Gafsa Rock Phosphate Research Articles

Eficiência de fosfato natural reativo aplicado em misturas com superfosfato triplo em milho e soja

O objetivo deste trabalho foi avaliar o efeito do modo de aplicação do superfosfato triplo (SFT), do fosfato natural reativo de Gafsa e da mistura entre essas fontes no aproveitamento do fósforo (P) por plantas de milho e de soja. Os experimentos foram realizados em casa de vegetação, e as plantas foram cultivadas em vasos com Latossolo Vermelho-Amarelo distrófico. As fontes fosfatadas foram aplicadas isoladamente ou em misturas (proporção 1:1), à dose de 90 mg kg-1 de P, de modo não localizado ou localizado no solo. Para a quantificação do P absorvido pelas plantas das diferentes fontes, empregaram-se tratamentos com o solo e com o SFT marcados com 32P. O aproveitamento do fósforo do superfosfato triplo aplicado de forma localizada (9,8%) foi superior ao da não localizada (7%). A aplicação não localizada do fosfato natural reativo proporcionou maior aproveitamento do fósforo (3,8%), em comparação à localizada (0,5%). Em comparação à aplicação isolada do fosfato de Gafsa, o aproveitamento do fósforo pelas plantas de milho e soja aumentou quando essa fonte foi aplicada como mistura compactada; em presença do superfosfato triplo, a aplicação do fosfato natural reativo de Gafsa de modo não localizado proporcionou maior aproveitamento do P pelas plantas de soja. O aproveitamento do fósforo do fosfato natural de Gafsa aumenta quando aplicado ao solo com o superfosfato triplo, e esse efeito depende do método de aplicação das fontes fosfatadas.

Dissolution of phosphorus from animal bone char in 12 soils

Heat-treated animal bone char (ABC) has not previously been evaluated for its potential as a phosphorus (P) fertilizer. ABC, Gafsa phosphate rock (GPR) and triple superphosphate fertilizer (TSP) were incubated in 12 soils. Dissolved-P was assessed by extraction with NaOH and bioavailability with the Olsen extractant. The rate of P dissolution from ABC was described almost equally well by the Elovich and Power equations. After 145 days, the fraction of P dissolved ranged from 0 to 73% and to 56% for ABC and GPR, respectively. The most important soil properties determining P dissolution from ABC were pH and P sorption. P dissolution was not significant at soil pH >6.1 (ABC) and >5 (GPR) and the lower the pH, the greater the Dissolved-P. Dissolved-P also correlated positively and significantly with inorganic P sorption, measured by the Freundlich isotherm and the P sorption index of Bache and Williams (1971). Soil pH and P sorption index could be combined in multiple regression equations that use readily measured soil properties to predict the potential for ABC dissolution in a soil. Dissolution of P from GPR correlated with soil pH and exchangeable acidity. In comparison with GPR, ABC was a better source of available P, assessed by Olsen-P. In most soils, ABC increased Olsen-P immediately after application, including soils of relatively high pH in which GPR was ineffective. ABC is a P fertilizer of solubility intermediate between GPR and TSP.

Disponibilidade e níveis críticos de fósforo em milho e solos fertilizados com fontes fosfatadas

This study had as objective to evaluate the availability and the critical levels of phosphorus in maize plants, by different chemical extractors, in two soils (Ultisol and Oxisol) with different phosphorus (P) adsorption capacity factor and fertilized with Gafsa rock phosphate or triple superphosphate. The results showed that Mehlich-1, Mehlich-3 and Bray-1 were equally efficient in the evaluation of P availability in the treatments with triple superphosphate. For the rock phosphate only the extractors Mehlich-3 and Bray-1 were adequate in this evaluation. The highest values of critical level in the soil, with exception of the Mehlich-1, were observed in soils fertilized with triple superphosphate. The critical level of phosphorus in the shoot dry matter was inversely correlated with the capacity factor of soil and directly correlated with the solubility of the phosphorus source. The necessary dose to reach this critical level was directly correlated with the capacity factor and inversely correlated with the solubility of the source. The triple superphosphate provided higher concentration of P in the shoot dry matter and was more efficient than rock phosphate in the production of dry matter in the Oxisol.

