【作者】 马璠；

【导师】 吴发启；

【作者基本信息】 西北农林科技大学 ， 水土保持与荒漠化防治， 2009， 博士

【摘要】 土壤侵蚀已成为全球性的严重环境问题,而坡耕地是土壤侵蚀发生的主要策源地。农作物作为坡耕地的主要覆盖物,对坡耕地土壤侵蚀的发生和发展有着重要影响。因此,深入研究作物植被对土壤侵蚀的作用,对经济有效地防治侵蚀、完善土壤侵蚀理论有重要的意义。本文以黄土高原主要种植作物玉米、大豆、谷子和小麦为对象,采用室内外人工模拟降雨、田间入渗测定、土壤化学分析等手段,研究了作物植被对降雨再分配、溅蚀、降雨入渗、坡面产流产沙、坡面土壤养分流失等方面的作用,得到了以下主要结论:(1)作物冠层可将降雨大致分配为冠下穿透雨、茎秆流和冠层截留三部分。随玉米、大豆和谷子的生长,穿透雨量占总降雨量比例分别在约94%~36%、95%~73%,以及85%~55%之间逐渐降低;小麦的冠下穿透雨量所占比例随小麦生长(从返青起身到抽穗后)变化趋势不明显,在约76%~82%之间变化。玉米、大豆和谷子冠下穿透雨量的空间分布很不均匀,局部地点降雨强度可达初始降雨的2~3倍,小麦冠下穿透雨量分布相对均匀。茎秆流量占总降雨比例随玉米、大豆和谷子的生长,分别在约5%~68%、2%~22%,以及7%~32%之间逐渐增加;小麦植株群体不适用茎秆流概念,顺植株流下的水量被定义为小麦行内水量,在总降雨量中约占18%~24%。本研究还提出了物理意义相对明确的单株玉米茎秆流模型。玉米、大豆、谷子和小麦的冠层截留量(换算为作物所占地面上的水深)在作物生长过程中分别在约0.02 mm~0.4 mm、0.05 mm~1 mm、0.05 mm~0.35 mm,以及0.5 mm~1.5 mm之间变化,作物冠层截留量不是降雨再分配的主要部分。(2)在生长过程中,玉米、大豆、谷子和小麦冠下的平均溅蚀速率与裸地溅蚀速率的比值分别在约40%~80%、25%~60%、45%~89%,以及3%~12%之间变化。大豆冠下平均溅蚀速率随冠层生长逐渐降低,其它三种作物冠下平均溅蚀速率则在作物生长过程中无规律波动。三种禾本科作物冠下的溅蚀速率在80 mm/h雨强下与裸地对照值相比的降低幅度大于在40 mm/h雨强下的降低幅度,大豆在这方面的规律不明显。作物冠下的溅蚀往往集中到少数几个地点发生,溅蚀速率空间变异极大。(3)在一个生长季内,作物没有对土壤的入渗能力产生显著影响,但是随着作物的生长,降雨在坡面的入渗显著增加。玉米、大豆、谷子和小麦在生长过程中,分别能将降雨在坡面的入渗量相对裸地提高15%~51%、8%~45%、5%~58%,以及110%~120%以上。作物对降雨入渗的促进作用主要不是通过提高土壤入渗能力,而是通过阻滞降雨和径流在坡面的运动,延长径流在一定尺度坡面上的停留时间来实现的。(4)玉米、大豆、谷子在生长过程中,分别能将产流量相对裸地降低约11%~42%、7%~38%,以及2%~43%;将产沙量分别降低约27%~76%、21%~78%,以及24%~84%。小麦在春季返青期,就能将产流量和产沙量分别降低至裸地的11%左右和1.15%左右,在抽穗后,则进一步降低至裸地的约2.36%和约0.25%,在收割后,产流量和产沙量仍然维持在与收割前相近的极低水平上。本研究以通用土壤流失方程USLE中的覆盖管理因子C为理论指导,计算了作物植被影响下的土壤流失比率(作物覆盖条件下土地的土壤流失量与裸地土壤流失量的比值),并拟合了玉米、大豆和谷子三种作物覆盖下,土壤流失比率与冠层叶面积指数之间的关系式,在种植上述三种作物的条件下,坡面土壤流失比率的变化与叶面积指数之间分别呈现出幂函数、线性函数和对数函数关系。(5)在本研究中,种植玉米条件下,侵蚀泥沙中养分浓度和养分富集率与裸地的侵蚀泥沙无显著差异,在种植大豆和谷子条件下,侵蚀泥沙中养分浓度和养分富集率高于裸地的侵蚀泥沙,有统计意义上的显著差异。坡面表层土壤浓度在一个作物生长季内降低趋势不明显。不同覆盖条件、降雨强度以及坡度等因素对坡面养分流失的影响主要不是通过改变泥沙养分浓度,而是通过改变泥沙流失总量来实现的,坡面养分流失总量的变化与泥沙流失量的变化趋势相同。更多还原

