Pi Fractions Research Articles

Calibration of Near-Infrared Spectra for Phosphorus Fractions in Grassland Soils on the Tibetan Plateau

Soil phosphorus (P) is essential for plant growth and influences biological processes. Determining the amounts of available P to plants has been challenging, and many different approaches exist. The traditional Hedley sequential extraction method and its subsequent modification are applied to determine different soil P forms, which is critical for understanding its dynamics and availability. However, quantifying organic and inorganic P (Po & Pi) in different extracts is labor-intensive and rarely used with large sample numbers. As an alternative, near-infrared spectroscopy (NIRS) has been employed to determine different P fractions at reasonable costs in a short time. This study aimed to test whether the analysis of P fractions with NIRS is an appropriate method to disentangle the effects of P limitation on high-altitude grassland ecosystems, particularly with fertilizer amendments. We explored NIRS in soils from the grassland soil samples on the northern Tibetan Plateau. First, we extracted the P fractions of 191 samples from the Haibei Alpine Meadow Ecosystem Research Station at four depth increments (0–10 cm, 10–20 cm, 20–40 cm, and 40–70 cm), including nutrient additions of nitrogen (N) and P. We compared the results of the Hedley extraction with the laboratory-based NIRS model. The fractionation data were correlated with the corresponding NIRS soil spectra; the coefficient of determination (R2) of the NIRS calibrations to predict P in P fractions ranged between 0.12 and 0.90; the ratio of (standard error of) prediction to the standard deviation (RPD) ranged between 1.07 and 3.21; the ratio of performance to inter-quartile distance (RPIQ) ranged from 0.3 to 4.3; and the model prediction quality was higher for Po than Pi fractions, and decreased with fertilizer amendment. However, the external-validation results were not precise enough for the labile P fractions (RPD < 1.4) due to the limited number of samples. The results indicate that using NIRS to predict the more stable P pools, combined with Hedley fractionation focusing on the labile P pool, can be a promising approach for soils in alpine grasslands on the Tibetan Plateau.

Correlation of bacterial community with phosphorus fraction drives discovery of Actinobacteria involved soil phosphorus transformation during the trichlorfon degradation

Trichlorfon (TCF) is a broad-spectrum phosphorus (P)-containing pesticide, yet its effects on soil P fraction transformation and bacterial communities during the TCF degradation in soils is unknown. In this study, we investigated soil TCF degradation behavior at different contents of 50, 100 and 200 mg/kg, and analyzed residual TCF contents and metabolites by gas chromatography mass spectrometry after 216-h incubation. Our results suggested that TCF was gradually degraded in soils and was be initially hydrolyzed to dichlorvos via P–C bond cleavage and then other P-containing metabolites. By analyzing different P fractions and soil microbial community composition, we found significant increases of soil available phosphorus contents from 2.76 mg/kg (control) to 3.23 mg/kg (TCF-50), 5.12 mg/kg (TCF-100) and 5.72 mg/kg (TCF-200), respectively. Inorganic CaCl2–P was easily and instantly transformed to primary mineral inorganic P (Pi) forms of HCl–P and citrate-P, while the proportion of enzyme-P (a labile organic P) fluctuated throughout TCF degradation process. Soil available P contents and Pi fractions were significantly correlated with the relative abundance of Actinobacteria. These results highlighted that Actinobacteria is the dominant soil species utilizing TCF as P sources to increase its community richness, and subsequently affect the transformation of P fractions to regulate soil P cycle. Our study gives new understanding on the microorganisms can involve soil P transformation during organophosphorus pesticides degradation in soils, highlighting the importance of bacteria in P transformation and pesticides soil decontamination.

