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Nonexchangeable K release and supplying power of Indo-Gangetic alluvial soils
Geoderma 108 (2002) 197 – 206 www.elsevier.com/locate/geoderma
Nonexchangeable K release and supplying power of Indo-Gangetic alluvial soils D.S. Benipal a, N.S. Pasricha b,* b
a Punjab Agricultural University, Ludhiana 141004, Punjab, India Potash Research Institute of India, Sector-19, Gurgaon 122001, Haryana, India
Received 17 November 2000; received in revised form 4 January 2002; accepted 15 March 2002
Abstract Nonexchangeable K release in facilitating its uptake from 12 alluvial soils of three distinct agroecozones of northwestern Indo-gangetic plain has been investigated. The initial exchangeable K contents of 53, 39 and 261 mg/kg, declined by 32%, 43% and 19% in soils of submontane, central plain and southwestern arid zone, respectively, after cropping successively with maize, wheat and guinea grass. We studied the nonexchangeable K release to plant roots in green house and to H + resin in laboratory. Release of K was quantitatively recovered as cumulative uptake by maize, wheat and guinea grass. Cumulative K uptake was significantly related to nonexchangeable K released to plant roots (r = 0.85) and K released to H + -resin (0.71). Relationship between initial level of exchangeable K and cumulative K uptake in maize, wheat and guinea grass on these soils was highly significant (r = 98). A significant correlation between nonexchangeable K released to H + -resin and plant roots (r = 0.92) provides a commendable evidence for reliability of laboratory method for use in K release studies. D 2002 Elsevier Science B.V. All rights reserved. Keywords: H+-resin extraction; Decline in soil test K; Alluvial soils; Kinetics of K release
1. Introduction Inherent potassium status of a soil largely depends on the rate and amount of nonexchangeable potassium release (Hundal and Pasricha, 1993). The K releasing and supplying power of soils are often used as synonyms, but the two terms have distinctly different implications. The former refers to the gross availability of the nutrient in the soil while the latter denotes its actual uptake by plants (Ramanathan and Krishnamoorty, *
Corresponding author. E-mail address: [email protected] (N.S. Pasricha).
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1982). The ease with which K is released from nonexchangeable sources is an index of the ability of the soil to supply K to the plant not receiving any potassium fertilizer (Parker et al., 1989b). Crop removal of K often exceeds annual addition (Duxbury et al., 2000) without any appreciable change in the available K status of soils, thereby suggesting that part of nonexchangeable K becomes available to plants. However, under exhaustive cropping, the exchangeable K gets depleted (Sharma and Minhas, 1996; Brar and Pasricha, 1998) and gets stabilised at a particular level, which is usually referred to as the minimal level (Havlin and Westfall, 1985). In soils where such a level of exchangeable K has been reached, the supply of the nutrient has to come almost entirely from the nonexchangeable form. The contribution of nonexchangeable K release to K availability has been studied extensively by Sparks (1989, 2000), Parker et al. (1989a,b), Mengel and Uhlenbecker (1993) and Mengel and Rahmatullah (1994). However, a majority of the K release data in the literature have been reported for highly weathered, relatively acid, K responsive soils of moderate to high rainfall climates. Until recently, few K release studies have been reported for neutral to alkaline soils of alluvial origin in Indo-gangetic plains where mean annual rainfall ranges from < 400 to > 800 mm. On many of these soils, response to K is not distinct due to native high exchangeable K or release of mineral K (Dhillon and Pasricha, 2000). Therefore, more information is needed on the nature and rate of nonexchangeable K release in these soils. Therefore, the present investigation was undertaken to study the rate of release of nonexchangeable K from upper Indo-gangetic alluvial plain soils representing three different agroecozones and the capacity of these soils to supply plant with nonexchangeable K as assessed by a pot culture experiment.
2. Material and methods 2.1. Physicochemical properties of soils Twelve surface soil samples (0 –30 cm) were collected from widely differing locations in Punjab representing three agroecozones designated as Zone-I, Zone-II and Zone-III depending upon the total amount of mean annual rainfall and temperature. The rainfall is markedly seasonal and wettest months approximately coincide with period of maximum temperature (40 – 45 jC). The number of rain days (>1.0 mm) ranges from approximately 180 in Zone-I where the mean annual rainfall is 900 mm to as low as 90 days in the arid region of Zone-III where mean annual rainfall is less than 400 mm. The central plain of Zone-II, which accounts for 70% of the total cultivated area, has an approximately 120 rain days in which the mean annual total rainfall is 600 mm. Average annual evaporation varies approximately inversely with the mean annual rainfall. The soil samples were air dried in shade and ground to pass through a 2-mm sieve for greenhouse and laboratory experiments. Basic physicochemical properties of the soils are shown in Table 1. Soil pH and electrical conductivity were determined using a 1:2 soil to water suspension, organic carbon was determined by following Walkley and Black’s (1934) method. Rapid titration method of Puri (1930) was used for estimating calcium carbonate equivalent of the soils and the cation exchange capacity was determined by the
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Table 1 Some physicochemical properties of the soils Sample number
pH (1:2)
EC (1:2) (dSm 1)
CaCO3 (%)
Sand (%)
Silt (%)
Clay (%)
5.0 4.2 1.9 2.0 1.7
45.2 73.5 67.0 22.1 27.8
48.6 10.5 13.0 57.9 42.2
6.0 16.0 20.0 20.0 30.0
Central plain zone (average annual rainfall 400 – 800 mm) S6 7.3 0.51 7.1 13.9 S7 7.6 0.21 2.1 5.6 S8 7.8 0.17 4.7 3.6 S9 7.8 0.32 6.9 8.9
1.8 Traces 0.9 1.9
24.3 77.9 79.4 69.6
29.7 4.1 6.6 6.4
46.0 18.0 14.0 24.0
Southwestern S10 S11 S12
5.0 3.0 3.0
70.1 73.4 53.9
13.9 12.6 14.1
16.0 14.0 32.0
Submontaneous region S1 7.7 S2 7.8 S3 7.6 S4 7.0 S5 7.0
O.M. (g/kg)
CEC (cmol/kg)
(average annual rainfall 800 – 1000 mm) 0.50 4.6 13.2 0.45 1.9 10.8 0.75 4.5 8.0 0.61 5.5 12.0 0.53 6.5 12.3
zone (average annual rainfall < 400 mm) 8.7 0.82 6.7 9.2 8.2 0.48 2.8 4.2 8.0 0.83 5.2 12.0
