Increased phosphorus availability from sewage sludge ashes to maize in a crop rotation with clover

A recycling of Phosphorus (P) from the human food chain is mandatory to secure the future P supply for food production. However, many available recycled P fertilizers from sewage sludge do not have an adequate P bioavailability and, thus, are not suitable for their application in soils with pH >5.5–6.0, unless being combined with efficient mobilization measures. The aim of the study was to test the P mobilization ability of red clover (Trifolium pratense L.) from two thermally recycled P fertilizers for a subsequently grown maize. Two sewage sludge ashes (SSA) were investigated in a pot experiment at soil pH 7.5 with red clover differing in its nitrogen (N) supply (added N fertilizer or biological N₂ fixation (BNF)), followed by maize (Zea maize L.). Shoot dry matter of maize was almost doubled when N supply of previous grown clover was covered by BNF, instead of receiving added N fertilizer. Similarly, shoot P removal of maize following clover with BNF was significantly increased. It is suggested that the P mobilization is related to the BNF, and a proton release of N₂ fixing clover roots led to the measured decrease in soil pH and thereby increased P availability of the tested fertilizers.     

Phosphorus Availability and Transformation as Affected by Repeated Phosphorus Additions in an Ultisol

Phosphorus (P) solubility and transformation in soils determine its availability to plants and loss potential to the environment, and soil P dynamics is impacted by fertilization and soil properties. A Ultisol sample was interacted with 20 mg L^?1 P solution from one to ten times. The P-reacted soils were then analyzed for water-soluble P (0.01 M calcium chloride (CaCl₂)–extractable P); plant-available P (Olsen P); ammonium chloride P, aluminum P, iron P (NH₄Cl-P, Al-P, Fe-P, respectively); and occluded P (Oc-P). The degree of P saturation (DPS) was calculated from ammonium oxalate–extractable Al, Fe, and P. The amount of P sorbed by the soil was highly correlated with the frequency of P addition with high percentage of P adsorbed initially and gradually decreased as the P addition continued. The relative abundance of the five P fractions in the P-reacted soil was in the order of Fe-P (36.5 percent) > Al-P (35.6 percent) > Oc-P (22.8 percent) > Ca-P (2.7 percent) > NH₄Cl-P (2.3 percent). Both Olsen P and CaCl₂-P were significantly increased by the repeated P addition process and highly correlated in an exponential function. The DPS was increased above the so-called critical point of 25 percent after the first P saturation process and kept increasing as the P addition continued. The P availability and adsorption in the soil were controlled by soil free and amorphous Al and Fe. The results suggest that repeated P application will build soil P to an excessive level, and consequently result in poor P-use efficiency and high P-loss potential to surface and groundwater.     

Effect of liming and phosphate application on sudangrass growth and phosphorus availability in two temperate acid soils

Abstract

A pot experiment was carried out in the greenhouse with two loamy sand Dystric Cambisols derived from schist to investigate the effect of liming and phosphorus (P) application on plant growth and P availability and its assessment by four soil test methods: 0.01M calcium chloride (CaCl₂), cation anion exchange membrane (CAEM), Egnér‐Riehm, and Olsen procedures. Soils were first incubated for two weeks with lime at four levels, depending on their content of exchangeable aluminum (Al). Phosphorus was added at two rates (75 and 150 mg P kg^‐1) and the incubation proceeded for an additional two‐week period. Sudangrass (Sorghum sudanenses cv. Tama) was then planted and harvested four weeks later. During incubation and plant growth, soils were maintained at 70% of field moisture capacity. Although pH value and soil extractable P in original soils were similar, the results showed a significant difference on the effect of liming and P application. Acidity was the major limitation for DM yield in the soil with the highest amount of exchangeable Al, while P availability was the main constraint in the other soil. Liming above pH (0.01M CaCl₂) 5.3–5.5 did not increase DM yield in either soil and showed a negative effect on one soil (9.7 to 6.9 and 10.2 to 7.8 g pot^‐1). Phosphorus content and uptake by sudangrass increased with liming, revealing a positive effect of lime on the availability of P to plants. Added P showed a lower efficiency in the soil with highest amounts of Al compounds. Soil tests performed after the execution of the pot experiment showed variable tendencies to predict P availability, according to the nature of the procedures and soils. Soluble‐P in 0.01M CaCl₂ increased with the rise of soil pH. Extractable CAEM‐P and Egnér‐Riehm‐P also increased with liming, but reflected the soil depletion caused by plant uptake. Extractable Olsen‐P presented the most inconclusive results, suggesting the limitation of this method for acid soils which have been limed.     

