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1.
Phosphorus (P) deficiency is one of the main constraints on crop production in Arenosols (acid sandy soil). The high cost of P fertilizers may represent an insurmountable obstacle in many poor countries, leaving the exploitation of their own calcareous and phosphate rocks as the only low-cost and long-term alternative. Biochar is suggested to have positive effects on soil properties; however, there is no published research on the synergistic effects of biochar and rocky materials in modifying soil properties. The aim of this study was to investigate the chemical and biochemical responses of an acid Arenosol treated with phosphate rock (PR), calcareous rock (CR), and biochar (BC), and the implications for corn yield. A soil from Marracuene District, Mozambique was used, where corn was grown for 90 d with the soil treated with:no addition (control), water-soluble zinc phosphite fertilizer (WSP), PR, WSP+CR, WSP+BC, WSP+CR+BC, PR+BC, and PR+CR+BC. Biochar was produced by pyrolysis of babycorn peels for 4 h at 450℃ and applied at 11 g kg-1. The soil pHH2O increased from about 4.54 in the control to 7.38 in the PR+CR+BC treatment. Easily oxidizable organic carbon, cation exchange capacity, and available P were higher in the treatments containing BC than in the control. The treatments containing CR and/or BC led to the highest activities of alkaline phosphomonoesterase, phosphodiesterase, and α-glucosidase, which increased P availability and gave the greatest biomass and yields. We suggest that biochar provides additional soluble P and supplies adsorption sites for phosphate, preventing its evolution to unavailable forms. Thus, PR applied together with BC contributed to an 840% yield increase compared to the control. The treatments containing WSP and BC facilitated phosphite oxidation to phosphate and increased crop yield.  相似文献   

2.
Abstract

The quality of phosphate rock (PR) is declining and the use of lower quality PR results In lower water‐soluble and higher citrate‐soluble P in the fertilizer product. A greenhouse study was conducted to evaluate the plant availability of P in commercial superphosphate fertilizers having various levels of water‐soluble P. Seven commercial fertilizers, Including 6 granular concentrated superphosphates and one normal superphosphate, were evaluated. Reagent grade monocalcium phosphate served as a control. The fertilizers were manufactured from PR deposits located in the United States (Florida, Idaho and North Carolina) and Morocco. Water‐soluble P ranged from 77 to 92 X of the total fertilizer P. Citrate‐soluble, water‐insoluble P ranged from 7 to 20 % of the total fertilizer P. Four of the 5 American fertilizers had a lower percentage of water‐soluble P as compared to the concentrated superphosphate from Morocco. Fertilizers manufactured from U.S. phosphate deposits contained an average of 6 times more Fe and 4 times more Al than the Moroccan concentrated superphosphate.

Each source was added to a Mountvlew slit loam soil (pH = 6.5) at rates to supply 0, 10, 20, 30, 40 and 50 mg P kg‐1soil (0, 22.9, 45.8, 68.7, 91.6, and 114.5 ppm P2O5, respectively). Sorghum‐sudangrass (Sorghum bicolor) was harvested at 28 and 56 days after planting in the treated soil. Herbage yields and the P concentration in harvested forage were not affected by the source of added P. The effect of the rate of added P on forage yield and P concentration was described by polynomial regression. The granular concentrated superphosphate fertilizers used in this study contained ≥ 80 % of their plant available P in a water‐soluble form and were as effective as reagent grade monocalcium phosphate. Thus the level of water‐soluble P that will be required to reduce the performance of a fertilizer is lower than the levels currently found in American commercial concentrated superphosphates  相似文献   

3.

Effect of poultry manure (PM) and four inorganic phosphorus (P) fertilizers sources, i.e., diammonium phosphate (DAP), single super phosphate (SSP), nitrophos (NP) and triple super phosphate (TSP) on crop production and P utilization efficiency (PUE) of maize was studied. Both inorganic P fertilizers and PM applied alone or combined in 50:50 proportions at equivalent rate of 90 kg P2O5 ha?1. Results indicated that inorganic P sources with PM significantly increased plant height, leaf area and chlorophyll content. Average values showed that combined application of inorganic P with PM increased grain yield by 19 and 41% over inorganic P and PM alone, respectively. Similarly, increase in P-uptake due to the combined application of inorganic P + PM was 17% compared to sole inorganic P. Phosphorus utilization efficiency of inorganic P was increased with PM and the highest PUE was recorded in DAP + PM. Generally, combination of DAP + PM proved superior over the remaining P fertilizers.  相似文献   

