Factors affecting the solubility of phosphate rock residues in 2% citric acid and 2% formic acid

The 2% citric and formic acid solubilities of phosphate rock residues extracted from partially acidulated materials (20 and 35% acidulation) manufactured from two phosphate rocks (both ground and unground) in the presence of monocalcium phosphate, monosodium phosphate, calcium chloride, calcium sulphate, calcium carbonate, sodium carbonate and aluminium and iron sulphates have been examined. Such figures have been compared with previous results obtained for the equivalent unprocessed phosphate rocks. In general the effects of additives on the solubility of the phosphate rock residues were similar to those found for unprocessed phosphate rocks. However, the solubility figures were considerably lower for the 20% acidulated residues, while 2% formic acid solubilities for the 35% acidulated residues were also reduced. This would indicate that some deactivation of the phosphate rock had taken place during acidulation, the degree of which was dependent on the acidulation level and could be more readily observed in changes in 2% formic acid solubility than in 2% citric acid figures.     

Evaluation of double extraction techniques as solubility tests for fertiliser products containing phosphate rock components

Alternative extraction techniques for assessing the available P content in multi-component fertilisers such as partially acidulated phosphate rocks have been examined. Two types of double extraction method have been investigated, one involving sequential extraction procedures, and a second examining both the initial fertiliser and its residue independently, using either water or cold neutral ammonium citrate as the first extractant, and either 2% citric or 2% formic acid as the second solvent. The latter method, which used cold neutral ammonium citrate as the initial extractant, produced the most consistent results and provided a reproducible assessment of the solubility of the phosphate rock residue; it was not obvious which second solvent was preferable. Comparisons between the original phosphate rocks and their extracted residues indicated that there were many subtle influences which affected the solubility of the phosphate rock components, but a general deactivation of phosphate rock residues on acidulation as previously suggested was not apparent. Before any particular method can be recommended as an alternative to existing one step extraction techniques it is necessary to confirm its validity through agronomic trials.     

The use of chemical solubility tests in comparing phosphate fertilisers

The standard solubility tests as used in New Zealand for assessing single superphosphate have been applied to alternative high analysis fertilisers such as triple superphosphate and partially acidulated phosphate rocks using phosphoric acid. Under differing experimental conditions it has been established that the phosphate rock component has a variable solubility in 2% citric acid at all levels, and in neutral ammonium citrate at high levels of PR content, making comparisons between percentages of soluble P derived from different fertilisers inappropriate for chemical or agronomic assessment. Only water, which extracts all the monocalcium phosphate component but none of the phosphate rock, can be used to compare the efficiency of the acidulation process, and neutral ammonium citrate can be used to assess the amount of phosphate rock remaining when the acidulation level is in excess of 50%. 2% formic acid produced almost identical results to 2% citric acid for partially acidulated materials and therefore cannot be recommended as an alternative, improved extractant for fertilisers containing large proportions of residual phosphate rock.     

Influence of manufacturing variables on characteristics and the agronomic value of partially acidulated phosphate fertilizers

Partially acidulated phosphate fertilizers are manufactured either by direct partial acidulation of phosphate rocks (PRs) with sulphuric and/or phosphoric acid (directly acidulated PAPR) or indirectly by mixing reactive phosphate rocks (RPRs) with single superphosphate (SSP-RPR mixture). This form of low cost fertilizer manufacture is suitable for improving the agronomic value of unreactive PRs or production of high analysis fertilizers that can have agronomic values similar to fully acidulated phosphate fertilizers.The solubility characteristics of the directly acidulated PAPRs are affected by the type, composition and concentration of the acid used for acidulation, degree of acidulation, nature and fineness of PR and the method of manufacture. In general, partial acidulation with phosphoric acids which contain minimum amounts of metallic impurities acidulates more PR and results in more soluble P in the product. In the case of SSP-RPR mixtures made by adding RPR to immature SSP, the nature of PR used for SSP manufacture and the time of addition of RPR to ex-den SSP mixture affects the quality of the product. In order to minimize the selective reaction of the RPR with residual acid present in the ex-den SSP reaction mixture, RPR should not be added until PR acidulation (used for SSP) is essentially complete.The agronomic value of partially acidulated phosphate fertilizers is affected by the amount of water soluble P and the solubility of residual PR. None of the single extraction tests such as 2% citric acid, 2% formic acid and neutral ammonium citrate appear to be appropriate as indicators of plant available P in these fertilizers. Double extraction procedures which remove both the soluble P and the residual P have been investigated, but need to be correlated with agronomic data before they can be adopted as quality tests.     

