collected at an adjacent site on the same soil type (Site P10). Copper was a major contaminant in all topsoils, varying from 65 (Soil P5) to 2600 mg Cu kg−1 (Soil P7), exceeding background values for French sandy soils. As and Cr did not accumulate in soil, except at Site P8 (52 mg As kg−1 and 87 mg Cr kg−1) where CCA-treated posts were stacked. Soil ecotoxicity was assessed with bioassays using radish, lettuce, slug Arion rufus L., and earthworm Dendrobaena octaedra (Savigny). There were significantly differences in lettuce germination rate, lettuce leaf yield, radish root and leaf yields, slug herbivory, and earthworm avoidance. An additional bioassay showed higher negative impacts on bean shoot and root yields, Rhizobium nodule counts on Bean roots, and guaiacol peroxidase activity in primary Bean leaves for soil from Site P7, with and without fertilisation, than for soil from Site P10, despite both soils having a similar value for computed free ion Cu2+ activity in the soil solution (pCu2+). Beans grown in soil from Site P7 that had been fertilised showed elevated foliar Cu content and phytotoxic symptoms. Soils from Sites P7 (treatment plant) and P6 (storage of treated utility poles) had the highest ecotoxicity, whereas soil from Site P10 (high organic matter content and cation exchange capacity) had the lowest. Except at Site P10, the soil factor pCu2+ computed with soil pH and total soil Cu could be used to predict soil ecotoxicity.
The fallout radionuclide cesium-137 (137Cs) has been widely employed as a tracer for assessment of soil loss from thick uniform soils; however, few studies have been conducted on thin stony soils on slopes underlain by carbonate rocks which are widely distributed in karst areas. Information derived from 137Cs measurement of soil samples collected along a carbonate rock slope with thin stony soil where neither soil erosion nor deposition occurred was used to investigate the characteristics of 137Cs redistribution in a karst area of Southwest China. The results indicated that the 137Cs inventories of the surface soil on the slope studied were much lower than that of the local 137Cs reference inventory and the 137Cs activities were much higher than those on slopes with thick uniform soils. The spatial distribution of 137Cs inventories was characterized by considerable variation. The high 137Cs depletion in the stony soil of the slope studied was mainly because a considerable proportion of the fallout input of 137Cs could be lost with runoff and the dissolution of carbonate particles in the soil promoted the loss of 137Cs. These demonstrated that the rates of soil loss could not be estimated from the degree of depletion of the 137Cs inventory relative to the local reference inventory for the thin stony soil of the rocky slope underlain by carbonate rocks in the study area in the way that has been widely used in areas with thick uniform soils.
The structure and diversity of the bacterial communities in rhizosphere soils of native Phragmites australis and Scirpus mariqueter and alien Spartina alterniflora in the Yangtze River Estuary were investigated by constructing 16S ribosomal DNA (rDNA) clone libraries. The bacterial diversity was quantified by placing the clones into operational taxonomic unit (OTU) groups at the level of sequence similarity of > 97%. Phylogenetic analysis of the resulting 398 clone sequences indicated a high diversity of bacteria in the rhizosphere soils of these plants. The members of Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria of the phylum Proteobacteria were the most abundant in rhizobacteria. Chao 1 nonparametric diversity estimator coupled with the reciprocal of Simpson's index (1/D) was applied to sequence data obtained from each library to evaluate total sequence diversity and quantitatively compare the level of dominance. The results showed that Phragmites, Scirpus, and Spartina rhizosphere soils contained 200, 668, and 382 OTUs, respectively. The bacterial communities in the Spartina and Phragmites rhizosphere soils displayed species dominance revealed by 1/D, whereas the bacterial community in Scirpus rhizosphere soil had uniform distributions of species abundance. Overall, analysis of 16S rDNA clone libraries from the rhizosphere soils indicates that the changes in bacterial composition may occur concomitantly with the shift of species composition in plant communities.
A long-term (21-year) field experiment was performed to study the responses of soil inorganic P fractions and P availability to annual fertilizer P application in a calcareous soil on the Loess Plateau of China. Soil Olsen-P contents increased by 3.7, 5.2, 11.2 and 20.6 mg P kg−1 after 21-year annual fertilizer P application at 20, 39, 59, and 79 kg P ha−1, respectively. Long-term fertilizer P addition also increased soil total P and inorganic P (Pi) contents significantly. The contents of inorganic P fractions were in the order of Ca10-P > Ca8-P > Fe-P > Al-P > occluded P > Ca2-P in the soil receiving annual fertilizer P application. Fertilizer P application increased Ca8-P, Al-P and Ca2-P contents as well as their percentages relative to Pi. Pi application increased Fe-P and occluded P contents but nor their percentages. Soil Ca10-P content remained unchanged after fertilizer P application while its percentage relative to Pi declined with increasing fertilizer P rate. All Pi fractions but Ca10-P were correlated with Olsen-P significantly. 90% of variations in Olsen-P could be explained by Pi fractions, and the direct contribution of Ca8-P was predominant. Long-term annual superphosphate application would facilitate the accumulation of soil Ca8-P, and thus improve soil P availability.
A study was conducted in the forest-steppe region of the Loess Plateau to provide insight into the factors affecting the process of vegetation establishment, and to provide recommendations for the selection of indigenous species in order to speed up the succession process and to allow the establishment of vegetation more resistant to soil erosion. Four distinctive vegetation types were identified, and their distribution was affected not only by the time since abandonment but also by other environmental factors, mainly soil water and total P in the upper soil layers. One of the vegetation types, dominated by Artemisia scoparia, formed the early successional stage after abandonment while the other three types formed later successional stages with their distribution determined by the soil water content and total P. It can be concluded that the selection of appropriate species for introduction to accelerate succession should be determined by the local conditions and especially the total P concentration and soil water content.
The changes of microbial biomass carbon (MBC) and nitrogen (MBN) and microbial community in the topsoil of the abandoned agricultural land on the semi-arid Loess Plateau in China during the natural succession were evaluated to understand the relationship between microbial community and soil properties. MBC and MBN were measured using fumigation extraction, and microbial community was analyzed by the method of fatty acid methyl ester (FAME). The contents of organic C, total N, MBC, MBN, total FAME, fungal FAME, bacterial FAME and Gram-negative bacterial FAME at the natural succession sites were higher than those of the agricultural land, but lower than those of the natural vegetation sites. The MBC, MBN and total FAME were closely correlated with organic C and total N. Furthermore, organic C and total N were found to be positively correlated with fungal FAME, bacterial FAME, fungal/bacterial and Gram-negative bacterial FAME. Natural succession would be useful for improving soil microbial properties and might be an important alternative for sustaining soil quality on the semi-arid Loess Plateau in China.
To evaluate the effect of groundwater irrigation on the polycyclic aromatic hydrocarbons (PAHs) pollution abatement and soil microbial characteristics, a case study was performed in the Shenfu irrigation area of Shenyang, Northeast China, where the irrigation with petroleum wastewater had lasted for more than fifty years, and then groundwater irrigation instead of wastewater irrigation was applied due to the gradually serious PAHs pollution in soil. Soil chemical properties, including PAHs and nutrients contents, and soil microbial characteristics, including microbial biomass carbon, substrate-induced respiration, microbial quotient (qM), metabolic quotient (qCO2), dehydrogenase (DH), polyphenol oxidase (PO), urease (UR) and cellulase (CE) in surface and subsurface were determined. Total organic C, total N, total P, and available K were significantly different between the sites studied. The PAHs concentrations ranged from 610.9 to 6 362.8 μg kg−1 in the surface layers (0-20 cm) and from 404.6 to 4 318.5 μg kg−1 in the subsurface layers (20-40 cm). From the principal component analysis, the first principal component was primarily weighed by total PAHs, total organic C, total N, total P and available K, and it was the main factor that influencing the soil microbial characteristics. Among the tested microbial characteristics, DH, PO, UR, CE, qM and qCO2 were more sensitive to the PAHs stress than the others, thus they could serve as useful ecological assessment indicators for soil PAHs pollution.
