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【目的】灌溉是设施土壤水分的主要来源,也是影响土壤结构稳定性的重要因子。探究不同灌水控制下限对设施土壤团聚体分布特征和稳定性的影响,为设施农业合理水分调控、促进设施土壤结构改善提供理论依据。【方法】选用6年膜下滴灌试验地为对象,供试作物为番茄(Lycopersicon esculentum Mill.),种植模式为沟垄覆膜。设置了3个灌水控制下限,其土壤水吸力值分别为20、30及40 k Pa(分别记为D20、D30、D40),灌水控制上限均为6 k Pa。各小区以埋设深度30 cm的张力计指示土壤水分变化,确定灌水时间和灌水量。通过干筛法和湿筛法测定了土壤团聚体的组成,>0.25 mm团聚体含量(R0.25)、平均重量直径(MWD)、几何平均直径(GMD)、分形维数(D)、以及土壤结构破坏率(RDS)和不稳定团粒指数(El T)。【结果】在0—30 cm土层,D40处理的土壤电导率(EC)、阳离子交换量(CEC)和容重都显著低于D20和D30处理(D40D30>D20)(P<0.05)。通过干筛法和湿筛法对团聚体数量和大小的测定发现,在0—30 cm土层,土壤机械稳定性团聚体主要集中在>2和1—0.25 mm粒级(23.01%—39.98%),而水稳性团聚体主要集中在1—0.25和0.25—0.053 mm粒级(31.08—47.27%)。在0—20 cm土层,D30处理的R0.25、平均重量直径(MWD)和几何平均直径(GMD)均高于D20和D40处理;但在20—30 cm土层,D20处理的水稳性团聚体的含量高于D30和D40处理。不同灌水控制下限下的土壤结构破坏率(RDS)和不稳定团粒指数(El T)随土壤深度增加而增加,且RDS与El T的变化规律相似。在0—20 cm土层,D30处理的土壤结构破坏率(RDS)和不稳定团粒指数(El T)显著低于D20和D40处理(P<0.05)。但在20—30 cm土层,D20处理的土壤结构破坏率(RDS)比D30和D40处理分别低了12.2%和16.8%。干筛下在10—20 cm土层内,D20、D30、D40处理的分形维数最小,分别是2.13、2.08、2.19;湿筛下在10—20 cm土层内,D40、D30、D40处理的分形维数最小,分别是2.31、1.99、2.12。结果表现出,与D20和D40处理相比,D30处理显著降低了团聚体中的分形维数(D)。【结论】在保证设施番茄产量和节约用水的条件下,将土壤水吸力30 k Pa作为膜下滴灌灌水控制下限,有利于土壤结构的形成和稳定。
【Objective】 Irrigation is the main source of soil moisture in facilities and also an important factor affecting the stability of soil structure. To investigate the influence of different irrigation control limits on the distribution characteristics and stability of soil aggregate, and to provide a theoretical basis for the rational regulation of water in facilities agriculture and the improvement of soil structure in facilities. 【Method】 Six years of drip irrigation under plastic film were selected as experimental objects. The test material was Lycopersicon esculentum Mill. The planting pattern was furrow-furrow. Three lower limits of irrigation control were set, and the values of soil water suction were 20,30 and 40 kPa (D20, D30 and D40 respectively), and the upper limit of irrigation control was 6 kPa. In each plot, the soil moisture was indicated by the tension meter embedded at a depth of 30 cm, and the irrigation time and irrigation volume were determined. The composition of soil aggregates, the aggregate content> 0.25 mm, the average weight diameter (MWD), the geometric mean diameter (GMD) and the fractal dimension (D) were determined by dry sieving and wet sieving. Soil structure failure rate (RDS) and unstable aggregate index (El T). 【Result】 The soil EC (EC), cation exchange capacity (CEC) and bulk density of D40 treatments were significantly lower than those of D20 and D30 treatments (D40 D30> D20) (P <0.05). The determination of the number and size of aggregates by dry sieving and wet sieving found that at 0-30 cm soil aggregates of soil mechanical stability mainly concentrated in the fractions of> 2 and 1-0.25 mm (23.01% -39.98% ), While water-stable aggregates mainly concentrated in the fractions of 1-0.25 and 0.25-0.053 mm (31.08-47.27%). In 0-20 cm soil layer, R0.25, MWD and GMD of D30 were higher than those of D20 and D40, but D20-treated water was stable in 20-30 cm soil layer Aggregate content was higher than D30 and D40 treatment. The soil structural failure rate (RDS) and unstable aggregate index (El T) increased with soil depth under different irrigation control lower limits, and the variation regularities of RDS and El T were similar. In 0-20 cm soil layer, soil structure destruction rate (RDS) and unstable aggregate index (El T) of D30 were significantly lower than those of D20 and D40 (P <0.05). However, in 20-30 cm soil layer, the soil structure destruction rate (RDS) of D20 was 12.2% and 16.8% lower than that of D30 and D40, respectively. In the 10-20 cm soil layer, the fractal dimensions of D20, D30 and D40 in the dry sieve were the lowest, which were 2.13, 2.08 and 2.19, respectively. In the 10-20 cm soil layer under the wet sieve, D40, D30 and D40 The fractal dimension of the smallest, respectively, 2.31,1.99,2.12. The results showed that D30 treatment significantly reduced the fractal dimension (D) in aggregates compared to D20 and D40 treatments. 【Conclusion】 Under the condition of ensuring tomato yield and conserving water in facilities, the soil water suction of 30 kPa was taken as the lower control limit of drip irrigation under mulch, which is beneficial to the formation and stability of soil structure.