Concentrated Superphosphate Research Articles

Interaction of Phosphorus Rates and Soil pH on Soybean Yield and Soil Solution Composition of Two Phosphorus‐Sufficient Ultisols

AbstractBecause growers continue to use phosphorus (P) fertilizer on soils that test high in available P, two field experiments were conducted to determine what nutritional problem, if any, would develop in soybeans (Glycine max L.) when high levels of P were established on Ultisols. Soil pH levels, ranging from 5.0 to > 7.0, were established by differential limiting; five P rates as concentrated superphosphate were superimposed on the pH levels. Zinc (Zn) deficiency was induced by high P rates and high pH, and the magnitude of yield reduction corresponded with the intensity of deficiency symptoms on foliage. Leaf Zn, acid‐extractable soil Zn, and soil solution Zn were poor indicators of Zn deficiency. The ratio of P/Zn in leaves was a fair indicator in one soil and a poor one in the other, possibly because of differences in availability of subsoil Zn. Soil solution Zn, which ranged between 0.1 and 5.1 µM, was affected by pH but not P level. Soil solution P, which ranged between 5 and 230 µM, was affected primarily by P rates. Both SO4 and Si concentrations in soil solutions were increased by increasing P rates. Calculated ion activity products for Ca5OH(PO4)3 showed numerous soil solutions to be supersaturated with respect to hydroxyapatite.

Phosphoric Acid Anticrustant Improves Seedling Emergence and P Content1

Abstract Phosphoric acid (H3PO4), applied as an over-the-row banded spray to Willamette silt loam, significantly hastened the emergence of seedlings of carrot (Daucus carota L.), cauliflower (Brassica oleracea L. var. botrytis), cucumber (Cucumis sativus L.), lettuce (Lactuca sativa L.), and onion (Allium cepa L.). Final stands were usually improved. The effect was particularly pronounced in early plantings. Banded H3PO4 decreased soil crusting as measured by decreased mechanical resistance to penetration of the soil surface. Phosphorus content of seedlings of carrot, cucumber, lettuce, and onion was significantly increased with H3PO4 anticrustant. Yields were usually greater on soils treated with H3PO4 than on soils treated with either broadcast or subsurface banded applications of concentrated superphosphate (CSP). Subsurface bands of CSP resulted in poorer stands, lower leaf P content, and smaller yields of carrot, lettuce and onion than did banded H3PO4 at the same rate of P application. However, both leaf P content and yield of cucumber tended to be greater with CSP than with H3PO4. Phosphoric acid treatment improved stand of carrot and lettuce at soil pH between 5.0 and 6.1 but decreased stand at pH 6.6.

Resposta do sorgo sacarino (Sorghum bicolor (L.) Moench) ao emprego de fontes e doses de fósforo em condições de casa de vegetação: I. Latossolo vermelho escuro

Foi estudada a eficiência do fosfato de Catalão, (FG), como fornecedor de P para o sorgo sacarino comparando-a com a do super triplo (ST) em LEa do Estado de Goiás. Usaram-se doses de P2O5, em presença e ausência de calagem. O efeito residual foi estimado em 2 cultivos sucessivos. Foram obtidas as seguintes conclusões principais: o ST mostrou-se uma fonte de P2O5 superior ao FG; a calagem aumentou o aproveitamento do FG; a produção de matéria seca não foi influenciada pelo método de aplicação do PG; a absorção de P foi influenciada favoravelmente pela calagem principalmente no 2° e 3° cultivos; houve correlação positiva e significativa entre P residual (Olsen) e produção; a produção de matéria seca no 2° e 3° cultivos se correlacionou mais estreitamente com o teor de Ca do que com o de P disponível no solo.

