Agronomic Effectiveness Of Phosphate Rocks Research Articles

Enhancement Effect of Water-Soluble Phosphorus on Agronomic Effectiveness of Phosphate Rocks

ABSTRACTDirect application of phosphate rocks (PRs) with low/medium in reactivity has shown to be low in agronomic effectiveness for cereal crops. Presence of water-soluble P (WSP) in the vicinity of PR can significantly enhance the rooting system at the early stage of plant growth. This, in turn, can enable the plant to utilize the associated PR more effectively than the use of PR alone at planting. This report presents the results of several greenhouse experiments that show the granulated (WSP+PR) products by dry compaction process using different low-reactive PR sources were as effective as WSP fertilizers viz triple superphosphate (TSP) and monoammonium phosphate (MAP). The test plants were maize (30 days) and soybean and upland rice were grown to maturity on acid or neutral soils. Based on the results obtained a P ratio of 50:50 between WSP and PR is recommended for the granulated (WSP+PR) products that can achieve crop yields at the same levels as that with the WSP fertilizers.Abbreviations: phosphate rock, PR; water-soluble P, WSP; dry-matter yield, DMY

Eficiência técnica de fertilizantes fosfatados em latossolo sob plantio direto

Pouco se conhece sobre a eficiência relativa de fosfatos solúveis e naturais em sistemas de alta produtividade de culturas em plantio direto no centro-sul do Paraná. Este trabalho objetivou avaliar a eficiência agronômica de fosfatos naturais reativos em comparação a um fosfato solúvel na produtividade de várias espécies vegetais anuais em dois ciclos de um sistema de rotação de culturas trienal. O experimento foi conduzido sobre um Latossolo Bruno, em Guarapuava, PR, de 2000 a 2006. Dois fosfatos naturais reativos (FNR: Gafsa e Arad) e um fosfato solúvel (superfosfato triplo, SFT) foram aplicados, a lanço, nas doses de 0, 40, 80 e 160 kg ha-1 de P2O5, no início do primeiro e do segundo ciclo de rotação de culturas trienal (aveia branca/milho/trigo/soja/cevada/soja). À exceção da cevada, a produtividade das culturas não foi alterada pela adição de qualquer dos fosfatos no primeiro ciclo de rotação, provavelmente, devido ao alto teor de P previamente existente no solo (8,7 mg dm-3 na camada de 0-10 cm). No segundo ciclo de rotação, quando o solo tinha 4,1 mg dm-3 de P, a aplicação de P na semeadura da aveia branca incrementou em 11 % a produtividade das culturas de verão e em 20 % a das culturas de inverno, tendo o menor incremento ocorrido no milho (8 %) e o maior na cevada (44 %). Neste ciclo, o SFT proporcionou maior produtividade do que os FNR nas culturas de inverno (aveia branca, trigo e cevada), numa média de 11 %, não tendo havido diferença de produtividade entre os FNR. O fosfato solúvel em água é mais eficiente do que os fosfatos naturais reativos em solos sob plantio direto, tanto no efeito imediato quanto na fase residual. Apesar disso, não é necessário aplicar fertilizantes fosfatados para obter alta produtividade em solos com altos teores de P em plantio direto, a não ser para culturas muito exigentes, a exemplo da cevada.

Relative Agronomic Effectiveness of Phosphate Rock Compared With Triple Superphosphate for Initial Canola, Wheat, or Ryegrass, and Residual Wheat in Two Acid Soils