A field experiment was conducted to investigate the effects of soil amendments (lime, nano-Si foliar solution and used diatomite) on the growth and metal uptake of three maize (Zea mays L.) cultivars grown in a Cd and Zn-contaminated acidic soil. The addition of lime significantly increased the maize grain yields and decreased the concentrations of Zn and Cd in the grains and shoots of maize when compared with the control. Among the three maize cultivars, Yunshi-5 accumulated the lowest amounts of Cd and Zn in the grain. The concentrations of Zn and Cd in the grain of Yunshi-5 conformed to the Chinese feed standards. These data revealed that a combination of low metal-accumulating maize and chemical fixation could effectively provide a barrier to prevent metals from entering the human food chain.
Developing high-yielding rice (Oryza sativa L.) cultivars depends on having a better understanding of nitrogen (N) accumulation and translocation to the ear during the reproductive stage. Field experiments were carried out to evaluate the genetic variation for N accumulation and translocation in different Japonica rice cultivars at different N rates and to identify any relationship to grain yield in southeast China. Four Japonica cultivars with similar agronomic characteristics were grown at two experimental sites in 2004 with three N rates of 0, 60, and 180 kg N ha−1. Dry weights and N contents of rice plants were measured at tillering, initiation, anthesis, and maturity. Grain yields exhibited significant differences (P < 0.05) among the cultivars and N application rates. Increasing N rates improved N uptake at anthesis and maturity in all four cultivars (P < 0.05). N translocation from vegetative organs to the grains increased with enhanced N rates (P < 0.05). N translocation to the grains ranged from 9 to 64 kg N ha−1 and N-translocation effciency from 33% to 68%. Grain yield was linear to N uptake at anthesis (r2 = 0.78**) and N translocation (r2 = 0.67**). Thus, cultivars with a high N uptake at anthesis, low residual N in the straw at maturity, and appropriate low N fertilizer supply in southeast China should effciently increase N-recovery rate while maintaining grain yield and soil fertility.
The safe recycling of fly ash (FA) and sewage sludge (SS) in the agricultural processes comprises an important environmental technology on waste management. Soils amended with FA and SS may change their ability to adsorb heavy metals due to either increase of soil pH or decomposition of sludge-borne organic matter. Thus, Cd and Pb sorption was investigated by 1-month incubation under soil moisture content at field capacity and room temperature with an acidic Typic Haploxeroalf from central Greece amended with varying amounts of FA and SS. Batch experiments were conducted by equilibrating the soil samples with CaCl2 solutions containing 0–400 mg Pb L−1 or 0–100 mg Cd L−1. The results showed that the Freundlich equation described well the Cd and Pb sorption. Distribution coefficient (Kd) values of Pb were higher than those of Cd in all the treatments of this study. Application of FA increased Kd values for Cd and Pb to 8.2 and 2.3 times more than the controls, respectively. Simultaneous applications of FA and SS caused a Kd increase of 3.8 and 2.1 times compared to the treatments that received only SS for Cd and Pb, respectively. Treatment of SS alone did not significantly change Cd and Pb sorption compared to the controls. The sorption reactions seemed to be mainly affected by soil pH, which was revealed by the significant correlations of Cd and Pb sorption with soil pH. These suggested that fly ash was very useful as a low-cost adsorbent for Cd and Pb and could be used as an ameliorant for biosolid-amended acidic soils.
Long-term changes in soil pH, the current status of soil acidification, and the response of bulk soil and soil water pH to experimental nitrogen addition under three subtropical forests were investigated in Dinghushan Biosphere Reserve of subtropical China. The results showed that the mineral soil pH at 0–20 cm depth declined significantly from 4.60–4.75 in 1980s to 3.84–4.02 in 2005. Nitrogen addition resulted in the decrease of pH in both bulk soil and soil water collected at 20-cm depth. The rapid decline of soil pH was attributed to long-term high atmospheric acid deposition (nitrogen and sulphur) therein. The forest at earlier succession stage with originally higher soil pH appeared to be more vulnerable to acid deposition than that at later succession stage with originally low soil pH.
Soil acidification is an important process in land degradation around the world as well as in China. Acidification of Alfisols was investigated in the tea gardens with various years of tea cultivation in the eastern China. Cultivation of tea plants caused soil acidification and soil acidity increased with the increase of tea cultivation period. Soil pH of composite samples from cultivated layers decreased by 1.37, 1.62 and 1.85, respectively, after 13, 34 and 54 years of tea plantation, as compared to the surface soil obtained from the unused land. Soil acidification rates at early stages of tea cultivation were found to be higher than those at the later stages. The acidification rate for the period of 0–13 years was as high as 4.40 kmol H+ ha−1 year−1 for the cultivated layer samples. Soil acidification induced the decrease of soil exchangeable base cations and base cation saturation and thus increased the soil exchangeable acidity. Soil acidification also caused the decrease of soil cation exchange capacity, especially for the 54-year-old tea garden. Soil acidification induced by tea plantation also led to the increase of soil exchangeable Al and soluble Al, which was responsible for the Al toxicity to plants.
Input of large amounts of N and S compounds into forest ecosystems through atmospheric deposition is a significant risk for soil acidification in the oil sands region of Alberta. We evaluated the sensitivity of forest soils to acidification in two watersheds (Lake 287 and Lake 185) with contrasting hydrological regimes as a part of a larger project assessing the role of N and S cycling in soil acidification in forest ecosystems. Fifty six forest soil samples were collected from the two watersheds by horizon from 10 monitoring plots dominated by either jack pine (Pinus banksiana) or aspen (Populus tremuloides). Soils in the two watersheds were extremely to moderately acidic with pH (CaCl2) ranging from 2.83 to 4.91. Soil acid-base chemistry variables such as pH, base saturation, Al saturation, and acid-buffering capacity measured using the acetic acid equilibrium procedure indicated that soils in Lake 287 were more acidified than those in Lake 185. Acid-buffering capacity decreased in the order of forest floor > subsurface mineral soil > surface mineral soil. The most dramatic differences in percent Ca and Al saturations between the two watersheds were found in the surface mineral soil horizon. Percent Ca and Al saturation in the surface mineral soil in Lake 287 were 15% and 70%, respectively; the percent Ca saturation value fell within a critical range proposed in the literature that indicates soil acidification. Our results suggest that the soils in the two watersheds have low acid buffering capacity and would be sensitive to increased acidic deposition in the region.
It is imperative to choose some low cost, available and effective ameliorants to correct soil acidity in southern China for sustainable agriculture. The present investigation dealt with the possible role of industrial byproducts, i.e., coal fly ash (CFA), alkaline slag (AS), red mud (RM) and phosphogypsum (PG) in correcting acidity and aluminum (Al) toxicity of soils under tea plantation using an indoor incubation experiment. Results indicated that CFA, AS and RM increased soil pH, while PG decreased the pHs of an Ultisol and an Alfisol. The increment of soil pH followed the order of RM > AS > CFA. All the industrial byproducts invariably decreased exchangeable Al and hence increased exchangeable Ca, Mg, K and Na and effective cation exchange capacity. RM, AS and lime decreased total soluble Al, exchangeable Al and organically bound Al. Formation and retention of hydroxyl-Al polymers were the principal mechanism through which Al phytotoxicity was alleviated by application of these amendments. In addition, the heavy metal contents in the four industrial byproducts constituted a limited environmental hazard in a short time at the rates normally used in agriculture. Therefore, the short-term use of the byproducts, especially AS and RM, as amendments for soil acidity and Al toxicity in acid soils may be a potential alternative to the traditional use of mined gypsum and lime.
