Plant availability of phosphorus in four superphosphate fertilizers varying in water-insoluble phosphate compounds

There is concern that the use of lower quality phosphate rock can result in elevated amounts of Fe-Al-P water-insoluble compounds in fertilizers and, consequently, low agronomic effectiveness. Therefore, studies were conducted to evaluate the effect of some of these compounds on plant growth. Four commercial superphosphates varying in chemical composition (two single and two triple superphosphates) were selected for the study. Fertilizer impurities were collected as water-insoluble residues by washing each P source with deionized water. A modal analysis, based primarily on elemental chemical analysis and x-ray diffractometry, was used to estimate the chemical composition of each P source. Water-soluble monocalcium phosphate (MCP) and the water-leached fertilizer residues were prepared to give a range of fertilizers in terms of water-soluble phosphorus (WSP) (0-100% of the available P as MCP). The water-leached fractions, MCP, and the mixtures of MCP with water-leached fractions were applied to supply 40 mg available P kg(1) to a thermic Rhodic Kanhapludult with pH values of 5.2 +/- 0.05 (unlimed) and 6.4 +/- 0.08 (limed). Wheat (Triticum aestivum L.) grown in a greenhouse for 101 d served as the test crop. The requirement for WSP was source and pH dependent. At a soil pH of 5.2, the fertilizers required 73 to 95% WSP to reach the maximum dry-matter yield, while they required 60 to 86% WSP at pH 6.4. To reach 90% of the maximum yield, all superphosphate fertilizers required <50% WSP. These results show that it is not always necessary to have high water solubility as required by legislation in many countries.

Activity of phosphorus of synthetic Fe-K-P compounds in superphosphate fertilizers as affected by pH and ionic strength

The concentration of orthophosphate ions released from Fe-K-P compounds (Fe3KH8(PO4)6 .6H2O and Fe3KH14(PO4)8 .4H2O) present in superphosphates increases with pH, which initially suggests that the agronomic effectiveness of P fertilizers containing high amounts of these compounds would also increase with soil pH but studies considering activity, instead of concentration, are necessary. With this purpose, both compounds were synthesized under laboratory conditions, characterized by elemental chemical analysis, optical microscopy, X ray diffractometry, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and used in a solubility study. Solutions of 0.01, 0.05 and 0.1 mol L-1 NaCl with pH adjusted to 3.0, 4.0, 5.0, 5.5, 6.0, 6.5, 7.0 and 7.5 were prepared for the solubility study of H8-syn, H14-syn and a phosphate rock (PR) from Brazil. The orthophosphate activity as H2PO4- and HPO4(2-) was calculated in each situation as related to pH and ionic strength using software MINTEQ. The remaining precipitates after equilibrium were chemically analyzed and subjected to X ray, SEM and EDS. Results of chemical analysis and instrumental techniques confirmed the preparation method. The activity of orthophosphate ions of both compounds tended to decrease under increasing pH and/or ionic strength of the solution, which in turn suggests that an increase in the solution pH does not necessarily promote an increase in the P bioavailability for plant uptake. This can be important when evaluating agronomic data of P fertilizers with high contents of these two Fe-K-P compounds.

Agronomic effectiveness of cationic phosphate impurities present in superphosphate fertilizers as affected by soil pH

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 [Fe 3 KH 8 (PO 4 ) 6·6H 2 O, H8, and Fe 3 KH 14 (PO 4 ) 8·4H 2 O, H14] were prepared and characterized. These P sources were used to provide 30 and 60 mg P kg -1 as neutral ammonium citrate (NAC)+H 2 O-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. Copyright © Taylor & Francis Group, LLC.

Are Reactive Rock Phosphate and Superphosphate Mixtures Suitable for No-Till Soybean?