Direct application of phosphate rock (PR) may provide the essential phosphorus (P) nutrient for crop production in acid soils. However, the agronomic effectiveness of PR depends on several factors including PR reactivity, soil properties, and crop species. This greenhouse study investigated the effects of PR reactivity, soil pH, Al saturation, and crop species on the initial and residual relative agronomic effectiveness (RAE) of PR compared with water-soluble triple superphosphate (TSP) in two acid soils (Hartsells pH 4.8 and Hiwassee pH 5.4). Three PR sources, Tunisia, Mali, and Togo, representing high, medium, and low PR reactivity, respectively, were used. The soils were treated with P sources at 0, 25, 50, 100, 200, and 500 mg P kg−1 soil. Wheat, ryegrass, and canola were the test crops in the first season, and wheat was used as a residual crop after all three initial crops in the second season. Soil samples were collected for chemical analyses at 0 and 500 mg P kg−1 soil after the first crops. The initial RAE of PR for crop species followed: canola > ryegrass = wheat in the Hartsells soil and canola > ryegrass > wheat in the Hiwassee soil. However, the residual crop of wheat after wheat, wheat after ryegrass, and wheat after canola did not show any significant effect of previous crop. Among P sources, both initial and residual RAE followed: TSP > Tunisia PR > Mali PR ≥ Togo PR for all the crops and soils except for the initial canola crop grown in Hiwassee soil where all PR sources were as effective as TSP. In general, the RAE of PR in Hiwassee soil was higher than that of Hartsells because of the negative effects of soil acidity and Al saturation on crop growth in the Hartsells soil. A significant relationship between available P after first crops and residual wheat grain yield was found in the Hiwassee soil.

Plant- and microbial-based mechanisms to improve the agronomic effectiveness of phosphate rock: a review

Deficiency in plant-available phosphorus is considered to be a major limiting factor to food production in many agricultural soils. Mineral resources are necessary to restore soil phosphorus content. In regions where conventional fertilizers are not used due to cost limitations or to mitigate adverse environmental effects, local sources of phosphate rock are being increasingly recognized for potential use as alternative phosphorus fertilizers. The main obstacle associated with using directly applied ground phosphate rock is that the phosphate released is often unable to supply sufficient plant-available phosphorus for crop uptake. Plantand microbial-based mechanisms are low-cost, appropriate technologies to enhance the solubilization and increase the agronomic effectiveness of phosphate rock. Common mechanisms of phosphate rock dissolution including proton and organic acid production will be reviewed for both plants and microorganisms. This review will also address possibilities for future research directions and applications to agriculture, as well as highlight ongoing research at the University of Guelph, Guelph, Canada.

Agronomic effectiveness of biofertilizers with phosphate rock, sulphur and Acidithiobacillus for yam bean grown on a Brazilian tableland acidic soil

Phosphate rocks have low available P and soluble P fertilizers have been preferably used in plant crop production, although economic and effective P sources are needed. Experiments were carried out on a Brazilian Typic Fragiudult soil with low available P to evaluate the agronomic effectiveness of phosphate rock (PR) compared with soluble phosphate fertilizer. Yam bean ( Pachyrhizus erosus) inoculated with rhizobia (strains NFB 747 and NFB 748) or not inoculated was the test crop. Biofertilizers were produced in field furrows by mixing phosphate rock (PR) and sulphur inoculated with Acidithiobacillus (S+ Ac) in different rates (50, 100, 150 and 200 g S kg −1 PR), with 60 days of incubation. Treatments were carried out with PR; biofertilizers B 50, B 100, B 150, B 200; triple super phosphate (TSP); B 200 without Acidithiobacillus and a control treatment without P application (P 0). TSP and biofertilizers plus S inoculated with Acidithiobacillus increased plant growth. Soil acidity and available P increased when biofertilizers B 150 and B 200 were applied. We conclude that biofertilizers may be used as P source; however, long term use will reduce soil pH and potentially reduce crop growth.

Relative Agronomic Effectiveness of phosphate rocks and P adsorption characteristics of an Oxic Rhodustalf in Eastern India

AbstractThe Relative Agronomic Effectiveness (RAE) of rock phosphates as compared to water soluble Triple Super Phosphate was measured on direct, residual, and cumulative application of the P fertilizers in a field experiment with rice on an Oxic‐Rhodustalf in the eastern plateau region of India. The fertilizers were Morocco Rock Phosphate (MORP), Mussoorie Rock Phosphate (MRP), Partially Acidulated Rock Phosphate (PARP), and Triple Super Phosphate (TSP). The RAE of the rock phosphates were lower for direct application (54–80 %) and cumulative application (70–93 %) of P but roughly equal or larger for the residual effect (92–142 %) as compared to TSP. The P adsorption characteristic of the experimental soil conformed to the linear relationship of both Freundlich and Langmuir isotherm equation. The adsorption data when plotted according to Langmuir equation deviated from a single linear relationship at higher concentration (10 μg ml–1), thereby giving two adsorption maximum values ( 68.49 μg g–1 and 256.41 μg g–1) and binding energies ( 2.86 ml μg–1 and 0.089 ml μg–1) for the soil. Two populations of P adsorption site with widely different affinity for P probably existed in the soil.

