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Phosphorus (P) use efficiency in alkaline/calcareous soils is only 20% due to precipitation of P2O5 with calcium and magnesium. However, coating Diammonium Phosphate (DAP) with phosphorus solubilizing bacteria (PSB) is more appropriate to increase fertilizer use efficiency. Therefore, with the aim to use inorganic fertilizers more effectively present study was conducted to investigate comparative effect of coated DAP with PSB strains Bacillus subtilis ZE15 (MN003400), Bacillus subtilis ZR3 (MN007185), Bacillus megaterium ZE32 (MN003401) and Bacillus megaterium ZR19 (MN007186) and their extracted metabolites with uncoated DAP under axenic conditions. Gene sequencing was done against various sources of phosphorus to analyze genes responsible for phosphatase activity. Alkaline phosphatase (ALP) gene amplicon of 380bp from all tested strains was showed in 1% w/v gel. Release pattern of P was also improved with coated fertilizer. The results showed that coated phosphatic fertilizer enhanced shoot dry weight by 43 and 46% under bacterial and metabolites coating respectively. Shoot and root length up to 44 and 42% with metabolites coated DAP and 41% with bacterial coated DAP. Physiological attributes also showed significant improvement with coated DAP over conventional. The results supported the application of coated DAP as a useful medium to raise crop yield even at lower application rates i.e., 50 and 75% DAP than non-coated 100% DAP application which advocated this coating technique a promising approach for advancing circular economy and sustainable development in modern agriculture. [ABSTRACT FROM AUTHOR]

Soil legacy phosphorus (P) accumulated due to the long-term continuous application of P fertilizers in agricultural fields accumulated in the soil for years, as sparingly soluble forms. This can be made as a possible soil P source using P-activators. In this study, a laboratory incubation and a pot experiment were conducted to evaluate the potential of some P activators (Phosphorus solubilizing bacteria, phytase, humic acid, oxalic acid) in increasing the availability of residual phosphorus in calcareous soil. For the incubation experiment, the P activators were applied alone and in combination. Soil samples were analyzed at subsequent intervals for soil available P, alkaline phosphatase activity, and sequential P fractions. The results showed that phytase application with humic acid (HA) increased the available soil P (12.4 kg ha−1) and alkaline phosphatase activity (47.42 µg p-nitrophenol released g−1 soil hr−1) followed by phosphorus solubilizing Bacteria (PSB) with humic acid and PSB with phytase treatments. All treatments have a significant effect on different soil P-fractions. A greater reduction in calcium phosphate fraction was noted in phytase and humic acid application. The combined application of P-activators performed better than their sole application. The best three treatments selected from the laboratory incubated experiment were used for the pot experiment with maize, along with the different dosages of P fertilizer. The morphological parameters were observed on the 30th and 60th days of the maize crop. The results of plant height, chlorophyll index, and dry matter production showed that the application of phytase and HA with 100% recommended dose of P was statistically comparable with phytase and HA with 75% recommended dose of P. The findings have illustrated the extent of P release by different P activators in increasing the legacy P availability. The application of phytase and HA with 25% reduced dose of P fertilizers will promote the availability of legacy P in calcareous soils through solubilization. [ABSTRACT FROM AUTHOR]

Background: Over the years, the excessive P fertilizer application to crop fields resulted in the build up of insoluble phosphorus pool in soil known as legacy phosphorus. This represents a vast and largely untapped resource in soil. The current study was conducted to evaluate the potential of some P activators (Phosphorus solubilising bacteria, phytase, humic acid, farmyard manure) on increasing the plant availability of legacy P in calcareous soil. Methods: A field experiment was conducted with maize hybrid COH(M) 6. The P activators were combined and applied along with the different doses of P fertilizer (100%, 75% and 50% soil test dose of single super phosphate). Result: Farmyard Manure (FYM) application with Humic acid (HA) showed the increased Olsen P under 100% and 75% of P application. The phosphorus activation response of FYM+HA applied plots showed a higher value than other treatments. The maize yield and P uptake obtained with FYM and HA were statistically comparable at 100% and 75% soil test dose of P. The findings have illustrated that even the reduced amount of P fertilizer application can support the crop growth due to the release of legacy P if they are applied along with P-activators such as FYM and HA. [ABSTRACT FROM AUTHOR]

Contrasting fertilization modifies soil phosphorus (P) transformation and bioavailability, which impact crop P uptake and P migration in the soil profile. A long-term (25-year) fertilizer experiment was employed to investigate crop yield, P uptake and changes in sequentially extracted P fractions in the soil profile, and their relationships on a calcareous soil derived from loess material under a winter wheat and summer maize double-cropping system. The experiment involved seven nutrient management treatments: control (CK, no nutrient input), N, NK, NP, and NPK, representing various combinations of synthetic nitrogen (N), phosphate (P), and potassium (K) applications, as well as combinations of NPK fertilizers with either crop residues (SNPK, where S refers to maize stalk or wheat straw) or manure (MNPK, where M refers to dairy manure). Wheat and maize yields were significantly higher with P input fertilizer relative to the P-omitted treatments. Long-term application of P-containing fertilizers markedly raised the contents of inorganic (Pi) and organic (Po) P fractions at 0–20 cm depth compared with the P-omitted treatments. Moreover, both Pi and Po fractions were markedly higher under MNPK than under NPK and SNPK treatments. For achieving high yield for wheat and maize, the critical contents of labile P were 54 and 63 mg kg−1, and those of moderately labile P were 48 and 49 mg kg−1, respectively, defined by the linear plateau model. In addition, the change points of labile P and moderately labile P were 99 and 70 mg kg−1, above which CaCl2-P content significantly increased. Moreover, long-term P input significantly accumulated different P fractions in the deeper soil layers up to 100 cm, with large portions of organic P being a composite of labile and moderately labile P, especially in MNPK treatment. Our results suggest that excessive P supply with organic manure resulted in massive P accumulation in the topsoil and promoted soil P fraction transformation and availability in the deep soil layers, especially in an organic P form that has often been neglected. [ABSTRACT FROM AUTHOR]

The study was designed to quantify the contents of Pi fractions and correlate them with the P capacity factor of soils in the Brazilian semiarid region. We also evaluated the effect of soil P doses contact time and P availability for maize plants in alkaline soils of the Brazilian semiarid region. Soil samples were collected between the Piranhas-Açu (RN) and Jaguaribe (CE) rivers valleys. The maximum phosphate sorption capacity was highly correlated with the values of remaining P, indicating that it can be used as a measure to estimate the P capacity factor of these soils. Maximum P sorption capacity correlated with Fe2O3 and Ca2+ contents and pH values. These results demonstrate that P sorption is explained by P adsorption on the surface of iron oxides and by its precipitation with Ca2+ in alkaline soils. The contact time increases promote plant P contents decreased substantially in the first 30 to 60 days after fertilization and decreased until 120 days of incubation but then tended to stabilize at the longest soil P contact times. The clay content and P-remnant estimate the P capacity factor in alkaline soils. In alkaline soils, there is a predominance of P–Ca and P–Fe. The availability of P stabilizes after 120 days. The largest corn biomass occurs between the P doses of 256–288 mg dm−3. [ABSTRACT FROM AUTHOR]

The Lijiang River Basin covers great variation in altitude, soil and vegetation types. In order to study the characteristics of its soil nutrients and enzymes activities, we determined soil nutrient contents and activities of several extracellular enzymes (amylase, sucrose, urease, protease and catalase)of the surface soils(0-20 cm)of typical vegetation types [natural forest, bamboo (Phyllostachys edulis)forest, Pinus massoniana forest, orchard and rice paddy field] with calcareous soils and acid soils in the Lijiang River Basin. The results were as follows: (1) The soils at high altitude had greater total nitrogen (TN), total phosphorus (TP), available phosphorus (AP) contents as well as amylase, sucrose, urease and protease activities, whereas the catalase activity was to the contrary. (2) Compared with the acid soils, the calcareous soils had higher contents of total phosphorus(TP)and available phosphorus (AP). Among the acid soils, vegetation types had greater impact on soil nitrogen and phosphorus contents. In general, anthropogenic vegetation resulted in decrease of nitrogen content and increases of phosphorus content; while the nutrients in the calcareous soils had relatively little variation among different vegetation types. (3) Compared with the natural forest soils, soils from the anthropogenic vegetation had lower nitrogen related enzyme activities; whereas the carbon related enzyme activities was less impacted. The enzymatic stoichiometry revealed that soils of natural forests were nitrogen limited whereas those of anthropogenic vegetation was carbon limited. (4) The results of canonical correspondence analysis (CCA) showed that soil physiochemical properties in the first and second axes explained 86.56% of the variation of soil enzyme activities with the contribution order of TN>pH>NH4+>AP>TP>NO3-, with the first three as the main impacts. All the above results indicate that acid soils in the Lijiang River Basin have great ecological sensitivities; vegetation changes easily result in nutrient imbalance, therefore, in order to improve the sustainable utility of landscape resources of the Lijiang River Basin, special attention should be paid to the conservation of soil nutrients and prevention of the loss of soil organic matter. This study provides theoretical base for the scientific conservation and development of local ecosystem. [ABSTRACT FROM AUTHOR]