Properties of unreacted rock residues in partially acidulated phosphate rocks affecting their reactivity

The nonacidulated P fraction of partially acidulated phosphate rocks (PAPR) was obtained by extraction with alkaline ammonium citrate solution. Investigations on this unacidulated rock residues using standard analytical techniques and electronbeam microanalysis showed a surface coating with highly increased fluorine content surrounding the unreacted phosphate rock particles. The coating may be responsible for low reactivity of the residues and their inferior agronomic effectiveness as compared to the original mother rock phosphate. Furthermore, the existence of dicalciumphosphate and Fe—Al—P compounds in PAPR products make solubility tests based on alkaline ammonium citrate appropriate to gauge the acidulated and easily plant available P fraction. Only after the removal of these compounds with citrate solution is an assessment of the potential agronomic value of the nonacidulated rock residues in 2% formic acid possible.     

Effects of partial acidulation on chemical and mineralogical characteristics of residual phosphate rocks

Original phosphate rocks (PR) and water insoluble residues (WIR) from mixtures of reactive PRs and single superphosphate, known commercially as longlife single superphosphate (LLSSP), and from partially acidulated PRs (PAPR), were compared in terms of their elemental content, chemical reactivity as indicated by the apatite unit cell a dimension and solubility. Phosphate rock reactivity is known to be inversely related to the a dimension. Partial acidulation (20%) with commercial grade phosphoric acid resulted in an increase in aluminium (Al), iron (Fe) and fluoride (F) concentrations in the WIRs. The apatite a dimensions of WIRs from LLSSPs were greater than those of the respective original North Carolina (NC), Khouribga (KR), Jordan (JR), Sechura (SE) and Arad (AR) PRs added to single superphosphate (SSP), made from Nauru PR (NR)) to produce the LLSSPs. This was attributed to the presence of the less reactive NR in the WIRs left-over from the SSP. Partial acidulation with phosphoric acid increased the apatite a dimensions of NC and ElHassa (EH) PRs. The increase in apatite a dimension of NC and EH was probably due to selective dissolution of a more reactive fraction of the PRs during partial acidulation. Changes in the apatite a dimension following partial acidulation with phosphoric acid were not significant for the other PRs studied, e.g. Gafsa (GF), KR and AR, although differential X-ray diffractograms (DXRD) indicated that the material dissolved during partial acidulation was more reactive than the WIRs and the original PRs. The apatite a dimension of NC PR was not affected by pretreatment with 2% or 4% citric acid (CTA). The contrasting response in a of NC PR to acidulation with phosphoric and citric acids may be related to differences in the strength of these acids, and/or to the differing environments under which the reactions took place.The 2% CTA and formic acid (FMA) solubilities of the WIRs from LLSSPs and PAPRs were markedly lower than those of the original PRs. This reduction in solubility of PRs following partial acidulation was probably related to changes in mineralogical and chemical composition of the WIRs as indicated by the increases in apatite a dimension of some residual PRs and shifts in peak positions in DXRD, to increases in the concentrations of Fe, Al and F compounds, and to coating effects of PR particles by Fe, Al and F compounds. This, in turn, may reduce the agronomic value of the residual PR component of PAPR and LLSSP fertilizers, particularly over the short-term.The solubility of residual PRs following pretreatment with 2% or 4% CTA was slightly lower than that of the original PRs. The pretreatment caused no significant change in the apatite a dimension of NC PR. The complexing effects of CTA and its lack of Fe and Al impurities may have prevented the formation of Fe, Al and F compounds. The effect of citric acid on PR reactivity is thus quite different from that of the mineral acids used to prepare LLSSPs and PAPRs.     

Characterizing the dissolution of phosphate rock materials by electro-ultrafiltration

Electro-ultrafiltration (EUF) was evaluated as a potential technique for characterizing the dissolution and assessing the chemical reactivity of contrasting phosphate rock (PR) materials. The types of rock used were: three reactive rocks, Sechura phosphate rock (SPR), North Carolina phosphate rock (NCPR), and Chatham Rise phosphorite (CRP), which contains significant amounts of calcium carbonate; one unreactive rock, Tennessee phosphate rock (TPR); and one iron and aluminium phosphate, calcined Christmas Island C grade phosphate rock (Calciphos). Dissolution of SPR increased as the solution:solid ratio increased to 250:1, the voltage was increased from 0 to 400 V, and the ionic strength of the extracting solution was increased. The neutralizing effect of any CaCO₃ present in PR materials, which is a major limitation with single chemical extraction procedures, does not appear to be a problem with EUF. A limitation of using de-ionized water as the extracting solution with EUF is the small amounts (1 to 6%) of total of P extracted. Addition of NaCl to the extracting solution increased the dissolution of all PR materials, although this varied with the PR. With both de-ionized water and NaCl as the extracting solution, EUF was inferior to 2% formic acid for assessing agronomic effectiveness of the PR materials. EUF appears to be of limited value in assessing the chemical reactivity of PR materials.     

