IMHE OpenIR  > 山地表生过程与生态调控重点实验室
耕作侵蚀对紫色土坡耕地水蚀的作用机制
Alternative TitleImpact of tillage erosion on water erosion on sloping farmland of Purple soil
Language中文
王勇
Thesis Advisor张建辉
2015
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Name博士
Degree Discipline土壤学
Keyword耕作侵蚀 水蚀 土壤再分布 边界效应 水土流失
Abstract研究已证实耕作侵蚀与水蚀是我国长江上游紫色土坡耕地区域两大主要侵蚀类型,目前国内外还未见关于耕作侵蚀对水蚀作用机制的研究。为了探讨耕作侵蚀是加强还是减弱了水蚀作用的问题,本文以长江上游紫色土典型坡耕地为研究对象,采用137Cs示踪技术、常规顺坡耕作、模拟强烈耕作(短期内连续数次耕作)、人工降雨及地学统计学分析相结合的方法,系统研究了紫色土坡耕地耕作侵蚀对坡面水蚀的作用机制,主要研究结果和结论如下: 1、强烈耕作引起坡面土壤垂直和水平方向再分布 模拟耕作试验结果表明:与耕作前相比,20次耕作后137Cs面积浓度在坡顶(0 m)、肩坡(5 m)、中坡(10 m)分别降低了16.18%、33.08%、7.49%;而在背坡(15 m)和坡趾(20 m)位置分别增加了10.15%和50.58%,说明强烈耕作引起了坡面土壤发生明显的空间再分布。配对样本T检验结果显示:与耕作前相比,通过20次耕作后,土壤深度在0 m,5 m位置发生了显著减少(P<0.05),而在20 m位置发生了显著增加(P<0.05),在10和15 m位置变化不明显(P>0.05)。模拟耕作前土壤有机质的深度分布满足回归方程(Y=a Ln (X) + b),然而通过20次模拟耕作后并不再满足该方程,这主要是由于耕作的混合效应弱化了有机质浓度在垂直方向上的变异性。37Cs残余率分布结果显示:强烈耕作引起土壤净侵蚀和净沉积分别发生在上坡和下坡的边界处,而中坡仅仅起类似于传送带的作用传输来自上坡的土壤,阐明了耕作侵蚀的边界效应非常强烈。 2、耕作引起土壤团聚体及抗蚀性的变化 与耕作前相比较,20次耕作后<0.25 mm粒径非水稳性团聚体含量比耕作前增加了36.98%(32.62—42.14%)。强烈耕作导致水稳性团聚体的平均质量直径(MWD)、平均几何直径(GMD)、团聚体结构破坏率(PAD)以及土壤可蚀性K值在坡耕地不同景观位置均发生了显著的增减。20次耕作后团聚体结构破坏率(PAD)比耕作前增加了61.09%(42.76—68.50%),土壤可蚀性K值比耕作前增加了42.27%(24.59—61.34%),随着坡长增加,MWD和GMD值逐渐增加,而PAD和K值不断减小,揭示了耕作侵蚀造成坡面土壤抗蚀性明显降低,而顺坡向下抗蚀性逐渐增强。强烈耕作对坡耕地土壤结构稳定性具有两方面的重要影响:即耕作引起土壤向下坡传输和耕作过程伴随着机械破碎的双重作用共同改变了坡面土壤结构的稳定性。 3、耕作侵蚀对土壤水分及入渗特征的影响 与对照地(等高耕作1次)相比,模拟耕作45次土壤水贮量在上坡部位降低了49.38%,在中坡和下坡部位分别增加了23.85%和15.80%。表明强烈耕作显著影响了坡面土壤水分的再分布。与对照地相比,45次耕作后坡面土壤持水量在上坡的低吸力段(0—330 KPa)下降了34.88%;而在下坡的高吸力段(330—15000 KPa)显著增加了125.00%。表明强烈耕作导致土壤在不同吸力条件下的持水量发生了显著变化。与对照地相比,上坡通过25次和45次耕作后累积入渗量分别减少了50.67%和68.44%。在下坡位置,25次和45次耕作后坡面土壤水分累积入渗量比对照地分别增加了13.76%和11.11%。对照地在中坡位置的累积入渗量比上坡高4.55%,比下坡高21.69%;45次耕作后土壤水分累积入渗量比上坡增加了3.39倍,比下坡增加了48.57%。结果表明:强烈耕作引起上坡侵蚀区土壤入渗速率和累积入渗量明显降低,导致地表径流量显著增加,从而增加水蚀强度;而在下坡堆积区域,土壤入渗速率和累积入渗量虽然暂时增加,但坡面汇流在下坡加剧,因而并未减少水蚀作用。 4、耕作侵蚀强度对坡面产沙的影响 在15度的径流小区内,通过模拟不同耕作年限,利用70 min人工降雨试验结果显示:坡面开始产流时间变化规律为:耕作52年(29 min 32 s)> 耕作31年(47 min 32 s)> 耕作10年(57 min 40 s)> 对照地(未产流),说明随着模拟耕作年限的增加,产流时间不断提前,径流量显著增加。在相同降雨时间内不同耕作位移量的细沟坡面平均产流产沙量的大小依次变化趋势均为:24.72 kg m–1 > 9.86 kg m–1 > 0 kg m–1,表明耕作位移量的增加将显著加剧了坡面水蚀,揭示耕作侵蚀对水蚀起着输送物质的作用。累积产沙量随着耕作侵蚀强度的增加(耕作年限和耕作位移量的增加)而显著增加,表明耕作侵蚀加速了紫色土坡耕地土壤水蚀作用。 不同耕作强度处理下坡面水动力参数(平均流速,径流深度,径流剪切力)在上坡和下坡位置发生了显著变化(P<0.05),表明耕作的边界效应显著影响了坡耕地坡面水动力特征。模拟耕作10、31、52年后坡面土壤可蚀性参数(K)分别为:8.49、16.35、33.11 g min–1 N–1;模拟耕作位移量为0、9.86、24.72 kg m–1的径流临界剪切力( )分别为0.75、0.59、0.38 Pa。结果表明随着耕作侵蚀强度的增加,坡面土壤可蚀性显著增加,径流剪切力明显减小,揭示了耕作侵蚀对水蚀的敏感性。
Other AbstractIt has been demonstrated that two erosion processes, water and tillage erosion, contribute to the total soil erosion in steeply sloping regions of the Upper Yangtze River Basin. Few studies have examined the effects of different tillage intensities on water erosion. Can tillage-induced soil redistribution lead to exaggerated (or retarded) runoff flow and sediment concentration in steeply sloping fields? The 137Cs tracing, traditionally tillage, simulated tillage by hoeing, artificial rainfall, and geostatistics analyses were used to examine the impacts of tillage erosion on water erosion on a purple soil of cultivated sloping land. The main results and conclusions are as follows: 1. Soil redistribution by intensive tillage Tillage simulation experiments indicate that 137Cs inventories under 