Characterization and Greenhouse Evaluation of Brazilian Calcined Nonapatite Phosphate Rocks for Rice

Little information is available on the agronomic effectiveness of calcined nonapatite phosphate rock (PR) sources containing crandallite minerals in the form of Ca–Fe–Al–P for flooded and upland rice (Oryza sativa L.). We conducted laboratory and greenhouse studies to (i) characterize the mineralogical composition, (ii) investigate the solubility and dissolution behavior, and (iii) evaluate the agronomic effectiveness of two nonapatite PR sources (Juquia and Sapucaia) from Brazil and compared them with (i) a highly reactive Gafsa PR (Tunisia) containing apatite in the form of Ca–P and (ii) a reference water‐soluble triple superphosphate (TSP) for flooded and upland rice. After calcination at 500°C for 4 h, the solubility of Juquia PR and Sapucaia PR in neutral ammonium citrate (NAC) significantly increased from almost nil to a maximum of 39.3 and 114 g P kg−1, respectively. X‐ray diffraction showed that crystalline crandallite mineral was transformed to an amophorus form after calcination. The solubility behavior of the two calcined PR sources followed the same trend as Gafsa PR, that is, P release decreased with increasing equilibrium pH in the 0.01 M KCl solution (pH 3.0–8.0). At pH 3, the solubility followed: Gafsa PR > calcined Sapucaia PR > calcined Juquia PR. No P release was detected from any of the PR sources at pH ≥ 5.0 in the solution, indicating the Ca–P characteristic of the Ca–Fe–Al–P mineral controlled P dissolution of the calcined PR. Without calcination, both Juquia PR and Sapucaia PR were totally ineffective for upland rice grown on a Hiwassee clay loam (fine, kaolinitic, thermic Rhodic Kanhapludult) with pH 5.4 whereas a significant P response was observed with the calcined PR samples. For flooded rice grown on Hiwassee soil, the calcined Juquia PR and Sapucaia PR were 66 and 72%, respectively, as effective as TSP in increasing rice grain yield whereas Gafsa PR was ineffective. For upland rice grown on the unlimed soil, Gafsa PR was as effective as TSP in increasing rice grain yield whereas calcined Juquia PR and Sapucaia PR were 89 and 83% of TSP. The effectiveness of Gafsa PR was reduced to 0% after the soil was limed to pH 7.0 whereas the two calcined PR sources were reduced to 49% of TSP. Soil available P extracted by iron oxide impregnated filter paper (Pi test) or anion‐exchange resin after rice harvest correlated well with P uptake by rice grain for flooded and upland rice.

Characteristics of phosphate rock materials and their dissolution in some acidic Indonesian soils

Dissolution of phosphate rock (PR) materials in soil is a primary concern for phosphorus (P) in the PR to become plant available. The dissolution of three PR materials, China PR (CPR), Ciamis PR (CiamisPR) and Gafsa PR (GPR), in eight acid Indonesian soils was evaluated in a closed incubation system. Dissolution of PR was measured from the increase in either 0.5M NaOH extractable P (ΔP) or 1M BaCl2-triethanolamine (TEA)-extractable Ca (ΔCa) in soils amended with PR compared with control soil. Dissolution of the CiamisPR was the highest (30 – 100%) followed by GPR (17 – 69%) and then by CPR (20 – 54%). The maximum dissolution of PR in soil followed the order: Bogor Ultisols ≥ Bogor Oxisols ≥ Subang Inceptisols > Bogor Inceptisols > Sukabumi Oxisols > Lebak Ultisols > Sukabumi Inceptisols ≥ Lampung Ultisols. A curvilinear relationship was obtained between PR dissolution and P retention capacity and between ΔP and ΔCa.

