Kone et al Potassium and soil colour

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Kone et al Potassium and soil colour
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  Published by Basic Research Journal of Soil and Environmental Science Basic Research Journal of Soil and Environmental Science ISSN 2345-4090 Vol. 2(4) pp. 46-55 July 2014 Available online http//www.basicresearchjournals.org Copyright ©2014 Basic Research Journal Full Length Research Paper Potassium supplying capacity as indicated by soil colour in Ferralsol environment Brahima Koné 1 ; Affi Jeanne Bongoua-Devisme 1 ; Kouadio Konan-Kan Hippolyte 1 ; Konan Kouamé Firmin 1  ; Traoré Mignina Joachim 1   Felix Houphouet Boigny University, Earth Science Unit, Soil science department, 22 BP 582 Abidjan 22 *Corresponding author: email: kbrahima@hotmail.com; Tel: +225 06546189   Accepted 25 July, 2014 ABSTRACT The use of soil colour as Munsell data was explored for in situ indication   of soil potassium (K) supplying capacity referring to soil contents of clay and exchangeable K as well as the ratio of K to soil capacity of exchangeable cation (CEC) of 998 aerobic soil samples from Cote d’Ivoire (7˚N - 10˚N) according to unequal stratified sampling. Soil horizons were classified as H1 (0 – 20 cm), H2 (20 – 60 cm), H3 (60 – 80 cm) and H4 (80 – 150 cm) and 10 class of soil redness were defined in increasing order. Highest value of K/CEC was recorded for 10YR in H2 of upper, middle and foot slopes like for 5YR in H4 at the summit. Highest soil K and K/CEC ratio accounted for redness class 2 meanwhile, lowest values are observed for redness class 10 also characterized by highest soil content of clay. Lowest subsoil contents of clay and K/CEC ratio were significantly ( P   < 0.01) observed for redness class 1 and 2 for H2 and H3 in some extend. Clay mineralogy, soil depth and topographic section were relevant aspects of soil K supplying capacity. Further investigations were suggested as specific ecological survey to improve the accuracy of the method. Keywords : Potassium, tropical soil, clay mineralogy, toposequence, colour hue, soil redness, indicator, Cote d’Ivoire INTRODUCTION Potassium (K) is a basic nutrient for plant and animal life and plays many essential roles in plant nutrition (Prabhu et al., 2007): The uptake of K is often greater than that of any other essential macronutrient in high-yielding cultivars and its deficiency symptoms initially appear on the lower (older) leaves. There is studious requirement for improving soil K management in order to sustain crop production in aerobic soil environment (Juo and Grimme, 1980; Bhandari et al., 2002; Lopez and Vlek, 2006). The K content of the lithosphere is approximately 2.6%, with an average of 0.83% in soils (Lindsay, 1979) which is supplied by parental rock minerals mainly composed of micas and feldspars (Sparks and Huang, 1985) highly abundant in the crystalline basement of West Africa. Hence, soil K deficiency was exclusively referred to degraded soils in there (Kang and Osiname, 1985) although, there are four forms of K in dynamic equilibrium (Brady and Weil, 1996): soluble K (0.1 – 0.2%), non exchangeable K (1 – 10%), and the mineral K (90 – 98%) in addition to exchangeable K (1 – 2%) which is the main form up taken by plant and characterized by a critical level ranging from 0.10 cmolkg -1  to 0.40 cmolkg -1  depending on crops and ecosystems (Doberman et al . , 2004; Dunn and Stevens, 2005; Koné et al., 2011). Experiences underlined limited capability of soil exchangeable K levels for predicting crop response since they give no direct indication of the release of currently unavailable soil K over a period of time (Mengel and  Published by Basic Research Journal of Soil and Environmental Science Bush, 1982). In fact, recent studies (Koné et al., 2013; 2014) in Ferralsol environment of Cote d’Ivoire highlighted soil K deficiency for rainfed rice cropping during the second year of land use unlikely observed for the subsequent third year. Soil K leaching (Rosolem, 2011; Sheldrick et al., 2002) and colloid mobility (Sirivithayapakorn, 2003) depending to weathering condition as well as K releasing from other pools (Mengel, 1982) in unknown time scale could be involved in these results. The importance