Evaluation of Chemical Extraction Methods for Available Potassium in Rice Soils of Meghalaya

Transcription

1 Journal of the Indian Society of Soil Science, Vol. 59, No. 3, pp (2011) Short Communication Evaluation of Chemical Extraction Methods for Available Potassium in Rice Soils of Meghalaya K. Laxminarayana 1, Sanjeeb Bharali and Patiram Division of Soil Science, ICAR Research Complex for NEH Region, Umiam, Meghalaya, Rice occupies 80% of the gross cropped area in Meghalaya and the total fertilizer consumption in the state was around 3.69 thousand tonnes (13.9 kg ha -1 ) with an N:P:K ratio of 6.5:1.7:1.0 in Around 15 Mha area is acidic (ph ) in the northeastern region. Deficiency of several nutrients including potassium due to erosion of top soil and unscientific methods of cultivation are responsible for lower crop productivity (Bhatt et al. 2004). Solution and exchangeable K are replenished by non-exchangeable K when the former are depleted by plant removal or leaching. Some non-exchangeable K held in the interlayers of expandable 2:1 type clay minerals such as illite and vermiculite can be released relatively easily to provide a substantial portion of the K removed by crops during the growing season (Richards et al. 1988). A potassium soil test should measure a proportional amount of the non-exchangeable K that can become available during the growing season, or it must show the relationship between readily available forms and the potential for release of non-exchangeable K over a wide range of soils (Cox et al. 1999). Various extractants have been tried for determining their suitability for fertilizer making recommendations of potassic fertilizers to rice across the globe. However such an information on universal reagent for assessing K availability in the soils of north eastern region. The present investigation was undertaken to evaluate various extractants to find out the most reliable soil test method for assessing K availability in the soils of Meghalaya. Fifty-three bulk soil samples were collected during from rice-growing areas representing six districts of Meghalaya viz., Ri-Bhoi - 21, Jaintia Hills - 6, East Khasi Hills - 8, West Khasi Hills - 6, West *Corresponding author ( klnarayana69@rediffmail.com) Present address Regional Centre of C.T.C.R.I., Dumduma Housing Board, Bhubaneswar, , Orissa Garo Hills - 7 and South Garo Hills - 5. The soils were analyzed for various forms of K viz., water soluble, exchangeable, non- exchangeable, lattice and total K. Available K in the soils was estimated by five extractants viz., 1) 1.0 N NH 4 OAc, ph 7.0 (Muhr et al. 1965), 2) 6.0 N H 2 SO 4 (Hunter and Pratt 1957), 3) 1.0 N HNO 3 (Wood and DeTurk 1941), 4) 0.5 N HCl (Garman 1957) and 5) 0.01 M CaCl 2 (Woodruff and McIntosh 1960). The soils varied widely in texture and belonged to textural classes clay loam-18, sandy clay loam-14, loam-14 and sandy loam-7, representing Ultisols, Inceptisols, Entisols and Alfisols. The soils were strongly to moderately acidic (ph ) and having 0.61 to 5.28 g kg -1 organic C and % total N; available N, P and K , and kg ha -1, respectively. Highest organic C and total N were observed in the rice soils of Upper Shillong in East Khasi Hills and Thadlaskein village of Jaintia Hills district of Meghalaya, which might be ascribed to low rate of mineralization due to lower soil ph, cooler temperature, high rainfall and lesser microbial population as well as deposition of huge amounts of fertilizer residues in the valley regions that were applied to the vegetable crops at high elevated hill tops. Five kg each of the 2.0 mm sieved soil was potted, thoroughly mixed with water and kept for submergence for 10 days. A uniform dose of 150 kg ha -1 in the form of urea in 3 equal doses at 0, 15 and 30 days after transplanting (DAT), entire P (39.3 kg ha -1 ) in the form of single super phosphate before planting were applied. Two levels of 0 and 75 kg ha -1 replicated thrice in a completely randomized block design, were applied in two equal splits in the form of muriate of potash before planting and 30 DAT. Thirty-days-old rice (cv Shah Sarang-1) seedlings were transplanted at two per hill and three hills per pot at equal spacing. Two cm standing water above the surface was maintained throughout the