Assessment of the relative agronomic effectiveness of phosphate rocks under glasshouse conditions

Six phosphate rocks (PRs) of varying reactivities were compared with monocalcium phosphate (MCP) in a glasshouse experiment growing perennial ryegrass (Lolium perenne cv. Nui) as the test plant on four soils of contrasting P sorption capacity and exchangeable Ca. The cumulative dry matter yield over 10 harvests showed a significant response to P application in all soils. Based on relative yield and P uptake, MCP was the most effective P fertilizer followed by the reactive phosphate rocks, which were superior to the unreactive rocks in all soils. The relative agronomic effectiveness (RAE) and substitution ratio (SR) of individual PR fertilizers, calculated with respect to MCP using the methods of vertical and horizontal comparison, respectively, were similar over a range of fertilizer rate. There was a decline or slight increase in the performance of PRs with time in the low P sorption soils but a consistent increase in the high P sorption soils. Some initial influence of exchangeable Ca content of the soils on the relative performance of PRs was also observed. Generally the PRs performed better in high P sorption soils than low P sorption soils and in low exchangeable Ca soils than high exchangeable Ca soils.     

Use of low grade phosphate rocks as biosuper fertilizer

A pot trial was conducted for 10 months to evaluate the fertilizer value of two low grade phosphate rocks applied either as biosuper (phosphate rock/sulphur granules, PR/S^*) or as untreated granulated rocks. The phosphate rocks were Chatham Rise nodules (CR), a marine deposit containing calcium phosphate and calcium carbonate, and the C grade ore from Christmas Island (CC) containing predominantly aluminiumiron phosphate and free oxides of iron and aluminium. Perennial ryegrass was grown as the test crop in a highly phosphate retentive allophanic soil, limed to pH 6.2. Single superphosphate was used as the standard fertilizer.Phosphate uptake and dry matter yields showed that biosuper prepared from CR was agronomically as effective as superphosphate whereas that prepared from CC was less effective. At the highest rate of application CR increased the yield of ryegrass by 80% over that of control but granulating it with sulphur increased the yield by 143%. The corresponding values for CC and CC/S were 39% and 50%. The time lags from the addition of CR/S and CC/S to apparent maximum phosphate availability were less than 18 and 49 days respectively.Olen bicarbonate extractable phosphate of soils increased by 100% and 33% respectively when CR and CC were added as biosuper in comparison with addition as phosphate rock granules.Liming the soil to raise its pH from 5.1 to 6.2 lowered the quantity of superphosphate needed to reach 90% of maximum yield by 23%.     

Chemical effects in the assessment of phosphate rock residues extracted from multicomponent fertilisers

Methods of obtaining reactive phosphate rock residues from multicomponent phosphate fertilisers which contain soluble phosphorus components have been examined. Extraction using cold neutral ammonium citrate has been found to be more suitable than water, as chemical reactions appear to occur in water extraction solutions to modify the residue, and more impurity species such as calcium sulphate and iron and aluminium phosphates remain in the residues to complicate the process of obtaining reliable solubility figures.Deactivation of the phosphate rock residues (as measured by decreased 2% formic acid solubilities) was found to be due to reactions occurring during the maturing process, and was dependent on the phosphate rock used, with North Carolina phosphate rock-based residues significantly affected, but Arad-based residues almost unaffected. However, for neutral ammonium citrate extractions, only North Carolina-based residues produced solubility figures lower than the original phosphate rock. Some selectivity of reaction in single superphosphate-reactive phosphate rock mixtures was indicated which further complicated assessment of the deactivation effect; however such an effect appeared to be much less significant than previously suggested.     

