Spatiotemporal variations of sand hydraulic conductivity by microbial application methods

The spatiotemporal distributions of microbes in soil by different methods could affect the efficacy of the microbes to reduce the soil hydraulic conductivity.In this study,the specimens of bio-mediated sands were prepared using three different methods,i.e.injecting,mixing,and pouring a given microbial so-lution onto compacted sand specimens.The hydraulic conductivity was measured by constant-head tests,while any soil microstructural changes due to addition of the microbes were observed by scan-ning electron microscope(SEM)and mercury intrusion porosimetry(MIP)tests.The amount of dextran concentration produced by microbes in each type of specimen was quantified by a refractometer.Results show that dextran production increased exponentially after 5-7 d of microbial settling with the supply of culture medium.The injection and mixing methods resulted in a similar amount and uniform dis-tribution of dextran in the specimens.The pouring method,however,produced a nonuniform distri-bution,with a higher concentration near the specimen surface.As the supply of culture medium discontinued,the dextran content near the surface produced by the pouring method decreased dramatically due to high competition for nutrients with foreign colonies.Average dextran concentration was negatively and correlated with hydraulic conductivity of bio-mediated soils exponentially,due to the clogging of large soil pores by dextran.The hydraulic conductivity of the injection and mixing cases did not change significantly when the supply of culture medium was absent.

Clay Materials for Ceramics Application from N’Djamena in the Chad Republic: Mineralogical, Physicochemical and Microstructural Characterization

Herein, we report some characteristics of the clayey materials (CMs) collected from Kaliwa (C1), Kabé (C2) and Malo (C3) district in N’Djamena (Chad). Three samples were characterized applying XRF, XRD, FTIR, SEM. In addition, TGA/DSC were performed to control decomposition/mass loss and show phase transitions respectively of CMs. Geochemical analysis by XRF reveals the following minerals composition: SiO2 (~57% - 66%), Al2O3 (~13% - 15%), Fe2O3 (~6% - 10%), TiO2 (~1% - 2%) were the predominant oxides with a reduced proportion in C1, and (~7%) of fluxing agents (K2O, CaO, Na2O). Negligible and trace of MgO (~1%) and P2O5 was noted. The mineralogical composition by XRD shows that, C1, C2 and C3 display close mineralogy with: Quartz (~50%), feldspar (~20%) as non-clay minerals, whereas clays minerals were mostly kaolinite (~15%), illite (~5%) and smectite (~10%). FTIR analysis exhibits almost seemingly similar absorption bands characteristic of hydroxyls elongation, OH valence vibration of Kaolinite and stretching vibration of some Metal-Oxygen bond. SEM micrographs of the samples exhibit microstructureformed by inter-aggregates particles with porous cavities. TGA/DSCconfirm the existence of quartz (570˚C to 870˚C), carbonates (600˚C - 760˚C), kaolinite (569˚C - 988˚C), illite (566˚C - 966˚C), MgO (410˚C - 720˚C) and smectite (650˚C - 900˚C). The overall characterization indicates that, these clayey soils exhibit good properties for ceramic application.

Soil enzymatic activities and microbial community structure with different application rates of Cd and Pb

This study focused on the changes of soil microbial diversity and potential inhibitory effects of heavy metals on soil enzymatic activities at different application rates of Cd and/or Pb. The soil used for experiments was collected from Beijing and classified as endoaquepts. Pots containing 500 g of the soil with different Cd and/or Pb application rates were incubated for a period of 0, 2, 9, 12 weeks in a glasshouse and the soil samples were analyzed for individual enzymes, including catalase, alkaline phosphatase and dehydrogenase, and the changes of microbial community structure. Results showed that heavy metals slightly inhibited the enzymatic activities in all the samples spiked with heavy metals. The extent of inhibition increased significantly with increasing level of heavy metals, and varied with the incubation periods. The soil bacterial community structure, as determined by polymerase chain reaction- denaturing gradient gel electrophoresis techniques, was different in the contaminated samples as compared to the control. The highest community change was observed in the samples amended with high level of Cd. Positive correlations were observed among the three enzymatic activities, but negative correlations were found between the amounts of the heavy metals and the enzymatic activities.

