The forms of aluminium in Stagnosols in Serbia V. Mrvić1, M. Jakovljević2, D. Stevanović2, D. Čakmak1 1Institute of Soil Science, Belgrade, Serbia 2Faculty of Agriculture, Belgrade, Serbia ABSTRACT The interactive relations of Al forms and the most important characteristics of Stagnosols were researched to dia- gnose which factors are the best to control the content of phytotoxic Al forms. The values of exchangeable Al (AlKCl) range from 0.0 to 560.7 mg/kg and increase with depth. The variation of exchangeable Al is high and it depends on the changes of all forms of soil acidity and the degree of base cation saturation. Their relation is best described by a non-linear function. The contents of total Al and Al extracted by ammonium oxalate in dark (Al amorphous, Aloxa) increase with depth, together with the increase of the content of clay particles. The values of Al extracted by sodium citrate/dithionite (Al crystalline, Aldit), 0.5M CuCl2 (AlCu) and 0.25M EDTA (AlEDTA) are in good correlati- on and they predominantly depend on the parameters of soil acidity. The value of AlCu-AlKCl (in eluvial horizons) is best represented by organically bound Al. Effects of the reserves of aluminium Aldit, AlCu and AlEDTA on the changes of exchangeable Al are higher (medium and high correlation), while the effects of the total Al and Aloxa are lower. Keywords: Stagnosol; soil; exchangeable Al; Al amorphous; Al crystalline; organic Al Stagnosols (FAO 2006) cover about 538 000 ha, 2003). Bouman et al. (1995) also reported that the or 6%, from the area of Serbia. One of the most low content of exchangeable Al in acid prairie soils important chemical characteristics of Stagnosols is can be the consequence of organically bound Al, that they are more or less leached, acid soils, and as well as of the inhibition of acid decomposition therefore one of the major problems is the elevated of minerals, the effect of high concentrations of 2+ content of mobile aluminium, which can be toxic soluble Mg and H4SiO4 on the stabilisation of for plants and other parts of the environment. clay minerals, climate conditions – soil freezing The study of Al regime in Stagnosols of Serbia and melting. was reported by several researchers (Nikodijević A significant issue that has not been sufficiently 1972, Jakovljević et al. 2001, Dugalić et al. 2002). investigated in Stagnosols is the content and the dy- They found that the content of exchangeable Al was namics of less readily available Al forms and their ef- variable per sites and profile depths and that the fect on available Al. According to Nikodijević (1972), interaction of pH and Al was high. It is concluded in some Stagnosol profiles in West Serbia total Al that liming is very efficacious for Al decrease, and varies from 5.8–7.9% in the topsoil horizon, 9–10.6% that fertilizing with phosphorus, humification, in Btg, and amorphous Al2O3 (Tamm method) in and deep tillage have positive effects. Ah horizon from 3200 to 4310 mg/kg, Btg horizon Soil reaction is one of the best parameters for from 4040 to 5750 mg/kg (it accounts for 2–4% of estimation of exchangeable Al content. Al solubil- the total Al). The correlation between exchangeable ity increases at the active soil acidity below 5.5. Al, total Al and amorphous Al is weak. In addition to soil reaction, Al dynamics is also In the studies of different types of soil, many affected by other factors, especially soil organic researchers conclude that the content of Al oxides matter content and composition. Acid cations in is not proportional to the content of exchange- the complexes or the chelates with organic matter able Al (Alvarez et al. 2002, Garcia-Rodeja et al. are not readily exchangeable by normal exchange 2004). McLaughlin et al. (1990) reported that in reactions (McLean 1965, Dijksta and Fitzhugh grassland soils in Australia, the values of Al amor- 482 PLANT SOIL ENVIRON., 53, 2007 (11): 482–489 phous oxides (extracted by NH4-oxalate) range AL solution (method by Egner-Riehm), and P from 470 to 2160 mg/kg; Al crystalline oxides was determined by colorimetry with molybdate, (extracted by Na citrate-dithionite) range from and K by flame photometry; hydrolytic acidity 206 to 1110 mg/kg; Al extracted by CuCl2 from (H meq/100 g) – after Kappen (extraction by 221 to 1050 mg/kg. These less available fractions CH3COONa, titration with 0.1M NaOH); the sum are in good correlation, but these forms and the of exchangeable basis (S) – after Kappen (extrac- content of toxic Al forms (extracted by KCl and tion by 0.1M HCl, titration with 0.1M NaOH); CaCl2) are in low correlation. Similar relations total capacity of cation adsorption (T) and de- are also reported by Jarvis (1986). gree of base saturation (V%) – was calculated; On the other hand, it is considered that Al solu- soil texture – combined method of sieving and bility is controlled by the amorphous forms of pipette method. Exchangeable Al (AlKCl) and Al(OH)3 rather than by its crystalline forms (Juo exchangeable acidity (meq/100 g) were deter- and Kamprath 1979). Jarvis (1986) reports that mined by extraction with 1M KCl and titration Al in the forms which are not well crystallised (Sokolov’s method). represents more labile reserves: exchangeable Al, The less available Al forms were determined electro-statically bound to negatively charged at the selected sites (45 samples). Total Al was clays or organic colloids; Al present in organic determined by digestion with HF and perchloric complexes, or as non-crystalline coatings on soil acid, on AAS with N2O-C2H2 flame (Barnhisel particles, and Al present as the microcrystalline and Bertsch 1982). phase of hydroxy-polymer components which Less available forms were also determined on occupy the clay mineral interlayers. AAS after the application of the procedure de- It is evident that, in accordance with Bertsch scribed by Jarvis (1986) and McLaughlin et al. and Bloom (1996), the methods of Al determina- (1990): Al crystalline (Aldit) – Na citrate-dithionite tion are not always selective for specific phases, solution (5 g soil were shaken for 1 h with 50 ml although there are some relations between opera- solution containing 0.15M Na citrate, 0.05M citric tionally defined, less available Al and the selective acid and 2 g/l Na dithionite); Al amorphous (Aloxa) extractants. – ammonium oxalate solution in the dark (1 g soil This study deals with the contents of different was shaken in the dark for 4 h with 50 ml of acidi- forms of Al (by depth, sites), their interdepend- fied 0.2M NH4 oxalate at pH 3.25); Al extracted ence, and their relation with Stagnosol character- by CuCl2 (AlCu) – 3 g soil was shaken for 2 h with istics. The aim of the study is to determine the 30 ml 0.5M CuCl2; Al extracted by EDTA (AlEDTA) most suitable factors to control the content of – 5 g soil was shaken for 1 h with 50 ml 0.25M EDTA Al phytotoxic form. [modification, the original method by Farmer et al. (1980) applies 0.5M EDTA]. All the suspensions were centrifuged for 20 min at 2500 relative cen- MATERIAL AND METHODS trifugal force and filtered (Whatman 42) before analysis. Al dynamics was assessed at 15 sites of lowland The study results were processed by mathemati- Stagnosols in the Northwest and East Serbia and in cal-statistical methods of regression analysis and the valley of the Zapadna Morava river. Lowland descriptive statistics (program SPSS 10.0.). Stagnosols in Serbia occur in temperate continental climate conditions, at the altitude of 100–350 m, on flat or mildly sloped lake, diluvial and river RESULTS AND DISCUSSION terraces. Closer data about the study area are presented in Table 1. Stagnosol characteristics and the content The samples were taken at each site from farm- of exchangeable Al land and meadow lands, from three characteristic horizons (Ah, Eg, EBtg or Btg) (90 samples). The Different factors of soil formation bring about basic characteristics of soil samples were deter- different Stagnosol characteristics. The structure mined by standard methods: pH of the soil solu- of the profiles to the analysed depth is Aoh-Eg-Btg; tion in water suspension (pH ) and in 1M KCl Aoh-Eg-EBtg; Aoh-EBtg-Btg. The thickness of H2O suspension (pHKCl) – potentiometrically; humus the humus – accumulation horizon is most often – by oxidation with solution KMnO4 (according 15–20 cm, the impermeable horizon is mainly at to Kotzman); available P and K – extraction with 40–60 cm. PLANT SOIL ENVIRON., 53, 2007 (11): 482–489 483 Table 1. Basic characteristics of the study area Mean annual Annual Sites of Stagnosol Area temperature precipitation Parent rock formation (°C) (mm) abrasion terraces aeolian sediments Northwest 11–12 650–850 and hillocks covering the Pleistocene Serbia of the Pannonian Sea sandy loams and clays Valley sandy-loessoid Pleistocene clays of the Zapadna 10–11 710–750 older river terraces and loams below which are older Morava river sediments of heavier composition mixture of clay Karbulovo and sands of indefinite age fluvial andesite gravel, East Serbia 10–11 610–690 diluvial terrace-Salaš covering clay sediments of the Sarmatian more acid sediments IV Danube terrace-Kladovo deposited in the already existing substrate Stagnosols are characterised by textural vari- loam) than Stagnosols in East Serbia, which have ability per profile depth, which is manifested in a higher percentage of coarse sand (on average the lighter soil texture of the eluvial horizons about 4–5 times) and less silt (on average 1.7 times). and in clay accumulation in the hardly perme- Eluvial horizons are sandy loam and sandy clay able illuvial horizon (Table 2).