Determination of exchangeable acidity,carbonate ions and change of buffer in triethanolamine‐buffered solutions percolated through soil samples containing carbonates

Abstract

The content of dissolved carbonates and exchanged acidity in triethanolamine‐buffered BaCl₂‐solutions which were percolated through soil samples containing carbonates is determined by two titration‐procedures to pH 4.0 and 10.25. because a single titration value gives no information of the amounts of both ionic species in solution. The amount of dissolved carbonates calculated on the bases of these titration‐procedures, however, is smaller than that determined by measuring the content of inorganic carbon in solution. The difference is attributed to the sorption of protonized triethanolamine‐buffer during percolation, which leads to an underestimation of CEC when measured by re‐exchanged Ba⁺⁺, whereas the amount of exchangeable bases is overestimated due to dissolution of carbonates. The amount of exchanged acidity calculated from the data obtained is surprisingly high and is at least partly attributed to the existence of HCO₃ ^‐ ‐sorbed on the surface of (wet) soils.     

Applications of fertilizer cations affect cadmium and zinc concentrations in soil solutions and uptake by plants

A pot experiment was conducted to study changes over time of Cd and Zn in soil solution and in plants. Radish was grown in a soil which had been contaminated with heavy metals prior to 1961. Constant amounts of a fertilizer solution (NH₄NO₃, KNO₃) were added daily. Soil solution was obtained at intervals by displacement with water. The cumulative additions of small amounts of fertilizers were made equal to the plants' requirements at the final harvest but were found to exceed them during most of the experiment. Excess fertilizers caused substantial increases of major (K, Ca, Mg) and heavy-metal (Cd, Zn) ions in soil solutions and a decrease in soil pH, probably due to ion-exchange mechanisms and the dissolution of carbonates. Uptake of Cd and Zn into leaves was correlated with the mass flow of Cd (adjusted r²= 0.798) and Zn (adjusted r²= 0.859). Uptake of K, Ca and Mg by the plants was independent of their concentrations in solution. It is concluded that, in order to study effects of plants on heavy-metal availability and obtain soil solution that has not been altered by fertilizer ions, nutrients must be added according to the needs and growth of the plants. This could be achieved by linking fertilizer additions to the rate of transpiration, as nutrient uptake and transpiration were closely correlated in this experiment.     

Effect of high ammonium levels on nitrification,soil acidification,and exchangeable cation dynamics

Abstract

In almond orchards which are fertilized and irrigated with drip systems, fertilizers are applied to a relatively small soil volumes several times during the growing season. Where NH₄‐based fertilizers are used, high NH₄ levels are anticipated in soil solution and on exchange sites. The effects of high NH₄ concentration on nitrification, soil acidification, and exchangeable cation dynamics were studied in an incubation experiment where 500 and 2000 mg N/kg soil were added as (NrL₄)₂SO₄. After incubation for 25 days with added (NH₄)₂SO₄, nitrifying bacteria were lower than the populations at the start of experiment. In the 2000 mg N/kg treatment, nitrification activity nearly ceased and soil acidification was reduced. Although nitrification activity was lower in the 500 mg N/kg treatment than in the control, after 10 days of incubation, nitrification activity lowered soil pH by 0.7 units. After the initial 10 days, soil pH was lowered to 4.8 and nitrification activity was depressed. Ammonium ions occupied about 20 and 36 % of the exchange capacity in the 500 and 2000 mg N/kg treatments respectively, and exchangeable Ca, Mg, and K were significantly lowered. Extractable acidity was less than 0.1 cmoiykg dry soil.     

Efficacy of single application ammonium sulfate in suppressing potato common scab

Abstract

The objective of this study was to suppress potato common scab by lowering the soil pH and increasing the concentration of water-soluble aluminum (Al) in soil with a single application of ammonium sulfate into each row. Superphosphate (P) and potassium sulfate (K) were applied to the surface soil horizon and ammonium sulfate (N) was applied only into the rows along which potato plants were to be planted. By this application method, the soil pH was lowered and the concentration of water-soluble Al was increased in the soil of the rows where potato tubers were grown. Potato common scab was suppressed in the soil containing water-soluble Al in concentrations of 0.2 to 0.3 mg L^?1 or higher. The pH of the soil fertilized as indicated above remained lower than that of the control soil to which the mixture of N, P, and K was uniformly applied. In soil types such as Haplic Andosols containing allophane at high concentrations of 71 g kg^?1 in Memanbetsu, the suppression of potato common scab by this single application of ammonium sulfate was less effective due to the low soluble Al concentration. In other soil types, the soil pH was easily controlled and common scab was suppressed by this method. The advantages of this method are that (a) it minimizes the use of fertilizers, thus reducing the adverse effects of unnecessary fertilizers on the soil; and (b) it lowers the cost by eliminating additional agricultural chemicals and extra fertilizers.     

