Improvement of Wolfberry(Lycium barbarum L.)Fruit Yield and Quality and Enhancement of Soil Fertility by Nitrogen Reduction Combined with Organic Fertilizers

Excessive amounts of nitrogen(N)fertilizers are applied during wolfberry production,resulting in some soil problems as well as potential environmental risks in the Qinghai-Tibet Plateau.In this study,organic fertilizers were used to replace part of the N fertilizer in wolfberry fields with different fertility levels.N fertilizer rates had 0,50,100,150,200,and 250 g N/plant.Organic fertilizer rates had 0,2,4,6,8,and 10 kg organic fertilizer/plant.The experimental treatments included 6 combinations of N0M10,N50M8,N100M6,N150M4,N200M2,and control was N250M0.The results showed that in the high-fertility soils,combinations of N150M4,N100M6 and N50M8 treatments were increased in yields,fruit shape index,flavonoid content,total phenol content,mineral nutrient content,and antioxidant activity of wolfberry fruits.Also they were improved in soil fertility and decreased in residual nitrate through the soil depth of 0-300 cm.In the soil with less fertility,fruit yield,amino acid contents,flavonoids,total phenols,mineral nutrients and antioxidant activity of fruits were increased by the N200M2,N150M4 and N100M6 treatments and soil fertility was improved as well.Also more residual nitrate was found in the depth of 0-100 cm of soil with both chemical and organic fertilizer compared with the control.Therefore,in the Qinghai-Tibet Plateau,combining decreased N fertilizer with organic fertilizer rather than chemical fertilizer alone could help farmers achieve satisfactory yields and quality of wolfberry fruits and reduce the risk of nitrate leaching.In conclusion,50-150 g/plant of N fertilizer combined with 4-8 kg/plant of organic fertilizer in high-fertility gardens and 100-200 g/plant of N fertilizer combined with 2-6 kg/plant of organic fertilizer in low-fertility gardens are recommended for wolfberry cultivation.

Short-term effects of organic amendments on soil fertility and root growth of rubber trees on Hainan Island, China

Rubber[Hevea brasiliensis(Willd.ex A.Juss.)Müll.Arg.]plantations are the largest cultivated forest type in tropical China.Returning organic materials to the soil will help to maintain the quality and growth of rubber trees.Although many studies have demonstrated that organic waste materials can be used to improve soil fertility and structure to promote root growth,few studies have studied the eff ects of organic amendments on soil fertility and root growth in rubber tree plantations.Here,bagasse,coconut husk or biochar were applied with a chemical fertilizer to test their eff ects on soil properties after 6 months and compared with the eff ects of only the chemical fertilizer.Results showed that the soil organic matter content,total nitrogen,available phosphorus and available potassium after the chemical fertilizer(F)treatment were all signifi cantly lower than after the chemical fertilizer+bagasse(Fba),chemical fertilizer+coconut husk(Fco)or chemical fertilizer+biochar(Fbi)(p<0.05).Soil pH in all organic amendments was higher than in the F treatment,but was only signifi cantly higher in the Fbi treatment.In contrast,soil bulk density in the F treatment was signifi cantly higher than in treatments with the organic amendments(p<0.05).When compared with the F treatment,soil root dry mass increased signifi-cantly by 190%,176%and 33%in Fba,Fco and Fbi treatments,respectively(p<0.05).Similar results were found for root activity,number of root tips,root length,root surface area and root volume.Conclusively,the application of bagasse,coconut husk and biochar increased soil fertility and promoted root growth of rubber trees in the short term.However,bagasse and coconut husk were more eff ective than biochar in improving root growth of rubber trees.

