Inorganic Phosphorus Fractions Research Articles

Organic phosphorus mineralization characteristics in sediments from the coastal salt marshes of a Chinese delta under simulated tidal cycles

Sediment organic phosphorus (OP) mineralization plays an important role in phosphorus cycling in coastal salt marshes. However, information on OP mineralization characteristics in sediments under tidal cycles is limited. Sediment cores were collected from salt marshes which were exposed to tidal cycles. A laboratory manipulation experiment was conducted under simulated tidal flooding cycles. After the completion of each incubation experiment, the inorganic phosphorus (IP) and OP fractions were analyzed and net phosphorus mineralization rates were calculated to investigate the sediment OP mineralization process. Sediment microbial characteristic and chemical properties were determined to identify factors that affect the mineralization of OP in the Yellow River Delta. During the first 2 days of incubation, the tidal cycles significantly increased the microbial biomass in the sediments, which accelerated the assimilation of IP by microorganisms and the transformation of IP into OP in their bodies, thereby causing a significant increase in OP in the sediments. After 2 days of incubation, the mineralization and immobilization of OP entered the adaptation stage and gradually reached the dynamic balance of various phosphorus fractions in sediments. The path analysis showed that microbial biomass phosphorus and carbon (MBP and MBC) and the activity of alkaline phosphatase (AKP) are the direct factors influencing OP mineralization in sediments. The indirect effects of soil organic matter (SOM), water content (WC), exchangeable aluminum (Al0), and exchangeable iron (Fe0) on net phosphorus mineralization rate were relatively high. In the laboratory experiments, we showed that the recovery of tidal cycles caused a fluctuation in OP mineralization and immobilization in sediments, which reached equilibrium over time. The tidal effect was conducive to maintaining the stability of phosphorus in sediments of coastal salt marshes. The findings of this study can contribute to protecting water quality and improving primary productivity in coastal salt marshes by regulating the tidal cycles and the key environmental factors (e.g., SOM, WC, Al0, and Fe0) influencing OP mineralization.

Changes in phosphorus fractions associated with soil chemical properties under long-term organic and inorganic fertilization in paddy soils of southern China.

The identification of phosphorus (P) fractions is essential for understanding the transformation and availability of P in paddy soils. To investigate the soil P fractions associated with soil properties under long-term fertilization, we selected three fertilization treatments, including no fertilization (CK), chemical fertilizers (NPK) and chemical fertilizers combined with manure (NPKM), from three long-term experiments located in Nanchang (NC), Jinxian (JX) and Ningxiang (NX). The results showed that chemical fertilizers combined with manure (NPKM) significantly (P ≤ 0.05) increased the soil total phosphorus, Olsen P and soil organic matter (SOM) by 2, 3 and 1 times, respectively, compared with the NPK treatment, and by 4, 17 and 2 times, respectively, compared with the CK treatment. NPKM significantly increased the grain yield compared with CK and NPK at all sites. The apparent P balance with NPK was higher in NC and NX but lower in JX compared with NPKM. Hedley fractionation revealed the predominance of most of the organic and inorganic phosphorus (Po and Pi) fractions with long-term fertilization, especially with the NPKM treatment, at all sites. The nonlabile P pool decreased by 14% and 18% whereas the moderately labile P pool proportions increased by 3 and 6 times with the NPK and NPKM treatments, respectively, compared to the CK treatment. The labile P pool showed a significant positive relationship with the SOM, total P and Olsen P contents. The moderately labile P was positively correlated with the total P and Olsen P. A significant positive correlation was observed between soil pH and the nonlabile P pool. Redundancy analysis revealed that the moderately labile P fraction (HCl dil. Pi fraction) was remarkably increased by the NPKM treatment and significantly correlated with the soil pH and total P concentration. The labile P fraction (NaHCO3-Pi) showed a strong relationship with the Olsen P and total P. However, the residual P fraction was negatively correlated with the HCl. dil. Pi fraction. We concluded that NPKM application improved P availability by many folds compared to NPK, which could lead to environmental pollution; therefore, the rate of combined application of manure and chemical fertilizer should be reduced compared to chemical fertilizer inputs to minimize the wastage of resources and environmental P losses.

