土壤磷酸盐氧同位素分析方法和应用研究进展

在一定温度下磷酸盐和周边水体氧的同位素分馏仅受生物活动控制,因此磷酸盐氧同位素成为生态系统中磷源和磷循环研究的良好示踪剂。介绍了磷酸盐氧同位素研究应用的理论基础和近几年来针对土壤富含有机质,氧元素来源多样的特点发展起来的土壤磷酸盐氧同位素的分析和纯化方法,综述了磷酸盐氧同位素在土壤磷源示踪和磷循环应用研究中的初步进展,并提出目前研究存在的局限和对未来工作的展望。

一些细菌和真菌的解磷能力及其机理初探

４株细菌和８株真菌培养６ｄ后，发现培养液中有机酸含量大幅度增加，ｐＨ大幅度地下降，磷的含量大幅度增加，真菌比细菌表现出更强的溶解磷矿粉的能力。不同的微生物分泌有机酸的数量和种类差别很大，真菌分泌的有机酸种类比细菌要多。但是，培养液中有机酸总量与解磷量之间并不存在显著的相关性。

Solubilization of Rock Phosphate in Liquid Culture by Fungal Isolates from Rhizosphere Soil

Rock phosphate （RP） is a low efficiency P fertilizer that is directly applied to the soil and can be solubilized by phosphate-solubilizing microorganisms （PSMs） in fermentation or soil conditions. This study investigated dynamic solubilization of 2 concentrations of rock phosphate in a liquid culture with different dosages of glucose by two fungal isolates,Aspergillus niger P39 and Penicillium oxalicum P66, from soybean and wheat rhizosphere soil. Although during the 20 day culture period A. niger P39 had a stronger ability to acidify the culture media than P. ozalicum P66, soluble P concentrations at glucose dosages of 30 and 50 g L^-1 with RP of 15 g L^-1 in the culture solution were much higher by P. oxalicum P66. The greater effectiveness of P. oxalicum P66 compared to A. niger P39 in the solubilization of RP was strongly associated with the production of organic acids. This study suggested that for RP solubilization the type rather than the concentration of PSM-produced organic acids was more important.

Kinetics of Phosphate Release from Three Phosphate-Treated Soils

Phosphate release from three selected soils after treatments of 1.6 and 2.4 mmol L-1 P was investigated using sequential extractions and fitted using six kinetic models, including zero order (Z), first order (F), second order (S), parabolic diffusion (PD), two constant rate (TC), and Elovich type (ET) equations. The results showed that the rate of P release was initially rapid and then gradually declined with time. Also, P release increased with added P. Total P release followed the order: paddy soil with 2.4 mmol L-1 P > red soil with 2.4 mmol L-1 P > paddy soil with 1.6 mmol L-1 P > fluvo-aquic soil with 2.4 mmol L-1 P > fluvo-aquic with 1.6 mmol L-1 P > red soil with 1.6 mmol L-1 P. For the two P treatments P release from the paddy soils in the first extraction was 44.3% and 45.6% of total released P, respectively, which were higher than those from red and fluvo-aquic soils. The ratio of P release at the end of release time was 14.0% and 13.1% in the paddy soil treated with 1.6 and 2.4 mmol L-1 P, respectively, but only 5.1% and 9.2% in the red soil and 7.0% and 5.2% in the fluvo-aquic soil, respectively. Comparison of the coefficients of determination (R2) indicated that ET, TC, and PD equations could describe the P release data better than Z, F, and S equations.

