| Summary: | 博士 === 臺灣大學 === 農業化學研究所 === 98 === Sewage sludge is abundant in nitrogen, phosphorus and other nutrients for plant growth. When sewage sludge is applied to land, the application rate designed to provide the amount of nitrogen needed by crop. However, applying sewage sludge to meet N needs of crops will add excess P result in an accumulation of soil P. Three soils (Pu, Sk, and Eh) were applied with sewage sludge compost (SSC) for laboratory incubation and pot experiments. The aims of the study were to investigate the effect of SSC application on (1) mineralization of organic C and organic N by laboratory incubation experiment, and (2) the uptake of N and P by leaf beet (Beta vulgaris L.) by pot experiment in three soils.
The results of incubation experiment indicated that the highest peaks for rate of CO2 evolution occurred at 3 d of incubation in all three soils. The Eh soil revealed the highest rate of CO2 evolution. These results presumably because microbial activity was increased under relatively high soil pH. The percentage of added organic C remained ranged from 84-94% for all treatments at the end of the incubation which suggests that decomposition of SSC might be quite stable. In the Pu and Sk soils, the NH4+–N concentrations were increased rapidly after 3 d of incubation. The maximum NH4+–N concentration was observed at 14–21 d of the incubation, and then gradually decreased as the incubation period progressed. These results suggest that ammonification was occurred in the Pu and Sk soils during the initial incubation period. The percentage of SSC organic N released did not exceed 8% in all three soils at the end of the incubation. This result suggested that the mineralization of organic N was low. In Pu and Sk soil, the pH increase might have resulted from the effect of ammonification of organic N and base cations released in SSC. However, in the Eh soil, soil pH decreased slowly after 3 d of incubation, the decrease in soil pH may be attributed to the acidic effect of the nitrification process. For all treatments, the concentration of Mehlich-3 extractable P remained unchanged during the incubation period.
The results of pot experiment showed that the application rate based on N need (BN) treatment resulted in highest soil electrical conductivity and contents of Mehlich-3 extractable P. For Pu and Sk soils, the dry matter yields of leaf beet increased significantly (P <0.05) in BN treatment compared with application rate based on P need (BP) treatment. However, in Eh soil, the dry matter yields of leaf beet were not significantly different in all treatments. In BN treatment, the uptake of N of leaf beet was lower in the Eh soil than in the other two soils. These results presumably because the relatively high EC value led to the disadvantageous effect of the growth of leaf beet.
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