Activity Coefficient Of Phosphorus Research Articles

Sustainable regulation of calcium magnesium phosphate and rapeseed cake on soil-tea system in Mount Lushan, China.

Lushan Yunwu tea quality is limited by soil acidity and sterility. This article examined a 3-year localization experiment at 1100m altitude to demonstrate the sustainable management of conditioners, calcium magnesium phosphate (P), rapeseed cake (C), and combination application (P + C) by one-time application on the soil-tea system in Mount Lushan. The study found that conditioners (P, C, P + C) reduced soil acidification and maintained a pH of 4.75-5.34, ideal for tea tree development for 3years. Phosphorus activation coefficient (PAC), nitrogen activation coefficient (NAC), and organic matter (OM) content were significantly higher (P < 0.05) in the first year after conditioner treatment, with P + C being the best. After P + C, PAC, NAC, and OM rose by 31.25%, 47.70%, and 10.06gkg-1 compared to CK. In comparison to the CK, tea's hundred-bud weight (BW), free amino acids (AA), tea polyphenols (TPC), and chlorophyll (Chl) content of P + C treatment got 29.98%, 14.41%, 22.49%, and 28.85% increase compared to that of the CK, respectively. In the second year, the three treatments of P, C and P + C still had significant moderating effects on the physicochemical properties of the soil and the quality indexes of the tea leaves. The PAC of the soil under the three treatments increased by 0.06%, 0.07% and 0.18%, respectively, as compared to the control.P + C increased BW, AA, TPC and Chl of tea for 2years. Three conditioners had 2-year regulatory impacts on soil fertility indicators, tea output, and quality. C and P + C both increased soil OM by 18.59% and 21.78% compared to CK in the third year, outperforming P treatment. Redundancy analysis revealed that the primary physicochemical factors influencing tea output and quality were soil OM and pH, with available phosphorus, urease, acid phosphatase, and available nitrogen following closely afterwards.

Sustainable regulation of calcium magnesium phosphate and rapeseed cake on soil-tea system in Mount Lushan, China.

Lushan Yunwu tea quality is limited by soil acidity and sterility. This article examined a 3-year localization experiment at 1100m altitude to demonstrate the sustainable management of conditioners, calcium magnesium phosphate (P), rapeseed cake (C), and combination application (P + C) by one-time application on the soil-tea system in Mount Lushan. The study found that conditioners (P, C, P + C) reduced soil acidification and maintained a pH of 4.75-5.34, ideal for tea tree development for 3years. Phosphorus activation coefficient (PAC), nitrogen activation coefficient (NAC), and organic matter (OM) content were significantly higher (P < 0.05) in the first year after conditioner treatment, with P + C being the best. After P + C, PAC, NAC, and OM rose by 31.25%, 47.70%, and 10.06gkg-1 compared to CK. In comparison to the CK, tea's hundred-bud weight (BW), free amino acids (AA), tea polyphenols (TPC), and chlorophyll (Chl) content of P + C treatment got 29.98%, 14.41%, 22.49%, and 28.85% increase compared to that of the CK, respectively. In the second year, the three treatments of P, C and P + C still had significant moderating effects on the physicochemical properties of the soil and the quality indexes of the tea leaves. The PAC of the soil under the three treatments increased by 0.06%, 0.07% and 0.18%, respectively, as compared to the control.P + C increased BW, AA, TPC and Chl of tea for 2years. Three conditioners had 2-year regulatory impacts on soil fertility indicators, tea output, and quality. C and P + C both increased soil OM by 18.59% and 21.78% compared to CK in the third year, outperforming P treatment. Redundancy analysis revealed that the primary physicochemical factors influencing tea output and quality were soil OM and pH, with available phosphorus, urease, acid phosphatase, and available nitrogen following closely afterwards.