Distribution of inorganic phosphorus and its response to the physicochemical characteristics of soil in Yeyahu Wetland, China

This research investigated spatial and vertical distribution of total phosphorus (TP), inorganic phosphorus (IP) and IP fractions as well as its responses to corresponding physicochemical properties in Yeyahu Wetland. The results shown that TP concentration varied from 335.37 to 683.32 mg kg−1, it was irregularly distributed in horizontal direction but decreased with the soil depth in vertical direction. The IP concentration varied from 249.43 to 387.49 mg kg−1, accounting for 60%–85% of TP. The order of contents were as follows: Ca-P > Fe-P > Ex-P > Al-P > Oc-P. In vertical direction, the Ca-P distributed roughly with IP because Ca-P was found to be the major species (up to 370 mg kg−1). Other forms were found to decrease with soil depth. According to redundancy analysis (RDA), Ex-P was positively correlated to organic matter content (r=0.637, P < 0.001), indicating that organic matter might be of the importance in maintaining P availability in soils. Anew, the TP correlated with the content of soil fine particles (2–20 μm) (r=0.629, P < 0.01), which suggested that fine particles were suitable for P adsorption in soils from Yeyahu Wetland. This study provided data support for sustainable development of wetland ecosystem.

Inorganic phosphorus fractions and crop productivity in response to different rates of phosphate-solubilising fungi Penicillium bilaii

Two field experiments were conducted at experimental farm of ICAR-Indian Agricultural Research Institute, New Delhi during 2014-15 to investigate the interactive effect of three rates of seed inoculation with wettable formulation of phosphate solubilising fungi (Penicillium bilaii) and two rates (60 kg and 30 kg P2O5/ha) of chemical phosphorus (P) fertilization on soil P availability and productivity in wheat (Triticum aestivum L.) and mustard (Brassica campestris L.) crops. Inorganic P distribution in different fractions was conducted by successive extraction of soil P with water, NaHCO3 (SB-P), NaOH (SH-P) and HCl. Application of fungal formulation @10.604 g/kg mustard seed and 4.894 g/kg wheat seed + 30 kg P2O5/ha as chemical P increased the SB-P fraction of mustard and wheat grown soil by 145.7% and 140.7%, respectively compared to their respective un-inoculated controls at maturity. HCl-P was the major fraction under wheat soil with average contribution of 46% and 64.8% of total extractable P at 60 and 120 d of crop growth whereas SH-P was the major fraction under mustard grown soil. Improved soil P availability due to fungal inoculation could explain the role of phosphate solubilising fungi in soil P mobilization. The crop productivity however, was highest with highest rate of chemical P and fungal based formulation.

Path analysis of phosphorus activation capacity as induced by low-molecular-weight organic acids in a black soil of Northeast China

PurposeThe present study was designed to assess the potential effects of low-molecular-weight organic acids on the activation of inorganic phosphorus, obtain exact information on the acidity effect of proton and complex effect of organic anion in P availability, and determine the components among phosphorus fractions that contributed the most to inorganic phosphorus activation in black soil.Materials and methodsBoth oxalic and citric acids treated with different concentrations and pH values were carefully selected. The activating amounts of total inorganic phosphorus and individual phosphorus fractions were estimated. Path analysis was used to analyze the direct and indirect effects on inorganic phosphorus activation.Results and discussionThe amount of total activating-Pi increased as the concentrations of oxalic and citric acids increased. When the concentrations were ≤ 1.0 mmol L−1, oxalic acid exhibited a lower capability than citric acid in total activating-Pi, but when the concentrations were ≥ 1.5 mmol L−1, oxalic acid exhibited a higher capability. The amount of total activating-Pi decreased as pH of LMWOAs increased. LMWOAs-induced Pi activation might be attributed to combine acidity and complex effects.ConclusionsCorrelation analysis showed that the activation of total Pi was significantly correlated with the activation of H2O-Pi, NaHCO3-Pi, NaOH-Pi, and HCl-Pi (p < 0.05). Path analysis revealed that soil activating-H2O-Pi mainly affected Pi activation through an indirect path. The contribution of activating-NaHCO3-Pi alone was maximal on the total activating-Pi by both the direct and indirect effects, followed by activating-NaOH-Pi and activating-HCl-Pi.