Liming in relation to soil acidity and p fertilizer efficiency

Abstract

An acid brown podzolic (pH 4.0) soil of wide distribution in Ireland was limed with Ca(OH)₂ to pH values of 5.2 and 7.4. With each increment of lime significant increases in growth and F uptake by Italian ryegrass occurred, the increases being greatest with the first increment. Increasing soil pH resulted in decreased extractable aluminum and iron as well as exchangeable hydrogen. Available P as measured by various extractants increased with increasing soil pH.

The relative performance of three P fertilizers, superphosphate, phospal and basic slag was affected by liming. Basic slag was more effective than superphosphate at pH 4.0, was as effective at pH 5.2 and was less effective at pH 7.4. Phospal was poorest at each pH level. While growth and P uptake increased with increasing P levels the relative responses to the three fertilizers decreased with increasing soil pH.     

Umsatz im Boden und Ertragswirkung rohphosphathaltiger Düngemittel

Turnover in soil and yield response of phosphate rock containing fertilizers Solubility of phosphate rocks is the better the higher the carbonate substitution in the given phosphate rock type. From the soil factors, pH is of importance. At soil pH < 5 phosphate rocks are fairly soluble and their yield effect equals that of fully processed fertilizers. In a soil pH range from 5 to 7, pH does not play such a decisive role as has been assumed. Other soil factors such as H⁺ buffer power of soil, Ca²⁺ and particularly the phosphate concentration in the soil solution are equally relevant for phosphate rock dissolution. The evaluation of numerous field experiments provided evidence that in the above cited pH range fully processed fertilizer phosphates are superior to phosphate rock containing fertilizers with regard to phosphate uptake, yield formation, and phosphate recovery. Also the residual effect of rock phosphate is poorer than that of fully processed phosphate fertilizers. There is some evidence that phosphate rocks show a relatively good response on deep rooting soils which allow a vigorous root growth and on soils with a sufficiently high level of soil moisture. In a soil pH range > 5 rock phosphate containing fertilizer are not suitable for maintenance fertilization, since under such conditions the phosphate concentration in the soil solution is relatively high thus suppressing the dissolution of phosphate rock.     

Formula fertilization of nitrogen and potassium fertilizers reduces cadmium accumulation in Panax notoginseng

ABSTRACT

This study investigated the effect of nitrogen (N) and potassium (K) formula fertilization on cadmium (Cd) accumulation in P. notoginseng. Field investigations as well as formulated N and K fertilizers application experiments were conducted. Field investigations showed that Cd accumulation decreased PNS content in the main roots of P. notoginseng, while PNS content was promoted by soil available potassium (AK) and K in the main roots. The Cd content in P. notoginseng and the bioavailable Cd content in the soil decreased with the increasing of total K (TK) and AK in the soil. The increase of soil pH, total organic matter (TOM) and cation exchange capacity (CEC) values can reduce the bioavailable Cd content in soil, thus reducing the Cd accumulation in P. notoginseng. Under current fertilization in P. notoginseng cultivation, decreased N fertilization can alleviate the deterioration of soil physical and chemical properties. Under identical N fertilization, increasing K fertilization promoted the PNS accumulation (0.3–38.3%), also improved soil physical and chemical properties. Formulated N and K fertilizers application (1:2) experiments showed that reducing application of N and increasing K fertilization could reduce the bioavailable Cd content in soil, and the Cd content also decreased by 0.5–69.6% in P. notoginseng.