The actinomycete populations and functions in cadmium (Cd) contaminated soil were investigated by the cultivation-independent molecular methods. The genomic DNA was extracted and purified from soil adulterated with various concentrations of Cd in the laboratory. The partial 16S rDNA genes were amplified by polymerase chain reaction (PCR) using specific primers bound to evolutionarily conserved regions within these actinomycete genes. The diversity in PCR-amplified products, as measured by denaturing gradient gel electrophoresis (EGGE), was used as a genetic fingerprint of the population. Principle component analysis and Shannon-Weaver diversity index (H) analyses were used to analyze the DGGE results. Results showed that the two principal components accounted for only a low level of the total variance. The value H in contaminated soil was lower than that in the control at later stages of cultivation, whereas at earlier stages it was higher. Among the six sampling time points, the first, fifth and sixth weeks had the highest values of H. Significantly negative correlations between bioavailable Cd concentration and H values existed in the samples from weeks 2 (R =0.929, P< 0.05) and 4 (R =0.909, P< 0.05). These results may shed light on the effect of Cd on the soil environment and the chemical behavior and toxicity of Cd to actinomycetes.
The enhanced biological phosphorus removal (EBPR) method is widely adopted for phosphorus removal from waste-water, yet little is known about its microbiological and molecular mechanisms. Therefore, it is difficult to predict and control the deterioration of the EBPR process in a large-scale municipal sewage treatment plant. This study used a novel strain isolated in the laboratory, Pseudomonas putida GM6, which had a high phosphate accumulating ability and could recover rapidly from the deteriorated system and enhance the capability of phosphorus removal in activated sludge. Strain GM6 marked with gfp gene, which was called GMTR, was delivered into a bench-scale sequencing batch reactor (SBR) of low efficiency, to investigate the colonization of GMTR and removal of phosphorus. After 21 days, the proportion of GMTR in the total bacteria of the sludge reached 9.2%, whereas the phosphorus removal rate was 96%, with an effluent concentration of about 0.2 mg L−1. In the reactor with the addition of GMTR, phosphorus was removed quickly, in 1 h under anaerobic conditions, and in 2 h under aerobic conditions. These evidences were characteristic of EBPR processes. Field testing was conducted at a hospital sewage treatment facility with low phosphorus removal capability. Twenty- one days after Pseudomonas putida GM6 was added, effluent phosphorus concentration remained around 0.3 mg L−1, corresponding to a removal rate of 96.8%. It was therefore demonstrated that Pseudomonas putida GM6couldbeused for a quick startup and enhancement of wastewater biological phosphorus removal, which provided a scientific basis for potential large-scale engineering application.
The nature of the interactions between microbes and roots of plants in a peaty soil were studied in a laboratory-based experiment by measuring activities of β-glucosidase, phosphatase, N-acetylglucosaminidase, and arylsulphatase. The
experiment was based on control (autoclaved), bacteria-inoculated, and plant (transplanted with Dactylorhiza) treatments, and samples were collected over 4 sampling intervals. Higher enzyme activities were associated with the bacteria-inoculated treatment, suggesting that soil enzyme activities are mainly of microbial origin. For example, β-glucosidase activity varied between 25-30μmol g−1 min−1 in the bacteria-inoculated samples whilst the activity of the control ranged between 4-12μmol g−1 min−1. A similar pattern was found for all other enzymes.At the end of the incubation, the microcosms were destructively sampled and the enzyme activities determined in bulk soil, rhizospheric soil, and on the root surface. Detailed measurement in different fractions of the peat indicated that higher activities were found in rhizosphere. However, the higher activities of β-glucosidase, N-acetylglucosaminidase, and arylsulphatase appeared to be associated with bacterial proliferation on the root surface, whilst a larger proportion of phosphatase appeared to be released from root surface.
Due to frequent soil Cd contamination and wide use of butachlor in China, there is a need to assess their combined toxicity to soil microorganisms. The combined effects of cadmium (Cd, 10 mg kg−1 soil) and herbicide butachlor (10, 50, and 100 mg kg−1 soil) on enzyme activities and microbial community structure in a paddy soil were assessed using the traditional enzyme assays and random amplified polymorphic DNA (RAPD) analysis. The results showed that urease and phosphatase activities were significantly reduced by high butachlor concentration (100 mg kg−1 soil). When the concentrations of Cd and butachlor added were at a ratio of 1:10, urease and phosphatase activities were significantly decreased whereas enzyme activities were greatly improved at the ratio of 1:5, which indicated that the combined effects of Cd and butachlor on soil urease and phosphatase activities depended largely on their addition concentration ratios. Random amplified polymorphic DNA (RAPD) analysis showed loss of original bands and appearance of new bands when compared with the control soil. Random amplified polymorphic DNA fingerprints suggested substantial differences between the control and treated soil samples, with apparent changes in the number and size of amplified DNA fragments. The addition of high concentration butachlor and the combined impacts of Cd and butachlor significantly affected the diversity of the microbial community. RAPD analysis in conjunction with other biomarkers such as soil enzyme parameters would prove a powerful ecotoxicological tool. Further investigations should be carried out to understand the clear link between RAPD patterns and enzyme activity.
Several newly developed capacitance sensors have simplified real-time determination of soil water content. Previous work has shown that salinity and temperature can affect these sensors, but relatively little has been done to correct these effects. The objectives of this study were to evaluate the effect of media temperature and salinity on the apparent water content measured with a single capacitance sensor (SCS), and to mitigate this effect using a temperature dependent scaled voltage technique under laboratory conditions. A column study was conducted containing two media: pure deionized water and quartz sand under varying water contents (0.05 to 0.30 cm3 cm−3) and salinity (0 to 80 mmol L−1). Media temperature was varied between 5 and 45 °C using an incubator. The SCS probes and thermocouples were placed in the middle of the columns and were logged at an interval of 1 minute. There was strong negative correlation between sensor reading and temperature of deionized water with a rate of −0.779 mV °C−1. Rates of SCS apparent output were 0.454 and 0.535 mV °C−1 for air in heating and cooling cycles, respectively. A similar positive correlation with temperature was observed in sand at different water contents. The SCS probe was less sensitive to temperature as salinity and water content increased. Using a temperature-corrected voltage calibration model, the effect of temperature was reduced by 98%. An analytical model for salinity correction was able to minimize the error as low as ± 2% over the salinity level tested.
A batch experiment was performed to investigate nonequilibrium adsorption behavior of atrazine (2-chloro-4-ethylami-no-6-isopropylamino-1,3,5-triazine) on a fluvo-aquic soil. The amount of atrazine sorbed increased with increasing adsorption contact periods. For a range of initial atrazine concentrations, the percentage of atrazine sorbed within 24 h ranged from 24% to 77% of the observed total amount sorbed for the longest contact period; when adsorption contact periods were more than 72 h, the deviations in curves fitted using a nonlinear Freundlich equation gradually became less. The op- posite trend was observed for the atrazine concentrations in solution. The effect of adsorption contact periods on atrazine adsorption behavior was evaluated by interpreting the temporal variations in linear and nonlinear Freundlich equation parameters obtained from the phase-distribution relationships. As the adsorption contact period increased, the nonlinear Freundlich capacity coeffcient kf showed a significant linear increase (r2 = 0:9063, P < 0:001). However, a significant negative linear correlation was observed for the nonlinear coeffcient n, a dimensionless parameter (r2 = 0:5666, P < 0:05). Furthermore, the linear distribution coeffcient kd ranged from 0.38 to 1.44 and exhibited a significant linear correlation to the adsorption contact period (r2 = 0:72, P < 0:01). The parameters kf and n obtained from a time-dependent isotherm rather than the distribution coeffcient kd estimated using the linear Freundlich equation were more appropriate to predict the herbicide residue in the field and thus more meaningful for environmental assessment.