Synergism Among VA Mycorrhiza, Phosphate Solubilizing Bacteria and Rhizobium for Symbiosis with Blackgram (Vigna mungo L.) Under Field Conditions

A field experiment was conducted at the G.B. Pant University Research Station, Ujhani (U.P.) in rainy (Kharif) season of the year 1994-1995 to study the effect of Rhizobium, VAM (vesicular arbuscular myc- orrhiza) and PSB (phosphate solubilizing bacteria) inoculation, with and without P, on blackgram (Vigna mungo L.) seed yield. Phosphorus application in soil with medium P content (5.4 mg kg～1) increased nodu- lation, grain yield, N and P in plant and grain over no phosphorus control. Forty kilograms of P-2O-5 each hactare recorded an increase of 20.6 % in nodule dry weight, significant increases of 0.35 g kg～(-1) in N con- centration and 1.28 g kg～(-1) in P concentration of plant over 20 kg P-2O-5 ha～(-1). Similar significant increases of 0.59 g kg～(-l) in grain yield and 0.54 and 0.23 g kg～(-1) in N and P concentrations of the grain, respectively, over 20 kg P-2O-5 ha～(-1) were also obtained with higher dose. Inoculation of Rhizobium ＋ VAM ＋ PSB at all the stages of plant growth recorded maximum increases in all the parameters studied. Dual inoculation of Rhizobium with either VAM or PSB was generally significant in the effect and better than that of VAM ＋ PSB, however, P accumulation in plant and grain was more with VAM ＋ PSB. Among single inocula tions, Rhizobium gave highest and 21.0 % more nodule number, 34.7 % more nodule dry mass, 0.73 g kg～(-1) more N in grain and 4.2 % higher grain yield over PSB. PSB, however, registered significant increases in P concentration in plant and grain over VAM and Rhizobium.

Changes in Phosphorus Fractions, pH, and Phosphatase Activity in Rhizosphere of Two Rice Genotypes

A rhizobox experiment with two phosphorus (P) treatments, zero-P (0 mg P kg-1) and plus-P (100 mg P kg-1) as Ca(H2PO4)2·H2O, was conducted to study the chemical and biochemical properties in the rhizosphere of two rice genotypes (cv. Zhongbu 51 and Pembe) different in P uptake ability and their relationship with the depletion of soil P fractions. Plant P uptake, pH, phosphatase activity, and soil P fractions in the rhizosphere were measured. Both total dry weight and total P uptake of Pembe were significantly (P < 0.05) higher than those of Zhongbu 51 in the zero-P and plus-P treatments. Significant depletions of resin-Pi, NaHCO3-Pi, NaHCO3-Po, and NaOH-Pi, where Pi stands for inorganic P and Po for organic P, were observed in the rhizosphere of both Zhongbu 51 and Pembe under both P treatments. Pembe showed a greater ability than Zhongbu 51 in depleting resin-Pi, NaHCO3-Pi, NaHCO3-Po, NaOH-Pi, and NaOH- Po in the rhizosphere. HCl-Pi and residual-P were not depleted in the rhizosphere of both genotypes, regardless of P treatments despite significant acidification in the rhizosphere of Pembe under zero-P treatment. Higher acid phosphatase (AcPME) activity and alkaline phosphatase (AlPME) activity were observed in the rhizosphere of both Zhongbu 51 and Pembe compared to the corresponding controls without plant. AcPME activity was negatively (P < 0.01) correlated to NaHCO3-Po concentration in the rhizosphere of both Zhongbu 51 and Pembe, suggesting that AcPME was associated with the mineralization of soil organic P.

Phosphate-solubilizing microbes in rhizosphere soils of 19 weeds in southeastern China

