Little is known about the effects of air-drying and freezing on the transformation of phosphorus (P) fractions in soils. It is important that the way in which soils respond to such perturbations is better understood as there are implications for both P availability and loss to surface waters from soils. In this study, the effects of air-drying and freezing were in- vestigated using two soils, one being a forest soil (FS) high in organic matter and the other being a sterile soil (SS) low in organic matter. Soil P was fractionated using a modified Hedley fractionation method to examine the changes of phos- phorus fractions induced by air-drying and freezing. Generally, there were no significant differences of total phosphorus among the three treatments (CV% < 10%). Compared with field moist soils, freezing the soil evoked few changes on phosphorus fractions except that the resin-P increased in FS soil. On the contrary, air-drying significantly changed the distribution of phosphors fractions for both soils: increased the labile-P (especially resin-P) and organic-P (NaHCO 3 -Po, NaOH-Po and Con.HCl-Po) at the expense of NaOH-Pi and occlude-P (Dil.HCl-P and Con.HCl-Pi). Resin-P significantly increased by 31% for SS soil and by 121% for FS soil upon air-drying. The effect of air-drying seemed to be more pro- nounced in the FS soil with high organic matter content. These results indicated that drying seem to drive the P transfor- mation form occlude-P to labile-P and organic-P and accelerated the weathering of stable P pool. This potentially could be significant for soil P supply to plants and P losses from soils to surface waters under changing patterns of rainfall and temperature as predicted by some climate change scenarios.
Stalks of sugar cane varieties CoLk 8102 and Co 1148 (Saccharum spp. hybrids) (after 10 months of growth), were cut to obtain single bud setts of the same girth (approximately 2.3 cm). These bud setts were raised in plastic trays filled with sand and earthen pots with soil and they were regularly irrigated so that settlings were raised after 35 d of planting. The pots were laid in six replications in completely randomized block design (CRD) and plants were irrigated with saline water under seven treatments (T1-T7) prepared by dissolving sodium chloride, sodium sulphate and their combinations in deionised water as given in Table 1. Phosphorus fractions were separated after 300 d of the growth in young leaf of both cultivars by method of Hall and Hodges (1966). Sucrose% was determined in cane juice by method of Meade and Chen (1977). Data are mean of three replicates and factorial analysis of the data was tested by analysis of variance (ANOVA). Regression analysis and correlation coefficients were calculated using MS Excel statistical tools to assess the interrelationships
These results have impacted the environment of the different watersheds that flow into the lake. If environmental managers determine that P is a problem in the receiving watershed, they can manage the release of P.  found that the significance of the source is supported by the spatial pattern and speciation of P (total P and inorganic P) in the upstream and downstream testing sites of the major fishing region. As environmental conditions change, phosphorus can be expelled from the soil into the surrounding water. The most essential variables can be estimated from domestic activities in urban and rural areas, agricultural production, and fertilizer use, contributing P to the river through soil loss and atmospheric deposition. This depends on the region, soil type and retention ability, as well as on the environment .
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In organic farming, compost and manure are important sources as P fertilizers. Compost/manure added to soil can enhance the availability of phosphorus through the direct release of P from the compost or indirectly through the release of humic acids to the soil. Humic substances can promote release of P by complexing Fe and Al de- rived from Fe- and Al-phosphates , and by the for- mation of Ca-humates when reacting with Ca-phosphates , both resulting in a release of the corresponding phosphate anions. Furthermore, organic farming pro- motes accumulation of organic matter, and this also leads to improved physical properties such as a lower bulk density with lower dry strength and increased friability . Moreover, to organic farming currently higher lev- els of biological activity were associated . However, a positive effect of soil tillage on soil nutrient availability was postulated especially for organic farming systems but was not sufficiently proven .
