Influence of phosphorus application on growth and cadmium uptake of spinach in two cadmium‐contaminated soils

A pot experiment was conducted to investigate the influence of phosphate (P) application on diethylene triamine pentaacetic acid (DTPA)–extractable cadmium (Cd) in soil and on growth and uptake of Cd by spinach (Spinacia oleracea L.). Two soils varying in texture were contaminated by application of five levels of Cd (NO₃)₂ (0, 20, 30, 40, and 60 mg Cd kg^–1). Three levels of KH₂PO₄ (0, 12, and 24 mg P kg^–1) were applied to determine immobilization of Cd by P. Spinach was grown for 60 d after seeding. Progressive contamination of soils through application of Cd affected dry‐matter yield (DMY) of spinach shoot differently in the two soils, with 67% reduction of DMY in the sandy soil and 34% in the silty‐loam soil. The application of P increased DMY of spinach from 4.53 to 6.06 g pot^–1 (34%) in silty‐loam soil and from 3.54 to 5.12 g pot^–1 (45%) in sandy soil. The contamination of soils increased Cd concentration in spinach shoots by 34 times in the sandy soil and 18 times in the silty‐loam soil. The application of P decreased Cd concentration in shoot. The decrease of Cd concentration was higher in the sandy soil in comparison to the silty‐loam soil. Phosphorus application enhanced DMY of spinach by decreasing Cd concentration in soil as well as in plants. The results indicate that Cd toxicity in soil can be alleviated by P application.     

Fertilizer effectiveness of three carbonate apatites on an acid ultisol

Abstract

Two properties that are detrimental to agronomic production with acid tropical soils are elevated aluminum concentrations and low phosphate availability. Direct application of carbonate apatites to acid tropical soils possessing low buffering capacity could possibly resolve this problem. The property that determines the effectiveness of directly‐applied carbonate apatites is the CO₃/PO₄ratio, which indicates the degree of anionic isomorphic substitution occurring within the mineral crystal lattice. Increasing ratios denote greater mineral solubility under acid‐soil conditions. Research was conducted to determine: a) fertilizer efficiency of three carbonate apatites (from North Carolina (NCPR), Central Florida (CFPR), and Kodjari, Upper Volta (KPR)), varying in CO₃/PO₄ratios, to that of triple superphosphate (TSP), and b) liming effects induced by the liberation of carbonates from each source, compared to CaCO₃. Maize (Zea mays L.) was grown in pots containing 3 kg of a Dothan fine sandy loam (fine, loamy siliceous, thermic, Typic Paleudult). Yield was lower from carbonate apatite sources than from TSP during the first cropping period, but was equal to TSP treatments for the second cropping period with rocks possessing a CO₃/PO₄ratio greater than 0.14. The liming effect induced by liberation of carbonates and phosphates from NCPR (400 mg P kg^‐1or 306 mg CO₃kg^‐1) equaled that from CaCO₃(600 mg CO₃kg^‐1) during the first cropping period. Over experimental duration, the soil pH was increased by 0.60, 1.26, and 1.10 pH units with a resulting decrease of 0.13, 0.17, and 0.14 cmol(+) extractable Al kg^‐1by CaCO₃(600 mg CO₃kg^‐1), NCPR (306 mg CO₃kg^‐1), and CFPR (171 mg CO₃kg^‐1), respectively     

