咸水灌溉对麦—玉两熟制农田土壤水稳性团聚体的影响

为探明咸水灌溉对麦—玉两熟轮作农田土壤团聚体的影响效应,在长期定位咸水灌溉试验(始于2006年)的基础上,研究了不同矿化度咸水连续灌溉第13~14年农田土壤盐分(EC e)及水稳性团聚体分布和稳定性指标的变化规律。试验设置5个灌溉水矿化度处理,分别为1,2,4,6,8 g/L。结果表明,0—40 cm土层土壤EC e随灌溉水矿化度增加而增大,4,6,8 g/L灌水处理与1 g/L处理间差异达显著水平。咸水灌溉改变土壤水稳性团聚体的粒级分布,灌溉水矿化度≤4 g/L时,0—40 cm土壤水稳性团聚体以大团聚体(>0.25 mm)为优势粒级,随灌溉水矿化度增加,大团聚体质量分数降低,微团聚体(0.053~0.25 mm)和粉+黏团聚体(<0.053 mm)质量分数增大,当灌溉水矿化度达到6 g/L时,粉+黏团聚体占比最大。咸水灌溉降低土壤水稳性团聚体的稳定性,随灌溉水矿化度的增加,土壤团聚体平均重量直径和几何平均直径减小,分形维数增大,但2 g/L与1 g/L灌水处理间无显著差异。在该研究灌溉制度下,≥4 g/L咸水灌溉显著增加土壤盐分,破坏土壤团粒结构,应谨慎使用。

Effect of Saline Water Irrigation on Soil Water-stable Aggregates in Wheat-maize Crop Double Cropping System

In this study,a long-term saline water irrigation experiment was carried out on wheat-maize farmland since 2006,and studied the change characteristics of soil salinity(EC e),water-stable aggregates particle size distribution and their stability index under the condition of continuous saline water irrigation with different salinity in the 13th and14th year(in 2018 and 2019).Five salinity levels of irrigation water were tested:2(T1),4(T2),6(T3),and 8(T4),and fresh groundwater(1 g/L)was used as control treatment(CK).The salinity level from T1 to T4 was formed by mixing sea salt into the freshwater.The results showed that saline water irrigation increased soil EC e.Compared with CK,the EC e in the treatment of 2 g/L showed no significant difference,but a significant increase when the salinity of irrigation water beyond 4 g/L.Saline water irrigation affected the particle size distribution of soil water-stable aggregates.When the salinity of irrigation water was less than 4 g/L,the macroaggregate(>0.25 mm)was the dominant particle size of soil water stable aggregates in 0—40 cm soil layer.With the increase of irrigation water salinity,the mass fraction of macroaggregate decreased,while the mass fraction of microaggregate(0.053~0.25 mm)and silt+clay aggregate(<0.053 mm)increased.When the salinity of irrigation water reached 6 g/L,silt+clay aggregate was dominant in 0—40 cm soil layer.With the increase of irrigation water salinity,the average weight diameter(MWD)and geometric mean diameter(GMD)of soil aggregates decreased,while the fractal dimension(D)increased,which meant that the stability of soil water stable aggregates decreased.Under this irrigation system,saline water with salinity greater than or equal to 4 g/L significantly increased soil salinity and destroyed soil aggregate structure,which should be used cautiously in the irrigation of wheat-maize crop system.