Apatite Rock Phosphate Research Articles

The combination of Arachis pintoi green manure and natural phosphate improves maize growth, soil microbial community structure and enzymatic activities

We investigated the effect of the co-composting of Arachis pintoi (AP) as green manure with different sources of rock phosphate on maize growth and soil properties. Composts were prepared combining AP and different rock phosphates (simple superphosphate, apatite rock phosphate, reactive rock phosphate and thermophosphate), alone or in combination with AP. The incorporation of AP and natural phosphate was conducted in a greenhouse, and we investigated its effects on plant total dry matter, phosphorus absorption, microbial biomass carbon and phosphorus, total organic carbon, soil basal respiration, enzymatic activities (acid phosphatase, alkaline phosphatase and urease) and the soil microbial structure community. The application of natural thermophosphate phosphates with AP is an efficient management strategy for maize cultivation, with increases of more than 124% in maize dry matter, more than 300% in P uptake and 62% in soil microbial biomass carbon. The use of Arachis pintoi as green manure, combined with natural phosphate sources, represents an alternative fertilisation approach for maize cultivated on Entisols, enhancing the bioavailability of P from natural rock phosphate. It is a sustainable and financially attractive option to ensure the environmental integrity of cultivation, food and soil security.

Beneficiation of rock phosphate fertilisers by mechano-milling

Mechano-milling is a process where materials are ball-milled at high energy to induce chemical and physical reactions. This study investigated the effect of milling on the properties and agronomic effectiveness of six apatite rock phosphates (RP). The effects of milling were evaluated by X-ray diffraction, BET-N2 surface area measurements, electron microscopy and solubility in 2% citric acid. Milling increased the solubility of RPs by increasing the proportion of X-ray amorphous material and reducing the size of remaining apatite crystals. However, milling also caused agglomeration of particles, which reduced the surface area. Milling increased the unit-cell a dimension of apatite, possibly due in part to the formation of low reactive fluorapatite such as occurs during calcination. These changes induced by mechano-milling might be expected to reduce the solubility of RPs; however, solubility increased because amorphisation was dominant. The fertiliser relative effectiveness of RPs based on phosphorus content of wheat plants was increased by a factor of up to three by milling. It is concluded that beneficiation of apatitic RPs by mechano-milling may greatly improve their agronomic effectiveness and milling may provide an economically and environmentally superior option for the manufacture of phosphate fertilisers and enable the utilisation of impure RPs.

Beneficiation of apatite rock phosphates by calcination: effects on chemical properties and fertiliser effectiveness

Apatitic rock phosphates (RP) are commonly calcined to remove impurities and to increase phosphorus (P) concentration but calcination decreases the agronomic effectiveness of RPs used for direct application to soils. This study investigated the effect of calcination on 6 apatite RPs (Christmas Island A-ore, Egypt, Morocco, North Carolina, Queensland, and Sechura). RPs were uncalcined (25°C) and calcined at 500°C, 900°C, and 1100°C. They were evaluated by X-ray diffraction (XRD) and BET-N 2 surface area technique. P dissolution in 2% citric acid with a 128 h extraction time was measured. Chemical results were compared with those from a plant growth experiment, where wheat was fertilised with the calcined RP products. Calcination at 1100°C reduced the agronomic effectiveness of apatite RPs by about 90%, by altering the crystal properties and the particle size of the RPs. Unit-cell a dimension increased from values of 9.324—9.375 Å to approximately 9.38 Å, indicating that the carbonate containing apatite RPs altered to less-soluble fluorapatite. Apatite average crystal size (coherently diffracting zone) more than doubled and BET-N 2 specific surface area decreased by 95%, due to crystal growth and sintering. Consequently, the extent of dissolution in 2% citric acid and agronomic effectiveness decreased substantially. Calcination at 500°C and 900°C produced similar but smaller changes in mineral properties. It is concluded that beneficiation of apatitic RP by calcination will adversely affect the agronomic effectiveness of RP used for direct application to soils.

