DIFFERENT FORMS OF POTASSIUM IN SOME SOILS OF CENTRAL SOUTHERN NIGERIA

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1 Indian J. Agric. Res., 39 (4) : , 2005 DIFFERENT FORMS OF POTASSIUM IN SOME SOILS OF CENTRAL SOUTHERN NIGERIA 1.0. Osernwota, A. Izevbigie, I.A. Ogboghodo and E.A. Aghirnien 1 Department of Soil Science, Ambrose Alii University, Ekpoma, Nigeria ABSTRACT In twenty composite surface (cm) and sub-surface (cm) soil samples coliected from different locations of Central Southern Nigeria, total, fixed, exchangeable and water soluble K Contents of the soils ranged from 300 to 1400, 27.8 to 109.2, 7.2 to 115 and 1.2 to mg/kg, respectively. Clay was negatively and significantly correlated with total K (r = -0.32*) and water Iuble K (r = -0.43**) whereas ph was positively and significantly correlated with total K (r = 0.51 eo,. The distribution of K in these soils appeared to be influenced by parent material, its deljree of weathering, and ph. Ninety per cent of the soils were deficient in exchangeable K. INTRODUCTION Soil Potassium exists in different forms such as soil solution, exchangeable cation and non-exchangeable as well as in mineral phases. The water soluble and exchangeable K are the main sources of K for crop but there are reports that plant can utilize considerable amount of non-exchangeable fixed K (Malavolta, 1985, Subba Rao, 1993). If the exchangeable K is removed by crops, more potassium would become exchangeable from the non-exchangeable form (Maurya and Gosh, 1972) and it showed a dynamic equilibrium among different forms of K. Ano (1994) evaluated the forms and distribution of potassium in some Southern Nigerian toposequences and concluded thatthe concentrations of the different forms of potassium were higher in the valley bottom profiles, low in the profiles on the crest and intermediate in the profiles of middle slope. Ana (1991) further reported what K status in coastal plain soils of Nigeria is greatly influenced by organic matter and soil ph. Further, K deficiency in some Ultisols of the defunct Bendel State of Central Southern Nigeria was reported by Osemwota et aj. (191) but information regardingk status in soils of Central Southern Nigeria is lacking and hence present investigation was carried out. MATERIAL AND METHODS The study area is located in between 5 45' and 7 38' latitude 5 4' and 6 31' longitude (Bast of the equator). The soil samples were collected from different locations within Central Southern Nigeria based on cropping history. In all the locations, composite soil samples were taken from depth em and em for surface and sub-surface soil, respectively. Core soil samples were taken from six points of about 5-10 m apart and bulked into bags. Composite samples were air dried, thoroughly mixed, crushedand sieved through 2 mm sieve and preserved in plastic containers with cover in dry cool place. ANALYTICAL PROCEDURE: Particle size analysis of the soil was done by the hydrometer method (Bouyoucos. 1951) with Calgon as the soil dipensiorg agent. Soil ph (1: 1 soil - water ratio) was determined with Bechman ph meter using a glass electrode. Organic carbon was determined by dichromate wet oxidation method of Walkley and Black (1934). I Department of Chemistry, Nigerian Institute for Oil Palm Research (NIFOR). Benin City. Nigeria.