procedure given by Rhoades (1982). The soils under investigation were neutral to slightly alkaline, low in soluble salt content (EC 0.17 to 0.83 dSm 1) and low in organic matter content. The calcium carbonate content was less than 5% in all but two soils. The soils were coarse to medium in texture. 2.2. Nonexchangeable K release under laboratory conditions A laboratory experiment was conducted with sieved soil for determining the kinetics of nonexchangeable K release to proton-saturated resin. Each of the soil samples was made homoionic by saturating with Ca2 + . For this purpose, 25 g soil sample was taken in a 1-l Erlenmeyer flask, and half litre of IN CaCl2 was added. The suspension was shaken for an hour, allowed to stand overnight and again shaken for 1 h the next day. The soil suspension was filtered through Whatman No. 1 filter paper followed by leaching with another litre of same solution. Several washings with deionised water were given to remove the excess of soluble salts until a negative test of AgNO3 for Cl . The soil was air dried and ground to pass a 1-mm sieve. Duplicate 1 g of Ca-saturated soil samples were added to 40-ml polypropylene centrifuge tube with 2 g of moist resin (Dowex 50 8, 20 – 50 mesh) already weighed and packed in nylon pouches, and 25 ml of 0.001 M HCl was added to each sample. Homoionic H + -resin was prepared by leaching the resin with 1 M HCl solution and washing out the excess salts with deionised water. The soil samples were equilibrated for period ranging from 0.25 to 100 h (0.25, 0.5, 1, 2, 5, 10, 25, 50 and 100 h) at 198 F 1 K in duplicate. At the end of the each reaction period, resin was immediately separated with fine spray of distilled water. The resin was then leached with 40 ml of 1 M NH4Cl to remove the released K and the leachate was brought to 50 ml volume and analysed for K flame photometrically.
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2.3. Nonexchangeable K release under greenhouse conditions To assess the K supplying power of soils; maize, wheat and guinea grass crops were grown successively in polythene-lined earthen pots filled with 4 kg of soil in three replicates. Four levels of K, viz. 0, 15, 30 and 60 mg/kg, were applied in the form of potassium chloride along with basic doses of N and P as urea and single super phosphate. After harvesting maize at 70 days growth, wheat and guinea grass crops were grown in succession, the pots were fertilised with N and P in the form of urea and single super phosphate without K fertilisation. Deionised water was used to irrigate the crop as and when required. Dry matter yield of the crops were recorded on an oven-dry basis. Potassium content in the dry matter was determined and cumulative K uptake calculated. 2.4. Initial and final (after culture) exchangeable K Initial and final (after culture) exchangeable K in the soil samples was determined by extraction with neutral 1 N NH4OAc (Knudsen et al., 1982). One gram of < 2 mm airdried soil was taken in a 50-ml Erlenmeyer flask. Ten milliliter of extraction solution was added to the flask and shaken at 198 F 1 K for 5 min with a rotating shaker at 200– 220 oscillations/min. The extract was filtered through Whatman no. 2 filter paper. Potassium in the clear extract was measured on flame photometer. 2.5. Clay mineral analysis Basally oriented clay samples prepared on glass slides were used for the identification of the clay minerals. X-ray diffraction patterns were obtained using a Philip PW1050 vertical goniometer with Ni filtered Cu-Ka radiations. Quantitative determination of the K minerals in the clay fraction was done following the procedure developed by Kodama et al. (1977).
3. Results 3.1. Plant response As evident from the data in Table 2, dry matter yield of only maize crop increased with the application of potassium. The increase in dry matter yield was significant in Zone-I (submontane) and Zone-II (central plain) soils. The response was maximum up to 60 mg/ kg levels in the central plain region; however, significant response in both the soils was up to only 30 mg/kg K. No such response was observed in Zone-III. Soils of southwestern arid region, which have a relatively high amount of NH4OAc extractable K compared to in central plain region and submontaneous region, did not show any response to potassium application. Subsequent crops of wheat and guinea grass showed no response on any of the soils. Maize is relatively more sensitive to nutrient level in the soil. Significant response in wheat and rice to K application in the submontenous region in alluvial soils testing low in available K has been reported by Singh et al. (2000). Potassium content in plant tissue of
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all the crops increased with potassium application irrespective of the fact whether or not there was any increase in dry matter yield. Amount of K removed in crop plants followed strictly the amount of initial exchangeable K content in these soils. Mean value of cumulative K uptake was 318, 215 and 603 mg/kg in submontaneous, central plain and southwestern zone, respectively (Table 2). Maximum removal (632 mg/kg) of K in plants was noticed at the highest level of its application (60 mg/kg) in ustochreptic comborthids of southwestern zone and minimum removal (195.9 mg/kg) in control treatments of typic ustochrepts of central plain region. Potassium removal in crop plants is a function of tissue concentration of K and dry matter yield. None of the crop grown on soils of southwestern region responded to K application in terms of dry matter production, but the cumulative uptake is highest in this zone. The dry matter yield of wheat and guinea grass were slightly higher in this zone, but the exceptionally high K removal in this zone can be ascribed to high levels of initial exchangeable K. 3.2. Decline in exchangeable K When crops are grown successively without K application, the available pool in the soil remains continuously under K stress, resulting to a decline in exchangeable K levels. Results on changes in NH4OAc-K show a rapid decline in exchangeable K of central plain region, while decline in southwestern region was relatively low (Table 3). The first two Table 2 Effect of K fertilization on dry matter and cumulative K uptake by maize, wheat and guinea grass grown in succession Fertilizer rate (K mg/kg)
Dry matter (g/pot) Maize
Guinea grass
Cumulative K uptake (mg/kg)
Wheat
I cut
II cut
Submontaneous region 0 40.7 15 41.6 30 43.6 60 44.7 CD ( P = 0.05) 2.3
7.6 7.7 7.8 8.1 NS
25.1 25.1 25.2 25.2 NS
22.8 23.1 23.1 23.2 NS
294.5 306.5 328.9 342.9
Central plain region 0 15 30 60 CD ( P = 0.05)
34.6 35.9 37.5 37.1 1.9
7.5 7.6 7.6 7.8 NS
23.1 23.1 23.2 23.3 NS
22.1 22.1 22.3 22.3 NS
195.9 201.1 229.8 234.5
Southwestern arid region 0 37.1 15 38.0 30 38.8 60 40.6 CD ( P = 0.05) NS