Phosphorus (P) use efficiency (FPUE) is very low due to fixation of P with the hydrous oxides of iron and aluminum in acid soils and calcium in neutral to calcareous soil. The roots of wheat (Triticum aestivum) excrete low molecular weight organic acids (LMWOAs) to increase P bioavailability in P-deficient soil through acidification, chelation, and exchange mechanisms. However, the amount of LMWOAs excreted in the rhizosphere is small, and they undergo rapid microbial degradation. The present study was undertaken by applying different levels of LMWOAs and phosphorus to the soil followed by sowing of wheat seeds to learn the impact of applying LMWOAs, especially oxalic (OA) and citric acid (CA), on the yield and FPUE of wheat. The results showed that application of P fertilizer along with OA and CA significantly increased the Olsen P concentration in soil and in turn increased P uptake, FPUE, and yields of wheat. Application of OA @ 15 mg kg−1 recorded 20% (±0.22%) and 30% (±0.55%) higher grain and straw yield, respectively, over control and was more effective than CA. Among LMWOAs, application of OA @ 15 mg kg−1 was more effective than CA. Therefore, the application of OA has the potential to reduce the excess application of phosphorus and its buildup in soils and cause eutrophication of water bodies. [ABSTRACT FROM AUTHOR]

Continuous application of phosphatic fertilizers in association with its low recovery results in the insoluble legacy P buildup in agricultural soils. In this study, a field experiment was conducted with maize hybrid COH(M) 6 to know the effect of different P activators (Farmyard Manure, Humic acid, Phosphorus Solubilising Bacteria, and Phytase) on increasing the legacy phosphorus (P) availability. The P activators were combined and applied along with the different doses of P fertilizer (100%, 75%, and 50% soil test dose of P fertilizer). The results showed that the application of Farmyard manure (FYM) and Humic acid (HA) significantly (p < 0.05) increased the soil available P (18.54 kg ha-1) and notably reduced the calcium P fraction (93.08 mg kg-1). The application of FYM and HA with 100% soil test dose of P showed a similar grain (9.98 kg ha-1) and stover P uptake (12.67 kg ha-1) response as that of FYM and HA with 75% soil test dose of P. The study suggested that FYM and HA application has activated the fixed calcium phosphorus in soil and increased its availability for crop utilization. The findings have illustrated that even the reduced dose of P fertilizer application can support the nutrient uptake if they are applied along with P-activators such as FYM and HA. This could promote soil health by reducing the P overload and further P loss in soil. [ABSTRACT FROM AUTHOR]

Ammonium polyphosphate (APP) is currently being increasingly used as source of phosphorus (P) fertilizer worldwide and has exhibited positive effects on soil P availability in calcareous soils. However, the mechanisms of APP-induced abiotic and biotic transformations of soil P remain elusive. Influences of APP application on P transformation in a calcareous soil were investigated in comparison to monoammonium phosphate (MAP). The application of APP significantly increased soil Olsen-P by 61.3% relative to MAP application. Specifically, APP application (i) significantly increased biologically-based P corresponding to P extracted by CaCl2, citric acid, and enzyme; (ii) increased labile Ca-P proportion (NaHCO3 extractable P) while decreased stable Ca-P proportion (H2SO4 extractable P); (iii) decreased organic P (Po) content. In APP-treated soil, the decrease in pH, crystal Fe and Al oxides together with the increase in organic C and complex Fe oxides contributed to the P sorption decrease and P desorption/dissolution increase. Meanwhile, APP significantly increased alkaline phosphatase activity and phoD gene abundance, which contributed to Po mineralization increase. Additionally, APP changed β-diversity and increased the relative abundance of Rhodobacterales and Myxococcales harboring pqqC gene, indicating the contribution of P solubilizing bacteria to inorganic P (Pi) dissolution. Redundancy analysis showed that soil pH can explain 70.4, 53.8, and 55.1% of the total variances observed in the composition of BBP, Pi and soil P sorption–desorption parameters, respectively. This suggests that the change of soil pH from APP application in this calcareous soil altered soil abiotic and biotic P transformation processes, promoting soil P availability. [ABSTRACT FROM AUTHOR]

This study aims to determine the effect of Bacillus megaterium var. phosphaticum applied together with rock phosphate on the yield of wheat grown in calcareous soil, some biological properties of soils and phosphorus fractions in the soil under greenhouse conditions. Considering the P fixation capacity of the soil used in the experiments and the amount of P present in the soil, the trial subjects were created based on randomized block designs with 3 replications, depending on whether 0, 25, 50, 75 and 100% of the P required to be given to the wheat plant was met from rock phosphate and whether it was bacterial or not, and finally wheat was grown. In the harvested plants, grain and stem weights were determined, grain and stem P contents were analysed and the amounts removed with grain and stem were calculated. Dehydrogenase (DHA) and phosphatase (PA) enzyme activities were performed in the soil samples taken after harvest. Soluble and loosely bound-P, Calcium-bound-P (Ca-P), Reductant soluble-P (RS-P) fractions and Olsen-P were determined in soil samples taken before planting and after harvest. The percent reduction in the fractions was calculated by using the pre-sowing and post-harvest values of these samples. According to the results, Bacillus megaterium DSM 3228 strain inoculated with rock phosphate increased grain and stem yield, grain and stem P content, and P amount removed by grain and stem of wheat. These parameters were found to be higher at high doses of P applied as rock phosphate. Inoculation increased the DHA and PA values of the soils. A decrease in P fraction forms with low solubility was determined by inoculation, some of this phosphorus was removed by plants and some of it was retained in the soil in different forms. [ABSTRACT FROM AUTHOR]

Sustainable forest management requires understanding of ecosystem phosphorus (P) cycling. Lang et al. (2017) [Biogeochemistry,https://doi.org/10.1007/s10533-017-0375-0] introduced the concept of P-acquiring vs. P-recycling nutrition strategies for European beech (Fagus sylvatica L.) forests on silicate parent material, and demonstrated a change from P-acquiring to P-recycling nutrition from P-rich to P-poor sites. The present study extends this silicate rock-based assessment to forest sites with soils formed from carbonate bedrock. For all sites, it presents a large set of general soil and bedrock chemistry data. It thoroughly describes the soil P status and generates a comprehensive concept on forest ecosystem P nutrition covering the majority of Central European forest soils. For this purpose, an Ecosystem P Nutrition Index (ENIP) was developed, which enabled the comparison of forest P nutrition strategies at the carbonate sites in our study among each other and also with those of the silicate sites investigated by Lang et al. (2017). The P status of forest soils on carbonate substrates was characterized by low soil P stocks and a large fraction of organic Ca-bound P (probably largely Ca phytate) during early stages of pedogenesis. Soil P stocks, particularly those in the mineral soil and of inorganic P forms, including Al- and Fe-bound P, became more abundant with progressing pedogenesis and accumulation of carbonate rock dissolution residue. Phosphorus-rich impure, silicate-enriched carbonate bedrock promoted the accumulation of dissolution residue and supported larger soil P stocks, mainly bound to Fe and Al minerals. In carbonate-derived soils, only low P amounts were bioavailable during early stages of pedogenesis, and, similar to P-poor silicate sites, P nutrition of beech forests depended on tight (re)cycling of P bound in forest floor soil organic matter (SOM). In contrast to P-poor silicate sites, where the ecosystem P nutrition strategy is direct biotic recycling of SOM-bound organic P, recycling during early stages of pedogenesis on carbonate substrates also involves the dissolution of stable Ca-Porg precipitates formed from phosphate released during SOM decomposition. In contrast to silicate sites, progressing pedogenesis and accumulation of P-enriched carbonate bedrock dissolution residue at the carbonate sites promote again P-acquiring mechanisms for ecosystem P nutrition. [ABSTRACT FROM AUTHOR]