Role of Arbuscular Mycorrhiza and Phosphorus in Acacia mangium-Peanut Agroforestry System for Rejuvenation of Tin Tailings

ABSTRACT Tin tailings are characterized by coarse sand; low in nutrient content, water-holding capacity, pH, organic matter and microbial activity; poor/absence of soil aggregation and high surface soil temperature. Therefore, the area is unsuitable for agriculture and forestry. An attempt was made to rejuvenate these lands into a sustainable production system through establishment of Acacia mangium and peanut (Arachis hypogaea L.) agroforestry (AF) system. Performance of A. mangium and peanut AF system with different P rates and arbuscular mycorrhiza (AM) inoculation was studied on degraded ex-tin mining land in Serdang, Malaysia. Three P rates viz. 0,50 and 100 g Gafsa phosphate rock (GPR) plant−1 in combination with and without AM were evaluated on A. mangium seedlings during 190 to 290 days after planting (DAP). The experiment was conducted in split-plot design with three replications. Peanut was sown in the alleys of A. mangium at 185 DAP. Three P rates at 0, 50 and 100 kg P ha−1 along with and without AM were studied on peanut. Growth of A. mangium given 50 g GPR plant 1 with AM was found higher throughout the study, while at 100 kg P ha−1 with AM was optimum for peanut. The application of AM and P fertilizer tended to increase soil organic-C, N and available P. There was an indication of improvement of soil fertility with such cropping, which might also ensure better future production.

Evaluation of residual values of different fertilisers at various rates used in phosphorus recapitalisation of an acid tropical soil

AbstractThe success of ‘phosphorus (P) recapitalisation’ depends on the changes in residual value (RV) over time. RVs of triple superphosphate (TSP), Gafsa phosphate rock (GPR) and Christmas Island phosphate rock (CIPR) were determined with and without manure bimonthly for 14 months. RV was calculated as the amount of previously applied fertiliser required to produce yield X divided by the amount of freshly applied TSP required to produce the same yield. Dry matter yield (DMY) response curves were curvilinear, with maximum DMY (11 t ha−1) occurring between 150 and 200 kg P ha−1 at 6 months and declining with time to 2–4 t ha−1 (14 months). Manure/fertiliser combinations increased DMY for CIPR but depressed DMY for TSP and GPR in all harvests except the first one. This can be attributed to nutrient imbalance caused by high P levels. RVs declined with time for fertilisers alone from 100–140% to 10–20% (14 months), while for fertiliser/manure combinations they declined from 110–180% to 10–20% (14 months). Increasing P rates from 100 to 300 kg P ha−1 resulted in the depression of initial RVs (100–140%) to 20–60% and later to 10–20% (14 months). Therefore P recapitalisation was not beneficial and hence annual P application would be recommended at 100–150 kg P ha−1. The phosphate rocks could effectively substitute for TSP.Copyright © 2006 Society of Chemical Industry

PREDICTING THE DISSOLUTION OF FOUR ROCK PHOSPHATES IN FLOODED ACID SULFATE SOILS OF THAILAND

The dissolution of rock phosphate (RP) in soils, a reaction fundamental to the effectiveness of direct application of RP, depends on both the RP and soil properties. Four RP materials of varying solubility, namely, Gafsa RP, Tilemsi RP, Taiba RP, and a local RP, Kanchanaburi RP, were incubated with six flooded acid sulfate soils to quantify factors affecting the dissolution of RP. The differences between dilute NaOH-P extracted from soils treated with and without RP materials (ANaOH-P) were used to estimate the dissolution of RP materials. A nonlinear Mitscherlich equation was used to describe the changes in ANaOH-P over incubation time. The coefficients of the fitted Mitscherlich equation were then regressed on soil and RP properties to develop an RP model. Soil acidity measured by pH and KCl-extractable aluminum (Al) were the soil properties that most affected RP dissolution and thus were included in the RP model. RP solubility as assessed using the second extraction with 2% citric acid as a percentage of rock and the particle size of RP (< 100 mesh) were the RP properties found most important in predicting dissolution and were include in the model. The calcium carbonate content of the RP affected the changes of pH in six acid sulfate soils after mixing with RP materials.