Comparative Effects of Rock Phosphates on Arbuscular Mycorrhizal Colonization of Trifolium pratense L.

Abstract

The effect of five rock phosphates with different solubility (from Algeria, North Florida, North Carolina, Senegal, and Morocco) and that of single superphosphate (SSP) alone or with lime was investigated on the root colonization of red clover with indigenous arbuscular mycorrhizal fungi (AMF). In a pot experiment, the phosphorus (P) sources were applied at four rates (0, 100, 400, and 1600 mg total P₂O₅ kg^?1 dry soil) to an acidic sandy soil (Nyírlugos) and to an acidic clay loam soil (Ragály). The arbuscule content of the roots was more sensitive to various rock phosphates than the infection frequency. No mycorrhizal colonization of roots was observed in the Nyírlugos soil at the 1600 mg P₂O₅ kg^?1 level of SSP or in either soil at the 1600 mg P₂O₅ kg^?1 level of SSP+lime, indicating that the mycorrhizal dependency of the host was eliminated by the highest soluble P concentrations in the soil.     

Reclamation of Alkali Soils: Influence of Amendments and Leaching on Transformation and Availability of Phosphorus

Abstract

Phosphorus (P) availability to plants in reclaimed alkali soils was the main objective of this study, which was also focused on P transformations, decrease in Olsen‐P content, and magnitude of P lost in leachate in course of amendment application and leaching. Liquid sodium bicarbonate (NaHCO₃) was added to nonalkali soils to set up four ESP (exchangeable sodium percentage) levels (viz., 2.9, 25.0, 50.0, and 75.0), but actual ESP levels obtained were 2.9, 24.6, 51.2, and 75.3. Amendments (viz., gypsum and pyrites) and P treatments (viz., 0 and 50 mg P Kg^?1) were mixed with dry, sieved soil before filling into PVC (polyvinyl chloride) drainage columns, which were then compacted to uniform bulk density and leached with deionized water for 30 days. Results indicated that the pH and electrical conductivity (EC) of the soils increased with increase in ESP level of the soil but decreased with amendment application. Phosphorus addition to alkali soils decreased the pH on day 30, but it could not affect the EC of the soils. Successive increase in the ESP level of the soil increased the pH and EC off the leachate. Gypsum‐amended soils exhibited lower pH and EC values than pyrite‐amended soils. The EC of the leachate decreased sharply with time in amended soils, but the pH decreased slowly. Phosphorus addition affected the leachate pH earlier than the soil pH. Cumulative volume of leachate decreased with increasing ESP levels, but it increased with amendment and phosphorus application. Leaching of P increased with increase in ESP levels, and the maximum cumulative loss of P was 11.2 mg Kg^?1 in the 75.3 ESP soil. Cumulative P lost in the pyrite‐amended soils was higher than the gypsum‐amended soils. Phosphorus leaching in the gypsum‐amended soils stopped at day 10 and beyond, but it continued until day 30 in the pyrite‐amended soils. Part of the applied P in alkali soils was also lost along with the native P, whereas it was protected in the nonalkali soils. OlsenP increased with increasing ESP levels, and alkali soils invariably contained higher Olsen P than nonalkali soils. At day 30, alkali soils contained much higher Olsen P (12.6 mg Kg^?1) than nonalkali soils (5.9 mg Kg^?1). In general, there was a decrease in the Olsen P with both of the amendments, but it decreased more with pyrites than with gypsum. Phosphorus added through monopotassium phosphate (KH₂PO₄) remained extractable by Olsen's extractant up to day 30. Results also indicated that percent distribution of ammonium chloride (NH₄Cl)‐P, calcium (Ca)‐P, and unknown P increased with rising ESP levels but iron (Fe)‐aluminum (Al)‐bound P and residual P decreased. Percent distribution of Ca‐P and unknown P exhibited an increase with time also. Unamended alkali soils contained more NH₄Cl‐P than amended ones. Iron and Al‐ bound P and residual P increased more with pyrites, whereas formation of Ca‐P and unknown P was enhanced with gypsum. Applied P tended to convert more into NH₄Cl‐P, Ca‐P, and residual P than to Fe‐Al‐bound P or unknown P fractions. Models developed to estimate Olsen P and P concentration in leachate, through pH or EC, have application value for P management in alkali soils that are leached after application of amendments.     