8.1 8.1 8.4 8.5 NS
27.6 27.7 27.9 27.8 NS
24.6 24.7 24.7 24.8 NS
574.7 597.2 608.3 632.0
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crops (maize and wheat) exhausted more K than the succeeding cuttings of guinea grass. Potassium content in almost all the soils reached minimal level immediately after the harvesting of maize and wheat crop. At the end of the experiment (after the harvesting of second cut of guinea grass), exchangeable K decreased to a level that can be considered to represent the steady-state level. After successive cropping with wheat, maize and guinea grass, the soils of southwestern region were still considered high in available K (>120 mg of K/kg) although these soils have reached the steady-state level of exchangeable K. Fertilizer K application would not be recommended on these soils. This showed a wide range of the minimal exchangeable K found in the studied soils. Maximum decline in exchangeable K was noticed in central plain soils having lowest amount of initial exchangeable K. After the harvesting of second cutting of guinea grass, exchangeable K declined to 68.3%, 57.2% and 80.8% in soils of submontaneous, central plain and southwestern zones of the state of Punjab. Havlin and Westfall (1985) in a greenhouse study reported that after 16 cuttings of alfalfa, exchangeable K levels in the clay, loam and sand textured soils declined by 43%, 33% and 58%, respectively. Ram and Prasad (1983) assessed K release from east khasi hills of India by exhaustive cropping wherein the levels of exchangeable K decreased by 13% to 80% after five crops of maize and fingermillet, and removal by the first two crops almost wholly accounted for the loss of exchangeable K. 3.3. Release of nonexchangeable K The quantities of K released to H-resin and cumulative K uptake by crops are measures of the release of nonexchangeable K. Nonexchangeable K release to crops grown in pot culture was calculated by the following K balance equation (Havlin and Westfall, 1985). Nonexchangeable K released ¼ C ðB AÞ
ð1Þ
where A and B are the final (after harvest of the second cutting of guinea grass) and initial (before cropping) exchangeable K, respectively, and C is the cumulative K uptake. Maximum release was observed in the soils of southwestern arid zone followed by submontaneous region and least in the central plain region (Table 3). Substantial release in southwestern zone could be the reason for higher initial exchangeable K level and nonresponse of crops to fertilizer K on these soils. Semiquantitative estimate of different clay minerals in the soil samples used for investigation is shown in Table 4. There are no systematic differences in the clay mineralogy of these soils. All these soils contain micas and K-feldspars, which are perhaps inherited from the alluvial parent materials. Most of Table 3 Percent decline in available K, cumulative uptake and nonexchangeable K released to plant roots Zone
Submontaneous Central plain Southwestern
Exchangeable K (mg/g) Initial
Final
Decline in exchangeable K (%)
52.6 39.0 261.0
35.9 22.3 210.9
31.75 42.82 19.20
Cumulative K uptake (mg/kg)
Nonexchangeable K released (mg/kg)
294.5 195.9 574.7
277.8 179.2 524.6
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Table 4 Semiquantitative estimate of different clay minerals in the soil samples used for investigation Clay mineral
Submontaneous zone (7)a
Central plain zone (5)
South western zone (4)
Smectite Vermiculite Chlorite Illite mica Kaolinite Mixed minerals
4 – 20 2 – 14 3 – 12 60 – 70 1–7 5 – 13
2 – 21 7 – 14 2–8 46 – 69 2–8 4–6
Traces – 3 9 – 14 6–9 55 – 65 4 – 11 7–8
a
Values in parenthesis are the number of soil samples examined.
the K in these soils resides in micas from which the release of K is quite rapid. Sidhu et al. (1993) reported that relatively altered states of sand fractions biotite and appreciable asymmetrical broadening of 10jA reflections from the finer fractions suggest that biotite and illite may be the main source of K supply to plants. They reported higher biotite content in the sand fraction of the aridic soils of southwestern region as compared to central plain and submontaneous regions. Relatively higher sand fraction (54 – 73%) and comparable illite content in clay fraction (16 – 32%) in the soils of arid zone of southwestern region (Zone-III) (Table 1) are, perhaps, responsible for higher exchangeable as well as nonexchangeable K contents in these soils. Farmers in this region are not advised to apply any K-fertilizers, so previous fertilization practices that could have built such high contents is ruled out. Sadusky et al. (1987) reported that 63– 68% of the total K released came from sand fractions of Delaware soils. Parker et al. (1989a,b) have also found that substantial amount of K is released from sand fractions of soils that are high in Kfeldspars. Recent research by Rahmatullah and Mengel (2000) also clearly indicates the role that sand and silt fractions of soils play in K release. As the solution K is removed in plant uptake, more K is released from nonexchangeable to exchangeable and solution pools. A sink for the released K is necessary for the reaction to move forward. Ratio of cumulative K uptake and nonexchangeable K released gives an idea about this drive. Higher ratio means greater drive for the release of nonexchangeable K. This ratio was 1.064, 1.093 and 1.096 for submontaneous, central plain and southwestern zones, respectively. Hundal and Pasricha (1993) observed apparent rate of nonexchangeable K release in the order of southwestern arid zone>central plain zone>submontaneous zone from the kinetic studies. The nonexchangeable K release to plant roots calculated by Eq. (1) and K released to H-resin in the laboratory were significantly related (r = 0.92) (Fig. 1). It was tested that the slope of 1.06 of the linear relationship between K released to crops and K release to Hresin is not significantly different from 1 (Fig. 1). This implies that the amount of K released to H-resin is similar to the amount released to plant roots except that an additional 50 mg K/kg is released to plant roots. Had there been no such additional release to the plant roots, the relationship between K release to crops and K release to H-resin would have passed through origin. Thus, the relationship between the availability of K to the plant roots and extraction by H-resin provides a commendable evidence for the reliability of laboratory method for assessing long-term K supply to the plants. Talukdar et al. (1992),
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Fig. 1. Relationship between nonexchangeable K released to H-resin and K release to crop roots.