Single superphosphate-reactive phosphate rock mixtures. 2. The effect of phosphate rock type and denning time on the amounts of acidulated and extractable phosphate

Ground samples of Nauru (N), Christmas Island A (X), Jordan (J) or North Carolina (NC) phosphate rocks (PRs) were acidulated with³²P spiked sulphuric acid to produce single superphosphate (SSP) reaction mixtures. Subsequently, single superphosphatereactive phosphate rock (SSP-RPR) mixtures were manufactured by adding reactive phosphate rock (RPR) as either ground or unground NCPR or ground JPR to SSP reaction mixtures that had been denned for either 22 or 47 minutes after acid addition. The solubility of P in the final SSP-RPR products was assessed either by extraction with water, 2% citric acid, 2% formic acid or 1M neutral ammonium citrate (NAC), or by calculation of the exchangeable P content of the fertilizer by isotopic dilution techniques. The measurement of exchangeable P allowed calculation of the amounts of acidulated P in the ex-den SSP and the amount of RPR P acidulated on addition to ex-den SSP containing free phosphoric acid.Among the PRs used for SSP manufacture, the highest degree of acidulation at the ex-den stage was obtained for NCPR (92%) and the lowest was obtained for XPR (75%). As a consequence, the presence of XPR in the SSP reaction mixture decreased the amount of exchangeable P in the SSP-RPR mixtures. Whereas initially the conversion of PR P increased with time of acidulation at 22 minutes and 47 minutes (i.e. the time of addition of RPR) the differences in the degree of acidulation of PR in the ex-den SSP were not large and hence had no significant effect on the extractability of P in the SSP-RPR mixtures.The nature of the RPR added to the ex-den SSP reaction mixture had a significant effect on the solubility of P in the SSP-RPR mixtures. SSP-RPR mixtures with added unground NCPR or ground JPR had lower P solubility than when ground NCPR was added. RPR P constituted between 38 and 46% of the total P in the SSP-RPR mixtures and at acid/PR (A/R) ratios of 0.60 to 0.70, between 28 to 49% of the RPR P was acidulated by the free acid in the SSP reaction mixture during manufacture.The results also indicate that RPR mixtures made using ex-den SSP made from unreactive PRs will always contain more unreactive PR residue than those made with mature SSP. However, given the practical difficulties of producing the SSP-RPR mixtures with mature SSP, denning times should be extended for as long as practicably possible.     

Investigations on interactions of phosphorus compounds in partially acidulated phosphate rock and fertilizer effectiveness

Khouribga phosphate rock was partially acidulated with 50 and 70% of the required H₂SO₄ for complete acidulation. The unreacted rock residue was isolated by subsequent extractions with water and alkaline ammonium citrate solution. P solubility in 2% formic acid of this residues was reduced as compared to the original Khouribga phosphate rock. This loss in reactivity consistently increased with the degree of acidulation. Plant response to fertilizer application emphasized the negative effect of partial acidulation in an acid soil. Mixtures of superphosphate and phosphate rock were more effective than partially acidulated phosphate rock.Applications of apatitic P did not affect P efficiency on a neutral soil. Differences between mixed and partially acidulated phosphate rock could therefore not be observed. The effectiveness of the products was due to their content of acidulated P.Hydrolysis of monocalciumphosphate caused a further acidulation of the residual apatite in moist incubated granules. The extent of these reactions, however, was too low to improve P efficiency significantly.     

Enantioselective hydrogenation of 2-methyl-2-pentenoic acid over cinchonidine-modified Pd/alumina

A chiral alkanoic acid was prepared with up to 52% excess of the (S) enantiomer by hydrogenating an,-unsaturated carboxylic acid with a cinchonidine-Pd/Al₂O₃ catalyst system. Favourable conditions are: high surface hydrogen concentration ( 60 bar hydrogen pressure, low catalyst concentration and apolar solvents), near ambient temperature and a cinchonidine/reactantmolar ratio of at least 0.4 mol%. It is proposed that high hydrogen solubility and the presence of 2-methyl-2-pentenoic acid reactant as dimers are advantageous for enantiodifferentiation.     

Chemical effects in commercial and laboratory mixtures of ‘reactive’ phosphate rock and acidulated fertilisers

The chemical analyses of different size fractions of a variety of commerical and laboratory prepared samples of partially acidulated phophate rocks and mixtures of reactive phosphate rock and single superphosphate (called LONGLIFE in New Zealand) have been studied. Whereas only minor chemical segregation effects have been observed for partially acidulated products quite a large bias has been established for LONGLIFE materials, and more especially commercial samples, where larger proportions of phosphate rock were found in the lower size fractions. This inhomogeneity was considered to arise from poor mixing of components and subsequent inconsistent granulation; more stringent rejection criteria for undersize material would greatly assist in improving the product quality. Chemical deactivation of the phosphate rock residue in LONGLIFE materials was also observed; this can be partially explained by a selective reaction of the reactive phosphate rock component with acid still present at the time of mixing with the single superphosphate component.     