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The P containing compounds of the freeze-dried flag leaf subsample were fractionated into the following four fractions; lipid-P (i.e. phospholipids), metabolic-P (easily soluble P-con- taining metabolites such as ATP and sugar phosphates), nucleic acid-P (P in RNA and DNA) and residual-P (phosphoproteins and unidentified residue) following a modified fractionation assay from Hidaka and Kitayama . Freeze dried flag leaf subsample was weighed into a 2 ml screw cap vial and extracted three times with 1 ml of a mix of chloro- form: methanol: formic acid (CMF, 12:6:1 v/v/v, 3 ml total per sample). The CMF extracted leaf residue was then extracted three times with chloroform: methanol: water (CMW, 1:2:0.8, v/v/v, total of 3.78 ml of CMW per sample). This extract was transferred to a 22 ml glass tube and 1.9 ml of chloroform washed water (10% of miliQ water + 90% of chloro- form) was added. This extract solution was mixed and partitioned into a lipid-rich organic (bottom) layer and a sugar- and nutrient-rich aqueous (upper) layer. The aqueous layer was transferred carefully into a 22 ml glass tube (Fraction 2a) and the bottom chloroform layer was dried under N (Fraction 1, lipid-P). After the CMF and CMW extraction, the leaf resi- due was washed with 1 ml of 85% methanol (Fraction 2b). After methanol extraction the residue was dried under N to remove the methanol, and then extracted twice with 1 ml of cold 5% trichloroacetic acid (TCA, 4˚C). Each extraction was for 1 h at 4˚C, the sample was mixed by inversion every 10 min and a total of 2 ml of 5% TCA was used for each sample (Fraction 2c). Fractions 2a, 2b and 2c were combined and taken into a new 22 ml glass tube to form the final Fraction 2 (metabolic-P). The leaf residue was again extracted with 1 ml of 2.5% TCA, three times at 95˚C for 1 h, a total of 3 ml 2.5% TCA supernatant was taken into a new 22 ml glass tube (Fraction 3; nucleic-P). Fraction 2 and 3 were dried in a rotary vac- uum concentrator (Martin Christ, Osterode am Harz, Germany) for 4 h at 50˚C. The extracted residue was dried under N (Fraction 4, residue-P). To measure the P concentra- tion of each fraction, each dried fraction was digested with 2.5 ml of HNO 3 using the
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(plant) availability in mineral soils is the Hedley fractionation method (Cross and Schlesinger, 1995; Hedley et al., 1982; Tiessen and Moir, 2008). The original method (Hedley et al., 1982), which was modified by Tiessen and Moir (2008), pro- vides a total of seven inorganic and four organic P fractions. These P fractions are often grouped into pools of distinct plant availability: a labile, fast cycling pool (labile P), which is considered to supply the short-term P demand of plants; a slow cycling pool (moderately labile P), which can be con- verted into labile P forms; and a pool of occluded P (stable P), which is assumed to hardly contribute to plant nutrition in the short-term (Guo and Yost, 1998; Stevenson and Cole, 1999; Johnson et al., 2003). There are a number of studies that have examined changes in P stocks in forest ecosystems using the Hedley fractionation method. Some of them have followed the development of P fractions over time to gain information on the relevance of these P fractions for tree nu- trition during ecosystem development (Richter et al., 2006; De Schrijver et al., 2012). In other studies, the influences of different forest management systems on the distribution of P fractions in soils were investigated (Alt et al., 2011). These were case studies at single sites or only at few different sites and thus had only a limited population of inference (the pop- ulation to which the results from the sample can be extrapo- lated) (Binkley and Menyailo, 2005). To our knowledge, no studies have currently addressed the distribution of Hedley P fractions and P pools in forest soils on the basis of large- scale inventories. Thus, there is little information on how different soil variables such as pH value, C and N content, or soil texture, which have been found to influence P avail- ability (Alt et al., 2011; Franzluebbers et al., 1996; Prescott et al., 1992; Silver et al., 2000; Stevenson and Cole, 1999; Thirukkumaran and Parkinson, 2000; Turner et al., 2007), affect the distribution of different P fractions across a vari- ety of forest soil types. Therefore, we determined the Hed- ley P fractions in mineral soil samples from 145 sites of the National Forest Soil Inventory of Germany, covering a wide range of P contents and many different soil parent materials (Niederberger et al., 2015). With this study we addressed the following questions:
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The most appropriate parametric model was selected for each regression series by minimizing the Akaike information criterion. Phosphorus contents, dry weights and P concentration measures for the no fertilizer treatment were best represented by a three parameter asymptotic exponential function. The tissue P concentration for the added fertilizer treatment was better represented by the four parameter logistic equation. The proportion of P derived from the biosolid was best described by the Michaelis-Menten model while the proportion of P derived from the fertilizer and from the soil in the treatment with fertilizer added was best described by the Weibull equation. Finally, the three-parameter logistic growth equation best described the proportion of P derived from the soil where no fertilizer P was added. Residuals for the most appropriate model were calculated against the predicted values and bootstrapped (R =1000) by randomly assigning the residuals to the fitted values and refitting the parametric functions. 16,17,18
Particle size distribution was conducted by pipette method using Na- hexametaphosphate as a dispersing agent as described by Klute (1986). Organic matter content was estimated by Walkley and Black method, total carbonates was determined using Collin's calcimeter, pH was determined electrometrically in 1:2.5 soil – water suspension using a pH meter, electrical conductivity of the soil paste extract was determined using electrical conductivity bridge and cationic and anionic composition of the soil paste extract were determined using the standard methods outlined by Page et al. (1982). Cation exchange capacity (CEC) was determined by displacing the exchangeable cations by NaCl as described by Polemio and Rhoades (1977). Total P was determined according to Olsen and Sommers (1982), AB-DTPA extractable fraction (the available P fraction) was determined according to Soltanpour and Schwab (1977). Inorganic P fractions were determined using the fractionation procedure of Olsen and Sommers (1982), involving sequential extraction with 0.1 N NaOH to remove non-occluded Fe,Al-P, 1.0 M NaCl and citrate bicarbonate (CB) to remove P sorbed by carbonate during NaOH extraction, citrate dithionate-bicarbonate (CDB) to remove P occluded within Fe and Al oxides and hydrous oxides and finally 1.0 N HCl to remove Ca-P. Some physical and chemical properties of the studied soils are shown in Table 1.