Effect of Long-Term Application of K Fertilizer and Wheat Straw to Soil on Crop Yield and Soil K Under Different Planting Systems

Effect of application of K fertilizer and wheat straw to soil on crop yield and status of soil K in the plough layer under different planting systems was studied. The experiments on long-term application of K fertilizer and wheat straw to soil in Hebei fluvo aquic soil and Shanxi brown soil in northern China were begun in 1992. The results showed that K fertilizer and straw could improve the yields of wheat and maize with the order of NPK ＋ St 〉 NPK 〉 NP ＋ St 〉 NP, and treatment of K fertilizer made a significant difference to NP, and the efficiency of K fertilizer in maize was higher than in wheat under rotation system of Hebei. In contrast with Shanxi, the wastage of soil potassium was a more serious issue in the rotation system in Hebei, only treatment of NPK ＋ St showed a surplus of potassium and the others showed a wane. K fertilizer and straw could improve the content of water-soluble K, nonspecifically adsorbed K, non-exchangeable K, mineral K, and total K in contrast to NP; however, K fertilizer and straw reduce the proportion of mineral K and improve proportion of other forms of potassium in the two locating sites. Compared with the beginning of orientation, temporal variability character of soil K content and proportion showed a difference between the two soil types; furthermore, there was a decrease in the content of mineral K and total K simultaneously in the two locating sites. As a whole, the effect of K fertilizer applied to soil directly excelled to wheat straw to soil. Wheat straw to soil was an effective measure to complement potassium to increase crop yield and retard the decrease of soil K.

Application of New-type Soil Stabilizer Q2 in Subgrade Construction

The research analyzed characters of soil stabilizer and detailed the solidification mechanism.Furthermore,new type soil stabilizer Q2 was used in a base of Beijing Vocational College of Agriculture and a solidified road with length of 250 m,width of 4 m and thickness of 0.25 m were constructed.The road was tested with an agricultural truck and subgrade tolerance to freezing was tested also.It is suggested that new type soil stabilizer would reduce construction cost of road,protect environment,and reduce construction period,with high value of application.

Effects of repeated applications of fungicide carbendazim on its persistence and microbial community in soil

Carbendazim, a systemic benzimidazole fungicide, is applied repeatedly to control plant diseases including soilborne diseases, over a growing season. Studies were carried out under laboratory conditions to assess the effects of repeated carbendazim applications on its persistence and microbial community in soil. The results indicate that dissipation of carbendazim in soil was accelerated with its application frequency. The degradation rate constant of carbendazim was increased significantly from 0.074 d-1 to 0.79 d-1. The corresponding half-life was shorten markedly from 9.3 d to 0.9 d after four repeated applications. No significant inhibitory effect of carbendazim on soil microbial utilization of the carbon sources was observed after first treatment, but a slight increase in average well color development （AWCD） was shown after second, third, and fourth applications. It suggested that soil microorganisms become adapted to carbendazim after repeated application. Simpson and Shannon indexes of soil microbial community from carbendazim treated soil were also similar to those from the control soil, indicating that the richness and dominant character of soil microorganisms remain unchangeable after repeated application. However, after first, second, and third addition of carbendazim, McIntosh indexes on day 21 were significantly higher compared with the control, suggesting that balance of soil microorganisms was altered due to the enrichment of the specific carbendazim-adapting strains in soil

Current Situation of Heavy Metal Pollution in Farmland Soil and Phytoremediation Application

Phytoremediation technology is a newly-developed way of soil heavy metal pollution repair with high efficiency and good ecological comprehensive benefit. This paper briefly introduces the soil heavy metal pollution status at home and abroad,and focuses on the analysis of harm,sources and current situation of soil heavy metal pollution at home and abroad as well as mechanism and application of phytoremediation.Finally it discusses the key problems in phytoremediation technology that need to resolve in the future.

Stability analysis method of geogrid reinforced expansive soil slopes and its engineering application

The traditional stability analysis method of geogrid reinforced slopes does not consider the effect of lateral swelling,so it is not applicable to reinforced expansive soil slopes.This paper reports a new stability analysis method for geogrid reinforced expansive soil slopes.The additional pullout force of the free zone due to the lateral swelling and the anti-pullout safety factor of each geogrid layer were obtained by ensuring the overall stability of the reinforced slope.The optimum design was carried out to treat an expansive soil cut slope in Hubei Province,China,by changing the spacing and length of geogrid reinforcement.Calculation results show that the additional pullout force caused by lateral swelling has a great influence on the anti-pullout stability of geogrids,and the local stability of the reinforced slope will be overestimated if the swelling effect of soil in the free zone is not considered.