2 250 INDIAN JOURNAL OF AGRICULTURAL RESEARCH Exchangeable cations and effective cation exchange capacity were determined by extracting the soil with INN.H 4 0A c (Schollenberger and Simon, 1945) atph 7. Exchangeable Na and Ca were determined by flame photometer while Mg was determined by atomic absorption spectrophotometer. Summation of exchangeable bases and exchange acidity gave ECEC value. Total nitogen was determined by Kjeldahl method. Free Fe and AI oxides were determined by dithionate citrate bicarbonate method (Mehra and Jackson, 1960). Water soluble and exchangeable K were determined in processed soil samples (2mm) and for other forms 100 mesh soil samples were used. Water soluble K was extracted in 1: 2 soil - water suspensions after shaking for two hours and allowing them to stand for an additional sixteen hours (Maclean, 1961). Exchangeable K was extracted from soil with INNH 4 0A c buffered at ph 7. The value includes both water soluqle and exchangeable forms. Water soluble K was subtracted from this value to obtain exchangeable K. Fixed K or nitric acid soluble K was obtained by extracting the soil with IM1N0 3 in 1 : 10 soil- acid suspension after ten minutes ofboiling. The difference between the value obtained and that of exchangeable K was styled difficultly exchangeable K (Graley et a/., 1960) or mobile K reserve (Wood and De Turk, 1941). Total K was obtained by digesting the soil with HF - HCIO.. mixture (Pratt, 1965). The K in the extracts were: determined by flame photometer (Model EEL). RESULTS AND DISCUSSION The salient physical and chemical properties of the soils are shown in Table 1. The soils had sand to loam in texture. The clay contenttendedto increase with depth. Thesoils were strongly to moderately acidic in reaction. These properties reflected that soils are highly weathered.. The ECEC, organic matterandtotal "P,, L':;/ nitrogen contents were generally low. Total K content of the soils ranged from 300 to 1400 mg/kg with a mean of mgjkg. In the surface and sub-surface soils, it ranged from 300 to 1400 mgjkg, 300 to 900 mgjkg with means of 599 and 462 mgjkg, respectively (Table 2). Total K content of the surface soils appeared higher than that of the sub-surface soils (on average basis). The total K content of the soils were generally low as compared to values obtained by Udo and Olajide (1981) in some ferruginous tropical soils. The ph was positively and significantly correlated with total K (r = 0.51***). Ano (1991) also observed strong relationships between total K and soil ph in coastal plain soils of Nigeria. On the basis of parent materials, the average total K values were 803.0, 545.0, 486.7,476.7,472.5 and mg/kg for soils from Basementcomplex, Imo Clay-Shale group, Bende-Ameki group, Colluvial/Alluvial material, coastal plain sand and false bedded sandstone, respectively. The Basement complex soils had higher total Kcontent (on average basis) than coastal plain soils (Table 2). This may be due to the fact that the Basement complex soils are derived from igneous and metamorphic rocks that are rich in K - bearing minerals whereas the coastal plain soils are derived from sedimentary rocks which are poor in K - bearing minerals. The tow total K content of most of these soils is also due to the fact that they are highly weathered. Clay content was negatively and significantly correlated with total K (r = 0.32*). Fixed K ranged from 27.8 to mglkg with mean of mgjkg. In the surface and sub-surface soils, it ranged from 27.8 to 102.1, 38.0 to mg/kg with means of and mg/kg, respectively. Based on parent materials, the average fixed Kvalues were 66.1,60.2,60.0,,

3 N (J'I... Table 1. Physico-chemical properties of soils in Central Southern Nigeria S.No. Location Taxonomy Depth ph O.M. Exchangeable bases Exchange ECEC Fep3 A1P3 Sand Sift Clay (Sub-group) (em) (HP) % acidity cmol (PI kg 1 % % % % % Ca Mg Na K cmol (p) kgl H+ A13+ Cmol (pi kg.1 1 Emwinyomwanru Typic Paleudult Ojekere Farms Arenic Tropulstalf Yusuf Kadiri Farms Rhodic Paleustalf w (Agbede) Obadan Rhodic Paleudult z Umokhu Nokhua Typic Paleudult N Uzea Rhodic Paleustalf (J'I !billo Arenic Tropustalf SOOO - OgOO Lithic Haplustalf km from Ayodo Typic Ustipsamment Ugonoba Rhodic Paleudult '

4 S.No. Location Taxonomy Depth ph O.M. Exchangeable bases Exchange ECEC Fep3 A1P3 Sand Silt Clay (Sub-group) (em) (HP) % acidity c mol (p) kg., % % % % % Ca Mg Na K c mol (pi kg., H+ A(3+ Z c mol (p) kg., 0 > 11 Ehor Rhodic Paleudult z University Farm Rhodic Paleudult c (Ekpoma) z 13 Melina Forest Lithic Troporthent » r f Iyanomo (51 Km Typic Paleudult » to Okene from Auchi) C) 15 Agenebode Typic Paleudult c 16 CRiN Typic Paleudult Uteh-Benin City Rhodic Paleudult r NIFOR Rhodic Paleudult m Ebelle Typic Tropudalf n :c 20lrrua Rhodic Paleudult l'v 01 l'v n

5 Vol. 39. No Table 2. Distribution of different forms of potassium in soils of Central Southern Nigeria S.No. locatlon Parent material Depth (em) H,o Soluble K Exchangeable K FixedK TotalK mglkg mg/kg mg/kg mg/kg 1. Emwinyomwanru Coastal plain sands Ojekere Farms lmo clay-shale group Yuslif Kadiri Farms Imo clay-shale group Obadan Coastal plain sands Umokhu Nokhua Coastal plain sands Uzea False bedded sandstone !billo Basement complex Sobe - Ogbe Basement complex 9 1 km from Ayodo Colluvial/alluvial material Ugonoba Costal plain sands Ehor Coastal plain sands University Farm Bende - Ameki group (Ekpomal Melina Forest Basement Complex yancmo Coastal plain sands (51 Km to Okenel Agenebode Colluvial/alluvial material CRIN Bende-Ameki group Uteh-Benin City Coastal plain sands NIFOR Coastal plain sands Ebelle Colluvium derived from Sand stone lrrua Coastal plain sands Table 3. Coefficients of correlation between forms of potassium and soil physico and chemical properties Water soluble K Exchangeable K Fixed K Total K ph (Hpl """ ECEC O.M Clay -0.43" " Silt Sand Fe A1P Significant at 5% level;.. Significant at 1% level; """ Significant at 0.1% level.