The relative effectiveness of superphosphate and rock phosphate for soils where vertical and lateral leaching of phosphate occurs

Laboratory studies have shown that up to 70% reactive rock phosphate dissolves in three soil types found in the high rainfall (> 800 mm annual average) area of south-western Australia. Three field experiments were undertaken on these soils to compare reactive apatite rock phosphate from North Carolina (NCRP) with single superphosphate (SSP) as fertilizers for subterranean clover (Trifolium subterraneum) pasture. Vertical leaching of phosphorus (P) occurs in one soil, a deep, very sandy, acid peaty sand. Lateral leaching of P occurs in the second soil, a shallow (3 cm) sand over a slowly permeable sandy clay loam. No leaching of P occurs in the third soil, a uniform, permeable red sandy loam with a moderate capacity to sorb P. All the soils remained moist to very wet for the 6 to 8 month growing season. Fertilizers were applied once only to different plots over a four-year period (1992 to 1995). Each year fertilizer effectiveness was determined relative to the effectiveness of freshly-applied (current) SSP using yield and P content of dried clover herbage and bicarbonate-soluble P extracted from the soil (soil test P) as indices of effectiveness.

Effect of fertilizer type, sampling depth, and years on Colwell soil test phosphorus for phosphorus leaching soils

The relationships between (i) soil test phosphorus (P) (Colwell sodium bicarbonate procedure) and the level of P applied (from 0 to 1000 kg total P ha−1) (relationship 1), and (ii) yield and soil-test P (relationship 2, the soil P test calibration), were measured in two field experiments on very sandy, P-leaching soils in the high rainfall (> 800 mm annual average) areas of south-western Australia. The soils were humic sandy podzols, or haplohumods, comprising 97% sand (20 to 2000 μm). The experiments started in April 1984 and were terminated at the end of 1990. Soil-test P, measured on soil samples collected to 5, 10 and 25 cm depth each January in the years after P application, was related to yields of dried clover (Trifolium subterraneum) herbage measured later in each year. The four P fertilizers studied were single superphosphate, coastal superphosphate (made by adding, just before granulation, extra rock phosphate together with elemental sulphur while manufacturing single superphosphate), apatite rock phosphate, and Calciphos.

Effectiveness of rock phosphate, coastal superphosphate and single superphosphate for pasture on deep sandy soils

The effectiveness of ‘coastal superphosphate’ and two rock phosphate fertilizers was compared with the effectiveness of single superphosphate for pasture production on deep, humic, sandy podzols in high rainfall (> 800 mm annual average) areas of south-western Australia. The pastures were subterranean clover (Trifolium subterraneum) or mixed subterraneum clover and serradella (Ornithopus compressus). ‘Coastal superphosphate’ was made by adding rock phosphate and elemental sulphur to superphosphate during manufacture, as it came out of the den before granulation. One rock phosphate was a 50% mixture of apatite rock phosphate from Nauru and Christmas Islands, and which was also used to make the single and ‘coastal’ superphosphate used in this study, and superphosphate made in Western Australia at the time these experiments started. The other rock phosphate was Calciphos, the fertilizer produced by heating (calcining), at about 500 °C, Christmas Island C-grade ore, a calcium iron aluminium rock phosphate. There were two types of experiments. In the three Type 1 experiments, levels of each fertilizer were applied annually. In the two Type 2 experiments, levels of fertilizer were applied once only to new plots in different years. ‘Coastal superphosphate’ was the most effective fertilizer in the Type 1 experiments, with both rock phosphates and single superphosphate being equally effective. All fertilizers were equally effective in the Type 2 experiments. There were large variations in fertiliser effectiveness values between yield measurements in the same or different years. It is known that P leaches from freshly-applied superphosphate in these soils. The extent of this leaching probably varies between yield measurements affecting effectiveness values determined for all fertilizers because the effectiveness values were calculated relative to the effectiveness of single superphosphate. The humic, sandy podzols remain wet during the growing season, are acidic, and are known from laboratory studies to possess adequate hydrogen ions to cause extensive dissolution of North Carolina rock phosphate so that rock phosphates are equally or more effective than single superphosphate in these soils. When elemental sulphur in ‘coastal superphosphate’ is oxidized to SO4 hydrogen ions are produced which in previous studies has been shown to enhance dissolution of rock phosphate in ‘biosuper’, a mixture of rock phosphate and elemental sulphur.