of soil K is further supported by the model of tropical soil fertility evaluation (QUEFTS) which also includes an algorithm of K-supplying capacity of the soil (StruifBontkes et al., 2003). Indeed, knowledge gap of process affecting K nutrition of plant can lead to erroneous land use planning and soil fertility management emphasizing the importance of soil content of total K which is highly depending to weatherable mineral-K (soil content of clay) relevant to kaolinization process under the tropics (Kukovsky, 1969). Therefore, in situ   indicator of soil K-supplying capacity could be of great interest for agricultural land use planning in tropical ecologies, especially for upland soil of Africa annually prone to the loss of 56 kg K 2 O/ha (Stoorvogel and Smaling, 1990). For this purpose, the use of soil colour in Ferralsol environment may be an accurate method on the basis of the relationship established with soil texture (Koné et al., 2009a) constituting nutrient capital reserves (Izac and Sanchez, 2001). In fact, it was reported a variation of soil concentration in exchangeable K in relation with soil pigmentation as yellow or red soil (Koné et al., 2009b). Ferralsols colour is due to its iron content (Mauricio and Ildeu, 2005) which is mainly related to soil colour hue (Segalen, 1969; Scheinot and Schwertmann, 1999). Although variable according to some observers, colour notation by Munsell chart is still the current reliable method of soil colour determination, especially in the field (Barrett, 2002; Islam et al., 2004). It reflects difference in mineralogical, organic, and texture compositions of soils (Stoner et al . , 1980) resulting to the pigmentation of white background of clay minerals, especially kaolinite and gibbsite which are relevant to soil mineral reserves (K ӓ mpf and Schwertmann, 1983; Fontes, 1988). Therefore, soil colour notation by Munsell chart may be an opportunity for scaling K supplying capacity of soil including exchangeable and reserve –K involving soil content of clay and exchangeable potassium percentage (Jones and Wild, 1975). Soil survey was conducted in Cote d’Ivoire above the latitude 7˚N using unequal stratified soil sampling method across different geology occurrences and ecosystems. Soil colour was determined by Munsell chart in order to i) characterize the levels of soil K and K/CEC by soil colour hue and ii) to defined the contribution of soil content of clay when predicting the levels of K and/or K/CEC. The study should provide in situ indicator of soil K supplying capacity on the basis of soil colour hue and/or redness Koné et al. 47 and/or content of clay. MATERIAL AND METHODS Study zone location The study was carried out at 19 sites on Ferralsols (WRB) located between latitude 7° N and 10° N in Côte d’Ivoire. This area covered the four major agro-ecologies described by Eldin (1971) - Sudan savannah with grassland, Guinea savannah with woodland, Derived savannah (a transition between savannah and forest agroecologies), and a zone located in the far western mountainous area of the country. Annual average rainfall ranged from 1200 to 2000 mm. Landscapes and soils The area surveyed abounds in landscapes with dismantled or unaffected summit ferruginous cuirass plateau landscapes with concave-convex or convex-concave sides, as well as variable rocky outcroppings. A few Inselbergs were also observed. The landside and length were varying accordingly. Upland soils were essentially Hyperdystric and Dystric Ferralsols followed by Ferralsol Plinthics. The world reference base for soil resources-WBSR was used for soil classification. Soil sampling Two hundred and eighty-nine (289) soil profiles were surveyed along representative catena of various landscapes at 19 sites, which were unequally distributed (Webster and Oliver, 1990) on three groups of Ferralsol in the study area. The identified horizons in the soil profiles were coded according to depth classes - H1 (0– 20 cm), H2 (20–60 cm), H3 (60–80 cm) and H4 (80–150 cm) dividing the soil profile into organic horizon (Diatta, 1996), minimum, medium and maximum crop rooting depths (Böhn, 1976; Chopart, 1985), somewhat consistent with soil profiles A, B, B/C, and C horizons as described earlier for the study area by Berger (1964). A total of 998 samples (2 kg each) were taken from horizons up to a maximum depth of 1.5 m. Laboratory analysis and classification of soil K contents Soil samples were dried under forced air at room temperature, followed by crushing and sieving through a 2.0 mm stainless steel sieve. Soil particle sizes (sand, clay and silt contents) were determined with the Robinson pipette method (Gee and Bauder, 1986).  