Low phosphorus (P) availability is one of the most important factors limiting plant growth in red soils across southeastern China. Many non\|symbiotic microorganisms in rhizosphere can enhance P solubility, but little is known about the magnitude of their phosphorus\|solubilizing ability (PSA) and the difference in phosphorus\|solubilizing microorganisms (PSM) among plant species. The number of phosphorus\|solubilizing microorganisms and their PSA in rhizosphere soils of 19 weed species in a citrus orchard on red soil at Changshan, Zhejiang, China, were investigated. Inorganic P (powdered phosphate rock, PR) and organic P (lecithin, OP) were respectively used as the sole P\|source to examine the PSA of isolated microbes. The PS actinomycetes community varied greatly among the different weed rhizospheres while the PS fungus community showed to be most stable to the weed rhizosphere. The highest number of PR\|PS and OP\|PS bacteria was found in rhizosphere soil of \%Mollugo pentaphyll\%, and the highest number of PR\|PS and OP\|PS actinomycetes was found in rhizosphere soil of \%Polygonum lapathifolium\%. The highest number of PR\|PS fungi was found in \%Erigeron annuus\% and \%Mollugo pentaphyll\% rhizosphere soil, and the highest number of OP\|PS fungi was found in rhizosphere soil of \%Mazus stachydifolius\%. \%Mazus stachydifolius\% showed the strongest PR\|PS ability (6340.75μg) while \%Eragrostis pilosa\% showed the strongest OP\|PS ability (1301.84μg). The PR\|PS ability and OP\|PS ability of \%Mollugo pentaphyll\% was 4432.87μg and 1122.05μg respectively. A significant correlation between the number of PR\|PSM and OP\|PSM was found. Significant correlation was only found between the PR\|PS fungi number and its PSA( r =0.75, P <0.05) and between the number of OP\|PS fungi and its PSA( r =0.87, P <0.01}). It indicated that plant species had significant influence on components of the non\|symbiotic PSM community and their activity in its rhizosphere soil. Fungi play a leading role in phosphorus solubilization in weed rhizopshere. It suggested that weed conservation could benefit soil microbe development in agroecosystems, especially in the initial stage of agroecosystem development because there is less organic carbon in bare soil. The results suggested that weed conservation could increase PSA of PSM.

Adsorption of Acid Phosphatase on Minerals and Soil Colloids in Presence of Citrate and Phosphate

The aim of this work was to study the influence of phosphate and citrate, which are common inorganic and organic anions in soils, on the adsorption of acid phosphatase by kaolin, goethite and the colloids separated from yellow-brown soil (YBS) and latosol (LS) in central-south China. The YBS colloid has the major clay mineral composition of 1.4 nm mineral, illite and kaolinite while the LS colloid mainly contains kaolinite and oxides. The adsorption isotherm of acid phosphatase on the examined soil colloids and minerals fitted to the Langmuir model. The amount of enzyme adsorbed in the absence of ligands was in the order of YBS colloid > LS colloid > kaolin ≈ goethite. In the presence of phosphate or citrate, the amounts of the enzyme adsorbed followed the sequence YBS colloid > kaolin > LS colloid > goethite. The presence of ligands also decreased the binding energy between the enzyme and soil colloids or minerals. With the increase of ligand concentration from 10 mmol L-1 to 400 m mol L-1, different behaviors for the adsorption of enzyme were found in the colloid and mineral systems studied. A sharp decrease in enzyme adsorption was observed on goethite while gradual decreases of enzyme adsorption were recorded in the two soil colloid systems. However, no any decrease was found for the amount of enzyme adsorbed on kaolin at higher ligand concentrations. When phosphate or citrate was introduced to the system before the addition of enzyme, the ligands usually enhanced the adsorption of enzyme. The results obtained in this study suggested the important role of kaolinite mineral in the adsorption of enzyme molecules in acidic soils in the presence of various ligands.

Soil Components Affecting Phosphate Sorption Parameters of Acid Paddy Soils in Guangdong Province

Soil components affecting phosphate sorption parameters were studied using acid paddy soils derived from basalt, granite, sand-shale and the Pearl River Delta sediments, respectively, in Guangdong Province. For each soil, seven 2.50 g subsamples were equilibrated with 50 mL 0.02 mol L-1 (pH=7.0) of KCI containing 0, 5, 10, 15, 25, 50 and 100 mg P kg-1, respectively, in order to derive P sorption parameters (P sorption maximum, P sorption intensity factor and maximum buffer capacity) by Langmuir isotherm equation. It was shown that the main soil components influencing phosphate sorption maximum (Xm) included soil clay, PH, amorphous iron oxide (Feo) and amorphous aluminum oxide (Alo), with their effects in the order of Alo > Feo > pH > clay. Among these components, pH had a negative effect, and the others had a positive effect. Organic matter (OM) was the only soil component influencing P sorption intensity factor (K). The main components influencing maximum phosphate buffer capacity (MBC) consisted of soil clay, OM,pH, Feo and Alo, with their effects in the order of Alo > OM > pH > Feo > clay. Path analysis indicated that among the components with positive effects on maximum phosphate buffer capacity (MBC), the effect was in the order of Alo > Feo > Clay, while among the components with negative effects, OM > pH. OM played an important role in mobilizing phosphate in acid paddy soils mainly through decreasing the sorption immensity of phosphate by soil particles.