Influence of chemical properties of soils on methane emission from rice paddies

Abstract

The relationships between methane (CH₄) emission from flooded rice paddies and soil chemical properties were investigated using eight different soils in a pot experiment. Since CH₄ is produced in paddy soil microbiologically when reducing conditions are sufficiently developed, the amounts of oxidizing agents including free iron (Fe)(III), amorphous Fe(III), easily reducible manganese (Mn), nitrate (NO₃ ^‐), and sulfate (SO₄ ^2‐), and indexes of reducing agents including total carbon (C), total nitrogen (N), and easily decomposable C, were measured as possible decreasing and increasing factors in CH₄ emission. The seasonal variations in CH₄ emission rates were similar in pattern among the soils used. However, the amount of emitted CH₄ varied largely, with the maximum total CH₄ emission (from a brown lowland soil, 1,535 mg pot^‐1) being 3.8 times that of the minimum (from a gley soil, 409 mg pot^‐1). No correlation was found between the total CH₄ emission and any single factor investigated. However, a statistically significant equation was found through multiple regression analysis: r=‐2.24x10² a+2.88b+6.20x10²; r ²=0.821; P<0.01; where Y is the amount of emitted CH₄ (mg pot^‐1), a is the amount of amorphous Fe(III) (mg pot^‐1), b is the amount of easily decomposable C (mg pot^‐1), and r ² is a multiple correlation coefficient adjusted for the degree of freedom. The amendment of ferric hydroxide [Fe(OH)₃] to a gray lowland soil significantly decreased the CH₄ emission from 1,099 to 592 mg pot^‐1. This measured amount agreed well with that estimated from the above equation, 554 mg pot^‐1.     

Effects of Phosphorus Additions on Lead,Cadmium, and Zinc Bioavailabilities in a Metal-Contaminated Soil

The use of phosphorus (P) to reduce lead (Pb)bioavailability is being proposed as an alternative to excavationand disposal as a remedial technology for Pb-contaminated soilsin residential areas. The objective of this study was todetermine the influence of P sources and rates andCaCO₃additions on the bioavailabilities of Pb, cadmium (Cd), and zinc(Zn) in a contaminated soil material using plants, a sequentialextraction procedure, and ion activities in equilibrium solutionas indicators. A contaminated soil containing 370 mg kg^-1 Cd, 2800 mg kg^-1 Pb and 29100 mg kg^-1 Zn was amended ina factorial arrangement of CaCO₃ (0 or 2000 mg kg^-1) and P as rock phosphate or KH₂PO₄ at 0:1, 2:1 or 4:1P:Pb mole ratios. A pot study was conducted using sorghum-sudangrass (Sorghum bicolor L. Moench). The addition of P did not influence Pb concentrations in plant tissue and had little effect on Cd concentrations. An interaction between P source and level of P addition was found for Zn concentrations in plant tissue; concentrations increased with increasing amounts of P from KH₂PO₄ anddecreased with increasing amounts of P from rock phosphate. Sequential extraction results suggested a much greater reduction in Pb bioavailability from treatment withKH₂PO₄ than with rock phosphate and that P influencedthe fractionations of Cd and Zn. Activities of Cd²⁺,Pb²⁺, and Zn²⁺ in equilibrium solutions generally weredecreased by rock phosphate and increased by KH₂PO₄. Saturation indices suggested the addition ofKH₂PO₄shifted the soil equilibrium from octavite to hydroxypyromorphite, whereas solid-phase control of Cd²⁺ andZn²⁺ was not influenced by soil amendments. A soluble Psource was more effective in reducing Pb bioavailability thanrock phosphate but had variable effects on Cd and Znbioavailabilities.     

Diagnosing phosphorus deficiency in irrigated durum wheat using basal stem phosphate tissue analysis