【Abstract】 Soil erosion is a severe global environmental problem. Slope land is the main original place of erosion. As the main cover on slope lands, agricultural crops play an important role in soil erosion processes of slope land. Therefore, the thorough research about the influences of crop cover on erosion is important to control erosion economically and effectively, as well as to improve soil erosion theory. This study took corn, soybean, millet, and wheat, which are widely planted on Loess Plateau, as main materials, using methods such as indoor and outdoor simulated rainfall, infiltration measurement in field, and chemical analysis, investigated the effects of crops on rainfall partitioning, splash detachment, rainfall infiltration, runoff and sediment yield, and nutrient losses from slope land. The results showed that:(1)The canopy of crops partitioned rainfall as there main parts: throughfall, stemflow, and interception storage. As corn, soybean, and millet grew, the ratios of throughfall to total rainfall declined from about 94 to 36%, 95 to 73%, and 85 to 55%, respectively; for wheat, the ratio had no obvious trend as growing (from returning green stage to after heading), and fluctuated between about 76 to 82%. The spatial distribution of throughfall under corn, soybean, and millet was uneven, throughfall intensities at some points under canopy were 2 or 3 times higher than initial rainfall; the distribution of throughfall under wheat canopy was relatively more even. As corn, soybean, and millet grew, the ratios of stemflow to total rainfall increased from about 5 to 68%, 2 to 22%, and 7 to 32%, respectively. The concept of stemflow was not suitable for wheat. Rain water moved along wheat plants was defined as intro-row water, which composed about 18 to 24% in total rainfall amount. A stemflow model for corn which had fairly good physical basis was built in this study. The interception storage (water depth on ground occupied by crops) on corn, soybean, millet, and wheat canopies changed from about 0.02 to 0.4 mm, 0.05 to 1 mm, 0.05 to 0.35 mm, and 0.5 to 1.5 mm, respectively. Interception storage on crop canopy was not a main part in rainfall partitioning process.(2)As crops grew, the ratios of average splash detachment rates under corn, soybean, millet, and wheat canopies to detachment rates on bare soil changed between about 40 to 80%, 25 to 60%, 45 to 89%, and 3 to 12%, respectively. The average detachment rate under soybean canopy decreased as canopy grew; for other three crops, the average detachment rates under canopy changed irregularly during growing stages. Under canopies of the three gramineous crops, the reduction of detachment rates compared to detachment rate on bare soil were greater under rainfall of 80 mm/h intensity than which under rainfall of 40 mm/h intensity; such phenomenon was not obvious under soybean canopy. Splash detachment often occurred at several points under crop canopy, and appeared extremely high spatial variation.(3)During one growing season, crops didn’t affect infiltration property of soil significantly. But, rainfall infiltration on slope increased significantly as crops grew. In the growing period, corn, soybean, millet, and wheat enhanced infiltration amount of rainfall by 15 to 51%, 8 to 45%, 5 to 58%, and 110 to 120% compared to bare slope, respectively. The promotion effects of crops on rainfall infiltration were largely caused by slowing down rainfall and runoff movement on slope and prolonging the staying time of runoff on slope with a certain scale, not caused by improving infiltration ability of soil.(4)As corn, soybean, and millet grew, compared to bare soil, crop covers reduced runoff yield by about 11 to 42%, 7 to 38%, and 2 to 43%, and reduced sediment yield by about 27 to 76%, 21 to 78%, and 24 to 84%, respectively. In spring, when wheat started to grow again, the runoff and sediment yield from wheat plots were about 11% and 1.15% of that from bare plots. After heading, those ratios reduced to 2.36% and 0.25%, respectively. Even after harvest, the runoff and sediment yield from wheat plots were at a low level as that before harvest. Soil loss ratios (ratio of soil loss under crop cover to that from bare soil slope) were calculated taking the cover and management factor C in USLE as basis. Soil loss ratios under corn, soybean, and millet cover conditions were decreased exponentially, linearly, and logarithmically as leaf area indexes of the three crop canopies increased, respectively.(5)In this study, nutrient concentrations and enrichment ratios of nutrients in sediment from corn plots were not significantly different from that from bare plots. Under soybean and millet cover, nutrient concentrations and enrichment ratios of nutrients in sediment were higher than that from bare plots, the differences were significant statistically. Nutrients concentrations in top soil on slope didn’t decline obviously during one growing season of crops. The influences of different cover conditions, rainfall intensities, and slope gradients on nutrient loss from slope were not caused by changing nutrients concentrations in sediment, but caused by changing total sediment yield. Nutrient loss and sediment loss had the same trend of changing.更多还原