Phosphorus Amendment of a Lead-Spiked Soil with Low Phosphorus Availability: Roles of Phosphorus on Soil and Plant Lead

Phosphorus (P) is both a macronutrient for plants and an effective amendment to reduce lead (Pb) toxicity in soil. Thus, in Pb-polluted soil with low P availability, P will act as a nutrient as well as a Pb-immobilizing agent. However, this has not been fully investigated. A soil with 2.50 mg kg^?1 Olsen P was spiked with soluble Pb and then amended with superphosphate to examine the effect of P on soil Pb availability and ryegrass (Lolium perenne L. cv. Aubisque) growth. It was found that P/Pb = 2 increased ryegrass yield by 804% and decreased root Pb concentration and soil diethylenetriaminepentaacetic acid (DTPA)–extractable Pb concentration by 25.6% and 1.0%, respectively. As P amendment increased to P/Pb = 4, both plant yield and root Pb concentration declined compared with P/Pb = 2. Results of the sequential extraction indicated that the proportion of carbonate phase Pb decreased, while that of the manganese oxide phase increased as P was added. The proportion of residual Pb was little affected by the amendment. The results suggest that in soils with low P availability and high Pb availability, availability of soil Pb and root concentration of Pb are less affected, whereas the toxicity of Pb is greatly depressed by the P amendment; P/Pb = 2 is high enough to alleviate the stresses of low P availability.     

Soil phosphorous buffer coefficient as influenced by time and rate of P addition

Abstract

This study was conducted to investigate the effect of time and rate of phosphorus (P) addition on phosphorus availability and phosphorus buffer coefficient in some calcareous soils. Phosphorus was added to the samples at rates of 0, 50, 100, 200, 400, 600 and 800 mg P kg^?1 soil. The samples were incubated for 0.041, 1, 7, 14, 21, 30, 60 and 90 days at constant temperature and moisture. Extractable phosphorus was determined after the incubation. The results showed a sharp decrease in available P within 1 h after P addition. There was a linear relation between added P and extractable P in all soils. The buffer coefficients of soils were estimated by Olsen P for above incubation periods. Generally the buffer coefficient decreased with increasing time of incubation. The results indicated that inputs of between 23 – 59 mg kg^?1 are required to raise Olsen P by 10 mg kg^?1 in these calcareous soils, which assuming 2500 t soil ha^?1, gives a required input of 58 – 148 kg P ha^?1.     

A comparison of 5 soil phosphorus extraction methods applied to different soils of South of Iran

Phosphorus (P) fertilization is commonly based on soil testing, for which a variety of different soil P extraction methods are in use. In this research, the correlation and calibration of five extraction techniques for available P were studied: Soltanpour and Schwab, Olsen, EDTA-Na₂, Paauw and Morgan in 168 different soil samples from 63000 ha of Sirjan pistachio orchards of Kerman province, Iran. The Morgan reagent extracted the most P and then EDTA-Na₂> Olsen> Soltanpour and Schwab> Paauw extracted more phosphorus, respectively. Positive and significant correlation (P < 0.05) existed among all extractants. The correlation coefficients between different extractants and plant P concentration indicated that, EDTA-Na₂ (P < 0.01), Olsen and Paauw methods (P < 0.05) had positive and significant correlation with leaf P concentration and thus with due attention to acceptable relationship with plant indices, the Olsen and EDTA-Na₂ methods could be used to advise on available P.     