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total P, Pi and Po fractions) in arable and mountain soils is presented. Besides, the detailed characterisation of P compounds in humic acids (HA) is also shown. The results obtained show that the highest content of the available P can be found in arable soils with a high input of fertilisers, and that the predominant part of Pi is included in hardly soluble fractions, mainly in the soil types with neutral soil reaction. Our data also show the correlation between total P and Po, the dominant form of P in the topsoil of mountain soils. Phosphomonoesters represent the major types of P in HA structure. The correlations between phosphomonoesters of type I and some humification parameters of HA and qualitative parameters of soil organic matter suggest that higher amounts of more recalcitrant monoesters can be found in more mature soil organic matter with a higher humification degree.
in plant biomass with combined P and N addition (Fig. 1a, b) and a negative correlation between plant P uptake and moderate-cycling IP fractions (Fig. 6a, b). Therefore, the de- crease in soil moderate-cycling IP fractions with N addition could have been due to enhanced plant P uptake (Fig. 1c, d) as a result of increased plant biomass (Figs. 1a, b and 7). Under N addition, simultaneous increases in soil Olsen- P output (plant uptake) and input pathways (transformation from soil moderate-cycling IP fractions) may have resulted in mostly nonsignificant difference in soil Olsen-P concen- trations between combined P and N addition and P addi- tion alone (Fig. 5a, b). Nitrogen addition can potentially in- crease soil P availability by promoting solubilization of soil IP fractions in the short term (Wang et al., 2016). How- ever, long-term N deposition resulted in soil IP-exhaustion, thereby constraining the growth of plants (Olander and Vi- tousek, 2000; Yang et al., 2014). Previous research has also found that decades of N addition could accelerate PO 3− 4 re- lease (Malik et al., 2012; Stroia et al., 2011) and enhance conversion of soil recalcitrant IP fractions to soil labile IP and moderate-cycling IP fractions as a result of soil acidifi- cation (Alt et al., 2013). Additionally, N addition was found to suppress acid and alkaline phosphatase enzymes, result- ing in a decrease in soil organic P mineralization in a similar semiarid grassland (Tian et al., 2016). Therefore, combined N and P addition might decrease soil IP fractions by reduc- ing the conversion of soil organic P to IP as compared to P addition alone. Our results clearly illustrate that N effects on soil IP fractions depended on P inputs, where combined N and P additions could accelerate conversion of soil moderate- cycling IP fractions into soil-available P and enhance plant P uptake and biomass (Fig. 7).
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The contents of different phosphorus fractions were determined using the sequential extraction scheme sug- gested by Psenner et al.  with the modifications of Hupfter et al.  (Figure 2), which based on differences in reactivity of solid phases to different extractant solutions. The extraction procedure divided inorganic phos- phorus (IP) fractions into loosely sorbed P (NH 4 Cl-P), redox-sensitive P (BD-P), metal oxide bound P (NaOH-P)
The effect of nitrogen and phosphorus inputs into water systems are not the same, and the total bacterial biomass has a stronger correlation to the concentration of total phosphorus in fresh and marine ecosystems than nitrogen (Li et al., 2004). Production of organic matter within an aquatic environment is a highly selective process, and phosphorus, nitrogen and carbon ratios in plankton tend to average 1:16:106, which is almost mirrored in surrounding waters at 1:15:105. This ratio is maintained because, in an environment containing a deficiency of nitrate relative to phosphate, nitrogen-fixing bacteria will have a competitive edge and increase nitrogen fixation, which will bring the ratio of nitrogen and phosphorus closer to the concentrations within their cells. However, with a relatively high concentration of nitrogen, non-nitrogen fixing organisms will have a competitive edge because nitrogen fixation is an energy sink. Consequently, the amount of fixed nitrogen entering the system will decline, bringing the ratio back to near cellular concentrations (Redfield, 1958; Tyrrell, 1999).