Distribution of C and inorganic phosphorus fractions in different aggregate sizes under forestry, agroforestry system and pasture

Distribution of C and inorganic phosphorus fractions in different aggregate sizes under forestry, agroforestry system and pasture

Distribution of inorganic phosphorus fractions in water-stable aggregates of soil from tea plantations converted from farmland in the hilly region of western Sichuan, China

Establishing tea plantations (Camellia sinensis L.) can markedly change the pools of soil inorganic phosphorus (P) especially in water-stable aggregates. However, the effects of different chronosequence phases on the quantity and quality of inorganic P fractions in such plantations are poorly understood. This study investigated the inorganic P fractions including the Al bound-P (Al-P), Fe bound-P (Fe-P), occluded-P (O-P), and Ca bound-P (Ca-P) in water-stable aggregates (WSAs) of soil from tea plantations converted from farmland. The investigations included 2–3 (CT2-3), 9–10 (CT9-10), and 16–17 years (CT16-17) and one abandoned land as contrast (CK), which is close to the three different-aged sites of soil from tea plantations converted from farmland in Zhongfeng Township of Mingshan County, Sichuan, southwest China. The dominant size fraction was the aggregate with 0.5–0.25 mm. Content of > 1 mm fraction gradually increased with the increasing age in tea plantations. The contribution rate is closely related to the content of WSAs. The highest content of Al-P was observed in the aggregate with 2 mm, and the distribution of O-P was uniform in soil from tea plantations converted from farmland at 0–20 and 20–40 cm soil depths, indicating that aggregate size fractions can influence the concentration of P in different P fractions. The contents of Al-P and Fe-P increased with the increasing age in tea plantations, whereas the contents of O-P and Ca-P decreased in CT16-17. The results of this study show that the distribution of inorganic P fractions can be influenced by aggregate size and inorganic P fractions which had low activity and are transformed into highly available fractions with the increasing age in tea plantations.

Fractionation of Inorganic Phosphorus and Aluminum in Red Acidic Soil and the Growth of Camellia oleifera

Aluminum (Al) toxicity and phosphorus (P) deficiency are two crucial factors limiting the production of Camellia oleifera, which is grown commercially in red acidic soils in Southern China. The current study characterized the different forms of P and Al in the red acidic soils of C. oleifera plantations. Soil and plant tissue samples taken from 32 Camellia plantations across Hunan province were analyzed. Furthermore, a pot experiment with nutrient solutions of different Al and P contents was carried out to investigate P and Al uptake and their effect on C. oleifera growth. The results showed that the P content extracted by NaOH (Fe-P) was the highest in all types of soil samples (rhizosphere, 0–20 cm, and 20–40 cm zones), followed by P extracted by NH4F (Al-P), H2SO4 (Ca-P), and Na3C6H5O7 (O-P). HCl (In-Al), NH4Ac (Ha-Al), and Na4P2O7·10H2O (Or-Al) extracted Al were the main forms and accounted for 22.8%, 23.1%, and 23.8% of total Al, respectively. KCl extracted Al (Ex-Al) contents in the rhizosphere, 0–20 cm, and 20–40 cm soil zones were 4.78, 4.86, and 4.59 mg·kg−1, respectively. P contents in roots, young leaves, and old leaves were 0.80, 0.82, and 0.64 mg·kg−1, respectively. The highest Al content of 11.35 g·kg−1 was found in the old leaves, followed by roots and young leaves. Correlation analyses revealed that P in roots was positively associated with available P (AP) and Al-P in rhizosphere. P in roots and young leaves also had a positive correlation with Ex-Al, whereas Al in old leaves was positively correlated with In-Al and total Al. Significant correlations between Al-P, Ex-Al, and AP were detected. The pot experiment indicated that adding Al or P alone increased plant growth and Al or P uptake, respectively. When adding both Al and P, significant synergistic effect was found. These results suggest that Al is beneficial to C. oleifera, which may be the adaptive mechanism of C. oleifera to use insoluble Al-P in red acidic soil.

Effects of P-efficient Transgenic Rice OsPT4 on Inorganic Phosphorus Fractions in Red Soil

Effects of P-efficient Transgenic Rice OsPT4 on Inorganic Phosphorus Fractions in Red Soil

Effects of the continuous use of organic manure and chemical fertilizer on soil inorganic phosphorus fractions in calcareous soil

