陇东雨养苹果覆膜对土壤团聚体结构稳定性与细根分布的影响

Effects of film mulching on soil aggregate structure stability and fine root distribution of rain-fed apple in eastern Gansu

不同的果园管理方式可影响果树根系生长、分布与土壤团聚体稳定性、有机碳固存,进而改变"根-土"复合体响应关系。对西北陇东旱塬不同覆膜年限(2 a、4 a和6 a)苹果园表层土壤(0—20 cm)细根生长进行调查,并采用干筛法和湿筛法相结合的方式对土壤团聚体进行分级(>2 mm, 0.5—2 mm, 0.25—0.5 mm和<0.25 mm)。计算团聚体稳定性参数[> 0.25 mm机械稳定性团聚体含量(DR_(0.25))、> 0.25 mm水稳性团聚体含量(WR;)、平均重量直径(MWD)、平均几何直径(GMD)、团聚体破坏率(PAD)、水稳系数(WSC)]和团聚体有机碳含量。分析细根生长与土壤物理结构对长期覆膜的响应,探明土壤团聚体稳定性与有机碳固持关系,揭示黄绵土物理结构稳定机制。结果表明:6 a处理通过增加表层土壤黏粒和物理性黏粒比例,改变孔隙结构,抑制细根生长,其根量、根长和根表面积仅为对照(CK)的20.97%、24.66%和41.25%;降低表层土壤团聚体力稳性,其DR_(0.25)、机械稳定性团聚体MWD和GMD仅为CK的82.2%、74.02%和59.38%;对水稳性团聚体的保护作用低于短期覆膜(2 a),其PAD和WSC为2 a处理的121.17%和54.56%。2 a处理可提高土壤团聚体的力稳性、水稳性和土壤团聚程度,使土壤结构得到改善。同时对机械稳定性、水稳性团聚体有机碳提升效果优于6 a处理,为6 a处理的115.66%和116.6%。大团聚体固持有机碳能力高于微团聚体,但由于长期覆膜团聚体稳定性的下降,6 a处理的DR_(0.25)为CK的82.2%,不利于对有机碳的保护,使土壤有机碳水平对团聚体稳定性变异决定性仅为29.55%。连续覆膜引发的频繁干湿交替增加了黏粒对土壤结构稳定性的影响权重,促使表土"隐形"退化,抑制苹果细根在表层土壤中的生长、分布。2 a处理对土壤团聚体结构有良好的保护作用,促进土壤有机碳累积。

Different orchard management methods can affect the growth and distribution of fruit roots, the stability of soil aggregates and the ability of organic carbon storage, and then change the response relationship of root-soil complex. The fine root growth of apple orchard surface soil(0—20 cm) with different plastic film mulching years(2 a, 4 a, and 6 a) was investigated in the dry tableland of Longdong, Northwest China. The combination of dry and wet screening methods was used to classify soil aggregates(>2 mm, 0.5—2 mm, 0.25—0.5 mm, and <0.25 mm). The aggregate stability index, including [> 0.25 mm Mechanical stability aggregates content(DR_(0.25)), > 0.25 mm water-stabled aggregates content(WR;), Mean weight diameter(MWD), geometric mean diameter(GMD), percentage of aggregate destruction rate(PAD), water stability coefficient(WSC), and the content of organic carbon were calculated. The response of soil physical structure and fine root growth to long-term film mulching was analyzed, the relationship between soil aggregate stability and organic carbon sequestration was explored, and the stability mechanism of physical structure of loess soil was revealed. The results showed that film-mulching six years inhibited fine root growth by increasing soil clay, the proportion of physical clay and changing pore structure, and the root weight, root length and root surface area were only 20.97%, 24.66% and 41.25% of conventional tillage(CK);The DR_(0.25), MWD and GMD of surface soil aggregates were 82.2%, 74.02% and 59.38% of CK;The protective effect of PAD and WSC were 121.17% and 54.56% of film-mulching two years, compared with that of short-term film mulching. Film-mulching two years improved the force stability and water stability of soil aggregates as well as the degree of soil aggregates, and improved the soil structure. At the same time, the organic carbon improvement effect of mechanical stability and water stability aggregates was better than that of film-mulching six years, which was 115.66% and 116.6% of film-mulching six years. Although the ability of large aggregates to hold organic carbon was higher than that of micro aggregates, due to the long-term stability decline of coated aggregates, the DR_(0.25)of film-mulching six years was only 82.2% of CK, which was not conducive to the protection of organic carbon, so that the decisive effect of soil organic carbon level on the stability variation of aggregates was only 29.55%. The frequent dry-wet alternation caused by continuous film mulching increased the influence weight of clay particles on soil structural stability, promoted the invisible degradation of the topsoil, and inhibited the growth and distribution of fine roots of apple in the topsoil. Film-mulching two years had a good protective effect on soil aggregate structure and promoted soil organic carbon accumulation.