Phosphorus Transformations Research Articles

The Effective Combination of Humic Acid Phosphate Fertilizer Regulating the Form Transformation of Phosphorus and the Chemical and Microbial Mechanism of Its Phosphorus Availability

In the process of phosphate fertilizer production, adding humic acid to produce humic-acid-value-added phosphate fertilizer can improve fertilizer efficiency and promote crop growth. Although studies have primarily focused on investigating the impact of humic acid’s structure and function on phosphorus availability in humic-acid-added phosphate fertilizers, there is limited research on the regulatory effects of phosphorus fertilizer structure and the synergistic mechanisms involving microorganisms. Therefore, this study aimed to examine the chemical and biological mechanisms underlying the increased efficiency of humic-acid-added phosphate fertilizers by implementing various treatment processes. These processes included physically blending humic acid with phosphate fertilizer (HA+P), chemically synthesizing humic acid phosphate fertilizer (HAP), using commercially available humic acid phosphate fertilizer (SHAP), employing ordinary potassium phosphate fertilizer (P), and implementing a control treatment with no phosphate fertilizer (CK). Investigating the synergistic mechanism of humic-acid-added phosphate fertilizers holds significant importance. The results showed that during the preparation of HAP at high temperature, a new absorption peak appeared at 1101 cm−1, and a new chemical bond -O- was formed. The hydroxyl fracture in humic acid combined with phosphoric acid to form a phosphate ester (P-O-C=O) structure. HAP residues were concentrated on the surface and loaded with more soil minerals. The content of highly active oxygen-containing functional groups—such as aromatic C-O, carboxyl/amide carbon and carbonyl carbon—increased significantly, while the content of alkyl carbon, oxyalkyl carbon, and aromatic carbon decreased. Upon combining humic acid with potassium phosphate, the carboxyl group and calcium ions formed the HA-m-P complex, increasing the content of soluble phosphate (H2PO4−) in the soil by 1.71%. Compared to HA+P treatment, HAP treatment significantly increased the soil’s available P content by 13.8–47.7% (P < 0.05). The plant height, stem diameter, and above-ground biomass of HAP treatment were increased by 21.3%, 15.31%, and 61.02%, respectively, and the total accumulations of N, P, and K nutrient elements were increased by 6.71%, 31.13%, and 41.40%, respectively, compared to the control treatment. The results of high-throughput sequencing showed that the rhizosphere soil of HA+P and HAP treatment was rich in bacterial groups, the soil microbial structure was changed, and the bacterial community diversity was increased under HAP treatment. The number of genes encoding phytase and alkaline phosphatase associated with organophosphorus dissolution increased by 3.23% and 2.90%, respectively, in HAP treatment. Humic acid phosphate fertilizer forms phosphate esters in the process of chemical preparation. After application, the soil’s microbial community structure is changed, and soil enzyme activity related to phosphorus transformation is improved to promote tomatoes’ absorption of soil nutrients, thus promoting tomato plant growth and nutrient accumulation.

Varying Phosphate Fertilizers Exerted Different Effects on Inorganic Phosphorus Transformation, Tobacco Growth, and Phosphorus Use Efficiency in Purple Soil

Varying Phosphate Fertilizers Exerted Different Effects on Inorganic Phosphorus Transformation, Tobacco Growth, and Phosphorus Use Efficiency in Purple Soil

Hydrophyte Debris Induced Sedimentary Phosphorus Release in Tuojiang Rivers, China.