Biochemical phosphorus transformations in a calcareous soil as affected by earthworm, cow manure and its biochar additions

Application of raw or char material may modify the influence of earthworm activity on soil phosphorus (P) transformation. The purpose of this study was to investigate the effect of cow manure or cow manure biochar addition and its interaction with earthworm on organic (Po) and inorganic (Pi) P fractions, alkaline phosphatase activity and P-solubilizing bacteria (PSB) in a calcareous soil of semi-arid region. For this purpose, the soil was amended with cow manure and its biochar in 4 levels (0, 1, 2 and 5%) in the absence and presence of earthworm (Eisenia fetida). The treatments were then incubated for 90 days. The monitoring of earthworms was also carried out after 30 and 90 days incubation. The results showed an increase in weight of earthworms in control and cow manure amended soils at both incubation times. However, application of cow manure biochar resulted in mortality and an initial weight loss of earthworms (36–85%) at 30 days incubation. This negative effect decreased over time, so that the earthworms recovered in 1% biochar amended soil. Amendment additions increased proportion of NaHCO3-Pi and NaOH-Pi but decreased proportion of HCl-Pi, residual-P, NaOH-Po and HCl-Po, making P more available in soil. The impact of cow manure biochar on the NaHCO3-Pi and NaOH-Pi fractions was stronger than that of cow manure. Earthworm decreased the proportion of Pi fractions but increased the proportion of Po fractions, indicating a transformation of P from Pi to Po forms. Alkaline phosphatase activity and PSB number were also increased as affected by earthworm and amendment (especially cow manure) additions. No significant interaction between earthworm and amendment additions was observed (p < 0.05), indicating that the influence of earthworm on P transformations was not dependent on amendment additions. Overall, we concluded that biochar can be useful for the amendment of semi-arid calcareous soil in terms of P availability, but the negative response of earthworms to biochar and its effect on other soil processes should be taken into consideration.

Changes in phosphorus fractions in response to long-term nitrogen fertilization in loess plateau of China

Phosphorus (P) fractions and their availability in soils can be affected by long-term nitrogen (N) fertilizer application, which can subsequently affect plant growth and productivity. The extent of P fixation at different N fertilization rates is still unclear and this study highlighted an appropriate N fertilization rate showing minimum P fixation and higher P content uptake by the plants. Paradox changes of P into various organic (Po) and inorganic (Pi) fractions and their contribution in P content uptake and yield was evaluated under long-term (12 year) application of different N rates (0, 80, 160, 240, and 320 kg N ha−1, hereafter, N0, N80, N160, N240, and N320, respectively) in winter wheat (Triticum aestivum L.). Phosphorus fractions were measured using Tiessen and Moir fractionation scheme modified from Hedley method. N rates significantly decreased available (especially NaHCO3-Pi) and residual fractions of P, when compared with N0. The NaHCO3-Pi showed a significant positive relationship with total plant P content and grain yield. Grain yield was maximum in N160 treatment with no significant difference between N160 and higher N levels. Increase in N rates from N0 to N320 little increased organic P fractions; NaHCO3-Po increased from 64.0 to 69.7 mg kg−1, HCl-Po increased from 60.5 to 87.1 mg kg−1, but NaOH-Po decreased from 46.5 to 31.2 mg kg−1. All Pi fractions increased, and maximum contents were observed for HClD- -Pi fraction ranging between 189–265 mg kg−1 from N0 to N320 treatments. HClD-Pi fraction was highest contributor (39%) in total P, which is transformable into available P with time. A decrease in residual P by 7.4% was observed in N320 compared with N0 treatment. Residual P fraction was positively correlated with grain yield, biomass, total P content uptake, and with the moderate available fractions (NaOH-Pi, NaOH-Po, and HClD-Pi). It can be concluded that excessive N fertilization does not always result in increased crop yield but can increase P fixation (HClD-Pi form) and decreases residual P contents. Therefore, optimum N fertilization should be applied keeping in view the crops requirement. This study advocates that N application at 160 kg N ha−1 can maintain higher wheat yield (5844 kg ha−1) in Loess Plateau, with no significant increases in P fixation and loss of residual P.

Does soil phosphomonoesterase activity reflect phosphorus pools estimated by Hedley phosphorus fractionation?