Effect of Intensive Inorganic Fertilizer Application on Microbial Properties in a Paddy Soil of Subtropical China

A field experiment with rice-rice rotation was conducted since 2002 in southeast China for investigating the response of soil microbial properties to intensive nitrogen fertilizer application. The tested soil was a subtropical paddy soil derived from Quaternary red clay. Differences between treatments existed in different application rates of urea when the experiment was designed. Urea was applied in five rates, i.e., 0, 0.5, 1, 1.5, and 2 U, equivalent to 0, 0.5, 1, 1.5, and 2 times the local average amount of urea application （900 kg urea ha-~ yr-~, equivalent to 414 kg N ha-1 yr-~）. In 2007, soil total nitrogen, available nitrogen, and soil organic carbon contents were increased by 10.2-27.9, 8.0-16.0, and 10.2-30.6%, respectively, in treatments with urea application rates of 0.5 to 2 U compared to control （0 U）. Microbial biomass carbon and nitrogen were also increased by 3.1-30.8 and 1.3-13.9%, respectively, in treatments with urea application. Basal respiration in treatments with urea input were 9.4-29.1% higher than that in control. However, changes of bacterial functional diversity had different trends. Urea fertilization enhanced bacterial functional diversity until treatment of 1 U, but re-decreased it from treatment of 1.5 U. Principal components analysis indicated that there were intimate relationships among soil organic matter, nitrogen nutrient, microbial biomass, and respiration. Nevertheless, microbial diversity was related to soil moisture contents after urea application. We conclude here that the application of N fertilizer improved soil microbial biomass and respiratory activity. But, microbial diversity was reduced when excessive urea was applied in the tested paddy soil.

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

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

Combined Application of Organic and Inorganic Fertilizers on Black Soil Fertility and Maize Yield

By two years （2007-2008） located fertilizer experiment, the effect of long-term combined application of organic and inorganic fertilizers on black soil fertility and crop yield was investigated in Shuangcheng City, Heilongjiang Province. The results showed that the combined application of organic and inorganic fertilizers could increase the organinc matter, alkaline nitrogen, available phosphorus and available potassium. At the same time, the increasing application of organic fertilizer could reduce the soil bulk density and improve the field moisture capacity. Field moisture capacity and organic matter of the combined application of high quantities of organic manure and inorganic fertilizers AtB5 treatment increased the fhstest, organic matter increased by 3.33 g. kg and field moisture capacity increased by 11.25% than the beginning of the experiment. Under the same fertilization, the combined application of organic and inorganic fertilizers＇ increasing production range was higher than the single chemical fertilizers＇ which was from 0.8% to 9.4%. The results showed that the combined application of organic and inorganic fertilizers could increase the nutrient contents of soil and also was the highest productivity contribution to black soil fertility. It was the best fertilization structure of increasing productivity level and improving the soil fertility.

Effects of water application intensity of microsprinkler irrigation on water and salt environment and crop growth in coastal saline soils

Laboratory and field experiments were conducted to investigate the effects of water application intensity（WAI） on soil salinity management and the growth of Festuca arundinacea（festuca） under three stages of water and salt management strategies using microsprinkler irrigation in Hebei Province, North China. The soil water content（è） and salinity of homogeneous coastal saline soils were evaluated under different water application intensities in the laboratory experiment. The results indicated that the WAI of microsprinkler irrigation influenced the è, electrical conductivity（ECe） and p H of saline soils. As the WAI increased, the average values of è and ECe in the 0–40 cm profile also increased, while their average values in the 40–60 cm profile decreased. The p H value also slightly decreased as depth increased, but no significant differences were observed between the different treatments. The time periods of the water redistribution treatments had no obvious effects. Based on the results for è, ECe and p H, a smaller WAI was more desirable. The field experiment was conducted after being considered the results of the technical parameter experiment and evaporation, wind and leaching duration. The field experiment included three stages of water and salt regulation, based on three soil matric potentials（SMP）, in which the SMP at a 20-cm depth below the surface was used to trigger irrigation. The results showed that the microsprinkler irrigation created an appropriate environment for festuca growth through the three stages of water and salt regulation. The low-salinity conditions that occurred at 0–10 cm depth during the first stage（-5 k Pa） continued to expand through the next two stages. The average p H value was less than 8.5. The tiller number of festuca increased as SMP decreased from the first stage to the third stage. After the three stages of water and salt regulation, the highly saline soil gradually changed to a low-saline soil. Overall, based on the salt desalinization, the microsprinkler irrigation and three stages of water and salt regulation could be successfully used to cultivate plants for the reclamation of coastal saline land in North China.