Efficiency of nitric phosphates and Mussoorie rock phosphate in three cycles of clusterbean–wheat and groundnut–wheat rotations

SUMMARYNitric phosphates containing 80, 50 and 30% water-soluble phosphorus, and Mussoorie rock phosphate, alone or with Amjhore pyrites, farmyard manure or straw, were compared relative to concentrated superphosphate for each of three cycles of a clusterbean–wheat and a groundnut–wheat rotation. Both the field experiments were made on alkaline P-deficient Samana sands. All phosphatic fertilizers were applied to each crop at the rate of 10, 20 and 30 kg P/ha. Dry forage of clusterbean, groundnut pods and grain yield of wheat were measured. The model of concurrent straight line response was employed to calculate availability coefficient ratios which express the relative effectiveness of the different phosphatic fertilizers.Nitric phosphate containing 80 % water-soluble phosphorus and concentrated superphosphate were almost equal in their effectiveness in both 3-year rotational studies of clusterbean–wheat and groundnut–wheat. The relative efficiency of the nitric phosphates increased with the amount of water-soluble phosphorus they contained. Mussoorie rock phosphate was the least effective source of fertilizer phosphorus, although its efficiency is considerably higher for the legume clusterbean and for groundnut than for the cereal wheat. The efficiency of Mussoorie rock phosphate increased when it was mixed with the soil together with Amjhore pyrites, farmyard manure and straw respectively. These materials were more effective for clusterbean and groundnut than for wheat.

Effects of incubation on forms of phosphorus added to an acid brown forest soil in Czechoslovakia

The effects of farmyard manure (FYM) and concentrated superphosphate (CSP) on the proportions of different fractions of inorganic P with the passage of time were studied through incubation of samples of an acid (pH 4.8, KCl) brown forest soil of Czechoslovakia. The application of FYM and CSP, either singly or in combination, resulted in appreciable increases in different forms of P over the controls. The amounts of P added to soil through FYM and CSP were recovered mainly in the (NH 4) 2SO 4-, CH 3COOH-, NH 4F- and NaOH-soluble fractions, whereas recovery in the H 2SO 4-soluble fraction was very small. The highest recovery of added P was in the (NH 4) 2SO 4-soluble fraction. The different fractions of P in the untreated as well as the incubated samples ranked in the order of NaOH-soluble P > (NH 4) 2SO 4-soluble P > NH 4F-soluble P > H 2SO 4-soluble P > CH 3COOH-soluble P, except after 15 and 45 days of incubation when CH 3COOH-soluble P was higher than the H 2SO 4-soluble fraction in samples that had received CSP and FYM+CSP. With prolongation of incubation time there was a decrease in (NH 4) 2SO 4-, CH 3COOH- and NH 4F-soluble P and a continuous increase in NaOH-soluble P, irrespective of treatments. The H 2SO 4-soluble P changed little during incubation. The use of FYM alone or with CSP resulted in a slower rate of decrease in the forms of P extracted with (NH 4) 2SO 4. Moreover, in the control the decrease in (NH 4) 2SO 4-, CH 3COOH- and NH 4F-soluble P and the consequent increase in the NaOH-soluble fraction were more pronounced after 90 and 180 days of incubation.

Dissolution of North Carolina Phosphate Rock in Acid Colombian Soils as Related to Soil Properties

AbstractInformation on the dissolution of phosphate rock in soils as related to soil properties is needed in order to understand the solubility behavior of the phosphate rock in soils as related to crop response. This study was conducted to determine the relationships between the dissolution rate of North Carolina phosphate rock and selected chemical properties of 16 acid Colombian soils. A modified Elovich equation, Ct =Co − (1/β) ln (αβ) − (1/β) ln t, was used to describe the dissolution of phosphate rock in the soils. In the equation, Ct is the P concentration in water extract at time t, Co is the maximum P concentration in the water extract when t→0, α and β are constants. Of the various soil properties studied, the best correlations of reactive Al were a simple linear relationship with β and a log‐log relationship with α. Results from tests with two other acid soils from Colombia showed these relationships allow prediction of the dissolution rate of the phosphate rock in other soils from a single measurement of reactive Al content.Phosphorus sorption capacities of the 16 soils were correlated with amounts of reactive Al or active Al but not with amounts of free Fe2O3 and exchangeable Al in the soils. Amounts of water‐extractable P in the soils treated with concentrated superphosphate (CSP) or the phosphate rock decreased as P sorption capacity increased; however, the relative amounts of water‐extractable P of the phosphate rock with respect to CSP increased as P sorption capacity increased. This suggests that the relative agronomic effectiveness of phosphate rock compared with CSP would be highest on the strongly P‐fixing soils.