4.
Abstract

The agronomic effectiveness of five partially acidulated phosphate rocks (PAPRs) and an unground phosphate rock (PR) were compared against single superphosphate (SSP) in a glasshouse experiment using a high phosphorus (P) retention soil at a near‐neutral pH (pH 6.5), and corn (Zea mays L.) as the test crop. The PAPRs were prepared by acidulating unground North Carolina PR with either phosphoric or sulphuric acid (expressed as Phos‐PAPR and SA‐PAPR, respectively) and at three levels of acidulation (20, 33, and 50%). The relative agronomic effectiveness (RAE) and substitution value (SV) of the test fertilizers, calculated with respect to SSP using the standard “vertical”; and “horizontal”; comparisons, showed that 50% phosphoric acidulated PAPR performed as effectively as SSP whereas the other fertilizers were less effective. The PR treatment showed a small yield response. The dry matter yield and P uptake were linearly related to water‐soluble P of the fertilizers up to 66% of total P and there was no advantage in acidulating fertilizers above this level of water‐soluble P using reactive PR. Whereas very little of the directly‐applied PR dissolved (3.4% of PR applied), PR applied as a component of PAPRs dissolved up to 22%. The dissolved proportion of added PR component increased with increasing water‐soluble P content of the fertilizer. The results suggest a greater efficiency of PAPR than SSP as a P supplier to plants.  相似文献   

5.
Abstract

Accurate measurement and characterization of phosphate rock dissolution are important for a better understanding of phosphorus (P) availability in soils. An incubation study was carried out on two New Zealand topsoils (0–15 cm; high P buffering capacity Craigieburn and low P buffering capacity Templeton) amended with North Carolina phosphate rock (NCPR) and water‐soluble phosphate (WSP) at 218 mg P kg?1 (equivalent to 60 kg P ha?1). Isotopic exchange kinetics was carried out after 12 h and 28 days of incubation to characterize P availability. This study showed that sensitivity of capacity factors (r1/R, n) to explain changes in E1min values was affected by the P buffering capacity of the soils. The recovery of applied P in the E pool (RecinE%) with extended incubation time was similar from the NCPR and WSP treatments (3.1–3.3%) in the Craigieburn soil compared with the Templeton soil in which RecinE% values were greater in WSP (9%) than NCPR (1.3%) treatment. The higher values of P derived from the applied P fertilizers in the E pool (PdffinE%>80%) suggested that the NCPR application in both soils would be efficient for increasing P availability to plants.  相似文献   

6.
Abstract

Plants grown in acidic soil usually require relatively high amounts of available phosphorus (P) to optimize growth and productivity, and sources of available P are often added to meet these requirements. Phosphorus may also be made available at relatively high rates in native soil when roots are colonized with arbuscular mycorrhizal fungi (AMF). Addition of P to soil usually reduces root‐AMF colonization and decreases beneficial effects ofAMF to plants. In glasshouse experiments, soil treatments of P [0 P (Control), 50 mg soluble‐P kg?1 as KH2PO4 (SP), and 200 mg P kg?1 as phosphate rock (PR)], organic matter (OM) at 12.5 g kg?1, AMF (Glomus darum), and various combinations of these (OM+SP, OM+PR, AMF+SP, AMF+PR, AMF+OM, AMF+OM+SP, and AMF+OM+PR) were added to steam treated acidic Lily soil (Typic Hapludult, pHw=5.8) to determine treatment effects on growth and mineral acquisition by chickpea (Cicer areitinum L.). The various treatment applications increased shoot dry matter (DM) above the Control, but not root DM. Percentage AMF‐root colonization increased 2‐fold or more when mycorrhizal plants were grown with AMF, OM+SP, and OM+PR. Regardless of P source, plant acquisition of P, sulfur (S), magnesium (Mg), calcium (Ca), and potassium (K) was enhanced compared to the Control, and mineral enhancement was greater in PR compared to SP plants. Mycorrhizal plants also had enhanced acquisition of macronutrients. OM+SP and OM+PR enhanced acquisition of P, K, and Mg, but not Ca. Concentrations of Fe, Mn, Cu, and Al were generally lower than Controls in SP, RP, AMF+PR, AMF+SP, and OM plants, and mycorrhizal plants especially had enhanced micronutrients. Relative agronomic effectiveness values for shoot DM and shoot P, Ca, and Mg contents were considerably higher for PR, including OM+PR, AMF+PR, and AMF+OM+PR, than for SP. PR and OM applications to AMF plants are low‐cost attractive and ecologically sound alternatives to intensive use of P fertilizers for crops grown in acidic soils.  相似文献   