Influence of arbuscular mycorrhiza and phosphate rock on uptake of major nutrients by Acacia mangium seedlings on degraded soil

To investigate the effects of arbuscular mycorrhiza (AM) and phosphorus (P) source on the uptake of major nutrients by Acacia mangium seedlings, three P sources were used: (1) Gafsa phosphate rock (GPR), (2) China phosphate rock (CPR), and (3) triple superphosphate (TSP). The plant samples were analyzed at 60, 75, 90, 105, 120, and 135 days after planting (DAP) for their N, P, K, Ca, and Mg contents. The uptake of these nutrients was significantly influenced by AM inoculation. Nutrient use efficiency in the AM-inoculated seedlings was also significantly higher than that in uninoculated seedlings. The effect of P sources on the uptake of these nutrients decreased in the order of TSP>GPR>CPR>control. There was a significant (P<0.05) interaction effect of AM and P source on P and K uptake by A. mangium. The uptake of P and K by mycorrhizal seedlings supplemented with TSP was significantly higher than that provided with other sources of P treatments. As a natural and cheaper P source, GPR might be used in combination with AM for growing A. mangium seedlings on degraded tin tailings.

Gafsa rock phosphate and triple superphosphate for dry matter production and P uptake by corn

Crops in general make poor use of phosphorous fertilizer and, as a result, recommended rates and production costs are very high. Phosphorus can be made more readily available to plants by proper management of phosphate fertilization, selecting both, type of fertilizer and application method. This study was carried out to evaluate the efficiency of the natural Gafsa rock phosphate and the triple superphosphate on dry matter production and P uptake by corn plants cultivated in a greenhouse. Fertilizers were applied localized and broadcast/incorporated on to two soils with contrasting phosphorus capacity factors (PCF). Rock phosphate broadcast application was as efficient as triple superphosphate in increasing corn plant dry matter in the Tropudult, with lower PCF. This effect was not observed on the Haplustox, owing to the lower P solubility due to the higher Ca concentration in this soil. Triple superphosphate rates increased plant P uptake in both soils and for both application forms. Rock phosphate resulted in higher P-content in plants, but only for broadcast application on the Ultisol.

Composição florística de pastagem natural afetada por fontes de fósforo, calagem e introdução de espécies forrageiras de estação fria

Uma das características das pastagens naturais do Rio Grande do Sul é a baixa produtividade de forragem no período do outono-inverno. Uma das alternativas para melhorar os sistemas de produção baseados nessas pastagens é a introdução de espécies forrageiras de crescimento inverno-primaveril e a fertilização e correção da acidez do solo. O presente trabalho teve por objetivo avaliar o efeito de fontes de fósforo, calcário e introdução de espécies forrageiras de inverno na dinâmica das espécies de uma pastagem natural. Os tratamentos testados foram: T1 - superfosfato simples + calcário + introdução de espécies; T2 - superfosfato triplo + calcário + introdução de espécies; T3 - superfosfato triplo + introdução de espécies; T4 - hiperfosfato de Gafsa + introdução de espécies; T5 - introdução de espécies sem fósforo ou calagem; T6 - testemunha com pastagem natural. Para a avaliação da composição florística da pastagem foram realizados levantamentos botânicos periódicos, durante vinte e dois meses, utilizando-se o método BOTANAL. Os resultados mostraram que os tratamentos testados não provocaram mudanças na composição botânica das espécies nativas no período de tempo avaliado.

Eficiência de dois fosfatos naturais farelados em função do tamanho da partícula

Este trabalho foi realizado com objetivo de relacionar o tamanho da partícula de dois fosfatos naturais com seu índice de eficiência agronômica (IEA) para fósforo acumulado em plantas de milho, em dois cultivos sucessivos, sem revolvimento do solo, em casa de vegetação, num LATOSSOLO VERMELHO Distrófico típico corrigido para pH 5,5. As fontes de fosfatos naturais utilizadas foram o fosfato de Gafsa e o fosfato de Gantour Black, com os seguintes tamanhos de partículas: a) &lt; 0,074mm, b) de 0,074 a 0,149mm, c) de 0,149 a 0,297mm, d) de 0,297 a 0,71mm, e) de 0,71 a 1,41mm, f) &gt;1,41mm e g) farelados, em que mais de 80% das partículas tinham tamanho entre 0,074 e 0,5mm. O superfosfato triplo, com grânulos entre 2 e 4mm, foi utilizado como fonte padrão comparativa de fósforo. No primeiro cultivo, os fosfatos naturais finamente moídos (&lt;0,074mm) apresentaram maior IEA; à medida que aumentou o tamanho das partículas diminuiu o IEA dos fosfatos naturais, entretanto, partículas com tamanho até 0,297mm foram reativas. No segundo cultivo, o IEA para partículas com tamanho entre 0,149 e 0,71mm, aumentou e o IEA dos fosfatos naturais farelados foi pouco reduzido em relação aos finamente moídos (&lt;0,074mm). Partículas maiores do que 0,71mm não reagiram durante os dois cultivos. Os fosfatos naturais na forma física farelada mantiveram IEA próximo a 40% nos dois cultivos do milho. O fosfato natural de Gafsa foi mais eficiente do que o fosfato de Gantour Black no suprimento de fósforo no crescimento inicial de plântulas de milho.