Effects of Corn Stover Incorporated in Dry Farmland on Soil Fertility

Seven years' field experiments on application of corn stover and/or cattle manure combined with chemical fertilizers were carried out in Shouyang Dryland Farming Experimental Station. Results showed that the increased available N in the plough layer was mainly influenced by the application of cattle manure; the available P was mainly influenced by the application of chemical fertilizer; the available K was mainly influenced by the incorporation of corn stover. The organic matter contents in the soils treated with corn stover or cattle manure were kept in balance under the experimental conditions. Corn yield and water use efficiency were influenced significantly not only by fertilizer N but also by incorporated corn stover. The results suggested that the highest N uptake, yield and water use efficiency could be obtained at rates of 105 kg fertilizer N, 6000 kg corn stover, and 1500 kg cattle manure per hectare. The experiments supplied information on nutrient recycling and use of corn stover as sources of fodder and organic fertilizer for balancing application of organic and inorganic fertilizer, improving soil fertility and increasing crop yield with incorporation of corn stover in soil.

Research Progress in the Effect and Mechanism of Fertilization Measures on Soil Fertility

This paper firstly summarized the domestic and foreign research progress in the relationship between fertilization measures and soil fertility. It elaborated the relationship between fertilization measures and basic physical and chemical properties,soil enzyme activity,soil microorganism fertility index,and soil animal fertility index. It pointed out future researches about the relationship between fertilization measures and soil fertility include:( i) the relationship between fine and high efficient input of organic fertilizer and soil fertility,( ii) in-depth research of soil zoology fertility index,( iii) soil biology about long-term fertilization,and( iv) soil fertilization and agricultural diffused pollution. It is intended to provide scientific reference for improving farmland soil fertility and maintaining excellent ecological environment of farmland through proper fertilization measures.

Indigenous arbuscular mycorrhizal fungi play a role in phosphorus depletion in organic manure amended high fertility soil

The species richness and propagule number of arbuscular mycorrhizal fungi(AMF)are high in intensively-managed agricultural soils.Past research has shown that AMF improve crop phosphorus(P)uptake under low soil P conditions,however it is unclear if AMF play a role in high Olsen-P soils.In this study,we investigated whether native fungal benefits exist under high P input field conditions in-situ and contribute to P utilization.We installed in-grow tubes which were sealed with different membrane pore sizes(30 or 0.45μm)to allow or prevent AMF hyphae access to the hyphal compartment and prevent cotton roots from penetrating the chamber.We used the depletion of soil available P(Olsen-P)in the hyphae accessed compartment to indicate P uptake by the native AMF community.Our results showed that the native AMF mediated P depletion and microbial biomass P(MBP)turnover and caused the largest Olsen-P depletion ratio and MBP turnover ratio in the high P treatments(Olsen-P:78.29 mg kg^(-1)).The cotton roots in each fertilization regime were colonized by a unique AMF community and Glomus and Paraglomus were the dominant genera,implying the longterm fertilization regimes domesticated the AMF community.We conclude that native AMF caused the P depletion and P turnover even under high soil Olsen-P conditions.

Agricultural extension approach:evidence from an Integrated Soil Fertility Management Project in Ethiopia

Agricultural extension is an approach to rural development and agricultural transformation in which training,demonstration and technology transfer are key to reducing rural poverty,ensuring food security,and sustainably managing natural resources.During recent decades,different extension approaches have been tested and validated by the Ethiopian government and nongovernmental organizations to stimulate participation in the agricultural extension system(AES).The most recent was a German-funded project entitled“Integrated Soil Fertility Management Project”(ISFM+),which employed a novel approach to piloting and upscaling proven technology and best practice.The purpose of this study was to analyze and document the modalities of ISFM+and illustrate its effects on technology uptake and dissemination.The study used a mixed methods approach to collect data.ATLAS.ti and SPSS were used for data management and analysis.Farmer Research and Extension Groups and Farmer Field Schools were found to be central to the participation process.Also,the ISFM+was found to aid technology transfer and helped to increase grain and residue yields as well as farmer livelihoods.Based on these empirical findings,it is argued that the ISFM+approach and technology should be integrated and institutionalized in the mainstream AES in order to promote their extensive application.