Phosphorus transformation and balancing under a long-term rice-rice cropping system in an inceptisol of India

Phosphatic fertilizers applied to soil, with time, alters into different insoluble soil phosphorus fractions. Since P fertilizers are expensive and raw material supplies are limited, it is essential to evaluate changes in phosphorus fractions and balance in soil in order to determine appropriate phosphorus fertilizer management strategies for sustainable yields. A long-term experiment (20 years) was conducted in an inceptisol with rice-rice cropping system. Soil samples were collected from six treated plots and one fallow; analyzed for phosphorus fractions using sequential extraction method. Phosphorus balance was computed. The results reveled that yield was 51.5, 112.0, 147.7 and 116.7% higher under 50% NPK, 100% NPK, 150% NPK and 100% NPK + FYM over control. Irrespective of the treatments, the abundance of the various fractions of phosphorus (P) in soil as follows: Organic P (32.4% of total P) > Calcium-P (27.76% of total P) > Mineral P (24.17% of total P) > Iron-P (6.65% of total P) > Aluminum-P (3.46% of total P) > Reductant soluble P (3.22% total P) > Occluded P (1.44% of total P) > Saloid P (0.89% total P). Phosphorus activation coefficient (%) was recorded higher under 150% NPK followed by 100% NPK + FYM > 100% NPK > 50% NPK > 100% N > control > Fallow. Hence, 100% NPK + FYM treatment has maintained phosphorus fractions in a good proportion and sustainable yields under rice-rice cropping system.

Response of green chiretta to different bio-fertilizers and their effect on phosphorus availability in the soil

When cultivating medicinal plants, the use of chemical substances such as pesticides and chemical fertilizers should be avoided, as these can be contaminated with hazardous substances. Bio-fertilizers are a good alternative for growing herbs, as they are produced from organic materials that contain fewer hazardous substances. The aim of this study was to investigate the effects of different bio-fertilizers on growth, yield, andrographolide content, nutrient accumulation, and different pigments in green chiretta. In addition, the effectiveness of bio-fertilizers on the convertible phosphorus content in the soil was investigated. The experimental design was a completely randomized design (CRD) with four treatments and four replicates. The details of the experiment were 1) control (no bio-fertilizer), 2) phosphate-solubilizing microorganisms (PSMs), 3) plant growth promoter, and 4) mycorrhiza. The findings revealed that the application of PSMs provided the highest leaf dry weight (yield) of green chiretta (20.8±3.58 g/plant). This treatment also gave the highest chlorophyll a, b and total chlorophyll content (699±70, 178±24, 880±94 mg/sqm, respectively) and andrographolide yield (0.38±0.06 g/plant). Regarding the phosphorus content in the soil, the PSMs application showed the highest available phosphorus and the highest phosphorus activation coefficient (PAC) in the soil, namely 52.0±4.76 mg/kg and 4.22±0.32 percent, respectively. These results indicate that the use of PSMs as a bio-fertilizer is most suitable for the cultivation of green chiretta, especially when this plant grows on acid sulfate soils.

Effect of lime application on phosphorus adsorption and desorption in post-active acid sulfate soil, Thailand

The application of lime is the general method of improving acid sulfate soils. However, if a lot of lime is applied, it can reduce the bioavailability of nutrients in the soil, especially phosphorus. The objective of this study was to investigate the effects of liming at different rates on the availability, adsorption, and desorption of phosphorus in two post-active acid sulfate soils (Ay and Se). The experiment was performed in the laboratory. The experiment was laid out in a completely randomized design (CRD) with four treatments and three replicates, i.e., the application of lime at a rate of 0 (control), 0.5, 1.0, and 2.0 times the lime requirement (LR). The lime requirements of the soils in the Ay and Se were 5,690 and 12,250 kg CaCO3/ha, respectively. The finding revealed that increasing the amount of lime could increase soil pH, available phosphorus, and the phosphorus activation coefficient. Application of lime at a dosage of 1.0-2.0 LR resulted in the highest phosphorus adsorption maximum (Qm) (380 mg/kg), while 0.5 LR resulted in the lowest Qm (353 mg/kg) in Se soil only. As lime dosage increased, phosphorus desorption maximum (Dm) and phosphorus desorption ratio (Dr) increased, with 2.0 LR yielding the highest values (124 mg/kg and 23.6 percent for Ay soil, and 77.3 mg/kg and 20.3 percent for Se soil, respectively). The results suggested that applying lime according to the lime requirement test, especially 2.0 LR, is the best option to promote the release of phosphorus in post-active acid sulfate soils.