Effects of Phosphorus Application in Different Soil Layers on Root Growth, Yield, and Water-Use Efficiency of Winter Wheat Grown Under Semi-Arid Conditions

Deep phosphorus application can be a usefull measure to improve crops＇ performance in semi-arid regions, but more knowledge of both its general effects and effects on specific crops is required to optimize treatments. Thus, the aims of this study were to evaluate the effects of phosphorus（P） application at different soil layers on root growth, grain yield, and water-use efficiency（WUE） of winter wheat grown on the semi-arid Loess Plateau of China and to explore the relationship between root distribution and grain yield. The experiment consisted of four P treatments in a randomized complete block design with three replicates and two cultivars： one drought-sensitive（Xiaoyan 22, XY22） and one drought-tolerant（Changhan 58, CH58）. The four P treatments were no P（control, CK）, surface P（SP）, deep P（DP）, and deep-band P application（DBP）. CH58 produced larger and deeper root systems, and had higher grain yields and WUE, under the deep P treatments（DP and DBP） than under SP, clearly showing that deep P placement had beneficial effects on the drought-tolerant cultivar. In contrast, the grain yield and root growth of XY22 did not differ between DP or DBP and SP treatments. Further, root dry weight（RW） and root length（RL） in deep soil layer（30-100 cm） were closely positively correlated with grain yield and WUE of CH58（but not XY22）, highlighting the connections between a well-developed subsoil root system and both high grain yield and WUE for the drought-tolerant cultivar. WUE correlated strongly with grain yield for both cultivars（r=0.94, P〈0.001）. In conclusion, deep application of P fertilizer is a practical and feasible means of increasing grain yield and WUE of rainfed winter wheat in semi-arid regions, by promoting deep root development of drought-tolerant cultivars.

The application and progress of bioelectrochemical systems (BESs) in soil remediation: A review

Soil pollution endangers human health and ecological balance,which is why finding a highly efficient way to deal with pollutants is necessary.Biological method is an environmentally friendly treatment method.Bioelectrochemical systems(BESs),which combine electrochemistry with biological methods,have been widely used to remediate polluted environments,including wastewater,sludge,sediment,and soil.In BESs,redox reactions occur on electrodes with electroactive bacteria,which convert pollutants into low-polluting or nonpolluting substances.With BESs being a promising technology in the remediation field,the decontamination mechanisms and applications in soil conducted by BESs have attracted much attention.Therefore,to better understand the research progress of BESs,this paper mainly summarizes the mechanism of different classified BESs.The applications of microbial fuel cells(MFCs)in four pollutants(petroleum,heavy metals,pesticides,antibiotics)and the possible applications of microbial electrolysis cells(MECs)in soil are discussed.The main problems in BESs and possible future development directions are also evaluated.

Effects of different levels of compost application on amounts and distribution of organic nitrogen forms in soil particle size fractions subjected mainly to double cropping

Effects of different levels of compost application on the amounts and percentage distribution of organic N forms in whole soils and particle size fractions were investigated. Soil samples were collected from three plots: (a) F, only chemical fertilizers;(b) F+LC, chemical fertilizers plus low level of compost;(c) F+HC, chemical fertilizers plus high level of compost. Each soil sample was divided into five fractions: coarse sand-sized aggregate (CSA), medium sand-sized aggregate (MSA), fine sand-sized aggregate (FSA), silt-sized aggregate (SIA) and clay-sized aggregate (CLA) fractions. The sand fractions were subdivided into decayed plants (DP) and mineral particles (MP). The amounts of total N and different organic N forms in the whole soils as well as size fractions generally increased with increasing the amount of compost. In the whole soils, percentage distribution of non-hydrolysable-N and amino sugar-N increased by compost application while the distribution values of the hydrolysable ammonium- N and unidentified-N decreased. The application did not affect the distribution degree of amino acid-N. In the size fractions, the distribution values of most organic N forms increased in the CSA-DP, MSA-DP and FSA-DP fractions by compost application. In the CLA fractions, the amounts and percentage distribution of organic N forms were the highest, although the application caused decreases in their distribution values. These findings indicate that the CLA fraction merit close attention as an important reservoir of various organic N.