Soil test calibration studies for formulation of phosphorus fertilizer recommendations for maize in Morogoro district,Tanzania. I. evaluation of soil test methods

Abstract

Optimum crop production depends, among other things, on the maintenance of adequate plant nutrients in the root zone. The objective of this study was to find a reliable index for assessing needs for supplemental phosphorus (P) in soils of Morogoro District, Tanzania. Six indices of P availability, namely: Bray and Kurtz No. 1 (BK1), Bray and KurtzNo.2 (BK2), Mehlich 1, Mehlich 3, Olsen and ammonium bicarbonate‐DTPA (AB‐DTPA), were evaluated. Evaluation of the P indices involved relating extractable P contents by different methods with crop response data expressed as relative yields. The response data was obtained from pot trials with soil samples from ten repesentative soils designated as benchmark soils of the district. Treatments were absolute control, 0, 10, 20, and 30 mg P kg^‐1 of soil. Correlation of maize relative yields with soil test values by the six indices of P availability resulted in correlation coefficients ranging from 0.65 to 0.90. The Olsen method gave the highest r value suggesting that it was superior to the others. However, using the Cate and Nelson approach, the Olsen and ammonium bicarbonate‐DTPA methods were found to be at par and superior to the others. They each accounted for 76% of the variations observed in maize relative yields, respectively. The critical P levels for the indices were 10.50 mg P kg^‐1 for Olsen and 2.80 mg P kg^‐1 for the AB‐DTPA method. Phosphorus fertility categories were delineated in relation to Olsen extractable P as: low (<6.50 mg P kg^‐1), medium (6.50 to 23.0 mg P kg^‐1), and high (>23.0 mg P kg^‐1). Based on this classification it was determined that 16%, 25 %, and 59% of the surveyed area had low, medium, and high P levels, respectively. About 40% of the surveyed area may, therefore, require fertilization with P for optimum yields.     

Comparison of Two Soil Phosphorus Analytical Methods in Croatia

Abstract

The purpose of this article was to compare soil phosphorus (P) extraction by sodium bicarbonate solution (Olsen P) and by ammonium lactate (AL P) and to create a model for prediction of Olsen P using ordinary soil‐fertility control data. The soils data used in this study included Olsen P, pH_KCl, pH_H2O, organic matter, AL P, and AL K. Soil pH_KCl ranged from 3.5 to 8, organic matter up to 5%, AL K up to 400 mg kg^?1, and AL P up to 200 mg kg^?1. Olsen P and AL P were significantly correlated, and the difference between them was influenced by soil pH. Regression models included all soil data grouped by soil pH range, which significantly decreased the difference between predicted and measured Olsen P. The validation of the model was conducted on new data sets from field fertilization trials. The results show that Olsen P can be related to AL P and used for fertilizer recommendations instead of AL P.     

EDTA extractable phosphorus in soils as related to available and inorganic phosphorus forms

Abstract

Twenty surface soil samples, representing two major soil orders alfisols and vertisols were extracted with 0.01N Na₂ EDTA solution (pH 4.8) at a soil/solution ratio of 1:25. Phosphorus in the extract was determined following ammonium molybdate‐stannous chloride colorimetric method. The EDTA extractable P showed significant positive correlations with extractable P according to the Olsen, Morgan, Bray 1 and 2 and also with inorganic phosphorus fractions associated with Al, Ca and Fe.     

