复合养殖对柑橘林土壤微团聚体分形特征及理化性质的影响

【目的】研究经济林复合经营模式中,鸡的养殖密度对林下表层(0～20 cm)土壤微团聚体特征和土壤理化性质的影响,并探讨特征微团聚体组成比例(PCM,<0.02 mm/(≥0.02～0.25 mm))、<0.02 mm与≥0.02～2.00 mm粒级含量的比值(RMD,<0.02 mm/(≥0.02～2.00 mm))和分形维数D与土壤理化性质之间的关系。【方法】以四川盆周低山丘陵区柑橘林地为对象,在试验区中建立20 m×20 m标准地各4块,设置3次重复,分别饲养鸡0、600、1 200和2 400 只/hm²,采用“S”形5点取样法分别采集0～20 cm土样,并测定土壤微团聚体组成、有机质、全氮、碱解氮、全磷、有效磷、全钾和速效钾含量及土壤物理性质。【结果】柑橘林下养鸡经济林的复合经营模式增加了土壤微团聚体大粒级(≥0.02～2.00 mm)颗粒含量,降低了小粒级(<0.02 mm)颗粒含量。随养鸡密度的增加,土壤PCM、RMD和D值均逐渐减小。不同养鸡密度的土壤PCM、RMD及D均与土壤含水量、非毛管孔隙、毛管孔隙、总孔隙、通气度以及土壤有机质、全氮、碱解氮、全磷、有效磷、全钾和速效钾等含量呈显著负相关(P<0.05),与土壤密度显著正相关。【结论】柑橘林下养鸡可促进土壤较小粒级的微团聚体向较大微团聚体的转化,能有效改善土壤微团聚体组成,降低土壤PCM、RMD和D; 土壤PCM、RMD和D可作为评价林下养鸡生态系统土壤理化性质的一项重要综合性定量指标。

Effects of compound management in citrus orchard on soil micro-aggregate fractal features and soil physical and chemical properties

【Objective】Soils in the surface layer(0-20 cm)were collected to determine soil micro-aggregate features and soil physical and chemical properties when chickens were raised in different densities(0, 600, 1 200, and 2 400 chickens per hm²). The proportion of characteristic soil micro-aggregates(PCM, <0.02 mm/(≥0.02-0.25 mm))and the ratio of soil micro-aggregates diameter(RMD, <0.02 mm/(≥0.02-2.00 mm))and the factal dimension(D)were calculated. The relationships of soil physical and chemical properties with these indices were evaluated. 【Method】Citrus orchards in a low hill area of Sichuan Basin were taken as objects and four 20 m×20 m sample plots were created, with three replicates each, and chickens were raised in each plot at one of four densities(0, 600, 1 200, or 2 400 chickens per hectare). The S type of the five-point sampling method was used for stratification and sampling of the soil(0-20 cm). The soil micro-aggregate composition, the contents of organic matter, total nitrogen, hydrolyzed nitrogen, total phosphorus, available phosphorus, total potassium, available potassium, and soil physical properties were measured. 【Result】 The results show that raising chickens in citrus orchards increases large particle(≥0.02-2.00 mm)content and decreases small particle(<0.02 mm)content in soil micro-aggregates. Moreover, PCM, RMD and D presented a decreasing trend as the density of chickens increased. PCM, RMD and D had significantly negative correlation(P<0.05)with soil water content, non-capillary porosity, capillary porosity, total porosity, ventilation degree, organic matter, total nitrogen, hydrolyzed nitrogen, total phosphorus, available phosphorus, total potassium, and available potassium while had significantly positive correlation with soil density. 【Conclusion】 These findings indicate that raising chickens in citrus orchards is beneficial for promoting transformation from smaller soil micro-aggregates to larger micro-aggregates and could improve soil micro-aggregate composition, while decreasing PCM, RMD, and D. PCM, RMD and D can be used as important comprehensive quantitative indices to evaluate soil physical and chemical properties when raising chickens in a forest ecosystem.