Understanding soil phosphorus (P) availability can benefit from characterizing P pools and processes governing P distribution among such pools. Hedley P fractionation has been widely used to characterize P pools, whereas soil phosphomonoesterase (PME) activity assays have been used to assess potential rates of organic P (Po) mineralization to available inorganic P (Pi). We evaluated 1) the extent to which P fractions are consistent with the theorized P pools and 2) relationships of PME activity with P fractions using observations compiled across diverse (agro)ecosystems. We hypothesized that P fractions are differentiated based on the form (i.e. organic and inorganic) and availability of P pools they estimate. Given that Pi is product and Po is substrate for PME, we further hypothesized that PME activity associates negatively with Pi fractions representing available P pool and positively with Po fractions. Factor analysis grouped measured P fractions into three pools: non-occluded Pi, soil organic P, and secondary Pi. These groupings generally supported the differentiation of P fractions by form (Pi vs Po) and availability of P pools they are commonly used to estimate but were also sensitive to the degree of soil weathering. Structural equation modeling supported biochemical mechanisms of product inhibition and substrate induction of PME activity and also identified an influence of weathering degree on relationships of specific measured P fractions with PME activity. This work demonstrates that evaluating PME activity in conjunction with P fractions can be a useful framework to better understand soil P cycling. Incorporating additional variables—such as Po fractionated physically or enzymatically, and phosphodiesterase activity—into the current statistical framework may further improve understanding of how soil P cycling determines P availability.

Biochar Alters Inorganic Phosphorus Fractions in Tobacco-growing Soil

It is important to consider tobacco stalks as sources of biochar and improve the soil quality of tobacco-producing areas in Southwest China. Therefore, in this study, we investigated the effects of biochar produced from tobacco stalks on soil inorganic phosphorus (P) fractions in bulk and rhizosphere soils. We also analyzed the factors influencing these effects in tobacco-planting fields. Biochar was applied to two experimental fields in Heishi and Qianxi in Bijie City, Guizhou Province in China, at application rates of 0, 5, 20, and 40 t ha−1. Subsequently, the soil inorganic P (Pi) fractions, pH, and exchangeable and hydrolytic acidities were analyzed, while the factors influencing the soil Pi fractions were determined by redundancy analysis (RDA). The results indicated that the biochar application rate, experimental site, and tobacco roots all affected the soil Pi fractions. Aluminum-phosphate (Al-P), iron-phosphate (Fe-P), and occluded-phosphate (O-P) levels in the bulk soil had significantly increased with biochar application in the Qianxi site. Meanwhile, there was a reduction in Al-P, Fe-P, and O-P levels in the rhizosphere soil in the Heishi site but not in the Qianxi site. The calcium-phosphate (Ca-P) levels in the soil were also greatly reduced in the Heishi site, while in the Qianxi site, the Ca-P levels were relatively constant in the bulk soil and increased in the rhizosphere soil. Furthermore, the exchangeable and hydrolytic acidities decreased with increasing biochar application. Soil Pi fractions varied according to biochar application rate and experimental site. We found that 20 t ha−1 was an appropriate biochar application rate for enhancing soil Pi fractions. In addition, the soil Pi fractions were negatively correlated with the dissolved organic carbon (DOC) content but were positively correlated with the hydrolytic acidity.

Influence of pre-crops on growth and phosphorus uptake of maize and wheat in relay strip intercropping

Relay strip intercropping systems have the advantage of increasing land yield, but there are few studies on how pre-crops affect the grain yield and phosphorus (P) use of subsequent crops in such systems. Field experiments were carried out for four consecutive years, covering two complete cycles of the crop sequence, to evaluate the effects of pre-crops on crop yield, P uptake, and topsoil P balance of maize and wheat. Three pre-crops were used, i.e. fallow, pea, and rutabaga planted with two P levels with (+P) and without (0P) P fertilizer applied to maize and/or the wheat season. Pea significantly improved grain yield in cycle 1 and grain yield, biomass and P uptake of subsequently grown maize in cycle 2, compared with fallow, and P fertilizer application had no effect on maize yield, P uptake and above-ground biomass in cycle 1, but significantly improved yield and P uptake in cycle 2. Regarding the subsequently grown wheat, on average, pea significantly increased the wheat average yield by 11.57 % and 4.27 % under the 0P and + P treatment, respectively; and rutabaga had 5.22 % and 6.40 % higher wheat average yield than under the same conditions of fallow. Pea prominently improved the above-ground biomass, P uptake; soil Olsen-P in the 0–20-cm soil profile, and the inorganic Pi fraction concentration after two consecutive cycles, with a significant positive correlation between Olsen-P and most Pi fractions. Rutabaga prominently improved above-ground biomass and P uptake. The above parameters performed better under pea than rutabaga. P fertilizer application during the maize season barely affected the growth or P uptake of subsequently grown wheat, P applied during the wheat season, however, significantly enhanced agronomic traits and P uptake, and this effect was more pronounced under pea. We therefore conclude that pea as pre-crop is instrumental for subsequent maize and wheat production, and provides more benefits for farmers.

