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1.
Abstract

Phosphorus (P) forms in soils determine the amount of P available for crops and the potential for this element to be released to water. Sequential chemical fractionation can provide some information about major P forms in soils, and allow one to distinguish iron (Fe)‐related phosphorus from calcium (Ca)‐bound P. The 31P nuclear magnetic resonance (NMR) spectroscopy has been used in the identification of organic P, precipitated Ca‐phosphates, and aluminum (Al)‐related P in acid soils. Three calcareous soils and four calcareous marsh soils were used in this study. These two types of soils differ in the nature of iron oxides, which are the main P sorbent surfaces. The ratio of low crystalline to high crystalline iron oxides is higher in marsh soils than in calcareous soils as a consequence of the special genesis and conditions of the soil (reduction‐oxidation cycles). Such a ratio is related to the proportion of occluded P in low crystalline oxides relative to that of high crystalline oxides. Citrate‐bicarbonate extractable P (CB‐P) in the fractionation schemes can be ascribed to adsorbed P and high soluble calcium phosphates. CB‐P is correlated with the sum of P fractions in all the soils, thus indicating that the amount of the P that can be easily released is related to the rate of P enrichment of the soil. The 31P NMR spectral data reveal that hydroxyapatite is the dominant P form in the soils studied. This is consistent with the fractionation data, where acid‐extractable P is the main P fraction. The spectra also provide some information about the amount of total inorganic P and Ca‐phosphates in calcareous soils.  相似文献   

2.
Abstract

Soil samples from different land use systems were collected before cropping (in spring) and after harvest (in fall) for organic phosphorus (P) extractions by 0.4M sodium hydroxide (NaOH) and characterization by 31P nuclear magnetic resonance spectroscopy. To prevent hydrolysis of organic P compounds prior to sample concentration, NaOH was removed from the NaOH soil extracts using a G‐25 Sephadex column. The 31P NMR spectra in the NaOH soil extracts showed the presence of glucose‐6 phosphate (up to 64%), glycerophosphate (up to 45%), nucleoside monophosphates (up to 91%), and polynucleotides (up to 58%) as the major forms of organic P in soils. The relative concentration of nucleoside monophosphates and polynucleotides decreased in some of the soils after harvest. The 31P NMR spectra of the extracts also revealed the presence of phosphoenolpyruvates, a previously unreported form of soil organic P.  相似文献   

3.
The extraction of soil organic phosphorus by the NaOH–EDTA procedure was assessed in detail for a tropical forest soil (clay‐loam, pH 4.3, total carbon 2.7%). Optimum conditions for the quantification of soil organic phosphorus and characterization of its composition by solution 31P NMR spectroscopy were extraction in a solution containing 0.25 m NaOH and 50 mm Na2EDTA in a 1:20 solid to solution ratio for 4 hours at ambient laboratory temperature. Replicate analyses yielded a coefficient of variation of 3% for organic phosphorus as a proportion of the spectral area. There was no significant difference in total phosphorus extraction from fresh and air‐dried soil, although slightly more organic phosphorus and less paramagnetic ions were extracted from dried soil. The procedure was not improved by changing the concentration of NaOH or EDTA, extraction time, or solid to solution ratio. Pre‐extraction with HCl or Na2EDTA did not increase subsequent organic phosphorus extraction in NaOH–EDTA or improve spectral resolution in solution 31P NMR spectroscopy. Post‐extraction treatment with Chelex resin did not improve spectral resolution, but removed small concentrations of phosphorus from the extracts. Increasing the pH of NaOH–EDTA extracts (up to 1.0 m NaOH) increased the concentration of phosphate monoesters, but decreased DNA to an undetectable level, indicating its hydrolysis in strong alkali. The standardized NaOH–EDTA extraction procedure is therefore recommended for the analysis of organic phosphorus in tropical forest soils.  相似文献   