Gibbs free binding energy and adsorption energy between cations and charged soil particles were used to evaluate the interactions between ions and soil particles. The distribution of Gibbs free adsorption energies could not be determined experimentally before the development of Wien effect measurements in dilute soil suspensions. In the current study, energy relationships between heavy metal ions and particles of Hapli-Udic Argosol (Alfisol) and Ferri-Udic Argosol were inferred from Wien effect measurements in dilute suspensions of homoionic soil particles (< 2μm) of the two soils, which were saturated with ions of five heavy metals, in deionized water. The mean Gibbs free binding energies of the heavy metal ions with Hapli-Udic Argosol and Ferri-Udic Argosol particles diminished in the order of Pb2+ > Cd2+ > Cu2+ > Zn2+ > Cr3+, where the range of binding energies for Hapli-Udic Argosol (7.25-9.32 kJ mol−1) was similar to that for Ferri-Udic Argosol (7.43-9.35 kJ mol−1). The electrical field-dependent mean Gibbs free adsorption energies of these heavy metal ions for Hapli-Udic Argosol and for Ferri-Udic Argosol descended in the order: Cu 2+≥Cd 2+≥Pb2+ > Zn2+ > Cr3+, and Cd2+ > Cu2+ > Pb2+ > Zn2+ > Cr3+, respectively. The mean Gibbs free adsorption energies of Cu2+, Zn2+, Cd2+, Pb2+, and Cr3+ at a field strength of 200 kV cm−1, for example, were in the range of 0.8-3.2 kJ mol−1 for the two soils.
AbstractA new competitive adsorption isothermal model (CAIM) was developed for the coexistent and competitive binding of heavy metals to the soil surface. This model extended the earlier adsorption isothermal models by considering more than one kind of ion adsorption on the soil surface. It was compared with the Langmuir model using different conditions, and it was found that CAIM, which was suitable for competitive ion adsorption at the soil solid-liquid surface, had more advantages than the Langmuir model. The new competitive adsorption isothermal model was used to fit the data of heavy metal (Zn and Cd) competitive adsorption by a yellow soil at two temperatures. The results showed that CAIM was appropriate for the competitive adsorption of heavy metals on the soil surface at different temperatures. The fitted parameters of CAIM had explicit physical meaning. The model allowed for the calculation of the standard molar Gibbs free energy change, the standard molar enthalpy change, and the standard molar entropy change of the competitive adsorption of the heavy metals, Zn and Cd, by the yellow soil at two temperatures using the thermodynamic equilibrium constants.
Evidence that nitrogen (N) fertilization tends to accelerate maturation as well as increase rates of growth has received little attention when diagnosing N deficiencies in corn (Zea mays L.). Such a tendency could be a potential source of errors when the diagnosis is solely based on comparing plants with different rates of growth. Whether N fertilization could accelerate rates of growth and maturation was tested in a field study with 12 paired plots representing relatively large variability in soil properties and landscape positions. The plots were located under conditions where preplant N fertilization reduced or avoided temporary N shortages for some plants but did not reduce for other plants early in the season. We measured corn heights to the youngest leaf collar, stages of growth and chlorophyll meter readings (CMRs). The added N advanced growth stages as well as increased corn heights and CMRs at any given time. Fertilization effects on corn heights, growth stages and ear weights were statistically significant (P < 0.05) despite substantial variability associated with landscape. Reductions in growth due to a temporary shortage of N within a growth stage might be partially offset by longer periods of growth within that stage to physiological maturity. Temporary shortages of N, therefore, may produce symptoms of N deficiency in situations where subsequent additions of N should not be expected to increase yields. Recognition of these two somewhat different effects (i.e., increase growth rates and advance growth stages) on corn growth could help to define N deficiency more precisely and to improve the accuracy of diagnosing N status in production agriculture.
The prediction of the oxidation rate of elemental sulfur (S0) is a critical step in sulfur (S) fertilizer strategy to supply plant-available sulfur. An incubation experiment was conducted to determine the rate and amount of S0 oxidation in relation to the contribution of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria. After 84 days, 16.3% and 22.4% of the total S0 applied to the soil were oxidized at 20 and 30 °C, respectively. The oxidation of S0 proved to be a two-step process with a rapid oxidation during the first 28 days and a slow oxidation from then on. The highest oxidation rate of 12.8 μg S cm−2 d−1 was measured during the first two weeks at 30 °C. At 20 °C the highest oxidation rate of 10.2 μg S cm−2 d−1 was obtained from two to four weeks after start of the experiment. On an average the soil pH declined by 3.6 and 4.0 units after two weeks of experiment. At the same time the electric conductivity increased nine times. With the oxidation of S0 the population of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased. The corresponding values for Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased from 2.9 × 105 and 1.4 × 105 g−1 soil at the start of the experiment to 4 × 108 and 5.6 × 108 g−1 soil 14 days after S0 application, respectively. No Thiobacillus spp. was present eight weeks after S0 application. The results suggested that oxidation of residual S0 completely relied on aerobic heterotrophic S-oxidizing bacteria.
Wet stability, penetration resistance (PR), and tensile strength (TS) of paddy soils under a fertilization experiment for 22 years were determined to elucidate the function of soil organic matter in paddy soil stabilization. The treatments included no fertilization (CK), normal chemical fertilization (NPK), double the NPK application rates (2NPK), and NPK mixed with organic manure (NPK+OM).Compared with CK, fertilization increased soil organic carbon (SOC) and soil porosity. The results of soil aggregate fragmentation degree (SAFD) showed that fast wetting by water was the key fragmentation mechanism. Among the treatments, the NPK+OM treatment had the largest size of water-stable aggregates and greatest normal mean weight diameter (NMWD) (P ≤ 0.05), but the lowest PR and TS in both cultivated horizon (Ap) and plow pan. The CK and 2NPK treatments were measured with PR > 2.0 MPa and friability index < 0.20, respectively, in the Ap horizon, suggesting that the soils was mechanically unfavourable to root growth and tillage. In the plow pan, the fertilization treatments had greater TS and PR than in CK. TS and PR of the tested soil aggregates were negatively correlated to SOC content and soil porosity. This study suggested that chemical fertilization could cause deterioration of mechanical properties while application of organic manure could improve soil stability and mechanical properties.
As an important component of the global carbon (C) budget, litter decomposition in terrestrial ecosystems is greatly affected by the increasing nitrogen (N) deposition observed globally. We hypothesized that different litter fractions derived from a single tree species may respond to N deposition differently depending on the quality of the litter substrate. To test the hypothesis, a two-year field experiment was conducted using the litterbag method in a Pleioblastus amarus plantation in the rainy region of Southwest China. Four N treatment levels were applied: control (no N added), low-N (50 kg N ha−1 year−1), medium-N (150 kg N ha−1 year−1), and high-N (300 kg N ha−1 year−1). We observed different patterns of mass loss for the three P. amarus litter fractions (leaves, sheaths, and twigs) of varying substrate quality in the control plots. There were two decomposition stages with different decay rates (fast rate in early stages and slow rate in the later stages) for leaves and sheaths, while we did not observe a slower phase for the decay of twigs during the 2-year study period. The annual decomposition rate (k) of twigs was significantly lower than that of leaves or sheaths. Addition of N slowed the decomposition of leaves and twigs in the later stages of decomposition by inhibiting the decay of lignin and cellulose, while addition of N did not affect the mass loss of sheaths during the study period. In the decomposition of all three litter fractions, experimental N deposition reduced the net N accumulation in the early stages and also decreased the net N release in the later stages. The results of this study suggest that litter substrate quality may be an important factor affecting litter decomposition in a bamboo ecosystem affected by N deposition.