Comparison of Iron Oxide–Impregnated Paper Strips with Other Extractants in Determining Available Soil Phosphorus

Abstract

Iron oxide–coated strips (P_i) can serve as a sink to continuously remove phosphorus (P) from solution. In this way, P extraction is analogous to the P absorption by plant roots. The objective of this study was to compare the iron oxide–coated paper strips with other chemical extraction methods to estimate the plant P availability for corn (Zea mays) growing in the greenhouse in some soils of Hamadan province of Iran. Sixteen soil samples with different physicochemical properties were analyzed for available P using Olsen, Colwell, Mehlich‐1, 0.01 M CaCl₂, AB‐DTPA, and 0.1 M HCl methods and p_i. Furthermore, the effects of two P levels (0 and 200 mg P kg^?1) on the plant indices (P uptake, relative yield, and plant responses) were studied in a greenhouse experiment using 10 soil samples. The results showed that the amount of extractable P decreased in the order of 0.01 M CaCl₂<AB‐DTPA<p_i<Olsen<Colwell<Mehlich‐1<0.1 M HCl. The amount of P extracted by the p_i method was significantly correlated with other extractants. The amounts of P extracted by all chemical methods were significantly correlated. The results of a pot experiment showed that the amount of P extracted by the p_i method was significantly correlated with the plant P uptake. However, the other methods were not significantly correlated with P uptake. The results of this experiment showed that p_i method was able to predict the plant availability of soil P.     

Soil test calibration studies for formulation of phosphorus fertilizer recommendations for maize in Morogoro district,Tanzania. II. estimation of optimum fertilizer rates

Abstract

Studies were conducted on some soils of Morogoro District to estimate economically optimum phosphorus (P) fertilizer recommendations for maize from soil tests. The studies involved the estimation of maize yield response to added P in pot and field experiments. Maize responded to added P at three sites. At all three sites, the residual effects of added P lasted up to three years suggesting that added P was not strongly fixed in these soils. Yield responses were related to extractable P contents by the Olsen and AB‐DTPA methods through a modification of the Mitscherlich‐Bray equation. Estimated model parameters were incorporated in equations for estimating optimum P fertilizer rates for different cost‐price ratios (p) and marginal rates of return (R). At the p and R values that prevailed in the study area during 1997, recommended P fertilizer rates (P_R) could be determined by the equation: P_R=68.497–1.191T (Olsen P). Calculated P fertilizer rates for P deficient sites in the district ranged from 15 to 60 kg P ha^‐1. This wide range underscored the importance of site specific fertilizer recommendations.     

Effect of Limestone of Different Sizes on Soil Extractable Phosphorus and Its Concentrations in Grass and Clover Species

Phosphorus (P) is often reported as a nutrient whose availability increases by lime application, although some research suggests a decline in the short-term P availability upon liming. This study addresses the effects of applying different sized limestone (2–4, 0.5–2, 0.25–0.5, and <0.25 mm) on the forms and availability of soil P, P concentrations and extraction by pasture, and yields of plant species. Soil P was partitioned into organic and inorganic forms, using an ignition method. Available P was determined by the Olsen and Mehlich 3 methods. Phosphorus in plants was determined after acid digestion. Most P was present in organic form. One year after sowing, inorganic P increased and organic P decreased. Liming had no significant influences on soil P. Phosphorus extracted by Mehlich 3 explained 40% of the total dry-matter yield in the first harvest. No significant effect of liming on P concentration in plants was observed.     

Changes of Soil Phosphorus Fractionation According to pH in Red Soils of China: An Incubation Experiment

Phosphorus (P) deficiency is one of the main problems limiting crop growth in red soils of southern China. The primary objective of this study was to examine P availability as a function of soil acidity. Soils were sampled from a long-term fertilization experiment and are referred as low-P (No P fertilization) and high-P (120 kg P₂O₅ ha^–1). Both low-P and high-P treatments were incubated adjusting soil pH to seven levels from 3.0 to 6.5 for 10, 20, 30 and 45 days. The pH, DIP, and Olsen-P were determined after each incubation period, and inorganic P fractions were measured at the end of incubation. For both low-P and high-P treatments, DIP decreased with rising pH value and increased with decreasing soil pH. Olsen-P, Ca-P (Ca₂-P, Ca₈-P, and Ca₁₀-P) and Al-P increased significantly with soil pH in low-P treatment. In high-P, Olsen-P increased with pH between 3.4 and 5.0 and was stable at higher pH. Moreover, Ca-P and Al-P increased significantly but Fe-P decreased with soil pH increase. The redundancy analysis showed that Ca-P, Al-P, and pH had positive effects on Olsen-P, but Occluded-P showed a negative correlation with Olsen-P in both soils. Our results confirmed that soil P availability was influenced by pH and that the changes in DIP and Olsen-P were linked to changes of inorganic fractions from occluded to Ca- and Al-bound forms. Managing soil acidity is a key issue regarding the availability of P in red soils of China and our results suggest that at least a pH of 5.0 should be targeted.     

