【目的】东北黑土区是我国重要的粮食基地,由于长期的不合理利用,黑土资源遭受严重的水力侵蚀。磁化率(MS)技术是一种快速、可靠、经济的土壤再分配评价方法。本研究旨在阐明土壤磁化率的时空分异特征,探讨磁化率指标评价土壤侵蚀的可行性。【方法】在黑龙江省鹤山农场选取3个开垦年限的典型黑土坡面,顺坡等间距布设坡面采样点,分别选取百米范围内的林地为参考样点,采集原状土壤剖面样品和非原状土壤表层样品,剖面样品的采样深度为60~100 cm(表层样品的采样深度为20 cm),测定样品磁化率等理化指标,分析不同开垦年限土壤磁化率的时空异质性,探讨黑土区坡耕地土壤侵蚀特征。【结果】不同土壤剖面磁化率均随土层深度的增加而降低,至母质层趋于平稳,符合弱磁性母质发育的温带土壤磁性特征;坡上和坡中耕层的低频磁化率平均值小于参考点,分别为24.1×10^-8和24.8×10^-8 m³/kg,坡下耕层低频磁化率平均值大于参考点,为39.7×10^-8 m³/kg,符合坡面土壤侵蚀的一般规律;开垦110 a的农地低频磁化率变化范围最大,为1.7×10^-8~88.7×10^-8 m³/kg,分别约为开垦年限60和30 a的1.4和1.9 倍。【结论】黑土区坡耕地表层土壤磁化率均具有坡面异质性,坡上和坡中为侵蚀区,坡下为沉积区,且开垦时间越长,耕地坡面土壤再分配程度越高,即开垦110 a坡面土壤侵蚀最为强烈。本研究验证了土壤磁性表征土壤侵蚀规律的可行性,揭示了不同开垦年限黑土坡耕地土壤侵蚀特点,研究结果能够为东北黑土区水土流失预报与防治提供理论依据,有利于区域农业可持续发展和生态环境保护。

【Objective】The Black Soil Region is an important food base, which has a vital strategic position to ensure the food security in China. However, due to the long-term unreasonable utilization, the black soil resources suffered from serious water erosion. The objective is to clarify the spatio-temporal characteristic of soil loss on cropland and discuss the feasibility of evaluating soil erosion by magnetic susceptibility. 【Method】Magnetic susceptibility (MS) had been proved to be a rapid, reliable, economic and nondestructive method in estimating hillslope soil redistribution. In this paper, three typical black soil slope transects were selected in Heshan Farm, Heilongjiang Province, and collected soil profile samples from surface to 60-100 cm depth, measured soil magnetic susceptibility. The MS was used as a tracer to analyze the spatio-temporal heterogeneity of soil susceptibility at slope scale and discussed the soil erosion patterns in Black Soil Region. 【Result】The results showed that MS of topsoils on all the slope were generally high, and decreased with the increasing of soil depth. MS at parent layers become stable, which was in line with the MS characteristics of temperate soil developed from weak magnetic parent materials. The average MS at upperslopes and middleslopes were less than that of reference sites, which were 24.1×10^-8 m³/kg and 24.8×10^-8 m³/kg, respectively, the average MS of lowerslopes were greater than that of reference sites, for 39.71×10^-8 m³/kg. It conformed to the general soil erosion pattern on hillslope that soil material deposited from its original position to the lower position. The whole slope were divided into erosion area and deposition area according to the topsoil MS of reference sites. The topsoil MS at the erosion area was lower than that of reference sites, while the topsoil MS at the deposition area was higher than that of reference sites. The topsoil particles were removed and transported at upperslopes and middleslopes, deposited at lowerslopes. With the increasing of cultivation periods, the MS between upperslopes and lowerslopes varied significantly which showed strong slope heterogeneity, and the cultivation periods were positively correlated to the soil redistribution. The range of MS on cropland reclaimed for 110 years was 1.7×10^-8-88.7×10^-8 m³/kg, which was about 1.4 and 1.9 times of cultivated for 60 and 30 a, respectively. 【Conclusion】The MS at topsoils of the black soil slope presented heterogeneity, that is, upperslopes and middleslopes located in the erosion area while lowerslopes were located in the deposition area. The longer the cultivation period, the higher the degree of soil redistribution on slope. Soil erosion was the most intense on the slope reclaimed 110 years ago. In view of the soil erosion in Black Soil Region, we should vigorously carry out the quality protection and improvement of cultivated land, encourage contour farming and strengthen the monitoring and investigation of soil conservation of black soil under a longer spatio-temporal series. The results can provide a theoretical basis for the prediction and prevention of water conservation and controlling soil erosion in Northeast China, which is conducive to the sustainable development of regional agriculture and ecological environmental protection.