Phosphorus is considered as a basic essential element for plant growth which cannot be substituted or manufactured and is, therefore, a scarce resource to ensure food security; its sound management is considered important. One of the factors that play a significant role in its management is the determination of the critical available phosphorous (P) level in soil, in order to decide whether to apply P fertilizers or not. Since several soil and plant factors affect the value of the critical available soil P, it is considered necessary to carry out special experiments, in order to determine the soil critical P value for an area and a specific crop. The purpose of the present study was to establish critical soil and plant P values for wheat. A greenhouse pot experiment was performed on seven representative calcareous soils from the Thessaly plain in central Greece. The soils were deficient in available P and so they were fertilized with various rates of P. At appropriate stages, the above-ground plant parts were harvested and analysed for basic nutrients, including P. At the same time, soil samples were also taken and analysed for available P. The Cate and Nelson technique was applied, to determine critical values of both soil and wheat tissue P values. It was found that the critical soil P is 11 mg P kg-1 and the critical value for wheat tissue is 0.24% P dry matter. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is the most deficient nutrient in agricultural soils after nitrogen. Additionally, exogenously applied P quickly transforms into less soluble compounds through various chemo-sorption reactions resulting in poor fertilizer use efficiency (15–25%). Therefore, this pot experiment was conducted to investigate the impact of foliar P (0, 45, 90 and 135 mM KH2PO4) in conjunction with soil applied P (0, 10 and 20 mg P kg−1) for enhanced growth and P use efficiency of maize and wheat in calcareous soils. There was a linear increase in plant height and biomass both with the increasing application of soil and foliar P in both wheat and maize crop. However, the effect of foliar P was more pronounced in P deficient condition compared to 10 or 20 mg P kg−1. Soil applied P at 10 and 20 mg P kg−1 increased plant dry biomass by 10.8 and 16.8% in maize and by 29.9 and 35.5% in wheat over control, respectively. Foliar P application didn't improve soil phosphorus. The interaction between soil and foliar P was significant (p ≤.05) showing that increase of either foliar or soil P application, tissue P content of both maize and wheat increased. In both season the higher foliar P solution resulted in higher P uptake though the increase in wheat were lower than maize. Therefore, the low recovery of soil P associated with poor soil characteristics could be corrected through its foliar application if administered at proper growth stage with suitable concentration strength and appropriate source. [ABSTRACT FROM AUTHOR]

Background and aims: Understanding how soil phosphorus (P) fractions change is critical to achieve more efficient soil P use in a highly P-sorbing calcareous soil. Methods: The fields were managed without or with annual P fertilizer (40 kg P ha− 1), continuously growing sole cropping or intercropping of maize and faba bean. Soil samples (0–200 mm) were collected at the start of the experiment and eight years later, and we evaluated P fractions using sequential fractionation. Results: Maize/faba bean intercropping had an average land equivalent ratio (LER) of 1.2, a similar P content as sole maize, while both acquired more P than sole faba bean. Compared with the original soil P fractions in 2009, three cropping systems, regardless of P fertilization, depleted the labile P pool (Resin-P and NaHCO3-Pi), while Residual-P and NaHCO3-Po accumulated. Eight years of no P input showed sole maize mainly depleted NaOH-Pi and conc. HCl-Pi, sole faba bean depleting NaOH-Po, while intercropping depleted the most abundant P fraction, 1 M HCl-Pi, in addition to NaOH-Pi. However, long-term P application caused the cropping systems to accumulate 1 M HCl-Pi while depleting the conc. HCl-Po fraction; both sole faba bean and intercropping showed accumulation of NaOH-Pi, while depleting NaOH-Po. Conclusions: Long-term appropriate P input enhanced the mineralization of mod-labile and non-labile organic P and accumulation of mod-labile inorganic P. Sole maize consistently depleted inorganic P and sole faba bean without P input depleted organic P, while intercropping accessed P pools varying with P input. [ABSTRACT FROM AUTHOR]

To study the effect of applying different phosphorus solubilizers on the insoluble phosphorus in the soil, so as to improve the utilization rate of the insoluble phosphorus. [Method] The indoor soil culture experiment method was used to study the activation effect of different phosphorus solubilizers on the insoluble phosphorus in calcareous soil. [Results] γ-polyglutamic acid treatment can increase the available phosphorus content of the soil, and the highest net increase of the available phosphorus content in the soil treated with phosphate rock powder and γ-polyglutamic acid compared with the control (only treated with phosphate rock powder) 60.10%. [Conclusion] γ-polyglutamic acid can promote the conversion of insoluble phosphorus to available phosphorus in the soil. [ABSTRACT FROM AUTHOR]

• Single or split alum applications increased p fixation in calcareous soil. • Organic matter weakened the p stabilisation of single alum application. • Alum split applications induced the formation of the non-crystalline fe/al. • Alum split applications transformed more soil labile p to non-labile p. High phosphorus (P) saturation arising from historic P inputs to protected vegetable fields (PVFs) drives high P mobilisation to waterbodies. Amendment of soils with alum has shown potential in terms of fixing labile P and protecting water quality. The present 15 month pot experiment investigated P stabilisation across single alum application (Alum-1 treatment, 20 g alum/kg soil incorporated into soil before the maize was sown), alum split applications (Alum-4 treatment, 5 g alum/kg soil incorporated into soil before each crop was sown i.e. 4 × 5 g/kg) and soil only treatment (Control). Results showed that the Alum-1 treatment caused the strongest stabilisation of soil labile P after maize plant removal, whereas the P stabilisation effect was gradually weakened due to the transformation of soil non-labile P to labile P and the reduced active Al3+ in soil solution. For the Alum-4 treatment, soil labile P decreased gradually with each crop planting and was lower than the Alum-1 treatment at the end of the final crop removal, without any impairment on plant growth. The better P stabilisation at the end of Alum-4 treatment was closely correlated with a progressive supply of Al3+ and a gradual decrease of pH, which resulted in higher contents of poorly-crystalline Al, Fe and exchangeable Ca. These aspects were conducive to increasing the soil P stabilisation and phosphate sorption. In terms of management, growers in continuous cropping systems could utilise split alum applications as a strategy to alleviate P losses in high-P enriched calcareous soil. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Background: P deficiency is very common in alkaline - calcareous soil. Therefore, application of foliar-absorbed fertilizers may be an effective strategy to overcome the low bioavailability of phosphorus in soil, by improving phosphorus use efficiency and reduced nutrients loses. Methods: A field experiment was carried out in 2006-07 growing season at El-Menia (southeastern Algeria) to evaluated the effect of two foliar P (agriphos and leader-start) and three soil P (TSP P 46, Fosfactyl NP 3:22 and NPKs 8:36:13,5+15) on yield and P use efficiency of durum wheat crop Triticum durum Desf. var. Carioca and on available P and total P in soil. Result: Data showed that significant effect of soil P fertilizer on grain yield components (ears m-2, grains ear-1 and the 1000 grains weight), grain P use efficiency and available P in soil. The best values were recorded by NPKs fertilizer, but no differences were observed for these parameters among foliar fertilizer sources. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) is a potential alternative to wet chemical methods for total soil phosphorus determination, but matrix effects related to physical and chemical sample properties need to be further understood. The aim of this study was to explore matrix effects linked to particle size distribution and chemical form of phosphorus on LIBS response and the ability of LIBS to predict total phosphorus in a range of different soil types. Univariate calibration curves were developed by spiking the soils with increasing doses of phosphorus, and limits of detection for LIBS determined phosphorous (P) (LIBS-P) were calculated. Different particle size distributions in otherwise identical soils were obtained by four milling treatments and effects of chemical form of phosphorus were examined by spiking soils with identical amounts of phosphorus in different chemical compounds. The LIBS-P response showed a high correlation (R2 > 0.99) with total phosphorus for all soils. Yet, the sensitivity of LIBS differed significantly among soils, as the slope of the calibration curves increased with increasing sand content, resulting in estimated limits of detection of 10 mg kg−1 for the sandiest and 122 mg · kg−1 for the most clayey soils. These limits indicate that quantitative evaluation of total phosphorus in sandy and loamy sandy soils by LIBS is feasible, since they are lower than typical total phosphorus concentrations in soil. A given milling treatment created different particle size distributions depending on soil type, and consequently different LIBS-P results. Thus, procedures that specify the required degree of homogenization of soil samples prior to analysis are needed. Sieving after milling could be an option, but that should be tested. The soils spiked with Fe(III) phosphate, potassium phosphate and phytic acid had similar LIBS-P, except for soils with hydroxyapatite, which resulted in markedly lower response. These results suggested that matrix effects related to the chemical nature of phosphorus would be minor for non-calcareous soils in humid regions, where apatites comprise only a small fraction of total phosphorus. Strategies to overcome matrix effects related to particle size and content of apatite-phosphorus by combining multivariate models and soil type groupings should be further investigated. [ABSTRACT FROM AUTHOR]

Increasingly, phosphorus (P) fertilizer is being applied in Inner Mongolia of China to overcome the problem of insolubility of phosphorus in calcareous soil and meet the growth demand of potato plants. As a result, phosphorus use efficiency (PUE) in potatoes decreases continually. In this four-year study in sandy soils, drip fertigating potatoes with phosphorus during the growth season improved phosphorus uptake, plant growth, tuber yield, and PUE. Results show that relative to a single phosphorus application, using a split phosphorus application regime through drip irrigation significantly increased the leaf area index (LAI) and phosphorus uptake rate in the mid and late growth stages of potatoes, and enhanced potato yield and PUE. We concluded that split phosphorus application has the potential to benefit sustainable potato production in Inner Mongolia of China. [ABSTRACT FROM AUTHOR]