Abstract

The occurrence of phosphorus (P) deficiencies in small grain crops are normally predicted through the use of preplant soil analysis and verified by tissue analysis for total ? often at the beginning of reproductive growth. Few studies have addressed the potential use of tissue phosphate (PO₄‐P) tests to characterize the ? status of grain crops during early vegetative growth which could allow for correction of ? deficiency in irrigated production systems during the current season. Three field experiments were conducted in southeastern Arizona from 1986–89 to examine the effects of ? applications, and residual soil ? on tissue phosphate (PO₄‐P) concentrations and yield of irrigated durum wheat (Triticum turgidum L. var durum cv. Aldura). Fertilizer ? additions resulted in significant increases in basal stem and leaf tissue PO₄‐P concentrations at GS 2, 6 and 10. Fertilizer ? applications of up to 40 kg P/ha increased extractable ? levels in the soil by 82% at the beginning of the next growing season but had no significant effect on grain yields or tissue PO₄‐P concentrations of the succeeding wheat crop. Band applications of ? resulted in higher tissue PO₄‐P concentrations versus broadcast applications. While both basal stem and upper leaf tissue PO₄‐P concentrations were responsive to differences in ? availability, routine use of basal stems for nitrate testing and significantly higher PO₄‐P levels in basal stems at GS 2 and GS 6 favor its use in diagnosing ? deficiency. Basal stem tissue PO₄‐P analysis seemed to accurately reflect ? nutrition of durum wheat from GS 2 to 10. Preliminary critical levels of PO₄‐P in basal stem tissue of irrigated durum wheat were 2000, 1200 and 500 mg/kg at GS 2, 6 and 10, respectively.     

Critical soil phosphorus of a low‐P loess‐derived soil as affected by storage temperature

Abstract

Overwintering soil temperature may influence crop response to phosphorus (P) and indices of P availability in the humid, temperate, transitional climate of Tennessee. The effects of P fertilization and soil incubation temperature on sorghumsudangrass (Sorghum bicolor x S. Sudanese) grown on a Typic Hapludalf was investigated in a greenhouse study. In order to determine the effect of temperature on P availability, soils were incubated prior to cropping, at a constant temperature of 6°C or an average diurnal temperature of 24 and 36°C. Reagent grade Ca(H₂PO₄)₂.H₂O was used as the fertilizer source and applied at rates of 0, 10, 20, and 30 mg P kg^‐1 for the first test and 0, 20, 40, 60, and 80 mg P kg_‐ ¹ for the second test. Critical P concentration in the shoots for optimum yield was found to be 1.3 mg g‐¹, corresponding to soil solution and labile P concentrations of 5.5 μmol L^‐1 and 167 μg g^‐1, respectively. Optimum yield occurred for applications of >65 mg P kg^‐1 and was unaffected by soil incubation temperature. Applied P rates affected extractable P by five chemical extractants (Bray I, Bray II, Mehlich I, Mehlich III, and Mississippi), but soil incubation temperature had no affect. The extractants, however, were poorly correlated to plant P uptake and no one extractant appeared preferable to the others as an indicator of P availability.     

RESPONSE OF SOYBEAN TO SOIL APPLIED SULFUR AND BORON IN A CALCAREOUS SOIL

A greenhouse experiment with soybean grown on sulfur (S) and boron (B) deficient calcareous soil was conducted for two years in northwest India to study the influence of increasing sulfur and boron levels on yield and its attributing characters at different growth stages (55 days, maturity). The treatments included four levels each of soil applied sulfur viz. 0, 6.5, 13.4, 20.1 mg S kg^?1 and boron viz. 0, 0.22, 0.44, 0.88 mg B kg^?1 at the time of sowing. The highest dry matter yield at 55 days after sowing, DAS (19.3 g pot^?1) and maturity (straw yield ?25.2 g pot^?1 and grain yield ?7.3 g pot^?1) was recorded with B_0.44 S_13.4 treatment combination. The combined applications of sulfur and boron yielded highest oil content with B_0.44S_13.4 (21.7%) treatment level. Chlorophyll ‘a’ and ‘b’ increased significantly with successive levels of sulfur and boron addition at 55 DAS. The mean sulfur and boron uptake in straw and grains increased significantly with increasing levels of sulfur and boron up to 13.4 mg kg^?1 and 0.44 mg kg^?1 and decreased non-significantly thereafter. At both the growth stages, a synergistic interactive effect of combined application of sulfur and boron was observed with B_0.44 S_13.4 treatment level for sulfur and boron uptake in straw and grains.     