Soil NH_4^+ Fixation and Fertilizer N Recovery as Affected by Soil Moisture and Fertilizer Application Methods

Ammonium fixation and the effects of soil moisture and application methods on fertilizer N recovery were investigated in two soils of Shaanxi Province,China,a Luvisol and an Entisol,through two experiments performed in the laboratory and in a glass shelter,respectively,by using ammonium bicarbonate (NH4HCO3). The laboratory closed incubation box experiment was conducted using the Luvisol to study NH4+ fixation rate at soil moisture levels of 10.1%,22.7% and 35.3% water filled pore space (WFPS). The fixed NH4+-N increased dramatically to 51% and 66%,67% and 74%,and 82% and 85% 1,2 and 36 h after fertilizer incorporation at moisture levels of 10.1% and 22.7% WFPS and 35.3%WFPS,respectively. The rapid NH4+ fixation rates at all moisture levels could help prevent NH4+ losses from ammonia volatilization. In the glass shelter pot experiment,N fertilizer was applied by either banding (in a concentrated strip)or incorporating (thoroughly mixing) with the Entisol and the Luvisol. An average of 74.2% of the added N fertilizer was recovered 26 days after application to the Luvisol,while only 61.4% could be recovered from the Entisol,due to higher NH4+ fixation capacity of the Luvisol. The amount of fixed NH4+ decreased with increasing WFPS. The amount of fixed NH4+ in the incorporated fertilizer treatment was,on average,10% higher than that in the banded treatment.Higher NH4+ fixation rates could prevent N loss and thus increase N recovery. The results from the Luvisol showed lower nitrogen recovery as soil moisture level increased,which could be explained by the fact that most of the fixed NH4+ was still not released when the soil moisture level was low. When the fertilizer was incorporated into the soil,the recovery of N increased,compared with the banded treatment,by an average of 26.2% in the Luvisol and 11.2% in the Entisol,which implied that when farmers applied fertilizer,it would be best to mix it well with the soil.

Distribution and accumulation of zinc and nitrogen in wheat grain pearling fractions in response to foliar zinc and soil nitrogen applications

Increasing zinc(Zn)concentration in wheat grain is important to minimize human dietary Zn deficiency.This study aimed to investigate the effect of foliar Zn and soil nitrogen(N)applications on the accumulation and distribution of N and Zn in grain pearling fractions,N remobilization,and the relationships between nutrient concentration in the vegetative tissues and grain or its fractions in two cropping years in the North China Plain.The results showed a progressive decrease in N and Zn concentrations from the outer to the inner parts of grain,with most of the accumulation in the core endosperm.Foliar Zn application significantly increased N concentration in the pericarp,and soil N application increased N concentration in each grain fraction.Both treatments significantly increased core endosperm Zn concentration.Foliar Zn had no effect on grain N and Zn distribution.Soil N application made N concentrated in the aleurone,promoted Zn translocation to the core endosperm and also increased N remobilization and its efficiency from the shoot to the grain,but no improved contribution to grain was found.N concentration in grain and its fractions were positively correlated with N in vegetative organs at anthesis and maturity,while positive correlations were obtained between N concentration in the pericarp and progressive central area of the endosperm and Zn concentration in the core endosperm.Thus,foliar Zn and soil N applications effectively increased yield and N and Zn concentrations in the wheat grain,particularly in the endosperm,and could be promising strategies to address Zn deficiency.

Nitrogen application and intercropping change microbial community diversity and physicochemical characteristics in mulberry and alfalfa rhizosphere soil