Aims: This study aimed to investigate the effects of coexistence with faba bean, a phosphorus (P)-efficient crop, on soil-accumulated P use by a maize/faba bean intercropping system on dynamic changes in soil P pool. Methods: Maize and faba bean were grown in P-accumulated soil as either sole cropping or intercropping. After one year (Stage I) or four years (Stage II) of no P application, soil samples were collected respectively and analyzed for soil P pools using sequential fractionation. Aboveground biomass and P content were annually measured from 2013 to 2016 to assess the annual P balance. Results: The intercropped maize/faba bean system showed a P-uptake advantage, with a Land Equivalent Ratio (LER) ranging from 1.2 to 1.5. The average shoot P content over the four years in intercropped maize and faba bean was significantly greater than that of the corresponding sole crops by 29% and 30%, respectively. Over the three-year P depletion period, the three cropping systems primarily depleted the 1 M HCl-Pi fraction, followed by sole maize, which depleted the NaOH-Pi and concentrated HCl-Po fractions. Sole faba bean depleted the alkali-soluble Po fraction (extracted by NaHCO3 and NaOH), and the intercropped maize/faba bean system depleted the conc. HCl-Po fraction, which was similar to the effect of sole maize. Conclusions: Both sole crops and intercrops mainly depleted 1 M HCl-Pi, but differed in Po depletion. Sole maize and maize/faba bean intercropping depleted the sparingly labile Po fraction, while sole faba bean depleted the labile and moderately labile Po fractions. [ABSTRACT FROM AUTHOR]

Background and aims: The decrease in cereal grain zinc (Zn) caused by phosphorus (P) application has attracted wide attention. However, optimizing P fertilization for both satisfactory grain yield and grain Zn concentration is still a problem due to a poor understanding of the relationship between P application rates and available soil P, and that of available soil P and soil Zn availability, relevant soil factors, and plant Zn uptake and utilization. Methods: A location-fixed field experiment was initiated in 2004 with winter wheat (Triticum aestivum L.) grown at five P rates of 0, 50, 100, 150, and 200 kg P2O5 ha−1, and soil and plant samples were collected during the three growing seasons of 2013–2016. Results: Winter wheat grain yield increased, and the grain Zn concentration decreased with increasing available soil P in a linear-plus-plateau manner. The grain yield plateau, averaging 6009 ± 155 kg ha−1, was reached at an available soil P concentration of 10.2 ± 2.5 mg kg−1, and the grain Zn plateau, averaging 22.4 ± 0.9 mg kg−1, was reached at an available soil P of 14.2 ± 1.8 mg kg−1. Shoot Zn uptake after flowering was not affected, while Zn remobilization from vegetative parts to grains and the Zn harvest index increased with P application at available soil P levels below 11.6 mg kg−1. The available soil Zn increased, and root mycorrhizal colonization was unaffected at lower available soil P levels. Conclusions: The decrease in wheat grain Zn concentration with increasing P application at lower available soil P levels was primarily explained by yield dilution effects, not the changes in available soil Zn and root mycorrhizal colonization. Under the experimental conditions, the available soil P would have to be as low as 0.7 ± 0.4 mg kg−1 to achieve the target grain Zn concentration of 40 mg kg−1, and at this level, the grain yield would only be 4127 ± 252 kg ha−1. [ABSTRACT FROM AUTHOR]

Metal oxide modified biochars are increasingly being used for intensive agricultural soil remediation, but there has been limited research on their effects on soil phosphorus transformation, soil enzyme activity, microbe community and plant growth. Two highly-performance metal oxides biochars (FeAl-biochar and MgAl-biochar) were investigated for their effects on soil phosphorus availability, fractions, enzyme activity, microbe community and plant growth in two typical intensive fertile agricultural soils. Adding raw biochar to acidic soil increased NH 4 Cl–P content, while metal oxide biochar reduced NH 4 Cl–P content by binding to phosphorus. Original biochar slightly reduced Al–P content in lateritic red soil, while metal oxide biochar increased it. LBC and FBC significantly reduced Ca 2 –P and Ca 8 –P properties while improving Al–P and Fe–P, respectively. Inorganic phosphorus-solubilizing bacteria increased in abundance with biochar amendment in both soil types, and biochar addition affected soil pH and phosphorus fractions, leading to changes in bacterial growth and community structure. Biochar's microporous structure allowed it to adsorb phosphorus and aluminum ions, making them more available for plants and reducing leaching. In calcareous soils, biochar additions may dominantly increase the Ca (hydro)oxides bounded P or soluble P instead of Fe–P or Al–P through biotic pathways, favoring plant growth. The recommendations for using metal oxides biochar for fertile soil management include using LBC biochar for optimal performance in both P leaching reduction and plant growth promotion, with the mechanisms differing depending on soil type. This research highlights the potential of metal oxide modified biochars for improving soil fertility and reducing phosphorus leaching, with specific recommendations for their use in different soil types. [Display omitted] • Two kinds of metal oxides biochar were fabricated for phosphorus management in fertile soils. • Metal oxides biochar more efficiently reduced labile soil phosphorus while not reduced the corp yield. • Ordinary biochar both increased the labile soil phosphorus. • Metal oxides biochars showed opposite effects on transformations of soil moderately labile P. • Stable soil phosphorus were slightly influenced by metal oxides. [ABSTRACT FROM AUTHOR]

Keywords: Phosphorus; Fractionation EN Phosphorus Fractionation 19 21 3 02/10/21 20210201 NES 210201 The recent article by Barrow et al. ([1]) concerning "The soil phosphate fractionation fallacy" is a welcome cautionary paper for phosphorus scientists to question how they approach the interpretation and practical use of phosphorus fractions in understanding the nature of soil phosphorus. I will not revisit their discussion, but reflect more broadly on my experience of the usefulness of phosphorus fractionation in driving forward a functional understanding of soil phosphorus behaviour, and more specifically, plant phosphorus acquisition. Implicit in those assumptions is that acid extractable phosphorus fractions, representing Ca-P, (and as has been made clear in these two articles, Fe-P) are less available to roots than a bicarbonate extractable fraction. [Extracted from the article]

Knowledge on P release characteristics and availability of different forms of soil phosphorus can be useful for crop production. Kinetics of P release and distribution of inorganic P from in calcareous soils at summit, shoulder, back slope, foot slope and toe slope of three soil toposequences (Fars province southern Iran) were determined and the relationship between P release and soil properties with phosphorus form was investigated. The kinetics of P release in the soils was determined by successive extraction with 0.01 M CaCl2 over a period of 72 hours. The kinetics of P release followed Elovich, power function and first order kinetic models. The results demonstrated that the pattern of P desorption was similar in all topographic units of the three regions at all times. The highest amount of P release was observed in the lower part of the slope specially in Eghlid and Abadeh (xeric and aridic regimes). Generally, the average content of cumulative phosphorus release and most forms of phosphorous and physical and chemical characteristics in Eghlid soils were greater than other studied soils. Different P forms were determined by sequential extraction; the fractionated inorganic P forms namely apatite type and dicalcium phosphate possessed the highest and the lowest amounts of P reserve in the soils, respectively. As a result, P release and various P forms distribution within the soil profiles along toposequences varied in different topographic units and increased down the slope with an irregular trend. Due to such variability, P fertilizers are recommended by consideration of the physiographic units. [ABSTRACT FROM AUTHOR]

Understanding soil P transformation is critical to optimizing P supply to crops while minimizing P loss to water. Nitrogen application in agricultural fields can cause acidification, changing soil chemistry and altering P cycling. In a calcareous vegetable field in China, 13 years of N application (1172 kg N ha−1 year−1) significantly decreased soil pH, CaCO3, and Mehlich-3 extractable (M3) Mg and increased M3-Fe and M3-Al. Nitrogen addition also increased microbial biomass C (MBC), decreased alkaline phosphomonoesterase (ALP) activity, and changed the total bacterial and phoD-harboring bacterial community composition. Soil total P, Olsen-P, and M3-P were not affected by N fertilization, but there were significant increases in soil total organic P (Po), NaOH-extractable Po, and the proportion of orthophosphate diesters. Redundancy analysis showed that soil pH, organic C, CaCO3, and ALP activity had significant effects on the compositions of soil P form (P < 0.05) and could explain 36.4, 13.3, 27.5, and 10.6% of the total variances observed in the composition of P forms. This suggests that soil acidification from N application in this P-rich calcareous soil altered soil abiotic P cycling processes through increasing the chemical adsorption of Po by Fe and Al. It also altered biotic P cycling processes by increasing microbial P uptake and immobilization and decreasing P biochemical mineralization, resulting in Po accumulation. [ABSTRACT FROM AUTHOR]