Livestock movement driven phosphorus transitions as core drivers of grassland vegetation dynamics

The Banni grasslands, located in the Kachchh district of India, have experienced significant degradation and a decrease in grassland productivity. Phosphorus is a crucial nutrient for grassland productivity, and its availability is often limited in these ecosystems. The study is a maiden attempt to understand the link between phosphorus availability, measured by the phosphorus activation coefficient (PAC), phosphate solubilizing microorganisms (PSM), vegetation patterns, indicated by normalized difference vegetation index (NDVI) and its relationship with livestock movement. Soil samples were collected from 45 locations spread across the three divisions of Banni grassland, and various soil parameters including phosphorus content, organic carbon, and microbial activity were analyzed. The results showed that the concentration of available phosphorus (AP) varied significantly among different divisions of the grassland, with division 1 having the highest AP concentration. The phosphorus activation coefficient (PAC) was also highest in division 2. Additionally, PSM diversity was significantly different among divisions, with division 2 exhibiting the highest PSM values. The NDVI values, representing vegetation density, varied across divisions, with division 1 having the highest overall NDVI. Statistical analysis revealed significant positive correlations between PAC, PSM, and NDVI. The research emphasizes the significance of PSM driven phosphorus availability in influencing vegetation dynamics within the Banni grassland ecosystem. The movement of livestock emerges as a key factor in introducing organic matter and phosphate solubilizing microorganisms, thereby facilitating the conversion of total phosphorus (TP) into forms accessible to plants. The study indicates that implementing effective phosphorus management practices, taking into account livestock movement and organic contributions, could enhance grassland productivity and ensure the long-term sustainability of the ecosystem. These findings offer valuable insights for more holistic and nuanced understanding of the complex relationships between phosphorus availability, phosphate solubilizing microorganisms, vegetation patterns, and sustainable management in the Banni grasslands and potentially in other ecosystems facing similar challenges.

Repercussions of fertilization with boron and enriched organic manure on soil chemical characteristics, boron and phosphorus fractions, and French bean productivity in an acidic Inceptisol of eastern Himalaya

Boron (B) and phosphorus (P) in the soil are dispersed in numerous geochemical fractions (forms) which depend primarily on physicochemical properties of soils, climate and management exercises, and each form is in dynamic equilibrium with each other. The study of these fractions caters for an advanced understanding of their bioavailability to plants. To better elucidate how the nexus of B and enriched farmyard manure (EFYM) synergy influences the soil chemical characteristics, B and P fractions, and French bean pod production, an investigation was undertaken during the three consecutive years from 2015 to 18 in acidic Inceptisol of eastern Himalaya. The experiment was laid out in symmetrical factorial design and the imposed treatments comprised four graded levels each of B (0, 0.5, 1 and 1.5 kg ha−1) and EFYM (0, 5, 10, 15 Mg ha−1). The results implied that the conjoint (interaction) application of a higher rate of B @ 1.5 kg ha−1 and EFYM @ 15 Mg ha−1 (B1.5EFYM15) levels were superior to other treatment combinations in improving soil chemical characteristics including pH, electrical conductivity (EC), soil organic carbon content (SOC) and reducing the concentration of iron oxides (Fe2O3) and aluminium oxides (Al2O3). Similarly, there was a significant increase of B fractions, total B, Hot water-soluble B (HWS-B), P fractions, total P and available P in the soil. Correspondingly, the maximum average French bean pod yield (FBPY) (12.04 Mg ha−1) was achieved under plots fertilized with B1.5EFYM15, while the minimum FBPY (7.82 Mg ha−1) was logged under B0EFYM0 (control). The correlation study exhibited a significant positive correlation amongst EC, SOC and cation exchange capacity (CEC) with both the B and P fractions. Of the various B fractions, readily soluble B (RSB) followed by organic bound B (OBB) was the most overriding B fraction affecting the available B. Likewise, concerning the P fraction, Resin P followed by bicarbonate extracted inorganic and organic P fractions (BiCPi and BiCPo), was realized to be the overriding P fraction implicated in affecting the available P. Higher phosphorus activation coefficient (PAC) was logged in those plots fertilized with B1.5EFYM15. The inclusive findings indicated that the addition of the successive increase in the level of B and EFYM up to B1.5EFYM15 can enhance the status of soil characteristics, diverse B fractions, total B, Hot water-soluble B (HWS-B), P fractions, Total P and available P and ultimately the FBPY in an acidic Inceptisol of eastern Himalaya.