2 296 JOURNAL OF THE INDIAN SOCIETY OF SOIL SCIENCE [Vol. 59 experiment and the crop was harvested at 60 DAT. The plants were washed thoroughly, oven-dried and dry matter yield (DMY) recorded. Total K in the plant samples was estimated and K uptake computed. Relative yield / relative K uptake was computed as: Relative yield/ relative K uptake = Yield/K uptake in control 100 ( ) Yield/ K uptake in K-treated pots Critical limits for available K by different extraction methods were derived by plotting scatter diagram relative yield/ uptake vs soil test values (Cate and Nelson 1965). The dry matter yield increased significantly with the addition of 75 kg ha -1 across all the soils (Table 1) with a yield response of % and relative yield of 48-83%. The K uptake ranged from 109 to 674 mg pot -1 in control and 263 to 1008 mg pot -1 in the K-treated pots with a wide variation in uptake response (27-247%). Presence of high amount of organic matter and total nitrogen in the soils of East Khasi Hills and Jaintia Hills showed lower yield and uptake response of and 30-32%, respectively. Wide variation in DMY, concentration and uptake of K by rice was observed which could be attributed to wide variations in physicochemical properties of the soil and accumulation as well as mineralization of organic matter in the valley areas, where the lowland paddy is being extensively cultivated. Total K in the soils varied from 1200 to 3950 mg kg -1 (Table 2). Water soluble K, low in all the soils, ranged from 7 to 66 mg kg -1. Exchangeable and non-exchangeable fractions of K varied from 39 to 345 and 87 to 415 mg kg -1, constituting 5.1 and 8.6% of total K, respectively. However, the lattice K constituted 85% of total K and ranged from 1028 to 3470 mg kg -1. Appreciably low levels of water soluble, exchangeable and non exchangeable of K in these soils might be due to continuous cropping in absence of additions of K through fertility (Santhy et al. 1998). The highest available K was extracted with 1.0 N HNO 3 (Table 2), ranging from 47 to 334 mg kg -1, which may be due to the fact that boiling of the soils with HNO 3 tends to cause more dissolution of fixed K into the soil solution. Extraction of soils with strong acids like 6.0 N H 2 SO 4 could also solubilize most of the fixed K. The available K extracted by NH 4 OAc ranged from 32 to 180 mg kg -1. The lowest amount of K was observed with CaCl 2, which may be ascribed to its low solubilization effect on non-exchangeable and lattice K forms. All the K availability indices showed highly significant relationship with solution and exchangeable K forms. All these extractants also showed significant relationship with non-exchangeable K which may be ascribed to release of some of the fixed K into the soil solution as and when the exchangeable K is depleted substantially or exhausted by cropping to attain the equilibrium (Sekhon et al. 1992). Ammonium acetate extractable K had significantly higher relationship with the solution, exchangeable and lattice K, emphasizing that this extractant has the potentiality to extract all forms of K and thus it could be adjudged as better method for determination of available K in these acidic soils. Exchangeable K alone accounted for 52.3% variation to the NH 4 OAc extractable K (Table 3), while the