Availability and fractionation of phosphorus in soils with different physicochemical characteristics

The total content of phosphorus (P) within soil does not reflect its availability for plants, the available form depending on the physical and chemical characteristics of the soil. The aim was to evaluate the availability of P, using Mehlich-1 and Mehlich-3 extractors, and to determine the different forms of inorganic P in different classes of soils. Samples from horizon A of five soil classes from the municipality of Lagoa Formosa, Minas Gerais, were used: Typical Dystrophic Litholytic Entisol (RLd), Typical Dystrophic Red Oxisol (LVd), Typical Dystrophic Tb Hapludox Inceptisol (CXbd), Typical Acriferic Red Oxisol (LVwf), and Typical Chernossolic Litholytic Entisol (RLm). The levels of available P, remaining P, and total P were determined. From the fractionation of inorganic P, it was determined: soluble P (“P-H2O”), P bonded to aluminum (P-Al), P bonded to iron (P-Fe), and P bonded to calcium (P-Ca). The Mehlich-1 and Mehlich-3 extractors had a high correlation coefficient, indicating that both methods could be used to extract available P from the soil. Mehlich-1 extracted more available P in the soil with a high calcium content (RLm). High levels of total P observed in LVwf and RLm were mainly due to the parent material of the soils. P-Fe and P-Al are the predominant inorganic P fractions in the most weathered (RLd, LVd, and LVwf) and acidic soils (Cxbd). In RLm, the inorganic P is predominantly P-Ca.

Dynamics of phosphorus fractions in soils treated with dairy manure

The evaluation of phosphorus (P) transformations in soil after application of manure or mineral P can improve soil management and optimise P use by plants. The objectives of the present study were to assess organic and inorganic P forms in two soils treated with dairy manure and triple superphosphate and to establish relationships between soil P fraction levels and P availability. Soil organic and inorganic P fractions were quantified using a pot experiment with two soils, a typical Hapludox and an arenic Hapludult, with three types of fertiliser treatments applied (no fertiliser application, application of dairy manure, and application of triple superphosphate, by adding 100 mg P dm–3 in the form of fertiliser in the two latter treatments) and four incubation times (15, 45, 90, and 180 days). Inorganic P was fractionated into aluminium-bound, iron-bound, occluded, and calcium-bound P. Organic P was extracted sequentially using sodium bicarbonate, hydrochloric acid, microbial biomass, sodium hydroxide, and residual organic P. After incubation, maize plants were cropped to quantify dry matter yield and absorbed P. Application of dairy manure resulted in a significant increase in most of the organic P fractions, and application of triple superphosphate led to a significant increase in inorganic P fractions. Both fertilisers raised labile organic P fractions in the two soils. The major sinks of P in Hapludox were occluded and fulvic acid-associated P. In contrast, the major sink of P in Hapludult was iron-bound P. The available P levels were stable after application of dairy manure, and decreased with time when fertilised with triple superphosphate. In the Hapludox, the organic P fractions had a significant positive correlation with P uptake by plants. The results suggest that organic P mineralisation plays a more significant role in plant P uptake in the Hapludox soil and inorganic P forms are the main contributors to plant P uptake in the Hapludult soil.

Inorganic P fractionation in Shrink-swell soils of Central India: A case study

Inorganic P fractions in shrink-swell soils representing six soil series of Adan river basin, Darwha tehsil, Yavatmal district, Maharashtra were studied to understand the relationship between the P fractions and soil properties. These clayey soils were neutral to strongly alkaline (pH 6.70 – 9.34), calcareous and low to medium in organic carbon. The sequential extraction of inorganic soil P fractions indicated relative abundance as Ca2-P<Fe-P<Al-P<O-P<Ca8-P<Ca10-P. The plant available forms of P (Ca2-P, Al-P and Fe-P) contributed nearly 10 per cent of total inorganic P while the rest was in unavailable forms. The correlation matrix indicated that plant available forms of P had significant negative correlation with soil pH, EC and CaCO3 and significant positive correlation with organic carbon. The P fractions showed significant correlation among each other which implies that available P forms are constantly replenished by other forms of P pools in the soils.

Sequential extraction of different pools of phosphorus in alluvial and acid soils of Uttarakhand

The sequencing and availability of inorganic and organic fractions of phosphorus at different days interval in two soils after the fertilizer (SSP) application was the objective of this investigation. The study helped to obtain the sequence of dominating pool of phosphorus at different days intervals and the rate of release in the soil. This sequential fractionation was used for two native soils i) Alluvial soil and ii) Acidic soil, with 0 to 80 ppm SSP/ 100 gm soil added in a pot experiment and the soil samples were analyzed at different days intervals started from 5 days to 60 days. The result revealed that amount of maximum total P fell in the range from 325.14 to 387.30 mg kg-1 and 284.60 to 330.25 mg kg-1 for alluvial soil and acid soil, respectively up to 30 days. In case of inorganic P fractions under alluvial soil the dominating species were like Ca-P > Fe-P > Al-P >Saloid-P, while under acidic soil the following order Fe-P > Al-P > Ca-P > Saloid-P was observed. These two observations also drew the concentration of organic-P fractions in soil. The work concluded that the availability of dominant phosphorus fraction up to 30 days received the maximum Ca-P concentration in alluvial soil and Fe-P up to 60 days in acidic soils, respectively.

