Effects of Long-term Fertilization on Micro-morphological Features in Purple Soil

[Objective] The study aimed to better understand the effect of different fertilizer treatments on micro-morphological characteristics of a purple soil at the 0-20 cm topsoil in a long-term fertilizer experiment. [Method] Soil micro-morphology was observed and analyzed under a single polarizing microscope. [Result] For the CK （no fertilizer） treatment, soil structure was dense with little porosity developed. Its soil microstructure was poor, sandy fabric-granular fabric. After continuously applied chemical fertilizers only for more than two decades, the soil particles did not evolve into soil structures and formed little porosity. The microstructures of soil in N, NP and NPK treatments were porphyroskelic fabric-fine sandy granular fabric, better than that of the soil in CK treatment. Adding manure obviously improved the quantity of groundmass and endowed the soil a loose structure and plenty porosity, enriched animal and plant residues, and well-formed iron-manganese nodules and humus ma- terials, all resulting in better micro-aggregates development. The type of soil microstructures in MNPK treatment was pectized-compacted takyric fabric-intertextic fabric, the best among all the treatments. [Conclusion] Combined application of both or- ganic and inorganic fertilizers can significantly improve the structure of the purple soil, enhance soil fertility and achieve soil sustainable development.

Tillage Pedogenesis of Purple Soils in Southwestern China

Land cultivation and tillage process, and their consequent impacts on soil erosion, have been criticized as the main cause of degradation of land or soil quality. However, purple soils, classified as Regosols in FAO Taxonomy or Entisols in USDA Taxonomy, are formed from purple rocks of the Trias- Cretaceous system, have been developed or at least accelerated the development due to continual tillage operation, especially digging and ridging. The present study took micromorphological investigation on the sedimentary rocks and the soils under different operations of tillage. Results show that the purple rock of Feixiangguan Formation of the Trias system （Tlf） is the easiest to physical weathering and the most fertile soil material enriched in nutrients, and it has been, therefore, mostly cultivated and intensively tilled around the year. It has the fastest soil formation rate. Soil formation rate in the cropland with conventional tillage is higher than that in the forestiand and the grassland. It implies that the artificial brokenness and tillage disturbance play a great role in physical weathering and initiating soil formation processes.

Effects of Application of Controlled Release Nitrogen Fertilizer on N_2O Emission in Slope Cultivated Land with Purple Soil

In order to study effects of application of contmllE=d release fertilizer on ni- trous oxide （N2O） emission in slope cultivated land with purple soil, four treatments including the control group （CK）, urea （UR）, controlled release nitrogen fertilizer （CR）, and controlled release nitrogen fertilizer＋urea （25%CR, 75%UR） were set up, and their impacts on maize yield, surface runoff and nitrogen loss in the growth pe- riod of maize and N2O emission were studied. The results show that maize yield, surface runoff, nitrogen loss from subsurface flow, and N2O emission in the control group was far lower than that in the fertilization treatments, revealing that fertilization was the main reason for nitrogen loss and N2O emission. Among the four treat- ments, nitrogen loss from subsurface flow in the treatment CR was the highest, up to 31.7 kg/hm^2, but N2O emission was 0.35 kg/hm^2, which was 37% less than that in the treatment UR. Nitrogen loss from subsurface flow in the treatment 25% CR was the lowest, only 20.9 kg/hm^2, and N2O emission was 15% less than that in the treatment UR. Nitrogen was slowly released from controlled release nitrogen fertilizer in the growth period, and controlled release nitrogen fertilizer could reduce N2O emis- .sion from slope cultivated land due to low content of soil inorganic nitrogen, but it could increase the nitrogen loss from subsurface flow. Therefore, the combination of controlled release fertilizer and urea can not only reduce N2O emission but also de- crease nitrogen loss from subsurface flow.