7.
Rock phosphate (RP) shows reduced dissolution in soils amended with limestone and when applied through spot application. A simple way to improve RP efficiency under these unfavorable conditions may be the combination with nitrogen (N) fertilizers which can increase the solubilization of apatite minerals and/or stimulate P uptake. In this context, we evaluated the agronomic effectiveness of a RP from Bayóvar, Peru (BY), combined with different N sources in spot application, in a clayey Oxisol (Typic Hapludox). The pot experiment consisted of a factorial scheme (3 × 2 × 2+4) in randomized block design with four replications. Treatments consisted of BY combined with three N sources (ammonium sulfate–BY+AS; urea–BY+U; potassium nitrate–BY+KN), in two forms (granulated or powdered), and in two N : P molar ratios (0.5 : 1.0 or 1 : 1) and four additional treatments [control: without P; monoammonium phosphate (MAP); powdered BY; granulated BY]. The products were incorporated into a 50 cm3 cylindrical soil volume (central and upper position in the pot: diameter 17 cm and height 15 cm) with three maize plants (Zea mays L.). Above‐ground biomass was sampled after 42 d after sowing, analyzed for N and P concentrations to calculate N and P uptake. Soil samples were taken from the cylindrical soil volume and measured for RP dissolution (ΔCa index), P availability (P‐resin index), and soil pH. Application of MAP increased soil P availability about 11 times compared with BY treatments. As a result, maize plants grew 3.8 times and absorbed 7.3 and 3.3 times more P and N compared to those fertilized with BY combined with N fertilizers. Compound fertilizers BY+AS and BY+KN had the same effect on N and P uptake, presenting an effectiveness about 12 and 19% greater than pure BY, respectively. Compound fertilizers with BY+AS were more effective in powdered form (with no N/P ratio effect), while BY+KN was more effective in granulated form and in 1 : 1 N : P ratio. BY+U combinations were less efficient in promoting plant P bioavailability than the other N sources. We conclude that Bayóvar RP has a low agronomic effectiveness for spot application, even when combined with N.  相似文献   

8.
Abstract

Tropical acidic soils require large inputs of nitrogen (N) and phosphorus (P) fertilizers to sustain crop production. Attempts to use phosphate rock (PR) as a cheaper P source have shown limited success because of low rock solubility. The objective of this study was to evaluate growth and P nutrition of aluminum (Al)‐tolerant maize inbreds fertilized with PR. Twelve Al‐tolerant inbreds from CIMMYT were planted in 2‐kg pots filled with an acidic soil very low in available P and fertilized with 0, 40, or 100 mg kg?1 of Riecito PR or triple superphosphate (SP). Plant shoots were harvested 35 days after planting, and biomass, root length, P uptake, and soil residual P were determined. Inbreds were able to sustain growth when fertilized with PR. There was indication that various mechanisms were involved in the responses to PR fertilization. Cultivars combining high uptake and conversion efficiencies should improve maize utilization of PR.  相似文献   

9.
Increasing soil phosphorus and organic matter content for crop production while reducing the cost of production are required to facilitate the achievement of green revolution in Africa. Field and pot experiments were laid out during 2012 and 2013 to assess the effects of combined application of Kodjari phosphate rock (PR) and water soluble phosphorus on sorghum yields, P uptake and Lixisol characteristics in the centre west of Burkina Faso. Five P fertilizers treatments (zero P, 100% TSP (triple super phosphate), 100% PR, 50% PR + 50% TSP, 75% PR + 25% TSP) and two cow manure treatments (zero, 5 t ha?1) were tested. In field experiment, 50% PR + 50% TSP was as effective as 100% TSP in increasing sorghum yield above the control by 30% in 2012 and 50% in 2013 and P uptake by 30% in both years. Manure had an additive effect on phosphorus fertilizers in increasing sorghum yields and P uptake. In pot experiment, increases of Ca uptake, soil pH and microbial P were observed with the application of 50% PR + 50% TSP. Our results suggest that formulation of fertilizer combining phosphate rock and mineral P would improve sorghum yields and income of smallholders.  相似文献   