Spatiotemporal Changes in Soil Nutrients:A Case Study in Taihu Region of China

The accurate assessment of the spatiotemporal changes in soil nutrients influenced by agricultural production provides the basis for development of management strategies to maintain soil fertility and balance soil nutrients. In this paper, we combined spatial measurements from 2 157 soil samples and geostatistical analysis to assess the spatiotemporal changes in soil organic carbon （SOC）, total nitrogen （TN）, available phosphorus （AP） and available potassium content （AK） from the first soil survey （in the 1980s） to the second soil survey （in the 2000s） in the Taihu region of Jiangsu Province in China. The results showed that average soil nutrients in three soil types all exhibited the increased levels in the 2000s （except for AK in the yellow brown soil）. The standard deviation of soil nutrient contents increased （except for TN in the paddy soil）. Agricultural production in the 20 years led to increases in SOC, TN, AP and AK by 74, 82, 89 and 65%, respectively, of the Taihu areas analyzed. From the 1980s to 2000s all the nugget/sill ratios of soil nutrients indices were between 25 and 75% （except for AK in the yellow brown soil in the 2000s）, indicating moderate spatial dependence. The ratio of AP in the yellow brown soil in the 2000s was 88.74%, showing weak spatial dependence. The spatial correlation range values for SOC, TN, AP and AK in the 2000s all decreased. The main areas showing declines in SOC, TN and AP were in the northwest. For AK, the main region with declining levels was in the east and middle of western areas. Apparently, the increase in soil nutrients in the Taihu region can be mainly attributed to the large increase in fertilizer inputs, change in crop systems and enhanced residues management since the 1980s. Future emphasis should be placed on avoiding excess fertilizer inputs and balancing the effects of the fertilizers in soils.

Drivers of the Chemical Quality of Market Gardening Soils in the Urban and Peri-Urban Environment of Bobo-Dioulasso (Burkina Faso): Impact of Fertilizers Sources and Sites Location

Urban and peri-urban agriculture plays a key role by providing many goods and services. In particular, it provides diversified food and employment for vulnerable groups (youth and women). However, it often involves negative externalities due to non-conventional soils fertility management practices. This study aimed to investigate the chemical quality of soils over six (06) sites of the market gardening area of Bobo-Dioulasso (Burkina Faso) as affected by fertilizers uses and sites location. Thirty (30) representative market gardening farms, located in urban, semi-urban and rural areas, were randomly selected from a baseline survey database. Within each farm, composite soil samples made up of 3 individual cores were taken over the 0 - 15 cm soil depth for determining soils carbon, total nitrogen, available phosphorus contents and pH-water. These data were normalized and summarized to compute a synthetic Soil Fertility Index (SFI). The data processing was focused on a Principal Component Analysis and an Ascendant Hierarchical Classification in order to make a typology of the vegetable farms. Fertilizers management effects on soils quality were compared through Variance Analysis (ANOVA) following a GLM procedure in Rstudio software. As main results, soils chemical parameters, except for available K, were affected by the location of the sites. Soils in urban farms are less acidic (on average pH = 6.9), while semi-urban and rural sites (Samadeni, Nakaguana) have more acidic soils. However, the latter site had the highest values of C and N. Moreover, the long-term application of organic matter sources results in improving of the chemical quality of the market garden soil. The SFI is positively correlated with the rate of applied organic fertilizers, and the cultivation duration. On the other hand, soil quality tends to decrease with the expansion of the area, due to a dilution effect of the organic fertilizer doses. All these results suggest that there is a real scope to reinforce the position of the market garden as an opportunity for recycling organic wastes and sequestration of carbon by promoting relevant fertilization packages that strongly rely on organic matters sources (Compost, Biochar, etc.).

Bacterial Community Structure and Diversity in a Black Soil as Affected by Long-Term Fertilization

Black soil （Mollisol） is one of the main soil types in northeastern China. Biolog and polymerase chain reactiondenaturing 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 com- ponent 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.