in a study of nonexchangeable K release from the depleted ustochrepts, found that total K uptake by both mustard and wheat crops and total amount of nonexchangeable K released to H-resin were significantly correlated. The nonexchangeable K release to crops (r = 0.85) and K release in the laboratory to H-resin (0.75) were significantly correlated with cumulative K uptake on these soils. However, the initial exchangeable K levels were highly correlated (r = 0.98) with cumulative K uptake by crops (Fig. 2). It also correlated
Fig. 2. Relationship between initial available K and cumulative K uptake in maize, wheat and guinea grass.
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Table 5 Correlation coefficients of nonexchangeable K release with yield, K uptake and initial exchangeable K Nonexchangeable K release
Cumulative yield Cumulative uptake Initial exchangeable K
Greenhouse (K-balance)
Laboratory (H-resin)
0.06 0.85 * 0.77 *
0.18 0.75 * 0.71 *
* Significant at 0.05 probability level.
significantly with nonexchangeable K released to plant roots (r = 0.77) and H-resin (r = 0.71). Havlin and Westfall (1985) also found similar type of relationship (r = 0.97) between the initial levels of NH4OAc extractable K and cumulative K uptake by alfalfa in calcareous soils. The correlation coefficients (r) of nonexchangeable K release with plant response, K-uptake and soil test K levels are shown in Table 5. It is evident from the data presented that nonexchangeable K was a good indicator of long-term K supply in these soils. Proton-saturated resin extractable nonexchangeable K was highly correlated to nonexchangeable K release to plant roots and initial exchangeable K was highly correlated to cumulative K uptake by crops. The relationship between the availability of K to plant roots and H-resin provides good evidence for the reliability of Hresin method for use in K release studies.
References Brar, B.S., Pasricha, N.S., 1998. Long term studies on integrated use of organic and inorganic fertilizers in maize – wheat – cowpea cropping system on alluvial soil of Punjab. Proc. National Workshop on ‘‘Integrated Nutrient Management’’ held at Indian Institute of Soil Science, Bhopal, India, April 2 – 4, 1998, 54 – 168. Dhillon, S.K., Pasricha, N.S., 2000. Quantity – intensity relationship as a measure of non-exchangeable K release to plant roots. J. Potassium Res. 16, 15 – 19. Duxbury, J.M., Abrol, I.P., Gupta, R.K., Bronson, K.F., 2000. Analysis of long-term soil fertility experiments with rice – wheat rotations in South Asia. In: Abrol, I.P., et al., (Eds.), Long-Term Soil Fertility Experiments in Rice – Wheat Cropping Systems. Rice – Wheat Consortium Paper Series, vol. 6 Rice – Wheat Consortium for the Indo-Gangetic Plains, New Delhi, India. Havlin, J.L., Westfall, D.G., 1985. Potassium release kinetics and plant response in calcareous soils. Soil Sci. Soc. Am. J. 49, 366 – 370. Hundal, L.S., Pasricha, N.S., 1993. Non-exchangeable potassium release kinetics in illitic soil profiles. Soil Sci. 156 (1), 34 – 41. Knudsen, D., Peterson, G.A., Pratt, P.F., 1982. Lithium, sodium and potassium. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Methods of Soil Analysis: Part II. Chemical and Microbiological Properties. American Soc. Agron. Soil Sci. Soc. America, Maddison, WI, pp. 225 – 245. Kodama, H., Scot, G.C., Miles, N.M., 1977. X-ray Quantitative Analysis of Mineral in Soils. Soil Res. Institute, Ottawa, Canada, p. 49. Mengel, K., Rahmatullah, K., 1994. Exploitation of potassium by various crop species from primary minerals in soils rich in micas. Biol. Fertil. Soils 17, 75 – 79. Mengel, K., Uhlenbecker, K., 1993. Determination of available interlayer potassium and its uptake by rye grass. Soil Sci. Soc. Am. J. 57, 761 – 766. Parker, D.R., Sparks, D.L., Hendricks, G.J., Sadusky, M.C., 1989a. Potassium in Atlantic coastal plain soils: I. Soil characterization and distribution of potassium. Soil Sci. Soc. Am. J. 53, 392 – 396.
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Parker, D.R., Hendricks, G.J., Sparks, D.L., 1989b. Potassium in Atlantic coastal plain soils: II. Crop responses and changes in soil potassium under intensive management. Soil Sci. Soc. Am. J. 53, 397 – 401. Puri, A.N., 1930. A new method of estimating total carbonates in soils. Bull.-Imp. Agric. Res., Pusa, 206 – 207. Rahmatullah, Mengel, K., 2000. Potassium release from mineral structures by H + ion resin. Geoderma 96, 291 – 305. Ram, P., Prasad, R.N., 1983. Potassium supplying power of soils from the East Khasi Hills of Meghalaya. J. Indian Soc. Soil Sci. 30, 268 – 271. Ramanathan, K.M., Krishnamoorty, K.K., 1982. Potassium releasing power viz-a-viz K supplying power of soils. J. Indian Soc. Soil Sci. 30, 176 – 179. Rhoades, J.D., 1982. Cation exchange capacity. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Methods of Soil Analysis: Part II. Chemical and Microbiological Properties. American Soc. Agron. Soil Sci. Soc. America, Maddison, WI, pp. 148 – 149. Sadusky, M.C., Sparks, D.L., Noll, M.R., Hendricks, G.J., 1987. Kinetics and mechanisms of potassium release from sandy soils. Soil Sci. Soc. Am. J. 51, 1460 – 1465. Sharma, S.P., Minhas, R.S., 1996. Need for continuous application of K along with N and P fertilizers for sustained productivity. J. Potassium Res. 12 (3), 283 – 289. Sidhu, P.S., Bhangu, S.S., Jassal, H.S., 1993. Mineralogy of potassium in some bench mark soils of Punjab. J. Potassium Res. 9 (3), 206 – 217. Singh, Y., Pasricha, N.S., Azad, A.S., 2000. Effect of N and K nutrition in relation to yield and nutrient uptake in wheat and rice grown in rotation. Annual Proj. Rep. Dept. of Soils, PAU, Ludhiana. Sparks, D.L., 1989. Kinetics of Soil Chemical Processes Academic Press, San Diego, CA. Sparks, D.L., 2000. Bioavailability of soil potassium. In: Sumner, M.E. (Ed.), Handbook of Soil Science. CRC Press, Boca Raton, FL, pp. D-38 – D-52. Talukdar, M.C., Khera, M.S., Barua, T.C., 1992. Kinetics of non-exchangeable potassium release from K depleted Ustochrepts. J. Potassium Res. 8, 38 – 43. Walkley, A., Black, I.A., 1934. An examination of the Degtijare method for determining soils organic matter and a proposed modification of the chromic acid titration method. Soil Sci. 37, 29 – 38.