20-operation tillage decreased by 16.18%, 33.08%, and 7.49%, respectively, for the summit (0 m), shoulder (5 m), and middle (10 m) slope positions, and increased by 10.15% and 50.58% for back (15 m) and toe (20 m) slope positions, respectively, implying that intensive tillage caused soil redistribution and downslope transport within the landscapes. An analysis of paired-sample t-tests showed a significant difference in the depth of soil profiles at the 0, 5, and 20 m positions between pre-tillage and 20-operation tillage (P<0.05), while there is no significant difference in the 10 and 15 m positions (P>0.05). The depth distribution of soil organic matter for pre-tillage can be described by the formula (Y=a Ln (X) + b), but it did not follow this formula after 20-operation tillage. This is because the mixing effect of tillage attenuates the variability of soil organic matter in the vertical direction. The distribution of 137Cs residual rate suggests that apparent changes in net erosion and deposition occur close to the upslope and downslope boundaries of the field and the middle slope acts as a conveyor belt. Our results suggest that intensive tillage have a significant boundary effects. 2. Change of soil and aggregate and anti-erodibility due to intensive tillage After 20-operation tillage the number of the small aggregates (<0.25 mm) increased by 36.98% (32.62—42.14%), as compared with pre-tillage. A significant difference (P<0.05) in mean weight diameter (MWD), geometric mean diameter (GMD), the percentage of aggregate destruction (PAD) and soil erodibility factor (K) occurred at the 0 m, 5 m, 15 m, and 20 m slope positions between pre-tillage and 20-operation tillage. Compared with before tillage, the PAD increased by 61.09% (42.76—68.50%), and K values increased by 42.27% (24.59—61.34%) after 20-operation tillage. With increasing in slope length, MWD and GMD values gradually increased, and PAD and K values increased after intensive tillage. These findings indicated that soil anti-erodibility remarkably decreased, and increased with increasing the slope length due to tillage erosion. Our results indicate that intensive tillage has a twofold influence: aggregate redistribution due to the soil transfer process and the mechanical breakage of macroaggregates and large clods. 3. Impacts of tillage erosion on soil water contents and infiltration Compared with the control (contour tillage), soil water contents significantly decreased by 49.38% after 45-operation tillage at the upper slope positions, and increased by 23.85% and 15.80% at the middle and lower slope positions, respectively. This indicates that intensive tillage influences redistribution of soil water contents, especially in the upper slope positions. The moisture-holding capacity for 45-operation tillage decreased by 34.88% in the low suction range (0—330 KPa) of the upper slope positions, and significantly increased by 125.00% in the high suction range (330—15000 KPa) of the lower slope positions, as compared with those of the control. The results imply that intensive tillage leads a remarkable change in the moisture-holding capacity in different suction ranges. As compared with the control, the cumulative infiltration decreased by 50.67% and 