Organic acid regulation of inorganic phosphorus release from Mollisols with different organic matter contents

AbstractPhosphorus (P) is used to enhance agricultural productivity. Organic acids increase the release of inorganic phosphorus (Pi) into soil solutions and thereby improve phosphorus utilization in soils; however, the effects of both organic acids and the soil organic matter contents on Pi release are poorly understood. To assess the importance of these factors in determining phosphorus availability, the release of soil Pi fractions (i.e. aluminium‐bound phosphorus (Al‐P), iron‐bound phosphorus (Fe‐P), occluded phosphorus (O‐P) and calcium‐bound phosphorus (Ca‐P)) was evaluated on addition of organic acids (citric, oxalic and malic acids) to soils from Mollisols region that had different organic matter contents and received phosphorus fertilizer. Biochemically produced humic acid was used to modify soil organic matter contents. Among Pi fractions, the Fe‐P fraction had the highest concentration in all the soils with different organic matter contents. In the presence of organic acids, the release of Pi fractions decreased as the soil organic matter increased. Among the fractions, Al‐P had the highest release, followed by Fe‐P. Comparison among various organic acids revealed that oxalic acid was the most effective for Pi release. Path analysis showed that Al‐P release had larger direct‐path and indirect‐path coefficients, which implied that Al‐P release had the largest contribution to total Pi (TPi) release. We concluded that the effectiveness of organic acids in improving soil phosphorus availability was most pronounced in soils with low organic matter contents, but further field‐scale research is needed to confirm this. Al‐P was the most effective source of inorganic phosphorus in Mollisols.

Soil phosphorus fractions and distributions in estuarine wetlands with different climax vegetation covers in the Yellow River Delta

To evaluate the relationship between phosphorus (P) fractions and physicochemical characteristics in soils of estuarine wetlands with different climax vegetation covers, surface 60-cm soil samples were collected in Suaeda heteroptera wetlands (SH), Tamarix chinensis wetlands (TC) and Phragmites australis wetlands (PA) in the Yellow River Delta during June 2017. Results showed that the inorganic phosphorus (Pi) in PA soils was significantly lower than that in TC and SH soils (p < 0.05), and the organic phosphorus (Po) showed the opposite pattern, with a rank of PA ≫ TC > SH. The available phosphorus (AP) had a high proportion at surface layer and decreased with increasing depth, with a rank of SH > TC > PA. D.HCl-Pi was the main component of the extracted Pi in all soil profiles, while C.HCl-Po, NaOH-Po and Bicarb-Po were the main components of the extracted Po in PA, TC and SH soils, respectively. Most of the Pi fractions were significantly positively correlated with Ca, Al and Fe in TC soils, whose correlations were better than those of SH and PA soils, and the Pi fractions were negatively correlated with the pH and sand contents. Our findings confirmed the complexity of the combination and unavailability of P fractions extracted by strong acids. Decreasing of sum of Po fractions (from14.72% in PA to 11.28% in SH) across a soil salinity gradient (1.0‰ to 12.0‰) provided valuable evidence of the mineralization of soil Po and that P. australis can enhance the biological functions of P. Although difference test revealed clear differences in soil physicochemical properties and slightly clear differences in P fractions, we did not extrapolate real correlations between soil P fractions and climax vegetation covers in this study. Research on the biological mechanism of climax vegetation covers and its influences on the plant absorption and utilization of P is our future direction.