inclusion of solution, non-exchangeable, lattice and total K influences the observed variation to an extent of 18.5% to the regression. However, the solution and exchangeable K accounted for 68, 66 and 44% variation to the available K pool as extracted by H 2 SO 4, HCl and CaCl 2 methods, respectively. Water soluble and non-exchangeable K accounted for 44% variation in the HNO 3 -K, indicating that boiling of soils with HNO 3 tends to cause more dissolution of non-exchangeable K and replenishes the exchangeable and solution forms of K. Exchangeable K alone accounted for 65% variation in the K uptake by rice, emphasizing that the exchangeable form mainly contributed for K nutrition of rice. However, NH 4 OAc extractable K accounted for 54.9% variation in the K uptake, indicating its superiority over the other extractants. Water soluble and exchangeable K showed highly significant relationship (Table 4) with K uptake by rice (r = 0.63 ** and 0.65 **, respectively), indicating that these two forms mainly contributed in K nutrition of rice. Ammonium acetate extractable K showed highly significant relationship with relative yield (r = 0.80 ** ), relative K uptake (r = 0.83 ** ) and control K uptake (r = 0.74 ** ), indicating its superiority in extraction of available K with a critical limit of 194 kg ha -1 (Fig. 1). The H 2 SO 4 extractable K showed significant relationship with K uptake and it could also be considered equally efficient for K estimation with a critical limit of 210 kg ha -1 (Fig. 2). Ammonium acetate extraction method for estimation of available K was found to be better than the other methods. The H 2 SO 4 method was also found to be equally efficient for K extraction and the fertility ratings need to be modified based on the derived critical limits while recommending K fertilizers for

3 2011] FORMS AND AVAILABILITY INDICES OF PHOSPHORUS IN RICE SOILS 297 Table 1. Effect of potassium on dry matter yield and K uptake Location/ No. of Dry matter yield (g pot -1 ) Yield Relative K uptake (mg pot -1 ) Uptake Relative District soils response yield response K uptake K 0 K 75 (%) (%) K 0 K 75 (%) (%) Ri-Bhoi (26.8) (39.0) (51.6) (67) (308) (605) (109.4) (49) Jaintia Hills (26.1) (33.2) (27.8) (78) (431) (656) (53.8) (66) East Khasi Hills (30.4) (39.9) (33.3) (76) (505) (728) (50.2) (68) West Khasi Hills (29.7) (40.7) (36.9) (74) (410) (671) (77.6) (59) West Garo Hills (23.9) (39.1) (68.8) (60) (195) (487) (170.6) (38) South Garo Hills (17.8) (31.4) (78.5) (56) (167) (443) (168.2) (38) Mean CD (P=0.05) for soils CD (P=0.05) for K levels CD (P=0.05) for interaction Figures in parentheses indicate the mean values Table 2. Extraction of available potassium and its fractions in rice soils of Meghalaya District and K fraction (mg kg -1 ) K availability index ( mg kg -1 ) no. of soils Total K Water Exch. K Non Lattice K NH 4 OAc-K H 2 SO 4 -K HNO 3 -K HCl-K CaCl 2 - K soluble K exch.-k Ri-Bhoi (3043) (20) (137) (270) (2616) (77) (90) (186) (79) (62) Jaintia Hills (3683) (53) (173) (265) (3193) (153) (126) (246) (129) (87) East Khasi Hills (3413) (40) (206) (315) (2852) (117) (119) (182) (104) (80) West Khasi Hills (2775) (38) (227) (300) (2210) (114) (149) (249) (131) (139) West Garo Hills (2486) (14) (80) (164) (2228) (49) (76) (131) (55) (45) South Garo Hills (1560) (22) (91) (142) (1306) (60) (74) (127) (74) (71) Mean SEm (±) Figures in parentheses indicate the mean values

