Swine (Sus domesticus) manure was comprehensively characterized with respect to Cu, Mn, and Zn in feed additives. This research was conducted to study the leachability and identify factors influencing the leachability of these elements from separated swine manure (SSM) composts to assess its environmental hazard. Several chemical properties were determined to assess the degree of maturity of eight SSM composts. A series of extraction schemes were used to determine base‐extractable metals and their distribution on humic substance fractions (humic acid, HA; fulvic acid, FA; and nonhumic fraction, NHF), chemical fractionation, synthetic acid rainwater (SAR) solubility, and extractability at various pH levels of metals in composts. We evaluated the influence of dissolved organic carbon from compost on the extractability of these metals. The SSM composts were enriched with Cu (154–1380 mg kg−1), Mn (239–976 mg kg−1), and Zn (372–2840 mg kg−1). The SAR and neutral‐pH extractable fractions of Cu, Mn, Zn, and organic C were generally low (<10% of their total content). Copper leachability in Sample F2 compost, however, was high (20%), resulting from immaturity and associated substantial dissolution of organic C (18%). High extractability (86%) of Cu from humic substances (HS) extraction and at high pH levels (>8) resulted from dissolution of organic matter. Conversely, the extractability of Mn and Zn at alkaline pH levels was low. The major portions of Cu, Mn, and Zn were found in the organic, oxide, and carbonate fractions, respectively, regardless of their content in these composts. The results of this study show that Cu in SSM compost is primarily bound to organics.
The qualitative and quantitative characteristics of soil organic carbon (SOC) and related humic acids (HAs) extracted from the soils of field plots were investigated after 8 years of annual paddy (Oryza sativa L.) and upland maize (Zea mays L.) rotation with various fertilizations. Seven fertilization treatments were selected: Ck (no inputs); Chem (chemical fertilizer of NPK); Comp (swine compost); Comp + 33% of Chem N rate; Comp + 67% of Chem N rate; GM (legume green manure) + 33% of Chem N rate; and peat + 33% of Chem N rate. Organic and inorganic nitrogen inputs of six treatments were equivalent with respect of nitrogen content, but Comp, GM, and peat treatments were complemented with various amounts of inorganic N. After harvest of the eighth paddy crop, surface soil samples collected from the plots were subjected to soil characterizations and extraction of humic substances, which were used for chemical, spectroscopic (FTIR, 13C NMR, ESR, X-ray diffractometry), delta13C, and 14C dating analyses. The yields of HAs extracted from the seven treatments were significantly different. Treatment containing persistent organic compound such as the peat + 33% N treatment increased the humification process in topsoils and produced higher yield of HA. Spectroscopic analyses revealed that fertilization treatments changed the functional groups, alkyl C, crystalline characteristics, and delta13C ratios of HAs and turnover rate of SOC considerably. The SOC of the peat + 33% N treatment had the highest mean residence time of 3100 years. Various fertilizer treatments are correlated with turnover rate of SOC and related HAs, which are associated with concerned carbon sequestration as well as mitigation of CO2 emission in the soil environment.
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