土壤有機碳濃度是土壤品質的重要指標之一，因此，維持與提高土壤有機碳濃度是使土壤能永續利用之 重要耕作管理。本研究目的在探討兩種輪作制度 (分別以Rot-1與Rot-2表示) 下，化學及有機質肥料單獨施用 與混合施用，經二十年後，對土壤有機碳濃度與土壤有機碳與氮之易變動庫與難分解庫濃度的影響。試驗材 料取自高雄區農業改良場旗南分場長期試驗田。共有三種施肥處理，分別為：(一) 只施化學肥料 (慣行區)； (二) 只施有機質肥料 (有機區)：(三) 以氮肥為基礎，化學及有機質肥料各半 (折衷區)。採取之土壤分別測定 土壤一般性質、水溶性有機碳及以鹽酸與硫酸溶液分別劃分易變動庫與難分解庫之土壤有機碳與氮濃度。結 果顯示在不同的輪作體系之下，施肥管理對土壤酸鹼度造成之影響不同。產酸之化學氮肥使土壤酸鹼度下 降，以在Rot-2影響較大。在Rot-2施用化學肥料，可以增加土壤有機碳，在Rot-1則無明顯之影響，惟施有機質 肥料，則在兩輪作系統土壤有機碳均有增加趨勢。輪作系統對土壤中易變動庫與難分解庫氮之影響不同，在 Rot-2之下，不論何種施肥管理，以鹽酸溶液所劃分之土壤氮，幾乎全在易變動庫中 (> 90%)，而在Rot-1則為 70-80%；以硫酸溶液劃分時，亦有相同之趨勢。長時期施用有機質肥料，可以累積土壤中的難分解碳與氮； 化學氮肥使土壤中難分解氮與碳庫較小，故有機質肥料之長期施用，明顯改善土壤品質；但是施肥管理對這 兩個參數之影響，卻因輪作系統而有大的不同，本研究顯示，Rot-1為比Rot-2較好的輪作系統。硫酸溶液水解 所得之五個碳劃份中，以總聚酚I碳庫佔總碳之比例最高 (30-50%)，其次為難分解碳庫 (30-40%)，再次為醣碳 庫 (15-22%)，再次為總聚酚II碳庫 (6-15%)，最少者為纖維素碳庫 (3-5%)。

Soil organic carbon (SOC) concentration is used as an indicator of soil quality. To maintain or enhance SOC concentration is an important soil management for soil sustainability. The objective of this study was to investigate the effects of different fertilization managements on the concentration and composition of SOC under two different cropping systems (Rot-1 and Rot-2). There were three fertilization treatments, namely (1) the application of chemical fertilizer only (Chem-F), (2) the application of organic fertilizer only and with the assumption that the 50% organic nitrogen (N) mineralized at each crop season (Org-F), and (3) the application of chemical and organic fertilizers with equal rate of available N. Soil samples were taken after 20 years. The soil chemical properties and water soluble organic carbon (WSOC) concentration were measured. In addition, the labile and recalcitrant C and N in soil were determined using the fractionations of hydrochloric acid solution and sulfuric acid solution, respectively. The results showed that the soil chemical properties were significantly affected by fertilization management. The application of acid-forming chemical N fertilizer resulted in lowering soil pH value. A greater effect of fertilizer on soil pH value was observed in the Rot-2 system. The concentrations of WSOC were low in all treatments, but the fertilization managements or cropping systems had no effect on the WSOC concentration. The effect of fertilization management on SOC concentration was different under different cropping systems. The increase in SOC in Chem-N treatment was observed in Rot-2, but not in Rot-1. Organic fertilizer treated plots had greater SOC concentration in both cropping systems. The cropping system affected the labile N pool differently. In Rot-2, almost all soil N was in the labile pool regardless of fertilization management. The results of two-step sulfuric acid solution fractionation were similar to that of hydrolyzing by hydrochloric acid solution. About 10-45% of soil N was in recalcitrant pool according to hydrolyzing by sulfuric acid solution. Fertilization management and the cropping system had significant effects on the concentrations of recalcitrant C and N. Long-term application of organic fertilizer resulted in an increase in recalcitrant C and N. Five fractions of the SOC was obtained after the treatment of sulfuric acid solution, and the proportion of C in different fractions to total SOC were in the following order: polyphenol I C (30-50%) > recalcitrant pool C (30-40%) > sacchride C (15-20%) > polyphenol II C (6-15%) > cellulose C (3-5%).