6 254 INDIAN JOURNAL OF AGRICULTURAL RESEARCH 55.7, 55.3 and 49.9mglkg for soils from colluvial/alluvial material. Imo Clay-Shale group, coastal plain sands, Basement complex, Bende-Ameki group and false bedded sandstone, respectively. The sub-soils appeared to fix more K than surface soils. Fixed K in the soils constituted per cent of the total K content but fixed K was not influenced by clay content of these soils (Table 3). It inferred the possibility of kaolinite dominted clays in soil. These soils may be considered to have inadequate level of mobile K reserve considering the values reported by Ekpete (1972). Rxed Kwas noi significantly correlated with any of the soil properties (Table 3). Exchangeable K varied from 7.2 to mglkg with a mean of mg/ kg. In the surface soils, it ranged from 13.8 to mglkgwhereas in the sub- surface soils, it varied from7.2 to mglkg with means of and mg/kg (Table 2), respectively. Exchangeable K content of the surface soils was higher than that of the subsoils (average basis). May be due to the influence of soil organic matter. On the basis of parent materials, the average exchangeable K values were 57.3, 37.5, 23.6, 21.9 and 20.1 mglkg for soils from Basement complex, Imo clay-shale group, coasted plain sands. Bende-Ameki group, Colluvial/Alluvial material and False bedded sandstone. respectively. Exchangeable K constituted 5.86 per cent of the total K content of the soils. Exchangeable Kwas not significantly correlated with any soil properties. Considering the critical level (78 mglkg) proposed by Haylock (1956), 90 per cent of the surface soils appearea deficient in exchangeable K. Water soluble Kin these soils appeared to below. It ranged from 1.2 to 18.0 mglkg with a mean of 6.01 mglkg. In the surface and sub-surface soils, it ranged from 2.6 to 18.0 mglkg. 1.2 to 10.4 mglkg with means of 7.53 and 4.50 mglkg, respectively. The clay content was negatively and significantly correlated with water soluble K (r = 0.43 ). Water soluble K constituted 1.11 per cent of the total K content of the soils. Based on parent materials, the average water soluble K values were , 3.4,3.2 and 2.0 mglkg for soils from Basement complex. coastal plain sands, Bende-Ameki group, colluvial/alluvial material and false bedded sand stone. respectively. CONCLUSION The soils under investigation are sand to loamy sand in texture with low ph, ECEC. total nitrogen and organic mattercontents. The soils appeared to have low levels of water soluble K and fixed K (mobile K reserve) to satisfy the needs of crops. The variation in the distribution of K in these soils appeared to be influenced by parent material. its weathering and ph. REFERENCES Ano. AA (1991). J. Potassium Res., 7: Ano. AA (1994). J. Potassium Res.. 10: Bouyoucos. G.H. (1951). Agron. J., 43: Ekpete. D.M. (1972). Georderma, 8: Graley. A.M. et al. (1960). Aust. J. Agric. Res., 11: Haylock. O.F. (1956). In: Methods of Soil Analysis Part 2. Agron. Mono. No.9. AS.A.. Madison. U.S.A. Malavolta. E. (1985). In: Potassium in Agriculture. (Munsen, R.EK ed.). AS.A., Madison. WI. P Maurya. R.R. and Gosh. AB. (1972). J. Indian Soc: Soil Sci., 20: Mclean. AJ. (1961). Can J. Soil Sci., 41: Mehra. O.P. and Jackson. M.L. (1960). In: Proc. 7 th Nat. Conf. on Clays and Clay Minerals. P Osemwota et al. (1991). Niger. J. Soil Sci.. 10:

7 Vol. 39, No.4, Pratt, P.F. (1965). In: Metl10d of SOU Analysis Part 2. (Black, C A. ed.). Agron. No.9 Am. Soc. Agron. Inc. Madison, Wise. U.S.A. Schollenberger, C.J. and Simon, R.H.(1945). Soil Sci.. 59: Subba Rao, A. (1993). J. Potassium Res., 9: Udo, E.J. and Olajide (1981). Niger. J. Soil Sci., 1: Walkley, A. and Black, L.A. (1934). Soil Sci., 37: Wood, LK and De Turk, E.E. (1914). Soil Sci. Soc. Am. Proc., 5: