EXTRACTABLE PHOSPHORUS AS AFFECTED BY HUMIC ACID APPLICATION IN SALT AFFECTED SOILS

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1 Sarhad J. Agric. Vol. 26, No. 3, EXTRACTABLE PHOSPHORUS AS AFFECTED BY HUMIC ACID APPLICATION IN SALT AFFECTED SOILS M. SHARIF, ABIDA, M.J. KHAN and IZHAR-UL-HAQ Department of Soil and Environmental Sciences, KPK, Agricultural University, Peshawar Pakistan. ABSTRACT To use of organic fertilizer sources for increasing crops production on sustainable basis has become imperative because the cost of chemical fertilizers is high. An experiment was conducted during 2006 on two saltaffected soils of District Charsadda to evaluate the effect of different levels of single super phosphate (SSP) alone and in combination with humic acid (HA) on phosphorus availability in an incubation study. Humic acid was applied at the rate of 0, 0.5 and 1.0 kg ha -1, while SSP was applied at the rate of 0, 60, 90 and 120 kg ha -1. Soil treated with different levels of SSP alone or reinforced with HA showed an initial decline in NaHCO 3 extractable P in the first 7 or 14 days and then rapid mineralization up to 84 days of incubation. The highest mean available P was recorded as 21.1 mg kg -1 in Majokay and 16.5 mg kg -1 in Meerabad soils. Weekly turnover increased at 0, 60, 90 and 120 kg P 2 O 5 ha -1 alone or reinforced with HA. The highest weekly P turnover rate in Majokay soil was 0.31 mg P kg -1 soil and in Meerabad 0.51 mg P kg -1 soil treated with 120 kg P 2 O 5 and 1.0 kg HA ha -1. Humic acid increased mineralization potential of 0, 60, 90 and 120 kg P 2 O 5 ha -1. The highest mineralization potential of Najokay soil was 14.9 kg P ha -1 season -1 and that of Meer abad soil was 24.8 kg P ha -1 season -1 treated with 120 kg P 2 O 5 ha -1 reinforced with 1.0 kg HA ha -1. Therefore, the results show that application of 120 kg SSP ha -1 reinforced with HA may be considered as an optimum dosage for the improvement of P mineralization in prevailing soil conditions. Key Words: Phosphorus mineralization, Single super phosphate levels, humic acid, Soil location and Incubation period. Citation: Sharif, M., Abida, M.J. Khan and I. Haq Extractabel phosphorus as affected by humic acid application in salt affected soils. Sarhad J. Agric. 26(3): INTRODUCTION The principal threats to sustainability of irrigated agriculture in Pakistan and the world are water logging and salinity. Pakistan has 6.2 million hectars area lying barren due to twin menace of salinity and water logging (Muhammad, 1993). Out of the total cultivated area in Pakistan, about 3.2 m ha at national level including m ha in KPK is salt affected (Chaudhry et al., 1978) resulting from natural as well as anthropogenic causes. Most of these lands are saline-sodic and sodic in nature, which restrict the hydraulic properties due to dispersion, translocation and deposition of clay platelets in the conducting pores as the dominant mechanism. The significant role of phosphorus in building up and sustaining land fertility has long been recognized by agricultural workers and farmers all over the world. In spite of the marked advancement in our knowledge about phosphorus behavior in soil, our understanding about phosphorus dynamics in the soil plant system is still far from completion. The dynamics of phosphorus transformation in the soil system and its fixation and released characteristics have been the subject of numerous research investigations (Dibb, 1990 and Glendinning, 1990) but in actual practice the most pertinent issue is to know how much phosphorus can be made available to growing crop from the native soil pool. Soils of Pakistan are generally deficient in nitrogen and 80% of them lack adequate content of phosphorus (Salim et al., 1986). Although the P content of our soils is adequate, their specific characteristic such as high ph and CaCo 3 contents and sodicity for hamper its availability to crops (Archer, 1988). Moreover, in contrast to nitrogen, no biological addition is available to phosphorus. Thus a great majority of soils need extraneous supplementation of phosphorus of sustained crop yield. Humic Acid (HA) is the active constituent of organic humus, which can play a very important role in soil conditioning and plant growth (Bendetti et al., 1996). Physically, it promotes good soil structure and increases the water holding capacity of the soil; biologically it enhances the growth of useful soil organisms, while chemically it serves as an adsorption and retention complex for inorganic plant nutrients (Brannon and Sommers, 1985). Humic