Phosphorus fertility recapitalization of nutrient-depleted tropical acid soils with reactive phosphate rock: An assessment using the isotopic exchange technique

A “soil P fertility recapitalization” initiative utilizinglarge rates of phosphate rocks (PRs) was proposed to improve the soil P statusand increase the sustainable food production in acid and P-deficient tropicalsoils. Two series of experiments were carried out using five tropical acidsoilstreated with heavy applications of Gafsa phosphate rock (GPR). In the firstseries, the soils were mixed with GPR at the following application rates: 0,500, 1000 and 2000 mg P·kg−1, andincubatedfor one month in moist conditions. In another series, 1000 mg Pkg−1 applied as GPR was added to three soils andincubated for 1.5 month; thereafter 50 mg P kg−1as triple superphosphate (TSP) were added. The 32P isotopic exchangemethod was utilized to assess the contribution of GPR to the available soil P.Changes in amounts, E, of P transferred with time as phosphate ions from thesoil particles to the soil solution as well as changes in pH, calcium andphosphate concentrations in soil suspensions were determined. It was foundthat:(i) the contribution of P from GPR to recapitalization of soil P fertility wasmainly assessed by E pool size, pH, calcium and phosphate concentrations; othervariables were not significant at the 0.1 level; (ii) heavy applications of GPRdid not saturate all the P sorption sites, P freshly applied as water-soluble Pwas still sorbed; (iii) recapitalization of soil P fertility using GPR waspartly obtained in some acid tropical soils; (iv) Upon dissolution, GPRprovidedcalcium ions to crops and to soils, thus reducing Al toxicity, but its limingeffect was limited. To explain these effects with heavy application rates ofGPR, it was postulated that a coating of Al and Fe compounds is formed aroundPRparticles with time, thus reducing further dissolution.

Avaliação do fosfato natural de Gafsa para recuperação de pastagem degradada em latossolo vermelho-escuro

Este experimento de campo, instalado em janeiro de 1994, teve os objetivos: 1) avaliar a eficiência do fosfato natural de Gafsa farelado (FGF) na recuperação de pastagem de Brachiaria decumbens cv. Basilisk num Latossolo Vermelho-Escuro textura argilosa do Distrito Federal, e 2) verificar efeitos de interações entre fontes de P (fosfato natural de Gafsa e superfosfato triplo (SFT) e incorporação do fosfato com grade e adubação complementar (N, Ca, Mg, K, S e micronutrientes), sobre a disponibilidade de forragem. Os fosfatos foram aplicados na dose de 100 kg ha-1 de P2O5. O delineamento foi o de blocos casualizados, com parcelas subdivididas, com o tratamento incorporação nas parcelas e o fatorial, fontes de P vs. adubação complementar, nas subparcelas, perfazendo 12 tratamentos com quatro repetições. A resposta à aplicação dos fosfatos só foi efetivada com aplicação simultânea de adubação complementar; a incorporação com grade foi essencial para aumentar a eficiência do FGF; ao ser incorporado com grade, o FGF teve desempenho tão bom quanto o SFT; sem incorporação, o FGF proporcionou produção de matéria seca inferior à proporcionada pelo SFT (p&lt;0,05).