Rainfall and Tillage Impacts on Soil Erosion of Sloping Cropland with Subtropical Monsoon Climate- A Case Study in Hilly Purple Soil area, China

Under global warming, storm events tend to intensify, particularly in monsoon-affected regions. As an important agricultural area in China, the purple soil region in the Sichuan Basin, where it has a prevailing monsoon climate, is threatened by serious soil erosion. Tillage operations alter runoff and soil erosion processes on croplands by changing the physical properties of the soil surface. To clarify the relationship between tillage and soil erosion in the purple soil region, three different tillage practices in this region were investigated at the plot scale over 4 years： bare land with minimum tillage （BL）, conventional tillage （CT） and seasonal no-tillage ridges （SNTR） which was initially designed to prevent soil erosion by contoured ridges and no-tillage techniques. The results showed that although there were no significant differences in the surface runoff and soil erosion among the three oractices, BL caused relatively high surface runoff and soil erosion, followed by CT and SNTR. Classification and comparison of the rainfall events based on cluster analysis （CA） verified that the surface runoff was not significantly different between most intensive event and long intensive events but was significantly different between most intensive and short and medium-duration events. Only the rainfall events with the highest rainfall intensity could trigger serious soil erosion, up to 1000 kg ha^-1 in the region. Further detailed investigations on the effects of tillage operations on the soil erosion in a subtropical region with a monsoon climate are needed to provide a basis for modeling catchments and designing better management practices.

Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions

Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots(10°, 16°, 20° and 26°) were established in theYanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studiesand calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient(16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil.

Transport of phosphorus in runoff and sediment with surface runoff from bare purple soil during indoor simulated rainfall

Phosphorus(P)in surface runoff from purple soil is a critical element of agricultural nonpoint source pollution,leading to eutrophication of surface waters in the Three Gorges Reservoir Area(TGRA)of China.This work aimed to understand the processes and mechanisms of P losses from bare purple soil.Based on an indoor rainfall simulation experiment,we focused on the processes of surface runoff and P losses via different hydrological pathways.Experimental treatments included three simulated rainfall intensities,four slope gradients,and three fertilizer treatments.P loss from sediment was the main pathway in the purple soil,and bioavailable P was mainly transferred in dissolved P(DP)of runoff water.The P loss loads tend to grow with the increase of the slope until 25°for the maximum load of runoff water and 20°for the maximum load of sediment.Concentrations of DP in the surface runoff after fertilizer application can exceed the estimates of those required for accelerated eutrophication.Sediment P control might be an essential way for reducing P loss in purple soil for the local government and farmers of TGRA.

Assessment of the Performance of WEPP in Purple Soil Area with Simulated Rainfall Experiments

The water erosion prediction project （WEPP） model is a popular water erosion prediction tool developed on the basis of the physical processes of water erosion. Although WEPP has been widely used around the world, its application in China is still insufficient. In this study, the performance of WEPP used to estimate the runoff and soil loss on purple soil （Calcaric Regosols in FAO taxonomy） sloping cropland was assessed with the data from runoff plots under simulated rainfall conditions. Based on measured soil properties, runoff and erosion parameters, namely effective hydraulic conductivity, inter-rill erodibility, rill erodibility, and critical shear stress were determined to be 2.68 mm h-1, 5.54 x l0^6 kg s-1 m-4, 0.027 s m-1 and 3-5 Pa, respectively, by using the recommended equations in the WEPP user manual. The simulated results were not good due to the low Nash efficiency of 0.41 for runoff and negative Nash efficiency for soil loss. After the four parameters were calibrated, WEPP performed better for soil loss prediction with a Nash efficiency of 0.76. The different results indicated that the equations recommended by WEPP to calculate parameters such as erodiblity and critical shear stress are not suitable for the purple soil areas, Sichuan Province, China. Although the predicted results can be accepted by optimizing the runoff and erosion parameters, more research related to the determination of erodibility and critical sheer stress must be conducted to improve the application of WEPP in the purple soil areas.

Nutrient Balance in Relation to High Yield and Good Quality of Potato on an Acid Purple Soil in Chongqing,China