Black soil (Mollisol) is one of the main soil types in northeastern China. Biolog and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) methods were used to examine the influence of various fertilizer combinations on the structure and function of the bacterial community in a black soil collected from Harbin, Heilongjiang Province. Biolog results showed that substrate richness and catabolic diversity of the soil bacterial community were the greatest in the chemical fertilizer and chemical fertilizer+manure treatments. The metabolic ability of the bacterial community in the manure treatment was similar to the control. DGGE fingerprinting indicated similarity in the distribution of most 16S rDNA bands among all treatments, suggesting that microorganisms with those bands were stable and not influenced by fertilization. However, chemical fertilizer increased the diversity of soil bacterial community. Principal component analysis of Biolog and DGGE data revealed that the structure and function of the bacterial community were similar in the control and manure treatments, suggesting that the application of manure increased the soil microbial population, but had no effect on the bacterial community structure. Catabolic function was similar in the chemical fertilizer and chemical fertilizer+manure treatments, but the composition structure of the soil microbes differed between them. The use of chemical fertilizers could result in a decline in the catabolic activity of fast-growing or eutrophic bacteria.
The binding of metallic contaminants (Pb, Cd, and Zn) and As on soil constituents was studied on four highly contaminated alluvial soil profiles from the mining/smelting district of Příbram (Czech Republic) using a combination of mineralogical and chemical methods. Sequential extraction analysis (SEA) was supplemented by mineralogical investigation of both bulk samples and heavy mineral fractions using X-ray diffraction analysis (XRD) and scanning electron microscopy with an energy dispersive X-ray spectrometer (SEM/EDS). The mineralogy of Fe and Mn oxides was studied by voltammetry of microparticles (VMP) and diffuse reflectance spectrometry (DRS). Zinc and Pb were predominantly bound in the reducible fraction attributed to Fe oxides and Mn oxides (mainly birnessite, Na4Mn14O27-9H2O), which were detected in soils by XRD and SEM/EDS. In contrast, Cd was the most mobile contaminant and was predominantly present in the exchangeable fraction. Arsenic was bound to the residual and reducible fractions (corresponding to Fe oxides or to unidentified Fe-Pb arsenates). SEM/EDS observations indicate the predominant affinity of Pb for Mn oxides, and to a lesser extent, for Fe oxides. Thus, a more suitable SEA procedure should be used for these mining-affected soils to distinguish between the contaminant fraction bound to Mn oxides and Fe oxides.
Fertilizers are heavily applied in orchards of the hilly and mountainous topography of South China and may increase nutrient loadings to receiving waters. A simple runoff collecting system was used to measure the effects of different fertilization treatments on total N and P concentrations of surface runoff in a Chinese chestnut (Castanea mollissima Blume) orchard in Dongyuan County, Guangdong Province, China, fn such orchards, fertilizer was typically applied in two short furrows or pits on either side of each tree. Treatments included three application depths (surface, 10 cm and 20 cm), and three application rates (low, median and high). Results showed that 90.5% of the runoff water samples had a total N concentration higher than 0.35 mg L−1 and 54.2% had a total P concentration higher than 0.1 mg L−1. Fertilizer application at all depths and at all but the lowest rate significantly increased total N and P concentrations in runoff water. Fertilization with chemical compound fertilizer at a soil depth of 20 cm produced significantly lower (P < 0.05) total N concentration in runoff than both surface and 10-cm depth fertilization, and significantly lower (P < 0.05) total P concentration in runoff than surface fertilization. Total N and P concentrations in runoff significantly increased with the application rate of organic fertilizers. With the exception of total P concentrations, which were not significantly different between the control and fertilization at a rate of 119 kg P ha−1 in organic form, all the other fertilization treatments produced significantly higher total N and total P concentrations in runoff than the control. A fertilization depth ≥ 20 cm and an application rate ≤ 72 kg N ha−1 or 119 kg P ha−1 for compound organic fertilizer was suggested to substantially reduce N and P runoff losses from hillslope orchards and to protect receiving waters in South China.
Soil potassium (K) deficiency has been increasing over recent decades as a result of higher inputs of N and P fertilizers concomitant with lower inputs of K fertilizers in China; however, the effects of interactions between N, P, and K of fertilizers on K status in soils have not been thoroughly investigated for optimizing N, P, and K fertilizer use efficiency. The influence of ammonium sulfate (AS), monocalcium phosphate (MCP), and potassium chloride application on K fractions in three typical soils of China was evaluated during 90-d laboratory soil incubation. The presence of AS significantly altered the distribution of native and added K in soils, while addition of MCP did not significantly affected K equilibrium in most cases. Addition of AS significantly increased water-soluble K (WSK), decreased exchangeable K (EK) in almost all the soils except the paddy soil that contained considerable amounts of 2:1 type clay minerals with K added, retarded the formation of fixed K in the soils with K added, and suppressed the release of fixed K in the three soils without K added. These interactions might be expected to influence the K availability to plants when the soil was fertilized with AS. To improve K fertilizer use efficiency, whether combined application of AS and K was to be recommended or avoided should depend on K status of the soil, soil properties, and cropping systems.
To assess the effect of rice straw mulching on changes of antagonistic bacteria and the incidence of wheat sharp eyespot, a multi-year field study was performed to compare unmulched plots and the plots mulched with rice straw for two or three years. Bacterial and fungal populations were evaluated in the cultures prepared from the wheat rhizosphere and bulk soils. Rice straw mulching increased the number of pseudomonas colony forming units in wheat rhizosphere and bulk soils. The proportion of total bacteria that were fluorescent pseudomonads was higher in mulched than in unmulched soil. Bacterial isolates antagonistic to Rhizoctonia cerealis were identified using an inhibition zone test. A series of these isolates were typed by partial sequencing of the 16S rRNA gene. Pseudomonads had higher antagonistic activity against R. cerealis than other species, and more than 80% of rhizosphere fluorescent pseudomonads were antagonistic to R. cerealis. The disease indices were lower in the mulched plots than in the unmulched control. These results suggest that rice straw mulching in a rice-wheat rotation increases the number of fluorescent pseudomonads. Additionally, these fluorescent pseudomonads may contribute to the control of wheat sharp eyespot.
A greenhouse experiment was conducted to test and compare the suitability of saline compost and saline irrigation water for nutrient status amendment of a slightly productive sandy clay loam soil, to study the macronutrient utilization and dry matter production of wheat (Triticum aestivum c.v. Gemmiza 7) grown in a modified soil environment and to determine the effects of compost and saline irrigation water on soil productivity. The sandy clay loam soil was treated with compost of five rates (0, 24, 36, 48, and 60 m3 ha−1, equivalent to 0, 3, 4.5, and 6 g kg−1 soil, respectively) and irrigation water of four salinity levels (0.50 (tap water), 4.9, 6.3, and 8.7 dS m−1). The results indicated that at harvest, the electrical conductivity (EC) of the soil was significantly (P < 0.05) changed by the compost application as compared to the control. In general, the soil salinity significantly increased with increasing application rates of compost. Soluble salts, K, Cl, HCO3, Na, Ca, and Mg, were significantly increased by the compost treatment. Soil sodium adsorption ratio (SAR) was significantly affected by the salinity levels of the irrigation water, and showed a slight response to the compost application. The soil organic carbon content was also significantly (P < 0.05) affected by application of compost, with a maximum value of 31.03 g kg−1 recorded at the compost rate of 60 m3 ha−1 and the irrigation water salinity level of 8.7 dS m−1 and a minimum value of 12.05 g kg−1 observed in the control. The compost application produced remarkable increases in wheat shoot dry matter production. The maximum dry matter production (75.11 g pot−1) occurred with 60 m3 ha−1 compost and normal irrigation water, with a minimum of 19.83 g pot−1 with no addition of compost and irrigation water at a salinity level of 8.70 dS m−1. Significant increases in wheat shoot contents of K, N, P, Na, and Cl were observed with addition of compost. The relatively high shoot N values may be attributed to increases in N availability in the tested soil caused by the compost application. Similarly, significant increases in the shoot contents of Na and Cl may be ascribed to the increase in soil soluble K and Cl. The increases in shoot P, N, and K contributed to the growth stimulation since P supplied by the compost was probably responsible in saline and alkaline soils where P solubility was very low.