Phosphorus Adsorption and Bioavailability in a Paddy Soil Amended with Pig Manure Compost and Decaying Rice Straw

Phosphorus (P) availability in soil is closely related not only to soil P content but also to soil physicochemical and biological properties, which are closely associated with P sorption and biochemical transformation. The aims of this study were to determine the effects of pig manure compost (PMC) or decaying rice straw (DRS) added to a paddy soil on soil pH, soil organic carbon (SOC), dissolved organic carbon (DOC), acid phosphatase, microbial biomass P, soil test P (Olsen P), and P uptake by rice (Oryza sativa L. cv. ‘Liaoyan’). Phosphorus adsorption characterization affected by PMC‐ or DRS‐derived DOC was also studied. Compared with the control, both PMC and DRS treatments increased soil pH, SOM, DOC, microbial biomass P, and Olsen P, and the activity of acid phosphatase during the 110‐day incubation period. Phosphorus adsorption in soil decreased with DOC extracted from PMC and DRS and was well fit by the Langmuir equation. The Olsen P in the PMC‐ and DRS‐treated soil was correlated with both DOC content and acid phosphatase activity. Both PMC and DRS treatments significantly increased dry‐matter yield and P uptake in rice shoot. In conclusion, the increased P availability in the paddy soil was not only a result of direct P supplied following organic manure incorporation, but also an indirect result of reduction in P sorption on the solid phase of the paddy soil by DOCs which were derived from DRS or PMC.     

Effect of Lime and Flooding on Phosphorus Availability and Rice Growth on Two Acidic Lowland Soils

Abstract

Loss of soil‐water saturation may impair growth of rainfed lowland rice by restricting nutrient uptake, including the uptake of added phosphorus (P). For acidic soils, reappearance of soluble aluminum (Al) following loss of soil‐water saturation may also restrict P uptake. The aim of this study was to determine whether liming, flooding, and P additions could ameliorate the effects of loss of soil‐water saturation on P uptake and growth of rice. In the first pot experiment, two acid lowland soils from Cambodia [Kandic Plinthaqult (black clay soil) and Plinthustalf (sandy soil)] were treated with P (45 mg P kg^?1 soil) either before or after flooding for 4 weeks to investigate the effect of flooding on effectiveness of P fertilizer for rice growth. After 4 weeks, soils were air dried and crushed and then wet to field capacity and upland rice was grown in them for an additional 6 weeks. Addition of P fertilizer before rather than after flooding depressed the growth of the subsequently planted upland rice. During flooding, there was an increase in both acetate‐extractable Fe and the phosphate sorption capacity of soils, and a close relationship between them (r²=0.96–0.98). When P was added before flooding, Olsen and Bray 1‐extractable P, shoot dry matter, and shoot P concentrations were depressed, indicating that flooding decreased availability of fertilizer P. A second pot experiment was conducted with three levels of lime as CaCO₃ [to establish pH (CaCl₂) in the oxidized soils at 4, 5, and 6] and four levels of P (0, 13, 26, and 52 mg P kg^?1 soil) added to the same two acid lowland rice soils under flooded and nonflooded conditions. Under continuously flooded conditions, pH increased to over 5.6 regardless of lime treatment, and there was no response of rice dry matter to liming after 6 weeks' growth, but the addition of P increased rice dry matter substantially in both soils. In nonflooded soils, when P was not applied, shoot dry matter was depressed by up to one‐half of that in plants grown under continuously flooded conditions. Under the nonflooded conditions, rice dry matter and leaf P increased with the addition of P, but less so than in flooded soils. Leaf P concentrations and shoot dry matter responded strongly to the addition of lime. The increase in shoot dry matter of rice with lime and P application in nonflooded soil was associated with a significant decline in soluble Al in the soil and an increase in plant P uptake. The current experiments show that the loss of soil‐water saturation may be associated with the inhibition of P absorption by excess soluble Al. By contrast, flooding decreased exchangeable Al to levels below the threshold for toxicity in rice. In addition, the decreased P availability with loss of soil‐water saturation may have been associated with a greater phosphate sorption capacity of the soils during flooding and after reoxidation due to occlusion of P within ferric oxyhydroxides formed.     