4.
Nanoparticles and colloids affect the storage and hence the availability of P in forest ecosystems. We investigated the fine colloids present in forest soils and their association with inorganic and organic P. To differentiate between the different P forms, we performed liquid‐state 31P‐nucelar magnetic resonance (31P‐NMR) measurements on forest bulk soil extracts, on colloid extracts and on the electrolyte phase of their soil suspensions. The 31P‐NMR spectra indicated that soil nanoparticles and colloids were more enriched with organic than with inorganic P forms compared to the electrolyte phase. The P concentration was enriched in the colloidal fraction in comparison to the bulk soil and the phosphate diesters were more dominant in the colloidal fraction when compared to the bulk soil. The colloidal P‐diester to P‐monoester ratios were 2 to 3 times higher in the colloidal fraction than in the bulk soil. In contrast, relatively large percentages of inorganic P were found in the electrolyte phase. Supplementary (not shown) Data are available at the JuSER Server (juser.fz‐juelich.de, reference number: FZJ‐2016‐01739) https://juser.fz‐juelich.de/record/283057 .  相似文献   

5.
Changes in phosphorus (P) during soil development are central to the understanding of labile P for plant productivity and soil P management. We used NaOH‐EDTA extraction with 31P nuclear magnetic resonance spectroscopy (31P NMR), sequential P fractionation, and general soil chemical characterization to better our understanding of P dynamics within two chronosequences (Manawatu and Reefton) and one Basalt maturity sequence under original native vegetation. With time, orthophosphate and orthophosphate monoesters tended to increase with organic C to a maximum of about two‐thirds of NaOH‐EDTA‐extractable P in young soils (16 000 years in the Reefton chronosequence), but gradually declined thereafter to about one‐third of NaOH‐EDTA‐extractable P in the oldest soils (130 000 years old). This coincided with a depletion of P from primary minerals (e.g. apatite) and readily available P for plant production. This depletion of inorganic P resulted in a greater reliance on organic P cycling via mineralization, hence the depletion of the normally recalcitrant monoester‐P pool. Concomitantly, the build‐up of labile P species (diesters and pyrophosphate) and scyllo‐ over myo‐inositol hexakisphosphate occurred as soils developed, and might be attributed to microbial activity, including scavenging for P. This work highlights the importance of organic P cycling during pedogenesis.  相似文献   

6.
Abstract

The chemical characterization of soil phosphorus (P) desorbed by anion and cation exchange membranes is of major importance to better understand which P forms are available to plants in short‐ and long‐term time periods. Two distinct soils, one acidic and one calcareous, were analyzed for P using two extraction procedures with mixed anion and cation exchange membranes. The short‐term (ST) experiment evaluated the effect of increasing the extraction periods up to 24 h, whereas the long‐term (LT) experiment consisted of a sequential extraction procedure using up to seven successive 24‐h extractions. In both experiments, the Chang and Jackson inorganic P fractionation methodology was carried out after each extraction treatment, and each treatment consisted of three replicates. Data were statistically analyzed by ANOVA and nonlinear regressions. In the ST experiment, increasing the extraction time increased the extracted P according to an asymptotic relationship (y=c?ab x ). Extracted P proceeded from the most labile fractions in the acidic soil. In calcareous soils, calcium phosphates may also contribute for extractable P. The LT experiment revealed that a single extraction, regardless of that extraction method, cannot predict the long‐term capacity of soils to supply P to the plants. An exponential relationship (P=a×n b ) was found between extracted P and the extraction number. Desorbed P proceeded from the most labile fractions in the acidic soil. However, in calcareous soils, some precaution is needed when considering the biological meaning of the results, because the occluded Fe phosphates also revealed significant decreases, probably due to the redox conditions in which these long extractions are performed.  相似文献   

7.
The speciation of phosphorus (P) in native and degraded peat soils is an analytical challenge, and synchrotron‐based P K‐edge X‐ray absorption near‐edge structure (XANES) is a suitable method to gain information on P species in soils and organic materials. The objective of the present study was to test if P K‐edge XANES reflected differences in P fractions in fen peat due to sequential extraction and peat degradation. We investigated each one top‐ and subsoil sample of a Fibric Histosol, which differed in the degree of humification (H8 vs. H5) and concentration of total P (Pt) (1944 mg kg–1 vs. 436 mg kg–1). In the topsoil, residual P, H2SO4‐P, and NaOH‐P accounted for roughly the same proportions of Pt (≈30%). In the subsoil, residual P (64% of Pt) was more abundant than NaOH‐P (21% of Pt) and H2SO4‐P (10% of Pt). Among many different P reference standards, the P XANES spectra reflected differences in mineral P more distinctive than in organic P compounds. Phosphorus XANES spectra of the residues after each sequential extraction step all showed a prominent white‐line peak at around 2152 eV. Stepwise removal of resin‐P, NaHCO3‐P, and NaOH‐P were reflected mainly by the peak intensity but scarcely by distinct spectral features. Extraction with H2SO4 led to the disappearance of spectral features of Ca and Mg phosphates which is a first direct hint to these compounds in the peat. In conclusion, a combined sequential fractionation and spectroscopic (31P NMR, P K‐ and L‐edge XANES with linear‐combination fits) approach is proposed to overcome limitations of the present study and gain more insight into the P species in peat soils.  相似文献   