Influences of nitrification inhibitor 3,4-dimethyl pyrazole phosphate on nitrogen and soil salt-ion leaching

An undisturbed heavy clay soil column experiment was conducted to examine the influence of the new nitrification inhibitor, 3,4- dimethylpyrazole phosphate （DMPP）, on nitrogen and soil salt-ion leaching. Regular urea was selected as the nitrogen source in the soil. The results showed that the cumulative leaching losses of soil nitrate-N under the treatment of urea with DMPP were from 57.5% to 63.3% lower than those of the treatment of urea without DMPP. The use of nitrification inhibitors as nitrate leaching retardants may be a proposal in regulations to prevent groundwater contaminant. However, there were no great difference between urea and urea with DMPP treatments on ammonium-N leaching. Moreover, the soil salt-ion leaching losses of Ca^2＋, Mg^2＋, K^＋, and Na^＋ were reduced from 26.6% to 28.8%, 21.3% to 27.8%, 33.3% to 35.5%, and 21.7% to 32.1%, respectively. So, the leaching losses of soil salt-ion were declined for nitrification inhibitor DMPP addition, being beneficial to shallow groundwater protection and growth of crop. These results indicated the possibility of ammonium or ammonium producing compounds using nitrification inhibitor DMPP to control the nitrate and nutrient cation leaching losses, minimizing the risk of nitrate pollution in shallow groundwater.

Ecological and Economic Benefits of Vegetation Management Measures in Citrus Orchards on Red Soils

A three-year experiment was conducted to investigate and compare the economic and ecological benefits of six types of vegetation management measures in citrus orchards of the hilly red soil region of the eastern part of China.Six vegetation treatments,including tillage without herbicide(clean tillage)and no tillage without herbicide(sod culture) and with herbicide paraquat(paraquat),glyphosate(glyphosate),glyphosate-glyphosate-paraquat(G-G-P),and paraquat- paraquat-glyphosate(P-P-G),were applied in the citrus orchards on a clayey red soil with slopes of 8°and 13°and a sandy soil with slope of 25°.The results showed that the sod culture,paraquat,glyphosate,G-G-P,and P-P-G treatments reduced surface runoff by 38.8%,42.5%,18.7%,28.7%,and 37.5%,then the soil-water losses by 55.5%,51.7%,39.9%,46.8%, and 50.0%,and the N,P,and K nutrient losses by 60.3%,50.2%,37.0%,41.8%,and 45.4%,respectively,as compared with the clean tillage treatment.The weed regeneration ratios with the treatments of clean tillage without herbicide,paraquat, glyphosate,G-G-P,and P-P-G were reduced by 55.1%,67.2%,30.3%,36.8%,and 51.2%,respectively,as compared with the sod culture.The sod culture,paraquat,glyphosate,G-G-P,and P-P-G treatments could increase the soil fertility (annual accumulation of N,P,K,and OM)by 7.1%,6.9%,5.3%,6.2%,and 6.6%,respectively,whereas the clean tillage treatment without herbicide reduced soil fertility by 4.4% after the three-year experiment.The citrus fruit yields in the treatments of paraquat,glyphosate,G-G-P,and P-P-G increased by 7%-10%;the soluble solid,total sugar,total acidity,sugar-acid ratio,and single fruit weight of citrus fruits of all treatments except sod culture significantly(P>0.05) exceeded that of the clean tillage treatment.In general,the paraquat treatment showed the best economic and ecological benefits among the six treatments;therefore,it could be regarded as the best available vegetation management measure in citrus orchards of hilly red soil region to retain water and soil,enhance soil fertility,and improve the yield and quality of citrus.

Effects of Long-Term Winter Planted Green Manure on Distribution and Storage of Organic Carbon and Nitrogen in Water-Stable Aggregates of Reddish Paddy Soil Under a Double-Rice Cropping System

In agricultural systems, maintenance of soil organic matter has long been recognized as a strategy to reduce soil degradation. Manure amendments and green manures are management practices that can increase some nutrient contents and improve soil aggregation. We investigated the effects of 28 yr of winter planted green manure on soil aggregate-size distribution and aggregateassociated carbon（C） and nitrogen（N）. The study was a randomized completed block design with three replicates. The treatments included rice-rice-fallow, rice-rice-rape, rice-rice-Chinese milk vetch and rice-rice-ryegrass. The experiment was established in 1982 on a silty light clayey paddy soil derived from Quaternary red clay（classified as Fe-Accumuli-Stagnic Anthrosols） with continuous early and late rice. In 2009, soil samples were collected（0-15 cm depth） from the field treatment plots and separated into water-stable aggregates of different sizes（i.e., 〉5, 2-5, 1-2, 0.5-1, 0.25-0.5 and 〈0.25 mm） by wet sieving. The long-term winter planted green manure significantly increased total C and N, and the formation of the 2-5-mm water-stable aggregate fraction. Compared with rice-rice-rape, rice-rice-Chinese milk vetch and rice-rice-ryegrass, the rice-rice-fallow significantly reduced 2-5-mm water-stable aggregates, with a significant redistribution of aggregates into micro-aggregates. Long-term winter planted green manure obviously improved C/N ratio and macro-aggregate-associated C and N. The highest contribution to soil fertility was from macro-aggregates of 2-5 mm in most cases.