Partially acidulated phosphate rocks made from phosphoric acid using direct acidulation-granulation techniques

Partially acidulated phosphate rocks were produced by spraying phosphoric acid onto North Carolina phosphate rock of three finenesses (unground, medium, or finely ground) in a pan or drum granulator. This direct acidulation-granulation procedure resulted in free-flowing granular products using laboratory acid up to stoichiometric levels of 30% (unground), 45% (medium) and in excess of 50% (fine). However, when less pure works grade acids were used the maximum levels of acidulation were reduced to 15%, 30% and 45% respectively with a corresponding greater difficulty in producing good granules.Mature product analyses indicated an analytical bias with granule size, the larger granules containing greater quantities of soluble phosphate in most instances. Physical tests on mature products indicated that all granules produced were inferior to those of the traditional New Zealand fertiliser single superphosphate.     

Studies in Kolbe electrosynthesis. I. Electrolysis of capric acid

A study of the various parameters affecting the Kolbe electro-synthesis reaction with capric acid has shown that amongst the water-solvent systems studied, a mixture of 30 vol.% of 2-methoxy ethanol with water is superior. The necessary conductance could be readily maintained by using potassium carbonate. The desirable conditions under which capric acid could be converted to the expected reaction product, octadecane, have been established. Continuous electrolysis was possible and yields of the order of 90% were readily achieved.     

Evaluating and quantifying the liming potential of phosphate rocks

The liming potential of phosphate rock was evaluated with theoreticalcalculations and quantified by laboratory titration and soil incubation. Threeanions present in the carbonate apatite structure of phosphate rock that canconsume protons and cause an increase in pH when dissolved from apatite arePO₄ ^3–, CO₃ ^2–, andF^–. The pKa for HF is so low that F^– has verylittle effect on increasing pH. The pKa for 2 protons onH₂PO₄ ^– and H₂CO₃are sufficiently high enough to cause an increase in pH withPO₄ ^3– and CO₃ ^2–releasedinto solution if the pH range is between 4 and 6. Because of the greater molarquantity of PO₄ ^3– compared toCO₃ ^2–, PO₄ ^3– exerts agreater affect on the liming potential of P rock. For a variety of phosphaterocks with a axes ranging from 9.322 to 9.374 Å in the carbonate apatitestructure, the theoretical % calcium carbonate equivalence (CCE) rangesfrom 59.5 to 62%. With the presence of gangue carbonate minerals from2.5to 10% on a weight basis in the phosphate rocks, the theoretical%CCE ranges from 59.5 to 63.1%. Use of AOAC method 955.01 forquantifying the %CCE of North Carolina phosphate rock (NCPR) and Idahophosphate rock (IDPR) resulted in %CCE ranging from 39.9 to 53.7%which were less than the theoretical values. The lower values measured in theAOAC method was presumed to be due to formation of CaHPO₄ orCaHPO₄·2H₂O precipitates which would result inlessthan 2 protons neutralized per mole of PO₄ ^3–released from carbonate apatite. The highly concentrated solution formed in themethod was considered not indicative of a soil solution and thus determined%CCE values would be suspect. A soil incubation study was conducted todetermine a more appropriate %CCE value in a soil environment usingCopper Basin, Tennessee soil with a soil pH of 4.2. Agricultural limestone,NCPR, IDPR, and a granulated IDPR were added to 100 g of soil atrates of 0.1, 0.3, 1, 3, and 10 g/kg soil, incubated for 105 daysat field moisture capacity, and analyzed for changes in soil pH and P. The%CCE of each phosphate rock addition was determined using limestone as astandard curve. The relationship between %CCE and % dissolved Pfollowed a quadratic model where%CCE=8.47+0.0078(%dissolved P)² (r²=0.84).At 0% dissolved P, the model predicted 8.47% CCE which wasprobably due to gangue carbonate minerals. The experimental model showedqualitative agreement with theory showing increased liming ability withincreased dissolved P from the P rock. However, the model showed lower%CCE than theoretical calculations when %P dissolved ranged from20 to 60%.     