Wheat response to combined application of nitrogen and phosphorus in a saline sandy loam soil

Fertilization with nitrogen (N) or phosphorus (P) can improve plant growth in saline soils. This study was undertaken to determine wheat (Triticum aestivum L; cv Krichauff) response to the combined application of N and P fertilizers in the sandy loam under saline conditions. Salinity was induced using sodium (Na⁺) and calcium (Ca²⁺) salts to achieve four levels of electrical conductivity in the extract of the saturated soil paste (EC_e), 2.2, 6.7, 9.2 and 11.8?dS?m^?1, while maintaining a low sodium adsorption ratio (SAR; ≤1). Nitrogen was applied as Ca(NO₃)₂?·?4H₂O at 50 (N50), 100 (N100) and 200 (N200)?mg?N?kg^?1 soil. Phosphorus was applied at 0 (P0), 30 (P30) and 60 (P60)?mg?kg^?1?soil in the form of KH₂PO₄. Results showed that increasing soil salinity had no effect on shoot N or P concentrations, but increased shoot Na⁺ and chlorine ion (Cl^?) concentrations and reduced dry weights of shoot and root in all treatments of N and P. At each salinity and P level, increasing application of N reduced dry weight of shoot. At each salinity and N level P fertilization increased dry weights of shoot and root and shoot P concentration. Addition of greater than N50 contributed to the soil salinity limiting plant growth, but increasing P addition up to 60?mg?P?kg^?1 soil reduced Cl^? absorption and enhanced the plant salt tolerance and thus plant growth. The positive effect of the combined addition of N and P on wheat growth in the saline sandy loam is noticeable, but only to a certain level of soil salinity beyond which salinity effect is dominant.     

Fertilizer ammonium : nitrate ratios determine phosphorus uptake by young maize plants

We investigated the interacting effects of inorganic nitrogen and the main inorganic phosphorus form in dairy manure (dicalcium phosphate, CaHPO₄) on growth, nutrient uptake, and rhizosphere pH of young maize plants. In a pot experiment, three levels of CaHPO₄ (0, 167, and 500 mg P pot^?1) were combined with nitrogen (637 mg N pot^?1) applied at five NH₄‐N : NO₃‐N ratios (0 : 100, 25 : 75, 50 : 50, 75 : 25, and 100 : 0) and a nitrification inhibitor in a concentrated layer of a typical acid sandy soil from Denmark. ¹⁵N‐labeled NH₄‐N was applied to differentiate the role of nitrification and to partition nitrogen uptake derived from NH₄‐N. Among treatments including nitrogen, shoot biomass, rooting and phosphorus uptake were significantly higher at the five‐leaf stage when CaHPO₄ was applied with NH₄‐N : NO₃‐N ratios of 50 : 50 and 75 : 25. In these treatments, rhizosphere pH dropped significantly in direct proportion with NH₄‐N uptake. The fertilizers in the concentrated layer had a root‐inhibiting effect in treatments without phosphorus supply and in treatments with pure NO₃‐N or NH₄‐N supply. Increased nitrogen uptake as NH₄‐N instead of NO₃‐N reduced rhizosphere pH and enhanced acquisition of applied CaHPO₄ by young maize plants, which may have positive implications for the enhanced utilization of manure phosphorus.     

Effect of microbial nitrogen immobilization during the growth period on the availability of nitrogen fertilizer for winter cereals

