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Influence of Phosphorus Fixing Agents on the Formation of Organic Phosphates in the Soil on the Addition of Phosphatic Fertilizer

A. Islam
Department of Soil Science, Dhaka University, Dhaka, Bangladesh

T. H. Khan
Department of Soil Science, Dhaka University, Dhaka, Bangladesh

Abstract/ Executive Summary:

Soil samples representing 0 - 6" depth and differing in pH, mechanical, chemical compositions were collected from Savar (Dhaka), Pak Tobacco Experiment Station (Rangpur), Benerpota Farm (Khulna), Arnritapur (Comilla), and Madaripur. Three phosphatic fertilizers - ordinary super phosphate, triple super phosphate and diammonium phosphate were included in the study. Each phosphatic fertilizer at the rate of 400 lbs of P per acre was added to 100 gms of the soils. The NH₄Cl-soluble, aluminium, iron and calcium phosphates of the soils at both moisture levels increased with the addition of fertilizers. The source of phosphorus did not appreciably affect the formation of the inorganic phosphates. The aluminium phosphates formed when fertilizers were added to the soils were not strictly governed by the pH of the soils. The correlation coefficient between aluminium phosphate formed and total AI₂0₃ contents of the soils were not statistically significant. A positive significant correlation was obtained between aluminium phosphate formed at both moisture levels and free AI₂0₃ contents of the soils. Therefore, it was concluded that these oxides were mainly responsible in fixing the added phosphates as aluminium phosphate. Coefficients of correlation calculated between iron phosphates formed at both moisture levels and the pH of the soils were significant. The negative correlation suggested that with the increased in pH of the soils, iron phosphate formation would be decreased. No significant correlation was obtained between total iron contents of the soils and the iron phosphates formed. The positive significant correlation was formed between iron phosphate formed and the free iron oxide contents of the soils. It was concluded that this form of iron was responsible for the retention of added phosphates as iron phosphate in soils. A positive significant correlation, obtained between calcium phosphate formed at both moisture levels and pH of the soils, indicated that with the increase in pH of the soils, the calcium phosphate formation also increased. Significant correlations were also obtained between calcium phosphates formed in the soils at both moisture levels and their free CaC0₃ as well as total CaO contents.

Keywords: Soil, Phosphorus, Organic phosphates, Phosphatic Fertilizer

Location: Savar, Dhaka, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

To study was conducted to observe the correlation between the inorganic phosphates formed in soils when phosphatic fertilizers were added and the phosphorus fixing agents.

Methodology:

Soil samples representing 0-6" depth and differing in pH, mechanical, chemical compositions were collected from Savar (Dhaka), Pak Tobacco Experiment Station (Rangpur), Benerpota Farm (Khulna), Amritapur (Comilla), and Madaripur. Three phosphatic fertilizers - ordinary super phosphate, triple super phosphate and diammonium phosphate were included in the study. Each phosphatic fertilizer at the rate of 400 lbs of P per acre was added to 100 gms of the soils. They were thoroughly mixed and placed in glass bottles. To each pot measured amount of water was added to bring the moisture level of the soils to approximately field capacity. The bottles were corked up and kept for the correlation study. A similar experiment was also set up to study the correlation under water logged condition. In this case, soil mixed with fertilizers were kept in glass bottles and then submerged with distilled water to a depth of about 1 inch. A blank experiment was set at each moisture level. The treatments were replicated twice. Soil samples representing each treatment were taken at the end of one week after the addition of fertilizers. Each sample was then analysed for the different inorganic phosphates following the fractionation procedure originally proposed by Chang and Jackson (1957) and subsequently modified by Chang and Liaw (1962). The methods adopted for the chemical analysis of soils are as follows: (a) pH was determined by glass electrode. The soil: water ratio was 2:5 (b) Organic carbon was determined volumetrically by wet-oxidation method of Walkley and Black, (1934). (c) Determination of total iron was carried out Colorirnetrically on an aliquot of the HCI extract of the Na₂C0₃ fusate of the soil. (d) Total AI was obtained by subtracting iron and titanium (Fe+Ti) from iron, aluminium and titanium (Fe +AI + Ti) and determined gravimetrically by precipating as hydroxides. (e) Total calcium contents of the soils were determined on an aliquot of the HCI extract of Na₂C0₃ fusate of the soils by E.D.T.A. method as described by Betz and Nolt. (f) Free ion oxide as determined by Karim's (1953) nascent hydrogen reduction method. (g) Free alumina was determined by alizarin's (0.5% solution) adsorption on an ignited mass of soil and subsequently abstracting the adsorbed alizarin by sodium oxalate buffered at pH 3.5 with oxalic acid and comparing this abstracted yellow solution with a standard solution of alizarin (quoted from Karim an Sultan, 1961). (h) Free CaC0₃ as determined by extracting the soil with dil HCI as outlined by Piper (1951).

Source of Information: Pak.J. Soil Sci. 13(1):32-43, 1967

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

A positive significant correlation, obtained between calcium phosphate formed at both moisture levels and pH of the soils, indicated that with the increase in pH of the soils, the calcium phosphate formation also increased. Significant correlations were also obtained between calcium phosphates formed in the soils at both moisture levels and their free CaC0₃ as well as total CaO contents. Therefore, it was concluded that both free CaC0₃ and other forms of calcium were able to fix added phosphorus as calcium phosphate. But the higher correlation coefficients between free CaC0₃ and calcium phosphate formed probably indicated that they were more active in reacting with added phosphates.

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