Hydrophyte debris decomposition may contribute to phosphorus (P) release from the sediments in riverine systems, but the transport and transformation of organic phosphorus during this process has not been studied well. Here, a ubiquitous hydrophyte in southern China (Alternanthera philoxeroides, A. philoxeroides) was selected to identify the processes and mechanisms of sedimentary P release in late autumn or early spring by laboratory incubation. The results showed that the physio-chemical interactions changed quickly during the beginning of the incubation, where the redox potential and dissolved oxygen at the water-sediment interface decreased rapidly, reaching reducing (299 mV) and anoxic (0.23mg∙L-1) conditions, respectively. Soluble reactive P, dissolved total P and total P concentrations in overlying water all increased with time from 0.011, 0.025 and 0.169mg∙L-1 to 0.100, 0.100 and 0.342mg∙L-1 on average, respectively. Furthermore, the decomposition of A. philoxeroides induced sedimentary organic P release to overlying water, including phosphate monoester (Mono-P), and orthophosphate diesters (Diesters-P). The proportions of Mono-P and Diesters-P were higher at 3 to 9 days than at 11 to 34 days, being 29.4% and 23.3 for Mono-P, 6.3% and 5.7% for Diesters-P, respectively. Orthophosphate (Ortho-P) increased from 63.6 to 69.7% during these timeframes, which indicated the transformations of both Mono-P and Diester-P to bio-available orthophosphate (Ortho-P), causing the rising P concentration in the overlying water. Our results revealed that hydrophyte debris decomposition in river systems might lead to autochthonous P contribution even without external P import from the watershed, accelerating the trophic state of receiving waterbodies.

Metal oxide modified biochars for fertile soil management: Effects on soil phosphorus transformation, enzyme activity, microbe community, and plant growth

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 NH4Cl–P content, while metal oxide biochar reduced NH4Cl–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 Ca2–P and Ca8–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.

Nitrogen addition impacts on soil phosphorus transformations depending upon its influences on soil organic carbon and microbial biomass in temperate larch forests across northern China

Globally increasing atmospheric nitrogen (N) deposition can affect soil phosphorus (P) transformations, yet the pathways and underlying mechanisms are largely unclear. Here, we sampled soils from five larch stands along a soil fertility gradient in northern China that have experienced long-term N addition (>5 years), and measured soil P fractions and biochemical properties. We found that the magnitude and direction of N addition effects on soil inorganic P and organic P fractions significantly varied with initial soil C:N ratio. Specifically, N addition significantly reduced almost all soil inorganic P fractions in the larch stand with the highest soil C:N ratio (18.35). In contrast, N addition significantly elevated NaOH-extractable organic P and total organic P in the larch stand with the highest soil C:N ratio while reduced labile organic P and total organic P in the stand with the lower soil C:N ratio (11.74). N addition-induced changes in inorganic P fractions were significantly correlated with that of soil organic C. Moreover, N addition-induced changes in organic P fractions were significantly correlated with those of microbial biomass and acid phosphatase activity. Taken together, our results indicate that N addition influenced soil P availability and fractions mainly by affecting soil organic C and microbial properties, which can improve our understanding of mechanisms of changes in soil P availability under the context of increasing N deposition.

Bibliometric analysis of global research on bioretention from 2007 to 2021.

Bioretention is a typical low impact development (LID) practice that helps reduce peak urban stormwater runoff and runoff pollutant concentrations (e.g., heavy metals, suspended solids, organic pollutants), which has become an important part of urban stormwater management over the past 15years. To understand the research hotspots and frontiers in the field of bioretention facility research and provide a reference for research into bioretention facilities, we conduct a statistical analysis of global bioretention literature published during 2007-2021 using the Web of Science core database and the data visualization and analysis software VOSviewer and HistCite. The number of published articles related to bioretention facilities shows a rising trend over the study period, with research from China contributing greatly to global research on bioretention facilities. However, the influence of articles needs to be increased. Recent studies mainly focus on the hydrologic effect and water purification effect of bioretention facilities and on the removal of nitrogen and phosphorus nutrients from runoff rainwater. Further studies should focus on the interaction of fillers, microorganisms, and plants in bioretention facilities and its impact on the migration, transformation, and concentrations of nitrogen and phosphorus; the purification effect and mechanism of specific emerging contaminants in runoff; the selection and configuration optimization of filler materials and plant species; and the optimization of the design parameters of the model for bioretention systems.