 Pot and field experiments were conducted to determine microbial immobilization of N fertilizer during growth periods of winter wheat and winter barley. In a pot experiment with winter wheat, Ca(¹⁵NO₃)₂ was applied at tillering [Zadok's growth stage (GS) 25)], stem elongation (GS 31) and ear emergence (GS 49). Rates of 100 mg N pot^–1, 200 mg N pot^–1 or 300 mg N pot^–1 were applied at each N application date. At crop maturity, ¹⁵N-labelled fertilizer N immobilization was highest at the highest N rate (3×300 mg N pot^–1). For each N-rate treatment about 50% of the total immobilized fertilizer N was immobilized from the first N dressing, and 30% and 20% of the total ¹⁵N immobilized was derived from the second and third applications, respectively. In field trials with winter wheat (three sites) and winter barley (one site) N was applied at the same growth stages as for the pot trial. N was also applied to fallow plots, but only at GS 25. N which was not recovered (neither in crops nor in soil mineral N pools) was considered to represent net immobilized N. A clear effect of N rate (51–255 kg N ha^–1) on net N immobilization was not found. The highest net N immobilization was found for the period between GS 25 (March) and GS 31 (late April) which amounted to 54–97% of the total net N immobilized at harvest (July/August). At GS 31, non-recovered N was found to be of similar magnitude for cropped and fallow plots, indicating that C from roots did not affect net N immobilization. Microbial biomass N (N_mic) was determined for cropped plots at GS 31. Although N_mic tended to be higher in fertilized than in unfertilized plots, fertilizer-induced increases in N_mic and net N immobilization were poorly correlated. It can be concluded that microbial immobilization of fertilizer N is particularly high after the first N application when crop growth and N uptake are low. Received: 6 July 1999     

Phosphorus deficiency diagnosis and fertilization in mungbean grown in rainfed calcareous soils of Pakistan

Abstract

Mungbean [Vigna radiata (L). Wilczek] grown in rainfed calcareous soils suffers with phosphorus (P) deficiency. In view of high cost and low use efficiency of P fertilizer, greenhouse, incubation, and field experiments were carried out for determining P deficiency diagnostic criteria and efficient method of P fertilizer application in mungbean. In a pot culture experiment using a P‐deficient Typic Ustocherpt, maximum increase in grain yield with P was 686% over the control; and fertilizer requirement for near‐maximum (95%) grain yield was 30 mg P kg^‐1 soil where fertilizer was mixed with the whole soil volume (broadcast) and 14 mg P kg^‐1 where mixed with 1/4th soil volume (band placement). In a field experiment on a P‐deficient Typic Camborthid, however, maximum increase in grain yield was 262% over the control. Band placement resulted in 73% fertilizer saving as P requirement was 66 kg ha^‐1 by broadcast and only 18 kg ha^‐1 by band placement. Critical P concentration range appears to be 0.27–0.33% in young whole shoots (≤30 cm tall) and 0.25–0.30% in recently matured leaves. In an incubation study using the same Typic Ustochrept, P extracted by the sodium bicarbonate (NaHCO₃), the ammonium bicarbonate‐diethlylenetriaminepentaacetic acid (AB)‐DTPA), and the Mehlich 3 soil tests correlated closely with each other, P concentration of whole shoots, and total P uptake by mungbean plants. Critical soil test P levels for pot grown mungbean were NaHCO₃,9 mg kg^‐1; AB‐DTPA, 7 mg kg^‐1; and Mehlich 3, 23 mg dm^‐3 soil. The more efficient and economical ‘universal’ soil test, AB‐DTPA, is recommended for P fertility evaluation of calcareous soils.     

Addition of phosphorus to soils with low to medium phosphorus retention capacities. II. effect on soil phosphorus extractability

Abstract

Knowledge of the change in soil extractable phosphorus (P) as a consequence of soil P fertilization could be useful in discriminating soils with a potential for soil P release to runoff or movement of P along the soil profile. In this research, soils with low to medium P retention capacity were equilibrated for 90 days with soluble P (KH₂PO₄) at rate of 100 mg P kg^‐1 soil. After this period, soil samples both with and without the P addition were analyzed using six conventional methods: 1) Olsen, 2) Bray 1,3) Mehlich3,4) Egner, 5) Houba, dilute CaCl₂ solution, and 6) distilled water, and three “innovative”; P‐sink methodologies: 1) Fe oxide‐coated paper strip, 2) anion exchange resin membrane, and 3) cation‐anion exchange resin membrane. The soils without P addition had low levels of extracted P as determined by all nine procedures. Net increases in the amount of P extracted from the soils with added P ranged from 4.2 mg kg^‐1 (CaCl₂ extraction) to 57.6 mg kg^‐1 (cation‐anion resin membrane extraction). Relationships between change in extracted P and i) physical and chemical characteristics, and ii) soil P sorption properties are also presented and discussed.     