4 298 JOURNAL OF THE INDIAN SOCIETY OF SOIL SCIENCE [Vol. 59 Table 3. Step-down regression equations between forms of K with availability indices and plant growth parameters Dependent variable Regression equation R 2 NH 4 OAc-K Y = ** X * X X X X ** Y = ** X ** X ** X ** X ** Y = ** ** X * X X ** Y = ** ** X * X ** Y = * ** X ** H 2 SO 4 -K Y = ** ** X * X X X ** Y = ** ** X ** X X ** Y = ** ** X ** X ** HNO 3 -K Y = ** ** X X X X ** Y = ** ** X X X ** Y = ** ** X * X ** HCl-K Y = ** ** X * X X X ** Y = ** ** X * X X ** Y = ** ** X X ** CaCl 2 -K Y = ** ** X * X X ** X ** Y = ** ** X * X ** X ** Y = * ** X * X ** K uptake Y = * X X X X ** Y = * X * X * X ** Y = * * X ** X ** Y = * ** X * K uptake Y = ** NH 4 OAc-K H 2 SO 4 -K HNO 3 -K 0.52 HCl-K CaCl 2 -K ** Y = ** NH 4 OAc-K H 2 SO 4 -K HNO 3 -K 0.50 HCl-K ** Y = ** NH 4 OAc-K H 2 SO 4 -K HNO 3 -K ** Y = ** NH 4 OAc-K ** H 2 SO 4 -K ** Y = * ** NH 4 OAc-K ** where, X 1, X 2, X 3, X 4 and X 5 represent water soluble, exchangeable, non-exchangeable, total and lattice K, respectively; ** and * significant at 1.0 and 5.0% level, respectively Table 4. Relationship between K fractions and availability indices with plant growth parameters Forms of K / availability index Relative yield Relative K uptake DMY (control) K uptake (control) Forms of K Water soluble K 0.64 ** 0.69 ** ** Exchangeable K 0.68 ** 0.70 ** ** Non-exchangeable K 0.55 ** 0.61 ** ** Total K 0.60 ** 0.62 ** ** Lattice K 0.53 ** 0.54 ** ** K availability index NH 4 OAc-K 0.80 ** 0.83 ** ** H 2 SO 4 -K 0.67 ** 0.70 ** ** HNO 3 -K 0.58 ** 0.59 ** ** HCl-K 0.57 ** 0.60 ** ** CaCl 2 -K 0.43 * 0.44 ** ** ** and * significant at 1.0 and 5.0% level, respectively Relative yield (%) Relative uptake (%) NH 4 OAc-K (kg ha -1 ) NH 4 OAc-K (kg ha -1 ) Fig. 1. Critical limit of ammonium acetate extractable K in rice soils

5 2011] FORMS AND AVAILABILITY INDICES OF PHOSPHORUS IN RICE SOILS 299 Relative yield (%) Relative uptake (%) H 2 SO 4 -K (kg ha -1 ) H 2 SO 4 -K (kg ha -1 ) Fig. 2. Critical limit of sulphuric acid extractable K in rice soils rice in the acid soils of Meghalaya in order to enhance the K use efficiency. References Bhatt, B.P., Patiram and Verma, N.D. (2004) Reformed farming system: Improving the productivity of shifting cultivation in North-Eastern Himalayan Region. In: Soil Biodiversity, Ecological Processes and Landscape Management (P.S. Ramakrishnan, K.G. Saxena, M.J. Swift, K.S. Rao and R.K. Maikhuri, Eds.), Oxford & IBH Publishing Co. Pvt. Ltd, New Delhi, pp Cate, R.B. Jr. and Nelson, L.A. (1965) Technical Bulletin 1, International Soil Testing Service Series, North Carolina State University, Raleigh. Cox, A.E., Joern, B.C., Brouder, S.M. and Gao, D. (1999) Plant-available potassium assessment with a modified sodium tetraphenylboron method. Soil Science Society of America Journal 63, Garman, W.W. (1957) Potassium release characteristics of several soils from Ohio and New York. Soil Science Society of America Proceedings 21, Hunter, A.H. and Pratt, P.F. (1957) Extraction of potassium from soils by sulphuric acid. Soil Science Society of America Proceedings 21, Muhr, G.R., Datta, N.P., Sankarasubramoney, H., Leley, V.K. and Donahue, R.L. (1965) Soil Testing in India, USAID, New Delhi, pp Richards, J.E., Bates, T.E. and Sheppard, S.C. (1988) Studies on the potassium supplying capacities of southern Ontario soils: I. Field and greenhouse experiments. Canadian Journal of Soil Science 68, Santhy, P., Jayasree Sankar, S., Muthuvel, P. and Selvi, D. (1998) Long-term fertilizer experiments - Status of N, P and K fractions in soil. Journal of the Indian Society of Soil Science 48, Sekhon, G.S., Brar, M.S. and Subba Rao, A. (1992) Potassium in Some Benchmark Soils of India. PRII Special Publication, Potash Research Institute of India, Gurgaon, Haryana. Wood, L.K. and DeTurk, E.E. (1941) The adsorption of potassium in soil in non-exchangeable forms. Soil Science Society of America Proceedings 5, Woodruff, C.M. and McIntosh, J.L. (1960) Testing soil for potassium. Proceedings of the 7 th International Congress of Soil Science, Madison, Wisconsin, pp Received December 2007; Accepted July 2011