Published by Basic Research Journal of Soil and Environmental Science 48. Basic Res. J. Soil Environ. Sci. Available potassium was extracted by shaking 1g of air dried soil in 10mL of 1 M NH4OAc for 5 min before the use of atomic emission in a Perkin Elmer Analyst 100 spectrometer (Page, 1982). Three class of soil exchangeable K content were defined as done by Berryman et al .  (1984) for tropical soils: L = Low soil content of K ranging below 0.15 cmolkg -1  M= Moderate soil content of K ranging between 0.15 to 0.30 cmolkg -1  H = High soil content of K ranging over 0.30 cmolkg -1 Cation Exchangeable Capacity (CEC) was determined when 3 g of air dried soil (1g peat) was leached with 60 mL 1 M   NH 4 OAc, pH 7, to saturate exchange sites with ammonium ions. Excess free ammonium ions were rinsed from the soil with isopropyl alcohol. Ammonium was determined on the KCl leachate by colorimetry ( λ  = 630 nm) on a Lachat QuikChem 8500 Flow Injection Analyzer using the salicylate/nitroprusside method. The critical level of K/CEC ratio in soil was fixed at 2% (Berryman et al., 1984). Soil colour identification The year 2000 revised washable edition of Munsell soil color charts (gretagmac ь eth, 2000) composed of 322 different standard colour ships was used in field during the survey for soil colour identification. Wet soil samples were compared with the standard colour ships respectively and the three components of the colour were recorded as “Hue (He)…Chroma (C)/Value (V)”. The redness ratio defined as RF by Santana (1984) was calculated for each of the soil samples: RF = (10 – He) + C/V [1] The redness data calculated was classified as 1 (0.3 – 1.2), 2 (1.3 – 2.1), 3 (2.2 – 3), 4 (3.1 – 3.9), 5 (4.0 – 4.8), 6 (4.9 – 5.7), 7 (5.8 – 6.6), 8 (6.7 – 7.5), 9 (7.6 – 8.4) and 10 (8.5 – 9.93). Statistical analysis By descriptive analysis, average values of soil contents of exchangeable K and Clay were determined as function of soil depth for each topographic section (S, US, MS and FS) using SPSS 10 package. Cross table analysis was done to determine the frequency of soil colour hue in a soil depth (H1, H2, H3 and H4) according to the topographic sections likewise for the levels (H = high, M = moderate and L = low) of exchangeable K according to the redness class (1, 2, 3…..9 and 10). Analyze of variance was done to determine the mean values of soil contents of exchangeable K and clay as for K/CEC ratio for recorded colour hue (2.5YR, 5YR, 7.5YR and 10YR) in a soil depth at each topographic position. Similar analysis was done for the ratio of K/CEC, soil contents of exchangeable K and clay according to redness class for the soil depths. Pearson correlation analysis was also performed between soil content of K and soil colour hue and redness as well as soil content of clay using the thickness of elementary soil horizon as weighted variable. SAS (version 8) was used for these statistical analyses and the critical level of probability was fixed at 0.05 ( α ). RESULTS Soil colour hue and the other soil parameters Table 1 shows the frequency of dominant soil colour hues (2.5YR, 5YR, 7.5YR and 10YR) as encountered in the studied zone for each topographic position along the toposequence and according to soil depth. There is significant (P- χ 2  < 0.0001) association of soil colour hue with the topographic positions indifferently to soil depths: Reddish (2.5YR and 5YR) soils are characterizing the hill slope (Summit and upper slope) while 10YR does so for the soil of foot slope (FS) when missing in the soil of the summit and likewise for the upper slope in some extend. This aspect is further illustrated by the decreasing of the frequency of 2.5YR from the summit to the foot slope contrasting with that of the 10YR as soil colour hue. Moreover, each of these hues of soil colour is characterized by the increase of soil content of clay indifferently to the topographic