柑橘林下养鸡对土壤团粒结构分形特征的影响

摘要

在四川盆周低山丘陵区柑橘Citrus reticulata林下养鸡Gallus domesticus,研究不同养鸡密度(0,600,1200和2400只·hm-2)对表层(0~20 cm)土壤团聚体组成、 分形维数、 理化性质、 微生物数量和土壤酶活性的影响,探讨分形维数与土壤理化性质、 微生物数量及土壤酶活性的关系.结果表明:林下养鸡使>0.25 mm粒径团聚体(干筛)和>0.25 mm粒径水稳性团聚体(湿筛)含量分别增加1.9%~5.0%和7.3%~24.5%,且随养鸡密度的增加而增加.土壤分形维数为2.174~2.760,且分形维数随养鸡密度、>0.25 mm粒径团聚体(干筛)和水稳性团聚体(湿筛)含量的增加而降低,与>0.25 mm和>5.00 mm水稳性团聚体含量呈极显著相关(P<0.01).林下养鸡降低了土壤容重、 改善了土壤孔隙,增加了土壤养分、 微生物数量和酶活性,其土壤肥力的提高作用随养鸡密度的增加而增加,且土壤理化性质、 微生物数量和酶活性与分形维数间呈显著相关(P<0.05).说明柑橘林下养鸡能有效改善土壤团聚体组成和土壤肥力,降低土壤团聚体和水稳性团聚体分形维数.%Raising chickens under trees or bushes could improve the soil. To research the influence of the sur-face layer's (0-20 cm) soil aggregate composition, fractal dimension, physical and chemical properties, micro-bial population, and enzyme activities for different chicken raising densities and to probe relationships between fractal dimension and soil physical and chemical properties, microbial population, and enzyme activities; citrus orchards in the Sichuan Basin low mountain hilly area were selected with four chicken density treatments (0, 600, 1200, and 2400 chichens per hm2) and each treatment had three replications; the 12 plots of 20 m ×20 m each were arranged in a randomized block design. Soils in the surface layer (0-20 cm) in each plot were collected, by snake-shaped five-point sampling method, to determine soil properties, such as soil aggregate composition and fractal dimension. Results showed a significant (P<0.05) increase of 1.9%-5.0% in content of the >0.25 mm particle-sized soil aggregates (dry-sieved) and 7.3%-24.5% in water-stable aggregates (wet-sieved) in citrus orchards that were raising chickens, with both increasing as chicken density increased. Soil fractal dimension ranged from 2.174 to 2.760 and significantly (P<0.05) decreased as chicken density (by 1.3%-8.7%) and the >0.25 mm particle-sized soil aggregates (dry-sieved) and water-stable aggregates (wet-sieved) increased. Soil fractal dimension was significantly correlated with the content of >0.25 mm (r=-0.929, P<0.05) and >0.50 mm (r=-0.915, P<0.05) particle-sized water-stable aggregates (wet-sieved). Raising chickens in citrus orchards significantly (P<0.05) decreased soil bulk density (except 600 chichens per hm2), significantly (P<0.05) improved soil total porosity (except 600 chichens per hm2), and significantly (P<0.05) increased nutrient content, microbial population, and enzyme activities; soil fertility also increased as chicken density increased. Soil physical and chemical properties, microbial population, and enzyme activities were significantly (P<0.05) correlated with soil fractal dimension. These findings indicated that raising chick-ens in citrus orchards could improve soil aggregate composition and soil fertility with fractal dimension of the soil aggregate and water-stable aggregate decreasing; fractal dimension of soil aggregate could also be used as an important comprehensive quantitative index to evaluate soil physical and chemical properties when raising chickens in a forest ecosystem.