68.44% at the upper slope positions, but increased by 13.76% and 11.11% at the lower slope positions, respectively, for 25- and 45-operation tillage. At the middle slope positions, the cumulative infiltration of the control increased by 4.55% and 21.69% compared with that of the upper and lower slope positions, respectively. Similarly, the cumulative infiltration by 45-operation tillage is 3.39 times higher than the upper slop position, and increased by 48.57% compared with the lower slope positions. Our studies indicate that infiltration rates and cumulative infiltration capacities significantly decreased with increasing tillage intensity, resulting in runoff amount increased at the upper slope positions. It is suggested that soil degradation by tillage erosion alters soil hydrological properties, thereby resulting in poor soil infiltrability which may enhance overland water flow in relation to water erosion. At the lower slope positions, though infiltration rates and cumulative infiltration capacities temporarily increased, slope conflux gradually aggravated at these slope positions. Therefore, water erosion did not decreased with an increase in tillage intensity. 4. Influences of tillage erosion on runoff amounts and sediment concentrations The artificial rainfall for the duration of 70 min was applied to the runoff plots with an average gradient of 15% by simulated different tillage periods. Runoff from the experimental plots began 29’32’’, 47’32’’, and 57’40’’ after the initiation of the rainfall for 52-, 31-, and 10-year tillage periods, respectively. However, no runoff occurred in the case of a no-tillage treatment (CK) during the rainfall event. These findings indicated that runoff generated easily with increasing of tillage periods. The mean runoff rates of different the soil flux under the same rainfall intensity was as follows: 24.72 kg m–1 > 9.86 kg m–1 >0 kg m–1, showing that water erosion increased with increasing of the soil flux. This is attributed to the fact that tillage erosion acts as a delivery mechanism for water erosion. The cumulative detachment amount significantly increased with increasing tillage intensity, suggesting that water erosion was markedly accelerated because of soil redistribution by intensive tillage. For each tillage treatment, a significant difference in the hydrodynamic characteristics (including mean flow velocity, runoff depth, and effective shear stress) occurred near the upper and lower slope boundaries of the field (P<0.05), indicating that the boundary effects of tillage impacts significantly the hydrodynamic characteristics. Soil erodibility factor (K) was 8.49、16.35、33.11 g min–1 N–1 after 10, 31, and 52-year tillage, respectively. Critical shear stress ( ) by the soil flux of 0, 9.86, and 24.72 kg m–1 was 0.75、0.59、0.38 Pa, respectively. This suggests that K values significantly increased, and gradually decreased with increasing tillage intensity. These results indicate that tillage erosion is quite sensitive to erosion in steeply sloping areas.
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/15053
Collection山地表生过程与生态调控重点实验室
Recommended Citation
GB/T 7714
王勇. 耕作侵蚀对紫色土坡耕地水蚀的作用机制[D]. 北京. 中国科学院大学,2015.
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