Agronomic effectiveness of phosphate rock and superphosphate for aluminum‐tolerant and non‐tolerant sorghum cultivars

About 35% of soils in Venezuela are acid and low in available phosphorus (P). To solve this problem farmers lime and apply phosphate fertilizers to the soils, but both lime and fertilizers are expensive. A good alternative to overcome soil acidity is the use of aluminum (Al)‐tolerant cultivars. The objective of this study was to test the hypothesis, by use of a pot experiment, that sorghum cultivars tolerant to Al toxicity are able to use P from phosphate rock more efficiently than are susceptible cultivars. Three sorghum (Sorghum bicolor L. Moench) cultivars, Chaguaramas III (Ch), AI‐tolerant, Decalb D59 (D59), and Pioneer 8225 (Pi), both Al‐susceptible, were grown in the greenhouse for 20 and 35 days in two acid soils fertilized with 0 and 100 mg P kg‐1 as triple superphosphate (SP) and Riecito phosphate rock (PR). Santa Maria soil was very low in available P (2 mg kg‐1) and highly saturated in Al saturation (64.5%) and Pao soil was higher in available P (20 mg kg‐1) and low in Al saturation (6.5%). Chaguaramas dry matter production, P uptake and root length was higher in Santa Maria soil as compared with Pi and D59 when grown with both SP and PR fertilization. Chaguaramas response to PR in Pao soil was not as good as in Santa Maria soil. The results of our experiment suggest that Al‐tolerant Ch is able to utilize P from PR more efficiently in soils like Santa Maria than Al‐susceptible cultivare Pi and D59.

Comparison of phosphate rock and triple superphosphate on a phosphorus‐deficient Kenyan soil

Soil phosphorus (P) deficiency is a constraint to crop production in many regions of sub‐Saharan Africa, which could be overcome through use of either soluble P fertilizer or sufficiently reactive phosphate rock (PR). A field study was conducted with corn (Zea mays L.) for three growing seasons (18 months) on a P‐deficient, acid soil in Kenya to compare a soluble P source (triple superphosphate, TSP) and relatively reactive Minjingu PR from Tanzania. In the 18 months following application of 250 kg P ha‐1, bicarbonate extractable inorganic soil P (Pi) was higher for application of TSP than PR, but Pi extracted with a mixed anion‐cation resin was comparable for TSP and PR. Inorganic P extracted by 0.1M NaOH, without prior extraction of resin and bicarbonate Pi, decreased during the 18 months following TSP application, but increased following PR application. After 18 months, about 7% of the added PR‐P remained as Ca‐bound P that was extracted with 1M HCl. The 1M HCl extractable P., however, underestimated residual PR‐P that gradually dissolved and supplied plant‐available P, as indicated by recovery of <40% of PR‐P added to soil in laboratory incubations even though PR solubility in HCl was >90%. Minjingu PR was an effective source of P for corn. Corn yields were comparable for TSP and PR, and the relative agronomic effectiveness of PR averaged 107% in Season 1 and 79% in Season 3. Anion resin and mixed anion‐cation resin appeared to be superior to bicarbonate and NaOH as a soil P test for use with both TSP‐ and PR‐treated soils.

The agronomic effectiveness of reactive phosphate rocks 2. Effect of phosphate rock reactivity

Summary. The chemical reactivity of apatite phosphate rock (PR) from Sechura (Bayovar), North Carolina, Egypt (Hamrawein), Morocco (Khouribja) and Queensland (Duchess), was estimated using the following methods (indices): percentage of the phosphorus (P) present in the PR that is soluble in one extraction with 2% citric acid and 2% formic acid, and variation in crystal chemistry determined using X-ray diffraction to measure the length of the unit cell a dimension. The indices were related to the agronomic effectiveness of the PRs for pasture using percentage of the maximum (relative) yields for PR and superphosphate. At most sites there was a statistically significant trend for the agronomic effectiveness of the PRs to increase with increasing reactivity of the PRs as assessed by the 3 indices. However, this was not the case for sites where: (i) leaching of water-soluble P from freshly-applied superphosphate occurs in wet years; and (ii) the agronomic effectiveness using SV 50 values of all the PRs was uniformly low so that no differences between the PRs could be detected. The relationship between the agronomic effectiveness (SV50) of PR and chemical reactivity of the PR were generally different each year and in most cases this variability was related to the variation in total annual rainfall. From this study it is concluded that PRs in which greater than 65–70% of their total P content is soluble in 2% formic acid are likely to be highly reactive and therefore agronomically effective P fertilisers for direct application to appropriate soils in suitable environments.