Nonexchangeable K release and supplying power of Indo-Gangetic alluvial soils D.S. Benipal a, N.S. Pasricha b,* b
a Punjab Agricultural University, Ludhiana 141004, Punjab, India Potash Research Institute of India, Sector-19, Gurgaon 122001, Haryana, India
Received 17 November 2000; received in revised form 4 January 2002; accepted 15 March 2002
Abstract Nonexchangeable K release in facilitating its uptake from 12 alluvial soils of three distinct agroecozones of northwestern Indo-gangetic plain has been investigated. The initial exchangeable K contents of 53, 39 and 261 mg/kg, declined by 32%, 43% and 19% in soils of submontane, central plain and southwestern arid zone, respectively, after cropping successively with maize, wheat and guinea grass. We studied the nonexchangeable K release to plant roots in green house and to H + resin in laboratory. Release of K was quantitatively recovered as cumulative uptake by maize, wheat and guinea grass. Cumulative K uptake was significantly related to nonexchangeable K released to plant roots (r = 0.85) and K released to H + -resin (0.71). Relationship between initial level of exchangeable K and cumulative K uptake in maize, wheat and guinea grass on these soils was highly significant (r = 98). A significant correlation between nonexchangeable K released to H + -resin and plant roots (r = 0.92) provides a commendable evidence for reliability of laboratory method for use in K release studies. D 2002 Elsevier Science B.V. All rights reserved. Keywords: H+-resin extraction; Decline in soil test K; Alluvial soils; Kinetics of K release
1. Introduction Inherent potassium status of a soil largely depends on the rate and amount of nonexchangeable potassium release (Hundal and Pasricha, 1993). The K releasing and supplying power of soils are often used as synonyms, but the two terms have distinctly different implications. The former refers to the gross availability of the nutrient in the soil while the latter denotes its actual uptake by plants (Ramanathan and Krishnamoorty, *
Corresponding author. E-mail address: [email protected] (N.S. Pasricha).
0016-7061/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 1 6 - 7 0 6 1 ( 0 2 ) 0 0 1 2 4 - 6
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1982). The ease with which K is released from nonexchangeable sources is an index of the ability of the soil to supply K to the plant not receiving any potassium fertilizer (Parker et al., 1989b). Crop removal of K often exceeds annual addition (Duxbury et al., 2000) without any appreciable change in the available K status of soils, thereby suggesting that part of nonexchangeable K becomes available to plants. However, under exhaustive cropping, the exchangeable K gets depleted (Sharma and Minhas, 1996; Brar and Pasricha, 1998) and gets stabilised at a particular level, which is usually referred to as the minimal level (Havlin and Westfall, 1985). In soils where such a level of exchangeable K has been reached, the supply of the nutrient has to come almost entirely from the nonexchangeable form. The contribution of nonexchangeable K release to K availability has been studied extensively by Sparks (1989, 2000), Parker et al. (1989a,b), Mengel and Uhlenbecker (1993) and Mengel and Rahmatullah (1994). However, a majority of the K release data in the literature have been reported for highly weathered, relatively acid, K responsive soils of moderate to high rainfall climates. Until recently, few K release studies have been reported for neutral to alkaline soils of alluvial origin in Indo-gangetic plains where mean annual rainfall ranges from < 400 to > 800 mm. On many of these soils, response to K is not distinct due to native high exchangeable K or release of mineral K (Dhillon and Pasricha, 2000). Therefore, more information is needed on the nature and rate of nonexchangeable K release in these soils. Therefore, the present investigation was undertaken to study the rate of release of nonexchangeable K from upper Indo-gangetic alluvial plain soils representing three different agroecozones and the capacity of these soils to supply plant with nonexchangeable K as assessed by a pot culture experiment.