A field experiment was carried out to study nutrient balance among N, P, K and Mg in potato cultivation on an acid purple soil in Chongqing, China. The experiment included 8 treatments with equal P rate of 120 kg P2O5 hm-2: N0K2, N1K2, N2K2, N3K2, N2K0, N2K1, N2K1Mg and N2K3, where N0, N1, N2 and N3 stand for the N rates of 0, 75, 150 and 225 kg N hm-2, and K0, K1, K2 and K3 for the K rates of 0, 165, 330 and 495 kg K2O hm-2, respectively. Among the treatments designed, Thatment N2K2 with a nutrient supply ratio of N:P2O5:K2O:MgO = 1.25:1:2.75:0.28 gave the highest tuber yield and dry matter, highest starch and Zn and lowest NO3- contents in tuber, and high N, P and K use efficiency with an uptake ratio of N:P:K:Mg = 11.38:1:13.32:0.33 by tuber. Yield and starch and protein contents of tuber were the lowest in Treatment N0K2. Dry matter was the lowest but protein and NO3- contents were the highest in Treatment N2K0. Treatment N2K1Mg had the highest N, P and K utilization rates. Statistical analysis showed that yields of tuber and starch were in a positive linear correlation with the uptake amount of various nutrients and protein of the potato tuber was in a significantly positive linear correlation with tuber N cotent and in a significantly negative linear correlation with tuber K and Mg contents. Balanced application of N, P, K and Mg fertilizers (Treatmeat N2K2) was recommended for realization of high yield and good quality in potato cultivation.

Soil carbon sequestration under long-term rice-based cropping systems of purple soil in Southwest China

Carbon sequestration in agricultural soils is a complex process controlled by farming practices, climate and some other environment factors. Since purple soils are unique in China and used as the main cropland in Sichuan Basin of China, it is of great importance to study and understand the impacts of different fertilizer amendments on soil organic carbon（SOC） changes with time. A research was carried out to investigate the relationship between soil carbon sequestration and organic carbon input as affected by different fertilizer treatments at two long-term rice-based cropping system experiments set up in early 1980 s. Each experiment consisted of six identical treatments, including（1） no fertilizer（CK）,（2） nitrogen and phosphorus fertilizers（NP）,（3） nitrogen, phosphorus and potassium fertilizers（NPK）,（4） fresh pig manure（M）,（5） nitrogen and phosphorus fertilizers plus manure（MNP）, and（6） nitrogen, phosphorus and potassium fertilizers plus manure（MNPK）. The results showed that annual harvestable carbon biomass was the highest in the treatment of MNPK, followed by MNP and NPK, then M and NP, and the lowest in CK. Most of fertilizer treatments resulted in a significant gain in SOC ranging from 6.48 to 2 9.13% compared with the CK, and raised soil carbon sequestration rate to 0.10–0.53 t ha–1 yr-1. Especially, addition of manure on the basis of mineral fertilizers was very conducive to SOC maintenance in this soil. SOC content and soil carbon sequestration rate under balanced fertilizer treatments（NPK and MNPK） in the calcareous purple soil（Suining） were higher than that in the acid purple soil（Leshan）. But carbon conversion rate at Leshan was 11.00%, almost 1.5 times of that（7.80%） at Suining. Significant linear correlations between soil carbon sequestration and carbon input were observed at both sites, signifying that the purple soil was not carbon-saturated and still had considerable potential to se questrate more carbon.

Subsurface Flow Processes in Sloping Cropland of Purple Soil

Subsurface flow is a prominent runoff process in sloping lands of purple soil in the upper Yangtze River basin.However,it remains difficult to identify and quantify.In this study,in situ runoff experimental plots were used to measure soil moisture dynamics using an array of time domain reflectometry(TDR) together with overland flow and subsurface flow using isolated collecting troughs.Frequency of preferential flow during rainfall events and the controls of subsurface flow processes were investigated through combined analysis of soil properties,topography,rainfall intensity,initial wetness,and tillage.Results showed that subsurface flow was ubiquitous in purple soil profiles due to welldeveloped macropores,especially in surface soils while frequency of preferential flow occurrence was very low(only 2 cases in plot C) during all 22 rainfall events.Dry antecedent moisture conditions promoted the occurrence of preferential flow.However,consecutive real-time monitoring of soil moisture at different depths and various slope positions implied the possible occurrence of multiple subsurface lateral flows during intensive storms.Rainfall intensity,tillage operation,and soil properties were recognized as main controls of subsurface flow in the study area,which allows the optimization of management practices for alleviating adverse environmental effects of subsurface flow in the region.