Application of Ground Phosphate Rock to Dimmish the Effects of Simulated Acid Rain on Soil Properties

The effects of simulated acid rain retained in soil on the properties of acid soil and its diminishing by application of ground phosphate rock were investigated by using the sorption method. Results show as follows: (1) For yellow brown soil, the effect of simulated acid rain on the properties of soil with a pH value of 5.9 was relatively small, except a great quantity of acid rain deposited on it. (2) For red soil, the effect of simulated acid rain on the properties of soil was significant. With the increase of the amount of acid deposition, the pH value of soil was declined, but the contents of exchangeable H+, Al3+ and Mn2+ and the amount of SO42- retention were increased. (3) Many properties of acid soils could be improved by applying ground phosphate rock. For example, pH value of soils and the amounts of available P and exchangeable Ca2+ and Mg2+ were increased, and the amounts of exchangeable H+ and Al3+ and SO42- retained was reduced. The application of ground posphate rock could effctively dimmish the pollution of acid rain to soil.

Types of Crystalline Iron Oxides and Phosphate Ad－sorption in Variable Charge Soils

The types, contents and morphologies of crystalline Fe oxides and their relations to phosphate adsorptionon the clay fractions in soils with variable charge in southern China were investigated by means of XRD, TEM,EMA and chemical analysis methods.Results indicated that the types and contents of crystalline Fe oxidesvaried with the soils examined. The dominant crystalline Fe oxide was hematite in the latosols and goethitesin the red soils.In yellow-brown soils, the only crystalline Fe oxide was goethite.The difference between Aldand Alo came mainly from the Al substituting for Fe in the pe oxides. The crystal morphology of goethiteappeared mainly as subrounded flat or iso-dimensional rather than acicular particles. Hematites occurredin plates of various thickness. Their MCDa/MCDc ratios in the latosols and red soils were generally above1.5 and below 1.5, respectively. The MCD values of goethites and hematites were 15-25nm and 20-35nm,and their specific surface areas were 80-120m￣2/g and 35-75m￣2/g, respectively.The goethite crystals weregenerally smaller. Variations of the total amounts of crystalline Fe oxi es in clay fractions were not related tophosphate adsorption. The types, contents and morphologies of crystalline Fe oxides in the soils remarkablyaffected phosphate adsorption characteristics of the soils. The phosphate adsorption of goethite was muchgreater than that of hematite. The higher the MCD /MCDc rotio of hematite, the lower the phosphateadsorption.

Effect of Compost Amendment on Heavy Metals, Nitrogen and Phosphorus in a Peat-Based Container Medium

A laboratory study was conducted to evaluate the effect of compost amendment on mobility and leaching potential of heavy metals, nitrogen （N） and phosphorus （P） from a peat-based commercial container medium containing 700 g kg^-1 peat, 200 g kg^-1 perlite and 100 g kg^-1 vermiculite at varying amendment rates of compost （0, 0.25, 0.50, 0.75 and 1.00 L L^-1）. Increasing compost amendment significantly and linearly increased the pH （P 〈 0.01）, the total concentrations of organic carbon （P 〈 0.05）, copper （Cu） （P 〈 0.01）, cadmium （ca） （P 〈 0.01）, and lead （Pb） （P 〈 0.01）, and increased the bulk density （P 〈 0.01） of the medium. The electrical conductivity （EC）, and total N and P of the medium increased significantly （P 〈 0.01） and quadratically with increasing compost amendment. The relationship of the C/N ratio of the medium with the compost amendment rate was decreasing, significant （P 〈 0.01） and cubic, while that of the total Zn was increasing, significant （P 〈 0.01） and cubic. Extractable P, NO3-N, and NH4-N increased initially with an increasing compost amendment of up to 0.50 L L^-1 and then decreased with further increasing compost rate. Increasing compost rates resulted in a highly significant （P 〈 0.01） and linear increase in total Cd, Cu, and Pb, and a highly significant （P 〈 0.01） and cubic increase in total Zn in the medium. Increasing compost rates also significantly （P 〈 0.01） increased extractable Cu （linearly） and Zn （quadratically）, but significantly （P 〈 0.01） decreased extractable Pb （linearly）. There was no significant effect of compost amendment on the extractable Cd concentration in the medium. However, with increasing compost rates from 0.25 to 1.00 L L^-1, extractability of P, Cd, Cu, Pb and Zn （extractable concentration as a percent of total） was decreased, indicating that compost amendment could lower the leachability of these elements from the medium.