Effect of soil amendments on fractionation of Selenium‐enriched soil

Abstract

This study was to determine the effect of soil amendments on the fractionation of selenium (Se) using incubation experiments under simulated upland and flooded conditions. The treatments were as follows: 1) control [soil + sodium selenite (Na₂SeO₃) (1 mg Se kg^‐1)]; 2) control + calcium carbonate (CaCO₃) (5 g kg^‐1); 3) control + alfalfa (40 g kg^‐1); and 4) control + CaCO₃ (5 g kg^‐1) + alfalfa (40 g kg^‐1). After a 90‐day incubation, soil was sampled and fractionated into five fractions: 1) potassium sulfate (K₂SO₄)‐soluble fraction (available to plants); 2) potassium dihydrogen phosphate (KH₂PO₄)‐exchangeable fraction (potentially available); 3) ammonium hydroxide (NH₃H₂O)‐soluble fraction (potentially available); 4) hydrochloric acid (HCl)‐extractable fraction (unavailable); and 5) residual fraction (unavailable). Compared with the control, CaCO₃ increased the K₂SO₄ fraction at the expense of the NH₃H₂O fraction. Alfalfa increased both the K₂SO₄ and residual fractions but reduced the KH₂PO₄ and NH₃H₂O fractions. The CaCO₃‐alfalfa treatment had a similar effect to the alfalfa treatment alone. The comparison between the upland and flooded conditions showed that the flooded condition generally increased the residual fraction and decreased the potentially‐available fractions. In general, CaCO₃ was a better amendment because it not only increased the available fraction but also maintained the potentially available fractions at a high level. The application of Na₂SeO₃ and use of appropriate soil amendments can improve Se availability in soil.     

The nature of humic acid‐apatite interaction products and their availability to plant growth

Abstract

An investigation was conducted to determine the nature of decomposition products resulting from the interaction between humic acid and apatite and assess their availability to plant growth. Interaction analyses were performed by shaking 200 mg apatite with 0 to 800 mg/L HA or FA solutions at pH 5 or 7 for 0 to 12 hr. Phosphorus concentrations were determined in the supernatants by spectrophotometry. The nature of P‐humic acid complexes was determined by ³¹P NMR analysis. Availability of these dissolution products was studied by growing corn plants in aerated hydroponics to which 200 mg apatite and 0 to 800 mg/L HA were added at pH 5 or 7. The results indicated that the rate of dissolution of apatite was parabolic in regression with time, and increased by increasing the amounts of HA or FA applied from 100 to 800 mg/L The dissolution reaction was influenced by pH, because larger amounts of PO₄ ³‐ions were detected at pH 5 than at pH 7. ³¹P NMR spectroscopy indicated the presence of P‐humic acid complexes, previously believed to be humophosphate esters. The PO₄ ^3‐ ion was complexed by HA at pH 7 or above, but PO₄ ^3‐ appeared to be released again as adsorbed and free ions at pH <5.0. Plant performance corresponded with increased PO₄ ^3‐concentrations at pH 5.0. No significant improvement over the control was observed in the growth of corn plants by apatite + HA treatments at pH 7. However, plant growth was increased significantly over the control by apatite + HA treatments at pH 5.0. Better growth performance of corn plants were noticed by apatite + HA than by KH₂PO₄ treatments at pH 5.0.     