Alleviation of Copper Toxicity to Maize by Phosphorus Fertilizer in Purple Soil

A pot experiment was conducted to evaluate the effects of phosphorus fertilizer in inhibiting the copper toxicity to maize(Zea mays L.) in neutral purple soil. Results indicated that the growth of the shoot and roots of maize plant was obviously reduced by copper and the height and biomass were significantly negatively correlated to the application levels of copper (r=-0.899**^-0.994**) at no P and low P (100 mg kg-1).However, the maize biomass was relatively increased and the high Cu (100 and 200 mg kg-1) induced toxicity of maize was greatly alleviated in all treatments with medium P (300 mg kg-1) and high P (500 mg kg-1).To maintain the normal growth of maize plant (≥3.68 g pot-1), the critical application rates of phosphorus fertilizer should be 160, 210, 300 and 500 mg P kg-1 at 10, 50, 100 and 200 mg Cu kg-1 levels of the soil,respectively. The increases in polyphenol oxidase and catalase activities in maize leaf and dehydrogenase activity in roots by phosphorus fertilizer were in the order of medium p>high p>low p>no P. Activities of polyphenol oxidase and catalase were significantly positively correlated to the application levels of copper (r=0.892**~0.924**), whereas that of dehydrogenase was just reverse (r=-0.966**) at no P. Medium and high P repressed the influence of copper on activities of three enzymes. Phosphorus fertilizer reduced the copper concentrations of maize roots and leaf and the change ranges of the P/Cu ratio of maize roots and the P/Cu, N/Cu and K/Cu ratios of maize leaf. The three ratios of maize leaf were 256±71.5, 2643±839 and 1133±440 at normal growth of maize plant, respectively. Soil available Cu could be markedly cut down by application of phosphorus fertilizer, especiallly at high phosphorus level.

Observation and modeling on irregular purple soil water infiltration process

The infiltration process is a critical link between surface water and groundwater. In this research, a specific device to observe infiltration processes in homogeneous and heterogeneous soils with triangular and inverted triangular profiles was designed, and the Green-Ampt model was employed for the process simulation. The results indicate that(1) the wetting front in coarse texture soils transports faster than in fine texture soils;(2) for the homogeneous case, the wetting front in triangularshaped soils transports faster than the inverted triangular type, but the triangular-shaped soils show a lower infiltration rate;(3) in the initial step, the wetting front in triangular-shaped soils shows higher transport speed, but depicts lower speed with increase in the time;(4) both the wetting front and infiltration rate show a significant exponential relation with the time. From these findings, an empirical model was developed which agrees well with the observed data and provides a useful method for this field of soil research.

Understory flora and community physiognomy of planted forests in the degraded purple soil ecosystem, South China

The flora and community physiognomy of degraded plantation ecosystems onpurple soil were investigated in Ninghua County of Fujian Province, China to understand therelationship between plant diversity and ecosystem processes.. Four different restorationcommunities (labeled as ecological restoration treatment Ⅰ, Ⅱ, Ⅲ and Ⅳ) were selected byspace-time replacement method according to the erosion intensity in degraded purple soil ecosystem.The results showed that there were totally 86 plant species belonging to 78 genera and 43 familiesin the degraded purple soil ecosystem. Of the 15 types of distribution area in spermatophyte genus,12 types were found in the purple soil ecosystem. Along restoration gradient from low to high, plantgrowth type and life form spectra became abundant more and more, and the spermatophyte genera foreach distribution area type and genera numbers for different foliage characters increased as well.It is concluded that the plant flora and physiognomy in ecological restoration process become morecomplex and diverse, indicating that the forest ecosystem on purple soil tends to be more stable.

Rill flow velocity affected by the subsurface water flow depth of purple soil in Southwest China

Subsurface water flow above the weakly permeable soil layer commonly occurs on purple soil slopes.However,it remains difficult to quantify the effect of subsurface water flow on the surface flow velocity.Laboratory experiments were performed to measure the rill flow velocity on purple soil slopes containing a subsurface water flow layer with the electrolyte tracer method considering 3 subsurface water flow depths(SWFDs:5,10,and 15 cm),3 flow rates(FRs:2,4,and 8 L min^(-1)),and 4 slope gradients(SGs:5°,10°,15°,and 20°).As a result,the pulse boundary model fit the electrolyte transport processes very well under the different SWFDs.The measured rill flow velocities were 0.202 to 0.610 m s^(-1) under the various SWFDs.Stepwise regression results indicated a positive dependence of the flow velocity on the FR and SG but a negative dependence on the SWFD.The SWFD had notable effects on the rill flow velocity.Decreasing the SWFD from 15 to 5 cm increased the flow velocity.Moreover,the flow velocities under the 10-and 15-cm SWFDs were 89%and 86%,respectively,of that under the 5-cm SWFD.The flow velocity under the 5-,10-and 15-cm SWFDs was decreased to 89%,80%,and 77%,respectively,of that on saturated soil slopes.The results will enhance the understanding of rill flow hydrological processes under SWFD impact.