Developing a fast and reliable soil testing method is critical for improving soil testing efficiency and ensuring reliable fertilizer recommendation. The objectives of this study were to evaluate sodium ethylene diamine tetra acetic acid (Na2-EDTA) as a replacement for ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA) to extract phosphorus (P) to determinate the relationships between extractable P and its uptake by crop in calcareous soils. Na2-EDTA and AB-DTPA was compared by the amounts of extracted P by analyzing soil samples collected from agricultural production areas. There were significant correlations between Na2-EDTA and AB-DTPA for soil test P based on soils collected from the agricultural field. Soil test P by both extractants was significantly correlated with plant P concentration. Na2-EDTA was identified as an alternate improved extraction method instead of AB-DTPA in calcareous soils based on this study. However, more work will be needed to identify the correlation of the two extractants and crop responses under a field condition. [ABSTRACT FROM AUTHOR]

Diffusive gradients in thin films (DGT) technology has been increasingly proved to be a promising tool for accurately predicting plant-available phosphorus (P) in soil using air-dried samples. However, the effects of the air-drying process on DGT-measured P are unknown compared to those of using moist samples in which plant roots survive throughout a growing season. We investigated the differences between the Olsen P and DGT P values in 58 air-dried and moist soil samples. The results showed that the discrepancy in the DGT P values between air-dried and moist samples increased with an increase in the organic P concentration in soils. It was presumed that the air-drying process converted some easily mineralized organic P into its inorganic form, thereby allowing it to be measured by the DGT method. The DGT P values in moist samples can be calculated from the values obtained in air-dried samples using the following equation:. However, the Olsen P values were highly correlated (R2 = 0.95) when using air-dried and moist samples, although significant differences were observed. We concluded that the effects of air-drying on predicting soil available P using the Olsen P method can be neglected due to the high correlation relationship. The availability of easily mineralized organic P needs to be further explored. [ABSTRACT FROM AUTHOR]

Soil P testing is critical to ensure the accuracy of fertilizer recommendations and to optimize crop yield while minimizing negative environmental consequences. Olsen-P is the most commonly used soil P test for alkaline calcareous soils found in Idaho and the western United States. The Bray-1 test is commonly used in the Pacific Northwest on neutral to acidic soils but underestimates P in alkaline calcareous soils. Mehlich-3 has been evaluated throughout various regions in the United States. Few data evaluating Mehlich-3 exist for soils in the western United States. Additionally, the comparatively newly developed Haney–Haney–Hossner–Arnold (H3A) test, a component of the soil health tool, has not been widely evaluated on alkaline calcareous soils. Soil samples from the 0- to 30-cm depth were collected from agricultural fields throughout Idaho and analyzed with Bray-1, H3A, Mehlich-3, and Olsen-P extractants. The results indicate that Olsen-P was correlated with Mehlich-3, whereas Bray-1 and H3A were not correlated with Olsen-P. Both Bray-1 and H3A resulted in lower values of extractable P than the Olsen-P test, whereas Mehlich-3 resulted in greater values. A threshold point in CaCO3 (i.e., inorganic C) of 6.7 and 5.1 mg kg-1 for the Bray-1 and H3A was obtained, respectively, which indicated that inorganic C concentrations at or above these levels resulted in a reduction in extractable soil P. Thus Mehlich-3 could be evaluated for use in alkaline calcareous soils, whereas Bray-1 and H3A have notable issues that would limit their applicability. [ABSTRACT FROM AUTHOR]

Abstract Soil microorganisms exuding organic acids have the potential to solubilize inorganic phosphorus (P), which could improve the P availability to plants growing on calcareous soil. The gluconic acid exuding bacteria Pseudomonas protegens CHA0 can solubilize P under glucose rich in vitro conditions, but evidence on the effectiveness in soil is lacking. This discrepancy in P solubilization between in vitro and in vivo is common for many P solubilizing bacteria. Possible causes for this discrepancy are rarely explored in soil using mechanism oriented approaches. Proposed reasons for limitation of bacterial P solubilization in soil are low persistence of the inoculant or low glucose availability in the plant rhizosphere. To test these two hypotheses we investigated the solubilization of 33P labeled synthetic hydroxyapatite (Ca33P) by the gluconic acid producing P. protegens CHA0 wild type and the mutant strain CHA1198 lacking the capacity to produce this acid, in a plant growth experiment with wheat (Triticum aestivum) and an incubation experiment. Neither in the plant growth- nor in the incubation experiment solubilization of Ca33P by strain CHA0 was detected, in spite the inoculated strain persisted in the rhizoplane of wheat and in the sterilized soil amended with glucose. No detected P solubilization in the sterilized inoculated soil suggests that glucose availability was the main limiting factor. The comparison of the results obtained from the two bacterial inoculants suggested that overall microbial activity, i.e., via protonation due to respiration, increased inorganic P mobilization. P solubilizing bacteria should be evaluated using a tracer and an appropriate bacterial control in order to reveal the mechanisms involved in increased plant available P in soil inoculated with P solubilizing bacteria. Highlights • P. protegens CHA0 wild type did not increase Ca33P solubilization in soil compared to its mutant. • Microbial competition was not a limiting factor for P solubilization. • Glucose addition did not increase P solubilization by the wild type. • Overall microbial activity increased inorganic P mobilization. [ABSTRACT FROM AUTHOR]

High levels of phosphorus (P) often induce zinc (Zn) deficiency in plants grown on Zn-poor soils. We investigated P-induced Zn deficiency in durum wheat (Triticum durum L. 'Carpio') grown on 16 noncalcareous and 31 calcareous soils differing in levels of available (Olsen) P and available (diethylenetriaminepentaacetic acid (DTPA)-extractable) Zn using micropots. A completely randomized factorial design with two levels of P (0 and 40 mg P kg−1 soil) and Zn (0 and 3 mg Zn kg−1 soil), i.e. four treatments ('control', + P, + Zn, and + PZn), were used. Grain yield of control plants depended mainly on the Olsen P level. Phosphorus had a negative effect on yield in 6 soils with Olsen P/ZnDTPA > 25, and Zn a positive one in 5 soils with Olsen P/ZnDTPA > 50; and the + PZn treatment generally resulted in the highest yield. Grain Zn concentration of control plants was negatively correlated with growth and Olsen P. Calcareous soils were less sensitive to P-induced Zn deficiency than noncalcareous soils because phosphate is sorbed by calcite rather than being co-adsorbed with Zn on the Fe oxides. Co-application of P and Zn to soil at low and application of Zn at high Olsen P ensured both maximum yield and grain Zn bioavailability. [ABSTRACT FROM AUTHOR]

Background and aims: Although phosphorus (P) application is known to affect the zinc (Zn) nutrition of crops, the underlying mechanisms and effects of soil type are unclear.Methods: A greenhouse pot experiment was conducted with wheat, two soils (calcareous and acid), and nine P fertilizer rates (0, 50, 100, 200, 400, 1000, 2000, 3000, and 5000 mg P2O5 kg−1 soil).Results: The effects of P application on the Zn content of shoots and roots in wheat and on the levels of available Zn in soil differed on the two soils. The wheat dry weight on both soils was highest with 2000 mg P2O5 kg−1. Total Zn accumulation was reduced above 2000 mg P2O5 kg−1 on the acid soil and above 100 mg P2O5 kg−1 on the calcareous soil. Available soil Zn declined when the Bray-P concentration reached about 34 mg kg−1 in the acid soil and when the Olsen-P concentration exceeded 200 mg kg−1 in the calcareous soil. Shoot Zn concentrations were negatively related to available soil P on the two soils.Conclusion: The negative effects of increasing P application rates on Zn accumulation by wheat differed between the two soils. The effects showed no close relationship to available soil Zn. [ABSTRACT FROM AUTHOR]

Management of phosphorus (P) loss in soils with heavy manure application requires improved understanding of the transformation characteristics of soil P. Influences of manure application on the forms and sorption-desorption characteristics of P in surface (0–30 cm) and subsurface (30–60 cm) layer of a calcareous soil were investigated in a six-year field trial in comparison to chemical fertilizer application. Hedley fractionation and P K-edge X-ray absorption near-edge structure spectroscopy were used to determine the soil P forms. Manure (M) and chemical fertilizer (F) treatments resulted in P accumulation in two soil depths, but the total P accumulation in surface soil with M treatment was significantly lower than F treatment with similar P surplus. Compared to control, M and F treatments were significantly increased the proportion of labile P at both depths. In surface soil, M treatment significantly decreased stable Ca-associated P proportion and increased Fe-associated P and inositol hexakisphosphate proportions. The accumulation and transformation of P in M treatment distinctly decreased P sorption maximun, sorption coefficient and buffer capacity, and increased the degree of P saturation and P desorption relative to F treatment. The soil properties of pH, organic carbon (OC), total nitrogen (TN), Mehlich-3 extractable Ca and Fe, and phytase in surface soil and pH, OC, TN, Mehlich-3 extractable Ca and dehydrogenase in subsurface soil had significant effects on the compositions of soil P ( P  < 0.05), respectively. Lowered pH due to manure application mainly contributed to P transformation and release in the calcareous soil. [ABSTRACT FROM AUTHOR]