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Characteristically, for a critical-phosphorus curve yield increases with phosphorus additions, but eventually plateaus when phosphorus is no longer the yield-limiting factor. The shape of the response indicates that phosphorus additions bring diminishing returns, and in Fig. 1, 90% of the maximum yield is attained by adding 464 ± 77.9 mg·kg −1 P in soil (about 557 kg·ha −1 P). This quantity may seem high, but it should be remembered that the initial available phosphorus (Olsen phosphorus) value of the soil was 6.7 mg·L −1 P, and that earlier it was explained that typically less than 8% of the added phosphorus is recovered in the crop. Changing the phosphorus status of an Index 0 soil to that of optimum available phosphorus concentration initially requires considerable inputs and increases in soils with higher PBI. In Fig. 1, 95% of the maximum yield is achieved at 600 ± 103 mg·kg −1 P in soil (about 720 kg·ha −1 P), further demonstrating that as the soil phosphorus status increases, a modest increase in yield requires considerable additional phosphorus fertilizer. Thus, farmers have to make decisions on what available phosphorus value to target in relation to potential profit.
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For this strategy to be effective appropriate target soil P concentrations need to be set. Reducing soil P concentrations to the agronomic optimum may not be sufficient to protect water quality in all cases McDowell et al. 2003b). While some forms of dissolved organic P (DOP) have been shown to be available for uptake by some algae via the release of phosphatase enzymes (Whitton et al. 1991), DRP is generally considered to be immediately and completely available and is considered to be the main phosphorus form contributing to eutrophication. The Australian and New Zealand Environment Conservation Council (ANZECC) guidelines suggest trigger values for DRP in upland and lowland New Zealand rivers of 9 and 10 µg P L -1 respectively (ANZECC 2000). This trigger value represents a concentration below which there is a low risk of adverse biological effects and could be used to relate WEP concentration within a soil to the potential risk of adverse water quality effects. As such, soils containing WEP concentrations above 0.01 mg P L -1 could be considered to pose an increased risk to water quality. However, this figure might be overly conservative as it assumes that the ratio of WEP to export DRP is 1:1, and its adoption as a soil P target may bring the STP concentration down to a level where productivity is compromised. Further work is required to determine a workable soil P target for different soil types and farming systems.
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The potentially plant available phosphorus in soil is generally more important for crop growth than the annually applied phos- phorus. In Finnish practice, however, the recommendations for phosphorus use are based on the fertilizer’s immediate effect on crop yields (see, e.g. Valkama et al. 2009). As shown in the opening section, omitting the transition dynamics of soil phosphorus results in false phosphorus application rec- ommendations. Saarela et al. (1995) dis- cuss optimal phosphorus use with varying STP levels and input and output prices. Their analysis accounts for the develop- ment of STP heuristically by discussing the long-term economic effects of altering the STP level – and thereby future profits. To date, the optimal choice of phospho- rus has not been presented as a problem of controlling the development of soil phos- phorus – a problem entailing a decision between the interdependent processes of crop growth and phosphorus losses. Valka- ma et al. (2009), for instance, recommend heavy reductions in overall phosphorus fer- tilization levels based on crop response to phosphorus fertilization. As the quality of surface waters is an extremely relevant is- sue in the Finnish political debate, and the role of agriculture is central to that issue, it would be important to have a common framework for analyzing the optimal use of phosphorus.
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Abstract. Riparian buffers can trap sediment and nutrients sourced from upper cropland, minimizing the eutrophication risk of water quality. This study aimed to investigate the distributions of soil inorganic phosphorus (Pi) forms among profile and particle-size fractions in an established riparian buffer and adjacent cropped area at the Dian lake, southwest- ern China. The Ca-bound fraction (62 %) was the major pro- portion of the Pi in the riparian soils. After 3 years’ restora- tion, buffer rehabilitation from cropped area had a limited impact on total phosphorus (TP) concentrations, but has con- tributed to a change in Pi forms. In the 0–20 cm soil layer, levels of the Olsen-P, non-occluded, Ca-bound, and total Pi were lower in the buffer than the cropped area; however, the Pi distribution between the cropped area and the buffer did not differ significantly as depth increased. The clay fraction corresponded to 57 % of TP and seemed to be both a sink for highly recalcitrant Pi and a source for labile Pi. The lower concentration of Pi forms in the silt and sand particle fraction in the surface soil was observed in the buffer area, which in- dicated that the Pi distribution in coarse particle fraction had sensitively responded to land use changes.