Extensive worldwide use of oxytetracycline (OTC), a member of the tetracyclines, has resulted in its accumulation in soils, posing a potential risk to food production and safety. A pair of OTC-sensitive (Heyou 1) and OTC-tolerant (Yannong 21) wheat (Triticum aestivum L.) cultivars was compared hydroponically at 0.01, 0.02, 0.04, and 0.08 mmol L−1 OTC in terms of wheat growth and photosynthesis. Biomass and shoot length decreased significantly with the addition of OTC, with the decreases in dry biomass and shoot length being 5.61%-13.75% and 3.33%-8.57% larger, respectively, for Heyou 1 than Yannong 21. Photosynthesis of Heyou 1 was suppressed by OTC as indicated by the significant decreases in photosynthetic rate (PN), transpiration rate (TR), and stomatal conductance (GS) and the significant increase in intercellular CO2 concentrations (CI), at all OTC levels. Stomatal limitation (LS) and water use efficiencies (WUE) of Heyou 1 also increased significantly, but not at 0.08 mmol L−1 OTC. However, photosynthesis of Yannong 21 was suppressed by OTC only at high OTC levels from 0.02 to 0.08 mmol L−1 as indicated by the decreases in PN, GS, TR, and LS; at 0.01 mmol L−1 OTC, PN, CI, GS, and TR significantly increased. It was noted that WUE of Yannong 21 was not affected by OTC addition. The results from this hydroponic test suggested that OTC had a potential risk to crop growth through inhibition of photosynthesis, requiring further confirmation with soil tests.
Micronutrient status in soils can be affected by long-term fertilization and intensive cropping. A 19-year experiment (1990–2008) was carried out to investigate the influence of different fertilization regimes on micronutrients in an Aquic Inceptisol and maize and wheat grains in Zhengzhou, China. The results showed that soil total Cu and Zn markedly declined after 19 years with application of N fertilizer alone. Soil total Fe and Mn were significantly increased mainly due to atmospheric deposition. Applications of P and organic fertilizer with incorporation of straws resulted in dramatic increases in soil total Cu, Zn, Fe, and Mn. Soil diethylenetriamine pentaacetic acid (DTPA)-extractable Cu in all treatments sharply decreased from initially 1.12 to about 0.8 mg kg−1. The treatments with organic fertilizer had the highest soil DTPA-extractable Cu, Zn, Fe, and Mn after 19 years of cropping and fertilization, thus demonstrating the important role of organic fertilizer application in improving available micronutrient status. Cu and Zn contents in wheat grains in the no-P treatments were significantly higher than those of the treatments with P application. In addition, Fe and Mn contents in wheat grains were positively correlated with their soil DTPA-extractable concentrations. These indicated that the long-term application of organic fertilizer resulted in significant increases in soil total and available micronutrient concentrations and remarkable reduction in wheat grain Cu and Zn contents, which was due to high soil available P.
Raw sewage is widely used on agricultural soils in urban areas of developing countries to meet water shortages. Although it is a good source of plant nutrients, such sewage also increases the heavy metal load to soils, which may impact the food chain. Management options for sewage contaminated soils includes addition of nontoxic compounds such as lime, calcium sulfate and organic matter, which form insoluble metal complexes, thus reducing metal phytoavailability to plants. In this paper we review the variation in irrigation quality of sewage at different sites and its impact on the quality of soils and vegetables. Although quality of sewage was highly variable at source, yet the effluent from food industries was relatively safe for irrigation. In comparison effluent samples collected from textile, dyeing, calendaring, steel industry, hospitals and clinical laboratories, foundries and tanneries were hazardous with respect to soluble salts, sodium adsorption ratio and heavy metals like zinc, copper, iron, manganese, nickel, cobalt and cadmium. The sewage quality in main drains was better than that at the industry outlet, but was still not safe for irrigation. In general, higher accumulation of metals in fruits and vegetable roots was recorded compared to that in plant leaves. Edible parts of vegetables (fruits and/or leaves) accumulated metals more than the permissible limits despite the soils contained ammonium bicarbonate diethylenetriaminepentaacetic acid extractable metals within a safe range. In either case further scientific investigations are needed to ensure safe management strategies. Cadmium appeared to be the most threatening metal especially in leafy vegetables. It is advisable to avoid leafy vegetables cultivation in sewage irrigated areas everywhere to restrict its entry into food chain.
Concentrations of Iron (Fe), As, and Cu in soil samples from the fields near the Baoshan Mine in Hunan Province, China, were analyzed and soil spectral reflectance was measured with an ASD FieldSpec FR spectroradiometer (Analytical Spectral Devices, Inc., USA) under laboratory condition. Partial least square regression (PLSR) models were constructed for predicting soil metal concentrations. The data pre-processing methods, first and second derivatives (FD and SD), baseline correction (BC), standard normal variate (SNV), multiplicative scatter correction (MSC), and continuum removal (CR), were used for the spectral reflectance data pretreatments. Then, the prediction results were evaluated by relative root mean square error (RRMSE) and coefficients of determination (R2). According to the criteria of minimal RRMSE and maximal R2, the PLSR models with the FD pretreatment (RRMSE = 0.24, R2 = 0.61), SNV pretreatment (RRMSE = 0.08, R2 = 0.78), and BC-pretreatment (RRMSE = 0.20, R2 = 0.41) were considered as the final models for predicting As, Fe, and Cu, respectively. Wavebands at around 460, 1 400, 1 900, and 2 200 nm were selected as important spectral variables to construct final models. In conclusion, concentrations of heavy metals in contaminated soils could be indirectly assessed by soil spectra according to the correlation between the spectrally featureless components and Fe; therefore, spectral reflectance would be an alternative tool for monitoring soil heavy metals contamination.
The saline wetlands, or "saladas", of Monegros Desert, NE Spain, contain biodiversity that depends on the establishment of a prognostic monitoring system that can warn of approaching irreversible damage. In the context of a lack of existing biodiversity inventories for the saladas, we determined their state of conservation and vulnerability using seven physical indicators: escarpment continuity, cropping, stone dumping, size, water occurrence, distance to roads, and proximity to irrigated areas. These features were combined into three meaningful indexes, i.e., conservation, current vulnerability, and future vulnerability, thus creating an assessment of the preservation or degradation of saladas in the context of encroaching agricultural irrigation projects. The proposed indexes produced consistent results and showed that a great number of the Monegros wetlands were threatened, regardless of their size or frequency of water occurrence. Only 20% of the saladas studied were classified as being in a good or very good conservation, whereas 50% were in bad or very bad shape. A high current vulnerability was found for 60% of the saladas. For saladas located in land to be irrigated, we predicted that 73% would have a high or very high future vulnerability. Currently, 58% of the saladas were in bad or very bad condition and fully 65% of the saladas, variable in size, presented a bad or very bad prognosis. Our approach provides a monitoring strategy for the conservation of saline wetlands threatened by agricultural intensification, especially irrigation.
The contributions of persistent organic pollutants (POPs) from the subtropical regions of China to pollution of the global environment have been paid great attention; however, little is known about the state of POPs in agricultural ecosystems within these regions of China. This study primarily revealed the state of the contamination and distribution of polycyclic aromatic hydrocarbons (PAH) in agricultural soils in the subtropical regions. 115 surface soils (0–20 cm) were sampled in the breadbaskets of these regions. The concentrations and types of PAH were determined using gas chromatography linked to mass spectrometry (GC-MS). The total PAH concentrations ranged from 22.1 to 1 256.9 ng g−1, with a mean of 318.2 ± 148.2 ng g−1. In general terms, the current PAH concentrations were lower than most PAH levels reported in a number of investigations from different countries and regions. PAH isomer ratios indicated that pyrolytic origins, such as fossil fuel combustion related to vehicle tail gas and industrial emissions, were the dominant sources of PAH in the southern subtropical areas of China. Although PAH concentrations decreased with decreasing pollution, population, and traffic density, to a great extent PAH compositions were similar throughout subtropical soils, with naphthalene, phenanthrene, fluoranthene, and benzo(b)fluoranthene being dominant.