Phosphorus (P)‐deficiency symptoms are known for Lupinus species grown in calcareous soil, but we do not know if this is due to high calcium (Ca) availability or low P availability in the soil. To address this problem, we explored both the effects of Ca and its interaction with P on nutrient status and growth of three Lupinus species. Two Ca‐sensitive genotypes (Lupinus angustifolius L. P26723 and Lupinus cosentinii Guss. P27225) and two Ca‐tolerant genotypes (L. angustifolius L. cv Mandelup and Lupinus pilosus Murr. P27440) were grown hydroponically at two P (0.1 and 10 μM) and three Ca (0.1, 0.6 and 6 mM) levels. Leaf symptoms and biomass were recorded, whole leaf and root nutrient concentrations were analysed, and leaf cellular P and Ca concentrations were determined. Phosphorus‐deficiency symptoms were only observed in the Ca‐sensitive genotypes. Among all the genotypes in this study, the Ca‐tolerant L. pilosus showed an ability to maintain stable leaf Ca and P concentrations whereas the Ca‐tolerant L. angustifolius cv Mandelup did not maintain a stable whole leaf Ca concentration, but maintained a low cytosolic Ca2+ concentration through effective Ca compartmentation. However, the two Ca‐sensitive genotypes, L. angustifolius P26723 and L. cosentinii, did not exhibit an ability to maintain a stable whole leaf Ca concentration or effectively compartmentalize Ca. Therefore, having the capacity to maintain a stable whole leaf Ca concentration or effectively compartmentalizing Ca in leaves are likely critical for Lupinus species to be Ca tolerant. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is a vital element for plant growth and maturity, yet most soils have low P availability. The aim of the present study was to synthesize a mixture of nanohydroxyapatite (nHA) and saturated nanoclinoptilolite (nCp) and compare its ability to improve the P solubility with that of a natural system (Cp/rock phosphate). Consequently, as nCp were saturated with different salt solutions, the P solution concentration decreased in the following order: ((NH4)2SO4) NH4-nCp > (NH4Cl) NH4-nCp > (KCl) K-nCp > (K2SO4) K-nCp. Higher P availability was achieved at higher ratios of nCp/nHA. The nCp/nHA appear twice more effective in P released than Cp/PR (42.73% vs 19.23%). The greatest increase (5 mg/L) in the quantity of P released was at a nCp/nHA ratio of 15. Parabolic diffusion and power function equations fitted best to the data. This work demonstrates that nCp/nHA can act as an effective P fertilizer in calcareous soils. [ABSTRACT FROM AUTHOR]

Four types of plant residues (fruit waste, potato, sunflower, and wheat) with wide ranges of carbon to nitrogen (C/N) and carbon to phosphorus (C/P) ratios were added to the soil at the rate of 20 g kg−1 (dry weight basis) and incubated for two months. In soils treated with plant residues, the P sorption ranged from 62.0% (potato) to 96.6% (wheat) and from 12.6% (fruit waste) to 50.6% (wheat) when 20 and 1500 mg P kg−1 were added to the soils, respectively. In general, incorporation of plant residues decreased maximum P sorption capacity but increased bonding energy. The maximum P sorption capacity was reduced from 586 mg kg−1to 500, 542, and 548 by wheat, fruit, and potato residues, respectively, but increased to 665 mg kg−1 by sunflower residue. At higher P addition, the highest percentage of desorbed P was observed in soils treated with wheat residue (49.9%); followed by fruit waste (46.5%), potato (43.5%), sunflower (38.8%) and control soils (37.0%). It indicated that the P content of the organic residues had an important role in the sorption and desorption of P in calcareous soils. Among organic residues, sunflower residue showed high sorption and low desorption of P in soils, indicating a higher potential of this organic residue for P retention and reducing surface and groundwater contamination in calcareous soils. [ABSTRACT FROM AUTHOR]

Adsorption and precipitation reactions often dictate the availability of phosphorus in soil environments. Tripolyphosphate (TPP) is considered a form of slow release P fertilizer in P limited soils, however, investigations of the chemical fate of TPP in soils are limited. It has been proposed that TPP rapidly hydrolyzes in the soil solution before adsorbing or precipitating with soil surfaces, but in model systems, TPP also adsorbs rapidly onto mineral surfaces. To study the adsorption behavior of TPP in calcareous soils, a short-term (48 h) TPP spike was performed under laboratory conditions. To determine the fate of TPP under field conditions, two different liquid TPP amendments were applied to a P limited subsurface field site via an in-ground injection system. Phosphorus speciation was assessed using X-ray absorption spectroscopy, total and labile extractable P, and X-ray diffraction. Adsorption of TPP to soil mineral surfaces was rapid (< 48 h) and persisted without fully hydrolyzing to ortho-P. Linear combination fitting of XAS data indicated that the distribution of adsorbed P was highest (~30-40%) throughout the site after the first TPP amendment application (high water volume and low TPP concentrations). In contrast, lower water volumes with more concentrated TPP resulted in lower relative fractions of adsorbed P (15-25%), but a significant increase in total P concentrations (~3000 mg P kg soil) and adsorbed P (60%) directly adjacent to the injection system. This demonstrates that TPP application increases the adsorbed P fraction of calcareous soils through rapid adsorption reactions with soil mineral surfaces. [ABSTRACT FROM AUTHOR]

Wetland soils act as a sink or source of phosphorus (P) to the overlaying water due to phosphorus sorption-desorption processes. Litter information is available on sorption and desorption behaviors of phosphorus in coastal wetlands with different flooding conditions. Laboratory experiments were conducted to investigate phosphorus sorption-desorption processes, fractions of adsorbed phosphorus, and the effects of salinity, pH and temperature on phosphorus sorption on soils in tidal-flooding wetlands (TW), freshwater-flooding wetlands (FW) and seasonal-flooding wetlands (SW) in the Yellow River Delta. Our results showed that the freshly adsorbed phosphorus dominantly exists in Occluded-P and Fe/Al P and their percentages increased with increasing phosphorus adsorbed. Phosphorus sorption isotherms could be better described by the modified Langmuir model than by the modified Freundlich model. A binomial equation could be properly used to describe the effects of salinity, pH, and temperature on phosphorus sorption. Phosphorus sorption generally increased with increasing salinity, pH, and temperature at lower ranges, while decreased in excess of some threshold values. The maximum phosphorus sorption capacity (Q max ) was larger for FW soils (256 mg/kg) compared with TW (218 mg/kg) and SW soils (235 mg/kg) ( p < 0.05). The percentage of phosphorus desorption (P des ) in the FW soils (7.5–63.5%) was much lower than those in TW (27.7–124.9%) and SW soils (19.2–108.5%). The initial soil organic matter, pH and the exchangeable Al, Fe and Cd contents were important factors influencing P sorption and desorption. The findings of this study indicate that freshwater restoration can contribute to controlling the eutrophication status of water bodies through increasing P sorption. [ABSTRACT FROM AUTHOR]

The present study investigated kinetics of phosphorus (P) release from some calcareous soils employing DGT technique. For these purpose, DGT were deployed in ten calcareous soils for different time periods between 4 h and 21 days and the accumulated P were used to calculate the distribution coefficient for labile metal, K dl , desorption rate constants (k − 1 ) and the rate at which the soil system can resupply P from solid phase to solution (Tc) using the DIFS model. The values of K dl calculated from DIFS ranged from 0.67 to 198 cm 3 /g. Response times (Tc) were so short in six studied soils with low Olsen-P. A short response time means that the rapid resupply from the solid phase and slow depletion over time of the available P pool occurs. By contrast, the four rests of the soils have a longer response time (about 40 min) and so little the resupply from the solid phase, leading to a progressive depletion. The P desorption rate (k − 1 ) parameter derived from DIFS were from 9.9 ∗ 10 − 6 to 21.12 ∗ 10 − 4 s − 1 with a mean 4.54 ∗ 10 − 4 and well-correlated with the content and/or the concentration of P in corn shoot (r = 0.74, P < 0.05) and root (r = 0.71, P < 0.05) confirming the importance of P desorption rate in plant P nutrition in the calcareous soils. In these study, the close correlation was obtained between clay and calcium carbonate equivalent concentration with P desorption rate that demonstrate DGT technique sensitive to soil properties and may allow the study of root-induced changes in rhizosphere. [ABSTRACT FROM AUTHOR]