Micronutrient availability in soils of Northwest Bosnia and Herzegovina in relation to silage maize production

Maize (Zea mays L.) is the most widely grown crop in Bosnia and Herzegovina especially in Northwest part of the country. Considering that, the maize is extremely sensitive to micronutrient deficiency the main aim of this study was to asses: (1) micronutrient availability in soil, (2) micronutrient status in silage maize; and (3) the relationship between micronutrient soil availability and maize plant concentration. Soil samples for micronutrient availability (n?=?112) were collected from 28 farms in 7 municipalities. Plant available micro- and macro- nutrients in soil were extracted using Mehlich-3, except plant available Se was extracted using 0.1M KH₂PO₄. Result showed that on average there was no significant difference between different soil types regarding their potential in plant available nutrients. P deficiency was present both, in soil and plants in whole region. Soil extractable P was ranging from 0.003–0.13?g?kg^?1 and total plant P was ranging from 0.79–4.95?g?kg^?1. Zinc deficiency was observed in two locations both in soil (0.71?mg?kg^?1; 0.79?mg?kg^?1) and plant (11.5?mg?kg^?1; 15.8?mg?kg^?1). Potential Se soil deficiency was observed on some locations, while Se plant status is not high enough to meet daily requirements of farm animals. Extractable soil nutrients could be used as relatively good predictor of potential soil and plant deficiencies, but soil nutrient interactions and climate conditions are highly effecting the plant uptake potential.     

Nutrient dynamics,dehydrogenase activity,and response of the rice plant to fertilization sources in an acid lateritic soil

Abstract

Rice variety IR 36, grown under flooding, was studied in 1998 to determine the effects of fly ash, organic, and inorganic fertilizers on changes in pH and organic carbon, release of nutrients (NH₄ ⁺-N, Bray's P, and NH₄OAc K), and dehydrogenase activity in an acid lateritic soil at 15-day intervals. Application of fly ash at 10?t?ha^?1 alone did not improve the availability of NH₄ ⁺-N, or P, as well as the rice grain yield. Availability of NH₄ ⁺-N (35.3–36.9?mg?kg^?1), and P (12.3–14.6?mg?kg^?1) at 15 days after transplanting, and rice grain yields (48.0–51.7?g per pot) were similar under the various fertilization sources such as inorganic fertilizer alone, inorganic fertilizer?+?fly ash or inorganic fertilizer?+?green manure?+?fly ash. Mean dehydrogenase activity was the highest (8.47?µg triphenyl formazon g^?1 24?h^?1) under the mixed fertilization treatments with green manure. At the end of the cropping season (75 days after transplanting), pH, organic carbon, and dehydrogenase activity were higher under the mixed fertilization treatments involving green manure by 3, 15 and 154%, respectively, compared with the inorganic fertilizer alone.     

Agronomic Effectiveness of Cationic Phosphate Impurities Present in Superphosphate Fertilizers as Affected by Soil pH

Abstract

The general concept that low‐water‐soluble phosphorus (P) fertilizers should be more agronomically effective when applied to acidic soils was developed based on sources containing mainly calcium (Ca)‐P compounds, but it may not hold true for sources with different chemical composition. To obtain information related to this issue, two important iron (Fe)–potassium (K)–P compounds present in superphosphates [Fe₃KH₈(PO₄)₆ · 6H₂O, H8, and Fe₃KH₁₄(PO₄)₈ · 4H₂O, H14] were prepared and characterized. These P sources were used to provide 30 and 60 mg P kg^?1 as neutral ammonium citrate (NAC)+H₂O‐soluble P. Reagent‐grade monocalcium phosphate (MCP) was used as a standard P source with high water solubility with an additional rate of 120 mg P kg^?1 included. Also, mixtures of both Fe‐K‐P compounds and MCP were prepared to provide 0, 25, 50, 75, and 100% of the total P as MCP. All sources were applied to a clayey loamy acid soil (pH 5.3) classified as Rhodic Kanhapludult. The soil was incubated at two rates (0 and 10 g kg^?1) of lime, which resulted in pH 5.4 and 6.8. Upland rice was cultivated to maturity. The H14 compound confirmed to be a highly effective source of P for the rice plants at both soil pH, as opposed to the H8, which was poorly effective when applied alone. When mixed with water‐soluble P (WSP), the H8 was able to provide P to the plants with the maximum yield of upland rice reached with 54.8 and 80.5% of WSP for pH 5.4 and 6.8, respectively. The high agronomic performance of the H14 compound clearly indicates that this low‐water‐soluble P source cannot be deemed as ineffective at high soil pH.     