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Characterization and greenhouse evaluation of Brazilian calcined nonapatite phosphate rocks for rice

Little information is available on the agronomic effectiveness of calcined nonapatite phosphate rock (PR) sources containing crandallite minerals in the form of Ca-Fe-Al-P for flooded and upland rice (Oryza sativa L.). We conducted laboratory and greenhouse studies to (i) characterize the mineralogical composition, (ii) investigate the solubility and dissolution behavior, and (iii) evaluate the agronomic effectiveness of two nonapatite PR sources (Juquia and Sapucaia) from Brazil and compared them with (i) a highly reactive Gafsa PR (Tunisia) containing apatite in the form of Ca-P and (ii) a reference water-soluble triple superphosphate (TSP) for flooded and upland rice. After calcination at 500 degrees C for 4 h, the solubility of Juquia PR and Sapucaia PR in neutral ammonium citrate (NAC) significantly increased from almost nil to a maximum of 39.3 and 114 g P kg(-1), respectively. X-ray diffraction showed that crystalline crandallite mineral was transformed to an amophorus form after calcination. The solubility behavior of the two calcined PR sources followed the same trend as Gafsa PR, that is, P release decreased with increasing equilibrium pH in the 0.01 M KCl solution (PH 3.0-8.0). At PH 3, the solubility followed: Gafsa PR > calcined Sapucaia PR > calcined Juquia PR. No P release was detected from any of the PR sources at pH >= 5.0 in the solution, indicating the Ca-P characteristic of the Ca-Fe-Al-P mineral controlled P dissolution of the calcined PR. Without calcination, both Juquia PR and Sapucaia PR were totally ineffective for upland rice grown on a Hiwassee clay loam (fine, kaolinitic, thermic Rhodic Kanhapludult) with pH 5.4 whereas a significant P response was observed with the calcined PR samples. For flooded rice grown on Hiwassee soil, the calcined Juquia PR and Sapucaia PR were 66 and 72%, respectively, as effective as TSP in increasing rice grain yield whereas Gafsa PR was ineffective. For upland rice grown on the unlimed soil, Gafsa PR was as effective as TSP in increasing rice grain yield whereas calcined Juquia PR and Sapucaia PR were 89 and 83% of TSP. The effectiveness of Gafsa PR was reduced to 0% after the soil was limed to pH 7.0 whereas the two calcined PR sources were reduced to 49% of TSP. Soil available P extracted by iron oxide impregnated filter paper (Pi test) or anion-exchange resin after rice harvest correlated well with P uptake by rice grain for flooded and upland rice.

Available Phosphorus Evaluated by Three Soil Tests in a Brazilian Tropical Oxisol Treated With Gypsum

Mehlich-1, resin-HCO(3), and Pi tests were used to assess available P in an acid tropical Oxisol in Brazil treated with gypsum, which has been preferred over lime to ameliorate the Al toxicity in the subsoil. The soil was incubated in the laboratory at rates up to 75 g kg(-1) of phosphogypsum (PG) containing 0.3% total P, natural gypsum, or reagent-grade gypsum, and up to 100 mg P kg(-1) as triple superphosphate (TSP) or phosphate rock (PR). In the greenhouse, two consecutive maize crops were grown on the soil treated with 50 mg P kg(-1) of TSP and PG rates up to 75 g kg(-1). The results of the incubation study showed that Mehlich-P and Pi-P increased with increasing PG rate for the treatments of TSP, PR, and control. Resin-HCO(3) underestimated available P from TSP and PR because of the reaction between resin-HCO(3) and gypsum. Mehlich-1 overestimated available P from PR compared with TSP because of an excessive dissolution of PR by the strongly acidic Mehlich-1. Pi underestimated available P from PR in the treatments of natural and reagent-grade gypsum because of Ca common-ion effect from gypsum on depressing PR dissolution. The results in terms of the effect of PG on available P are similar in both incubation and greenhouse studies. Both Mehlich-P and Pi-P correlated well with P uptake by maize, whereas resin-P did not.

Runoff and leachate losses of phosphorus in a sandy spodosol amended with biosolids

Florida Spodosols axe sandy, inherently low in Fe- and Al-based minerals, and sorb phosphorus (P) poorly. We evaluated runoff and leachate P losses from a typical Florida Spodosol amended with biosolids and triple superphosphate (TSP). Phosphorus losses were evaluated with traditional indoor rainfall simulations but used a double-deck box arrangement that allowed leaching and runoff to be determined simultaneously. Biosolids (Lakeland, OCUD, Milorganite, and Disney) represented contrasting values of total P, percent water-extractable p (PWEP), and percentage of solids. All P sources were surface applied at 224 kg P ha(-1), representing a soil P rate typical of N-based biosolids application. All biosolids-P sources lost less P than TSp, and leachate-P losses generally dominated. For Lakeland-amended I soil, bioavailable P (BAP) was mainly lost by runoff (81% of total BAP losses). This behavior was due to surface scaling and 1 drying after application of the slurry (31 g kg(-1) solids), material. For all other P sources, BAP losses in leachate were much,greater than in runoff, representing 94% of total BAP losses for TSP, 80% for Milorganite, 72% for Disney, and 69% for OCUD treatments. Phosphorus leaching can be extreme and represents a great concern in many coarse-textured Florida Spodosols, and other coastal plain soils with low P-sorption,capacities. The PWEP values of P sources were significantly correlared with total P and BAP losses in runoff and leachate. The PWEP of a source can serve as a good indicator of potential P loss when amended to sandy soils with low P-retention capacities.

