植茶年限对土壤水稳性团聚体腐殖质组分特征的影响

退耕植茶是川西低山丘陵区响应退耕还林工程实施的重要措施之一.为了研究茶园土壤团聚体中腐殖质组分的分布特征，反映植茶对土壤质量的影响，选取不同植茶年限（18、25、33、55 a）的老川茶园为研究对象，以邻近撂荒地为对照（CK），研究植茶对土壤团聚体中富里酸（FA）和胡敏酸（HA）分布的影响.结果表明:①不同植茶年限下，土壤富里酸含量（以质量分数计）在2.97~6.26 g/kg之间，胡敏酸含量在1.24~4.89 g/kg之间；随植茶年限的延长，土壤富里酸、胡敏酸含量先增加后降低，均在植茶25 a时达到最大值.②随着土壤团聚体粒径的减小，富里酸含量逐渐降低，胡敏酸则表现为≥5 mm粒径团聚体高于其他粒径.③土壤胡富比（HA/FA）在0.30~0.88之间，总体表现为≥5 mm和 < 0.25 mm粒径团聚体腐殖化程度较高，植茶25 a时大团聚体数量的增加有利于有机质含量和品质的提高.④逐步回归分析表明，≥5、2~5、0.25~0.5和 < 0.25 mm粒级团聚体中有机碳组分对水稳性团聚体的形成和稳定的影响较大.研究显示，植茶有利于土壤团聚体中腐殖质各组分的积累和腐殖化程度的增强，可增加土壤有机碳的稳定性；植茶25 a时土壤碳汇效应较强，植茶33 a后土壤固碳能力有所下降，可通过改善茶园施肥管理等措施保持茶园土壤的结构和肥力，以实现茶园土壤的可持续利用. 

Effect of Tea Plantation Age on Humus Fractions in Soil Water-Stable Aggregates

Changing farmlands to tea plantation is an important measure in response to the Grain for Green Project in the hilly region of western Sichuan Province, China. The distribution characteristics of humus fractions in soil aggregates of tea garden were studied in order to reflect the influence of tea plantation on soil quality, and to provide theoretical basis for the sustainable utilization of tea garden soil. Soil samples were collected from an abandoned land (CK) and four tea plantations with different ages (18, 25, 33, 55 years old), and examined for the distribution of humus fractions (FA, HA) in soil aggregates. The results showed that:(1) The fulvic acid (FA) content varied from 2.97 g/kg to 6.26 g/kg, while the humic acid (HA) content varied from 1.24 g/kg to 4.89 g/kg. The contents of fulvic acid and humic acid first increased and then decreased with increasing age of tea plantation, and reached to peak point with tea plantation age of 25 years. (2) With decrease in size of the soil aggregates, fulvic acid content decreased gradually, while humic acid content was higher in aggregate size of ≥ 5 mm than others. (3) The ratio of HA to FA varied from 0.30 to 0.88. ≥ 5 and < 0.25 mm aggregates showed a higher humification degree. The increase of large aggregates was beneficial to the improvement of organic matter content and quality in soils with tea plantation for 25 years. (4) The result of stepwise regression analysis showed that soil organic carbon fractions in ≥ 5, 2-5 and < 0.25 mm aggregates influenced the stability of soil aggregates. The findings suggested that tea plantation was beneficial for accumulation of humus in soil aggregates, for enhancement of humification and to increase the soil organic carbon stability. The soil carbon sink effect was strongest in the tea plantation for 25 years. After long-term tea planting (33 a), the humus content and soil C sequestration capacity decreased. So the soil structure and fertility of tea garden could be maintained by improving the management of fertilization for sustainable utilization of tea garden soils.