东北典型黑土区农耕土壤团聚体流失特征

CHARACTERISTICS OF SOIL AGGREGATE LOSS IN CROPLANDS IN THE TYPICAL BLACK SOIL REGION OF NORTHEAST CHINA

通过野外原位模拟降雨试验，研究了东北典型黑土区 3 种降雨强度（30、60 和 90 mm h–1）下农耕地坡面侵蚀过程的土壤团聚体流失特征，分析了流失团聚体特征指标（平均重量直径（MWD）、几何平均直径（GMD）、分形维数（D）、平均重量比表面积（MWSSA）、≥1 mm 粒级团聚体比例（PA1）、≥2 mm 粒级团聚体比例（PA2）、≥0.25 mm 粒级团聚体比例（PA0.25））的变化规律。结果表明：降雨强度对典型黑土区农耕地坡面侵蚀有显著影响；次降雨初期侵蚀量占整个降雨过程总侵蚀量的比例随着降雨强度的增加而增大。在 30 mm h–1降雨强度下，团聚体流失以〈0.25 mm 粒级团聚体为主，其占团聚体流失总量的 90.0%；在 60 mm h–1降雨强度下，团聚体流失以〈0.25 和 0.5~1 mm 粒级团聚体为主，二者占团聚体流失总量的 63.7%；而 90 mm h–1降雨强度下，团聚体流失以〈0.25 和 2~5 mm 粒级团聚体为主，二者分别占团聚体流失总量的 31.7%和 31.2%。PA0.25、PA1、PA2、MWD 和 GMD 与降雨强度和含沙量之间均呈现极显著正相关关系；MWSSA 和 D 与降雨强度和含沙量之间呈现极显著负相关关系。研究结果还表明，PA1、MWD 和 GMD 皆能较好地表征典型黑土区农耕土壤的团聚体流失特征。

Studies on soil aggregate loss in the process of soil erosion have an important significance in exposing mechanism of soil erosion. Rainfall intensity, as an important parameter in characterizing rainfall events, plays a significant role in soil erosion. A large number of studies have shown that there is a certain relationship between rainfall and composition of erosion sediment. However, most studies on soil aggregate loss in the process of soil erosion were conducted in the laboratory, which might affect some of the soil properties, especially the distribution of soil aggregates, when soil samples were collected and moved from the field to the laboratory. In this study, an in-situ field simulated rainfall experiment was conducted on a cropland in the typical black soil region of Heilongjiang Province to investigate characteristics of soil aggregate loss in the process of soil erosion. The experiment was designed to have three rainfall intensities, i.e., 30, 60 and 90 mm h-I and a set duration, 40 min, for each simulated rainfall event. Variations of characteristic indices of soil aggregate loss, such as mean weight diameter （ MWD ） , geometric mean diameter （ GMD ） , fractal dimension （D） , mean weight soil specific area （MWSSA） , ≥ 1 mm soil aggregates （PA1 ） , ≥ 2 mm soil aggregates （PA2 ） and ≥ 0.25 mm soil aggregates （PAo.25） , as affected by rainfall intensity, were analyzed. The runoff plots （ 10 × 1 m, each） of the experiment were deployed in a cropland on a sunny slope, 5° in gradient. The soil of the cropland was typical black soil 38.9% in clay, 55.3% in silt, 5.8% in sand and 28.8 g kg-1 in organic matter, 1.10 g cm-3 in bulk density and 6.65 in pH. Results show that rainfall intensity had some significant effects on runoff and soil loss. The ratio of soil loss in the first 20 minutes of a rainfall event to total soil loss increased with increasing rainfall intensity. The sediment resulting from a rainfall event, 30 mm h-1 in intensity, was dominated with 〈0.25 mm soil aggregates, which made up 90.0% of the total soil aggregate loss; the sediment from a rainfall event, 60 mm h-l in intensity, was mainly composed of 〈0.25 and 0.5 - 1 mm soil aggregates, which accounted for 63.7% of the total soil aggregate loss; and the sediment from a rainfall event, 90 mm h-1 in intensity was mainly of 〈0.25 and 2 - 5 mm soil aggregates, which amounted to 31.7% and 31.2% of the total soil aggregate loss, respectively. Rainfall intensity was found to have very significantly positive relationships with PA0.25, PAl, PA2, MWD and GMD, but very significantly negative ones with MWSSA and D. It was also found that indices of PAl, MWD and GMD are all good indicators characterizing soil aggregate loss in croplands in the typical black soil region of Northeast China.