黄土高原长期种植苜蓿对土壤硫、钙、镁的影响

以22年定位试验为基础,研究黄土高原长期种植紫花苜蓿(Medicago sativa L.)情况下土壤硫、钙、镁组分的变化。结果表明:长期施P使苜蓿连作耕层土壤总硫、有效硫、水溶性硫、吸附性硫、HCl可溶性硫、总无机硫和有机硫含量分别增加9.41%、62.41%、47.51%、30.07%、2.25%、5.38%和17.54%;长期施NPM使苜蓿连作耕层土壤总硫、有效硫、水溶性硫、吸附性硫、HCl可溶性硫、总无机硫和有机硫含量分别增加20.89%、98.31%、68.44%、57.34%、8.07%、12.54%和37.69%。长期施P使苜蓿连作耕层土壤全钙、有效钙、水溶态钙、交换态钙和酸溶态钙含量增加分别增加4.64%、4.27%、11.66%、4.05%和8.59%,但残余态钙含量降低2.21%;长期施NPM使苜蓿连作耕层土壤全钙、有效钙、水溶态钙、交换态钙和酸溶态钙含量增加分别增加8.69%、8.30%、51.59%、6.73%和27.77%,但残余态钙含量降低26.23%。长期施NPM使苜蓿连作耕层土壤全镁、有效镁、水溶态镁、交换态镁、酸溶态镁和残余态镁含量分别增加7.38%、61.98%、63.16%、61.85%、5.81%和8.97%。此外,有效硫在土壤剖面上出现双累积峰,有向深层土壤迁移的特征;有效钙、有效镁在土壤剖面上存在淋溶累积现象。此研究结果可为苜蓿种植和管理提供依据。     

云雾山不同草地群落土壤活性有机碳分布特征

为探讨黄土高原草地植被演替过程活性有机碳的变化规律,揭示草地退耕后的分布特征,在云雾山草原区采集不同草地群落土壤,采用高锰酸钾氧化法对0~100 cm土层活性有机碳进行分析。结果表明:不同草地群落土壤活性有机碳含量均高于坡耕地,活性有机碳含量大小顺序为:长芒草(Stipa bungeana Trin.)群落>大针茅(Stipa grandis P.Smirn.)群落>铁杆蒿(Artemisia gmelinii Web.ex Stechm.)群落>百里香(Thymus mongolicus Ronn.)群落>退耕草地>坡耕地,且群落间差异达极显著水平(P<0.01);在恢复初期(坡耕地-退耕草地-百里香)活性有机碳含量增加较多,恢复到长芒草群落活性有机碳含量达到最大值,趋于稳定;活性有机碳的密度与含量表现出相同的变化规律,并随着土层的加深而呈现减小趋势。相关性分析表明,活性有机碳含量与土壤总有机碳含量呈极显著线性正相关关系(r=0.9742),土壤活性有机碳比总有机碳更能反映草地植被恢复初期土壤有机碳库的变化。     

紫花苜蓿和短花针茅根系分布与土壤水分研究

以陕北农牧交错带人工草种紫花苜蓿(Medicago sativa L.)和天然草种短花针茅(Stipa breviflora Griseb.)为对象,采用根钻法调查两个草种的根系垂直分布以及刈割后苜蓿根系变化特征,并通过定位观测研究土壤水分动态变化。结果表明:紫花苜蓿和短花针茅根系密度随土壤深度增加而减少,而且均以直径小于等于1 mm的须根为主;0~50 cm土层紫花苜蓿和短花针茅根系量分别占0~100 cm剖面总量的67%和84%。紫花苜蓿和短花针茅根系分布与土壤水分消耗特征吻合。生长旺盛期苜蓿大量消耗0~140 cm土层土壤水分,5-9月平均有效土壤储水不足10 mm;生长季末深层(140~280 cm)土壤储水也逐渐降低,约为裸地储水量的50%。短花针茅0~280cm剖面土壤水分状况明显好于苜蓿地,比苜蓿地多储水100 mm左右;主要消耗浅层(0~50 cm)土壤水分,深层水分利用较少。     

黄土丘陵区不同恢复年限草地土壤微团粒分形特征

运用分形理论研究黄土丘陵区不同恢复年限草地土壤微团粒的粒径组成、分形维数特征及与土壤理化性质关系,使分形学在土壤微团粒性状与土壤肥力特征研究中得到进一步应用,并为评价草地生态系统土壤特征及生态恢复提供新方法。结果表明:表土层分形维数随植被恢复年限的增加而减少;剖面土壤沙粒含量越高,微团粒分形维数越低,粘粒规律相反,而粉粒与分形维数相关性不显著;土壤质地由粗到细使得分形维数由小到大变化;分形维数也可有效地表征不同植被恢复年限的草地土壤结构和养分的变化趋势;分形维数与土壤容重、非活性孔度、全磷、速效钾及氨态氮之间存在正相关性,与土壤活性孔度、孔隙比、有机质、全氮、碱解氮及硝态氮表现出负相关。     

利用DEM模型求算磨西台地堆积物体积

基于GIS的DEM模型,求算磨西台地堆积物的体积,为1.172×10⁹ m³.计算结果表明,采用可视化方法的计算结果与估算结果基本一致,该结果具有一定的参考价值,并对该方法的精度及注意问题进行了讨论.通过计算磨西台地的体积,可以定量分析当时冰川堆积和泥石流发生的强度,为进一步研究当时环境演变与台地的形成过程,提供有力的数据支持.     

Factors affecting transpiration of Pinus tabulaeformis in a semi-arid region of the Loess Plateau

The effects of soil water and meteorological factors affecting transpiration of Pinus tabulaeformis were studied under different levels of soil water content to offer a scientific basis for increasing efforts in afforestation survival and management of soil water in forested land. Under artificial control methods for soil water and potting experiments, the transpiration rate (T _r) of P. tabulaeformis and environmental factors were measured using a portable steady porometer (Li-1600) and a speedy weight method (BP-3400) during a representative fine day in the growing season of 2004. The results indicated that the diurnal course of T _r and R _st of P. tabulaeformis displayed a double-peaked curve and a “W” curve under different levels of soil water content. Given a representative fine day, the T _r could be represented as a cubic relation with soil water content (SWC). The SWC which caused maximum T _r values of P. tabulaeformis was 17.7%, 19.8%, and 17.5% in July, August and October respectively. T _r was affected not only by physiological characteristics, but also by SWC and meteorological factors. T _r was significantly correlated with meteorological factors when the soil water was sufficient, but this correlation would decrease under conditions of serious water stress. Under such stress conditions, air temperature was the primary factor to affect T _r in July and August and photosynthetically active radiation (PAR) was the primary factor in October. When soil water is sufficient, the main factors affecting T _r were relative humidity (RH), air temperature (T _a) and leaf temperature (T _l) in July, August and October respectively. __________ Translated from Science of Soil and Water Conservation, 2007, 5(1): 49–54 [译自: 中国水土保持科学]     

Soil structure changes induced by the tropical earthworm Pontoscolex corethrurus and organic inputs in a Peruvian ultisol

Inoculation of Pontoscolex corethrurus (Glossoscolecidae, Oligochaeta) in a Peruvian ultisol under several treatments (without or with organic input) has been previously shown to increase macroaggregation and bulk density and to decrease water infiltration and soil moisture. In the present study, we used image analysis of thin sections of soil to understand the impact of earthworm on the structure of the upper layer of the soil. Morphological analysis allowed to quantify the abundance of casts, soil compactness, pore morphology and connections between different pore classes. This approach was applied to experiments carried out at Yurimaguas (Peru), in four plots. Two of them had been inoculated with Pontoscolex corethrurus. In each case, one control plot was conducted without organic input, the other with crop residues and legume green manure. Morphological parameters were measured in fourteen horizontal sections within the first 3 cm. They showed compaction of soil surface due to cast coalescence in plots with earthworms but without organic input and illustrated the typical crumb structure induced by earthworms in plots with organic input.     