A 4-year field trial with three treatments and three types of annually rotated vegetables was conducted in calcareous soil in a greenhouse using a phosphorus (P) fractionation method based on the inorganic P fraction classification system described by Jiang-Gu. With the same nutrient input, vegetable yields and P uptake were more stable under the chemical fertilizer (CF) treatment than under the organic manure (OM) treatment, and the average utilization rate of P fertilizer (URP) values were 5.27% and 11.40% under the OM and CF treatments, respectively, over the 4 years. Compared with the values in 2009, the values of the inorganic P (Pi) fractionation, including Ca-P, Al-P and Fe-P, significantly increased over time by 310.89 mg·kg−1, 36.21 mg·kg−1, and 18.77 mg·kg−1, respectively, with OM treatment and by 86.92 mg·kg−1, 175.87 mg·kg−1, and 24.27 mg·kg−1 with CF treatment. These results suggest that 1) large amounts of P were released from Ca2-P, Ca8-P and Al-P and were taken up by vegetables in the calcareous soil, and 2) the excessive application of P fertilizer, especially OM, resulted in a substantial accumulation of Pi (Ca2-P, Ca8-P and Al-P), which increased the risk of pollution from organic farming diffusing into the surface water.

沉积物磷形态分析的固体浓度效应

以渤海埕岛油田区沉积物样品为例，探讨沉积物无机P形态分析过程中的固体浓度效应。4步顺序提取不同固体浓度(0.1 g/50 mL和0.2 g/50 mL)沉积物中的无机P，结果表明：沉积物中HCl-P含量最高，其次为BD-P和OH-P，含量最少的是loosely-P；沉积物磷形态分析过程中存在显著的固体浓度效应，表现为随着沉积物固体浓度增大，测得各形态P含量减少；沉积物中不同形态P受固体浓度的影响程度不同，强碱或强酸作为提取剂能有效抑制固体浓度效应，但不能完全消除。 We performed inorganic phosphorus (P) fractionation experiments of the sediments sampled from Chengdao oil field of Bohai, to explore the solid concentration effect on the process of sediments inorganic P fractionation. Four steps sequential extraction of inorganic P from sediments with different solid concentrations (0.1 g/50 mL and 0.2 g/50 mL) were done. The results showed that: the highest content in sediment is HCl-P, followed by BD-P and OH-P, and the least is loosely-P; the P components content decreased by the increased solid concentration, which confirmed solid concentration effect have influences on the processes of sediments inorganic P fractionation; the degree of impact of solid concentration effect on different P components is not equivalent. Strong acids or alkali can effectively inhibit this impact, but cannot counteract it thoroughly.

Phosphorus fractions and correlation with soil attributes in a chronosequence of agricultural under no-tillage

In no-tillage (NT) soils, changes in the quantity and quality of soil organic matter (SOM) have been observed over time. These changes can interfere with the dynamics of P in surface soil layers. Thus, the objectives of this study were: to evaluate the organic and inorganic fractions of P and their degree of lability (labile, moderately labile, and moderately recalcitrant) in an Oxisol under NT for 6 years (NT6), 14 years (NT14), and 22 years (NT22) and cultivated with a succession of soybean and corn/wheat. The fractions were evaluated for 16 years of NT, with the last four years under integrated corn second crop and Brachiaria (NT16+B). We also analyzed an area of native forest, as well as analyzing the correlations between the results of the P fractions of these areas with other attributes such as total carbon content, vegetable waste deposited on the ground, phosphorus and humic fractions remaining in SOM. From each of the areas, samples were collected at 0.00-0.05 m and 0.05-0.10 m. A completely randomized design with 5 replicates was used. Management of phosphorus fertilization and SOM following adoption of the SPD of time (6 to 22 years) increased the levels of all fractions of inorganic P (0.0 to 0.10 m), as well as the fractions of labile (0.05-0.10 m), moderately labile (0.0-0.10 m), and moderately recalcitrant (0.05-0.10 m) organic phosphorus. The correlation matrix shows interactions between the evaluated soil attributes, especially between inorganic phosphorus fractions and fulvic and humic acids and between the moderately recalcitrant organic phosphorus and humin fraction.

Characteristics of soil aggregates and inorganic phosphorus fractions in soils returned from cropland to tea