Distribution and Release Potential of Soil Phosphorus Fractions in Water-level Fluctuation Zone of the Tributary Bay, Three Gorges Reservoir

After repeated wetting-drying cycles, the migration and transformation of phosphorus in the water-level fluctuation zone (WLFZ) are accelerated, and the eutrophication of tributary bays in the reservoir becomes increasingly serious. Soils in the WLFZ of a typical tributary of the Three Gorges Reservoir were collected, and then phosphorus forms and the degree of phosphorus saturation (DPS) were determined to analyze the phosphorus release potential. The results showed that, ① the average contents of total phosphorus (TP), inorganic phosphorus (IP), and organic phosphorus (OP) of soils in the WLFZ were 771.80, 485.33, and 166.30 mg·kg-1, respectively. The non-labile IP and OP were the dominate speciation of IP and OP, respectively. ② The distribution of P forms of soils in the WLFZ was affected by wetting-drying cycle. The contents of Ex-P and NaHCO3-Po of soils in the WLFZ were significantly higher than those in the contrasted soils, whereas the contents of Fe-P, HCl-Po, and Fulvic-Po decreased significantly along the elevation (P<0.05). The alternative wetting-drying cycle promoted the generation of labile P and the release and accumulation of moderately labile P of soils in the WLFZ. ③The content and proportion of bioavailable phosphorus (Bio-P) of soils in the WLFZ were in the range of 49.19-148.78 mg·kg-1 and 7.17%-24.78%, and the degree of phosphorus sorption (DPS) was in the range of 5.85%-22.00%. At present, the phosphorus release risk of soils in the WLFZ was low. The soil at 170 m elevation requires further attention. Fe-P, HCl-Po, and Fulvic-Po contributed significantly to phosphorus release. The increase in pH promoted the release of Fe-P. Alkaline phosphomonoesterase (ALP) was an important participant in the transformation of OP. Additionally, organic matter (OM) was the main source of OP.

Review of Phosphorus Chemistry in the Thermal Conversion of Biomass: Progress and Perspectives

Phosphorus is vital for all life, which means that phosphorus is present in all biomass to some extent. Some types of biomass, such as certain agricultural residues, animal biomass, and sewage sludge, contain high levels of phosphorus. In thermal conversion of biomass, high levels of phosphorus can cause various operational problems. Extensive work has been carried out to understand the phosphorus chemistry taking place at higher temperatures. However, until now, knowledge about transformation chemistry and fate of phosphorus during thermal conversion of biomass was not easily accessible in one place. In this work, the outcome of an extensive literature review has been summarized. First, an introduction to the role of phosphorus in biomass, and in what forms it may be present, is given. Different analytical techniques relevant for characterization of phosphorus in biomass, biomass char, and biomass ash are described. A classification of phosphorus-rich biomass is proposed, and the potential of different phosphorus-rich biomass types is presented. To provide a common basis for the field of high-temperature phosphorus chemistry, fundamental chemistry relevant for thermal conversion of biomass is first discussed. This includes the gas phase chemistry and reaction pathways of light phosphorus species, pyrolysis, and combustion of organophosphorus compounds, and solid, liquid, and gaseous interactions with other ash-forming elements. Thereafter, an in-depth review of phosphorus transformations in biomass, including decomposition of organic phosphorus, ash transformations in the condensed phase, release to the gas phase, and formation of particulate matter in the flue gas follows. Finally, the review covers research focusing on phosphorus in different application aspects, such as the use of phosphorus as an additive to mitigate operational problems related to slag and deposit formation, the behavior of phosphorus in fluidized bed technologies, corrosion, and the deactivation of SCR catalysts.

The impact of potential leakage from the sub-seabed CO2 storage site on the phosphorus transformation in marine sediments – An experimental study