Phosphate Distribution and Movement in Soil－Root In－terface Zone：I． The Influence of Transpiration Rate

The experiments were conducted in the artificial climate laboratory using ￣(32)P labelled soil and soil-rootplane system to investigate phosphate distribution and its movement in the soil-root interface zone andtheir relations with phosphate uptake by plant as well as transpiration rate (atmosphere humidity). It wasfound that although the phosphate in the soilroot interface zone was of depletive distribution as a functionC/Co = ax￣b(C/Co is the relative content of fertilizer phosphate in a distance from the root surface x, aand b are the regression constants), and a relative accumulation zone of phosphate within 0.5 mm near theroot surface was often observed especially in the heavier texture soils because of root phosphate secretion.The depletion intensity of phosphate in the soil-root interface zone was in agreement with the phosphateuptake by plants under two humidities very well. However, the effects of air humidity on characteristics ofthe phosphate distribution near wheat or maize root surface were different. Wheat grew better under loweratmosphere humidity while maize, under higher humidity, which caused a more intensive uptake and thusa stronger depletion of phosphate in the rhizosphere. Moreover, the depletion intensity was greater by thebottom or the middle part of wheat roots and by the top or the middle part of maize roots. The depletivedistribution of phosphate in the rhizosphere soil and the relative contribution of phosphate diffusion to plant,which was more than 98% in the cultural experiments, indicated that diffusion was a major process forphosphorus supply to plants.

Effective remediation of cadmium and lead contaminated soils by a novel slow-release phosphate amendment

Phosphate is widely used to immobilize cadmium(Cd)and lead(Pb)in soils through the insoluble metal phosphate precipitation.However,an increase in the phosphorus content of the environment can cause new pollution.In this study,five slow-release phosphate amendments(SRPAs)were synthesized and their characteristics including BET,SEM,FTIR,swelling ratio,and thephosphorus release were determined.The results show that SRPA was a sphere with a network structure with a specific surface area of 5 to 7.18 m^(2)/g andcontained phosphate,hydroxyl,carboxyl and other functional groups.Among five SRPAs,S3 sample showed good performance for phosphate release.Phosphate release from SRPA was well fitted with Ritger-Peppas model with constant n between 0.45 and 0.85,indicating that the phosphate release was in accordance with non-Fickian diffusion.As compared with monocalcium phosphate(MCP),SRPA application led to a lower concentration of water-soluble phosphorus in the soil sample and higher remediation efficiencies of Cd and Pb.The remediation efficiencies of water-soluble Cd and Pb in soil with SRPA were 97.1%and 97.9%,respectively.The remediation efficiencies of bioavailable Cd and Pb were 71.85%and 76.47%,respectively.The results of Tessier extraction showed that the exchangeable and carbonatebound fractions of Cd and Pb in the soil sample after SRPA application significantly reduced,while the residual fraction increased,indicating the stability of heavy metals increased.