2. Material and methods 2.1. Physicochemical properties of soils Twelve surface soil samples (0 –30 cm) were collected from widely differing locations in Punjab representing three agroecozones designated as Zone-I, Zone-II and Zone-III depending upon the total amount of mean annual rainfall and temperature. The rainfall is markedly seasonal and wettest months approximately coincide with period of maximum temperature (40 – 45 jC). The number of rain days (>1.0 mm) ranges from approximately 180 in Zone-I where the mean annual rainfall is 900 mm to as low as 90 days in the arid region of Zone-III where mean annual rainfall is less than 400 mm. The central plain of Zone-II, which accounts for 70% of the total cultivated area, has an approximately 120 rain days in which the mean annual total rainfall is 600 mm. Average annual evaporation varies approximately inversely with the mean annual rainfall. The soil samples were air dried in shade and ground to pass through a 2-mm sieve for greenhouse and laboratory experiments. Basic physicochemical properties of the soils are shown in Table 1. Soil pH and electrical conductivity were determined using a 1:2 soil to water suspension, organic carbon was determined by following Walkley and Black’s (1934) method. Rapid titration method of Puri (1930) was used for estimating calcium carbonate equivalent of the soils and the cation exchange capacity was determined by the
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Table 1 Some physicochemical properties of the soils Sample number
pH (1:2)
EC (1:2) (dSm 1)
CaCO3 (%)
Sand (%)
Silt (%)
Clay (%)
5.0 4.2 1.9 2.0 1.7
45.2 73.5 67.0 22.1 27.8
48.6 10.5 13.0 57.9 42.2
6.0 16.0 20.0 20.0 30.0
Central plain zone (average annual rainfall 400 – 800 mm) S6 7.3 0.51 7.1 13.9 S7 7.6 0.21 2.1 5.6 S8 7.8 0.17 4.7 3.6 S9 7.8 0.32 6.9 8.9
1.8 Traces 0.9 1.9
24.3 77.9 79.4 69.6
29.7 4.1 6.6 6.4
46.0 18.0 14.0 24.0
Southwestern S10 S11 S12
5.0 3.0 3.0
70.1 73.4 53.9
13.9 12.6 14.1
16.0 14.0 32.0
Submontaneous region S1 7.7 S2 7.8 S3 7.6 S4 7.0 S5 7.0
O.M. (g/kg)
CEC (cmol/kg)
(average annual rainfall 800 – 1000 mm) 0.50 4.6 13.2 0.45 1.9 10.8 0.75 4.5 8.0 0.61 5.5 12.0 0.53 6.5 12.3
zone (average annual rainfall < 400 mm) 8.7 0.82 6.7 9.2 8.2 0.48 2.8 4.2 8.0 0.83 5.2 12.0
procedure given by Rhoades (1982). The soils under investigation were neutral to slightly alkaline, low in soluble salt content (EC 0.17 to 0.83 dSm 1) and low in organic matter content. The calcium carbonate content was less than 5% in all but two soils. The soils were coarse to medium in texture. 2.2. Nonexchangeable K release under laboratory conditions A laboratory experiment was conducted with sieved soil for determining the kinetics of nonexchangeable K release to proton-saturated resin. Each of the soil samples was made homoionic by saturating with Ca2 + . For this purpose, 25 g soil sample was taken in a 1-l Erlenmeyer flask, and half litre of IN CaCl2 was added. The suspension was shaken for an hour, allowed to stand overnight and again shaken for 1 h the next day. The soil suspension was filtered through Whatman No. 1 filter paper followed by leaching with another litre of same solution. Several washings with deionised water were given to remove the excess of soluble salts until a negative test of AgNO3 for Cl . The soil was air dried and ground to pass a 1-mm sieve. Duplicate 1 g of Ca-saturated soil samples were added to 40-ml polypropylene centrifuge tube with 2 g of moist resin (Dowex 50 8, 20 – 50 mesh) already weighed and packed in nylon pouches, and 25 ml of 0.001 M HCl was added to each sample. Homoionic H + -resin was prepared by leaching the resin with 1 M HCl solution and washing out the excess salts with deionised water. The soil samples were equilibrated for period ranging from 0.25 to 100 h (0.25, 0.5, 1, 2, 5, 10, 25, 50 and 100 h) at 198 F 1 K in duplicate. At the end of the each reaction period, resin was immediately separated with fine spray of distilled water. The resin was then leached with 40 ml of 1 M NH4Cl to remove the released K and the leachate was brought to 50 ml volume and analysed for K flame photometrically.
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2.3. Nonexchangeable K release under greenhouse conditions To assess the K supplying power of soils; maize, wheat and guinea grass crops were grown successively in polythene-lined earthen pots filled with 4 kg of soil in three replicates. Four levels of K, viz. 0, 15, 30 and 60 mg/kg, were applied in the form of potassium chloride along with basic doses of N and P as urea and single super phosphate. After harvesting maize at 70 days growth, wheat and guinea grass crops were grown in succession, the pots were fertilised with N and P in the form of urea and single super phosphate without K fertilisation. Deionised water was used to irrigate the crop as and when required. Dry matter yield of the crops were recorded on an oven-dry basis. Potassium content in the dry matter was determined and cumulative K uptake calculated. 2.4. Initial and final (after culture) exchangeable K Initial and final (after culture) exchangeable K in the soil samples was determined by extraction with neutral 1 N NH4OAc (Knudsen et al., 1982). One gram of < 2 mm airdried soil was taken in a 50-ml Erlenmeyer flask. Ten milliliter of extraction solution was added to the flask and shaken at 198 F 1 K for 5 min with a rotating shaker at 200– 220 oscillations/min. The extract was filtered through Whatman no. 2 filter paper. Potassium in the clear extract was measured on flame photometer. 2.5. Clay mineral analysis Basally oriented clay samples prepared on glass slides were used for the identification of the clay minerals. X-ray diffraction patterns were obtained using a Philip PW1050 vertical goniometer with Ni filtered Cu-Ka radiations. Quantitative determination of the K minerals in the clay fraction was done following the procedure developed by Kodama et al. (1977).