Effectiveness of two partially acidulated rock phosphates, coastal superphosphate and Ecophos, compared with North Carolina reactive rock phosphate and superphosphate

The effectiveness of coastal superphosphate, a partially acidulated rock phosphate (PARP) made from apatite, and Ecophos, a PARP made from calcium iron aluminium (crandallite millisite) rock phosphate, was compared in pot experiments with the effectiveness of ordinary superphosphate (OSP) and North Carolina reactive apatite rock phosphate (NCRP). There were three experiments using different lateritic soils collected in Western Australia. Fertilizer effectiveness was measured using yield of dried wheat (Triticum aestivum) tops grown for 28 days. Three successive crops were grown. The phosphorous (P) fertilizers were applied and mixed with the soils before sowing the first crop. In addition, OSP was added to extra pots before sowing crops 2 and 3 in order to measure the effectiveness of the original P fertilizers relative to freshly-applied OSP for these crops.

Residual value of superphosphate and queensland rock phosphate measured using yields of serradella, burr medic and subterranean clover grown in rotation with wheat and bicarbonate‐extractable soil phosphorus

Abstract The residual value of ordinary (single) superphosphate (SP) and Queensland (Duchess) apatite rock phosphate was measured in a pot experiment using yields of three legume species (serradella, Ornithopus compressus; medic, Medicago polymorpha var. brevispina; clover, Trifolium subterraneum) fertilized with mineral nitrogen (N) grown in rotation with wheat (Triticum aestivum). The plants were grown in a glasshouse in a sandy soil (pH in CaCl2 ‐ 5.8) for 30 to 34 days. There were four crops: legume, wheat, legume, and wheat. The phosphate (P) requirement of the plant species was determined from the amount of P required to produce 90% of the maximum yield. Soil samples were taken before sowing each crop to measure bicarbonate‐extractable soil P (soil test P) which was related to the yields of that crop. Relative to freshly‐applied (FSP), the residual value of SP declined by about 60% between the first and second crop, and by a further 25% by the fourth crop. For crop 3, the residual value of SP varied...

Summary of research on soil testing for rock phosphate fertilizers in Western Australia

The relationship between plant yield and values of soils tests for phosphorus (P) was studied in long-term field experiments in south-western Australia for soil previously fertilized with rock phosphate and superphosphate. The rock phosphates studied were: Queensland (Duchess) apatite rock phosphate; reactive apatite rock phosphate from North Carolina; and rock phosphate from Christmas Island (as either C-grade ore or Calciphos). The P fertilizers were applied once only at the start of each experiment, and in subsequent years, soil samples were collected in January-March to measure soil test values. These were compared with plant yields measured later on in that year. The Colwell alkaline bicarbonate soil test was used in all years in all experiments. Olsen, Bray, lactate and Troug tests were used in some years in some experiments. For all soil tests the relationships between yield and soil test values was generally different for rock phosphate and superphosphate. For a given source of P, none of the different soil test reagents was significantly superior for predicting plant yields. The relationship between yield and soil test value was also generally different for different plant species. At one site cultivation was included as a treatment and the relationship varied depending on the cultivation treatment of the topsoil before sowing oats (Avena sativa). The relationship between yield and soil test also differed between years.

Agronomic effectiveness of partially acidulated rock phosphate and fused calcium-magnesium phosphate compared with superphosphate

