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Turkan Unsal, Sonay Sözüdoğru Ok Soil Science Department, Agricultural Faculty, Ankara University, 06110 Ankara Turkey ABSTRACT Humic acids extracted from different organic wastes have been characterised by chemical methods. The chemical properties of HAs showed changes depending on the source from which they were obtained. The C content in HAs from organic wastes fluctuated around the C value in soil HA with the exception of CB and TD. Compared with soil HA, The N contents of HAs from SS and BFS and TD were much higher and those in HAs from CCSM and CGM are slightly higher whereas N contents of HAs from RTW and CB were lower.E4:E6 ratios for HAs in organic wastes were found generally higher than that for soil HA which indicating that low degree of condensation and humification. The carboxyl and phenolic-OH group contents ranged from 0.51 to 2.23 and from 11.10 to 20.73 respectively. High values of carboxyl and phenolic-OH contents indicated that materials still within early stages of humification. INTRODUCTION Organic matter content strongly affects the soil fertility by increasing the availability of plant nutrients, by improving the soil structure and the water-holding capacity, and by acting as an accumulation phase for toxic, heavy metals in the soil environment (Stevenson, 1985). Therefore the recycling of organic wastes through their application to the soil can be an important, promising practice for agricultural activities. The soil has almost unlimited capacity to accept large quantities of those materials and transform them through biodegradation processes leading to humic substance synthesis. Part of this newly formed organic matter (humic acids) has a great influence on soil fertility (Lee and Bartlett, 1976), due to its carboxyl and phenolic-OH groups that interact with various soil components. A better understanding of the chemical and physical characteristics of these acids is necessary to comprehend the transformations the acids will undergo after different times in the soil environment. The aim of this study was to investigate chemical characteristics of humic acids already present in organic wastes, before they are added to soil, and compare with those of soil HA. MATERIALS & METHODS Sewage sludge (SS), beer factory sludge (BFS), raw tea waste (RTW), composted grape marc (CGM) and composted spend mushroom (CSM), composted bark (CB), and tobacco dust (TD) were as used organic waste samples. An inorganic soil sample also was used for comparison. The extraction of humic acids (HAS) from raw samples was performed according to Schnitzer (1982), (Figure 1). Before extraction raw organic waste samples were analysed for moisture, pH (Gabriels and Verdonck, 1992), organic matter (DIN, 1978), organic C (Nelson and Sommers, 1982) and total nitrogen (Bremner, 1982) content. Humic acids obtained after extraction were subjected to moisture, ash and E4:E6 (Chen et al. 1977), organic C (Nelson and Sommers, 1982) total nitrogen (Bremner, 1982), total acidity and carboxyl groups (Martin et al. 1963) content analyses. Phenolic-OH were obtained by difference.  Figure 1. Extraction, fractionation and purification of humic acids. RESULTS & DISCUSSION Analytical data for the organic wastes investigated are presented in Table 1. The analytical data illustrate important differences among the wastes.  PH values of SS, CGM and SMW were alkaline while CB, RTW and TD had an acidic pH, and BFS had the neutral pH. The organic matter content of the samples ranged from 17.20 to 94.89 %. RTW had the highest organic matter wastes. The organic C content of RTW, with the exception of TD, was much higher than those of the others. The N content was highest in BFS followed by TD>CGM>CB>DTW>SCM>SS and lowest in the soil as expected. Depending on the stage of decomposition that organic wastes have undergone, C/N ratios ranged from 4.38 to 23.27. All these findings agree closely with those of several authors who worked with similar organic wastes (Baran et al. 1995; Kütük et al. 1995; Birben, 1998; Ataman 1999; Baran et al, 1998) Humic acids : Yield of extracted and purified humic acids from organic wastes and the soil expressed as mg g-1 and as % of organic C are presented in Table 2.  