2 M. Sharif et al. Extractable phosphorus as affected by Humic Acid application 382 acid is a naturally occurring polymeric organic compound and is designated by nature to perform a wide variety of functions (Schnitzer and Khan, 1972; Sposito, 1989). It is produced through decay/oxidation of organic matter through microbial action and is naturally found in soil, peat, rivers, oceans and in lignitic coals (Lawson and Stewart, 1989). It can convert elements into forms suitable for assimilation by plant due to its ability to form complexes (Vaughan and Donald, 1976) and can break Fe or Al bond P in acidic soil and that with Ca in alkaline soil and release this P in soil solution and thus improves its availability for plant growth (Malcolm and Vaughan, 1979; Hajra and Debnath, 1987). Humic Acids have been complexed with sodium, potassium, manganese, zinc, calcium, iron, copper and with various other elements to overcome a particular element deficiency in soil (Yingei, 1988). The physicochemical activity, the structure and the mechanism of the stimulating effect of HA on various crops and soil conditions have been envisaged by various workers (Malik et al., 1979). It contains 51-57% organic C, 4-6% N and 0.2 to 1% P and has potential to improve crops yield due to its capability of supplying N and P to the plants together with the improvement in the physicochemical and biological environment of the soils (Brannon and Sommers, 1985). The utilization of humic acid can be made effectively to boost up agricultural production. Pots and field experiments conducted by this group (Sharif et al., 2002 a and 2002 b) on calcareous soil showed increases in crops yield ranging from 25 to 40 %. To take advantage of the facts that HA offers great promise for agricultural utilization; we investigate the affect of different levels of SSP alone and in combination with HA on phosphorus mineralization in the laboratory incubation experiment using salt-affected soils of two different locations of district Charsadda, KPK. MATERIALS AND METHODS In order to monitor changes in AB-DTPA extractable soil P resulting with the addition of humic acid and fertilizer phosphorus, an experiment was conducted in the laboratory of Soil and Environmental Sciences, KPK Agricultural University, Peshawar during the year 2006 using an incubator. Two hundred gram soil was taken in wide mouth plastic containers of diameter and height of 8.25 cm each and mixed with different levels of fertilizer SSP alone and in combinations with HA. There were 12 treatments and 4 replications of the experiment containing 0, 60, 90 and 120 kg ha -1 P 2 O 5 and 0, 0.5 and 1.0 kg ha -1 HA. One replicate of each treatment was placed in each of three chambers of incubator in completely randomized design (CRD) at 25 o C and incubated for 12 weeks using the incubator technique of Jenkinson and Powlson (1976). Soils in the bottles were kept at field capacity level by the addition of distilled water with the help of Pasteur pipette to compensate of moisture loss. AB-DTPA extractable phosphorus was measured with the help of Spectronic 601 spectrophotometer at 0, 7, 14, 28, 56 and 84 days of incubation interval (Soltanpur and Schwab, 1977). Mean available P was determined by adding extractable P at 0, 7, 14, 28, 56 and 84 days of incubation and then divided by total number of observations. The change in P content (Weekly turnover) was calculated by subtracting the initial P extracted by AB-DPTA at time zero from the final P extracted after 12 weeks of incubation and dividing by total numbers of weeks. Mineralization potential in kg P ha -1 week -1 was calculated by multiplying P content week -1 with 2. Mineralization potential season -1 was calculated by multiplying mineralization potential week -1 with 26.Composite soil samples of the salt affected area of district Charsadda were collected at depth of 0-20 cm and analyzed for various physicochemical properties using standard analytical procedures. Soil texture was determined by hydrometer method as described by Koehler et al., (1984). AB-DTPA extractable P was analyzed by the method as described by Soltanpour and Schawab (1977). Soil ph and electrical conductivity were determined in soil and water suspension of 1:5 by McClean (1982). Soil organic matter content was determined by using K 2 Cr 2 O 7 as an oxidizing agent as described by Nelson and Sommer (1982). Alkaline earth carbonate and bicarbonate, Na, Ca+Mg and SAR in soils under investigation were determined by the methods as outlined by Black, Lime was determined by the method of Richard, 1954, while moisture content of the soil was determined by the method of Atkinson et al., (1958). The data collected were analyzed statistically according to the procedures given by Steel and Torrie (1980) using MStatC package and least significant difference (LSD) test was used for any significant difference among the treatments. RESULTS AND DISCUSSION Composite soil samples were collected from two locations i.e., Majokay and Meer Abad of the saltsaffected areas of District Charsadda during Data showed that soils of both sites were silty clay loam, highly alkaline in reaction with ph values greater than 8.0, moderately calcareous with lime content less than 15%.