With soils returned from cropland to tea planting for different ages (2-3, 9-10 and 16-17 years old) as the object, and the nearby cropland soil as the control in Zhongfeng Township, Mingshan County, Ya'an, Sichuan Province, field investigation and laboratory analysis were combined to investigate the characteristics of soil aggregates and inorganic phosphorus fractions in response to the returning from cropland to tea. The particle size of >2 mm was the dominant aggregate size for the cropland and tea soils. With the increasing age, soil aggregate content of >5 mm particle size increased, while that of <5 mm particle size decreased gradually. In the earlier ages, for the mean mass diameter (MWD) and the geometry mass diameter (GWD), there was no significant difference between the cropland and tea soils. The MWD and GMD for the tea soils of 9-10 years and 16-17 years increased with the increasing age and were higher than those of the control. Compared with the cropland, the tea soils showed higher contents of Al-P and Fe-P, and lower content of O-P. The content of O-P in different particle size of aggregates reduced with the increasing age, while that of Al-P and Fe-P increased with the increasing age. The contents of Al-P and Ca-P in the cropland and tea soils increased with the decrease of the particle size and reached the maximum value in the particle size of <0.25 mm. The highest content of Fe-P was observed in the particle size of <0.25 mm, followed by 2-5 mm and 0.25-0.5 mm. Besides, with the returning fromcropland to tea planting, O-P gradually accumulated in smaller particle size and possessed higher content in the particle size of <2 mm.

Elucidation of Taste- and Odor-Producing Bacteria and Toxigenic Cyanobacteria in a Midwestern Drinking Water Supply Reservoir by Shotgun Metagenomic Analysis.

While commonplace in clinical settings, DNA-based assays for identification or enumeration of drinking water pathogens and other biological contaminants remain widely unadopted by the monitoring community. In this study, shotgun metagenomics was used to identify taste-and-odor producers and toxin-producing cyanobacteria over a 2-year period in a drinking water reservoir. The sequencing data implicated several cyanobacteria, including Anabaena spp., Microcystis spp., and an unresolved member of the order Oscillatoriales as the likely principal producers of geosmin, microcystin, and 2-methylisoborneol (MIB), respectively. To further demonstrate this, quantitative PCR (qPCR) assays targeting geosmin-producing Anabaena and microcystin-producing Microcystis were utilized, and these data were fitted using generalized linear models and compared with routine monitoring data, including microscopic cell counts, sonde-based physicochemical analyses, and assays of all inorganic and organic nitrogen and phosphorus forms and fractions. The qPCR assays explained the greatest variation in observed geosmin (adjusted R(2) = 0.71) and microcystin (adjusted R(2) = 0.84) concentrations over the study period, highlighting their potential for routine monitoring applications. The origin of the monoterpene cyclase required for MIB biosynthesis was putatively linked to a periphytic cyanobacterial mat attached to the concrete drinking water inflow structure. We conclude that shotgun metagenomics can be used to identify microbial agents involved in water quality deterioration and to guide PCR assay selection or design for routine monitoring purposes. Finally, we offer estimates of microbial diversity and metagenomic coverage of our data sets for reference to others wishing to apply shotgun metagenomics to other lacustrine systems. Cyanobacterial toxins and microbial taste-and-odor compounds are a growing concern for drinking water utilities reliant upon surface water resources. Specific identification of the microorganism(s) responsible for water quality degradation is often complicated by the presence of co-occurring taxa capable of producing these undesirable metabolites. Here we present a framework for how shotgun metagenomics can be used to definitively identify problematic microorganisms and how these data can guide the development of rapid genetic assays for routine monitoring purposes.

Soil maturity assessment in Indo-Gangetic alluvium of Bihar using soil inorganic phosphorus fractions based weathering index: A comparative approach

Soil maturity assessment in Indo-Gangetic alluvium of Bihar using soil inorganic phosphorus fractions based weathering index: A comparative approach

Effects of inorganic phosphorus fractions under different tillage practices on wheat (&lt;em&gt;Triticum aestivum&lt;/em&gt;) in an acid soil of West Bengal (India)

Phosphorus (P) is an essential element for plant growth and is usually applied to soil as inorganic P fertilizer. An experiment was conducted to study the effect of inorganic phosphorus fractions and tillage operations (conventional and zero tillage) on the yield of the crop. The field experiment was laid out in a randomized block design with nine treatments replicated three times. Recommended dose (RD) of fertilizer (kg/ha) of N:P:K @100:60:40 (RD) was modified in different treatments as ; T 1 (untreated control), T 2 (NP as RD), T 3 (K+P as RD),T 4 (NK as RD +P as 25% of RD)], T 5 [NK as RD and P as 50% of RD ],T 6 [NK as RD and P as 75% of RD; T 7 [NKP as RD], T 8 [NK as RD and P as125% of RD ] and T 9 [NK as RD and P as 150% of RD] . Surface soils were collected (0-20 cm depth) from each plot and important soil properties were studied. The soil was acidic in reac-tion having pH- 5.6 and EC of 0.06 dSm -1 . The available N-P-K in soil was 126.34 kg/ha, 20.13 kg/ha and 133.28 kg/ha respectively. The inorganic forms of phosphorus (Ca-P, Al-P, Fe-P, Re-P), in soils during the experimental period showed higher fractions in the conventional tillage than the zero tillage operation. The Al-P fraction of soil affected significantly (P=0.05) towards the yield of the crop (wheat) compared to other P-fractions.