Multivariate statistical technique was used to determine the potassium (K+) status and to assess soil fertility and K leaching potential in some calcareous soils. Water-soluble K+ (H2O-K) and ammonium acetate-extractable K+ (NH4OAc-K) ranged from 0.019 to 0.590 (mean value 0.095) and 0.390 to 3.320 (mean value 0.954) cmolc kg−1, respectively. The nitric acid-extractable K+ (HNO3-K) varied from 1.03 to 13.63 (mean value 5.37) cmolc kg−1. The proportion of H2O-K ranged from 0.34% to 14.8% of HNO3-K, and 2.2% to 53.2% of NH4OAc-K. The proportion of NH4OAc-K ranged from 5.8% to 80% of HNO3-K (mean value 23% of HNO3-K). The tendency of the soil to lose K+ by leaching was examined by determining K+-Ca2+ exchange isotherms. The soils mostly had moderate to high values of K+ sorption capacity, ranging from 10% to 58% (mean value 28%) of added K+. The Gapon coefficient varied widely from 1.1 to 12.0 (L mol−1)−1/2. Clay minerals were dominated by illite, smectites and vermiculite with small amounts of kaolinite. Principal component analysis (PCA) showed that the first four components accounted for 27.7%, 21.4%, 13.8%, and 8.9% of total variation, respectively. The non-hierarchical cluster analysis (k-means clustering) grouped 75 sampling sites into six clusters, based on the similarity of soil quality characteristics. The results suggested that such classes could form a basis for variable-rate application to maintain an adequate K+ status for crop production and to reduce potential K+ loss from soil by leaching.
Irrational irrigation practices in the Arys Turkestan Canal command area in the southern part of Kazakhstan have led to the formation of soils with poor physical and chemical properties. To study whether irrigation and leaching practices and/or groundwater rise have contributed to the accumulation of Mg2+ on the cation exchange complex of these soils, historical changes in soil and groundwater quality were used as source data and the Visual MINTEQ model was applied to analyze the chemical composition of water and soils in the study area. The imposed irrigation regime and the leaching of light sierosem soils led to the dissolution and subsequent leaching of inherent gypsum and organic matter from the soil profile. Further, the domination of bicarbonate in the irrigation water promoted weathering of the carbonate minerals present as calcite. The higher concentrations of Mg2+ in comparison to Ca2+ in the irrigation water resulted in the replacement of Na+ by Mg2+ on the cation exchange complex. In the lower part of the command area, shallow groundwater has contributed to the accumulation of Na+ and to a large extent of Mg2+ on the cation exchange sites.
On-farm experiments were conducted in farmers' fields at 6 different sites in Western Usambara Mountains (WUM) in northern Tanzania during the 2000-2001 cropping season. The objectives were to study the effects of Tughutu (Vernonia subligera O. Hoffn) pruning in combination with Minjingu phosphate rock (MPR) or triple super phosphate (TSP) supply on the concentration of P in the tissues and seed yields of common bean, and to assess the economic returns of these different technologies to farmers. The experimental design was a randomized complete block with each of the 6 farmers' fields used as a replicate. The treatments included: control, MPR or TSP each at 26 kg P ha−1, Tughutu at 2.5 t ha−1, and Tughutu at 2.5 t ha−1 combined with MPR or TSP at 26 kg P ha−1.Addition of MPR or TSP alone significantly raised P concentration in bean shoots from 1.27 mg g−1 to 1.70 and 1.95 mg g−1 respectively. Combining MPR or TSP with Tughutu increased P concentration above the proposed deficiency level of 2 mg g−1. The relative agronomic effectiveness (RAE) of MPR ranged from 12.5% to 45.0%. Seed yields of common bean was markedly increased by 28%-104% from MPR or TSP supply alone, and 148%-219% from Tughutu application combined with 26 kg P ha−1 of MPR or TSP relative to the control. With Tughutu alone, seed yield increased by 53%.From economic analysis, the increase in seed yield with the supply of MPR or TSP combined with Tughutu translated into a significantly (P ≤ 0.001) higher marginal rate of return and dollar profit for common bean farmers in WUM in northern Tanzania. It is concluded that Tughutu and its combined application with MPR or TSP is an appropriate integrated nutrient management strategy that may increase bean yields and dollar profit to the rural poor communities in Tanzania.
Alfalfa cropping has been considered an efficient method of increasing soil fertility. Usually nitrogen increase in root nodules is considered to be the major beneficial effect. A 21-year time series (five sampling periods) of alfalfa cultivation plots on a loess soil, initially containing illite and chlorite, in Lanzhou of northwestern China was selected to investigate the relationships among alfalfa cropping, soil potassium (K) content and soil clay minerals. The results indicated that soil K significantly accumulated after cropping, with a peak value at about 15 years, and decreased afterwards. The accumulated K was associated with the K increase in the well-crystallized illite, which was not extracted by the traditional laboratory K extraction methods in assessing bioavailability. The steep decline in soil K content after 15-year cropping was in accord with the observed fertility loss in the alfalfa soil. Plant biomass productivity peaked at near 9 years of culture, whereas soil K and clay minerals continued to increase until cropping for 15 years. This suggested that K increased in the topsoil came from the deep root zone. Thus alfalfa continued to store K in clays even after peak production occurred. Nitrogen did not follow these trends, showing a general decline compared with the native prairie soils that had not been cropped. Therefore, the traditional alfalfa cropping can increase K content in the topsoil.
Spartina alterniflora Loisel, a species vegetating in intertidal flats along the eastern coast of the United States, was introduced in China almost 30 years ago and has become an urgent topic due to its invasiveness in the coastal zone of China. The impacts of this alien species S. alterniflora on intertidal ecosystem processes in the Jiangsu coastland were investigated by comparing the sediment nutrient availability and trace element concentration characteristics in a mudflat and those of a four-year old Spartina salt marsh that had earlier been a mudflat. At each study site, fifteen plots were sampled in different seasons to determine the sediment characteristics along the tidal flats. The results suggested that Spartina salt marsh sediments had significantly higher total N, available P, and water content, but lower pH and bulk density than mudflat sediments. Sediment salinity, water content, total N, organic C, and available P decreased along a seaward gradient in the Spartina salt marsh and increased with vegetation biomass. Furthermore, the concentrations of trace elements and some metal elements in the sediment were higher under Spartina although these increases were not significant. Also, in the Spartina marsh, some heavy metals were concentrated in the surface layer of the sediment. The Spartina salt marsh in this study was only four years old; therefore, it is suggested that further study of this alien species on a longer time frame in the Jiangsu coastland should be carried out.
The growth performance of pakchoi (Brassica chinensis L.) in relation to soil cadmium (Cd) fractionations was investigated to evaluate the remediating effect of poultry manure compost on Cd-contaminated soil. A yellow-brown soil (Alfisol) treated with various levels of Cd (0–50 mg Cd kg−1 soil) was amended with increasing amounts of compost from 0 to 120 g kg−1. Compost application transformed 47.8%–69.8% of soluble/exchangeable Cd to the organic-bound fraction, and consequently decreased Cd uptake of pakchoi by 56.2%–62.5% as compared with unamended soil. Alleviation of Cd bioavailability by compost was attributed primarily to the increase of soil pH and complexation of Cd by organic matter including dissolved organic matter. In general, the improvement of pakchoi performance was more pronounced in higher Cd-contaminated soil. Addition of large amount of compost also favored the anti-oxidative capability of pakchoi against Cd toxicity. This low cost remediation method seems to be very effective in the restoration of Cd-contaminated soils.
