The Adsorption And Biodegradation Of Soluble Organic Nitrogen, Carbon In Soil

Soluble organic matter was an important component in the solutions in terrestrial and aquatic ecosystems through its influence on nutrient availability, toxicity, and transport of metals and contaminants. Soluble organic matter in soils plays a key role in the biogeochemistry of carbon, nitrogen, in pedogenesis in soils. Soluble organic matter represents a potential supply of organic nutrients to soil microflora and plant. More attention has often been focused on the behavior of SOC (soluble organic carbon) in forest soils, and less attention to the roles of SON(soluble organic nitrogen)or SOC in agricultural soils. The contents of SOC and SON will be increased when large amounts of organic fertilizers are applied to soil. In these soils, SOC and SON perhaps has important role in regulating C and N cycles. However, information about the properties of adsorption and biodegradation of SOC and SON in soil, and nitrogen supplied in agricultural soils is limited.In this study, the contents of SOC and SON in different manures were measured. The adsorption of SOC and SON separated from the manure by different soils was evaluated, and the effect of temperature on adsorption was also determined. The incubation experiment were carried out to study the changes of concentration and structural components and biodegradation of SOC, and the relationship between SON and nitrogen mineralization in soils on the loess Plateau in China. The main results showed as follows:1. A laboratory experiment was conducted to measure the concentration of SON and SOC extracted with water and 0.01 mol L-1CaCI2 from different types of organic manure. Additional characteristics were also evaluated. Results showed that the average concentration of water extractable SON in the seven manures was 105.2 mg L-1. The average concentration of CaCl2 extractable SON was 91.6 mg L-1. SON in the manures accounted for 70% of the total soluble nitrogen (TSN) and 5% of the total nitrogen (TN). On a dry weight basis, the average content of water extractable SON was 1188 mg and average CaCl2 extractable SON was 1037 mg kg-1. The average concentration of water extractable SOC in the seven manure types was 695 mg L-1. CaCl2 extractable SOC averaged 622 mg L-1. SOC accounted for 2% of the total organic carbon (TOC) in the manure. On a dry weight basis, the average content of water extractable SON in the manure was 7873 mg kg-1. CaCL2 extractable SON averaged 7054 mg kg-1. The ratio of SOC/SON in the manures was about 6.8. There was a significant correlation between SON and SOC (P<0.05) in the manure. A negative correlation was observed between the concentration of SON and NO3--N (P<0.05). The results indicate that SON and SOC are important constituents in organic manure. More attention should be paid to these constituents in order to reduce nitrogen and carbon loss from manure fertilizer to the environment.2. Soil samples, collected from farmlands and woodlands in different areas of the Loess Plateau, were incubated aerobically in the lab for 35 days. Results show that the concentration of soluble organic carbon (SOC) in the samples decreased, while the concentration of soluble organic nitrogen (SON) increased significantly during incubation. Typ -Eum -Orthic Anthrosols was much higher than Typic Hapli-Ustic Argosols and Typ-Ishumisols in SOC and SON at the beginning of and throughout the incubation. In the case of Typ-Ishumisols, woodland was significantly higher than farmland in SOC and SON. Incubation significantly increased UV 280 and HIXem values of soluble organic matter. The rising trend of the latter was especially significant on Day 8 and Day 35. The SOC/SON ratio of the samples gradually declined with the incubation going on. It was discovered through correlation analysis that the increase in UV 280 value was positively correlated with the decrease in SOC on Day 35, and that remarkable negative relationship between initial HIXem and the decrease in SOC on Day 8, which suggests that UV 280 and HIXem are suitable indicators that may to a certain extent reflect changes in types and structures of SOM in the soil.3. Soluble organic carbon (SOC) and nitrogen (SON) extracted from soils are important components of nitrogen in terrestrial ecosystems. Adsorption is one of mechanism to control their mobility in soil. A laboratory experiment was conducted to study the adsorption of SOC and SON separated from manures by two contrasting agricultural soils from the Guanzhong plain of Shaanxi Province. There were significantly linear relationships between the quantity of SON and SOC adsorbed on soils and the initial SON and SOC concentration added into the solution; and the adsorption of SON and SOC by two soils could be fitted by the initial mass isotherm model. The quantities of SON and SOC adsorbed by Argosols were higher than that of Anthrosols. The percentage of adsorption of SON and SOC by Anthrosols was 24.3 % and 18.8 %, respectively; the corresponding values for Argosols were 38.3 % and18.6 %, respectively. The adsorption rates of SON and SOC by the two soils was low, indicating high mobility of SON and SOC in the soils. Compared to the adsorption capacity of SON and SOC, the SON adsorbed by soils was stronger than SOC, indicating the high potential leaching of SOC from agricultural soils.4. Experiments on the sorption of SON and SOC in agricultural soils at different temperatures and the change of UV280 absorbance and HIXem (Humification index) after absorption were conducted. The results showed that absorption isotherm of SON and SOC in the soils were fit for the initial mass isotherm. Temperature had a strong effect on the absorption of SON and SOC. With increasing temperature, the absorption affinity of SON and SOC were gradually decreased, and the initial net release of SON and SOC from the soil samples strongly increased. The values of the specific absorbance at 280 nm and the humification indices deduced from emission fluorescence spectra(HIXem) increased during absorption. These indicated that aromatic and complex compounds were left during absorption. Adsorption capacity of SON is stronger than SOC. We conclude that SOC is more susceptible to leach from agricultural soils than SON. We assume that SON and SOC had the higher mobile.5. We conducted a laboratory incubation of arable and forest soils in different areas of the Loess Plateau at 20°C for 35-day. During incubation experiment, biodegradability experiment of soluble organic carbon (SOC) which extracted from different period of incubation was carried out for 7-day. We aimed to clarify the content and the biodegradation of SOC derived from different period of incubation and to relate its extent to properties such as UV absorbance and emission scan fluorescence spectroscopy. The result showed that the concentration of SOC in the samples decreased during incubation, while incubation significantly increased UV 280 and HIXem values of soluble organic matter. The mean rates of biodegradation (% of initial SOC) of SOC extracted from day-0, day-8 and day-35 was 48.1%, 35.2% and 34.8% respectively. In the all, the extent of biodegradation of SOC showed a decreased tread with the extent of decomposition of organic matter increased. There was no significant relationship between the rate of biodegradation (% of initial SOC) of SOC and the UV280 and HIXem initial values of soluble organic matter.6. Laboratory analysis was conducted to investigate nitrogen mineralization of soils in The Loess Plateau of China. The aims of our study were to determine the content of SON(soluble organic nitrogen), and the percent of TSN(total soluble nitrogen) to SON, and the relate SON to mineralized nitrogen. Results showed that the content of SON of all soils increased significantly during incubation. The percent of TSN to SON was the highest at start stage. From day-0 to day-3, the percent declined to the lowest level. After that the percent increased gradually. In the end of incubation, SON accounted for 24% of TSN. Soil mean mineralization potential (N0) based on total soluble nitrogen (45.8 mg kg-1) was a quarter higher than mean mineralization potential (36.5 mg kg-1), which was based on mineralized inorganic nitrogen. The positive relationship was found between the content of SON and mineralization potential that based on mineralized inorganic nitrogen, but not reach significant level. Our results suggested that in order to evaluate nitrogen mineralization, the content of SON was only measured during incubation may underestimate mineralization potential and the amount of nitrogen losses.