Abbreviation: PNS: P. notoginseng saponins; F(EXC): Exchangeable fraction; F(Carb): Bound to carbonates fraction; F(Fe-MnOX): Bound to iron and manganese oxides fraction; F(OM): Bound to organic matter fraction; F(RES): Residual fraction; AK: Available potassium; TK: Total potassium; CEC: Cation exchange capacity; TOM: Total organic matter     

Precipitation of secondary phases of iron and its role in controlling the mobility of potentially toxic elements in soils in a semiarid river basin in Northwest Mexico

Purpose

Soils have the ability to retain potentially toxic elements (PTEs) through different chemical processes that promote low mobility of these elements, such as the precipitation of secondary phases of Fe, which facilitate the adsorption/co-precipitation of PTEs. The main objective of this study was to evaluate the mobility of PTEs present in an acid solution in two soils with different concentrations of calcite, understanding the role of secondary iron phases in the retention of these elements.

Materials and methods

To evaluate this phenomenon, intact soil columns of two different types of soils from the Sonora River in Northwest Mexico were exposed to an acid solution with high concentration of dissolved PTEs (mainly Fe, Al, and Cu).

Results and discussion

The Tinajas soil was free of carbonates while the Bacanuchi soil had more carbonate content than the Tinajas soil. Secondary precipitates corresponding to secondary phases of iron (mainly ferrihydrite and jarosite) were identified by X-ray diffraction. Using scanning electron microscopy, the PTEs retained in the soils were identified. The presence of calcite favored the neutral pH values in the collected leachates in the Bacanuchi soil; consequently, the mobility of the PTEs present in the acid solution was nullified. Furthermore, this process facilitated the retention of the toxic elements in the Bacanuchi soil.

Conclusions

The retention of PTEs was 100% in the Bacanuchi soil where the natural acid-neutralizing capacity in this soil was associated with calcite. The formation of secondary phases of Fe, among them ferrihydrite, jarosite, and schwertmannite, mainly in Bacanuchi soil, promoted the retention of Al, As, Cd, Cu, Fe, Mn, and Pb (elements analyzed in this work). Results of this work can provide key insights to improve cleanup and conservation strategies in mining sites.

     

High‐Energy Milling Improves the Effectiveness of Silicate Rock Fertilizers: A Glasshouse Assessment

Abstract

The effectiveness of intensively milled gneiss and potassium (K-feldspar) as K fertilizers was evaluated through a glasshouse experiment with ryegrass. Plant were grown on two soil types for 12 months. Results show that the agronomic effectiveness of milled gneiss was nearly as great as potassium sulfate (K₂SO₄), but milled K‐feldspar was much less effective because of the relatively small extent of dissolution of K‐feldspar in the soil. The positive effects of K‐silicate rock fertilizers (K‐SRFs) included increases in plant biomass, uptake of K and silicon (Si), and soil pH with increasing application rate of the K‐SRFs. The application of K‐SRFs will be most advantageous for amending K‐deficient soils, and high‐energy milling provides a simple method for manufacturing effective multinutrient SRFs.     

Phosphorus sorption and availability indices as affected by properties of calcareous soils

Abstract

The Olsen solution is usually considered the best extractant for estimating P availability in calcareous soils, but predictability of the response to P fertilizers is often low under field conditions. In this study, soil characteristics influencing P sorption and extractability were evaluated. Forty‐one soils varying in CaCO₃, pH, and clay content were selected from pastures to minimize the effect of recent P additions. A P sorption index (PSI) determined from a single addition of 150 mg P/100 g soil was related to soil Ca and CaCO₃, but the correlation coefficients were rather low (r = 0.46 and 0.38, respectively). A P availability index (PAI), determined from the increase in extractable soil P after adding 50 mg P/kg to a suspension and allowing it to dry, was correlated quite well with cation exchange capacity and clay content (r = ‐0.61 for each) in soils with pH < 8.8. The PAI also had a positive relationship with the density of the processed soil sample (r = 0.60). The relationship between PAI and soil Ca (r = ‐0.51) was also better than that between PSI and soil Ca. Inclusion of initial soil P and organic carbon along with CEC increased the predictability of PAI from 37% to 59%. In soils with pH > 8.8, soil pH was the dominant factor controlling the PAI (r = 0.92).     