The Long Term Evolution of Phosphates from the Cambic Chernozem at ARDS Caracal, Romania

The decreasing of the plant available phosphorus of Romanian soils after 1990 is a major concern in relation with the lowered yields of the major crops. This fact is correlated with a rudimentary technology where the fertilization is a secondary issue. Thus, the fertilizer consumption, after 1990, has drastically decreased to 41.3 kg/ha NPK on arable land over 129.9 kg/ha in 1986 and from 86.4 kg/ha to 26.3 kg/ha on agricultural land. As a result, the phosphorus fertilizer quantities applied by small farmers are very small or inexistent. In order to determine the soil available phosphorus content in Romania, it was analyzed the evolution of soil phosphorus supplying degree on a cambic chernozem （one of the most fertile soils in Romania） from Agricultural Research and Development Station （ARDS） Caracal between 1986-1992 and 2000-2005. This analysis has shown the following issues： very well supplied soils by available phosphorus no more exist since 2006, the ones with a good supplying degree have decreased from 616 ha to 107 ha, which means from 24.8% to 4.3% yet the low supplied soils have increased from 526 ha to 1,129 ha （23.1% to 45.5%） and the very low supplied ones have increased from 198 ha to 776 ha （7.9% to 31.2%）. As a consequence of low fertilizer quantities and the decreasing of the soil supplying degree by available phosphorus the average yield in this farm has decreased from 5,776 to 3,707 kg/ha.

Phosphate Rock Fertilizer in Acid Soils: Comparing Phosphate Extraction Methods for Measuring Dissolution

Three phosphate extraction methods were used to investigate the dissolution, availability and transformation of Kunyang phosphate rock (KPR) in two surface acid soils. Dissolution was determined by measuring the increase in the amounts of soluble and adsorbed inorganic phosphate fractions, and did not differ significantly among the three methods. Significant correlations were obtained among P fractions got by the three extraction methods. Dissolution continued until the end of the 90 day incubation period. At the end of the period, much of the applied phosphate recovered in both soils were in the Al and Fe P or in the hydroxide and bicarbonate extractable inorganic P fractions. The dissolution of KPR in the two soils was also similar: increased addition of phosphate rock resulted in decreased dissolution. The similarity in the order and extent of dissolution in the two soils was probably due to the similarity in each soil of several factors that are known to influence phosphate rock dissolution, namely low CEC, pH, P level, and base status; and high clay and free iron and aluminum oxide contents. The results suggested that KPR could be an alternative P source in the long, if not the short, term in the soils, provided that those factors influencing P availability in the soils are not limiting.

Phosphate Sorption-Desorption Characteristics in Two Inceptisols and an Alfisol of Chattisgarh, India

Two Inceptisols and an Alfisol of the Indravati Catchment area in Chattisgarh, India, comprising several gradientsin physical and chemical properties were studied to relate phosphate sorption and desorption to soil properties. Fromthe P isotherm curve, the standard P requirement (SPR) of the soils was determined. Phosphate sorption data were alsofitted both to the Langmuir and Freundlich Equations. The mean sorption maximum values for three different soil serieswere: Bastar > Geedam > Mosodi. The fraction of added phosphate sorbed for the 3 series followed this same trend asdid SPR; the phosphate sorption maximum and the maximum phosphate buffering capacity, which were estimated by theLangmuir isotherm; and the Freundlich constant 1/n. However, phosphate desorption, as well as the maximum recoverypercent did not follow this order. The phosphate affinity constant (K) was also different following the same progressionfor the 3 soil series as the Freundlich constant K’, which measured sorption strength. Meanwhile, an inverse order existedfor K and K’ versus the percent desorbed relative to the sorbed as well as the maximum recovery percent. In addition,significant correlation coefficients among sorption parameters of P and soil factors were found.