Growth and nutrient accumulation in mycorrhized papaya seedlings cultivated in a phosphorus-fertilized substrate

ABSTRACT The indiscriminate use of mineral fertilizers in papaya orchards has increased production costs, and the use of arbuscular mycorrhizal fungi is a promising alternative to reduce such expenses. Therefore, the present research aimed at studying the efficiency of arbuscular mycorrhizal fungi (AMF) on dry matter and nutrient accumulation in Sunrise Solo papaya seedlings, by applying doses of P2O5 (triple superphosphate) that are harmful to the symbiosis. The experiment was carried out in a protected environment and was set up in a randomized block design with four replications, and consisted of four P2O5 doses (0, 672, 1386 and 2100 mg dm-3), three mycorrhizal fungi species (Gigaspora margarita, Entrophospora colombiana and Scutellospora heterogama) and the control treatment (mycorrhiza-free). Shoot and root dry matter as well as nitrogen, phosphorus and potassium contents in leaf and root tissues were assessed. Mycorrhizal inoculation promoted a 30% increase in shoot dry matter in relation to the control treatment. Mycorrhizal fungi promoted increases in leaf and root nitrogen content up to 672 mg dm-3 P2O5. Inoculation of E. colombiana favored the highest gains in root and shoot dry matter. P2O5 fertilization increased foliar and root phosphorus content.

Gradual correction of phosphorus availability in the no-tillage system

ABSTRACT In areas cultivated under no-tillage system, the availability of phosphorus (P) can be raised by means of the gradual corrective fertilization, applying phosphorus into sowing furrows at doses higher than those required by the crops. The objective of this work was to establish the amount of P to be applied in soybean crop to increase content of P to pre-established values at the depth of 0.0 to 0.10 m. An experiment was carried out on a clayey Haplorthox soil with a randomized block experimental design distributed in split-split plot, with four replications. Two soybean crop systems (single or intercropped with Panicum maximum Jaca cv. Aruana) were evaluated in the plots. In addition, it was evaluated four P levels (0, 60, 120 and 180 kg ha-1 P2O5) applied in the first year in the split plots; and four P levels (0, 30, 60 and 90 kg ha-1 P2O5) applied in the two subsequent crops in the split-split plot. Contents of P were extracted by Mehlich-1 and Anion Exchange Resin methods from soil samples collected in the split-split plot. It was found that it is necessary to apply 19.4 or 11.1 kg ha-1 of P2O5, via triple superphosphate as source, to increase 1 mg dm-3 of P extracted by Mehlich-1 or Resin, respectively, in the 0.0 to 0.10 m layer of depth. The soil drain P character decreases as the amount of this nutrient supplied in the previous crops is increased.

Pesquisas sôbre a análise estatística de experiências de adubação com o auxílio da lei de Mitscherlich

Statistical analyses of an experiment on wheat were carried out with the aid of Mitscherlich's law. The experiment was made in Ponta Grossa, Paraná, by the Ministry of Agriculture of Brasil. Lime, in the form of Ca(OH)2, was applied at the levels of 0, 2, 4, 6 and 8 metric tons per hectare. A 5 x 5 Latin square was used. Lime was applied in 1940 and wheat was cultivated in the same plots for several years. The following fertilizers were annually used for all plots: NaNO3 100 kilograms per hectare, Superphosphate 350 kilograms per hectare, K2S04 80 kilograms per hectare. The statistical analysis of the data collected in 1941, 1942, 1943, 1947 and 1948, carried out in accordance with the methods previously introduced by Pimentel Gomes and Malavolta (1949 a, 1949 b) and Pimentel Gomes (1950), proved: I. That Mitscherlich's law could be correctly applied to the data. II. That there was a statistically significant effect of lime on wheat yield. III. That the optimum amount of lime to be applied to the soil lies between 5 and 15 hundred kilograms of Ca(OH)2 per hectare. IV. That there is a migration of calcium from some plots to others, in such a way that the data obtained in 1947 and 1948 are not representative of the amounts of lime applied in 1940. V. That the analysis of variance can be used, as the Bartlett test shows that the variances at the distinct levele of lime application are not statistically different. It must be noted that, with improved variety and fertilization, the yield was rised to about 2500 kilograms per hectare in 1947, and 1600 in 1948, being only of about 100 kilograms per hectare in 1940.

