水蚀风蚀交错区坡地退耕草地的水转化特征及养分流失研究

发布时间：2018-07-26 10:28

【摘要】：为了解黄土高原水蚀风蚀区坡地退耕还草后的水分养分变化特征,利用2003年开始的野外坡面径流小区定位观测土壤水分和土壤侵蚀及养分流失,分析坡地退耕还草多年后的土壤水分动态变化和土壤含水量对沙黄土坡面土壤侵蚀及养分流失的影响。主要结果表明:(1)坡地退耕还草后,土壤水分含量降低,多年以后,苜蓿地的土壤水分含量显著低于坡耕地,含水量已接近或者达到萎蔫含水量。撂荒草地土壤水分含量稍低于坡耕地,尽管坡耕地有较多的径流,但是土壤水分含量保持在较高水平。2010年季初3个处理土壤剖面平均含水量分别为7.4%,12.6%,12.5%,丰水年降水(669.4 mm)可以不同程度地补充土壤剖面水分,补充深度较一般年份深110 cm左右,苜蓿地、撂荒地、坡耕地土壤水分分别恢复到10.0%,14.5%,15.5%,分别增加了35.1%,15.1%,24.0%。因此,坡耕地退耕种植紫花苜蓿导致土壤水分含量显著降低,只有在丰水年土壤水分含量才有较明显的恢复。但是紫花苜蓿和撂荒草地能有效减少坡面产流产沙,在5年的研究中,仅有3次产流产沙记录,而坡耕地产流产沙共达23次。(2)土壤水分是影响黄土高原坡面产生径流的众多因素之一,土壤前期含水量是决定产生的径流量和泥沙量的一个重要因素。本研究基于4年测量数据,利用Hydrus-1D模型模拟农田浅层(0~6 cm)土壤水分含量日变化,EF值达到0.64,得到的前期含水量值可以用来分析其与坡地土壤侵蚀之间的关系。径流量和产沙量随着降雨量和土壤前期含水量的增加而增加。在侵蚀性降雨事件发生时,当前期含水量大于0.12 cm3 cm-3时,产生径流的概率为85%。因此,Hydrus-1D模型可以为准确预测坡地土壤侵蚀提供前期含水量数据。(3)黄土高原水蚀风蚀区降雨特性成为该区产生土壤侵蚀和养分流失的决定因素。径流量和泥沙量随降雨量的增加而增加,泥沙量随着径流量的增加而增加,两者存在极显著线性相关。在径流率相同的情况下,径流量大的径流携带更多的泥沙。与试验小区土壤颗粒相比,泥沙中黏粒和粉粒含量略有增加。(4)径流中有效磷含量随时间变化比较稳定,相差不大;硝态氮和铵态氮含量随时间变化波动大。泥沙中全氮和全磷含量随时间相差不大,有效磷也随时间变化不大,铵态氮含量与硝态氮含量随时间变化趋势相反,有机质含量随时间相差不大。径流中硝态氮含量、有效磷含量随土壤前期含水量的增加而增加;土壤前期含水量增加,径流中铵态氮含量并不会增加。泥沙中养分含量并不会受土壤前期含水量的影响,而会随降雨量和雨强增加而增加。
[Abstract]:In order to understand the change characteristics of soil moisture and nutrients after returning farmland to grass in wind-erosion area of the Loess Plateau, soil moisture, soil erosion and nutrient loss were observed by using field runoff plot, which began in 2003. The dynamic changes of soil moisture and the effects of soil water content on soil erosion and nutrient loss on sandy loess slope were analyzed after returning farmland to grass for many years. The main results were as follows: (1) the soil moisture content of alfalfa field was significantly lower than that of sloping farmland after returning farmland to grass, and the soil moisture content of alfalfa field was close to or reached wilting water content. The soil moisture content of abandoned grassland is slightly lower than that of sloping land, although there is more runoff in sloping land. But the soil moisture content was kept at a high level. The average water content of the three treatments in the early season of 2010 was respectively 7.4 and 12.60.The annual precipitation (669.4 mm) can replenish the soil profile water in varying degrees, and the depth of the soil profile is about 110cm deeper than that of the normal year. The soil moisture of alfalfa field, abandoned land and sloping land was restored to 10.0 and 14.5and 15.5g, respectively, and increased 35.1g 15.1g and 24.0g, respectively. Therefore, the soil moisture content decreased significantly when alfalfa was planted in sloping farmland, and only in the high water year could the soil moisture content recover obviously. But alfalfa and abandoned grassland can effectively reduce the yield of abortion and sediment on the slope. In the 5 years study, there were only three records of abortion and sediment yield. Soil moisture is one of the most important factors affecting runoff on the slope of the Loess Plateau, and the water content in the early stage of soil is an important factor to determine runoff and sediment yield. Based on the data of 4 years, the Hydrus-1D model was used to simulate the diurnal variation of soil water content (EF) in shallow layer (0 ~ 6 cm) of farmland to reach 0.64, which can be used to analyze the relationship between the diurnal variation of soil moisture content and soil erosion in sloping land. Runoff and sediment yield increased with the increase of rainfall and soil water content. When the erosive rainfall event occurs and the water content of the current period is greater than 0. 12 cm3 cm-3, the probability of runoff generation is 85%. Therefore, Hydrus-1D model can provide early water content data for accurate prediction of slope soil erosion. (3) rainfall characteristics of water erosion wind erosion area on the Loess Plateau are the determinants of soil erosion and nutrient loss in this area. The runoff and sediment amount increased with the increase of rainfall, and the amount of sediment increased with the increase of runoff, and there was an extremely significant linear correlation between them. In the case of the same runoff rate, the runoff with large runoff carries more sediment. Compared with the soil particles, the clay and silt contents in the sediment increased slightly. (4) the content of available phosphorus in runoff changed steadily with time, but the content of nitrate and ammonium changed greatly with time. The content of total nitrogen and total phosphorus in sediment varies little with time, and the content of available phosphorus does not change with time. The content of ammonium nitrogen and nitrate nitrogen changes with time, but the content of organic matter does not change with time. The content of nitrate nitrogen and available phosphorus in runoff increased with the increase of soil water content, but the content of ammonium nitrogen in runoff did not increase. The nutrient content in the sediment is not affected by the water content in the early stage of the soil, but increases with the increase of rainfall and rainfall intensity.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：S157.1

【共引文献】