Effect of Long-Term Rice Straw Return on Soil Glomalin, Carbon and Nitrogen

A long-term experiment was conducted to investigate how long-term fertilization and rice straw incorporation into soil affect soil glomalin, C and N. The combined application of chemical fertilizer and straw resulted in a significant increase in both soil easily extractable glomalin (EEG) and total glomalin (TG) concentrations, as compared with application of only chemical fertilizer or no fertilizer application. The EEG and TG concentrations of the NPKS (nitrogen, phosphorus, and potassium fertilizer application + rice straw return) plot were 4.68% and 5.67% higher than those of the CK (unfertilized control) plot, and 9.87% and 6.23% higher than those of the NPK (nitrogen, phosphorus, and potassium fertilizer applied annually) plot, respectively. Application of only chemical fertilizer did not cause a statistically significant change of soil glomalin compared with no fertilizer application. The changes of soil organic C (SOC) and total N (TN) contents demonstrated a similar trend to soil glomalin in these plots. The SOC and TN contents of NPKS plot were 15.01% and 9.18% higher than those of the CK plot, and 8.85% and 14.76% higher than those of the NPK plot, respectively. Rice straw return also enhanced the contents of microbial biomass C (MBC) and microbial biomass N (MBN) in the NPKS plot by 7.76% for MBC and 31.42% for MBN compared with the CK plot, and 12.66% for MBC and 15.07% for MBN compared with the NPK plots, respectively. Application of only chemical fertilizer, however, increased MBN concentration, but decreased MBC concentration in soil.

Effect of Sprinkler and Border Irrigation on Topsoil Structure in Winter Wheat Field

A two-year experiment was carried out on the effect of sprinkler irrigation on the topsoil structure in a winter wheat field. A border-irrigated field was used as the control group. The total soil porosity, pore size distribution, pore shape distribution, soil cracks and soil compaction were measured. The sprinkler irrigation brought significant changes to the total soil porosity, capillary porosity, air-filled porosity and pore shape of topsoil layers in comparison with the border irrigation. The total porosity and air-filled porosity of the topsoil in the sprinkler irrigation were higher than those in the border irrigation. The changes in the air-filled and elongated pores were the main reasons for the changes in total porosity. The porosities of round and irregular pores in topsoil under sprinkler irrigation were lower than those under border irrigation. Sprinkler irrigation produced smaller soil cracks than border irrigation did, so sprinkler irrigation may restrain the development of macropore flow in comparison with border irrigation. The topsoil was looser under sprinkler irrigation than under border irrigation. According to the conditions of topsoil structure, it is preferable for crops to grow under sprinkler irrigation than under border irrigation.

Emission and Fixation of CO_2 from Soil System as Influenced by Long-Term Application of Organic Manure in Paddy Soils

The observations of 25-yr long-term experiment in Zhejiang paddy soils showed that the soil organic matter could increase continuously with applying organic manure, and the increase in rate enhanced along with the application rates of organic manure. By mathematical modeling, the soil organic matter increased by 22 kg when 1 t of fresh FYM was applied. The CO2 emission resulting from the mineralization of soil organic matter increased with the increase in the application rate of the organic manure as well as the increase in the root residues. It is expected that the CO2 emission will be at 10.04-21.61 t ha-1 yr-1 when 16.5-49.5 t ha-1 yr-1 of fresh FYM is applied. The soil organic carbon from mineralization and release of applied organic carbon (fresh FYM and root residues) will affect the CO2 concentration in the atmosphere. So, the higher the application rate of organic manure, the more is the fixed organic carbon. The CO2 fixation will be at 1.885-3.463 t ha-1 yr-1 when 16.5-49.5 t ha-1 yr-1 of fresh FYM is applied. Thus, the CO2 fixation will increase by 46.7 kg by applying 1 t fresh FYM. To apply organic manure continuously in rice fields may reduce the contribution to the increase of CO2 concentration in the atmosphere.