Phosphorus fractions in soil after successive crops of Pinus taeda L. without fertilization

ABSTRACT: Pinus cultivation without fertilization is a common practice in southern Brazil, which can induce a decline in the availability of phosphorus (P) in the soil. The purpose of this study was to evaluate the changes in phosphorus fractions in a Humic Cambisol subjected to continuous Pinus taeda L. cultivation without fertilization. Two forest stands were evaluated, after 16 years of Pinus cultivation (1st crop) and 49 years (3rd crop), when soil samples were collected (layers 0-10, 10-20, 20-40, 40-60, and 60-80cm) from six trenches per forest. In soil samples, the P contained in organic (Po) and inorganic (Pi) forms was determined by sequential chemical fractionation. Labile inorganic P fractions remained unchanged after the different cultivation periods. However, the labile organic fractions declined from the first to the third cycle (from 70.6 to 39.8mg dm-3 in the 0-10cm layer), indicating that these forms influence the buffering capacity of labile Pi. The moderately labile organic P acted as a P drain, increasing its percentage of the total, from 34.7 to 56.3%, from the first to the third crop. Soil cultivation for 49 years with Pinus taeda resulted in a reduction of the organic P content, indicating that for this soil use, this P form should be used to diagnose P availability and fertilization requirements.

Comparison of phosphorus fraction distribution and influencing factors of suspended and surface sediments in the Tiaoxi watershed, China

Suspended and surface sediments from the Tiaoxi watershed, fed by the Xitiaoxi and Dongtiaoxi rivers, were analyzed for total phosphorus (TP) and the inorganic P fractions of loosely adsorbed P that were extractable with NH4Cl (NH4Cl-P), reductant P (BD-P), metal oxide-bound P extractable with NaOH (NaOH-P), and calcium-bound, HCl-extractable P (HCl-P), while other physicochemical compositions were also determined. The spatial variations of P fractions in these sediments were investigated, and the major factors influencing the various fractions were explored by multivariate statistics. Compared to surface sediments, suspended sediments contained considerably higher concentrations of total nitrogen, TP, organic matter, Al, Fe, Mn and biologically available P (BAP, given as NH4Cl-P, BD-P and NaOH-P combined) and lower concentrations of Si, Ca and HCl-P in the studied catchments. Dongtiaoxi sediments had higher TP, inorganic phosphorus and HCl-P concentrations and a lower BAP content compared with Xitiaoxi sediments, trends that were associated with local geological backgrounds, landscapes and anthropogenic characteristics. The results of principal component analysis showed different effects of sediment properties on P fraction distributions for Xitiaoxi and Dongtiaoxi sediments. The sediment components and structure exert a strong influence on BAP in Xitiaoxi sediments, in contrast to Dongtiaoxi sediments, where P fractions are mainly affected by urbanization and other anthropogenic activities such as shipping.

Use of near-infrared spectroscopy to assess phosphorus fractions of different plant availability in forest soils

The analysis of soil phosphorus (P) in fractions of different plant availability is a common approach to characterize the P status of forest soils. However, quantification of organic and inorganic P fractions in different extracts is labor intensive and therefore rarely applied for large sample numbers. Therefore, we examined whether different P fractions can be predicted using near-infrared spectroscopy (NIRS). We used the Hedley sequential extraction method (modified by Tiessen and Moir, 2008) with increasingly strong extractants to determine P in fractions of different plant availability and measured near-infrared (NIR) spectra for soil samples from sites of the German forest soil inventory and from a nature reserve in southeastern China. The R2 of NIRS calibrations to predict P in individual Hedley fractions ranged between 0.08 and 0.85. When these fractions were combined into labile, moderately labile and stable P pools, R2 of calibration models was between 0.38 and 0.88 (all significant). Model prediction quality was higher for organic than for inorganic P fractions and increased with the homogeneity of soil properties in soil sample sets. Useable models were obtained for samples originating from one soil type in subtropical China, whereas prediction models for sample sets from a range of soil types in Germany were only moderately useable or not useable. Our results indicate that prediction of Hedley P fractions with NIRS can be a promising approach to replace conventional analysis, if models are developed for sets of soil samples with similar physical and chemical properties, e.g., from the same soil type or study site.