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Research Article

Effect of Incubation Period on the Phosphate Adsorption in Seven Soil Series of Pakistan

Muhammad Yaseen, Nisar Ahmad, Abdul Razzaq and Nasir Mahmood
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A laboratory experiment was conducted to study the effect of incubation period on the phosphorus adsorption by the Pindorian, Satghrah, Shandara, Wazirabad, Balkassar, Hafizabad and Missa soil series of Pakistan. Five levels of P (50, 100, 200, 400 and 800 μg P/g of soil) were added to these samples and incubated for 1, 7 and 15 days. Results showed that the amount of adsorbed P increased by increasing the incubation period from 1 to 15 days. The highest adsorption was found after 15 days incubation period and lowest P was adsorbed after incubation period of one day in all the soils and each level of P application.

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  How to cite this article:

Muhammad Yaseen, Nisar Ahmad, Abdul Razzaq and Nasir Mahmood, 1999. Effect of Incubation Period on the Phosphate Adsorption in Seven Soil Series of Pakistan. Pakistan Journal of Biological Sciences, 2: 357-359.

DOI: 10.3923/pjbs.1999.357.359



The supply of P is much important in arid/semi arid regions where its availability is a problem due to its adsorption/ precipitin on CaCO3 and clay contents. These reactions convert the added P into insoluble or less soluble phosphate compounds and the availability of added P to plants hampered. Transformation of P into insoluble and slowly soluble compounds is considered as primary cause of the in efficient utilization of phosphate fertilizers (Sharpley, 1983). Chaudhry and Qureshi (1980) reported the average phosphorus fixation of 71, 62, 56 and 29 per cent of the added P in clayey, clay loam, sandy loam and loamy sand soils respectively after one month of incubation. Agbenin and Tiessen (1995) investigated the time dependent phosphate sorption and found that after 50 days, sorption approached a steady state in all soils. Mendoza and Barrow (1987) incubated the five Argentinean soils for period of up to 60 days and found that the amount of P extracted from the soil decreased as the period and temperature of incubation increased. Biswas and Ghoshi (1988) found a decrease in recovery of added P in alkaline alluvial soils with the increase in time and temperature of incubation. Garcia-Rodeja and Gil-sotres (1995) found that the concentration of desorbed P increases with time.

The objective of the present study was to investigate the effect of incubation period (time of contact between soil and P1 on the phosphate adsorption.

Materials and Methods

A laboratory study was conducted in the Department of Soil Science, University of Agriculture, Faisalabad. Surface (0-15 cm) soil samples of Pindorian, Satghrah, Shandara, Wazirabad, Balkassar, Hafizabad. and Missa were collected, dried, ground and sieved through a 2 mm sieve. The soil samples were analysed for EC, pH, texture (Moodie et al., 1959) and CaCO3, (Richards, 1954) (Table 1). Phosphorus was extracted by NaHCO3 and analysed by using the method described by Watanabe and Olsen (1965).

Incubation experiment: Duplicate samples of 2.5 g from each soil were mixed with 25 ml solution of KH2PO4 prepared in 0.01 M CaCI2, containing 5, 10, 20, 40 and 80 μg P ml–1 in a centrifuge tube. Similarly, two more sets of centrifuge tubes were prepared by taking 2.5 g soil and adding 25 ml of each solution. After 24 hour shaking at 25°C, the first set of tubes were centrifuged immediately while the second and third set were incubated for 7 and 14 days respectively, following shaking daily for an hour. After incubation, these sets were also centrifuged at 2500 rpm for 5 minutes. The supernatant was filtered through whatman filter paper No. 42 and filtrate was used for P analysis. The difference between the amount of P added to the soil samples and estimated from the filtrate gave the amount of adsorbed P.

Results and Discussion

The amount of P adsorbed by the soils after the incubation period of 1, 7 and 15 days, is presented in Table 2, 3 and 4 respectively. Results showed that by increasing the time of incubation, the P-adsorption was increased in all the soils. The highest amount of adsorbed P was found after an incubation period of 15 days and minimum adsorption was observed after 24 hours incubation period at each level of P-application. In the Pindorian soil, at the highest level of P-application, the maximum amount of P was adsorbed after 24 hours incubation and after that (with increasing contact time), the quantity of adsorbed P decreased. But the difference in amounts of P adsorbed after 24 hours, 7 and 15 days incubation were very small and negligible.

The Satghrah soil adsorbed 354.0 μg g–1 in 24 hours incubation, 374.5 μg g–1 in 7 days and 380.1 μg P g–1 of soil in 15 days incubation period at 80 μg ml–1 concentration in the soil solution.

Shandara soil reached to its maximum P adsorption capacity in 7 days at 5 μg P ml–1 in soil solution but at higher P concentrations 110, 20 and 40 μg ml–1), the maximum P adsorption capacity attained in 15 days incubation period. Again at highest level of P application, the maximum P was adsorbed in 7 days.

At lower rate (5 μg ml–1 p in soil solution) of P-application, the Wazirabad soil adsorbed 42.5, 44.7 and 49.2 μg P g–1 soil after a incubation period of 24 hours, 7 and 15 days.

Table 1:Physical and chemical characteristics of the soils

Table 2:Phosphorus adsorption by the soils after an incubation period of 24 hours

Table 3:Phosphorus adsorption by the soils after an incubation period of 7 days

Table 4:Phosphorus adsorption by the soils after an incubation of 15 days

At highest rate of P application (80 μg P ml–1 in soil solution), this soil adsorbed 67.3, 131.8 and 135.8 μg P g–1 soil after 24 hours, 7 and 15 days incubation period respectively.

The P adsorption capacities of the Balkassar, Hafizabad and Missa soils also increased with increasing the incubation time. The highest amounts of P adsorbed were related to the maximum incubation time (15 days) and lowest values for P-adsorption were found in minimum incubation time in all the three calcarious soils.

These results guided towards the point that the steady state condition (equilibrium) attained within 7 day incubation. The further increase in incubation time did not show the further adsorption with same rate. The reason might be that the maximum number of adsorption sit were saturated after 7 days and after that, a steady stat condition of equilibrium reached with in a period of 15 days. Tisdale et al. (1985) reported the similar results. Then reported that the amounts of P sorbed by soils are depend on the saturation of sorption complex or the number of sites available for reaction with added Agbenin and Tiessen (1995) investigated the time dependent P sorption of 5 soils and found a rapid initial phase followed by a slower sorption phase. At 50 days, sorption reached a steady state in all soils. Chand et. al. (1995) found that the steady state equilibrium in low-P fixing alluvial soils is attained within two days. The results of incubation experiments on 19 soils showed that in all soils and at all P rates, availability index decreased with time (Afif et al., 1993).

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3:  Biswas, P.P. and G. Ghoshi, 1988. Temperature effect on kinetics of P availability from partially water soluble and citrate soluble P fraction on nitrophosphate in alkaline alluvial soils. J. Indian Soc. Soil Sci., 36: 48-52.

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