3 Sarhad J. Agric. Vol. 26, No. 3, Electrical conductivity of Majokay soil was 5.6 dsm -1 with 1.1% of organic matter content and that of Meer Abad was 3.9 dsm -1 with 0.79% soil organic matter content. Soluble cations and anions and AB-DTPA extractable nutrients concentration of the soils under investigation are given in Table I. Table I Soluble cations and anions and AB-DTPA extractable nutrients concentration of the soils under investigation. Nutrients Majokay soil Meer Abad soil SAR (mmol L -1 ) - Na Ca ++ + Mg CO HCO (mg kg -1 ) - AB-DTPA extractable P " K " Mn " Zn " Fe " Cu Concentration of AB-DTPA Extractable P at different Levels of Incubation Period AB-DTPA extractable P was determined at 0, 7, 14, 28, 56 and 84 days of incubation in the laboratory. Two soils of different locations Majokay and Meer Abad area of district Charsadda were used for P mineralization. The results (Table II and III) show that a slow and gradual increase in AB-DTPA extractable P up to 84 days of incubation in soils of both locations when treated with 0.5 and 1.0 kg HA ha -1 alone and was more pronounced in soils treated with HA and SSP. Mean extractable P values were 19.2 and 21.1 mg kg -1 soil in Majokay and 14.3 and 16.5 mg kg -1 soil in Meer Abad when treaded with 0.5 and 1.0 kg HA ha -1 with 120 kg SSP ha -1, respectively. Lower extractable P concentrations of 6.8 and 5.1 mg kg -1 soil were observed in Majokay and Meer Abad, respectively when not treated with HA (Table II-III). Data indicate that AB-DTPA extractable P in soils of both sites treated with 60 kg P 2 O 5 ha -1 alone decreased in first 14 days and then rapid mineralization was recorded up to 84 days of incubation, while 60 kg P 2 O 5 in combination with 0.5 and 1.0 kg HA ha -1 showed rapid initial decline up to 7 days followed by rapid release up to 84 days. Similar results were obtained for the treatments receiving 90 kg P 2 O 5 and 120 kg P 2 O 5 ha -1 alone and in combination with 0.5 and 1.0 kg HA ha -1 (Table II - III). Table II Effect of different levels of SSP alone and in combination with HA on P availability during incubation of soil of Majokay Incubation period (day) Mean Available P P 2 O 5 HA (Kg ha -1 ) AB-DTPA Extractable P (mg kg -1 soil) (mg kg -1 soil) j i g f hi h e e d c b a Mean d e de c b a * Means with different letter(s) in column and rows are significantly different at P<0.05.

4 M. Sharif et al. Extractable phosphorus as affected by Humic Acid application 384 Table III Effect of different levels of SSP alone and in combination with HA on P availability during incubation of soil of Meer Abad. Incubation period (days) Mean Available P P 2 O 5 HA (mg kg -1 soil) (Kg ha -1 ) AB-DTPA Extractable P (mg kg -1 soil) k j h g j i f e d c b a Mean 9.41 e 9.28 e 9.63 d c b a * Means with different letter(s) in column and rows are significantly different at P<0.05. Values of extractable P were increased with 0, 60, 90 and 120 kg P 2 O 5 ha -1 applied alone or reinforced with HA. Highest mean extractable P was recorded in the treatment receiving 120 kg P 2 O 5 ha -1 in combination with 1.0 kg HA ha -1. Percent increases in mean extractable P in soil of Majokay due to 0.5 kg HA ha -1 against 0, 60, 90 and 120 kg P 2 O 5 ha -1 were 23%, 19.7%, 4% and 11.8% and due to 1.0 kg HA ha -1 against 0, 60, 90 and 120 kg P 2 O 5 ha -1 were 28.0%, 18.3%, 8.3% and 9.9%, respectively. The increases in mean extractable P in soil of Meer Abad due to 0.5 kg HA ha -1 against 0, 60, 90 and 120 kg P 2 O 5 ha -1 were 50.9%, 6.5%, 5.6% and 5.7% and due to 1.0 kg HA ha -1 were 63.8%, 6.0%, 15.1% and 15.6%, respectively (Table II and III). Turnover and Mineralization Potential of Phosphorus Weekly P turnover and mineralization potential in soil of Majokay and Meer Abad, district Charsadda as influenced by different levels of SSP alone and in combination with HA are presented in Table IV - V. Data indicate that the rate of changes of extractable P (weekly turnover) ranged from to mg P kg -1 soil of Majokay soil treated with different levels of SSP alone and in combination with HA and ranged from 0.13 to mg P kg -1 soil for soil of Meer Abad area treated with different levels of SSP alone and in