8.
The nature of organic phosphorus (Po) in animal waste and in soil is important from both plant nutrition and environmental perspectives. The objectives of this study were (1) to monitor the nature of Po in different animal wastes and biosolids using solution state 31P NMR spectroscopy and (2) to understand the nature of Po as affected by crop P removal in soil amended with different animal wastes and biosolids under greenhouse conditions. Two types of stockpiled cattle (Bos taurus) manure (CM1 and CM2), solid turkey (Meleagris gallopava) litter (TL), solid hog (Sus scrofa) manure (HM), and aerobically digested biosolids (SS) were used. Two kg of Wabash silt loam soil was amended with 0 or 150 mg P kg?1 from the P sources. Seven harvests of corn (Zea mays L.) were collected, each 35 days after sowing. Organic P was extracted with 0.4 M NaOH from soil samples collected before cropping and after the seventh harvest, as well as from each P source. 31P NMR analysis suggested that sugar phosphomonoester was present in all P sources and was the dominant constituent of both CM1 and CM2. Phosphomonoester was detected in large amounts in TL, HM, and SS. Prior to crop P removal, the application of all P sources caused the relative content of sugar phosphomonoester to be greater than the control. Crop P removal resulted in reductions in the relative content of sugar phosphodiesters and phosphodiester in CM1‐ and CM2‐amended soils, respectively. Phosphomonoester was also decreased in TL‐, HM‐, and SS‐amended soils in response to cropping.  相似文献   

9.
Abstract

The nature of organic and inorganic phosphorus (P) in fertilized and unfertilized samples of Vilcun soil, a Chilean medial mesic typic Dystrandept which was studied through 31phosphorus‐nuclear magnetic resonance (31P‐NMR) analysis carried out on a single alkaline extraction. The total P contents ranged from 1,506 mg P kg‐1 (B horizon, unfertilized soil) to 7,541 mg P kg‐1 (A horizon, fertilized soil). The magnitude of the P signal (SEM‐EDAX results) appears to be related to that of the iron (Fe) signal. Signals of 31P‐NMR spectra are attributable to inorganic orthophosphate, and orthophosphate monoesters and diesters. No important differences between horizons were observed. Apparently in this soil, P are mainly associated with iron oxides and organic matter. The organic P forms were not readily subjected to mineralization.  相似文献   

10.
Abstract

Knowledge of the change in soil extractable phosphorus (P) as a consequence of soil P fertilization could be useful in discriminating soils with a potential for soil P release to runoff or movement of P along the soil profile. In this research, soils with low to medium P retention capacity were equilibrated for 90 days with soluble P (KH2PO4) at rate of 100 mg P kg‐1 soil. After this period, soil samples both with and without the P addition were analyzed using six conventional methods: 1) Olsen, 2) Bray 1,3) Mehlich3,4) Egner, 5) Houba, dilute CaCl2 solution, and 6) distilled water, and three “innovative”; P‐sink methodologies: 1) Fe oxide‐coated paper strip, 2) anion exchange resin membrane, and 3) cation‐anion exchange resin membrane. The soils without P addition had low levels of extracted P as determined by all nine procedures. Net increases in the amount of P extracted from the soils with added P ranged from 4.2 mg kg‐1 (CaCl2 extraction) to 57.6 mg kg‐1 (cation‐anion resin membrane extraction). Relationships between change in extracted P and i) physical and chemical characteristics, and ii) soil P sorption properties are also presented and discussed.  相似文献   