Increases in the Cation Exchange Capacity of Variable Charge Soils Following Superphosphate Applications

AbstractThe cation exchange capacity (CEC) of soils from field plots which were fertilized with concentrated superphosphate for 8 years has been measured. The superphosphate was added in amounts equivalent to those needed to raise solution P to 0.001 to 1.6 µg/ml in the adsorption isotherm. Three variable charge soils from Hawaii, a Hydrandept, a Gibbsihumox, and a Eutrostox were examined, using a new method for estimating the CEC of variable charge soils. This method takes account of pH and ionic strength conditions in the field. Agronomically significant increases in CEC of the surface horizons with increasing superphosphate application were obtained. As a result, the leaching of applied nutrients, Ca, Mg, and K, was retarded, and greater quantities of these cations were present in the 0–50 cm profile than in the plots receiving no P, despite the fact that more cations were removed from the P treated plots by crops grown in succession.

Nutritional Quality of Vegetable Crops as Affected by Phosphorus and Zinc Fertilizers1

AbstractThe nutritional quality as well as the yield of the portions of vegetable plants used for human consumption should be considered in fertilization programs.The purpose of this study was to Determine the effects of rates of concentrated superphosphate and zinc sources on some nutritionally important factors including the concentration of P, Zn, phytic acid (myoinositol hexaphosphoric acid), and oxalic acid in the edible portions of four vegetables. The plants, pea (Pisum sativum L.), snap bean [Phaseolus vulgaris (L.) var. humilis], cabbage (Brassica oleracea var. capitata), and table beet (Beta vulgaris L.) were grown on a Honeoye fine sandy loam (Glossoboric Rapludalf, fine loamy, mixed mesic) derived from calcareous glacial till. These crops were fertilized with concentrated superphosphate (CSP) at rates of 0, 30, 60, and 120 kg P/ha, and ZnSO4 or ZnCl2 at rates of 0, 5, 20, and 80 kg Zn/ha applied in a band at planting time in a factorially designed experiment. The plants were sampled at processing stage except that pea and snap bean seeds were also sampled at full maturity. Increasing fertilizer CSP rates increased yields and P concentrations in all crops. Fertilizer CSP increased phytic acid concentrations in immature and mature pea seeds and in mature snap bean seeds. Oxalic acid concentrations in table beet plants decreased with increasing rates of CSP fertilizer. Fertilizer CSP without Zn fertilizer decreased Zn concentrations in the plants, but CSP with Zn fertilizer generally increased Zn concentrations. Fertilizer Zn did not affect yields nor cause visible plant toxicities. However, Zn fertilizer increased Zn concentrations in the plants, especially when applied with high rates of CSP fertilizer. Thus, CSP fertilization without Zn fertilization of vegetable crops can reduce their nutritional quality by lowering their Zn concentrations. However, the concomitant use of Zn fertilizer, with high rates of CSP fertilization, can improve the nutritional quality of vegetable crops with respect to Zn.