Eficiência de extratores de fósforo em dois latossolos do Mato Grosso do Sul

Com o objetivo de avaliar a eficiência de três extratores de P em dois latossolos (LEa e LRa) do Mato Grosso do Sul, foi conduzido um experimento em casa de vegetação, com três fontes de P (superfosfato triplo, fosfatos naturais de Araxá e de Gafsa), em cinco doses (0, 50, 150, 450 e 600 mg P kg-1 de solo). Utilizou-se o feijoeiro como planta-teste. Os parâmetros produção de matéria seca, P acumulado na parte aérea, altura das plantas e número de folhas trifolioladas foram correlacionados com os teores de P extraídos pelos métodos de Mehlich-1, Mehlich-3 e resina trocadora de íons. Os métodos da resina e Mehlich-3 foram mais sensíveis às variações de solos. Quanto à eficiência, os extratores classificaram-se na seguinte ordem: resina &gt; Mehlich-3 &gt; Mehlich-1. O método da resina, independentemente do tipo de solo e da fonte de P utilizada, apresentou as melhores correlações com as características das plantas avaliadas, mostrando-se mais adequado em estimar o P disponível. Os teores de P extraídos entre Mehlich-3 e resina são altamente correlacionados entre si.

EFICIÊNCIA AGRONÔMICA DE FOSFATOS NATURAIS REATIVOS NA CULTURA DO MILHO

O presente trabalho teve como objetivo avaliar o comportamento agronômico de fosfatos naturais estrangeiros quanto a produção de grãos de milho comparando com o superfosfato triplo. O ensaio foi conduzido em um latossolo vermelho amarelo de textura média no município de Uberlândia-MG. Os tratamentos empregados foram: fosfato Arad e Gafsa nas doses de P205 de 100 e 200 kg ha-1 e fosfato Marrocos e superfosfato triplo nas dosagens de 0, 50, 100, 200 e 400 kg ha-1. A capacidade dos fosfatos naturais Arad, Marrocos e Gafsa em fornecer fósforo para o milho foi de 60, 80 e 97%, respectivamente, quando comparados com o superfosfato triplo. Houve correlação positiva entre os teores de P nas folhas do milho e a produtividade. A avaliação do P disponível no solo foi mais bem representada pelo método da resina comparado com o método Mehlich-1.

EFICIÊNCIA RELATIVA DE FONTES DE FÓSFORO DE DIFERENTES SOLUBILIDADES NA CULTURA DO ARROZ

Foi realizado um experimento em casa de vegetação com arroz, para verificar se os fosfatos solúveis em ácido cítrico a 2% ou citrato de amônio apresentam a mesma eficiência agronômica que os fosfatos solúveis em água e comparar a eficiência dos extratores de resina e Mehlich com a disponibilidade de fósforo no solo. As fontes testadas foram superfosfatos simples (SPS), multifosfato magnesiano (MFM), termofosfato magnesiano (TFM), fosfato de Araxá (FA) e fosfato de Gafsa (FG), nas doses de 0, 50 e 150mg P/dm3. Na dose de 50mg P/dm3 as fontes apresentaram índice de eficiência agronômica (IEA), em relação ao SPS (IEA = 100%), de 106%, 98%, 95% e 16%, respectivamente para o MFM, TFM, FG e FA. Na maior dose (150 mg P/dm3) os IEA foram de 86%, 82%, 84% e 22% para as fontes na mesma ordem, sendo as três primeiras estatisticamente iguais ao SPS, demonstrando que os fosfatos solúveis em ácido cítrico ou citrato apresentaram eficiência agronômica similar à de fosfatos solúveis em água. Comparando-se a resina trocadora de íons e o extrator de Mehlich como extratores de P do solo, observou-se que a resina forneceu as melhores correlações entre o fósforo do solo e produção de matéria seca (r = 0,82 resina e r = 0,08 Mehlich) e quantidade de fósforo absorvido pelas plantas de arroz (r = 0,89 resina e r = 0,15 Mehlich).