The agronomic effectiveness of two partially acidulated rock phosphate (PARP) fertilizers, made from either North Carolina or Moroccan apatite rock phosphate, and a fused calcium-magnesium phosphate (thermal phosphate or TP), was compared with the effectiveness of superphosphate in two glasshouse experiments. A different lateritic soil from Western Australia was used for each experiment. Oats (Avena sativa) were grown in one experiment and triticale (×Triticosecale) in the other. Fertilizer effectiveness was measured using (i) yield of dried tops, (ii) P content (P concentration in tissue multiplied by yield) of dried tops, and (iii) bicarbonate-extractable soil P (soil test value). The following relationships differed for the different fertilizers: (i) yield of dried tops and P content in the dried tops; (ii) yield and soil test values. Consequently the fertilizer effectiveness values calculated using yield data differed from those calculated using P content or soil test data. Freshly-applied superphosphate was always the most effective fertilizer regardless of the method used to calculate fertilizer effectiveness values. For one of the soils, as calculated using yield data, relative to freshly-applied superphosphate, the PARP and TP fertilizers were 15 to 30% as effective for the first crop, and 20 to 50% as effective for the second crop. The second soil was more acidic, and for the first crop the PARP and TP fertilizers were 80 to 90% as effective as freshly-applied superphosphate, but all fertilizers were only 5 to 15% as effective for the second crop. For each soil, the two PARP fertilizers had similar fertilizer effectiveness values. Generally the TP fertilizer was more effective than the PARP fertilizers.

The effect of apatite and elemental sulphur mixtures on growth and P content ofCentrocema pubescens

Two glasshouse pot experiments and one incubation experiment were undertaken to measure the effectiveness of Sri Lanka (Eppawala) apatite rock phosphate as a fertilizer for the perennial legumeCentrocema pubescens. The apatite was applied alone, or as a mixture with elemental sulphur and soil containingThiobacelli bacteria either as powder or pellets that were either uncoated or coated with rubber (to reduce the rate of release of P thereby increasing P release for a longer-term).

The residual value of superphosphate and rock phosphates for lateritic soils and its evaluation using three soil phosphate tests

The residual value of superphosphate and several rock phosphates was measured in three field experiments in Western Australia. The rock phosphates were Christmas Island C-grade ore, calcined C-grade ore (Calciphos) and apatite rock phosphates. The predictive capacity of the Colwell, Olsen and Bray 1 soil tests for phosphate were also evaluated.

Effect of level of application on the relative effectiveness of rock phosphate

Responses of yellow serradella, slender serradella and subterranean clover to applications of superphosphate and Queensland apatite rock phosphate were compared in a field experiment in Western Australia. The rock phosphate was applied as a fine powder to a very sandy soil with a low buffering capacity for phosphate and for pH. At low levels of application, rock phosphate was about a tenth as effective as superphosphate — that is, ten times as much was required to give the same yield. With increasing levels of application, the relative effectiveness of rock phosphate declined to well below one per cent and hence more than 100 times as much was required to give the same yield. The decreasing relative effectiveness was incorporated into response equations. These were used to demonstrate that the decreasing relative effectiveness can be statistically tested and shown to be highly significant. A simulation study using the model of Kirk and Nye showed that a decrease in relative effectiveness with increasing level of application is especially likely when the particles of rock phosphate are very small, when the levels of application are high, and when the soil's buffering capacity for phosphate and for pH is low.

The effectiveness of rock phosphate fertilisers in Australian agriculture: a review

Plant responses to apatite rock phosphates and Calciphos, a calcined calcium iron-aluminium rock phosphate fertiliser, have been measured in many pot and field experiments in Australia, but there is no consistent view of the agronomic effectiveness of these fertilisers. Quantitative indices of the effectiveness of freshly applied rock phosphates relative to freshly applied superphosphate (relative effectiveness or RE values) have been calculated from the data for 164 Australian pot and field experiments on the basis of the substitution value of the rock phosphates for superphosphate. RE values range from <0.1 to 2.5, with the mean value for apatite rock phosphates being 0.26 compared with 0.42 for Calciphos. Statistical analysis of the data demonstrate that variations in RE values were primarily due to systematic differences in experimental design and fertiliser solubility, and not to differences in soil pH, plant species, the capacity of the soil to adsorb P and mean annual rainfall. All RE values >0.4 were obtained from experiments in which only 1 or 2 levels of fertiliser were applied to soils that were poorly responsive to applied P; thus it was not possible to define the complete response curves required to obtain precise values of RE. In most cases, RE values were < 0.4 for experiments in which several levels of fertiliser P were applied to highly P-responsive soils so that complete response curves were defined and precise values of RE estimated. The effectiveness of previously applied rock phosphate (i.e, residual value) remained low and approximately constant for several years after application, being 5-30% as effective as freshly applied superphosphate for the various experiments. The corresponding average value of the relative effectiveness of superphosphate declined by 40% in the first year after application, by a further 15% in the second year, and by a further 30% over the remaining 6 years. However, the magnitude of these declines in relative effectiveness differed substantially between individual sites. The residual value of both the superphosphate and rock phosphate fertilisers appears not to have been systematically influenced by soil type, soil pH, the capacity of the soil to adsorb P, mean annual rainfall, and whether the fertilisers were topdressed or were incorporated. However, there is a need for additional experiments to investigate the influence of these factors on fertiliser effectiveness. It is concluded that, on the basis of published data, rock phosphate fertilisers cannot be regarded as economic substitutes for fertilisers containing water-soluble P for most agricultural applications in Australia. This is because, relative to freshly applied superphosphate, the fertiliser effectiveness of rock phosphates is low in the year of application and it remains low in subsequent years so that uneconomical, very high rates of application of rock phosphate are required.