A preliminary comparison of the ammonium acetate‐edta soil phosphorus extraction method to the bray‐1 and olsen soil phosphorus extraction methods

Abstract

The ammonium acetate (NH₄OAc)‐EDTA soil phosphorus (P) extraction method was compared to either the Bray‐1 soil P extraction method for non‐calcareous soils or the Olsen soil P extraction method for calcareous soils to predict com and wheat plant tissue P concentration and grain yield responses. The NH₄OAc‐EDTA method predicted yield and tissue P concentration responses to P fertilizer applications more accurately than the Olsen method at three of five sites. Both the Bray‐1 and NH₄OAc‐EDTA methods were successful in predicting corn and wheat yield responses to P fertilizer applications in non‐ calcareous soils in many locations. However, a direct comparison of extracted soil P levels showed that the NH₄OAc‐EDTA method extracted soil P at levels which were more closely related to the Bray‐1 method than the Olsen method.     

Wheat p requirements on calcareous Morrocan soils: III evaluation by isotherms compared to Olsen extractable P

Abstract

Phosphorus fertilizer recommendations were compared by interpretations from P isotherms, Olsen extractable P and the Mitscherlich‐Bray model based on the Olsen method for 15 soils from the Chaouia (dryland) region of Morocco. The P isotherms were fit to straight line and second degree polynomial equations. The P buffer indexes (PBI) derived from the isotherms were not significantly correlated to P buffer capacities as measured by a single P buffer capacity index, but negatively correlated to Olsen P (r = ‐0.63), relative yield (r = ‐0.76) and P uptake (r = ‐0.66). Phosphorus in solution was a quadratic function of P added in 0.01 M CaCl₂equilibrium solution. The P fertilizer recommendations to maintain soil solution P concentrations at 0.01, 0.12 and 0.20 mg P L^‐1were higher than recommended by direct interpretation of plant response to Olsen extractable P and the quantity based on the Mitscherlich‐Bray model as calculated from Olsen available P values. The P fertilizer recommended to maintain soil solution P of 0.10 mg P L^‐1was significantly correlated with Olsen P (r = 0.71) as was that recommended Mitscherlich‐Bray log transformation model (r = 0.81), and nonlinear least square estimation (r = 0.78). Field research will be needed to evaluate if the P fertilizer recommended to maintain this solution P concentration is adequate for maximum economic wheat grain yield under field conditions     

Phosphorus Release Characteristics from Biosolids-Derived Organomineral Fertilizers

This study investigated the availability of phosphorus (P) following soil application of a novel biosolids-derived organomineral fertilizer (OMF₁₅; 15:4:4) in comparison with single superphosphate (0:18:0). Two soil types of contrasting characteristics were incubated over a period of 90 days at 25 °C and maintained near field capacity. Phosphorus was applied at rates equivalent to 0 (control), 150, and 300 kg ha^?1 of P₂O₅, respectively. Availability of P from OMF₁₅ was low throughout the experiment accounting for less than 6.5% of total OMF₁₅-P applied. It was shown that after the 90 days incubation period, the overall increase in soil extractable P in OMF₁₅-treated soil was marginal in both soil types. For single superphosphate (SSP), P availability ranged from 16% to 46% of total SSP-P applied. Application of SSP increased soil extractable P levels significantly (P < 0.001) compared with unfertilized control soils. The results of this study aided the development of fertilization strategies for the best use of OMF produced from nutrient-enriched biosolids granules for applications in winter cereal and grass crops in England.