positions (Figure 1). However, the values are very closed depending to soil depth, especially for 2.5YR and 5YR likewise for 7.5YR and 10YR. Nevertheless, FS is characterized by difference of soil content of clay between the dominant soil colour hues represented by 7.5YR and 10 YR except in the topsoil (H1): highest clay content accounts for 7.5YR. In turn, soil content of K is decreasing in soil depth except for 7.5YR in the summit likewise for 2.5YR and 10YR in the middle slope position (Figure 2). These particulars cases points out the increase of soil content of K in the subsoil as H3 and H4 depending to colour hue and the topographic sections. No significant difference is observed (Table 2) between the mean values of soil content of K and K/CEC ratio respectively according to soil colour hues in the topsoil H1 whatever the topographic sections contrasting with the results obtained in 20 – 60 cm (H2): highest values of K/CEC ratio are significantly ( P   < 0.05) noticed for yellowish soil of 10YR from the upper slope to the foot slope. Similar observation accounts for soil content of K ( P   = 0.0002) at upper slope position in H2 as well as in H4 for the summit where 5YR is characterizing the richer soil in exchangeable K and the highest ratio of K/CEC. Roughly, the soil colour hues are more relevant to soil K/CEC ratio emphasizing highest value for 10YR in H2 of US, MS and FS while, 5YR does so in H4 of the soil at the summit. None of such results is observed for H1 and H3.  Published by Basic Research Journal of Soil and Environmental Science Koné et al. 49 Table 1 . Soil color hue frequency (%) as encountered by topographic section within a soil depth in the studied area Frequency (%) Depth Hue S US MS FS H1 (0-20 cm) 2.5YR 75.1 9.1 4.1 --- 5YR 22.4 77.8 25.8 --- 7.5YR 2.4 13.1 52.6 39.5 10YR --- --- 17.5 60.5 H2 (20-60 cm) 2.5YR 79.0 17.2 8.0 --- 5YR 19.8 74.6 30.0 --- 7.5YR 1.2 7.4 48.0 44.2 10YR --- 0.8 14.0 55.8 H3 (60-80 cm) 2.5YR 75.4 25.0 8.1 --- 5YR 23.0 69.4 48.4 --- 7.5YR 1.6 5.6 40.3 36.0 10YR --- --- 3.2 64.0 H4 (80-150 cm) 2.5YR 81.6 32.5 5.3 --- 5YR 18.4 60.0 44.7 --- 7.5YR --- 7.5 34.2 18.2 10YR --- --- 15.8 81.8 Df 9 χ  test probability <0.001 Number of samples 998 --- : not available Summit (S) Upper slope (US) Middle slope (MS)   Foot slope (FS) Figure 1 . Soil content of clay according to soil color hue (2.5YR, 5YR, 7.5YR and 10YR) in different depth (H1, H2, H3 and H4) for each topographic section (S, US, MS and FS)    Published by Basic Research Journal of Soil and Environmental Science 50. Basic Res. J. Soil Environ. Sci. Summit (S) Upper slope (US)   Middle slope (MS) Foot slope (FS)   Figure 2 . Soil content of K according to soil color hue (2.5YR, 5YR, 7.5YR and 10YR) in different depth (H1, H2, H3 and H4) for each topographic section (S, US, MS and FS)   Table 2 . Ratio of K/CEC and the content of K in a soil depth (H1, H2, H3 and H4) according to soil colour hue (2.5YR, 5YR, 7.5YR and 10YR) at different topographic sections. S US MS FS K(cmol kg -1 ) K/CEC (%) K(cmol kg -1 ) K/CEC (%) K(cmol kg -1 ) K/CEC (%) K(cmol kg -1 ) K/CEC (%) H1 2.5YR 0.30a 4.15a 0.30a 3.60a 0.34a 4.20a ------ ------ 5YR 0.35a 4.17a 0.31a 4.55a 0.29a 4.85a ------ ------ 7.5YR 0.10a 2.33a 0.21a 3.40a 0.25a 3.88a 0.23a 4.38a 10YR ------ ------ ------ ------ 0.34a 4.32a 0.40a 6.77a P>F 0.351 0.581 0.387 0.509 0.764 0.372 0.450 0.445 H2 2.5YR 0.22a 3.19a 0.19b 2.86b 0.18a 2.26b ------ ------ 5YR 0.19a 2.96a 0.17b 2.83b 0.21a 3.84ab ------ ------ 7.5YR 0.13a 2.58a 0.11b 3.19b 0.14a 2.56b 0.15a 2.50b 10YR ------ ------ 0.70a 8.80a 0.27a 5.11a 0.19a 4.72a P>F 0.636 0.856 0.0002 0.015 0.142 0.011 0.236 0.011 H3 2.5YR 0.16a 2.35a 0.12a 2.39a 0.25a 2.60a ------ ------ 5YR 0.18a 2.98a 0.16a 2.56a 0.16a 2.97a ------ ------ 7.5YR 0.22a 5.61a 0.08a 2.38a 0.14a 2.60a 0.14a 2.09a 10YR ------ ------ ------ ------ 0.20a 6.35a 0.10a 2.87a P>F 0.240 0.082 0.123 0.893 0.594 0.426 0.401 0.050 H4 2.5YR 0.14b 1.86b 0.16a 2.02a 0.20a 2.33a ------ ------ 5YR 0.37a 6.15a 0.11a 1.65a 0.11a 1.93a ------ ------ 7.5YR ------ ------ 0.10a 2.77a 0.14a 2.91a 0.13a 1.42a 10YR ------ ------ ------ ------ 1.82a 12.82a 0.09a 1.94a P>F 0.0005 0.0002 0.102 0.184 0.155 0.183 0.399 0.665 ------: not much
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