Significant Effects of Long-Term Application of Straw and Manure Combined with NPK Fertilizers on Olsen P and PAC in Red Soil

The application of manure (M) and straw (S) will increase the Olsen P and phosphorus activation coefficient (PAC) in soil. Clarifying the increasing trend of Olsen P and PAC is crucial for rational fertilization. This study fitted the equation between the accumulated P surplus, Olsen P, and PAC in four treatments for 28 years and analyzed the changes and rates of P fractions. The results showed Olsen P and PAC increase linearly with NPK and NPKS treatments; for every 100 kg ha−1 of P surplus, Olsen P increased by 5.9 and 6.7 mg kg−1, and PAC increased by 0.52% and 0.50%. With M and MNPK treatments, the sigmoid curve equation was the best fitting method. The equilibrium values were 167 and 164 mg kg−1 for Olsen P, and 10.4 and 10.2 mg kg−1 for PAC. There was a correlation between Al-P, Ca2-P, Resin-P, NaOH-Pi, C/N, SOC, and pH, which had the highest interpretation rates for Olsen P and PAC. Manure is significantly better than straw in improving Olsen P in red soil. It is recommended to reduce the amount of manure applied for a long time to avoid a zero increase in Olsen P.

Long-Term Organic Manure Substitution Increases Yield and Phosphorus Use Efficiency in a Double-Rice System by Altering Soil Phosphorus Uptake and Apparent Balance

The excessive use of chemical phosphorus (P) fertilizer can lower grain yield and P use efficiency (PUE) by aggravating soil acidity. Substituting organic manure for chemical fertilizer can alleviate the problem, although the long-term effect of organic manure incorporation is unknown. We conceptualized that substituting organic manure for chemical fertilizer may result in higher crop yields and PUE. Therefore, the impact of long-term fertilizer treatments: (i) CK (control), (ii) PK (phosphorus and potassium fertilizer), (iii) NP (nitrogen and P fertilizer), (iv) NK fertilizer, (v) NPK fertilizer, and (vi) NPKM (30% NPK fertilizer plus 70% manure) on rice yield, PUE, P uptake, and apparent balance (APB) was investigated. The results showed that rice yield under different fertilizer treatments ranged from 6.2 to 11.8 t ha−1 (1984–1995), 7.9 to 12.7 t ha−1 (1996–2007), and 6.6 to 12.8 t ha−1 (2008–2018). The rice yield under NPKM was greatly improved compared to other treatments, except with that of NPK (1984–1995). Soil organic carbon (SOC), available P and phosphorus activation coefficient (PAC) under NPKM were significantly higher than other treatments during 1984–2018. Soil pH (1984–2018) was greatly higher under CK and NPKM than under other treatments. Soil total P under PK, NP, NPK, and NPKM was significantly higher than under CK and NK (1984–2018). Compared to other treatments, P uptake was significantly higher under NPKM, except with that of NPK (1984–1995 and 2008–2018). The average PUE (1984–2018) was 10.7, 20.2, 36.1, and 44.2 kg kg−1 under PK, NP, NPK, and NPKM, respectively. The APB under NPKM was significantly lower as compared to PK, NP, and NPK treatments. Therefore, we conclude that in addition to improving soil organic carbon, cations inputs from organic manure can be a factor for the increase in soil pH, making organic manure substitution for chemical fertilizer a more efficient strategy for increasing PUE and crop yield.

Effects of straw mulching and phosphorus application on forms and availability of soil phosphorus in hilly dryland of Sichuan, China

We conducted a two-factor split-plot experiment to examine the alteration of soil inorganic phosphorus forms and phosphorus availability under straw mulching and phosphorus fertilizer rates. The main factor was straw mulching and non-mulching, while the sub-factor was phosphorus supply rates, including 0, 75, and 120 kg·hm-2. We analyzed the characteristics of phosphorus adsorption-desorption, the content of inorganic phosphorus components and their relationship with available phosphorus in hilly upland purple soil in Sichuan. Results showed that compared with the non-mulching, the maximum phosphorus adsorption capacity of straw mulching was notably decreased by 7.7% and 7.4% in the two experimental years from 2018 to 2020. The degree of phosphorus saturation and readily desorbable phosphorus of straw mulching were remarkably increased by 35.4% and 21.6% in 2019 and 18.6% and 35.2% in 2020, respectively. The maximum buffer capacity of phosphorus was not different between straw mulching and non-mulching. The maximum phosphorus adsorption capacity and maximum buffer capacity of phosphorus were significantly lower, and the degree of phosphorus saturation was notably higher in the phosphorus application treatment than that under no phosphorus treatment. The readily desorbable phosphorus increased with the increases of phosphorus rates. The contents of dicalcium phosphate (Ca2-P), octa-calcium phosphate (Ca8-P) and iron phosphorus (Fe-P) in straw mulching treatment were notably higher than those in non-mulching treatment, whereas the content of aluminum phosphorus (Al-P) significantly lower under the straw mulching. Meanwhile, the contents of occluded phosphate (O-P) and apatite (Ca10-P) tended to decrease in the straw mulching compared with that under the non-mulching. Phosphorus application increased the content of different inorganic phosphorus components. Compared with the non-mulching, soil available phosphorus content and the phosphorus activation coefficient of straw mulching remarkably increased by 23.2% and 21.3% in 2019, and 9.6% and 8.9% in 2020, respectively. Soil available phosphorus content and phosphorus activation coefficient increased with the increases of phosphorus rate. Results of regression analysis showed that the contribution of inorganic phosphorus components to the availability of available phosphorus in purple soil was Ca2-P > Fe-P > Al-P > Ca8-P > Ca10-P > O-P. Therefore, straw mulching combined with a reasonable phosphorus fertilizer rate could promote the decomposition and transformation of insoluble soil phosphorus to moderately active or easily absorbed phosphorus forms, reduce soil phosphorus adsorption, stimulate soil phosphorus desorption, and improve soil phosphorus availability. Based on the economic benefits, phosphate fertilizer application at the rate of 75 kg·hm-2 combined with straw mulching was recommended in Sichuan hilly dryland, which would be more beneficial in improving soil phosphorus availability.

