横、顺坡垄作对黑土坡面侵蚀-沉积周期规律的影响

The Influence of Transverse and Longitudinal Ridge Tillage on Soil Erosion and Deposition Cycles for Mollisol Slope

我国东北黑土区的水土流失和土地退化正严重制约着东北地区农业经济发展,威胁国家粮食生产安全。掌握不同垄作方向耕作措施下的东北黑土区土壤侵蚀规律,对合理布设水保措施、控制水土流失等具有重要意义。采用^(137)Cs示踪技术并结合小波分析方法,对不同垄作方向坡耕地土壤侵蚀-沉积速率的空间变化规律开展研究。结果表明:(1)横、顺坡垄作坡面^(137)Cs平均浓度分别为1802 Bq·m^(-2)和1770 Bq·m^(-2),均小于当地背景值2417 Bq·m^(-2),说明在两种垄作方向下均发生了不同程度的土壤侵蚀。(2)横坡垄作的坡面平均侵蚀速率(1341 t·km^(-2)·a^(-1))小于顺坡垄作(1477 t·km^(-2)·a^(-1)),表明在长期平均条件下前者的水土保持作用优于后者。尽管研究区土壤侵蚀属于轻度侵蚀,但其侵蚀速率远大于黑土区的土壤容许流失量(200 t·km^(-2)·a^(-1)),因而在本研究区进行水土流失综合治理已迫在眉睫。(3)横、顺坡垄作在整个坡面均存在侵蚀-沉积的周期性变化规律,顺坡垄作存在一个45 m的主周期和一个75 m的次周期,而横坡垄作只存在一个45 m的主周期。准确把握土壤侵蚀-沉积在坡面的周期性变化规律,可为坡面水土保持措施的精确布设提供科学的理论依据。

【Objective】The black soil region of Northeast China is an important commodity grain production base in China.The long-term high-intensity utilization and unplanned agricultural cultivation measures led to serious soil fertility decline,grain yield reduction,and soil erosion in some areas.Soil erosion and land degradation in the black soil region seriously restricted the development of the agricultural economy in Northeast China.This threatened national food production and security.Ridge tillage is the most common cultivation method in the black soil region of Northeast China.However,the long-term effects of different ridge direction on slope erosion and deposition has never been evaluated.Therefore,understanding soil erosion and deposition on slopes with different ridge directions is of great significance for the development and deployment of soil and water conservation measures and the control of soil loss in the black soil area of Northeast China.【Method】^(137)Cs is an artificial radionuclide produced by atmospheric nuclear test and nuclear leakage.Its half-life is 30.2 years.The nuclide is strongly adsorbed by clay particles in soils after settling to the surface,and it is difficult to be leached by water.This implies that it only moves mechanically with soil particles.Therefore,it is regarded as a good tracer and widely used in the study of soil erosion rate.In this study,^(137)Cs tracer technology combined with wavelet analysis method was used to study the spatial variation of soil erosion and deposition rate on slopes with different ridge planting directions.【Result】(1)The average concentration of^(137)Cs on slopes with horizontal and longitudinal ridges was 1802 Bq·m^(-2)and 1770 Bq·m^(-2),respectively,which were lower than the local background value of 2417 Bq·m^(-2).(2)The slope erosion and deposition rate were between-700 to 2662 t·km^(-2)·a^(-1)with an average of 1341 t·km^(-2)·a^(-1)on slopes with horizontal ridges,and that on slopes with longitudinal ridges was between-726 to 3327 t·km^(-2)·a^(-1)with an average of 1466 t·km^(-2)·a^(-1).These results showed that the average erosion rate of slopes with horizontal ridges was lower than that with longitudinal ridges.(3)Different periodic change of erosion and deposition on 140 m long slopes were observed.There was a 45 m main period and a 75 m secondary period of erosion and deposition on slopes with longitudinal ridges,while only a 45 m main period was observed on slopes with horizontal ridges.【Conclusion】The periodic change of erosion and deposition on slope surface is mainly caused by the change of transportation capacity of rainfall-runoff and snowmelt runoff along the slope.Different degrees of soil erosion occurred on slopes with different ridge directions,and the slopes with horizontal ridges showed less soil loss than those with longitudinal ridges.Although soil erosion in the study area was mild,its average soil erosion rate is far greater than the allowable soil loss(200 t·km^(-2)·a^(-1))in the black soil region of China.Thus,there is an urgent need for comprehensive control of soil erosion in this area.This study could provide a scientific and theoretical basis for the precise layout of soil and water conservation measures such as;(i)reinforcement of ridge platform and(ii)arrangement of contour plant belt on strong erosion positions of slopes.This could prevent the destruction of ridges by runoff and effectively reduce slope soil erosion.