Reactions of Partially Acidulated Phosphate Rock with Soils from the Tropics

AbstractEqual amounts of water‐soluble P in the form of granulated partially‐acidulated phosphate rock (20% by H3PO4) and concentrated superphosphate (CSP) were added to two Nigerian savanna soils and an Oxisol from Colombia. The amount of water‐extractable P was higher in soils treated with partially‐acidulated phosphate rock. Addition of phosphate rock to CSP resulted in an increase in the water‐extractable P. The results suggest that the presence of phosphate rock in partially acidulated phosphate rock or in the mixture of CSP and phosphate rock slowed down the immobilization of watersoluble P by reacting with some of the acidity produced during monocalcium phosphate hydrolysis, thus reducing the amount of acid available to solubilize soil Al and Fe. Reaction of acid with phosphate rock could release additional P to the watersoluble pool. The relative effectiveness of partially acidulated phosphate rock was highest in the Oxisol which had the highest capacity to sorb P.

Nutrient Uptake in Fertilized Plantations of American Sycamore

AbstractAnnual applications of ammonium nitrate (169 kg/ha elemental N), alone and in combination with concentrated superphosphate (112 kg/ha elemental P), increased biomass of 4‐ and 5‐year‐old American sycamore (Platanus occidentalis L.) by approximately 45 and 205% on a bottomland and a terrace site, respectively, in the Ohio River Valley region of western Kentucky. Growth response and nutrient contents of trees fertilized with N and P were not significantly different from those receiving N only. After 5 years, N fertilization has increased elemental content of aboveground tree components by 189% for N, 48% for P, 90% for K, 93% for Ca, and 106% for Mg. Initial spacing of the seedlings in these closely‐spaced (0.3 by 0.9 m, 0.9 by 0.9 m, 1.8 by 0.9 m) trials did not have a significant effect on nutrient contents. Recovery of added N, as indicated by increased above ground tree contents after 5 years, represented 11 and 14% of the quantity added in fertilizer applications on the bottomland and terrace, respectively. After 5 years, levels of available P in soils receiving annual P fertilization had increased by 140 kg/ha, representing about 25% of the total P added. After 5 years exchangeable Ca had decreased in the bottomland soils and exchangeable K, Ca, and Mg had decreased in the less fertile terrace soil.

Kinetics of Dissolution of Phosphate Rocks in Soils

AbstractA modified Elovich equation in the form of Ct = C0 − (1/β)ln (αβ) − (1/β) ln t was derived to describe the kinetics of dissolution of three phosphate rocks (North Carolina, central Florida, and Tennessee) in three soils (one soil from Florida and two Nigerian soils). The equation fitted the experimental data the best among various models of kinetics. Comparisons of dissolution rates of various phosphate rocks in a given soil or a given phosphate rock in various soils can be made by comparing the values of three parameters—C0, α, and β—in the equation where C0 is the maximum P concentration in the soil solution that a phosphate rock can provide in a soil (Ct is the P concentration at time t), and α and β are constants. It was found that C0 increased as α increased and/or β decreased in a given system.Temperature was found to have no significant effect on the dissolution of phosphate rock in the soil. This implies that phosphorus retention by the tropical soils treated with phospate rock may be much less affected by temperature as compared with water‐soluble P fertilizers such as concentrated superphosphate.