Phosphorous (P) has a significant role in root growth, fruit and seed development, and plant disease resistance. Currently, no P fertilizer recommendations are available for vegetables grown on calcareous soils in Florida. The objective of this study was to evaluate the impact of different P rates on leaf tissue P concentration (LTPC), plant growth, biomass accumulation, fruit yield, and postharvest quality of tomato (Solanum lycopersicum L.) grown on a calcareous soil. The experiment was conducted with soils containing 13 to 15 mg·kg-1 of P extracted by ammonium bicarbonatediethylenetriaminepentaacetic acid (AB-DTPA). Phosphorus fertilizers were applied at rates of 0, 29, 49, 78, 98, and 118 kg·ha-1 of P before laying polyethylene mulch. Tomatoes were grown using drip irrigation during the winter seasons of 2014 and 2015. No significant responses to P rates were found in LTPC during both growing seasons. Plant height, stem diameter, and leaf chlorophyll content at 30 days after transplanting (DAT) were significantly affected by P rates in 2015, but not in 2014. The responses of plant biomass were predicted by linear models at 60 DAT in 2014 and at 30 DAT in 2015. There were no significant differences in plant biomass at 95 DAT in both years. At the first and second combined harvest, the extralarge fruit yield was unaffected in 2014, but predicted by a quadratic-plateau model with a critical rate of 75 kg·ha-1 in 2015. The total season marketable yields (TSMY) and postharvest qualities were not significantly affected by P rates in either year. Phosphorous rate of 75 kg·ha-1 was sufficient to grow a tomato crop during the winter season in calcareous soils with 13-15 mg·kg-1 of AB-DTPAextractable P. [ABSTRACT FROM AUTHOR]

Understanding the role of organic acids on phosphorus (P) sorption capacity of soils is very important for its economic and friendly management. Combining P application with low-molecular weight organic acids could result in its higher plant availability for prolonged time. Therefore, citric and oxalic acid (at the rate of 1.0 mM kg−1soil) were evaluated for their effect on P sorption capacity and its plant availability in two different textured calcareous soils. Organic acids decreased P sorption capacity and organic carbon partition coefficient (Koc) whereas increased Gibbs free energy (ΔG) of P. Organic-acid-treated soils required lesser quantity of P fertilizer to produce soil solution P concentration optimum for plant growth (external P requirement [EPR0.2]), that is, 0.2 mg L−1. Citric acid was efficient than oxalic acid in the above effects. P sorption parameters of Freundlich model were negatively correlated with lime potential and ΔGwhereas had positive correlation (P < 0.05) with EPR0.2andKoc. Incubation with oxalic acid increased available P in loamy sand and loam soil by 20% and 30%, respectively. Thus, organic acids could help reduce application rate of P fertilizer through lowering its adsorption in highly P-fixing soils without compromise on yield. [ABSTRACT FROM AUTHOR]

In this work four stable bio-waste composts (C1, C2, C3, C4) were selected on the basis of their increasing water soluble P (H 2 O-P). The P speciation was assessed via sequential chemical extraction (SCE) on the same products. Moreover, the plant-available P was assessed via apparent recovery fraction approach (ARF) in a pot test on ryegrass over 21 weeks at 15 mg P kg − 1 of soil. An inorganic P source (P-chem) was added as a reference at the same P rate in addition to a non-fertilized control (Control). SCE showed that the sparingly soluble P (HCl-P) was the most important fraction in all composts: C1 (HCl 65% > NaHCO 3 17% = NaOH 17% > H 2 O 1%); C2: (HCl 51% > NaOH 23% > NaHCO 3 18% > H 2 O 7%); C3: (HCl 58% > NaOH 21% > NaHCO 3 12% > H 2 O 9%); C4: (HCl 39% > NaOH 23% > NaHCO 3 22% > H 2 O 16%). The plant test showed that the different treatments had a different ARF (%) at the first harvest: P-chem (14.7)> C4 (14.4)> C3 (14.1)> C2 (3.4)>C1 (3.1), compared to the cumulated ARF (%) of the six harvests: C4 (50.1)> C3 (35.0)> C1 (21.1)> C2 (18.3)> P-chem (17.4). Data showed a good correlation of H 2 O-P vs. plant ARF at the first harvest and a good correlation of labile P (H 2 O-P + NaHCO 3 -P) vs. total plant ARF over 21 weeks. The free and labile P forms from SCE can be a valuable tool in the assessment of fast and middle term plant-available P from stable bio-waste composts in calcareous soils. [ABSTRACT FROM AUTHOR]

Accurate estimation of phosphorus (P) leaching is important because excess P may reduce surface and ground water quality. Little attention has been paid to estimate P leaching from soil tests in calcareous soils. The relation between different soil tests P (STP), P sorption index (PSI) and degree of P saturation (DPS) and leaching of P were examined for assessing the risk of P loss from calcareous soils. Columns leaching repacked with native soils were leached with either distilled water or 10 mM CaCl 2 solutions, separately. Four leaching events were performed at four days, and 28.7 mm of distilled water or 10 mM CaCl 2 solutions was applied at each leaching events. Compared with distilled water, CaCl 2 had a small ability to solubilize P from soils. Concentration of P in leachate in both leaching solutions was exceeding 0.1 mg l −1 associated with eutrophication. Cumulative P leached P was ranged from 0.17 to 18.59 mg P kg −1 and 0.21–8.16 mg P kg −1 , when distilled water and 10 mM CaCl 2 solutions were applied, respectively and it was higher in sandy clay loam soils compared with clay soils. Among evaluated environmental soil P tests, P CaCl2-3h (P extracted by 10 mM CaCl 2 for 3 h), P CaCl2-1h (P extracted by 10 mM CaCl 2 for 1 h) were more accurate than other soil P tests for predicting P concentration in the leachates in both leaching solutions and accounting for 83% and 72% of variation of P concentration, respectively. The water extractable P (WEP) (r = 0.771) and Olsen-P (P Ols )(r = 0.739) were significantly related to the leached P concentration using distilled water solution in a split line model, with a change point of 27.4 mg P kg −1 and 61.5 mg P kg −1 , respectively. Various DPS were calculated and related to the leached P concentration. Based on P extracted by Mehlich-3 (P M3 ) and HCl (P HCl ) and PSI, the change point of the relationship between leached P concentration and DPS M3-3 ( P M 3 ( P M 3 + PSI ) × 100 ) and DPS HCl-2 ( P HCl ( P HCl + PSI ) × 100 ) for both leaching solutions was approximately the same, thus a mean value of 49% for DPS M3-3 and 73% for DPS HCl-2 was obtained. Soils were grouped into four categories of increasing P leaching potential based on WEP, P Ols , and DPS M3-3 . The results indicated that 8.00%–25.50% of the soil grouped in no risk category whereas 8.00%–13.70% of the soils fell into the high risk category. [ABSTRACT FROM AUTHOR]

In a field trial, Dalbergia sissoo biochar was used to investigate its potential for improving growth, yield and nutrient recovery of wheat (Triticum aestivum L.), at varying fertilizer rates under calcareous soil. Two biochar levels (0.0 and 1.0% of soil weight) were used along with five fertilizer rates i.e. 0, 25, 50, 75 and 100% of recommended inorganic fertilizer dose (RFD). Seeds of wheat cultivar Faisalabad-2008 were sown in the field using 2 factorial-randomized complete block design. At reduced fertilizer rates, biochar application improved plant growth parameters i.e. plant height, spike length, number of tillers hill-1 and grain yield over the respective treatments having inorganic fertilizer without biochar. Regarding nitrogen (N), phosphorus (P) and potassium (K) content, the highest statistical results were achieved at reduced fertilizer doses along with biochar application i.e. N and P content in wheat straw and grain at 50% RFD, straw N and P uptake at 75% RFD, grain N and K uptake at 50% RFD and grain P uptake at 75% RFD. The highest N, P and K recovery was calculated in the treatments having 50% RFD + biochar with 95%, 25% RFD + biochar with 38% and 25% RFD with 117%, respectively. In comparison with control treatment (without fertilizer and biochar), biochar application improved soil CEC up to 40%. With biochar application, no any significant change was observed in other soil chemical properties i.e. pH and EC. The results suggested that 1.0% biochar along with reduced fertilizer doses, could be effectively used to improve wheat growth, yield, nutrient content and nutrient uptake under field condition. Moreover, 1.0% biochar along with 75% of RFD can be effectively used in place of 100% RFD to get the highest yield. [ABSTRACT FROM AUTHOR]

Soil phosphorus (P) tests are designed to indicate plant-available inorganic orthophosphate (P i ), but fail to account for P i that may become available through organic phosphorus (P o ) mineralization. This P source may be especially important in soils with low concentrations of solution and labile P i . We assessed gross P o mineralization and immobilization using labeling with 33 P in four calcareous Alfisols with varying concentrations of Olsen soil test P that were collected from forage fields of dairy farms in Ontario, Canada. Rapid microbial 33 P uptake during incubation was found for the soils with the lowest available P i as indicated by both Olsen soil test P and water-extractable P i . The tracer incorporation into microbial P after 8 days ranged from 7 to 44% of applied 33 P and was negatively related to water-extractable P i following a power-type relationship. As concentrations of microbial P were similar in all soils, this suggests faster turnover of P in the microbial biomass at water-extractable P i below 0.1 mg P kg −1 soil. Daily gross P o mineralization rates ranged from 0.2 to 2.8 mg P kg −1 soil d −1 and contributed 7–56% of the isotopically-exchangeable P in 8 days. Based on these findings, microbial processes have the potential to make a significant contribution to forage P nutrition. [ABSTRACT FROM AUTHOR]