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.     

Ameliorative Effects of Potassium Phosphate on Salt‐Stressed Pepper and Cucumber

Abstract

Bell pepper (Capsicum annuum cv. Urfa Isoto) and cucumber (Cucumis sativus cv. Beith Alpha F1) were grown in pots containing field soil to investigate the effects of supplementary potassium phosphate applied to the root zone of salt‐stressed plants. Treatments were (1) control: soil alone (C); (2) salt treatment: C plus 3.5 g NaCl kg^?1 soil (C + S); and (3) supplementary potassium phosphate: C + S plus supplementary 136 or 272 mg KH₂PO₄ kg^?1 soil (C + S + KP). Plants grown in saline treatment produced less dry matter, fruit yield, and chlorophyll than those in the control. Supplementary 136 or 272 mg KH₂PO₄ kg^?1 soil resulted in increases in dry matter, fruit yield, and chlorophyll concentrations compared to salt‐stressed (C + S) treatment. Membrane permeability in leaf cells (as assessed by electrolyte leakage from leaves) was impaired by NaCl application. Supplementary KH₂PO₄ reduced electrolyte leakage especially at the higher rate. Sodium (Na) concentration in plant tissues increased in leaves and roots in the NaCl treatment. Concentrations of potassium (K) and Phosphorus (P) in leaves were lowered in salt treatment and almost fully restored by supplementary KH₂PO₄ at 272 mg kg^?1 soil. These results clearly show that supplementary KH₂PO₄ can partly mitigate the adverse effects of high salinity on both fruit yield and whole plant biomass in pepper and cucumber plants.     

Resource manipulation in uranium and arsenic attenuation by Lemna gibba L. (duckweed) in tailing water of a former uranium mine

Influences of phosphorus and nitrogen on uranium and arsenic accumulation in Lemna gibba L. were investigated in the laboratory hydroponic cultures and in the field pot experiments. The initial uranium and arsenic concentrations in solutions for the hydroponic cultures were 1000 μ g l^?1 each, while in situ trials used tailing water containing 198.7 ± 20.0 μ g U l^?1 and 75.0 ± 0.4 μ g As l^?1 at a former uranium mine in eastern Germany. A test of three PO₄ ^3? concentrations (0.01, 13.6 and 40.0 mg l^?1) in the hydroponic cultures, highest uranium accumulated in L. gibba under the culture with highest PO₄ ^3?. Significant differences in uranium accumulation were between 0.01 mg l^?1 and 13.6 mg l^?1 PO₄ ^3? cultures only (ANOVA p = 0.05). In the field, addition of 40.0 mg l^?1 PO₄ ^3? increased the bioaccumulation of uranium significantly. Contrary, high PO₄ ^3? concentrations suppressed the bioaccumulation of arsenic in both the laboratory and the field. The bioaccumulation of both uranium and arsenic increased slightly with the increase of NH₄ ⁺ concentration. However, high NH₄ ⁺ concentrations reduced the yield in the control experiments. The concentration of uranium rose temporarily to 856.0 ± 294.0 μ g l^?1, while the concentration of arsenic sunk slightly and temporarily immediately after amending the tailing waters with 40 mg l^?1 PO₄ ^3?. The speciation of uranium in the tailing water was modelled with geochemical code PhreeqC, which predicted that uranyl carbonate species dominated before addition of phosphates, but after increasing the PO₄ ^3? concentrations, uranyl phosphates species became dominant. Addition of NH₄ ⁺ to the tailing water had negligible influence on free available uranium and arsenic concentrations. Thus, manipulations to enhance uranium and arsenic attenuation by L. gibba has limitation when the amendments interact with other elements including the contaminants in the milieu, and when the target contaminants have antagonistic behaviour in the tailing water.