Evaluation of agronomic effectiveness of phosphate rocks for aluminum‐tolerant soybean cultivar

Abstract The effect of liming on the agronomic effectiveness of three phosphate rocks (PRs) Pesca and Huila from Colombia and Sechura from Peru as compared with TSP was evaluated in a greenhouse experiment for an Al‐tolerant soybean cultivar grown on an acid Ultisol. On both unlimed (pH 4.4) and limed (pH 5.0) soils, the agronomic effectiveness of P sources in terms of increasing seed yield followed the order of TSP > Sechura PR > Huila PR > Pesca PR > check, an order similar to that of solubility of P sources. Liming slightly decreased the effectiveness of Pesca PR, whereas liming had no effect on Huila PR. A significant increase in agronomic effectiveness was observed upon liming for Sechura PR and TSP. Soil‐available P as extracted by the Pi method was closely related to the amount of N fixed by soybean crop that, in turn, was related to the soybean seed yield. Values of relative agronomic effectiveness (RAE) of PRs with respect to TSP were calculated by assuming the check = 0% and TSP = 100%. On unlimed soil, the RAE values of PRs were: Pesca PR = 31%, Huila PR = 42%, Sechura PR = 84%. On the limed soil, the RAE values were: Pesca PR = 8%, Huila PR = 24%, Sechura PR = 66%. It can be concluded that the use of PR with respect to that of TSP for soybean crop is more favorable in the unlimed soil than in the limed soil, provided that the soybean plant is relatively Al‐tolerant.

Agronomic evaluation of fertilizers with special reference to natural and modified phosphate rock

Most of the phosphate fertilizes currently used worldwide (16 million tonnes of P) are water soluble. Direct application of phosphate rock accounts for just 3.5%. Since most phosphate rock is used to produce water-soluble phosphate fertilizer, about 150 million tonnes of byproduct phosphogypsum are produced annually on a worldwide basis. This has given rise to concerns about its management and disposal in an environmentally acceptable manner. Despite the small amount of phosphate rock presently used for direct application, its use is becoming increasingly common in the developing countries, especially Latin America, due to the high cost of water-soluble phosphate fertilizers and to the variety of soils, crops and climatic conditions of the region. Agronomic effectiveness of phosphate rocks has been measured by the concept of Relative Agronomic Effectiveness where the yields are compared to those obtained with Triple Superphosphate (TSP) or Diammonium Phosphate (DAP). Phosphorus uptake as a response of the phosphate rock applied is measure by tissue analysis. This methodology is already ‘standard’ for the member countries of the Latin America Phosphate Rock Network.

Factors affecting the agronomic effectiveness of phosphate rock for direct application

Phosphorus (P) is critically needed to improve soil fertility for sustainable crop production in large areas of developing countries. In recent years, phosphate rock (PR) for direct application has been tested in tropical acid soils as a potential alternative to conventional water-soluble P fertilizers like single superphosphate (SSP) and triple superphosphate (TSP). Some developing countries have PR deposits which, if used to supplement other imported P fertilizers, would allow a saving of much needed foreign exchange. Solubility of P fertilizers is not the only criterion in selection of the most suitable P fertilizer. This paper discusses the results of experiments to compare the relative agronomic effectiveness (RAE) of various PR sources with respect to SSP or TSP as influenced by four important factors: PR sources, soil properties, management practices, and crop species. Under certain conditions, PRs can be agronomically effective.