The distribution, effectiveness and environmental threshold of soil aggregate phosphorus fractions in the sub‐alpine region of Southwest China

AbstractThis article is a study of total phosphorus (TP), available phosphorus (AP) and phosphorus (P) fractions of soil aggregates along an altitude gradient in the sub‐alpine region of Southwest China. We conclude that soil aggregate TP and AP contents are higher at 3980 m and 3347 m; there are no significant differences in soil aggregate TP at any altitude (p &gt; 0.05); the AP and phosphorus activation coefficient (PAC) are higher in 0.25–0.5 mm aggregate. Soil aggregates TPi &gt; TPo at 3009 m and TPo &gt; TPi at 3347, 3654 and 3980 m. Using multiple stepwise regression analysis, we conclude that NaOH‐Pi is the key fraction of AP supply, NaHCO3‐Pi and NaOH‐Pi are important fractions of CaCl2‐P. Through piecewise linear fitting of soil aggregate AP and CaCl2‐P, the soil P environmental threshold obtained is 27.766 mg kg−1 in this region. Also we got &lt;0.25 mm, 0.25–0.5 mm aggregates at 3980 m which have high soil P loss risk. Our study fills in gap about the distribution of P fraction in aggregates and effects of soil P fraction for AP and CaCl2‐P in high‐altitude areas. Our study provides a reference and scientific basis for understanding the soil aggregate P storage capacity and the biological effectiveness of P fractions at high altitudes. Our study on the P environmental threshold provides a reference for soil P storage capacity. Our study provides a reference value for the soil P loss risk management, and sustainable development of soil ecosystems in the sub‐alpine region of Southwest China.

The Variation of Soil Phosphorus Fractions and Microbial Community Composition under Consecutive Cucumber Cropping in a Greenhouse

The distribution of phosphorus (P) fractions in soil plays a decisive role in soil P bioavailability; however, the characteristics of soil P fractions under consecutive cropping in a solar greenhouse remain unclear. To evaluate the effects of the long-term successive vegetable cropping on soil P fractions and the microbial community composition in greenhouse soil, a continuous long-term cropping experiment was conducted using cucumber (Cucumis sativus L.) in a solar greenhouse starting from 2006 to 2018. Soil P fractions and the microbial community composition were determined using the Hedley continuous extraction method and the phospholipid fatty acid (PLFA) method, respectively, in the 1st, 9th, 13th, and 21st rounds of cultivation. The soil total phosphorus (TP) content increased from 0.90 g·kg−1 in the 1st round to 3.07 g·kg−1 in the 21st round of cucumber cultivation. With an increase in continuous cropping rounds, soil available phosphorus (AP) increased and the phosphorus activation coefficient (PAC) decreased, with no significant difference between the 13th and 21st rounds. After 21 rounds of continuous cropping, the soil organic matter (SOM) content was 16.34 g·kg−1, 1.42 times that of the 1st round. The abundance of soil bacteria, actinomycetes, Gram-negative bacteria (G−), Gram-positive bacteria (G+), and total PLFAs initially increased with continuous cropping rounds, but then decreased significantly, and the ratios of fungi:bacteria (F/B) and G+/G− bacteria also increased significantly with continuous cropping rounds. The contents of soil labile P, moderately labile P, and non-labile P increased significantly over 21 continuous cropping rounds. Together, these results demonstrate that long-term continuous cropping can directly lead to the accumulation of P fractions, but it can also affect the abundance of actinomycetes through SOM enrichment, which indirectly leads to the accumulation of non-labile P. This study provides a theoretical basis for future soil P fertilizer management and vegetable production sustainability.