Vinhaça e adubos minerais(I)

In this paper it is studied the action of vinasse as compared to mineral fertilizers. Beans, corn, cotton and sesame were cultivated in randomized blocks receiving the following treatments: A = mineral fertilizers (N, P, K); V = vinasse at the rate of 1,000,000 liters per Ha; AV = mineral fertilizers + vinasse; T = control. Statistical analysis of the experiments has consistently revealed the superiority of vinasse either combined or not with the mineral fertilizers over the remaining treatments. There was no significant difference between V and AV which shows the surprizing role of vinasse when applied to light soils such as those employed in the present experiments. By employing 1,000,000 liters of vinasse to the hectare the following amounts of nutrientes were applied to the crops in this experiment: 470 Kg of nitrogen 50 Kg of P2O5 and 3,100 Kg of K2O corresponds to 3,133 Kg of Chilean nitrate/ha 250 Kg of superphosphate and 5,160 Kg of muriate of potash Hence one cannot say that the action of vinasse is of a purely physical nature. In our opinion its outstanding action is due to: 1st raise in the pH value of the soil; 2nd addition of a tremendous amount of plant nutrients; 3rd supplying organic matter in a very finely divided state with all its benefical effects in soil structure, water holding capacity, adsorption of nutrients to prevent leaching, etc. A rotation experiment is now being carried out to study the residual effect of vinasse.

Competição entre adubos fosfatados em milho (Zea mays L)

This paper relates the results of an experiment designed to study the comparative effects of several phosphates applied to corn crops. The following phosphates were applied to a latin square of 6x6: Latif (a rock phosphate), fospal, superphosphate, fertifos, hiperfosfato and serranafosfato (a fusion phosphate). The nutrients were employd at the rates of 200 kg of N (as Chilean nitrate), 200kg of K2O (as muriate of potash) and 200 kg of P205. To correct the acidity and to improve the poor physical conditions of the sandy soil studied limestone (450 kg/Ha) and cotton seed meal (900 kg/Ha) were added to all plots; liming was made one month in advance to the planting. In the second year, in the same place, the split-plot technique was used: half plot received only N and K20 whereas the other half received the same treatment as the year before. The results can be summarized as follows: 1. in the first year, superphosphate of lime, produced better results than the other phosphates; there was no significant difference among fertifos, serranafosfato, and hiperfosfato but these phosphates proved to be superior to fospal and Latif; 2. in the second year, superphosphate, fertifos and serranafosfato produced practically the same effect, being better than hiperfosfato, fospal, and Latif which did not differ signicantly; 3. the increase in yield due to the reapplication of phosphates to the half plots was not advantageous under an economic point of view; however, it is interesting to note that the yield was still benefited in spite of the heavy doses of phosphates applied the year before.

Experiências de adubação mineral e orgânica com Capim Kikuyu (Pennisetum clandestinum Hochst.)