11.
Phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy is widely used to identify and quantify phosphorus (P) forms in soil. This study aimed to determine whether narrowing the soil to extractant sodium hydroxide–ethylenediaminetetraacetic acid (NaOH-EDTA) ratio from 1:20 to values as low as 1:4 would improve sensitivity of solution 31P NMR spectroscopy without degrading resolution or quantitation. Four Australian soils were tested using four ratios. The narrowest ratio of 1:4 gave the best quality NMR spectra in terms of signal-to-noise ratio. Peak resolution was not degraded on narrowing the ratio. There was no clear effect of narrowing the extraction ratio on extraction efficiency or the distribution of signal among chemical shift regions (orthophosphate, monoester P, diester P, and pyrophosphate). We conclude that a ratio of 1:4 improved NMR analysis for these particular soils and should be considered for other soils, particularly low-P soils, where NMR sensitivity is limiting.  相似文献   

12.
There is at present little information on the long‐term stability of phosphorus sequestered in wetlands. Phosphorus sequestered during high loading periods may be relatively unstable and easily remobilized following changes in nutrient status or hydrological regime, but the chemical forms of sequestered phosphorus that do remobilize are largely unknown at this time. A lack of suitable analytical techniques has contributed to this dearth of knowledge regarding the stability of soil organic phosphorus. We analysed phosphorus in soils from the ‘head’ of Rescue Strand tree island and an adjacent marsh in the Florida Everglades by 31P nuclear magnetic resonance (NMR) spectroscopy and high‐resolution mass spectrometry. Tree islands are important areas of biodiversity within the Everglades and offer a unique opportunity to study phosphorus sequestration because they are exposed to large phosphorus loads and appear to be natural nutrient sinks. The 31P NMR profiling of extracts from surface and sediment samples in the tree island indicates that phosphorus input to Rescue Strand tree island soils is mostly in the form of inorganic ortho‐phosphate and is either refractory when deposited or rapidly recycled by the native vegetation into a stable phosphorus pool largely resistant to re‐utilization by plants or microbes. Mass spectrometry revealed the presence of inositol hexakisphosphate, a common organic monophosphate ester not previously observed in Everglades’ soils.  相似文献   

13.
The solubility and forms of phosphorus (P) were investigated in manures from chicken and pigs, eight whole soil samples and clay-, silt-, and sand-size separates from an arable and a grassland soil. Total P (Pt) in liquid pig manure (16.2 g kg–1) and dry chicken manure (26.2 g kg–1) was distributed between residual P (39–41% Pt), H2SO4–P (17–27% Pt), labile resin- and NaHCO3–P (24–39% Pt), and NaOH-P (3–10% Pt). Most soils had larger proportions of NaOH-P and residual P, indicating reactions of manure-derived P compounds with pedogenic oxides and humic substances. Clay-size separates had the highest P-concentrations in all fractions and were particularly enriched in exchangeable and labile P forms. Solution 31P-nuclear magnetic resonance (NMR) spectra of 0.5 M NaOH extracts from manures and some soil samples showed greater signal intensities for orthophosphate and monoester P than 0.1 M NaOH extracts. This can be explained by alkaline hydrolysis phosphate diesters at higher NaOH concentrations and/or by preferential extraction of diesters at lower concentrations. The 31P-NMR spectra showed differences between the two manures and confirmed that increasing proportions of ester-P can be expected if they are spread to soils. The NaOH extracts of soil samples were characterized by large proportions of orthophosphate-P (mean 77% of assigned P compounds), which seemed to be slightly enriched in clay fractions whereas the extracts from silt contained more ester-P. Sequential extractions and 31P-NMR spectroscopy both showed that these excessively manured soils are likely to lose large amounts of P. Received: 15 July 1996  相似文献   

14.
The decrease of NMR visibility of the C signal in soil samples due to the association between organic carbon (OC) and the topsoil mineral surface was investigated. CPMAS 13C‐NMR spectra were obtained for soil particle‐size fractions (< 2 μm, 2–20 μm, > 20 μm) and bulk soils from an agricultural topsoil (Chernozem) that had received three different amendments (no fertilization, mineral fertilization (NPK), mineral (NPK) and organic (cattle manure) fertilizations) at Bad Lauchstädt, Germany. The soil organic carbon content of the three soils depended on the degree of soil fertilization. There was no constant relationship between the total NMR signal intensity and the total amount of organic carbon (TOC) for all size fractions. Indeed, a key role played in the C signal intensity by the paramagnetic ferric ion from the clay content in soil fractions and bulk soils was confirmed. Thus, we describe the variations of C signal intensity by taking into account the distribution of clay‐associated OC and non‐associated OC pools. Depending on the amendment, the C signal visibility was weakened by a factor of 2–4 for the clay‐associated OC. This estimation was rendered possible by combining mineral specific surface area (SSA) measurements with the N2 gas adsorption method (BET method) and determination of TOC and iron concentrations. This approach contributes to the quantitative evaluation of the CPMAS 13C‐NMR detection.  相似文献   

