Thermogravimetric evaluation of chitin degradation in soil: implication for the enhancement of ammonification of native organic nitrogen by chitin addition
2018
Kumeta, Yuta | Inami, Kaori | Ishimaru, Kozue | Yamazaki, Yasushi | Sameshima-Saito, Reiko | Saito, Akihiro
Degradation of chitin, which is an aminopolysaccharide used as a soil amendment, has been often monitored in soil via its degradation products such as carbon dioxide and ammonium. We report here the applicability of thermogravimetry to measure the amount of chitin added to soil. The maximum pyrolysis rate of the upland surface soil of Brown Forest soil supplemented with chitin was strongly correlated with added chitin content (r = 0.999) when the content exceeded 6.0 g kg⁻¹. The maximum pyrolysis rates of chitin-added soil (around 385°C) was distinctive from those of soil supplemented with cellulose, chitosan, N-acetylglucosamine, and N,N’-diacetylchitobiose (around 340°C, 300°C, 200°C, and 240°C, respectively), indicating the specific detection of chitin. Soil incubation study demonstrated that 60 g kg⁻¹ chitin added to the soil declined exponentially (r = 0.993) within days and could not be detected at 90 days after the addition of chitin. Total carbon (C) content also decreased within days whereas total nitrogen (N) remained almost constant over the 90 days. The amount of ammonium-N increased in the initial 30 days after the addition of chitin and reached about 3.6 g kg⁻¹, which corresponded to the amount of N in the added chitin (4.1 g kg⁻¹) while the amount of nitrite-N and nitrate-N were below 2.0 and 15 mg kg⁻¹, respectively. Comparison of the measured ammonium-N and total-C contents with those calculated from the measured chitin-content implied that addition of chitin enhanced degradation of native organic compounds in soil.
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