Agronomic and Economic Potential of Tughutu and Minjingu Phosphate Rock as Alternative Phosphorus Sources for Bean Growers

On-farm experiments were conducted in farmers' fields at 6 different sites in Western Usambara Mountains(WUM)in northern Tanzania during the 2000-2001 cropping season.The objectives were to study the effects of Tughutu(Vernonia subligera O.Hoffn)pruning in combination with Minjingu phosphate rock(MPR)or triple super phosphate(TSP)supply on the concentration of P in the tissues and seed yields of common bean,and to assess the economic returns of these different technologies to farmers.The experimental design was a randomized complete block with each of the 6 farmers' fields used as a replicate.The treatments included:control,MPR or TSP each at 26 kg P ha^(-1),Tughutu at 2.5 t ha^(-1), and Tughutu at 2.5 t ha^(-1)combined with MPR or TSP at 26 kg P ha^(-1). Addition of MPR or TSP alone significantly raised P concentration in bean shoots from 1.27 mg g^(-1)to 1.70 and 1.95 mg g^(-1)respectively.Combining MPR or TSP with Tughutu increased P concentration above the proposed deficiency level of 2 mg g^(-1).The relative agronomic effectiveness(RAE)of MPR ranged from 12.5% to 45.0%.Seed yields of common bean was markedly increased by 28%-104% from MPR or TSP supply alone,and 148%-219% from Tughutu application combined with 26 kg P ha^(-1)of MPR or TSP relative to the control.With Tughutu alone,seed yield increased by 53%. From economic analysis,the increase in seed yield with the supply of MPR or TSP combined with Tughutu translated into a significantly(P≤0.001)higher marginal rate of return and dollar profit for common bean farmers in WUM in northern Tanzania.It is concluded that Tughutu and its combined application with MPR or TSP is an appropriate integrated nutrient management strategy that may increase bean yields and dollar profit to the rural poor communities in Tanzania.

Phosphate Distribution and Movement in Soil-Root In-terface Zone: II. The Infinence of Soil Water Contentand Application Rates of Phosphate

The phosphate in the soil-root interface zone under various soil water contents and application rates ofphosphate was still of depletion distribution which could be described by a power function in the form ofC/Co= ax￣b(C/Co is the relative content of fertilized phosphate in a distance from the root surface x, a andb are the regression constants). The depletion rate of phosphate in soil near the root surface was higher andthe depletion range was narrower under lower soil moisture. On the contrary, at higher soil water content thedepletion range was wider, generally The application rate of phosphate led to the greater depletion intensityof phosphorus was higher in the heavier texture soils. In general, the depletion intensity in the soils, whichdecreased with increasing clay content or increa.sing buffering power of soil, decreased in the order as loessalsoil and black fou soil> lou soil> yellow cinnamon soil when 50 or 100 mg of phosphorus were applied in theform of KH_2PO_4. This result indicated that the phosphate distribution and its movement in the soil-rootinterface zone closely related with the buffering capacity of soil.

Agronomic Potential of Partially Acidnlated Rock Phos－phates in Acid Soils of Subtropical China

A glasshouse experiment was conducted to evaluate the agronomic potential of four partially acidulatedrock phosphates (PARP) in three representative soils sampled from subtropical China. The PARPs weremanufactured by attacking a moderately reactive phosphate rock either with sulfuric acid alone or withcombination of sulfuric and phosphoric acids at 30 or 60 percent of acidulation. Shoot dry weight and Paccumulation of six successive cuttings of ryegrass were used to compare the agronomic potential of thesefertilizers with that of the raw rock phosphate (RP) and monocalcium phosphate (MCP). Results indicatedthat the effectiveness of various phosphates was determined both by the solubility of the phosphates andby the acidity and P-fixing capacity of the soils. The higher the watersoluble P contained, the better theeffectiveness of the fertilizer was. Although plant P accumulation of PARP treatments was constantly lowerthan that of MCP treatment, some PARPs could still get a dry matter production similar to that of MCPtreatment. PARP SP60, which was acidulated with a mixture of sulfuric acid and phosphoric acid at 60percent of acidulation and contained the highest soluble P, was as effective as MCP in terms of dry matterproduction on all the soils. 560 and C1, which were both acidulated with sulfuric acid with the formerat 60 percent of acidulation and the latter at 30 percent but with a further addition of monoarninoniumphosphate, were more than 80 percent as effective as MCP. Raw RP also showed a reasonable effectivenesswhich increased with soil acidity. It was suggested from the study that some of these PARPs could beexpected to have a comparable field performance as soluble P fertilizers in the acid soil regions.