A new approach to the determination of phosphate rock dissolution in organic soils using graphite furnace atomic absorption spectrophotometry

Abstract The determination of phosphorus (P) in 0.5M NaOH extracting solution following the dissolution of phosphate rock (PR) materials in mineral soils is frequently done using a molybdenum blue method. For organic soils, 0.5M NaOH soil extracts usually give dark color solutions. This dark color solution reduces the intensity of light in spectrophotometer, thus, underestimating the dissolution of PR in organic soils compared to mineral soils. A new approach using a graphite furnace atomic absorption spectrophotometer (GFAAS) was evaluated for measuring P in pure solutions; and this was used for measuring the dissolution of PR in organic soils. The P standard solutions prepared in distilled water, 1% humic acid, 1% fulvic acid, 0.5M NaOH, 0.5M NaOH+1% humic acid, and 0.5M NaOH+1% fulvic acid were used for establishing the standard curve and the selection of matrix modifier. The organic soils at different degree of decomposition (saprist, hemist, and fibrist) were incubated with gafsa phosphate rock (GPR), Christmas Island A‐grade phosphate rock (CIPR), and triple superphosphate (TSP) each at a rate of 0, 500, and 1000 mg P/kg soil. The dissolution of PR was measured using 0.5M NaOH‐extractable P and 0.5M BaC12/TEA‐extractable Ca. The measurement of peak area gave the highest sensitivity reading (p=0.01) compared to peak height; and lanthanum nitrate was the most suitable matrix modifier for determination of P in distilled water, 1% humic acid, 1% fulvic acid, 0.5MNaOH, 0.5MNaOH+l% humic acid, and 0.5M NaOH+1% fulvic acid. The dissolution of PR as measured by 0.5M NaOH decreases in the following sequence: Sapric (B) > Hemic > Fibric > Sapric (D). Absolute amounts of P increased with increasing levels of P addition; and TSP gave the highest dissolution value followed by GPR, and CIPR. The dissolution of PR in organic soils using 0.5M NaOH extracting solution can be accurately determined by GFAAS method.

Dissolution of phosphate rock in the rhizosphere of upland rice soils

Abstract The availability of nutrients is high in the rhizosphere of plants. However, the information on level of phosphorus (H2PO‐ 4) and calcium (Ca2+) following the dissolution of phosphate rock (PR) material in the rhizosphere is still lacking. The release of phosphorus (H2PO‐ 4) and calcium (Ca2+) from 0 and 500 mg P/kg soil of Hamrewein phosphate rock (HPR) and gafsa phosphate rock (GPR) added to Bungor (Typic Paleudult), Sedu (Typic Sulfaquept), and Tin tailing soils packed in seven‐compartment each of 5‐mm thickness rhizobox and sown with upland rice (Buntar variety) was determined by using either 0.5M NaOH‐extractable P (δP) or 0.5M NaHCO3‐extractable P (δPb) and 0.5M BaCl2/TEA‐extractable Ca (δCa). The amounts of δCa and δpHw increased within the rhizosphere having the highest value in the central compartment. In contrast, δP and δPb decreased within the rhizosphere having the lowest value in the central compartment. Sedu soil gave the highest value of δPb (135.4 mg P/kg soil), δP (230.5 mg P/kg...

Cowpea varietal differences in uptake of phosphorus from Gafsa phosphate rock in a low-P Ultisol

A greenhouse experiment was conducted to evaluate varietal differences in the uptake and availability of P from Gafsa phosphate rock (PR) to five cowpea cultivars grown in a low-P Paleustult soil from Ghana, using the A value technique. The32P radioisotope used as a tracer was32P-labelled triple superphosphate (TSP). Each cultivar received sole or a combined application of the two fertilizers (TSP, PR). From these treatments it was possible to estimate for each cultivar, AR + AS, AS and by difference AR (AR and AS stand for A values for phosphate rock and soil, respectively). Using this approach we measured significant genotypic differences in P uptake from PR and AR values. The ranking of the cultivars in P uptake from PR was the same as for AR, i.e. Asontem > Vallenga > Soronko > IT81D-1137 > Amantin. Similarly, ranking for uptake from soil P was the same as AS, i.e. Vallenga, Soronko, IT81D-1137, Asontem and Amantin. Thus although PR could not be labelled directly, using the A value approach it was possible to distinguish between P availability from PR and soil to the plant. The recoveries of applied TSP ranged from 8.0% to 9.4% and those of PR from 2.3% to 3%.