The initial and residual agronomic effectiveness of some Indian, USA and Australian rock phosphates

The initial and residual agronomic effectiveness of six apatite rock phosphates from India, one from the USA (North Carolina) and one from Australia (Queensland) were evaluated in a pot trial with wheat on a lateritic soil. All of the Indian rock phosphates were very poor sources of phosphorus. Values of initial effectiveness relative to monocalcium phosphate ranged from < 0.0001 to 0.02 and from < 0.0001 to 0.008 for measurements based on yield and phosphorus uptake respectively. The residual effectiveness relative to freshly applied monocalcium phosphate was determined by growing a second crop on the fertilized soils. The effectiveness of the Indian rock phosphates remained very low ranging from < 0.0001 to 0.002 and from < 0.0001 to 0.0004 for yield and phosphorus uptake respectively. Queensland and North Carolina rock phosphates were much superior to the Indian sources with initial effectiveness values in terms of yield of 0.08 and 0.37 and residual effectiveness values of 0.02 and 0.15 respectively. For each crop there was a single relationship between yield and phosphorus uptake (i.e. internal efficiency) for all phosphorus sources showing that variations in yield response were due solely to differences in phosphorus availability. Sodium bicarbonate extractable phosphorus values for fertilized soils sampled shortly after fertilization were not predictive of yield unless different calibration curves were used for the different phosphorus fertilizers.

Comparison of three soil tests for phosphate on lateritic soil fertilized with superphosphate, crandallite rock phosphates and apatite rock phosphates

Different amounts of superphosphate, crandallite-millisite rock phosphate (three different samples of C-ore from Christmas Island), 500�C calcined C-ore (three different samples of Calciphos) and apatite rock phosphate (two different samples from the Duchess deposit, Queensland) were applied once only in May 1977 on lateritic soil in Western Australia. Samples of the top 10 cm of soil were collected in the summer (January-February) of 1979 and 1980 for measurement of extractable soil phosphate by the Colwell, Olsen and Bray soil tests, and the data were compared with dry matter production of subterranean clover pasture in the following spring (August). For each fertilizer in each year, the Olsen and Brayl soil test values (as dependent variables) were closely correlated with the Colwell soil test values (independent variable), and the Bray 1 soil test (dependent variable) was closely correlated with the Olsen soil test (independent variable). For the relationship between yield and soil test values, separate calibrations were required in most cases for each fertilizer and each soil test, and these calibrations showed large differences in two successive years. None of the soil tests was significantly better for predicting clover yields for the different fertilizers applied two and three years previously.

Effectiveness of topdressed and incorporated superphosphate and Duchess rock phosphate for subterranean clover on sandy soils near Esperance Western Australia