Applying manure to crops may alter P speciation in the soil profile and thus affect its availability for plant uptake and transport to surface waters. The goal of this research was to determine how repeated manure amendments affect P speciation within calcareous soil. Soil samples were collected in 2013, 2014 and 2015 from two depths to analyze differences in P composition following annual applications of 17 Mg ha-1 manure, 52 Mg ha-1 manure, or NH4H2,PO4 fertilizer and control plots (no P). To speciate the soil P, sequential chemical extraction, P K-edge X-ray adsorption near-edge structure (XANES) spectroscopy, 31P nuclear magnetic resonance spectroscopy, and microprobe element mapping were used. Total P concentration in the manure-amended soils increased over 3 yr. The highest soil test P concentrations were in the 52 Mg ha-1 plots. Most extractable P in the sequential extraction procedure was removed with the most aggressive extractant, suggesting that the predominant form of P is associated with Ca-P minerals. The XANES results showed that P species were similar among all amendments and years: 54 to 74% Ca-P minerals (e.g., hydroxyapatite), 25 to 35% adsorbed P, and 0 to 19% organic P (predominantly phytic acid). Despite the poorly soluble Ca-P species predominating in all soils, soil test P increased in the manure-amended soils. The P speciation results provide a baseline to compare how long-term changes affect P availability and will be useful for designing long-term scenarios in manure-amended calcareous soils to limit excess soil P that could leach into water. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the influence of soil texture on phosphorus (P) extractability and sorption from a wide range of calcareous soils across Hamedan, western Iran. Fifty seven soil samples were selected and partitioned into five types on the basis of soil texture (clay, sandy, sandy clay loam, sandy loam and mixed loam) and the P extracted with calcium chloride (P CaCl2 ), citrate (P citrate ), HCl (P HCl ), Olsen (P Ols ), and Mehlich-3 (P M3 ) solutions. On the average, the P extracted was in the order P HCl > P M3 > P citrate > P Ols > P CaCl2 . The P extracted by P citrate , P HCl , P Ols , and P M3 methods were significantly higher in sandy, sandy clay loam and sandy loam textures than clay and mixed loam textures, while soil phosphorus buffer capacity (PBC) was significantly higher in clay and mixed loam soil textures. The correlation analysis revealed a significant positive relationship between silt content Freundlich sorption coefficient (K F ), maximum P sorption (Q max ), linear distribution coefficient (K d ), and PBC. All extractions were highly correlated with each other and among soil components with silt content. The principal component analysis (PCA) performed on data identified five principal components describing 74.5% of total variation. The results point to soil texture as an important factor and that silt was the crucial soil property associated with P sorption and its extractability in these calcareous soils. DPS M3-2 ( P M 3 P M 3 + Q max × 100 ) and DPS citrate ( P citrate P citrate + Q max × 100 ) proved to be good indicators of soil's potential P release in these calcareous soils. Among the DPS, 21% of soils reported DPS M3-2 , values higher than the environmental threshold, indicating build-up of P and P release. Most of the studied sandy clay loam soils had exceeded the environmentally unacceptable P concentration. Various management practices should be taken into account to reduce P losses from these soils. Further inorganic and organic P fertilizer inputs should be reduced in some parts of studied area. [ABSTRACT FROM AUTHOR]

The depletion of phosphate rock reserves makes necessary the finding and characterization of new phosphorus (P) sources to ensure a sustainable P fertilization. This research deals with the effect of the application of organic materials derived from the winery and distillery industries on P availability in two calcareous soils. Soils were treated with five organic materials providing different amounts of P: two raw wastes (exhausted grape marc and grape stalk) and three composts made with different proportions of these materials or including cake lees as well. The soils were incubated for 16 weeks determining soil pH, dissolved organic carbon and Olsen P in five samplings with time. At the end of the incubation, inorganic P was fractionated to NaOH–NaCl–P, citrate-bicarbonate-dithionite–P (CBD–P), and HCl–P and the P sorption index (PSI) was also determined. The increment in Olsen P was firstly positively related to the amount of P applied, being higher in the composted materials, but along time the effect of other factors such as the organic matter incorporation influenced these changes. After 16 weeks of incubation, the enhancement of Olsen P produced by the different materials equalized (8.9 mg kg − 1 on average), despite of the different amounts of P applied with each one. Increasing the P applied with the organic materials in these soils enhanced P retained in the sparingly soluble P fraction (HCl–P) whereas the addition of raw materials slightly released P from this fraction, recovering more P in the most labile pool (NaOH–NaCl–P). It can be concluded that the winery and distillery derived materials had a positive effect on soil P availability and that P in excess would be retained due to the calcareous nature of these soils, avoiding contamination risks. [ABSTRACT FROM AUTHOR]

A sequential fractionation method proposed by Jiang and Gu (1989) distinguished three types of calcium phosphates (Ca-P) according to their different plant availabilities. Three extractants, NaHCO 3 , NH 4 Ac, and H 2 SO 4 were used to extract Ca 2 -P, Ca 8 -P, and Ca 10 -P types, respectively, from soil. This sequential fractionation method was tested and modified for analyzing the P chemistry of a calcareous soil. The solubility test and the model diagrams of the stability of the major Ca-P minerals showed that NaHCO 3 was able to extract brushite (Ca 2 -P type), and NH 4 Ac extracted brushite and β-tricalcium P (Ca 8 -P type) as well as hydroxyapatite (Ca 10 -P type). Therefore the P forms targeted by extraction with NH 4 Ac should include both Ca 8 -and Ca 10 -P types. The sum of the P extracted by all extractants in the sequential fractionation method in the calcareous soil was in agreement with the total P measured by the perchloric acid digestion method. A proportion of organic P measured by the sequential fractionation method was in agreement with the result from solution 31 P NMR spectroscopy. This study showed that the modified sequential fractionation method and its target P forms would be useful for quantifying and characterizing inorganic and organic P in a calcareous soil, even though it should be used in combination with other techniques, such as solution 31 P NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Effective soil phosphorus (P) management requires the understanding of P forms and its availability. The amount and distribution of P in different fractions of 15 soil samples of Fars province, Iran were determined by sequential extraction methods. The relationships of the P distribution among each other and with soil characteristics were investigated. Total P of different soils ranged from 349 to 994.3 cmol.kg-1. The clay contents of different samples ranged from 18% to 53%, CEC from 8.5 to 24.9 (cmol(+)kg-1) and the CCE from 20.6% to 64%. The amount of different P forms Ca2-P (dicalcium phosphates), Ca8-P (octacalcium phosphates), Al-P (Alphosphates), Fe-P (Fe-phosphates) and P as Ca10-P (apatite) were determined. The relative abundance of other inorganic P forms was in the order of Ca10 - P > Ca8- P > Al -P> Fe-P>Ca2-P > Occl-P. Simple correlation coefficients showed that Olsen-P had a significant correlation with total-P, Ca2-P, Ca8-P and Al-P. A Significant correlation was also observed between the P forms, which is presumably a reflection of the existence of a dynamic relation between the chemical forms of Phosphorus in soil. Clay with total-p and Apatite; total P with Olsen, Al-P and Organic-P; CEC with total-P and Organic-P have positive significant correlation. Sand with Ca10-P and Al-P; organic-p and Al-P with pH have negative significant correlation. [ABSTRACT FROM AUTHOR]

Application of phosphorus (P) fertilizers to P-deficient soils can also result in P accumulation. In this study, soil P status and P uptake by apple trees were investigated in 5-, 10-, and 15-year-old orchards in the semi-arid Loess Plateau, China, and subset soils with different soil P statuses (14–90 Olsen-P mg kg−1) were selected to evaluate the characteristic P adsorption. Due to the low P-use efficiency (4–6%), total soil P increased from 540 mg kg−1 to 904 mg kg−1, Olsen-P ranged from 3.4 mg kg−1 to 30.7 mg kg−1, and CaCl2-P increased from less than 0.1 mg kg−1 to 0.66 mg kg−1 under continuous P fertilization. The P sorption isotherms for each apple orchard were found to fit the Langmuir isotherm model (R2 = 0.91–0.98). K (binding energy) and Qm (P sorption maximum) decreased, whereas DPS (degree of phosphorus sorption) increased with increasing P concentration. CaCl2-P increased significantly with the increase of Olsen-P, especially above the change point of 46.1 mg kg−1. Application of surplus P could result in P enrichment in P-deficient soil which has high P fixation capacity, thus posing a significant environmental risk. [ABSTRACT FROM AUTHOR]