10.
Abstract

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

11.
Abstract

The effectiveness of the application of raw (PR‐1), and partially acidulated phosphate rock (PR), at 25% (PR‐25) and at 50% (PR‐50), was investigated to reduce extractability and plant uptake of Pb, Cd, Cu, Ni, and Zn in three calciorthids soils.Furthermore, the effects of soil treatments on metal extractability were evaluated by sequential extraction. Similarly, such effects were assessed on the phytoavailability of metals of maize (Zea mays L.) through a pot experiment. Water‐soluble and exchangeable metal fractions (the bioavailable fractions) were influenced distinctively by PR treatments and soil properties. In addition, decrease of soluble and exchangeable metal fractions was compensated by an increase in metal extracted from other fractions. Most bioavailable soil metals correlated significantly with their associated level in plant tissue. Finally, plant metal uptake decreased with PR treatments, suggesting that PR application was likely to be effective in controlling metal immobilization in these soils.  相似文献   

12.
Abstract

Based on the problems that arises from the presence of cationic impurities in rock phosphates for fertilizer production, a greenhouse experiment consisting of two consecutive corn crops was conducted in order to evaluate the plant availability of phosphorus (P) in the fraction soluble only in neutral ammonium citrate (NAC) and also in the NAC+H2O fraction of acidulated phosphate fertilizers produced from Brazilian raw materials with different amounts of cationic impurities. The experiment was conducted with samples of a Red‐Yellow Latosol (Typic Hapludox) in a completely randomized design with four replications. Four acidulated phosphates obtained by sulfuric acid (H2SO4) solubilization of different Brazilian raw materials were studied. Monocalcium phosphate [Ca(H2PO4)H2O] (MCP) was included as a standard source of P as well as samples which were previously leached to remove the water‐soluble P, and therefore, contained essentially the NAC‐soluble fraction. The fertilizers were thoroughly mixed with the whole soil in the pots (mixed application), or with only 1% of its volume (localized application), at the rates of 50 and 100 mg P kg‐1, based on the calculated content of P soluble in NAC+H2O. Corn (Zea mays L.) was the test crop grown in two sequences of 35 days. After each 35‐day period, dry matter yield and P accumulated in the plant tops were determined. Results were evaluated by analysis of variance considering the factors, (i) acidulated phosphates, (ii) rate of P application, (iii) leaching, and (iv) methods of application. In a second analysis, the leached phosphates were considered as additional levels of the phosphate factor as well as for MCP. The Tukey test at the 0.05 significance level was utilized for mean separation. Results from this study clearly demonstrated that increasing the amounts of cationic impurities in the raw materials decreased the concentration of water‐soluble P and NAC+H2O‐soluble P as well as water‐soluble P and NAC+H2O‐soluble P ratio of the fertilizer obtained. From the results in the first corn cropping, the P in the NAC fraction for the studied Brazilian phosphate was not as available to plants as was the P in the NAC+H2O fraction or in the pure MCP. The NAC+H2O method was not an adequate index for evaluating the P availability of the studied sources. No interaction between P sources, leaching, and method of application was found in the second corn cropping.  相似文献   

13.
Abstract

A possible way to improve phosphate rock (PR) agronomic performance is through the addition of elemental sulfur (S0). We used 32P isotope dilution method to assess the P taken up by crops treated with PR. Two experiments, one with common bean and other with upland rice, were carried out, to evaluate the effect of S0 on the agronomic performance of two contrasting PR, applied in different methods. Gafsa (GPR) and Patos de Minas (PPR) were used as the high and low reactivity PR, respectively. The experiments were arranged in completely randomized design on factorial structure 2?×?2 × 2?+?2; which means 2 PR (GPR and PPR) versus 2?S0 condition (with or without-S0) versus 2 application methods (band and broadcast) plus 2 additional treatments (control and triple superphosphate). In band application the S0 increased the amount of P uptake by plants from fertilizer of GPR from 2.57 to 9.86?mg pot?1 for common bean and of 2.26 to 7.05?mg pot?1 to rice. Regardless the management adopted, less than 2% of P applied as PPR has been taken up by crops. The addition of S0 as a strategy to increase the agronomic performance of PR is PR characteristics dependent and fertilizers placement.  相似文献   