대청호 추소리 수역의 퇴적물이 조류 성장에 미치는 영향

In order to investigate the effect of internal loading from sediment on algal blooming at Chusori area in Daechung Reservoir, the amount and contamination level of sediment and the release rate of total phosphorus were analyzed. The sedimentary layer was consisted with two layers, and the average depth of upper and lower ones were 0.35 and 1.44 m, respectively. The fraction of inorganic phosphorus in the sediment was higher than that of organic phosphorus, and the fractions of phosphorus which responsible for internal loading were very high as in the range of 72.7 and 80.2% of inorganic phosphorus. The C/N ratio of sediment taken with core sampler indicated the organic compounds are originated from settled algae from water body. The average release rate of total phosphorus from sediment was . These results indicated that the internal loading from sediment contributes the excessive algal growth at Churosi area, and the countermeasures to improve the quality of sediments are required to manage algal blooming in Daechung Reservoir.

The rhizosphere effect of some wheat cultivars on inorganic phosphorus fractions in a phosphorus-deficient calcareous soil

Knowledge of the distribution and changes of soil phosphorus fractions in the rhizosphere, helps to determine efficiency of different crop cultivars in phosphorus acquisition. This study was conducted in order to evaluate the rhizosphere effect of some wheat cultivars on inorganic phosphorus fractions. A greenhouse experiment as a factorial in completely randomized design was conducted with 10 treatments and 3 replications. Experimental factors were different plant cultivars (4 wheat cultivars and control) and soil-sampling zone (rhizosphere and non-rhizosphere). A rhizobag technique was used to separate rooted and non-rooted inside each pot representing the two soil sampling zones. Based on fractionation results, the order of inorganic phosphorus fractions in the studied soil were apatite-P> OCP-P> DCP-P> Al-P> Fe-P> O-P which were found to be in the order of 830, 123, 17, 16, 14 and 0 g kg-1, respectively. The concentration of the most inorganic phosphorus fractions between rhizosphere and non-rhizosphere soil was significantly different. All plant cultivars decreased inorganic phosphorus forms significantly. This difference was not equal for all cultivars and all fractions. Organic P was significantly higher in the rhizosphere soil compared to non-rhizosphere soil. Soluble phosphorus was not significantly differed between rhizosphere and non-rhizosphere soil. Root induced chemical changes; root morphology, microbial populations, pH changes etc. can be determining factors on phosphorus depletion differences among plant cultivars and soil sampling zone. Key words: Phosphorus, fractionation, rhizosphere, rhizobag, wheat.

Inorganic phosphorus fractions and recovery efficiency in aerobic rice (Oryza sativa) in relation to sources and levels of phosphorus

Inorganic phosphorus fractions and recovery efficiency in aerobic rice (Oryza sativa) in relation to sources and levels of phosphorus

Long-term manuring and fertilization influence soil inorganic phosphorus transformation vis-a-vis rice yield in a rice–wheat cropping system

A study on the rice–wheat cropping system was conducted at Bidhan Chandra Krishi Viswavidyalaya, West Bengal, India, to assess the effects of long-term manuring and fertilization on transformation of the inorganic phosphorus (P) fraction in soil after 22 years of the crop cycle. Soil samples were collected after Kharif from seven treated plots having different types of organic amendments like farm yard manure, paddy straw and green manuring with 50% substitution of nitrogen levels in rice crop only. The result showed that the yield trend of rice was maintained due to the buildup of P from various organic inputs. Although cultivation for 22 years without adding any fertilizer caused a significant decrease in almost all the forms of P viz. avail-P, saloid P, iron phosphorus fraction (Fe–P), aluminum phosphorus fraction (Al–P), calcium phosphorus fraction (Ca–P) and total P in control. Partial substitution of inorganic fertilizer N (50%) with organics, however, caused a significant increase in almost all the P fractions in soil over the control. The relative abundance of all the fractions of inorganic P irrespective of treatments was as follows: Fe–P > reductant soluble P fraction > occluded P > Al–P > Ca–P > saloid P. Saloid and Fe–P were the dominating fractions responsible for 92% variation of available P and total P levels, respectively.