Corn Response to S‐Coated and Non‐Coated Superphosphates and Residual Effects1

AbstractMaintaining sufficient available P to crops, including corn (Zea mays L.), has long been recognized as a limiting feature to maximum production in most soils. Providing the P in a pellet should permit soluble P to saturate the soil with P at the pellet while preserving a portion as reserve in the pellet. To test this hypothesis, pelletized ordinary superphosphate (OSP), concentrated superphosphate uncoated (CSP), or coated with S and sealant (SCSP) were compared in a Rhodic Paleudult (a Red Bay, fine, sandy loam), previously uncultivated. This soil was gibbsitic and gave a maximum P sorption of 2,670 kg/P ha and had, at preplant, 11 kg P/ha extractable by 0.03 N NH4F in 0.1 N HC1. The major experiment was a randomized block design with each main plot split for banded and broadcast P placement with the CSP and SCSP compared at 28, 56, 112, and 140 kg P/ha. A secondary experiment compared OSP and SCSP combinations, all broadcast at 84 kg P/ha. The first year, corn cultivar ‘Pioneer 3009B’ was grown. The second year, plots previously receiving broadcast P were refertilized at one‐half the prior P level of CSP and SCSP while plots with banded P received no further P. The third year, no further P was added. The latter 2 years, corn cultivar ‘Pioneer 3369A’ was planted.Greatest increase in corn grain yield was obtained for the first 28 kg P/ha and further response was linear at 200 kg/ha yield for each additional 28 kg/P applied. Yield response was not significantly different either for P sources or for placement. The second year, residual P from that applied the first year gave linear corn grain yield response which was similar to that found when an additional P fertilization was made. The third year, grain yields gave better response to two, rather than one, annual P fertilization. There was no grain yield advantage to blending OSP and SCSP pellets either in the first or third year. Soil test values and ear leaf P values showed linear responses to rates of applied P.

EFFECT OF MANURE ON SOLUBILITY OF PHOSPHORUS IN CALCAREOUS SOILS

We studied the effects of farmyard manure, with and without concentrated superphosphate on the solubility of phosphorus in three calcareous soils. Concentrated superphosphate, at rates of 0, 10, 20, 40, and 60 parts per million of phosphorus, and air-dried manure, at rates of 0,11, 22, and 44 metric tons per hectare, were mixed with the soils, and the soils were wetted and dried four times in the greenhouse. Adding manure and phosphorus together (mixed treatment) to Pierre and Apishapa soils increased soluble phosphorus in 0.01 M CaCl2 more than each treatment when added separately (unmixed treatment). However, adding farmyard manure and concentrated superphosphate together to the Tripp soil, at the higher rates of fertilizer, did not increase the soluble phosphorus in CaCl2 as much as each treatment separately. However, the mixed treatments had higher HCO3-extractable phosphorus for all three soils than the sum of separate effects from the unmixed treatments. Adding 44-metric tons of farmyard manure per hectare to Pierre, Apishapa, and Tripp soils increased soluble phosphorus in NaHCO3 equivalent to 27, 21, and 21 parts per million of phosphorus as concentrated superphosphate, respectively. Solubility data suggested that octocalcium phosphate could be present in the Tripp soil, since most of the experimental points for mixed treatments plotted near the stability isotherm of this phosphate mineral.

Effects of Phosphorus Fertilizer and Lime on the As, Cr, Pb, and V Content of Soils and Plants

AbstractThe occurrence in fertilizer materials of small quantities of chemical elements not essential to plants suggests that the soil may become contaminated with these elements due to the use of fertilizers. Two experimental sites: a Nicollet clay loam fertilized with 0, 1,111, 2,222, 4,444, and 8,888 kg/ha of concentrated superphosphate (CSP) and 20.2 metric tons of lime, and a Port Byron silt loam fertilized for 19 years with 99, 73, 82, and 352 kg/ha annually of CSP, calcium metaphosphate, phosphoric acid, and southern rock phosphate, respectively, were sampled to determine if significant amounts of arsenic (As), chromium (Cr), lead (Pb), or vanadium (V) had been added from use of these fertilizer materials. There was no indication of increased As, Cr, Pb, or V from the addition of P fertilizers to either the Nicollet or Port Byron soils. The addition of lime increased the Cr content of the Nicollet soil by approximately 3 ppm, but there was no increase in As, Pb, or V. There was no increase in As, Cr, Pb, or V from addition of CSP in soil samples from below the Ap horizon to a depth of 47.5 cm. Soil samples from a representative Nicollet soil suggest that higher As, Cr, Pb, and V concentrations in the A and B horizons are due to leaching of CaCO3 into the C horizon. Corn (Zea mays L.) plant growth and grain yields were similar for all CSP and lime treatments. The results of this study indicate that the use of P fertilizers at the rates presently applied would not add substantially to the natural levels of As, Cr, Pb, and V in the soil.