3. Results 3.1. Plant response As evident from the data in Table 2, dry matter yield of only maize crop increased with the application of potassium. The increase in dry matter yield was significant in Zone-I (submontane) and Zone-II (central plain) soils. The response was maximum up to 60 mg/ kg levels in the central plain region; however, significant response in both the soils was up to only 30 mg/kg K. No such response was observed in Zone-III. Soils of southwestern arid region, which have a relatively high amount of NH4OAc extractable K compared to in central plain region and submontaneous region, did not show any response to potassium application. Subsequent crops of wheat and guinea grass showed no response on any of the soils. Maize is relatively more sensitive to nutrient level in the soil. Significant response in wheat and rice to K application in the submontenous region in alluvial soils testing low in available K has been reported by Singh et al. (2000). Potassium content in plant tissue of
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all the crops increased with potassium application irrespective of the fact whether or not there was any increase in dry matter yield. Amount of K removed in crop plants followed strictly the amount of initial exchangeable K content in these soils. Mean value of cumulative K uptake was 318, 215 and 603 mg/kg in submontaneous, central plain and southwestern zone, respectively (Table 2). Maximum removal (632 mg/kg) of K in plants was noticed at the highest level of its application (60 mg/kg) in ustochreptic comborthids of southwestern zone and minimum removal (195.9 mg/kg) in control treatments of typic ustochrepts of central plain region. Potassium removal in crop plants is a function of tissue concentration of K and dry matter yield. None of the crop grown on soils of southwestern region responded to K application in terms of dry matter production, but the cumulative uptake is highest in this zone. The dry matter yield of wheat and guinea grass were slightly higher in this zone, but the exceptionally high K removal in this zone can be ascribed to high levels of initial exchangeable K. 3.2. Decline in exchangeable K When crops are grown successively without K application, the available pool in the soil remains continuously under K stress, resulting to a decline in exchangeable K levels. Results on changes in NH4OAc-K show a rapid decline in exchangeable K of central plain region, while decline in southwestern region was relatively low (Table 3). The first two Table 2 Effect of K fertilization on dry matter and cumulative K uptake by maize, wheat and guinea grass grown in succession Fertilizer rate (K mg/kg)
Dry matter (g/pot) Maize
Guinea grass
Cumulative K uptake (mg/kg)
Wheat
I cut
II cut
Submontaneous region 0 40.7 15 41.6 30 43.6 60 44.7 CD ( P = 0.05) 2.3
7.6 7.7 7.8 8.1 NS
25.1 25.1 25.2 25.2 NS
22.8 23.1 23.1 23.2 NS
294.5 306.5 328.9 342.9
Central plain region 0 15 30 60 CD ( P = 0.05)
34.6 35.9 37.5 37.1 1.9
7.5 7.6 7.6 7.8 NS
23.1 23.1 23.2 23.3 NS
22.1 22.1 22.3 22.3 NS
195.9 201.1 229.8 234.5
Southwestern arid region 0 37.1 15 38.0 30 38.8 60 40.6 CD ( P = 0.05) NS
8.1 8.1 8.4 8.5 NS
27.6 27.7 27.9 27.8 NS
24.6 24.7 24.7 24.8 NS
574.7 597.2 608.3 632.0
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crops (maize and wheat) exhausted more K than the succeeding cuttings of guinea grass. Potassium content in almost all the soils reached minimal level immediately after the harvesting of maize and wheat crop. At the end of the experiment (after the harvesting of second cut of guinea grass), exchangeable K decreased to a level that can be considered to represent the steady-state level. After successive cropping with wheat, maize and guinea grass, the soils of southwestern region were still considered high in available K (>120 mg of K/kg) although these soils have reached the steady-state level of exchangeable K. Fertilizer K application would not be recommended on these soils. This showed a wide range of the minimal exchangeable K found in the studied soils. Maximum decline in exchangeable K was noticed in central plain soils having lowest amount of initial exchangeable K. After the harvesting of second cutting of guinea grass, exchangeable K declined to 68.3%, 57.2% and 80.8% in soils of submontaneous, central plain and southwestern zones of the state of Punjab. Havlin and Westfall (1985) in a greenhouse study reported that after 16 cuttings of alfalfa, exchangeable K levels in the clay, loam and sand textured soils declined by 43%, 33% and 58%, respectively. Ram and Prasad (1983) assessed K release from east khasi hills of India by exhaustive cropping wherein the levels of exchangeable K decreased by 13% to 80% after five crops of maize and fingermillet, and removal by the first two crops almost wholly accounted for the loss of exchangeable K. 3.3. Release of nonexchangeable K The quantities of K released to H-resin and cumulative K uptake by crops are measures of the release of nonexchangeable K. Nonexchangeable K release to crops grown in pot culture was calculated by the following K balance equation (Havlin and Westfall, 1985). Nonexchangeable K released ¼ C ðB AÞ
ð1Þ
where A and B are the final (after harvest of the second cutting of guinea grass) and initial (before cropping) exchangeable K, respectively, and C is the cumulative K uptake. Maximum release was observed in the soils of southwestern arid zone followed by submontaneous region and least in the central plain region (Table 3). Substantial release in southwestern zone could be the reason for higher initial exchangeable K level and nonresponse of crops to fertilizer K on these soils. Semiquantitative estimate of different clay minerals in the soil samples used for investigation is shown in Table 4. There are no systematic differences in the clay mineralogy of these soils. All these soils contain micas and K-feldspars, which are perhaps inherited from the alluvial parent materials. Most of Table 3 Percent decline in available K, cumulative uptake and nonexchangeable K released to plant roots Zone
Submontaneous Central plain Southwestern
Exchangeable K (mg/g) Initial
Final
Decline in exchangeable K (%)
52.6 39.0 261.0
35.9 22.3 210.9
31.75 42.82 19.20
Cumulative K uptake (mg/kg)
Nonexchangeable K released (mg/kg)
294.5 195.9 574.7
277.8 179.2 524.6
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Table 4 Semiquantitative estimate of different clay minerals in the soil samples used for investigation Clay mineral
Submontaneous zone (7)a
Central plain zone (5)
South western zone (4)
Smectite Vermiculite Chlorite Illite mica Kaolinite Mixed minerals
4 – 20 2 – 14 3 – 12 60 – 70 1–7 5 – 13
2 – 21 7 – 14 2–8 46 – 69 2–8 4–6
Traces – 3 9 – 14 6–9 55 – 65 4 – 11 7–8
a
Values in parenthesis are the number of soil samples examined.