Kikuio grass (Pennisetum clandestinum Hochst) is beyond any doubt, a pasture very important for farm animals; since its chemical composition is very similar to that of alfalfa, the present field trial was carried out; a randomized block design with 8 treatments was selected as follows: 1 N - P - K - Ca - Mg (complete manuring) 2 N - P - K - Ca----- (without Mg) 3 N - P - K-------Mg (without Ca) 4 ----P - K - Ca - Mg (without N) 5 N------K - Ca Mg (without P) 6 N - P - Ca - Mg (without K) 7 organic matter (without mineral fertilizers) 8 control Nitrogen was applied as NaN03 (topdressed) and as ammonium sulfate; P2O5 was given as superphosphate associated to bonemeal; K2O was applied as muriate, CaO as "sambaquis" (oyster shells); MgO was given as MgSO4 (topdressed). The source of organic matter was farmyard manure. As far yields are concerned the following observations were made: 1. treatment n. 7 was superior to all others; 2. considering the mineral fertilizers, good responses were due to N and P2O5; 3. the control yield was exceedingly poor, being inferior to all the others treatments; The chemical analyses revealed that: 1. the protein content decreased accordingly to this order: 7, 6, 5 and 1; treatment 4 (without N) gave the lowest protein content; 2. treatment n. 4 produced the highest fat content; treatment no. 7 ranked second; no. 8 gave the lowest fat content; 3. crude fiber: highest - treatment 7; lowest - 8; 4. ashes: the ashes content was higher in treatment 5; proprobably because the most abundant element in the ashes is K, the ash content of treatment 6 (no K) was very low; 5. non nitrogenous substances (determined by difference) - high in treatment 8 and low in treatment 7; 6. mineral elements in the ashes - the element omitted from a given treatment was very low in the grasses therein obtained; this shows the relative poverty of the soil in that element. As general remark the Authors suggest the use of farmyard manure in the fertilization of Kikuio grass; farmyard manure could probably substitute wither green manure or compost.

Adubação do milho: estudo comparativo sobre a colocação da mistura de adubos nos sulcos de semeadura e em sulcos laterais ao sulco de semeadura

The results reported in this paper did not show statistical differences in production of seeds, number of plants and number of ears when corn fertilizer (combination of Chilean nitrate, superphosphate and potassium chloride) was applied either in the sowing furrow or in lateral furrows (one or both side). The treatments with fertilizer were better than the treatment without fertilizer used for comparisons. Cotton seed meal, used in combination with superphosphate and potassium chloride, placed in the sowing furrow, reduces statistically the number of plants in the row when compared with the treatments where applications were made only in lateral furrows. However, this reduction of plants did not affect significantly the number of ears and the production in the treatments.

Tracer studies in the coffee plant (Coffea arabica L.)

Due to the great importance of coffee to the Brazilian economy, a good deal of the work carried out in the "Laboratório de Isótopos", E. E. A. "Luiz de Queiroz", Piracicaba, S. Paulo, Brazil, was dedicated to the study of some problems involving that plant. The first one was designed to verify a few aspects of the control of zinc deficiency which is common in many types of soils in Brazil. An experiment conducted in nutrient solution showed that the leaf absorption of the radiozinc was eight times as high as the root uptake; the lower surface of the leaves is particularly suited for this kind of absorption. Among the heavy metal micronutrients, only iron did not affect the absorption of the radiozinc; manganese, copper, and molybdenum brought about a decrease of fifty per cent in total uptake. In another pot experiment in which two soils typical of the coffee growing regions were used, namely, a sandy soil called "arenito de Bauru" and a heavy one, "terra roxa", only O.l and 0.2 per cent of the activity supplied to the roots was recovered", respectively. This indicates that under field conditions the farmer should not attempt to correct zinc deficiency by applying zinc salts to the soil: leaf sprays should be used wherever necessary. In order to find out the most suitable way to supply phosphatic fertilizers to the coffee plant, under normal farm conditions, an experiment with tagged superphosphate was carried out with the following methods of distribution of this material: (1) topdressed in a circular area around the trees; (2) placed in the bottom of a 15 cm deep furrow made around the plant; (3) placed in a semicircular furrow, as in the previous treatment; (4) sprayed directly to the leaves. It was verified that in the first case, circa 10 per cent of the phosphorus in the leaves came from the superphosphate; for the other treatments, the results ware, respectively: 2.4, 1.7, and 38.0 per cent. It is interesting to mention that the first and the last methods of distribution were those less used by the farmers; now they are being introduced in many coffee plantations. In a previous trial it was demonstrated that urea sprays were an adequate way to correct nitrogen deficiency under field conditions. An experiment was then set up in which urea-C14 was used to study the metabolism of this fertilizer in coffee leaves. In was verified that in a 9 hours period circa 95 per cent of the urea supplied to the leaves had been absorbed. The distribution of the nitrogen of the urea was followed by standard chemical procedures. On the other hand the fate of the carbonic moiety was studied with the aid of the radiochromatographic technique. Thus, the incorporation of C14 in aminoacids, sugars and organic acids was ascertained. Data obtained in this work gave a definite support to the idea that in coffee leaves, as in a few other higher plants, a mechanism similar to the urea cycle of animals does exist.