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50 If ( H * ), 200-400 mesh, and the column was eluted with water at room temperature, 10 ml, fractions were collected, the ninhydrin-reacting material appearing in the seventh to fourteenth fractions. These fractions were subjected to paper electrophoresis in potassium dihydrogen phosphate- sodium hydroxide buffer mixture^ ( 0,05 M ), pH 7*0, for 1 hr* at 20 V / cm* using 0-phosphorylethanolamine and ethanolamine as markers. The dried paper was sprayed with ninhydrin. Only one spot was detected in each case, suggesting that fractions 7-14 contained only a single ninbydrin reacting substance, this substance having a
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Abstract. This paper introduces new insights into the hydro- chemical functioning of lowland river systems using field- based spectrophotometric and electrode technologies. The streamwater concentrations of nitrogen species and phospho- rus fractions were measured at hourly intervals on a con- tinuous basis at two contrasting sites on tributaries of the River Thames – one draining a rural catchment, the River En- borne, and one draining a more urban system, The Cut. The measurements complement those from an existing network of multi-parameter water quality sondes maintained across the Thames catchment and weekly monitoring based on grab samples. The results of the sub-daily monitoring show that streamwater phosphorus concentrations display highly com- plex dynamics under storm conditions dependent on the an- tecedent catchment wetness, and that diurnal phosphorus and nitrogen cycles occur under low flow conditions. The diurnal patterns highlight the dominance of sewage inputs in con- trolling the streamwater phosphorus and nitrogen concentra- tions at low flows, even at a distance of 7 km from the nearest sewage treatment works in the rural River Enborne. The time of sample collection is important when judging water qual- ity against ecological thresholds or standards. An exhaustion of the supply of phosphorus from diffuse and multiple septic tank sources during storm events was evident and load es- timation was not improved by sub-daily monitoring beyond that achieved by daily sampling because of the eventual re- duction in the phosphorus mass entering the stream during
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Inputs of phosphorus (P), mainly in the form of mineral fertilizers derived from phosphate rock, are essential to enhance and maintain the productivity of agroecosystems, including grasslands (Smit et al., 2009). However, most of the P applied in fertiliser is not immediately utilised or retained by plants and grazing animals and therefore accumulates in the soil as various inorganic and organic P forms of different labilities (commonly referred to as “legacy P” or “residual P”) (Haynes and Williams, 1993; Sattari et al., 2012; Stutter et al., 2012; Nash et al., 2014). There are also ongoing concerns and debate around addressing the adverse environmental impacts of high P inputs and the long-term future supply and cost of finite phosphate rock resources (Cordell et al., 2009; Haygarth et al., 2013; Ulrich and Frossard, 2014). These issues have highlighted the need to reassess and improve the overall utilisation efficiency of P inputs in agroecosystems, including the potential to enhance mobilisation of and use of P accumulated in soil from previous inputs (Condron et al., 2013; Haygarth et al., 2013; George et al., 2016).
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97.15% grain and therefore the chemical analysis of the Since the diets in the present study contained diets should reflect that of the test grain used as the different amounts of non-phytate phosphorus and principle ingredient in the diet. The results of the chemical phytase it was not possible to separate the effects of non- analyses conducted on the diets (Table 1) were within the phytate phosphorus level and endogenous phytase in range of those previously reported for corn, wheat, oat grains on the resultant phosphorus digestibility and barley in standard industry publications, such as the coefficients obtained. However, an interesting comparison United States-Canadian Tables of Feed Composition can be made between the diets containing either oat or (National Research Council, 1982), Feedstuff’s Ingredient Harrington barley that contained only small differences in Analysis Table (Dale, 1995), as well as the Nutrient non-phytate phosphorus (0.90 vs. 1.10 g kgG ), but had a Requirements of Swine (National Research Council, 1998). five-fold difference in analyzed activity of endogenous Notable exceptions would be the higher ether extract and phytase enzyme. In spite of the substantially higher lower neutral detergent fibre content of the high fat-low amount of phytase in the barley diet, there was no lignin oat cultivar and the lower phytate content of the improvement in the apparent digestibility of phosphorus, low phytate barley compared with literature values for which suggests that there is very little contribution to Harrington barley. The aforementioned differences can phosphorus digestibility from the phytase enzymes be attributed to selection for these specific traits by naturally associated with the grains.