Phosphorus transitions in traditional eco-knowledge versus chemical based agri-amendment systems of stress-prone semi-arid tropics: Finding the real game-changer

Fixation of Phosphorus into locked forms hampers the availability of this important soil element. Phosphate Solubilising Microorganisms (PSM) play an important role of solubilisation and mineralization of these fixed forms into bio-available forms through reactions that are complex but provide simple solutions to P deficiency in soils. Semi-arid soil may have high total phosphorus concentrations but as most of the P is in an unavailable form, it leads to deficiency of this essential macronutrient in the crop. The use of microbial inoculants (biofertilisers) that possess the Phosphate solubilizing activities in agricultural soils is considered as an eco-friendly alternative to chemical based P fertilizers. The present study is a first of its kind attempt to understand the impact of Traditional Ecological Knowledge (TEK) (A1) vis-à-vis conventional chemical intensive integrated (A2) based agriculture amendment systems in altering/modifying the Phosphorus dynamics of the soil in the semiarid tropical region of Kachchh, Western India. The study was carried out for the pre, mid and post-harvest phases of crops for six seasons spread across 4 years.Higher Phosphorus Activation Coefficient (PAC), which is the ratio of available P (AP) to total P (TP) was observed in A1, that coincided with higher soil organic carbon (SOC) as well, across all seasons. The present study tried to answer questions as to how indigenous knowledge-based systems suited to local supply/demand complex system are precursors/indicators of a better microcosm in agriculture ecology studies that owing to its organic matter content improves SOC and PAC and in turn the overall P availability.

Biochar impacts on phosphorus cycling in rice ecosystem

Biochar can affect the phosphorus (P) cycle in the rice ecosystem through various pathways. Pot experiments were conducted to investigate the risk of P contamination and the P supply rate to crops with the application of maize straw-derived biochar (BM) and P fertilizer. The biochar increased 18.3% and 8.45% total phosphorus (TP) concentration in the low-P level and high-P level soils, respectively. The addition of biochar increased the phosphorus activation coefficient (PAC) by 9.00% at low-P levels, while the PAC was reduced by 10.4% at high-P levels. The results suggested that biochar could serve as either a source or a sink for P. The P concentration in the dithionite-citrate-bicarbonate (DCB) extracts on the root surfaces in biochar-treated soils increased by 467.1% and 46.1% in the low-P level and high-P level soils, respectively. It may cause by the acidification of soils near the root and the increase in Fe plaque. The results also showed the addition of biochar increased the DCB-P concentration and subsequently promoted rice growth. The biochar additions enhanced bacterial community richness and diversity, while the P supplementations inhibited bacterial growth. Redundancy analysis (RDA) showed that available nitrogen (AN), Fe-P, Ca-P, P uptake and, DCB extracted Fe (DCB-Fe) were significantly correlated with microbial community composition and explained 46.8%, 37.1%, 38.0%, 37.5% and 36.7% of the total community variability, respectively. This study provided evidence that biochar might affect the P cycle by impacting the microbial community composition and the Fe-reducing processes in the rice ecosystem.

Biochar addition to soil highly increases P retention and decreases the risk of phosphate contamination of waters

Phosphorus loss from agricultural soils is an important cause of eutrophication. The diversity of soil conditions and biochar feedstocks induces various effects on P retention after biochar application. Here, the effect of biochars at three application rates (0/1/5%, w/w) on P sorption and desorption in paddy soil with two levels of P application, 0 and 60 mg kg−1, were evaluated. Results show a notable reduction of the phosphorus activation coefficient (PAC, AP (available P)/TP (total P)) with biochar addition, thus suppressing the risk of P loss by the formation of Ca–P and Fe–P. The Langmuir sorption maximum (Qm) increased by 20.7–21.6%, 18.5–40.6% and 14.1–31.2% in amendments of biochar obtained from pig manure, corn straw and pine, respectively. The P sorption index (PSI) and maximum buffer capacity (MBC) in soils with biochar obtained from different feedstocks ranged in order from pig manure > corn straw > pine. Pig manure biochar had no significant effect on P retention due to changes in Ca/Mg/P by adjusting the pH, electronegativity and P content, resulting in anion repulsion. However, pine-derived biochar was favorable for the accumulation of thermally stable carbon dominated by aromatic carbon as well as lower alkalinity, promoting P sorption and suppressing P availability, especially at low P levels. In this study, we show that adding woody biochar to soil can simultaneously suppress nonpoint source pollution and reduce P fertilizer inputs.