15.
Abstract

Cyclophosphates are not adsorbed by soil constituents and can be mobile in the soil profile. Mobile phosphorus (P) sources are of interest in soil science and for agronomic practices. Cyclotri (Na3P3O9; C3P), and cyclotetraphosphate (Na4P4O10; C4P) were compared to linear, ortho‐, pyro‐, and tripolyphosphate in four soils with different chemical, physical, and biological properties to determine their mobility and availability to corn (Zea mays, L.) in laboratory and greenhouse experiments. Cyclophosphate (C3P and C4P) hydrolysis products were evaluated by ion chromatography after incubating for 6 to 192 h with 100 and 200 µg P g?1 soil. Phosphorus distribution and mobility, and plant availability and uptake with time, were determined in 45‐cm columns for four soils. Cyclophosphates sorbed less and moved deeper in all soils compared to the linear phosphates. The results showed that after 24 h a large proportion of cyclophosphates (34% of C3P and 37% of C4P) remained unhydrolyzed in Falba sandy acid soil. Split application of C3P and C4P at planting and at booting stage increased corn yield in sandy acid soil. Results of this experiment suggest that P deficiency after plant establishment can be corrected with cyclophosphates in soils with a low potential for cyclo‐P hydrolysis.  相似文献   

16.
In semi‐arid northern Tanzania, the native woodland is being rapidly cleared and replaced by low input agriculture. This has resulted in pronounced environmental degradation, and in particular loss of phosphorus (P) from the soil. We have used sequential extraction and 31P‐NMR to investigate the effects of land use changes, i.e. native woodland, degraded woodland, cultivation for 3 and 15 years and homestead fields where manure was applied, on the amount and structural composition of P in this soil. Clearing and continuous cultivation reduced both organic and inorganic P in the soil. The difference in the amount of organic P from the bulk soil of the fields cultivated for 3 and 15 years was not statistically significant (P < 0.05), suggesting that most of the depletion in organic P occurred during the first 3 years of cultivation. By contrast, in the homesteads, there was much organic and inorganic P in the soil. The 31P‐NMR revealed that cultivation resulted in a 53% depletion of orthophosphate diester P, whereas only a 30% and 39% reduction of orthophosphate monoester P was found in the bulk soil after 3 and 15 years of cultivation, respectively. These results concur with the suggestion that diester P constitutes more easily mineralizable forms of organic P in soil than does monoester P. Our 31P‐NMR also showed that 70% of the inorganic orthophosphate P was depleted from the coarse and fine sand separates as a result of cultivation. The influence of clearing and subsequent cropping on the amount and forms of P was more pronounced in the coarse and fine sand than in the silt and clay, stressing the importance of particle size and chemical properties such as organic matter and oxides in the availability of P in this soil. Our results show that the current low input agricultural practice is not sustainable, and that practices must be developed to combat the ongoing degradation of the soil. A combined use of available organic materials such as animal manure with the judicious use of inorganic fertilizers can replenish the soil's fertility.  相似文献   

17.
Abstract

Investigating the relation between concentration or release of phosphorus (P) into soil solution (CaCl2‐P, determined by 0.01 M CaCl2 extraction of soils) and soil test phosphorus (Olsen P, or 0.5 N NaHCO3‐extractable soil phosphorus) for 10 widely ranging and variously managed soils from central Italy, a change point was evident where the slopes of two linear relationships meet. In other words, it was possible to distinguish two sections of the plots of CaCl2‐P against Olsen P, for which increases of CaCl2‐P per unit of soil test P increase were significantly (p<0.05) greater above than below these change points. Values of change point ranged from 14.8 to 253.1 mg kg?1 Olsen P and were very closely correlated (p<0.001) to phosphorus sorption capacity of soils. Similar change points were also previously observed when Olsen P (and also Mehlich 3 P) of surface soils was related to the P concentration of surface runoff and subsurface drainage. Because insufficient data are available relating P in surface soils and amount of P loss by overland, subsurface, or drainage flow, using the CaCl2 extraction of soil can be convenient to determine a change point in soil test P, which may be used in support of agricultural and environmental P management.  相似文献   