Selective sequential dissolution techniques for trace metals in arid‐zone soils: The carbonate dissolution step

Abstract

Dissolution capacity and kinetics of carbonates by sodium acetate (NaOAc)‐acetic acid (HOAc) at various pHs were studied. A comparative study of the selectivity, specificity, and effectivity of NaOAc‐HOAc solution on carbonate bound fraction during the sequential selective dissolution procedure was conducted by comparing the dissolution of major and trace elements from arid zone soils by this buffer solution at various pHs. The effect of the pH of NaOAc‐HOAc solution on the following fractions in the sequential selective dissolution procedure was also studied. NaOAc‐HOAc solution at pH 5.5 at a soil to solution ratio of 1:25, can dissolve all the carbonate from calcareous soils with 10–20% of carbonate; at pH 5.0 it can dissolve all the carbonate in soils with about 30–50% calcium carbonate (CaCO₃). A second extraction with fresh buffer solution at pH 5.0 is required for soils with more than 50% of carbonate. Six hours of extraction time is generally sufficient for complete carbonate dissolution. For most of agricultural soils in arid and semi‐arid zones, the attack of the buffer solution at pH 5.0 on other solid‐phases seems to be limited. But the buffer solution at pH 5.5 would be better for some forest soils with low carbonate content and high organic matter content. The part of carbonate fraction not be dissolved in this step is released in the following steps: easily reducible oxides fraction (ERO), organic matter fraction (OM), and reducible oxides fraction (RO), leading to gross misinterpretation of the elemental partitioning in arid zone soils.     

Persistence of CaCl2 washing effect for amelioration of a Cd-contaminated paddy field soil

Abstract

Soil washing is one of the methods used to remediate soil contaminated with heavy metals, and when the contaminated elements have been effectively removed the washed soil can be used for agriculture. Soil washing was conducted using 0.5 mol L^?1 CaCl₂ solution at pH 4 as an extracting agent to remediate a paddy field soil contaminated with Cd. Dolomite powder was applied to neutralize the soil to the original pH 6.2. After CaCl₂ washing, the content of Cd extractable in 0.1 mol L^?1 HCl decreased from 2.4 to 0.8 mg kg^?1. Subsequently, a pot experiment was carried out to evaluate the effect of soil washing on Cd concentration in polished rice (Cd_pr) for three successive years. Using the washed soil, Cd_pr was ≤ 0.2 mg kg^?1 with and without a treatment that simulates midseason drainage, whereas it was > 0.5 mg kg^?1 in the unwashed soil with the midseason drainage treatment. The reasons for low Cd_pr growth in the washed soil were the low content of exchangeable Cd in the soil and the resultant high soil pH (> 7). To evaluate the effect of soil pH on Cd_pr in the fourth year, we adjusted soil pH to 5 with H₂SO₄ before transplanting rice seedlings. The Cd_pr in the washed soil with the midseason drainage treatment increased to 0.47 mg kg^?1, whereas it was less than 0.2 mg kg^?1 under continuous flooding. Thus, high pH or whole season flooding are important to keep Cd_pr at ≤ 0.2 mg kg^?1 even after soil washing. With the application of dolomite and other ordinary fertilizers, soil properties were little affected by the present soil washing procedure because the difference in rice yield between the washed and unwashed plots was not significant within each year.     

SOIL NUTRIENT CHANGES WITH FERTILIZER TYPE IN CASSAVA-BASED CROPPING SYSTEM

ABSTRACT

The changes in soil nutrient status following the application of different fertilizer types were studied in field experiments involving maize-melon intercrop relayed into a cassava-soybean intercrop between 1995 and 1997. The soil at the experimental site was a Kanhaplic Haplustalf, which was under continuous cultivation with arable crops for seven years and fallow for four years. The effects of organic and inorganic fertilizers were investigated singly and in combination. The type of fertilizer had no significant effect on the soil pH, although, cropping significantly lowered the pH from 6.0 to 5.7. Cropping also significantly reduced the soil organic matter and total nitrogen (N). The soil organic matter (OM) and total N were most depleted with organic fertilizer application. Complementary application of organic and inorganic fertilizers limited the degree of depletion from 31.0 to 12.1 g kg^?1 of OM and 1.8 to 0.6 g kg^?1 total N. Soil available P was increased (60%) by inorganic fertilizer while the organic fertilizer increased it by 145% and the combined fertilizer by 186%. Exchangeable calcium (Ca) was depleted by about 12% with organic fertilizer application, 15% by inorganic fertilizer and about 19% with complementary application of organic and inorganic fertilizers. Exchangeable sodium (Na) was reduced from 0.43 to about 0.38 cmol kg^?1 while magnesium (Mg) was increased from 0.5 to about 0.6 cmol kg^?1.     