Impact of slag composition activity on the behavior of phosphorus in the smelting reduction process of high-phosphorus iron ores

Apply the slag ion theory to calculate the distribution ratio formula of phosphorus in the smelting reduction process of high-phosphorus iron ores, according to which it is found that main factors affecting the distribution ratio of phosphorus are ferrous oxide activity, phosphorus capacity of slag, and phosphorus activity coefficient in molten iron. Through thermodynamic theory and experimental research on dephosphorization, it comes out that the distribution ratio of phosphorus increases with the increase of ferrous oxide activity in slag, the linear regression slope is 1.65, approximate to 2.5 in the classic formula. With the increase of basicity, the phosphorus capacity of slag would increase. Both dissolved oxygen and dissolved carbon in molten iron can increase the activity coefficient of phosphorus in molten iron. It would have beneficial to the distribution and the transfer of phosphorus to slag. Both the weighted basicity of slag (B) and the distribution ratio of phosphorus (Lp) can accurately describe the distribution ratio of phosphorus in the smelting reduction process of high-phosphorus iron ores.

Characterizing differences in the phosphorus activation coefficient of three typical cropland soils and the influencing factors under long-term fertilization.

The phosphorus activation coefficient (PAC, the ratio of available P to total P) is an important indicator of soil P availability and the transformation of P fractions. Understanding the details of the PAC is useful to estimate soil available P status and to provide P management guidance. In this research, soils from five long-term (23 years) fertilization treatments in three croplands were selected to examine the relationships between the PAC and P fractions and to analyse the influencing factors. PAC was affected by both soil types and fertilization treatments. Compared to the unfertilized control (CK) treatment, long-term P application significantly increased the PAC, all of the inorganic P (Pi) fractions and most of the organic P (Po) fractions in all the three soils, particularly in chemical fertilizer combined with manure treatment (NPKM). The PAC was significantly correlated to all of the Pi fractions proportions (P<0.05) except for Dil. HCl-Pi and Conc. HCl-Pi. Compared with CK, the chemical P and chemical P combined with manure treatments increased the ratio of total Pi fractions to total Po fractions (Pit/Pot); furthermore, NPKM significantly increased the organic C (Co) content and decreased the Co/Pot ratio. Stepwise multiple regressions showed that PAC = 0.93 Co+0.69 Pit/Pot-0.07 Co/Pot-0.27CaCO3-3.79 (R2 = 0.924, P<0.001). In addition, the variance partitioning analysis showed that more variance of PAC is explained by soil factors (29.53%) than by P input (0.19%) and climate (0.25%) factors. Our findings demonstrate that P application increased the PAC by changing the Co content and the proportion of P fractions. Moreover, soil factors were the most important drivers of P transformations, and NPKM was optimal for improving soil fertility in Chinese croplands.

Thermodynamics of Phosphorus in Solvent Refining of Silicon Using Ferrosilicon Alloys