Intercropping of mulberry(Morus alba L.)and alfalfa(Medicago sativa L.)is a new forestry-grass compound model in China,which can provide high forage yields with high protein.Nitrogen application is one of the important factors determining the production and quality of this system.To elucidate the advantages of intercropping and nitrogen application,we analyzed the changes of physicochemical properties,enzyme activities,and microbial communities in the rhizosphere soil.We used principal components analysis(PCA)and redundancy discriminators analysis to clarify the relationships among treatments and between treatments and environmental factors,respectively.The results showed that nitrogen application significantly increased pH value,available nitrogen content,soil water content(SWC),and urea(URE)activity in rhizosphere soil of monoculture mulberry.In contrast,intercropping and intercropping+N significantly decreased pH and SWC in mulberry treatments.Nitrogen,intercropping and intercropping+N sharply reduced soil organic matter content and SWC in alfalfa treatments.Nitrogen,intercropping,and intercropping+N increased the values of McIntosh diversity(U),Simpson diversity(D),and Shannon-Weaver diversity(H’)in mulberry treatments.However,PC A scatter plots showed clustering of monoculture mulberry with nitrogen(MNE)and intercropping mulberry without nitrogen(M0).Intercropping reduced both H’and D but nitrogen application showed no effect on diversity of microbial communities in alfalfa.There were obvious differences in using the six types of carbon sources between mulberry and alfalfa treatments.Nitrogen and intercropping increased the numbers of sole carbon substrate in mulberry treatments where the relative use rate exceeded 4%.While the numbers declined in alfalfa with nitrogen and intercropping.RDA indicated that URE was positive when intercropping mulberry was treated with nitrogen,but was negative in monoculture alfalfa treated with nitrogen.Soil pH and SWC were positive with mulberry treatments but were negative with alfalfa treatments.Intercropping with alfalfa benefited mulberry in the absence of nitrogen application.Intercropping with alfalfa and nitrogen application could improve the microbial community function and diversity in rhizosphere soil of mulberry.The microbial community in rhizosphere soil of mulberry and alfalfa is strategically complementary in terms of using carbon sources.

Effects of Different Nitrogen Applications on Soil Physical, Chemical Properties and Yield in Maize (<i>Zea mays</i>L.)

Application of nitrogen (N) fertilizer is one of the most important approaches on improving maize grain yield. However, as is known to all, overuse N fertilizer not only leads to decline of N use efficiency and maize yield, but also leads to potential risk to environment pollution. This experiment was conducted to determine the effects of N fertilizer applications with nine different treatments on soil physical-chemical characters and maize grain yield using hybrid variety Zhengdan 958 in 2011 and 2012. Results indicated that the soil bulk densities of T2 (CK) and T1 were the lowest compared to other treatments in 2011 and 2012, respectively, whereas the soil bulk density of T5 in 2011 and T3 in 2012 were higher than other treatments. The soil porosity and field capacity of T5 in 2011 and T3 in 2012 were lower than other treatments, but those of CK in 2011 and T1 in 2012 were higher than other treatments. The pH values of T3 to T7 were lower than other treatments. These results indicated that the soil bulk densities were increased, whereas the soil porosity, field capacity and values pH were decreased by N application at different stages. N application could increase the N contents of leaf and stem, whereas less or excess N application should not significant improve maize yield. Although the soil organic matter and total N contents of T3 were the highest in both 2011 and 2012, the yield of T4 is the highest in both 2011 and 2012. The application amount, period and times of N fertilizer were important to maize yield.

Advances in Cotton Tolerance to Heavy Metal Stress and Applications to Remediate Heavy Metal-Contaminated Farmland Soil

Heavy metal-contaminated soil is one of the major environmental pollution problems of agricultural production and human health in the world.Remediation of heavy metals in soil is one of the most popular research subjects.Different remediation strategies have been reported to remove heavy metals from contaminated soil,among which phytoremediation is the most important one.Compared with other major crops,cotton shows the strongest and most widespread resistance to abiotic stresses,such as heavy metals.Although heavy metal stress adversely affects the growth and development of cotton,cotton possesses a set of sophisticated stress-resistance strategies.As the main product of cotton is nonedible fibers,which have a large biomass and strong heavy metal absorption and enrichment capacities,cotton is an ideal crop to restore heavy metal-contaminated soils and has unique advantages in terms of both ecological and economic benefits,with great application prospects.In this review,based on domestic and foreign research results in recent years,the effects of heavy metals on cotton growth and product quality were analyzed,the heavy metal absorption,accumulation,translocation and enrichment characteristics of cotton plants were summarized,and the adaptation and tolerance mechanisms of cotton to heavy metals were explored.Furthermore,the view that cotton is an effective crop to remediate heavy metal pollution in farmland soil has been proposed,and popularization and application suggestions for planting cotton to repair heavy metal pollution have been put forward to provide a reference for the comprehensive evaluation of the economic feasibility of cotton to repair heavy metal pollution in farmland soil.