Carbon Capture and Storage (CCS) in the sub-seabed geological formations is a method of mitigation of carbon dioxide (CO2) emissions to avoid anthropogenic climate change. While CCS can be one of the most promising technologies to reduce atmospheric CO2 in the short and medium term, it raises serious concerns about the potential leakage of gas from storage sites. In the present study, the impact of acidification induced by CO2 leakage from a sub-seabed storage site on geochemical pools, and thus the mobility, of phosphorus (P) in sediment was investigated during laboratory experiments. The experiments were conducted in a hyperbaric chamber at a hydrostatic pressure of 900 kPa, which simulates pressure conditions at a potential sub-seabed CO2 storage site in the southern Baltic Sea. We performed three separate experiments in which the partial pressure of CO2 was: 352 μatm (corresponding pH = 7.7); 1815 μatm (corresponding pH = 7.0), and 9150 μatm (corresponding pH = 6.3). Under pH 7.0 and 6.3, apatite P is transformed into organic and non-apatite inorganic forms, which are less stable than CaP bonds and can be more easily released into the water column. At pH 7.7, P released during mineralization of organic matter and microbial reduction of FeP phases is bound with Ca, and the concentration of this form increases. The obtained results indicate that acidification of bottom water can reduce the efficiency of P burial in marine sediments, which contributes to an increase in P concentration in the water column and promote eutrophication especially in shallow areas.

Dosage effects of organic manure on bacterial community assemblage and phosphorus transformation profiles in greenhouse soil.

Manure is a potential substitute for chemical phosphate fertilizer, especially in intensive agriculture, such as greenhouse farming, but the associations between soil phosphorus (P) availability and the soil microbial community under manure application instead of chemical phosphate fertilizers are still rarely addressed. In this study, a field experiment in greenhouse farming with manure application instead of chemical phosphate fertilizers was established, including five treatments: a control with conventional fertilization and chemical phosphate fertilizer substitution treatments using manure as the sole P resource at 25% (0.25 Po), 50% (0.50 Po), 75% (0.75 Po), and 100% (1.00 Po) of the control. Except for 1.00 Po, all the treatments applied with manure harbored similar levels of available P (AP) as the control. Most of the bacterial taxa involved in P transformation were enriched in manure treatments. Treatments of 0.25 Po and 0.50 Po significantly enhanced bacterial inorganic P (Pi) dissolution capacity, while 0.25 Po decreased bacterial organic P (Po) mineralization capacity. In contrast, the 0.75 Po and 1.00 Po treatments significantly decreased the bacterial Pi dissolution capacity and increased the Po mineralization capacity. Further analysis revealed that the changes in the bacterial community were significantly correlated with soil pH, total carbon (TC), total nitrogen (TN), and AP. These results revealed the dosage effect of the impact of manure on soil P availability and microbial P transformation capacity and emphasized that an appropriate dosage of organic manure is important in practical production.

Migration and Transformation of Phosphorus from Phosphogypsum Leachate with High Fluorine Concentration in Soils with Different pH Values

Migration and Transformation of Phosphorus from Phosphogypsum Leachate with High Fluorine Concentration in Soils with Different pH Values

Side effect of organic fertilizing on the phosphorus transformation and balance over 27 years of maize monoculture

Side effect of organic fertilizing on the phosphorus transformation and balance over 27 years of maize monoculture

The Influence of Municipal Solid Waste Compost on the Tranformations of Phosphorus Forms in Soil

Searching for a renewable phosphorus (P) source for agricultural soils has become a challenge of particular importance on a global scale. Depletion of the world’s phosphate resources as well as the risk of environmental problems caused by excessive P mobility have placed this topic among the most important environmental issues. The aim of this study was to analyse the transformation of phosphorus forms in municipal solid waste compost (MSWC) at different maturity stages, to assess the effects of their application on soil phosphorus status and to evaluate the suitability of MSWC for agricultural soils as a potential phosphorus source. The application of MSWC to the soil had a positive effect on the content of available P. The content of potentially mobile P forms increased significantly in the soil, primarily after the introduction of immature MSWC and confirmed by the significant correlations with the applied P indicators. However, the results indicate that the MSWC does not pose a serious environmental risk and could become a potential source of P in the soil, although the material used for this purpose should be mature. This study also indicated that the assessment of using compost as a P source should not be based on P total content alone, but should include the content of different P forms and specific P-related indicators, to reflect both the P availability and the potential environmental risks.