combination with HA, while it was P kg -1 soil for control of Majokay soil and mg P kg -1 in soil of Meer Abad area. Weekly turnover increased at 0, 60, 90 and 120 kg P 2 O 5 ha -1 applied alone or reinforced with HA. Highest weekly turnover of mg P kg -1 soil and mg P kg -1 soil were recorded in Majokay and Meer Abad soils, respectively treated with 120 kg P 2 O 5 ha -1 and 1.0 kg HA ha -1 (Table IV -V). Table IV Effect of different levels of SSP alone and in combination with HA on weekly turnover and mineralization potential of soil of Majokay, district Charsadda. Incubation period Weekly Mineralization P 2 O 5 HA 0 84 Turnover potential (Kg ha -1 ) (days) (mg P kg -1 soil) (kg P ha -1 season -1 )

5 Sarhad J. Agric. Vol. 26, No. 3, Data show that HA could increase mineralization potential of 0, 60, 90 and 120 kg P 2 O 5 ha -1. Highest mineralization potential of 14.9 kg P ha -1 season -1 was recoded for the treatment receiving 1.0 kg HA ha -1 with 120 kg P 2 O 5 ha -1 followed by 14.8 kg P ha -1 season -1 in the treatment receiving 1.0 kg HA ha -1 with 90 kg P 2 O 5 ha -1 in soil of Majokay area, while higher mineralization potential of 24.8 kg P ha -1 season -1 was found for the treatment receiving 120 kg P 2 O 5 ha -1 reinforced with 1.0 kg HA ha -1 followed by 18.5 kg P ha -1 season -1 in the treatment receiving 90 kg P 2 O 5 ha -1 reinforced with 1.0 kg HA ha -1 in soil of Meer Abad area. Table V Effect of different levels of SSP alone and in combination with HA on weekly turnover and mineralization potential of soil of Meer Abad, district Charsadda. Incubation period Weekly Turnover Mineralization potential P 2 O 5 HA 0 84 (Kg ha -1 ) (days) (mg P kg -1 soil) (kg P ha -1 season -1 ) It was observed that P mineralization potential increased with the increase in levels of P fertilizers applied alone and in combination with different levels of HA. The highest mineralization potential was recorded in the treatment receiving120 kg P 2 O 5 ha -1 reinforced with 1.0 kg HA ha -1 in both soil may be due to P mineralization capability of HA. These results are in agreement with the findings of Enwezor (1976) who studied P mineralization in air dried samples at 30 C and reported that 6.6 mg P kg -1 soil was mineralized after 12 weeks of incubation (0.55 mg P kg -1 week -1 ). Hedley et al., (1982) found that 9 months incubation caused labile P (resin plus bicarbonate P) to decrease by 11 mg P kg -1 soil (0.3 mg P kg -1 soil week -1 ). CONCLUSION It is concluded that soil treated with different levels of SSP alone and reinforced with humic acid showed an initial decline in AB-DTPA extractable P in first 7 and 14 days and then rapid mineralization up to 84 days of incubation period. The application of SSP at the rate of 120 kg P 2 O 5 ha -1 reinforced with 1.0 kg HA was more effective in making the soil environment conducive for soil phosphorus mineralization and hence for plant nutrients availability under the given soils conditions. Addition of HA with SSP for improving crops production is feasible for being indigenous raw material, single micro dose application and reduced cost of transportation and distribution. REFERENCES Archer, J Crop nutrition and fertilizer use. Farming Pess Ltd., Ipswich, Suffolk. Atkinson, H.J., G.R. Giles and J.R.Wright Chemical methods of soil analysis. Chem. Div. Sci. Services, Canad. Deptt. of Agric. Ottawa, Canada. Benedetti, A., A. Figliolia, C. Izza, S. Canali and G. Rossi Some thoughts on the physiological effects of humic acids; interaction with mineral fertilizers. Agrochime. 40:5-6, Black, C.A Methods of Soil analysis part-ii. Amer. Soc. Agron. Inc. Madison, Wisconsin, USA. Brannon, C.A. and L.E. Sommers Preparation and characterization of model humic polymers containing organic P. Soil Biol. Biochem.17:2, Chaudhry, M.B., M.A. Mian and M. Rafiq Nature and magnitude of salinity and drainage problems in Pakistan. Pak. J. Forestry. 28 (2): Dibb, D.W., P.E. Flexen and L.S. Murphy Balanced fertilization with particular reference to phosphates. Fert. Res. 26: Enwezer, W.O Mineralization of N and P in organic materials of varying C: N ratios. Plant & Soil. 44:

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