Among sources the yield of HAs was the maximum for CB followed by CGM>RTW>BFS>SS>CSM>TD and the soil. This was probably due to the variation in the composition and differential degradation of lignins. The highest yield of CB HAs is probably due to the greater content of humified organic matter caused by longer period of bark decomposition. The very low amount of HAs extracted from TD, which has a much higher content of organic C might be attributed not only to the shorter period of decomposition but also to the slow humification process of tobacco dust. Organic C and N content, C/N ratio, and E4:E6 ratios of humic acids are shown in Table 2. The C content in HAs from organic wastes fluctuated around the C value in soil HA, with the exception of CB and TD. Compared with soil HA, the N contents of HAS from SS and BFS and TD were much higher and those in HAs from TD, CSM and CGM are slightly higher, whereas N contents of HAs from RTW and CB were lower. As a consequence the C/N ratios of BFS and SS HAs were much lower, those of CGM and CSM were lower and those of TD, RTW on CB were higher than value measured for soil HA. All these findings are close to the values found by other authors for similar materials (Schnitzer and Khan, 1972; Hernandez et al. 1993). The great difference between the N content of the HA extracted from the composts and that from the sludges is due to the short transformation processes that the materials have undergone which are not sufficient to degrade the nitrojen compounds (Hernandez et al. 1993). The E4:E6 ratios for HAs in organic wastes were found generally higher than that for soil HA (Table 2). The results suggest that HAs in organic wastes are characterised by a low degree of condensation and humification with respect to soil HA (Senesi and Brunetti, 1992). The carboxylic and phenolic-OH group contents and as a consequence, the total acidity of HAs of organic wastes are much higher, or higher than the corresponding value for soil HA (Table 3). As can be seen from the Table, the majority of total acidity of HAs consists of phenolic-OH groups. With few exceptions, the values for those parameters generally were higher than those of other studies for similar wastes. . However in several studies phenolic-OH group content were also found to be higher than that of carboxylic group ( Senesi and Brunetti 1996). This may be attributed to using different methods for the determination of functional groups. Composting studies indicate that, with increasing time of composting phenolic -OH contents degreases and COOH group content increases. On the other hand higher values than in soil HA are reported for carboxyl group content in HAs from composted bark and farmyard manure and for phenolic-OH group content in some sewage sludge HAs (Senesi and Brunetti 1996).  The results indicated that the chemical, properties of humic acids changed depending on the source from which they were obtained. Senesi et al. (1995) stated that, soil application of partially humified organic wastes of any origin affects, to a measurable extent, the composition, structure and chemistry of nature soil HA. These modifications appear to be more extensive in the FAS than in HAS of an amended soil. With increasing time after amendment addition, however, the observed structural and chemical modifications which have occurred in the amended soil humic substances become less and less apparent, especially in the HA fraction, with a clear trend approaching the molecular properties typical of native soil humic substances (Senesi and Brunetti, 1996). Therefore this is an important result which supports the application of recycling partially humified organic wastes as beneficial soil amendments. REFERENCES Ataman Ş. (1999). Ankara atıksu arıtma tesisi, arıtma çamurunun toprak biyolojik aktivitesi üzerine etkisi. Master Tezi. Ankara Üniversitesi, Ziraat Fakültesi Toprak Bölümü. Ankara. Baran A., Çaycı G. ve İnal A. (1995). Farklı tarımsal atıkların bazı fiziksel ve kimyasal özellikleri. Pamukkale Üniv.Müh.Fak.Mühendislik Bilimleri Dergisi. 1 (2-3): 169-172. Baran A., Çaycı G. and Sözüdoğru Ok S. (1998). The effects of beer factory sludge and some soil properties. International Symposium on Arid Region Soil. Menemen-İzmir-Turkey, 21-24 September. Birben H. (1998). Atık mantar kompostunun begonya (Begonia Semmperflorens) bitkisinin gelişimi üzerine etkisi. Master Tezi. Ankara Üniversitesi Ziraat Fak.Toprak Böl. Ankara. Bremner S.M. (1982). Total nitrogen. Methods of Soil Analysis. Part 2. 595-624, ASA-SSSA.USA. Schnitzer M. and Khan S.U. (1972). Humic substances in the Environment. Marcel Dekker. Newyork. 57-60. Chen Y., Senesi N. and Schnitzer M. (1977). Information provided on humic substances by E4/E6 ratios. Soil Sci. Am.J. 41: 352-358. DIN 11542 (1978). Torf für Fartenbau und Lanwirtschaft. Gabriels R. and Verdonck O. (1992). Reference methods for analysis of compost. In: Composting and compost quality assurance criteria. 173-183. Hernandez M.T., Morena J.J. and Costa F. (1993). Infrared spectroscopic characterisation of sewage sludge humic acids. 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In: Piccolo A., (ed.) Kumic Substances in Terrestrial Ecosystems. Amsterdam, Elsevier (in press). Senesi N. and Brunetti G. (1996). Chemical and Physico-Chemical Parameters for Quality Evaluation of Humic Substances Produced During Composting. The Science of Composting, European Commun Int. Symp-Blackie Acamic Professional. Stevenson F.J. (1985). Geochemistry of soil humic substances. In: Humic substances in soil, sediment and water. 6-R. Aiken, D.M. Mc Knight, R.L. Wershaw and P. Mac Carthy, Wiley-Interscience, New York. p. 13-52. |