Migration and Conversion of Phosphorus in Hydrothermal Carbonization of Municipal Sludge with Hydrochloric Acid

Phosphate ore is a non-renewable resource, so finding a replacement is necessary. Municipal sludge has significant recycling potential because of its high phosphorus content and large discharge characteristics. The migration and transformation of phosphorus in municipal sludge treated with different concentrations of HCl were studied using the standards, measurements, and testing phosphorus extraction protocol from two aspects: phosphorus complexation and mineral form. After the hydrothermal carbonization treatment without HCl, the hydrochar retained 99.7% of phosphorus in the sludge, and the organophosphorus percentage was about 30%. In the hydrothermal carbonization treatment with the addition of 0.5–2.5% HCl, the phosphorus content in the hydrochar decreased gradually from 99.5% (46.18 mg/g) to 91.8% (64.17 mg/g) that of the original sludge, and the proportion of non-apatite inorganic phosphorus increased from 34% to 94%. Hydrochloric acid provides a low-pH environment and promotes the dissolution of calcium-related phosphorus precipitates and enhances the dehydration reaction. This study provides technical support for the recovery of phosphorus resources from municipal sludge.

Phod-harboring bacterial communities mediated slow and fast phosphorus transformation in alkaline soil of a Robinia pseudoacacia afforestation chronosequence

Phod-harboring bacterial communities mediated slow and fast phosphorus transformation in alkaline soil of a Robinia pseudoacacia afforestation chronosequence

Evolution of phosphorus with the promotion of KOH in supercritical water gasification of dewatered cyanobacteria from ion perspective

Phosphorus is a very important resource, and dewatered cyanobacteria contains a large amount of it. Basic additives, such as KOH, are often used to promote hydrogen production during supercritical water gasification (SCWG) of biomass, but their effects phosphorus transformation have rarely been investigated. In this study, SCWG of dewatered cyanobacteria with potassium salt and KOH was conducted in autoclave at 400 °C for 10 min, to investigate the effect of K+ on the transformation of phosphorus under neutral and alkaline conditions. Results showed that K+ increased the proportion of phosphorus in the solid phase from 88.4% to 90.8–98.3%. Furthermore, K+ could promote the transformation of iron-combined phosphorus to calcium-combined phosphorus and occluded phosphate. Only when the reaction environment was alkaline, the proportion of phosphorus in the solid phase was significantly reduced to a minimum of 26.1%. When the amount of OH− was sufficient, can this part of phosphorus and organic phosphorus, which was decomposed and transformed by the promotion of OH−, be transferred to the liquid products. Results from this study laid a foundation simultaneously for hydrogen production and phosphorus recovery more environmentally and high-effectively.

Effect of environmental factors on phosphorus transformation during the growth of submerged macrophytes

Three submerged macrophytes, Hydrilla verticillata, Vallisneria natans, and Potamogeton crispus, were planted in winter and spring to investigate the environmental mechanism of phosphorus transformation during submerged macrophyte growth periods. The experimental buckets each contained 4,832.80 g of dry sediment (depth: 10 cm) and 100 L water. The phosphorus (P) fractions in the water and sediment were investigated along with the environmental factors, including pH, dissolved oxygen (DO), and redox potential (ORP). The concentrations of the different forms of P in the water and sediment were lower in the submerged macrophyte groups. Submerged macrophyte uptake was the primary reason for the decrease in P in the water and sediment. At the end of the experiment, the total amounts of phosphorus accumulated by H. verticillata, V. natans, and P. crispus were 156.05 g, 282.24 g, and 115.84 g, respectively, and the three submerged macrophytes enriched P by 4.18%, 7.56%, and 3.10%. The levels of the environmental factors pH, DO, and ORP were higher in the submerged macrophyte groups than the control groups. The environmental factors had different effects on the different forms of P during growth of the submerged macrophytes. H. verticillata primarily acted on the soluble reactive phosphorus (SRP) through environmental factors, while P. crispus acted on the dissolved total phosphorous, SRP, dissolved organic phosphorus, and particulate phosphorous through these factors. V. natans had a weak impact on P content in the water through the environmental factors. Hence, the transformation of P between the sediment and water was affected by environmental factors. Overall, the results of this study reveal the effects of environmental factors under submerged macrophyte growth on water purification as well as the migration and transformation of P in the sediment and on the surface and provide a theoretical basis for the ecological restoration of eutrophicated shallow lakes.