In nutrient-limited alpine meadows, nitrogen (N) mineralization is prior to soil microbial immobilization; therefore, increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils. In addition, low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization. A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau. Two levels of NH4NO3 (N) or glucose (C) were added, with a blank without addition of C or N as the control, before incubation at 5, 15, or 25 °C for 28 d. CO2 efflux was measured during the 28-d incubation, and the mineral N was measured at the beginning and end of the incubation, in order to test two hypotheses: 1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive. The results showed a negative correlation between CO2 efflux and net N immobilization in the control. External inorganic N supply did not change the negative correlation. The external labile C supply shifted the linear correlation from negative to positive under the low C addition level. However, under the high C level, no correlation was found. These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures. Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.
Atlantic rankers belong to the group of “cryptopodzolic rankers”, which are ubiquitous in the mountainous cool/temperate humid regions of Western Europe. The rankers of Galicia (NW Spain) formed by thousands of years of colluviation. The preponderance of Al-stabilised organic matter (OM) masks the horizonation and polycyclic character (i.e., stratification) of these soils. Cryptopodzolic rankers are generally thought to be the outcome of podzolisation. This soil type is part of the recent discussion on how to classify soils developed from nonvolcanic parent material having andic properties.To better understand the formation processes of these soils, the Al and Fe fractionation of four typical Atlantic rankers were studied by selective dissolution in acid NH4-oxalate, Na-pyrophosphate and the chlorides of K, La and Cu. A high-resolution sampling approach allowed us to investigate the soils in greater detail than simply sampling by horizon. The rankers studied display a distribution of Fe- and Al-OM complexes that is typical of cryptopodzolic soils. However, these organomineral associations were probably immobile due to the high Al saturation. We argue that the soils owe their characteristic chemical status to external factors rather than to translocation of organomineral associations: variations in Al-OM concentrations could be linked to changes in weathering/leaching intensity and colluviation rates caused by anthropogenic disturbances or changes in regional climate regime.
A hydroponics experiment was conducted to evaluate the role of potassium (K) and silicon (Si) in mitigating the deleterious effects of NaCl on sugarcane genotypes differing in salt tolerance. Two salt-sensitive (CPF 243 and SPF 213) and two salt-tolerant (HSF 240 and CP 77-400) sugarcane genotypes were grown for six weeks in ½ strength Johnson's nutrient solution. The nutrient solution was salinized by two NaCl levels (0 and 100 mmol L−1 NaCl) and supplied with two levels of K (0 and 3 mmol L−1) and Si (0 and 2 mmol L−1). Applied NaCl enhanced Na+ concentration in plant tissues and significantly (P ≤ 0.05) reduced shoot and root dry matter in four sugarcane genotypes. However, the magnitude of reduction was much greater in salt-sensitive genotypes than salt-tolerant genotypes. The salts interfered with the absorption of K+ and Ca2+ and significantly (P ≤ 0.05) decreased their uptake in sugarcane genotypes. Addition of K and Si either alone or in combination significantly (P ≤ 0.05) inhibited the uptake and transport of Na+ from roots to shoots and improved dry matter yields under NaCl conditions. Potassium uptake, K+/Na+ ratios, and Ca2+ and Si uptake were also significantly (P ≤ 0.05) increased by the addition of K and/or Si to the root medium. In this study, K and Si-enhanced salt tolerance in sugarcane genotypes was ascribed to decreased Na+ concentration and increased K+ with a resultant improvement in K+/Na+ ratio, which is a good indicator to assess plant tolerance to salt stress. However, further verification of these results is warranted under field conditions.
The effects of long-term (19 years) different land use and fertilization on activity and composition of ammonia-oxidizing bacteria (AOB) in an aquic brown soil were investigated in a field experiment in Liaoning Province, China. The 19-year experiment conducted from 1990 to 2008 involved seven treatments designed: cropping rotation of soybean-corn-corn with no fertilizer (control, CK), recycled manure (RM), fertilizer nitrogen (N), phosphorous (P) and potassium (K) (NPK), NPK+RM, and no-crop bare land, mowed fallow, and non-mowed fallow. The results showed that the potential nitrification rates of the RM, NPK+RM, mowed fallow, and non-mowed fallow treatments were significantly higher (P < 0.05) than those of the CK and NPK treatments, indicating that the long-term applications of recycled manure and return of plant residues both significantly increased the activity of AOB. Although the application of NPK did not enhance soil potential nitrification because of decreased pH, available K had an important effect on potential nitrification. Denaturing gradient gel electrophoresis (DGGE) fingerprint profiles showed that no-crop treatments had an increase in the diversity of the AOB community compared to the CK, RM, and NPK treatments, implying that agricultural practices, especially tillage, had an adverse effect on the soil AOB community. The NPK+RM treatment had the most diverse DGGE patterns possibly because of the increased available P in this treatment. A phylogenetic analysis showed that most of the DGGE bands derived belonged to Nitrosospira cluster 3, not Nitrosospira cluster 2. These demonstrated that different land use and fertilization significantly influenced the activity and composition of the AOB community by altering the soil properties, mainly including pH, total C, available K, and available P.
A variable-charge (VC) and a permanent-charge paddy soil (PC) were selected to study nitrate-N (NO−3-N) and ammonium-N (NH+4-N) leaching with N isotopes for one consecutive year. An irrigation and intermittent drainage pattern was adopted to mimic natural occurrence of rainfall during the upland crop season and drainage management during the flooded rice season. Treatments to each soil type were no-N controls (CK), 15N-labeled (NH4)2SO4 (NS), and milk vetch (NV) applied at a rate equivalent to 238 kg N ha−1 to unplanted lysimeters, totaling six treatments in triplicates. Results indicated that the soil type dominated N leaching characteristics. In the case of PC, NO−3-N accounted for 78% of the total leached inorganic N; NS was prone to leach three times more than the NV, being 8.2% and 2.4% of added 15N respectively; and > 85% of leached NO−3-N came from native N in the soil. In the case of VC, NH+4-N made up to 92% of the total inorganic N in leachate. Moreover, NH+4-N particularly high during the flooded season. NO−3-N leaching in VC occurred later at a lower rate compared to that in PC. The findings of this study indicate that NO−3-N leaching during the drained season in permanent-charge paddy soils and NH+4-N leaching in variable-charge soils deserve more attention for regional environmental control.
Taihu Lake region is one of the most industrialized areas in China, and the surface water is progressively susceptible to anthropogenic pollution. The physicochemical parameters of surface water quality were determined at 20 sampling sites in Taihu Lake region, China in spring, summer, autumn, and winter seasons of 2005–2006 to assess the effect of human activities on the surface water quality. Principal component analysis (PCA) and cluster analysis (CA) were used to identify characteristics of the water quality in the studied water bodies. PCA extracted the first three principal components (PCs), explaining 80.84% of the total variance of the raw data. Especially, PC1 (38.91%) was associated with NH4-N, total N, soluble reactive phosphorus, and total P. PC2 (22.70%) was characterized by NO3-N and temperature. PC3 (19.23%) was mainly associated with pH and dissolved organic carbon. CA showed that streams were influenced by urban residential subsistence and livestock farming contributed significantly to PC1 throughout the year. The streams influenced by farmland runoff contributed most to PC2 in spring and winter compared with other streams. PC3 was affected mainly by aquiculture in spring, rural residential subsistence in summer, and livestock farming in fall and winter seasons. Further analyses showed that farmlands contributed significantly to nitrogen pollution of Taihu Lake, while urban residential subsistence and livestock farming also polluted water quality of Taihu Lake in rainy season. The results would be helpful for the authorities to take sound actions for an effective management of water quality in Taihu Lake region.