Changes in Phosphorus Fractions and Its Availability Status in Relation to Long Term P Fertilization in Loess Plateau of China

Excessive phosphorus (P) application can alter soil P availability and limit plant growth by compacting soil and fixation of P into different organic and inorganic forms. However, it remains uncertain whether these changes happen after limited fertilization or an excessive rate applied under the winter wheat cropping system. The current study aimed to identify the transformation of P into different organic (Po) and inorganic (Pi) fractions, and their role in the plant P uptake and winter wheat (Triticum aestivum L.) production. A long-term study (12 years) was conducted to assess the changes in soil Pi and Po fractions in response to different P rates (0, 50, 100, 150, and 200 kg P2O5 ha−1) applied to winter wheat. Phosphorus fractions were determined using the Hedley modified Tiessen and Moir fractionation scheme. Our findings demonstrated that different P rates significantly increased the available P, particularly NaHCO3-Pi, in the inorganic P fractions compared to P0 treatment. NaHCO3-Pi showed a strong relationship with grain yield (R2 = 0.91) and P uptake (R2 = 0.80). Grain yield was significantly higher in the P100 treatment, but no significant difference was observed between P100 and P200 treatments. The P200 treatment had a maximum grain P content and plant P uptake. Compared with the P0 treatment, all organic fractions yielded the highest Po with the P rate increase, ranging from 27.3 to 75.6 mg kg−1, 27.2 to 35.6 mg kg−1, and 58.8 to 124 mg kg−1 for NaHCO3-Po, NaOH-Po, and HCl-Po, respectively. Among all Pi fractions, the maximum fraction, known as apatite (HClD-Pi), was found in the P200 treatment with the range of 165 to 245.9 mg kg−1. HClD-Pi accounted for 32% of total P, which can be transformed into the available P form with the passage of time. An increase of 78% in residual P was found under the treatment of P200. The residual P fraction was positively correlated with grain yield, P uptake, and other inorganic fractions. It can be concluded that application of P increases P availability and grain yield with an increase in its application rate, but too much use of P can cause soil pollution and higher fixation of P. Consequently, a balanced application of fertilizer is recommended to reduce its fixation and increase its availability for higher crop yield.

Interacting effects of urea and water addition on soil mineral‐bound phosphorus dynamics in semi‐arid grasslands with different land‐use history

AbstractNitrogen (N) addition and precipitation increment can greatly influence soil phosphorus (P) dynamics, with much emphasis on total and available P, yet little is known about their interactive effects on soil mineral‐bound inorganic P (Pi) fractions under different historical land uses of grasslands and old fields. Thus, we compared (i) plant readily available P, (ii) less available Pi (sum of NH4F‐extractable Pi, NaOH‐Na2CO3‐extractable Pi and NaHCO3‐extracted Pi), (iii) refractory forms of Pi (NH4Ac‐extractable Pi, H2SO4‐extractable Pi and Na3(citrate)‐dithionite‐extractable Pi) and (iv) organic P under the same urea and water treatments in an old‐field grassland with a semi‐arid steppe. Soil total P remained unchanged with 10‐year urea addition in both sites, with lower organic P but higher Pi concentrations in the old field. Urea addition promoted transformation of refractory Pi into less available Pi in both sites, which potentially was related to higher plant productivity and thus enhanced plant P accumulation. Specifically, urea addition increased less available Pi fractions by as much as 42%, but decreased refractory Pi fractions by as much as 24%, for two sites under ambient precipitation. Water addition decreased less available Pi in the steppe under higher urea addition rates, whereas it increased less available and refractory Pi but only in the control plot of the old field. Irrespective of urea and water treatments, the old field had a higher Pi pool, which could replenish plant readily available P in the longer term and be less prone to P‐limitation than the steppe. We conclude that conversion of semi‐arid steppe to farmland causes long‐term increases in the soil Pi pool, possibly by enhancing organic P mineralization and anthropogenic fertilization during cultivation. Urea addition accelerated soil P cycling via promoting refractory Pi, transforming into less available Pi, with the process being strongly mediated by water availability, whereas the projected precipitation increment could decrease less available Pi via promoting plant P uptake and P leaching out of the plant–soil system.Highlights Urea addition promoted transformation of refractory Pi into less available Pi fractions. Water addition counteracted the positive urea effect on NH4F‐Pi in both steppe and old field. Less responsive organic P suggested that Pi fractions were more essential in soil P cycling. Water addition decreased NH4F‐Pi in both sites, potentially due to higher plant uptake and leaching. Conversion of steppe to farmland increased the soil Pi pool by enhancing organic P mineralization.