Effects of biochar on water movement characteristics in sandy soil under drip irrigation

Biochar addition can improve the physical and hydraulic characteristics of sandy soil.This study investigated the effects of biochar on water holding capacity and water movement in sandy soil under drip irrigation.By indoor simulation experiments,the effects of biochar application at five levels(0%,1%,2%,4%and 6%)on the soil water retention curve,infiltration characteristics of drip irrigation and water distribution were tested and analyzed.The results showed that biochar addition rate was positively correlated with water holding capacity of sandy soil and soil available water.Within the same infiltration time,with an increasing amount of added biochar,the diffusion distance of the horizontal wetting front(HWF)tended to decrease,while the infiltration distance of vertical wetting front(VWF)initially declined and then rose.The features of wetted bodies changed from"broad-shallow"to"narrow-deep"type.The relationship between the transport distances of HWF and VWF and the infiltration time was described by a power function.At the same distance from the point source,the larger the amount of added biochar,the higher the soil water content.Biochar had a great influence on the water content of the layer with biochar(0–200 mm)and had some effects at 200–250 mm without biochar;but it had less influence on the soil water content deeper than 250 mm.For the application rate of biochar of 4%,most water was retained within 0–250 mm soil layer.However,when biochar application amount was high(6%),it would be helpful for water infiltration.During the improvement of sandy soil,biochar application rate of 4%in the plow layer had the best effect.

A Field Study on Effects of Nitrogen Fertilization Modes on Nutrient Uptake,Crop Yield and Soil Biological Properties in Rice-Wheat Rotation System

Rational application of nitrogen （N） fertilizers is an important measure to raise N fertilizer recovery rate and reduce N loss.A two-year field experiment of rice-wheat rotation was employed to study the effects of N fertilization modes including a N fertilizer reduction and an organic manure replacement on crop yield,nutrient uptake,soil enzyme activity,and number of microbes as well as diversity of microbes.The result showed that 20% reduction of traditional N fertilizer dose of local farmers did not significantly change crop yield,N uptake,soil enzyme activity,and the number of microbes （bacteria,actinomycetes,and fungi）.On the basis of 20% reduction of N fertilizer,50% replacement of N fertilizer by organic manure increased the activity of sucrose,protease,urease,and phosphatase by 46-62,27-89,33-46,and 35-74%,respectively,and the number of microbes,i.e.,bacteria,actinomycetes,and fungi by 36-150,11-153,and 43-56%,respectively.Further,organic fertilizer replacement had a Shannon＇s diversity index （H） of 2.18,which was higher than that of other modes of single N fertilizer application.The results suggested that reducing N fertilizer by 20% and applying organic manure in the experimental areas could effectively lower the production costs and significantly improve soil fertility and biological properties.

Analysis of Heavy Metal Sources for Vegetable Soils from Shandong Province, China

Heavy metal pollution in agricultural soils has serious negative influence on human health. Concentrations of Cd, Hg, As, Pb, Cr, Cu, Zn, and Ni in top soils （0-20 cm） of greenhouses and farmlands from four main vegetable production areas Shouguang, Laiyang, Jinxiang, and Zhangqiu in Shandong Province, one of the most rapidly developing regions in China, were measured in this study. Shouguang is mainly occupied by greenhouse vegetables and the other three areas are mainly open field culture. Total of 149 soil samples were collected. The average concentrations of the eight heavy metals of the tested 149 soil samples were all below the threshold values according to ＂Farmland environmental quality evaluation standards for edible agricultural products （HJ332-2006）＂ of China. However, most of the studied heavy metals were present at higher concentrations than those of the natural background levels in local agricultural soils. Among the total 149 soil samples, 22 samples were contaminated by Cd, Ni, Cu, or Hg. Comparisons showed that the main pollution element in greenhouse vegetable soils was Cd, while that of open field vegetable soils was Cu. The results of principal components analysis （PCA） suggested that concentrations of Cr, As, and Ni were mainly controlled by parent rocks; Hg and Pb were affected by anthropogenic activities such as vehicle and industrial fumes and waste water irrigation. Meanwhile, concentrations of Cd, Cu, and Zn were affected mainly by the use of agrochemicals. Most of the heavy metals were positively correlated with each other in concentration. Appropriate measures should be taken to effectively control heavy metal levels in vegetable soils and thus protect human health.