Use of phosphate rocks in the tropics

The use of finely ground phosphate rocks (PRs) as directly applied P fertilizers in tropical farming systems is a cheaper alternative to acidulated, water-soluble P products. However, the effectiveness of PRs in tropical environments depends on the extent to which the required P uptake rate of the crop plant can be maintained by the rate of PR dissolution in that soil. That extent that this outcome is achieved depends on the properties of the PR, the soil, climate, plant factors, and on management practice. Environmental conditions in the surface layers of highly weathered soils in the humid tropics are generally conducive of the attainment of satisfactory rates of PR dissolution, especially as the reactivity of the PR increases. In soils with very high P sorption capacities, however, the agronomic effectiveness of PRs is reduced as the acquisition of dissolved P by plant roots is restricted by competition from P sorption processes in the soil.

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.

Influence of pH, time and rate of application on phosphate rock dissolution and availability to pastures

The agronomic effectiveness of an unground reactive phosphate rock from Sechura, Peru, was compared with that of monocalcium phosphate in a severely P deficient and highly P retentive soil (vitrandept) over a period of three years. Soil pHs were adjusted to pH 5.1, 5.3, 5.6 and 6.4. The sward consisted mostly of ryegrass (Lolium perenne) and white clover (Trifolium repens). Fertilisers were applied at six rates at pH 5.3 and three rates at other pHs in the first year. For two of the rates fertilisers were reapplied in the second year. Dry matter yields, P uptake and ground cover of clover were determined during the experimental period. In phosphate rock treated plots a negative linear relationship was obtained between soil pH and the logarithm of yield. The agronomic effectiveness of phosphate rock relative to monocalcium phosphate increased with time at all pHs. Calculated at fertiliser rates which produced near maximum yields, relative agronomic effectiveness at soil pHs 5.1, 5.3, 5.6 and 6.4 were respectively 58, 60, 18, and 5 in year one; 118, 125, 77 and 38 in year three. At pH 5.3, as the rate of application increased the relative agronomic effectiveness of the phosphate rock generally decreased in year one but was enhanced in the intermediate rates in years two and three. The data for ground cover of clover gave a similar trend to that for herbage yield and P uptake.

Ability of chemical extraction procedures to assess the agronomic effectiveness of phosphate rock materials

Abstract The ability of 7 chemical extraction procedures to assess the agronomic effectiveness of phosphate rock (PR) was evaluated using perennial ryegrass and white clover grown in 6 soils in a glasshouse. Of the conventional, single chemicalextraction procedures evaluated, 2% formic acid appeared to be the most useful. Two 2% citric acid procedures (which produced very similar results) and neutral ammonium citrate (NAC) at the first extraction were poor indicators of agronomic effectiveness. Of the sequential extraction procedures investigated, the 2% formic acid (sum of 2 extractions), both of the 2% citric acid (sum of 3 extractions), and the NAC (sum of 4 extractions) gave the best correlation with agronomic performance. The use of sequential extractions also improved the predictive ability of these extractants in the longerterm, a limitation shown by the conventional, single chemical-extraction procedures. Sequential extraction appears to be the only extraction technique suitable for assessing the ...

Dissolution of North Carolina Phosphate Rock in Acid Colombian Soils as Related to Soil Properties

AbstractInformation on the dissolution of phosphate rock in soils as related to soil properties is needed in order to understand the solubility behavior of the phosphate rock in soils as related to crop response. This study was conducted to determine the relationships between the dissolution rate of North Carolina phosphate rock and selected chemical properties of 16 acid Colombian soils. A modified Elovich equation, Ct =Co − (1/β) ln (αβ) − (1/β) ln t, was used to describe the dissolution of phosphate rock in the soils. In the equation, Ct is the P concentration in water extract at time t, Co is the maximum P concentration in the water extract when t→0, α and β are constants. Of the various soil properties studied, the best correlations of reactive Al were a simple linear relationship with β and a log‐log relationship with α. Results from tests with two other acid soils from Colombia showed these relationships allow prediction of the dissolution rate of the phosphate rock in other soils from a single measurement of reactive Al content.Phosphorus sorption capacities of the 16 soils were correlated with amounts of reactive Al or active Al but not with amounts of free Fe2O3 and exchangeable Al in the soils. Amounts of water‐extractable P in the soils treated with concentrated superphosphate (CSP) or the phosphate rock decreased as P sorption capacity increased; however, the relative amounts of water‐extractable P of the phosphate rock with respect to CSP increased as P sorption capacity increased. This suggests that the relative agronomic effectiveness of phosphate rock compared with CSP would be highest on the strongly P‐fixing soils.