Distribution of Soil Phosphorus Fractions as a Function of Long-Term Soil Tillage and Phosphate Fertilization Management

The forms in which phosphorus (P) accumulates in soils are dependent on management practices, fertilizer sources, and methods of application, which may promote distinct P solubility and plant uptake. We aimed here to evaluate how soil tillage and phosphate fertilization strategies affected soil P fractions over 17 years and to identify best management practices for improving labile P fractions. The experiment was conducted in a very clayey Rhodic Ferralsol (Oxisol) with initially very low P availability, during 17 years under soybean and corn, fertilized with 35 kg P ha?1 year?1 . Treatments were two soil management systems (CT-conventional tillage and NT-no-till) and four phosphate fertilization strategies (TSP ? triple superphosphate or RRP ? reactive rock phosphate, applied to the crop furrow or broadcast). Soil samples were taken at five depth layers, and organic (Po), inorganic (Pi), and total P (Pt) were determined by Hedley?s sequential fractionation. CT resulted in a more homogeneous distribution of Pi fractions throughout the soil profile, while under NT there was a steep depth gradient characterized by Pi accumulation in the fertilizer application zone. NT resulted in accumulation of Pi in more labile fractions and higher accumulation of Po physically protected by aggregation, both compared to CT. Also, under NT with RRP, there was a great accumulation of Pi associated with calcium (HCl Pi) compared to TSP, especially when the fertilizer was broadcast applied. An accumulation of Po down to 20 cm (CT) and 10 cm (NT) was also detected, compared to Cerrado natural soil. NT and RRP positively affected legacy P fractions and can be recommended as strategies to improve P fertilizer use efficiency. Keywords: no-tillage, P fractionation, legacy P, P source, P distribution

Phosphorus fractions in Andisol and Ultisol inoculated with Bacillus thuringiensis and phosphorus uptake by wheat

Only a small portion of soil phosphorus (P) is available to plants on a short-term basis, and therefore, P taken up by crops in one growing season is small compared to total P (Pt) content of the soil. A group of soil microorganisms capable of transforming insoluble P into soluble and plant accessible forms. The objective of this study was to evaluate the changes in soil P-pools and P uptake by wheat crops as influenced by inoculation with Bacillus thuringiensis in two soils (Andisol and Ultisol), the experiment was conducted in pots under greenhouse conditions using a completely randomized design. Wheat plants were inoculated and re-inoculated at 20 and 46 days after sowing, respectively, with B. thuringiensis; and, plant sampling were performed after 46, 66 and 87 and soil at 87 days based on the Zadoks growth scale, and the soil was submitted by Hedley’s P fractions. The inoculation with B. thuringiensis affected significantly some P organic P (Po) and inorganic P (Pi) fractions in both soils (Andisol and Ultisol), improved P uptake by wheat crop in (Ultisol) and decreased significantly in (Andisol). The positive effect was more consistent in Ultisol than in Andisol, this strain can be solubilized P fraction extracted with conc. HCl-Po and HCl 1 mol.

Biochar and phosphorus fertilization improved soil quality and inorganic phosphorus fractions in saline-alkaline soils

ABSTRACT The establishment of high-yielding agricultural production systems is severely restricted by low soil organic carbon (SOC) and high Na+ concentration in saline-alkaline soils. In order to confirm the effects of biochar and phosphorus (P) fertilization on SOC sequestration, soil physical structure and inorganic P (Pi) fractions, as well as optimize the amount of P fertilizer, a field experiment was designed with two factors: with biochar at 0 (C0), 1% (C1) and 3% (C2); with P at 0 (P0), 64 (P1) and 128 kg ha−1 (P2). The results indicated that biochar input enhanced SOC, however, the effect of P application on SOC and soil physical structure were negligible. Compared to C0, SOC was increased by 98–113% for C1 and 180–195% for C2. Due to the SOC enhancement and reduction of soil Na+ concentration, biochar input decreased ρb, increased MWD and WSMA. For Pi fractions, soil Olsen-P, Ca2-P, Ca8-P, Fe-P and Al-P were increased, mainly due to the direct supply, retention and the improvement of biological availability. Overall, C2P1 was the most efficiency treatment to enhance SOC, improve soil physical structure, and C2P2 avail to increase the supply capacity of soil P, but had no significant difference with that in C2P1.