Long-Term Effect of Fertilizer and Rice Straw on Mineral Composition and Potassium Adsorption in a Reddish Paddy Soil

Increasing K＋ adsorption can be an effective alternative in building an available K pool in soils to optimize crop recovery and minimize losses into the environment. We hypothesized that long-term fertilization might change K＋ adsorption because of changes in the chemical and mineralogical properties of a rice （Oryza sativa L.）. The aims of this study were （i） to determine clay minerals in paddy soil clay size fractions using X-ray diffraction methods and a numerical diagramdecomposition method; （ii） to measure K＋ adsorption isotherms before and after H202 oxidation of organic matter, and （iii） to investigate whether K＋ adsorption is correlated with changes in soil chemical and mineral properties. The 30-yr longterm fertilization treatments caused little change in soil organic C （SOC） but a large variation in soil mineral composition. The whole-clay fraction （〈5 Jam） corresponded more to the fertilization treatment than the fine-clay fraction （〈1 gin） in terms of percentage of illite peak area. The total percentage of vermiculite-chlorite peak area was significantly negatively correlated with the total percentage ofillite peak area in the 〈5 lam soil particles （R=-0.946, P〈0.0006）. Different fertilization treatments gave significantly different results in K＋ adsorption. The SOC oxidation test showed positive effects of SOC on K＋ adsorption at lower K＋ concentration （≤120 mg L-0 and negative effects at higher K＋ concentration （240 mg L-l）. The K＋ adsorption by soil clay minerals after SOC oxidization accounted for 60-158% of that by unoxidized soils, suggesting a more important role of soil minerals than SOC on K＋ adsorption. The K＋ adsorption potential was significantly correlated to the amount of poorly crystallized illite present （R--0.879, P=0.012）. The availability of adsorbed K＋ for plant growth needs further study.

Effects of Long-Term Winter Planted Green Manure on Physical Properties of Reddish Paddy Soil Under a Double-Rice Cropping System

Soil physical properties are important indicators of the potential for agricultural production.Our objective was to evaluate the effects of long-term inputs of green manures on physical properties of a reddish paddy soil（Fe-Typic Hapli-Stagnic Anthrosols） under a double cropping system.The common cropping pattern before the study was early-late rice-fallow（winter）.The field treatments included rice-rice-fallow（R-R-WF）,rice-rice-rape（R-R-RP）,rice-rice-Chinese milk vetch（RR-MV）,and rice-rice-ryegrass（R-R-RG）.The rape,Chinese milk vetch and ryegrass were all incorporated as green manures 15 d before early rice transplanting during the following year.The soil bulk density in all green manure treatments was significantly reduced compared with the winter fallow treatment.Soil porosity with green manure applications was significantly higher than that under the winter fallow.The green manure treatments had higher 0.25-5 mm water stable aggregates and aggregates stabilities in the plow layer（0-15 cm depth） compared with the fallow treatment.The mean weight diameter（MWD） and normalized mean weight diameter（NMWD） of aggregates in the green manure treatment were larger than that with the winter fallow.Soil given green manure retained both a higher water holding capacity in the plow layer soil,and a larger volume of moisture at all matric potentials（-10,-33 and-100 kPa）.We conclude that the management of double-rice fields in southern central China should be encouraged to use green manures along with chemical fertilizers to increase SOC content,improve soil physical properties and soil fertility.