IMPACTS OF DIFFERENT TYPES OF LAND USE ON PROCESSES OF SOIL AND WATER LOSS OVER PURPLE SOIL SLOPELAND

Based on natural precipitation observations, impacts of different types of land use on processes of soil and water loss over purple soil related slopeland were studied by simulated rainfall experiments. Measurement data revealed that rainstorms and slope length are the essential factors accountable for soil and water loss on purple soil slopeland for intense rill erosion can be caused on 10 meter long purple soil slopes by high intensity rainfall. Under circumanstances of rainstorms, annual hedge plants grown on slopeland of 25 degrees can cause a reduction of runoff by 22 43 percent and that of erosion induced sand content by 94 98 percent. Stone bund horizontal terraces can lead to a runoff reduction by 62 67 percent in comparison with steep slopelands and that of erosion induced sediment by 97.8 99 percent. Soil and water loss can be substantially decreased on steep slopes by hedge plants with a cost of only 10 20 percent that of the stone bund horizontal terraces. Hence it is an effective way to control soil and water loss in terms of slopeland amelioration and utilization in the Three Gorges Reservoir Area.

Soil Aggregation and Its Relationship with Organic Carbon of Purple Soils in the Sichuan Basin,China

The interaction of soil aggregate dynamics with soil organic carbon is complex with varied spatio-temporal processes in macro-and micro-aggregates. This paper is to determine the aggregation of soil aggregates in purple soils （Regosols in FAO Taxonomy or Entisols in USDA Taxonomy） for four types of land use, cropland [corn （Zea mays L.）], orchard （citrus）, forestland （bamboo or cypress）, and barren land （wild grass）, and to explore their relationship with soil organic carbon in the Sichuan basin of southwestern China. Procedures and methods, including manual dry sieving procedure, Yoder＇s wet sieving procedure, pyrophosphates solution method, and Kachisky method, are used to acquire dry, wet, and chemically stable aggregates, and microaggregates. Light and heavy fractions of soil organic carbon were separated using 2.0 g·mL^-1 HgI2-KI mixed solution. The loosely, stably, and tightly combined organic carbon in heavy fraction were separated by extraction with 0.1 M NaOH and 0.1 M NaOH-0.1M Na4P2O7 mixed solution （pH 13）. The results show that the contents of dry and wet macroaggregates 〉0.25 mm in diameter were 974.1 and 900.0 g·kg^-1 highest in red brown purple soils under forestland, while 889.6 and 350.6 g·kg^-1 lowest in dark purple soil and lowest in grey brown purple soils under cropland, respectively. The chemical stability of macroaggregates was lowest in grey brown purple soil with 8.47% under cropland, and highest in red brown purple soil with 69.34% under barren land. The content of microaggregates in dark purple soils was 587g·kg^-1 higher than brown purple soils, while 655g·kg^-1 in red brown purple soils was similar to grey brown purple soils （651g·kg^-1）. Cropland conditions, only 38.4% of organic carbon was of the combined form, and 61.6% of that existed in light fraction. Forestland conditions, 90.7% of organic carbon in red brown purple soil was complexed with minerals as a form of humic substances. The contents and stability of wet aggregates 〉 0.25 mm, contents and stability of chemically stable aggregates 〉0.25 mm, contents of microaggregates 〉 0.01 mm, contents of aggregated primary particle （d〈0.01 mm） and degree of primary particles （d 〈0.01 mm） aggregation were closely related to the concentrations of total soil organic carbon, and loosely and tightly combined organic carbon in heavy fraction. Soil microaggregation could be associated with organic carbon concentration and its combined forms in heavy fraction. There was a direct relationship between microaggregation and macroaggregation of soil primary particles, because the contents of wet aggregates 〉 0.25 mm and its water stability of aggregates were highly correlated with the contents of aggregated primary particle （d 〈 0.01 mm） and the degree of primary particles （d 〈 0.01 mm） aggregation.