Mineral Composition and Dry Mass Production of Corn Plants Affected by Different Phosphate Sources and Different Soil Aluminum Saturation Levels

Abstract

The effects of different commercial phosphate fertilizers [Triple superphosphate (TSP), Tricalcium phosphate (TCP), and ARAD rock phosphate) and soil aluminum (Al) saturation (86, 29, and 0%) on the mineral composition and dry mass production of corn (Zea mays) plants were studied. As soil Al saturation values decreased, pH, calcium (Ca), and magnesium (Mg) levels in the soil increased. High Ca values in the shoot resulted in the reduction in potassium (K) concentrations. The high values of P availability in the soil for the ARAD source of P did not correspond to the high values of dry mass production of corn plants. The high values of corn mass production were noticed for the TSP phosphate source, and the mass productions values were reduced as the soil Al saturation values increased.     

Effect of Field Aging on Nickel Concentration in Soil Solutions

Abstract

The effect of field aging on nickel (Ni) concentration in soil solutions was studied on three soils, with pH 4.5, 6.1, and 7.6, that were spiked with Ni and aged outdoors for 5, 10, and 15 months. Field aging resulted in a minor decrease in total Ni content and a dramatic decrease in Ni concentration in soil solution. Nickel release isotherms in field‐aged soils differ from those in freshly spiked ones. The decrease in soluble Ni in noncalcareous soils at Ni loadings from 25 to 4800 mg kg^?1 followed a first‐order kinetic equation. In calcareous soil the observed relationships imply that soluble Ni may be controlled by dissolution of a surface precipitate either on the surface of soil carbonates [NiCO₃ or NiCO₃ · 2Ni(OH)₂] or on the surface of clay minerals (Ni‐aluminum double‐layer hydroxide).     

Effects of calcined magnesite,magnesium hydroxide and “geosan” on soil properties in declining spruce stands (NE Bavaria)

The results of pH-stat.-titrations at six pH levels show increasing reactivities of the fertilizers under investigation in the order magnesite < Geosan < Mg-hydroxide. Further differences exist in the acid neutralization capacity of the three samples. By 3 mo after fertilization, Mg concentrations in soil solution down to 70 cm soil depth significantly increased. Differences between the fertilizers reflect their reactivities. Fertilization increases soil nitrate concentrations by 50 to 100% up to 55 ppm. It is unclear why the control plots already show high nitrate contents in soil solution. The top mineral soil shows significant increases of base saturation after fertilization. The highly reactive Mg-hydroxide produces the highest Mg concentrations in the soil solution, whereas the slower soluble magnesite has a stronger effect on the exchange complex.     

Effects of calcined magnesite,magnesium hydroxide and “geosan” on soil properties in declining spruce stands (NE Bavaria)

The results of pH-stat.-titrations at six pH levels show increasing reactivities of the fertilizers under investigation in the order agnesite < Geosan < Mg-hydroxide. Further differences exist in the acid neutralization capacity of the three samples. By 3 mo after fertilization, Mg concentrations in soil solution down to 70 cm soil depth significantly increased. Differences between the fertilizers reflect their reactivities. Fertilization increases soil nitrate concentrations by 50 to 100% up to 55 ppm. It is unclear why the control plots already show high nitrate contents in soil solution. The top mineral soil shows significant increases of base saturation after fertilization. The highly reactive Mg-hydroxide produces the highest Mg concentrations in the soil solution, whereas the slower soluble magnesite has a stronger effect on the exchange complex.     

Influence of water solubility of granular zinc fertilizers on plant uptake and growth