The thermodynamics of phosphorus distribution between solid silicon and iron-silicon melt was studied to examine the degree of phosphorus removal from silicon by solvent refining with ferrosilicon alloys. The experiments were performed on silicon-iron-phosphorus alloys with ~80 wt pct silicon and ~20 wt pct iron. A phosphorus distribution coefficient, which is defined as the ratio of the mole fraction of phosphorus in solid to that of liquid is as follows: 0.22 ± 0.02 [1583 K (1310 °C)], 0.29 ± 0.02 [1533 K (1260 °C)], and 0.33 ± 0.02 [1483 K (1210 °C)]. The corresponding removal percentages of phosphorus were 86 pct [1583 K (1310 °C)], 75 pct [1533 K (1260 °C)], and 67 pct [1483 K (1210 °C)]. The average phosphorus content of the refined silicon in the current process would be more than two times less than that of the conventional solidification refining techniques. The values of interaction coefficient of phosphorus on iron \( (\varepsilon_{\text{Fe}}^{P} ) \) at different temperatures were obtained as −3460 ± 155 [1583 K (1310 °C)], −3595 ± 159 [1533 K (1260 °C)], and −3694 ± 119 [1483 K (1210 °C)]. The self-interaction parameters of phosphorus \( \left( {\varepsilon_{P}^{P} } \right) \)at different temperatures are as follows: 68 ± 4 [1583 K (1310 °C)], 78 ± 10 [1533 K (1260 °C)], and 103 ± 19 [(1483 K 1210 °C)]. The calculated values for the distribution coefficients of phosphorus at infinite dilution are 0.22 ± 0.00 [1583 K (1310 °C)], 0.30 ± 0.00 [1533 K (1260 °C)], and 0.34 ± 0.00 [1483 K (1210 °C)]. Considering the solid (red phosphorus) standard state for solid silicon, the activity coefficient of phosphorus in solid silicon is estimated as \( {{ln\gamma }}_{\text{P \, in \, solid \, Si}}^{^\circ } = - 17395\left( {\frac{1}{\text{T}}} \right) + 10 \).

Effect of Montmorillonite on Fractions and Availability of Phosphorus in Soils Applied with Organic Fertilizer

An incubation experiment was carried out to study the effect of montmorillonite on pH, the fractions and availability of phosphorus in a sandy yellow soil (SY) and a mineral flavicant soil (MF) applied with biogas residues of swine manure (BSR). The rates of montmorillonite applied were 0%, 5%, 7.5% and 10%, respectively. The results indicated that soil pH was not affected by BSR, but was significantly increased by montmorillonite. In both soils, application of BSR caused an increase in the content and proportion of Al-P during the incubation, and an increase in the content but a slight decrease in the proportion of Fe-P in later period of incubation. The concentration of O-P was not markedly changed, but its proportion was decreased by applying BSR in both soils. The changes of Ca-P varied with soils. BSR had no significant influence on Ca-P content, but decreased the proportion of Ca-P in SY, meanwhile, it increased both Ca-P content and proportion in MF. Addition of montmorillonite in soils applied with BSR decreased the contents and proportions of Al-P and O-P, and the proportion of Fe-P did not change the contents of Fe-P, but increased the content and proportion of Ca-P in SY. In MF, montmorillonite could decrease the contents and proportions of Fe-P and O-P, and the proportion of Al-P did not affect the content of Al-P, but increased the contents and proportions of Ca-P greatly. The contents of available phosphorus (A-P) were enhanced by 17.9%-38.0% and 17.1%-33.7% in SY and MF respectively, and the phosphorus activation coefficient (PVC) was significantly improved in both soils by applying BSR. The contents of A-P were reduced by 8.8%-35.5% and 1.1%-11.6% in SY and MF respectively. Correlation analysis showed that montmorillonite reduced the availability of phosphorus through increasing pH and contents of Ca-P, decreasing the content of Al-P in SY, and through increasing pH and decreasing content of Fe-P in MF. The availability of phosphorus in SY was influenced more obviously than that in MF by montmorillonite.

Evaporation Behavior of Phosphorus from Metallurgical Grade Silicon via Calcium-Based Slag Treatment and Hydrochloric Acid Leaching

Phosphorus removal from metallurgical grade silicon by CaO-SiO2-CaCl2 slag treatment, HCl leaching, and vacuum refining was investigated. The effect of different compositions of slag was evaluated. The calcium concentration in slag-treated silicon increased with increasing CaO/SiO2 mass ratio of slag, decreasing the evaporation efficiency of phosphorus in molten silicon. The total phosphorus removal efficiency changed from 93.0% to 98.3% when the slag-treated silicon was treated with HCl before vacuum refining. The final concentration of phosphorus in silicon was 0.43 ppmw. This is because phosphorus was removed from metallurgical-grade silicon as follows: Phosphorus reacts with slag at the silicon/slag interface and forms Ca3(PO4)2 and Ca3P2, most of which diffuse from the interface to the slag phase. The remaining Ca3(PO4)2 and Ca3P2 reduce the phosphorus removal efficiency by altering the activity coefficient of phosphorus in molten silicon. HCl leaching enhanced the phosphorus removal efficiency by removing the remaining Ca3(PO4)2 and Ca3P2. Therefore, the mass transfer of phosphorus from metallurgical-grade silicon was accelerated.