Management of runoff stored in small tanks for transplanted rice production in the mid-hills of Northwest Himalaya

Scarcity of water in upland areas limits the growing of transplanted rice and the yield of rice grown under rainfed conditions is very low. As the first priority for the use of runoff recycling based water resources is in the dry season followed by the monsoon season, a strategy has been developed to use the surplus water (occurring during the early monsoon season) to grow transplanted rice without compromising the dry season irrigation. Field experiments revealed that under the mid-hill conditions, transplanted rice can be grown as transplanted in 5 cm standing water and thereafter tainted, requiring only 3.0–3.5 cm of water with a yield reduction of about 25% as compared to generally recommended intermittent submergence (2 days after the disappearance of water) requiring 100–130 cm of water. However, the reduction in yield was not significant if 1 week of initial ponding just after transplanting was created. Based on rainfall-runoff analysis, graphs were developed for runoff and volume of water available in water tanks in different durations of early monsoon periods, command-catchment area ratio and the volume of water available after irrigation which is to be used in dry season, as a function of runoff curve numbers. These graphs can be consulted directly to plan irrigation systems for transplanted rice in upland areas.     

中国南北方植物对土壤加固机制的差异性

为深入分析植物对土壤加固的影响效益和机制,该研究选取重庆缙云山地区和陕西延安黄土丘陵区种植一年的乔木（火炬树、榆树）和灌木（荆条、酸枣）,该测定其根系形态、力学参数和土壤的抗剪强度,通过RBM_w模型计算根系固土效益,综合评估不同植物种的固土效能和贡献度。结果表明：2地种植的物种平均根直径的差异不显著（P > 0.05）,重庆种植的乔木(火炬树、榆树)的根长、分叉数和根尖数显著高于延安,灌木未出现显著差异（P < 0.05）。根系的抗拉强度与直径都符合负幂函数关系,其中平均抗拉强度最大的为荆条。除荆条外,同种植物根系的抗拉强度并未因不同地区的种植产生显著差异。4个植物种根系的固土效率为0.65～4.12 kPa,各物种间存在显著差异（P < 0.05）。重庆2种乔木种植下的根土复合体有效黏聚力高于裸地（约10%）,灌木种植下则普遍略低于裸地。除酸枣外,种植于重庆的4种植物的根系固土作用和效率都显著的高于延安（P < 0.05）。研究结果可为不同地区固土护坡的树种选择提供理论依据。     

Vegetation color exposure differences at the community and individual levels: An explanatory framework based on the neighborhood effect averaging problem

Urban green spaces have multiple benefits, yet their distribution is often uneven. Studies on green inequality frequently adopt static exposure assessments, disregarding exposure during individual mobility, resulting in potential biases known as the neighborhood effect bias. Neighborhood effect averaging problem (NEAP) shows that exposure based on personal mobility tends to be average for all participants, compared to exposure based on residence. This study examines the NEAP in the context of green inequality by considering the ornamental value of green space, specifically vegetation color diversity. Considering that vegetation color can attract attention and has health benefits, we hypothesized that it is a key feature related to NEAP, as residents may compensate for poor residential environment by accessing better environmental quality during daily mobility. To investigate this, we compared vegetation color exposure at community and individual levels, assessing whether NEAP exists. Our findings suggest that while communities with high economic levels had significantly higher exposure to vegetation color diversity, the exposure at the individual level tended to be average. Moreover, NEAP appears to be more of an issue when considering vegetation color diversity compared to a measure of total green space such as green view index. We acknowledge that due to the responsiveness of survey, the survey sample includes a higher proportion of the well-educated and employed individuals with potentially higher mobility, which may influence the results. Overall, this study provides supporting evidence for NEAP in the context of vegetation color exposure, but not green view index, emphasizing the critical role of enhancing the ornamental value of green space and strengthening the quality of green space in improving green inequality.