An investigation of extraction procedures for assessing the phosphate rock residue in multicomponent fertilisers

Five chemical extractants-water, neutral ammonium acetate, neutral ammonium citrate (hot and cold) and alkaline ammonium citrate-have been assessed on their ability to efficiently isolate the residual phosphate rock present in multicomponent fertilisers without affecting the phosphate rock. Phosphoric acid-based partially acidulated phosphate rocks (PAPRs) were manufactured along with several LONGLIFE (LL, single superphosphate to which reactive phosphate rock is added ex-den) materials for the assessment of these extractants.Each extractant was assessed by analysing the resultant residual phosphate rock isolated from each multicomponent fertiliser and comparing its chemical properties with the original phosphate rock used to manufacture the products. An analysis of extractable phosphorus was also undertaken. X-ray diffraction analysis was performed on selected phosphate rock residues as an independent method of examining the extraction techniques.Water and neutral ammonium acetate were found to be unsatisfactory for use as extractants; neither removed calcium sulphate when present, while the latter also did not appear to extract all the monocalcium phosphate component. The remaining three extractants all removed soluble phosphorus components and impurity species from the fertiliser products, leaving the residual phosphate rock relatively unaffected. Residue analyses were only slightly modified to those of the original rocks, although there were some inconsistencies in results obtained using hot neutral ammonium citrate. X-ray diffraction analysis showed no significant differences between residues produced from neutral ammonium citrate or alkaline ammonium citrate extractions, but water and neutral ammonium acetate residues confirmed the presence of calcium sulphate in LL and the presence of monocalcium phosphate in a neutral ammonium acetate extracted PAPR.From this study, cold neutral ammonium citrate and alkaline ammonium citrate appear to be equally suitable for isolating the phosphate rock from a multicomponent fertiliser, leaving the residual rock substantially unmodified from the original phosphate rock. However, there was a slight preference for cold neutral ammonium citrate due to its ease of preparation and use.     

The effect of carbon black filling and cross-linking in stretched SBR networks: a 2H-NMR study

Summary The line splitting v in ²H-NMR spectra of deuterated benzene in stretched crosslinked SBR depended linearly on the classical stretch term ² – 1/ for samples with and without carbon black filling. The ratio LS = v/(² – 1/) was measured in dependence on the solvent fraction . The extrapolated value L of this ratio at =0 gave a linear dependence on the inverse molecular mass 1/M_c of inter-crosslink chains. This was expected according to a simple model of chain dynamics and offers a further NMR-method for M_c-determination even in filled networks. However, the slope of the L(1/M_c)-line increases with an addition of carbon black which indicates a higher molecular order. Three reasons for this could be discussed. However, one of them is preferable.     

The agronomic value of co-granulated Christmas Island Grade C phosphate rock and elemental sulphur

Certain low grade phosphate rocks have low agronomic value as direct applied fertilizers and make poor quality superphosphates. With some rocks there is potential to increase their solubility in soils and hence the fertilizer value by mixing with finely divided elemental sulphur (S°). The agronomic value of a prototype low cost, granular P and S fertilizer, Christmas Island Grade C phosphate rock/elemental sulphur (Xmas C/S°), was compared against single superphosphate (SSP) and reactive phosphate rock (RPR)/S° dry blends, North Carolina phosphate rock/S° (NCPR/S°) and NCPR/50% S-super (granular SSP + 44% S°). An eight- month glasshouse trial using ryegrass (Lolium perenne L. cv. Nui), grown in a central yellow-grey earth (Aeric Fragiaqualf), indicated that fertilization with Xmas C/S° produced dry matter yields, between 54 to 73% and 10 to 40% lower than SSP and NCPR/S° blends respectively, and lower plant P and S uptake. Fertilization with Xmas C/S° however produced significantly higher yield and P and S uptake than unfertilized pots and pots receiving Xmas C PR and S° alone. The two RPR/S° dry blends, namely NCPR/S° and NCPR/50% S-super, produced significantly lower yield and P and S uptake than the same two fertilizers granulated with water. The difference in yields and P and S uptake between blends and granulated forms increased with time. The recovery of fertilizer P and S by plants ranged from 3 to 35% and 2 to 45% respectively with the lowest recoveries for Xmas C PR alone and S° alone and the highest for SSP and SSP + S°. During the period of plant growth the percentage of S° oxidised from the S°, Xmas C/S° co-granule, NCPR/S° physical blend and NCPR/S° granular treatments were 37, 32, 32 and 45% respectively. Field evaluations, or use, of the co-granule should consider it's slow P and S release rates.