长期施肥对紫色水稻土团聚体中有机碳和微生物的影响

【目的】土壤微生物在维持土壤肥力、土壤健康和提高作物产量等方面都具有非常重要的作用,探讨长期不同施肥措施对紫色水稻土团聚体微生物量及活性的影响,明确不同施肥制度下土壤不同粒级团聚体中微生物特性,为系统了解施肥管理对土壤肥力演变的影响提供理论依据。【方法】依托重庆市北碚区中性紫色水稻土22年的长期定位试验,选取对照(CK,不施肥)、氮磷钾(NPK)、稻草还田(S)、氮磷钾+稻草还田(NPK+S)4个处理,采集0—20 cm耕层土壤样品,采用湿筛法获得不同粒级土壤团聚体,研究不同粒级土壤团聚体中的有机碳以及微生物量、呼吸代谢熵等微生物特性。【结果】连续22年定位试验表明,与CK相比,各施肥处理均显著增加了耕层土壤中水稳性大团聚体(0.25 mm)含量,以NPK+S的促进作用最为明显,表明化肥与稻草还田长期配施有利于紫色水稻土水稳性大团聚体的形成;施肥还显著提高了团聚体稳定性和土壤有机碳水平,以稻草还田(S和NPK+S处理)效果最佳。长期施肥改变了土壤养分及生物活性在不同粒径团聚体上的分布。土壤中有机碳、微生物量碳、呼吸代谢熵在不同粒级团聚体中呈异质分布,在2.00—1.00 mm和1.00—0.25 mm两个级别的水稳性大团聚体中土壤有机碳、呼吸速率和代谢熵显著高于0.25—0.053 mm和0.053 mm两个级别的水稳性小团聚体。【结论】0.25 mm的水稳性团聚体是土壤有机碳和微生物量碳的主要载体,2.00—1.00 mm团聚体的生物活性最强;长期氮磷钾配施结合稻草还田显著提高了紫色水稻土团聚体的水稳性及大团聚体中有机碳和微生物量碳的含量,是改善紫色水稻土团粒结构和生物功能的有效措施。

Influence of Long-Term Fertilization Managements on Organic C and Microorganism in Different Aggregates in Purple Paddy Soil

【Objective】 Soil microorganisms play a critical role in the maintaining soil fertility, soil health and crop productivity. Soil microbial biomass carbon (C) concentration in different sizes of aggregates and aggregate distribution were studied in neutral purple paddy soil under long-term fertilization management. The aim of the study is to elucidate the relationship between long-term fertilization and microbial biomass dynamics in aggregate, in order to evaluate the influence of different fertilizer managements on evolution of soil fertility. 【Method】 Four treatments were conducted this research (1)CK；(2)NPK；(3)S；(4)NPK+S. Soils were sampled at 0-20 cm depth.Wet-sieving method was used to determine aggregate distribution of a neutral purple paddy soil after long-term fertilization management for 22 years. Soil microbial biomass C concentration and activity were determined at all aggregate levels.【Result】Long-term fertilization management after 22 years indicated that soil large aggregate content with sizes of ＞0.25 mm was significantly increased in treatments with inorganic nitrogen, phosphorus, and potassium fertilizer (NPK), with rice straw return (S), and with both (NPK+S), compared to the control. The increase was highest in NPK+S treatment where the aggregate stability was also shown to be the greatest, thus indicating the importance of inorganic fertilizer and organic residues in the formation and stability increases of large aggregate in purple soil. Fertilization increased aggregate stability and soil organic C content significantly, the increase was highest in S and NPK+S, indicating the importance of straw returning in the increase of aggregate stability and soil organic C. Long term fertilization changed the distribution of soil nutrition and microbial activity in soil aggregates. Further, soil organic C and microbial biomass C concentration varied in different aggregate sizes. In large water-stable aggregate (2.00-1.00 and 1.00-0.25 mm), organic C concentration, soil respiration rate and metabolic quotient were greater than in small aggregate (＜0.25 mm).【Conclusion】Aggregate larger than 0.25 mm had the greatest proportion of soil organic C and microbial biomass C, while microbial activity was greatest in 1.00-2.00 mm. Under such agroecosystem, long-term application of inorganic NPK fertilizer together with rice straw return greatly increased the proportion of large water-stable aggregate and the concentration of soil organic C and microbial biomass C. It is therefore an effective land management in improving aggregates distribution, increasing soil microbial function and productivity in purple paddy soil.