A Quantification of the Effects of Erosion on the Productivity of Purple Soils

Research on the effects of soil erosion on soil productivity has attracted increasing attention.Purple soil is one of the main soil types in China and plays an important role in the national economy.However,the relationship between erosion and the productivity of purple soils has not been well studied.The purpose of this research was to determine if soil depth,which is dependent on the rate of erosion,has an influence on crop yield and growth.Plot and pot experiments at different soil depths were performed.Results indicate that soils from different parental materials had different growth features and crop yields due to the differential fertility of the derived soils.The yield reduction rate increases exponentially with the depth of eroded soil(level of erosion).The yield reduction rate per unit eroded soil horizon(10 cm) is approximately 10.5% for maize and wheat.

Responses of Gardenia jasminoides Ellis Leaf Traits and Anatomical Structures to Drought Stress in Purple Soil

[Objectives]This study was conducted to investigate the response of Gardenia to purple soil drought stress,hoping to provide a reference for the selection of plants for vegetation restoration in purple soil regions.[Methods]The pot-weighing water control method was used to apply different degrees of drought stress to Gardenia seedlings in purple soil,and the effects of drought stress on the electrical conductivity,chlorophyll content,leaf morphology and structure of Gardenia leaves were explored.[Results]The leaf electrical conductivity increased with the increase of drought stress intensity,and the leaf electrical conductivity under severe drought stress increased by 59.93%compared with the control;the chlorophyll content of Gardenia showed a single-peak changing trend that increased and then decreased with the development of drought stress,and it was the highest in each stress stage under severe drought stress;the leaf thickness,palisade tissue thickness and sponge tissue thickness of Gardenia were reduced with the stress degree increasing,and showed the largest decreases under severe stress;the stomatal length,stomatal width and stomatal opening of Gardenia gradually decreased with the increase of stress,while the stomatal density gradually increased.[Conclusions]This study provides a technical and resource basis for vegetation restoration in purple soil.

Effect of nitrogen fertilizer on the uptake and utilization of potassium by various rice varieties in purple soil

Nitrogen and potassium are important nutrientelements for rice.Besides supplied by the or- ganic manure,potassium nutrition of ricecomes dominantly from purple soils in Sichuanbasin.Potassium exists abundantly in mineralforms in the purple soils.Availability of soilpotassium for crop depends on the potassiumforms,the uptake ability of crops,and fertiliz-er practices.A pot culture experiment wasconducted to study the kinetics of potassiumuptake in the purple soil(total N 22.64g·kg,total K 24.36g·kg,available N 102.6mg·kg,available K 140.6mg·kg,acidsoluble K 936.0mg·kg,and pH 6.8).Ma-terials used were three Fhybrid rices,Eryou

Distribution and Transformation of Native and Added Ni Fractions in Purple Soils from Sichuan Province

The distribution and transformation of added and native Ni in purple soils were investigated with both sequential extraction procedure and isotopic tracer technique.The distribution of added and native Ni was greatly dependent on soil properties.Low soil PH was favorable for soluble plus exchangeable (EX) Fraction,while Fe/Mn oxides and clay for Fe/Mn oxide bound (OX) and residual (RES) fractions. The added Ni,however,has not yet reached the distribution equilibrium up to the 150th day after incubation.This was reflected in the fact that the proportion of EX fraction from added Ni was 150%-600% as much as that of native Ni, while that of RES fraction was only about 80%.Once entering soil, the applied soluble Ni was rapidly transformed into Other fractions, but the organic complexed (OM) fraction of added Ni was relatively stable during incubation.The carbonate bound(CAB) fraction showed a progressive increase and attained a peak value after 0-14 d of incubation and thereafter decreased gradually. The occurrence time of this peak advanced as initial soil PH increased, but the peak would disappear when initial soil pH was higher than 7.5(or containing free CaCO3). The transformation processes of the EX,OX and RES fractions could be described by Elovich and two-constant rate equstions,and the rates were positively correlated with soil pH,CEC and clay.These findings could explain why there are differences in ecological and environmental effects of Ni in different soils and at various intervals.