the K in these soils resides in micas from which the release of K is quite rapid. Sidhu et al. (1993) reported that relatively altered states of sand fractions biotite and appreciable asymmetrical broadening of 10jA reflections from the finer fractions suggest that biotite and illite may be the main source of K supply to plants. They reported higher biotite content in the sand fraction of the aridic soils of southwestern region as compared to central plain and submontaneous regions. Relatively higher sand fraction (54 – 73%) and comparable illite content in clay fraction (16 – 32%) in the soils of arid zone of southwestern region (Zone-III) (Table 1) are, perhaps, responsible for higher exchangeable as well as nonexchangeable K contents in these soils. Farmers in this region are not advised to apply any K-fertilizers, so previous fertilization practices that could have built such high contents is ruled out. Sadusky et al. (1987) reported that 63– 68% of the total K released came from sand fractions of Delaware soils. Parker et al. (1989a,b) have also found that substantial amount of K is released from sand fractions of soils that are high in Kfeldspars. Recent research by Rahmatullah and Mengel (2000) also clearly indicates the role that sand and silt fractions of soils play in K release. As the solution K is removed in plant uptake, more K is released from nonexchangeable to exchangeable and solution pools. A sink for the released K is necessary for the reaction to move forward. Ratio of cumulative K uptake and nonexchangeable K released gives an idea about this drive. Higher ratio means greater drive for the release of nonexchangeable K. This ratio was 1.064, 1.093 and 1.096 for submontaneous, central plain and southwestern zones, respectively. Hundal and Pasricha (1993) observed apparent rate of nonexchangeable K release in the order of southwestern arid zone>central plain zone>submontaneous zone from the kinetic studies. The nonexchangeable K release to plant roots calculated by Eq. (1) and K released to H-resin in the laboratory were significantly related (r = 0.92) (Fig. 1). It was tested that the slope of 1.06 of the linear relationship between K released to crops and K release to Hresin is not significantly different from 1 (Fig. 1). This implies that the amount of K released to H-resin is similar to the amount released to plant roots except that an additional 50 mg K/kg is released to plant roots. Had there been no such additional release to the plant roots, the relationship between K release to crops and K release to H-resin would have passed through origin. Thus, the relationship between the availability of K to the plant roots and extraction by H-resin provides a commendable evidence for the reliability of laboratory method for assessing long-term K supply to the plants. Talukdar et al. (1992),
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Fig. 1. Relationship between nonexchangeable K released to H-resin and K release to crop roots.
in a study of nonexchangeable K release from the depleted ustochrepts, found that total K uptake by both mustard and wheat crops and total amount of nonexchangeable K released to H-resin were significantly correlated. The nonexchangeable K release to crops (r = 0.85) and K release in the laboratory to H-resin (0.75) were significantly correlated with cumulative K uptake on these soils. However, the initial exchangeable K levels were highly correlated (r = 0.98) with cumulative K uptake by crops (Fig. 2). It also correlated
Fig. 2. Relationship between initial available K and cumulative K uptake in maize, wheat and guinea grass.
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Table 5 Correlation coefficients of nonexchangeable K release with yield, K uptake and initial exchangeable K Nonexchangeable K release
Cumulative yield Cumulative uptake Initial exchangeable K
Greenhouse (K-balance)
Laboratory (H-resin)
0.06 0.85 * 0.77 *
0.18 0.75 * 0.71 *
* Significant at 0.05 probability level.
significantly with nonexchangeable K released to plant roots (r = 0.77) and H-resin (r = 0.71). Havlin and Westfall (1985) also found similar type of relationship (r = 0.97) between the initial levels of NH4OAc extractable K and cumulative K uptake by alfalfa in calcareous soils. The correlation coefficients (r) of nonexchangeable K release with plant response, K-uptake and soil test K levels are shown in Table 5. It is evident from the data presented that nonexchangeable K was a good indicator of long-term K supply in these soils. Proton-saturated resin extractable nonexchangeable K was highly correlated to nonexchangeable K release to plant roots and initial exchangeable K was highly correlated to cumulative K uptake by crops. The relationship between the availability of K to plant roots and H-resin provides good evidence for the reliability of Hresin method for use in K release studies.
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Parker, D.R., Hendricks, G.J., Sparks, D.L., 1989b. Potassium in Atlantic coastal plain soils: II. Crop responses and changes in soil potassium under intensive management. Soil Sci. Soc. Am. J. 53, 397 – 401. Puri, A.N., 1930. A new method of estimating total carbonates in soils. Bull.-Imp. Agric. Res., Pusa, 206 – 207. Rahmatullah, Mengel, K., 2000. Potassium release from mineral structures by H + ion resin. Geoderma 96, 291 – 305. Ram, P., Prasad, R.N., 1983. Potassium supplying power of soils from the East Khasi Hills of Meghalaya. J. Indian Soc. Soil Sci. 30, 268 – 271. Ramanathan, K.M., Krishnamoorty, K.K., 1982. Potassium releasing power viz-a-viz K supplying power of soils. J. Indian Soc. Soil Sci. 30, 176 – 179. Rhoades, J.D., 1982. Cation exchange capacity. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Methods of Soil Analysis: Part II. Chemical and Microbiological Properties. American Soc. Agron. Soil Sci. Soc. America, Maddison, WI, pp. 148 – 149. Sadusky, M.C., Sparks, D.L., Noll, M.R., Hendricks, G.J., 1987. Kinetics and mechanisms of potassium release from sandy soils. Soil Sci. Soc. Am. J. 51, 1460 – 1465. Sharma, S.P., Minhas, R.S., 1996. Need for continuous application of K along with N and P fertilizers for sustained productivity. J. Potassium Res. 12 (3), 283 – 289. Sidhu, P.S., Bhangu, S.S., Jassal, H.S., 1993. Mineralogy of potassium in some bench mark soils of Punjab. J. Potassium Res. 9 (3), 206 – 217. Singh, Y., Pasricha, N.S., Azad, A.S., 2000. Effect of N and K nutrition in relation to yield and nutrient uptake in wheat and rice grown in rotation. Annual Proj. Rep. Dept. of Soils, PAU, Ludhiana. Sparks, D.L., 1989. Kinetics of Soil Chemical Processes Academic Press, San Diego, CA. Sparks, D.L., 2000. Bioavailability of soil potassium. In: Sumner, M.E. (Ed.), Handbook of Soil Science. CRC Press, Boca Raton, FL, pp. D-38 – D-52. Talukdar, M.C., Khera, M.S., Barua, T.C., 1992. Kinetics of non-exchangeable potassium release from K depleted Ustochrepts. J. Potassium Res. 8, 38 – 43. Walkley, A., Black, I.A., 1934. An examination of the Degtijare method for determining soils organic matter and a proposed modification of the chromic acid titration method. Soil Sci. 37, 29 – 38.