Removal of Ten Elements by Vegetables and by Alfalfa1

Abstract Peas (Pisum sativum L.), table beets (Beta vulgaris L.), cabbage (Brassica oleracea L. capitata group), snap beans (Phaseolus vulgaris L.), sweet corn (Zea Mays L.), and alfalfa (Medicago sativa L.) were grown at 4 rates of concentrated superphosphate (CSP) and 4 rates of potassium chloride (KC1) fertilizers in a Honeoye fine sandy loam soil. Removal of P, K, Ca, Mg, Na, S, Cl, Zn, Mn, and Fe by each crop was determined. CSP increased the removal of P. KC1 increased the removal of K and Cl. Table beet plants removed more elements by weight and by equivalences of cations per ha than any other vegetable crop. Two years of alfalfa hay removed more elements per ha than 5 years of the harvested portions of the 5 vegetable crops. Vegetative structure of the crops had wider ranges than the reproductive structures in concentrations of P due to CSP fertilizer treatments and especially wide ranges of K and Cl due to the KC1 fertilizer treatments.

Nutrient Flux in Litter and Surface Soil after Nitrogen and Phosphorus Fertilization

AbstractThe effect of urea and concentrated superphosphate additions on the movement of N, P, K, and Ca from the litter and top 10 cm of the mineral soil via the soil solution was evaluated in an upland oak forest using tension lysimeters. The range in total flux values for each element over the study period were: N 24.8 to 1145.3; P 2.0 to 633.3; Ca 70.6 to 553.1; and K 49.5 to 94.0 kg/ha in response to various combinations of N and P fertilizer addition at levels of 0, 550, and 1100 kg/ha N and 0, 275, and 550 kg/ha P. Nitrogen fertilizer addition significantly increased the flux of N and K while reducing the flux of P and Ca. Phosphorus fertilizer addition significantly increased N, P Ca, and K fluxes. Solubilization of organic matter and the formation of insoluble calcium ammonium phosphate were important processes regulating the flux of N, P, Ca and K.

Fertilizer Placement Effects on Soybean Seed Yield, N2 Fixation, and 33P Uptake1

AbstractVarious recommendations on placement of fertilizer for soybeans [Glycine max (L.) Merrill] have been made (banded near the seed or midway between the rows and surface broadcast and left on the surface or incorporated). Because P is an immobile element in the soil, placement may be critical.This study was planned to evaluate the efficiency of P fertilizer utilization by field‐grown soybeans with different fertilizer placements using 33P labelled fertilizer (35 kg P/ha) on a Waukegan silt loam soil (Typic Hapludoll) low in plant available N and P. In addition, urea (30 kg N/ha) labelled with 15N was added to measure the effect of P fertilizer placement on N uptake and N2 fixation using the ‘A’ value concept. The ‘A’ value is a mathematical expression for calculating the amount of available nutrient element in a soil in terms of a fertilizer standard provided that the proportion of the nutrient in the plant derived from this standard is determined (usually by isotope labelling).Fertilizer placement was evaluated in the field by using unlabelled urea N and P (concentrated superphosphate) in plot areas 2.25 × 10 m; a sub‐plot within the larger plot received applications of 15N labelled urea and 33P labelled concentrated superphosphate. Total plant samples for 15N and 33P analysis were obtained with special precautions to recover all leaves. Analysis of 15N was performed with photospectrometry methods; 33P was measured using a liquid scintillation technique.Soybean seed yield and total P uptake were increased significantly by adding P fertilizer with no differences among the fertilizer placements (seed yield ranged from 3,811 to 4,035 kg/ha compared to 3,200 kg/ha for the control). The 33P labelled fertilizer provided a direct, quantitative measure of the efficiency of plant use of the added P and provided a basis of evaluating the fertilizer placements without the hazards associated with 33P over the 149‐day experiment.The ‘AN’ value concept (based on ‘A’ value procedures using a nodulating and nonnodulating crop) provided a reliable estimate of N2 fixation which agreed with Kjeldahl measurements.