14.
Huang  B.  Kuo  S.  Bembenek  R. 《Water, air, and soil pollution》2003,147(1-4):109-127
Some phosphorus and trace element fertilizers may contain elevatedamounts of toxic metals such as cadmium (Cd) and repeated uses of the fertilizers at high rates over time may increase Cd uptake by plants. This greenhouse study investigated the availability to leaf lettuce (Lactuca sativa L.) (Royal Green) of Cd in a western phosphate rock (PR), and a zinc (G-Zn) and an iron (IR) fertilizers that are by products of industrial wastes. The water-soluble CdCl2 was included in the study for comparison. Applications of Cd from the fertilizers orCdCl2 up to 16 times the Canadian Standards for maximum annual Cd loading limit increased soil total Cd. This was true also for the labileCd extractable by DTPA (diethylenetriaminepentaacetic acid) or 0.05 M CaCl2 for all Cd sources except IR. Lime and Cd source and rate allaffected Cd availability in the soil and accumulation by the plant. Theadded Cd from CdCl2 was more labile and readily available to the plant than the added Cd from the PR or G-Zn. Lettuce-Cd was best describedby CaCl2-Cd (r2 = 0.782), followed by DTPA-Cd (r2 = 0.686), with soil total Cd being least effective in predicting lettuce-Cd (r2 = 0.186). If soil total Cd has to be used in describing Cd accumulation bythe plant, it should be included with pH in a stepwise multiple regression. The Cd transfer coefficient for the fertilizers should be measured based on labile Cd extractable by CaCl2 or DPTA, instead of soil total Cd. The labile-based Cd transfer coefficient could improve the assessment ofthe risk of human exposure to the metal in the fertilizers through consumption of the food crop.  相似文献   

15.
Abstract

Contamination of soils with trace metals or semi‐metals has become a major public concern in recent years. Potential sources of these contaminants include commercial phosphorus (P) fertilizers and the phosphate rocks used in production of the P fertilizers. Solid commercial P fertilizers marketed in Iowa and phosphate rock samples (PRs) obtained from deposits around the world were analyzed for arsenic (As), molybdenum (Mo), selenium (Se), and tungsten (W). The fertilizer materials included 24 samples of triple superphosphate (TSP), 23 samples of monoammonium phosphate (MAP), and 25 samples of diammonium phosphate (DAP). Twelve PRs from different PR deposits in Africa, United States, and Peru were also analyzed. The concentrations of As and Mo were greater and more variable than those of Se and W in TSP, MAP, DAP, and PRs. The ranges and median values of As, expressed in mg/kg, were: TSP (2.4–18.5, 10.1), MAP (8.1–17.8, 12.4), DAP (6.8–15.6, 12.4), and PR (3.2–32.1, 9.6). The range and median values for Mo contents of TSP, MAP, DAP, and PR were: 8–17, 13; 12–17, 15; 10–21, 14; and 2–21, 6, mg/kg, respectively. The median values for the Se and W contents were: TSP (1.1 and 2.7), MAP (0.3 and 2.1), DAP (0.1 and 2.4), and PR (1.0 and 1.9). One each of the TSP and PRs contained much higher concentrations of Se than the other samples analyzed. The concentrations of As, Mo, Se, and W in the fertilizer materials and PRs analyzed were generally greater than those found in Iowa surface soils.  相似文献   