Calcium enhances phosphorus reclamation during biochar formation: Mechanisms and potential application as a phosphorus fertilizer in a paddy soil

Transformation of phosphorus (P) species during pyrolytic production of biochar from P-rich biowastes with a subsequent soil amendment is important to P reclamation. Aiming at increasing the content of plant-available P and restraining the formation of easily mobile P in pyrolysis product, this study used exogenous calcium ions (20 wt% CaCl2) addition prior to pyrolysis to regulate the pyrolytic transformation of P chemical fractions from sewage sludge and bone dreg. Results showed that active Ca catalyzed the decomposition of organic P to transform into inorganic orthophosphate. Based on Hedley’s sequential extraction method, this study found that addition of Ca ions remarkably reduced the content of soluble P, exchange P, Fe/Al bound P, and occluded P in biochar, while increased Ca bound P from 78 to 85% to 85–96%. Liquid 31P NMR indicated that exogenous Ca induced the crack of the P-O-P bond in pyrophosphate to become orthophosphates. It also explained why new orthophosphates including chlorapatite (Ca5(PO4)3Cl) and calcium hydroxyapatite (Ca10(PO4)6(OH)2) appeared in the Ca-composite biochar compared to pristine biochar. Combined with rapid P-release test in paddy soil (pH 6.27) and 30-days rice seedling growth test under flooded condition (10 wt% biochar addition ratio), it was confirmed that compared to pristine biochar, Ca-composite biochar released more P in paddy soil, but also promoted more P to be taken in by rice root and stalk. These results suggested that pretreating biowaste with Ca ion was a friendly approach to enhance P reclamation during biochar formation, making it a promising P fertilizer.

Phosphorus transformation behavior and phosphorus cycling genes expression in food waste composting with hydroxyapatite enhanced by phosphate-solubilizing bacteria

This study aimed to explore the effect of phosphate-solubilizing bacteria (PSB) Bacillus inoculation in the cooling stage on hydroxyapatite dissolution, phosphorus (P) forms transformation, and bacterial P cycling genes in food waste composting with hydroxyapatite. Results indicated that PSB inoculation promoted the dissolution of hydroxyapatite, increased P availability of compost by 8.1% and decreased the ratio of organic P to inorganic P by 10.2% based on sequential fractionation and 31P nuclear magnetic resonance spectroscopy. Illumina sequencing indicated Bacillus relative abundance after inoculation increased up to one time higher than control after the cooling stage. Network analysis and metabolic function of bacterial community analysis suggested inorganic P solubilizing genes of Bacillus and organic P mineralization genes of other genera were improved after inoculation in the core module. Therefore, bioaugmentation of PSB in the cooling stage may be a potential way to improve P bioavailability of bone and food waste in composting.

The content of phosphorus forms in calcareous irrigated serozems of the Tashkent region of Uzbekistan

In most cases, the irrigated soils of Uzbekistan provide low forms of phosphorus assimilated by plants due to their high fixation. Therefore, the bioavailability of P is one of the main factors limiting the yield of crops. The study aimed to identify the transformation of phosphorus in irrigated gray soils under the influence of the type of land use, age of development, and climate (location above sea level). For this purpose, the content of inorganic and organic pools of P was studied according to the Hedley method. The highest Pt values were noted in the soil of the Parkent region, where the amount of precipitation significantly exceeds that in other studied areas, as well as in the winterwheat-repeatedcrops-cotton (WW-RC-C) land use type with long-term use of high P fertilizer rates. In the studied soils, the share of Pi was 89-91%, while the share of Po was 9-11% of Pt. In the accumulation of labile P, in contrast to the accumulation of Pt, the greater availability of atmospheric precipitation and the WW-V type of land use, where the content of labile P. was significantly higher than in other studied soils. The obtained results indicate the need for individual consideration of the control of phosphorus nutrition of plants on soils used in various types of land use, their geographical location (altitude above sea level), and the age of development for agriculture, depending on the phosphate state of soils.