18.
The adsorption of phosphate by soil minerals controls availability of P to plants, but the chemical environments of adsorbed phosphate are poorly known. We used 31P MAS NMR to study the adsorption of phosphate on to boehmite (γ‐AlOOH) and γ‐Al2O3 with large surface areas. The solid phases were reacted in 0.1 m phosphate solutions at pH from 3 to 11 and in solutions with pH 5 at concentrations from 10?1 m to 10?4 m . The spectra suggested three different phosphate environments: (i) orthophosphate precipitated from the residual solution after vacuum filtering, (ii) surface‐adsorbed phosphate in inner‐sphere complexes, and (iii) Al‐phosphate precipitates on the surfaces of the minerals. The chemical shifts of both the inner‐sphere complexes and surface precipitates became progressively less shielded with increasing pH and decreasing concentration of phosphate solution. For the inner‐sphere complexes, we interpret these changes to be the result of decreasing phosphate protonation combined with rapid proton exchange among phosphate tetrahedra with different numbers of protons, which causes peak averaging. The chemical shifts of 31P of the Al‐phosphate precipitates were more negative than those of the surface phosphates at a given pH and solution concentration, probably because of a larger number of P–O–Al linkages per tetrahedron. The observed trend of decreasing shielding is probably due to the decreasing average number of P–O–Al linkages per tetrahedron combined with decreasing protonation and an increasing number of K+ next‐nearest neighbours. Even at small concentrations of phosphate solution, a significant amount of Al‐phosphate precipitate was present.  相似文献   

19.
《Geoderma》2006,130(1-2):176-189
The distribution and form of P in soil is central to the sustainability of agricultural practice. This study used sequential fractionation and 31P nuclear magnetic resonance spectroscopy (31P NMR) of NaOH–EDTA extracts to examine the influence of pastoral, native (undisturbed) and forest land use on soil P forms in 5 contrasting soils ranging from a Regosol to a Rendzina in Otago, New Zealand. Climatic factors likely to influence soil P distribution were negated by careful site selection. Together with a decrease in soil organic C (31%), total P decreased in forested soils (mean=674 mg kg−1) compared to native soils (mean=784 mg kg−1). In contrast, the ratio of inorganic to organic P increased (10%) probably due to mineralization of organic P in forest soils, while for pasture soils, accumulation of P in inorganic forms due to P inputs via fertilisers and animal dung was to blame. Investigation of the organic P forms in NaOH–EDTA extracts of each land use by 31P NMR indicated that diesters were greatest in the native soil (4–12% of total P in spectra), and declined as a proportion of total P in pasture soils and more so in forest soils. This was reflected in a decline of the diester to monoester ratio. However, the ratio was generally greater in forest than pasture soils and attributed to the labile nature of diesters, mineralization of monoesters in forest soils, and an increase in monoesters in pasture soils from inositol phosphates in plant debris. This effect was pronounced in the Regosol due to sandy texture and the preferential accumulation of plant debris in coarse particle size fractions. Due to the depletion of soil P reserves, forest soils in the area should be followed by pasture and well managed fertiliser additions before replanting.  相似文献   

20.
Abstract

A greenhouse pot culture study was conducted to evaluate the agronomic efficiency of two rock phosphates from Mussoorie (MRP) and Purulia (PRP) in two acidic soils from Dapoli (Maharashtra) and Aruvanthklu (Karnataka), India, by growing maize (cv. Ganga) as the test crop and using 32phosphorus (P) single superphosphate (32P=SSP) as a tracer (A‐value technique). Dry‐matter yield and P uptake increased significantly with the application of P fertilizers compared to control treatment (without P) in both the soils. There was no significant difference with respect to dry‐matter yield among the P fertilizer treatments. However, P uptake by the shoots was found to be significantly higher in the PRP treatment in only Dapoli soil compared to other P fertilizer treatments. Phosphorus derived from fertilizer decreased in rock phosphate treatments compared to standard 32P‐SSP treatment in both the soils, indicating an excess availability of P from the rock phosphates. A‐values of soil and rock phosphate indicate a relatively higher P availability from Aruvanthklu soil compared to Dapoli soil; A‐values for the rock phosphates were in the order PRP>MRP. The substitution ratio showed that the availability of P from both the rock phosphates were less than SSP in both the soils.  相似文献   

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