16.
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.  相似文献   

17.
Abstract

Greenhouse experiments were conducted at three locations to study the residual effect of phosphate on rice, grown successively for four seasons in North Sumatera, Indonesia. The soils used at the three locations were high in phosphate from continuous applications with phosphorus (P) fertilizers for 15 years. Rice (Oryzasaliva), variety IR‐64, was grown receiving treatments with 0, 50, 100, 150, and 200 kg ha‐1 superphosphate. These treatments, replicated three times, were applied only to the first crop. At the end of each growing period, rice yield was determined and the soil analyzed for available and acid extractable P content by the Olsen and HC1 extraction methods, respectively. The results indicated that the high concentration in available or acid extractable P content in the first season had resulted in the highest rice yields. Rice yield of the second crop decreased and remained constant at this level through the fourth crop. The phosphate levels in soil appeared to show a similar trend as rice yields. Both available and HC1 extractable P decreased in soils in the second and third growing season to level off at the fourth season. Apparently the plants were able to satisfy their P requirements from these residual P contents in soil during the second through the fourth growing season. It can be concluded that the use of P fertilizers can be reduced substantially both in total and frequency of applications.  相似文献   

18.
Abstract

A laboratory incubation experiment was conducted to evaluate the soil factors that influence the dissolution of two phosphate rocks (PRs) of different reactivity (Gafsa, GPR, reactive PR; and Togo‐Hahotoe, HPR, low reactivity PR) in seven agricultural soils from Cameroon having variable phosphorus (P)‐sorption capacities, organic carbon (C) contents, and exchangeable acidities. Ground PR was mixed with the soils at a rate of 500 mg P kg?1 soil and incubated at 30°C for 85 days. Dissolution of the PRs was determined at various intervals using the ΔNaOH‐P method (the difference of the amount of P extracted by 0.5 M NaOH between the PR‐treated soils and the control). Between 4 and 27% of HPR and 33 and 50% of GPR were dissolved in the soils. Calcium (Ca) saturation of cation exchange sites and proton supply strongly affected PR dissolution in these soils. Acid soils with pH‐(H2O)<5 (NKL, ODJ, NSM, MTF) dissolved more phosphate rock than those with pH‐(H2O)>5 (DSC, FGT, BAF). However, the lack of a sufficient Ca sink in the former constrained the dissolution of both PRs. The dissolution of GPR in the slightly acidic soils was limited by increase in Ca saturation and that of HPR was constrained by limited supply in protons. Generally, the dissolution of GPR was higher than that of HPR for each soil. The kinetics of dissolution of PR in the soils was best described by the power function equation P=AtB. More efficient use of PR in these soils can be achieved by raising the soil cation exchange capacity, thereby increasing the Ca sink size. This could be done by amending such soils with organic materials.  相似文献   

19.
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.  相似文献   

20.
ABSTRACT

Dissolution of phosphate rocks (PR) in soils requires an adequate supply of acid (H+) and the removal of the dissolved products [calcium (Ca2 +) and dihydrogen phosphate (H2PO4 ?)]. Plant roots may excrete H+ or OH? in quantities that are stoichiometrically equal to excess cation or anion uptake in order to maintain internal electroneutrality. Extrusion of H+ or OH? may affect rhizosphere pH and PR dissolution. Differences in rhizosphere acidity and solubilization of three PRs were compared with triple superphosphate between a grass (Brachiaria decumbens) and a legume (Stylosanthes guianensis) forage species at two pH levels (4.9 and 5.8) in a phosphorus (P)-deficient Ultisol with low Ca content. The experiment was performed in a growth chamber with pots designed to isolate rhizosphere and non-rhizosphere soil. Assessment of P solubility with chemical extractants led to ranking the PRs investigated as either low (Monte Fresco) or high solubility (Riecito and North Carolina). Solubilization of the PRs was influenced by both forage species and mineral composition of the PR. The low solubility PR had a higher content of calcite than the high solubility PRs, which led to increased soil pH values (> 7.0) and exchangeable Ca, and relatively little change in bicarbonate-extractable soil P. Rhizosphere soil pH decreased under Stylosanthes but increased under Brachiaria. The greater ability of Stylosanthes to acidify rhizosphere soil and solubilize PR relative to Brachiaria is attributed to differences between species in net ion uptake. Stylosanthes had an excess cation uptake, defined by a large Ca uptake and its dependence on N2 fixation, which induced a significant H+ extrusion from roots to maintain cell electroneutrality. Brachiaria had an excess of anion uptake, with nitrate (NO3 ?) comprising 92% of total anion uptake. Nitrate and sulfate (SO4 2 ?) reduction in Brachiaria root cells may have generated a significant amount of cytoplasmic hydroxide (OH?), which could have increased cytoplasmic pH and induced synthesis of organic acids and OH? extrusion from roots.  相似文献   

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