Uptake of Cadmium from Phosphate Fertilizers by Peas, Radishes, and Lettuce

AbstractCadmium uptake from phosphate fertilizers by radish (Raphanus sativus L.), lettuce (Latuca sativa L.), and garden peas (Pisum sativum L.) was investigated in the greenhouse. Fertilizer in all treatments was applied at the rate of 100 µg P/g soil to pots containing 4 kg soil. When reagent grade mono‐calcium phosphate was used as a P source on a coarse‐textured acid soil, Cd contents of edible radish roots and tops were < 0.4 µg/g dry weight; while the Cd content of lettuce, and pea seeds and foliage was < 0.2 µg/g. The use of concentrated superphosphate (CSP) containing 174 µg Cd/g resulted in plant Cd levels of 2.4, 3.4, 6.3, 0.9, and 0.5 µg/g for radish roots, radish tops, lettuce, pea seeds and pea foliage, respectively. On a medium‐textured calcareous soil the use of this CSP increased the Cd content of radish tops from 0.8 to 1.4 µg/g, while in lettuce the increase was from 0.8 to 1.2 µg/g. The effect on radish roots from calcareous soil was nonsignificant. Pea seeds and foliage on this soil were below our Cd detection limit of 0.2 µg/g. Uptake on both soils was a linear function of the Cd content of the fertilizer.With the acid soil, uptake of Cd from CSP was essentially the same when the fertilizer was placed in a spot 5 cm below the seed as when mixed with the soil. Di‐ammonium phosphate (DAP) containing 157 µg Cd/g resulted in similar uptake to the CSP when mixed with the soil, but spot placement of DAP almost completely eliminated Cd uptake from the fertilizer. In the calcareous soil spot placement increased Cd uptake from the CSP fertilizer but slightly depressed uptake from DAP.

Downward movement and transformation of phosphorus in soils after long-continued fertilizer application to coconut (Cocos nucifera)

SummaryDeterminations of sodium bicarbonate (pH 8·5) extractable P made on profiles of a sandy loam soil 7 and 8 years after fertilizer application to coconut in the Dry zone of Sri Lanka showed that the downward movement of P from concentrated superphosphate was greater than from rock phosphate (saphos). The surface layers (0–15 cm) of soil given concentrated superphosphate had higher P values (60 and 89 mg/kg for the 8th and 9th year respectively) than those given rock phosphate (3 and 16·5 mg/kg). At 40 cm depth the concentrated superphosphate treatment had 6 and 30 mg P/kg but the rook phosphate treatment had almost zero P at and below 40 cm.Phosphorus in the soil profile 8 years after fertilizer application was fractionated by the method of Chang & Jackson. Concentrated superphosphate treatment increased the Al-P and to a lesser degree Fe-P and Ca-P. Rock phosphate treatment increased the Ca-P and to a lesser extent Fe-P and Al-P. Phosphorus concentration in the 14th leaf was significantly correlated with Al-P, Fe-P and NaHCO3-P but not with Ca-P and organic P.The significance of the findings to phosphorus fertilizer application to coconut is discussed.

Phosphorus Fertilizer as a By‐product of Energy Production from Agricultural Wastes

AbstractThree pot experiments were conducted to test the utilization of ash from different kinds of animal manures and vegetative crop residues as source of phosphorus fertilizer. Corn (Zea mays L.) yield grown on phosphorus‐deficient soil (Aiken loam), treated with acidified ash at rates equivalent to 200, 400, 800, and 1,200 ppm P, responded almost like concentrated super phosphate (CSP) at the same rates.Yields from pots treated with ash acidified at 50% of its base equivalent were slightly less than those at 100% acidification. The leached acidified ash of agricultural waste materials proved to be a comparable source to CSP fertilizer.