Organic and inorganic forms of phosphorus in soils amended with sugar cane filter cake

AbstractStudies of phosphorus (P) behaviour in soils receiving sugar cane filter cake are important for determining doses, its contribution to P nutrition and maximizing fertilizer efficiency, especially in soils with low P availability. This study aimed to assess organic and inorganic forms of P in soils treated with sugar cane filter cake, and the relationship between these and plant available P. Soil inorganic (Pi) and organic (Po) phosphorus forms, organic carbon, pH and resin P were measured in two soils; a Typic Hapludox with clay texture and an Arenic Hapludult with loamy sand texture, subject to three fertilizer treatments (nil P control and 100 mg P dm−3 as filter cake and triple superphosphate). Inorganic P was fractionated to soluble/loosely bound, Al‐bound, Fe‐bound, occluded and Ca‐bound P forms. Organic P was fractionated into labile, fulvic, humic and residual Po forms. Plant dry matter yield and P uptake were also determined. Both fertilizers increased the Al‐ and Fe‐bound P fractions, with the increases caused by triple superphosphate 14.7 and 7.2 mg kg−1 higher than filter cake, respectively. Filter cake increased the fulvic Po by 40.9 mg kg−1, while triple superphosphate increased it by 28.5 mg kg−1, in the fine‐textured soil. Al‐, Fe‐bound and labile Po fractions in both soils had significant correlations (p &lt;. 01) with plant absorbed P (r = .75, .84 and .54, respectively). Filter cake resulted in lower Pi fractions and availability, and it has potential to partially replace mineral P fertilizer in fine‐textured soils and, entirely, in coarse‐textured soils.

Methodology and validation of a new tandem mass spectrometer method for the quantification of inorganic and organic 18O-phosphate species.

Phosphorus (P) fertilizers are crucial to achieve peak productivity in agricultural systems. However, the fate of P fertilizers via microorganism incorporation and the exchange processes between soil pools is not well understood. 18Oxygen-labelled phosphate (18O- Pi) can be tracked as it cycles through soil systems. Our study describes biological and geochemical P dynamics using a tandem mass spectrometry (MS/MS) method for the absolute quantification of 18O- Pi. Soil microcosms underwent three treatments: (i) 18O- Pi, (ii) unlabelled phosphate (16O- Pi) or (iii) Milli-Q control, dissolved in a bio-stimulatory solution. During a 6-week series the microcosms were sampled to measure P by Hedley sequential fractionation and DNA extraction samples digested to 3′-deoxynucleoside 5′-monophosphates (dNMP). A MS/MS attached to a HPLC analyzed each P-species through collision-induced dissociation. The resin-extractable and bicarbonate 18O- Pi and 16O- Pi fractions displayed similar precipitation and adsorption-desorption trends. Biotic activity measured in the NaOH and dNMP fractions rapidly delabelled 18O- Pi; however, the MS/MS measured some 18O that remained between the P backbone and deoxyribose sugars. After 6 weeks, the 18O- Pi had not reached the HCl soil pool, highlighting the long-term nature of P movement. Our methodology improves on previous isotopic tracking methods as endogenous P does not dilute the system, unlike 32P techniques, and measured total P is not a ratio, dissimilar from natural abundance techniques. Measuring 18O- Pi using MS/MS provides information to enhance land sustainability and stewardship practices regardless of soil type by understanding both the inorganic movement of P fertilizers and the dynamic P pool in microbial DNA.

Phosphate fertilizer addition increases the movement distance and content of the acid soil inorganic phosphorus fractions at green manure microsites

To investigate the movement and content of the acid soil Pi fractions at different distances from the green manure (GM) application site at a GM microsite, an incubation experiment was conducted. Stylosanthes GM (10 or 40 ton/ha) was applied with or without phosphate fertilizer (monocalcium phosphate, MCP) at a concentration of 44 kg/ha P, which was laid on the surface in soil cylinders. The GM/fertilizer and soil were incubated for 14 and 28 d. The results indicated the movement distance and content of the Pi fractions (Al-, Fe-, and Ca-associated Pi as well as occluded P) in the acid soil microsite were significantly increased after the addition of MCP; however, the movement distances of the Pi fractions were all less than 3 mm after incubation for 28 d. This information will improve the efficiency of combined P and GM use and decrease the environmental load due to P pollution caused by GM and phosphate fertilizer.