Abstract

Zinc (Zn) fertilizer application has increased during the past three decades. This increase has created the need for more information regarding the availability and agronomic effectiveness of Zn containing fertilizers because differences of opinions exist relating the relationships between Zn water solubility and plant availability. Plant availability of eight commercialized Zn fertilizer materials having different water solubilities was measured under greenhouse conditions. Corn (Zea mays L.) plants were grown for 40 days in a soil (loamy, mixed, mesic arenic Ustollic Haplargid) amended with lime to two pH's: 6.3 and 7.4. To evaluate the effect of pH, some Zn fertilizers were used at both soil pH levels while all Zn fertilizers were used in the pH 7.4 soil. The experimental design was a factorial combination of pH, Zn fertilizers, and Zn rates of 0,2.1,4.2,8.4 mg Zn kg^?1 soil. Dry matter production and Zn uptake increased significantly when the soil pH decreased from 7.4 to 6.3. The highest dry matter production was obtained with ZnSO₄ (ZnSO₄ H₂O, 99.9% total water soluble Zn), Zn20 (Zn oxysulfate, 98.3% total water soluble Zn), and Zn27 (Zn oxysulfate, 66.4% total water soluble Zn). While ZnFe (Zn iron ferrite, 0.3% total water soluble Zn), ZnK (Zn oxide, KO61, 1% total water soluble Zn), and ZnOS (Zn oxysulfate, 0.7% total water soluble Zn) were less effective followed by Zn40 (Zn oxysulfate, 26.5% total water soluble Zn) and ZnOxS (Zn oxysulfate, 11% total water soluble Zn). The same trend was observed for Zn concentration and uptake. Regression correlations showed that the higher the water solubility, the more effective the Zn fertilizer in increasing dry matter production. Assuming that 5 to 10 kg Zn ha^?1 are the rates commonly recommended, about 50% water soluble Zn is required to adequately supply the crop's needs. Lower fertilizer rates were needed as Zn solubility increased. The cadmium (Cd) and lead (Pb) concentrations and uptakes in corn forage were not significant for any of the sources and rates.     

Fertility and Mineralogy of an Aridisol Soil under Agroecological Management

ABSTRACT

Salinity is one of the most limiting environmental factors of crop production in the world. The objective of this study was to evaluate the relationships between soil agroecological management, mineralogy and fertility of an Aridisol soil in Atacama Desert. Studies were conducted in field and controlled conditions. Four zones were selected for the study. Zone 1. Alfalfa (Medicago sativa L.) silvopastoral system and organic fertilizers for 3 years. Zone 2. Integrated soil recovery system, subsoiling, organic fertilizers, and crop rotation for 8 years. Zone 3. Permanent cultivation of artichoke (Cinara sculemus L.) 3 years of management. Four experiments were realized in semi-controlled conditions, randomized block design. The experiment 1: 8 treatments and 5 replications, zeolite levels and combinations with organic fertilizers. Experiment 2 with zeolite levels, using a soil with established alfalfa for 3 years, 4 treatments and 5 replications. Experiments 3 and 4 were with non-saline sodic soil. The experiment 3 was established with levels of gypsum and experiment 4 with Zeolite levels, both with 4 treatments and 4 replicates. The alfalfa/organic matter/zeolite combinations produced changes in the soil from slightly sodic to non-sodic. Gypsum reduced the Exchangeable Sodium Percentage (ESP) and pH of non-saline sodic soils.     

Effects of iron,calcium, and organic matter on phosphorus behavior in fluvo-aquic soil: farmland investigation and aging experiments

Purpose

Excessive fertilization has led to a high risk of phosphorus (P) leaching and related problems in the North China Plain, where the most typical cropland soil is fluvo-aquic soil. The main factors controlling environmental P behavior and the acting time sequence of these factors in soil after long-term P fertilizer application have not been well recognized. A clear understanding is essential for effective P management.

Materials and methods

Effects of Fe minerals, calcium carbonate, and organic matter (OM) on P immobilization in fluvo-aquic soil were studied systematically through farmland investigation and aging experiments.

Results and discussion

Phosphorus associated with Ca was the primary fraction in fluvo-aquic soil. Even though there was no significant correlation between the total contents of P and Ca in soils, formation of P-Ca phases facilitated by Ca²⁺ in soil solution was a mechanism of P retention when soil received excess P fertilizer. Positive correlations between the contents of P and Fe and total organic carbon (TOC) indicate that Fe minerals and OM have significant effects on P immobilization. Through the aging experiments, P was found to primarily adsorb on goethite and gradually forms Ca-P compounds. Organic fertilizer caused P release and inhibition of P adsorption in the initial stages; however, OM derived from organic fertilizer might facilitate P immobilization in the long term through the formation of a P-Ca-OM complex.

Conclusions

Although superfluous application of P fertilizers leads to the gradual formation of Ca-P in fluvo-aquic soils, there is still a risk of P loss because P is not immediately adsorbed by Fe minerals. Moreover, application of organic fertilizers increases the risk of P loss. These results provide an important scientific basis for initiating P management policies for fluvo-aquic soils.