In 2 experiments on sandy soil near Esperance, W. A., superphosphate and Duchess (Queensland) apatite rock phosphate were either left on the soil surface after application (topdressed) or incorporated into the top 10 cm of the soil with a rotary hoe (incorporated). One experiment was on Fleming gravelly sand which had a greater capacity to adsorb phosphorus than did the deep yellow sand (Gibson sand) used in the other experiment. Dry matter or seed yield of subterranean clover and phosphorus content of dry herbage or seed were used as indicators of the effectiveness of the phosphorus treatments. Compared with topdressed superphosphate, incorporation of superphosphate did not greatly influence its effectiveness on the Gibson soil, but reduced its effectiveness by about 20% on the Fleming soil. Relative to topdressed rock phosphate, incorporation of rock phosphate almost doubled its effectiveness on the Fleming soil, and improved its effectiveness by about 1.5 times on the Gibson soil. Superphosphate was the more effective fertiliser. Relative to topdressed superphosphate, the effectiveness of topdressed and incorporated Duchess rock phosphate, respectively, was about 15 and 30% on the Fleming soil, and about 25 and 40% on the Gibson soil. There was no evidence of any leaching of phosphorus from Duchess rock phosphate from the 0-10 cm layer of either soil, nor of superphosphate on the Fleming soil. However, on the Gibson soil, there was some leaching of superphosphate to below 10cm, but not below 20 cm.

Granular reactive apatite rock phosphate is not an effective phosphorus fertilizer in the short term on lateritic soils in south-western Australia.

The effectiveness, as a phosphate fertilizer, of granular reactive rock phosphate (carbonate substituted apatite from North Carolina, U.S.A.), granular triple superphosphate and partly powdered Duchess non-reactive rock phosphate (low carbonate apatite from north-eastern Australia) was compared in three field experiments on different soil types in different climatic regions of south-western Australia. Calciphos (finely ground calcined crandallite rock phosphate from Christmas Island) was included in one experiment. The rock phosphates were incorporated into the soil and their effectiveness was compared with both topdressed and incorporated superphosphate. Different species were grown at each site (barley, triticale and subterranean clover). As determined on the basis of relative amounts of fertilizer required for constant yield, the effectiveness of all the rock phosphates relative to incorporated superphosphate was very low at each site throughout the growth of each species. Fertilizer effectiveness of rock phosphates was about one-fifth that of superphosphate for barley, and one-tenth for triticale and clover. The maximum yield obtained from rock phosphate was generally 88-100% that obtained from superphosphate. Incorporation did not greatly affect the effectiveness of superphosphate.

Responses of serradella and subterranean clover to phosphorus from superphosphate and Duchess rock phosphate

The responses of yellow serradella, slender serradella and subterranean clover to phosphorus from superphosphate and an apatite rock phosphate from Duchess, north-eastern Australia, were measured in a field experiment near Esperance, W.A. Over the 16 months of the experiment, dry herbage yields depended upon the phosphorus content of dried herbage. For each sampling time, the relationship between dry herbage yield and the phosphorus content of dried herbage was similar for both fertilizers and for all three species. At each rate of fertilizer application, the amount of phosphorus absorbed by the plants from the rock phosphate was less than that from superphosphate, and this limited yield. When fertilized with superphosphate, subterranean clover absorbed less phosphorus than the serradellas for each rate of fertilizer application, and this also reduced yield. Thus less phosphorus from superphosphate was required to produce serradella than was required to produce the same weight of subterranean clover. When fertilized with rock phosphate, 1982 herbage production was in the order: yellow serradella&gt; subterranean clover&gt;slender serradella. 1982 seed yields were: subterranean clover&gt;yellow serradella&gt; slender serradella. 1 983 herbage yields were: slender serradella&gt;yellow serradella&gt; subterranean clover. For herbage yields, for each rate of fertilizer application, this order was also dictated by the amount of phosphorus absorbed by each of the three species.

The initial and residual value for subterranean clover of phosphorus from crandallite rock phosphates, apatite rock phosphates and superphosphate

The residual value of phosphorus from superphosphate, crandallite rock phosphate (Christmas Island C-grade ore), 500°C calcined crandallite rock phosphate (Calciphos) and apatite rock phosphate from Queensland, Australia, was measured in a 6 year field experiment sited on lateritic soil in south-western Australia. Different amounts of each fertilizer were applied at the commencement of the experiment, and either left on the soil surface or mixed through the soil by cultivating to a depth of about 10 cm. Dry matter production of subterranean clover measured in spring (August) and bicarbonate-extractable phosphorus determined from soil samples collected in summer (January–February) were used as indicators of fertilizer effectiveness.