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.

Dinamika Fraksi Fosfor dan Sifat Kimia Tanah Sawah Terkait Indeks Pertanaman Padi Sawah dan Praktik Pengairan

Dinamika fraksi-fraksi P dan sifat kimia lainnya pada tanah sawah terkait dengan indeks pertanaman padi sawah (IP) dan kadar air tanah pada kondisi lapang (KAL). Penelitian eksploratif ini bertujuan mengevaluasi pengaruh IP berbeda yang direpresentasikan oleh dosis ameliorasi dan pemupukan serta KAL sebagai representasi praktik pengairan yang diaplikasikan oleh petani pada tanah sawah penelitian terhadap dinamika fraksi P, sifat kimia tanah lainnya dan produksi padi sawah. Contoh tanah komposit diambil pada lahan sawah yang sedang dibudidayakan petani dengan IP 100%, 200% dan 300% pada periode 7, 9, 11 dan 13 minggu setelah penggenangan awal. Fraksionasi P dilakukan untuk memperoleh fraksi PH2O, PNaHCO3-inorganik (Pi), PNaHCO3-organik (Po), PNaOH-Pi, PNaOH-Po dan PHCl tanah. Nilai KAL pada keempat waktu pengambilan contoh tanah pada IP 100% &lt; IP 200% ≈ IP 300%. Sifat-sifat kimia dan fraksi-fraksi Po pada IP 100% cenderung menurun, sedangkan fraksi-fraksi Pi cenderung meningkat dengan peningkatan KAL. Dinamika fraksi-fraksi P tanah pada ketiga IP terutama ditentukan oleh Corg. Peningkatan Corg tanah menurunkan kadar Pi pada IP 100% dan Po pada IP 200%, tetapi meningkatkan Pi pada IP 300%. Penurunan dosis P2O5 dan peningkatan dosis jerami menurunkan Eh tanah. Faktor yang paling berpengaruh terhadap produksi padi sawah adalah KAL.&#x0D; Kata kunci : Pupuk P, jerami padi, kadar air lapang tanah, fraksi P tanah

Differences in main processes to transform phosphorus influenced by ammonium nitrogen in flooded intensive agricultural and steppe soils

Exogenous ammonium nitrogen (AN) fertilization/deposition and the subsequently induced soil acidification, might exacerbate soil phosphorus (P) transformation and mobility, whereas poor understanding in abiotic and biotic processes still existed between intensively cultivated soil with high proportion of legacy inorganic P (Pi) in comparison to natural steppe soil with high proportion of organic P (Po). Column batch flooded experiment using vegetable (VEG) and steppe (STE) soils was conducted to investigate the P transformation and mobility influenced by 60-day intermittent elution with an (1500 mg N kg−1) solution or an acid sulfate (107 mmol H+ kg−1) solution. The results showed that AN elution significantly decreased the contents of all Pi fractions and strengthened Pi leaching, whereas acid elution increased the contents of Al-Pi, Fe-Pi, and reductant-soluble Pi and reduced P leaching in VEG soil. In contrast, AN elution increased the contents of soluble-Po and Al-(Pi + Po) and decreased Ca-P and Fe-Pi, no effects on P leaching, whereas acid elution increased the contents of soluble-(Pi + Po), Al-(Pi + Po), Fe-(Pi + Po) and reduced P leaching in STE soil. Variances analysis showed that pH and microbial biomass carbon were the most important factors to predict the P composition of the VEG and the STE soil, respectively. This indicated that AN elution released the soil mineral-bound phosphate with ammonia oxidation coupled with Fe(III) reduction, besides the same chemical influences on Fe/Al oxides as acid elution in VEG soil; while predominantly affected biochemical/biological processes of soil P by changing microbial biomass and enzyme activities in STE soil.