渭北不同园龄苹果园土壤团聚体状况及演变趋势研究

Status and Evolution of Soil Aggregates in Apple Orchards Different in Age in Weibei

为了探索果业生产和果园管理措施对土壤质量的影响,选取了渭北旱源苹果主产区彬县10a幼龄和21a老龄苹果园0~40 cm土壤为研究对象,以农田为对照,采用干筛法和湿筛法研究了不同种植年限果园土壤团聚状况与演变趋势。结果表明:渭北地区土壤机械稳定性团聚体以<0.25 mm微团聚体为优势级别,仅0~20 cm处随园龄递增果园土壤团聚化趋势较为明显,>0.25 mm土壤团聚体含量(DSAC0.25)、平均重量直径(MWD)和几何平均直径(GMD)均显著增大,团聚体分形维数(D)递减,但是,10~0.25 mm和5~1 mm最有价值团聚体和团聚体系数(KCTP)均在递减。渭北土壤水稳性团聚组成中约60%为<0.25 mm微团聚体,在0~30 cm处土壤水稳性团聚体的MWD、GMD和WSAC0.25呈现为农田(对照CK)>10a果园>21a果园,随园龄递增有明显增大趋势。>0.25 mm团聚体的破坏率(PAD0.25)随园龄增加显著增大,递增幅度随土层深度增加而递减。相关分析表明,土壤总有机碳(TOC)、颗粒态有机碳(POC)与机械稳定性团聚体各项指标呈极显著相关,土壤碳酸钙含量、黏粒含量与水稳定团聚体多项指标呈极显著相关,PAD0.25与土壤理化性质呈显著相关。研究表明,果树种植在表观上明显提高了渭北地区表层0~20 cm土壤机械稳定性大团聚体数量,增强了土壤抗风蚀能力,但却显著降低了土壤团聚体的农艺质量及其稳定性,果园土壤团聚体的农艺质量显著退化与有机物及碳酸钙含量递减有着直接关系。

【Objective】The semiarid region of Weibei is identified as one of the best＂eugenic＂ apple-producing areas in China,owing to its unique eco-environmental conditions.Since the 1980,Weibei has adjusted its agricultural structure by converting large areas of farmland into apple orchard,in order to improve local ecological landscape and economy.But this change in land-use and implementation of a series of unscientific orchard managements（e.g.,inappropriately increasing the application of inorganic fertilizers and pesticides）has led to soil quality degradation,such as declining soil micro-ecosystem biodiversity,soil nutrient imbalance,and their subsequent impacts on yield and quality of the fruit getting more and more significant with increasing age of the apple orchards.Soil aggregates and their stability influence a wide range of soil properties,including carbon stabilization,soil porosity,water infiltration,bulk density,water erosion resistance,etc.Aggregate stability is an issue that has been a focus of increasing attention in recent years as one of the soil properties that can serve as an important indicator of soil quality.So it is necessary to study status and evolution of soil aggregates as affected by changes in land use and management practice and ongoing cultivation as apple orchard in an attempt to provide a scientific basis for maintaining sustainable development of the apply industry and the ecology in the region.【Method】In this study,two apple orchards different in age（10a,juvenile and 21 a,over-mature）and a tract of farmland nearby were selected in the semiarid loess region of Weibei,Bin country,Shaanxi,China as objects for investigation of soil aggregates in the 0~40 cm soil layer.Soil samples collected from the sampling lots were analyzed for fractionation of soil aggregates with the dry-sieving and wet-sieving methods,and so for soil basic properties,and soil aggregate stability and correlation between the two.【Result】Results show that the fraction of 0.25 mm microaggregates dominated in the soil layers of the apple orchards and farmland（CK）.The topsoil（0~20 cm）in the apple orchards displayed a pronounced aggregation trend with age,which was embodied in significant increase in content of 0.25 mm soil aggregates（DSAC0.25）,mean weight diameter（MWD）and geometric mean diameter（GMD）and decrease in fractal dimension（D）,content of 10~0.25 mm and 5~1 mm valuable aggregates and coefficient of aggregate（KCTP）.The composition of water-stable soil aggregates in the soil of Weibei,about 60% was0.25 mm soil micro-aggregate.In terms MWD,GMD and WSAC0.25 of waterstable soil aggregates in the 0~30 cm soil layer,an decreasing order of CKOrchard of 10 a Orchard of 21 a was found,and the trend was getting more and more obvious with increasing orchard age.Soil water stable aggregates,soil structure,erosion resistance and fertility retention ability in the 0~30 cm soil layer of apple orchards decreased with increasing orchard age.WSAC0.25 was significantly lower than DSAC0.25.Destruction rate of0.25 mm soil aggregates（PAD0.25）also significantly increased with increasing orchard age,and the increase declined in extent with soil depth.Correlation analysis shows that soil total organic carbon（TOC）,and particulate organic carbon（POC）was closely related to various indices of mechanically-stable soil aggregates,while soil Ca CO3 content and clay content were significantly related to a number of indexes of water-stable soil aggregates,and PAD0.25 to soil physical and chemical properties.【Conclusion】Orchard plantation apparently increases the content of mechanically-stable soil macro-aggregate content in the 0~20 cm,soil aggregation level,and hence its resistance to wind erosion,but significantly reduces agronomical quality and stability of soil aggregates.The significant degradation of agronomical quality of soil aggregates in apple orchards is directly related to the decrease in soil organic matter and Ca CO3 content in the soil.It is,therefore,recommended that in this semiarid region,more input of easy-to-decompose organic manure,and appropriate soil management measures be adopted to improve stability of the soil in structure,solve the problem of soil degradation in orchards,and promote sustainable development of the apple industry in the region.