黄土高原旱地施肥对小麦与苜蓿土壤水分养分含量的影响

研究黄土高原旱地小麦(Wheat)和苜蓿(Alfalfa)连作20年后的产量、土壤水分及养分的变化。结果表明:磷肥对小麦增产不显著,而对苜蓿则增产显著(增产183.5%);施肥可以延缓苜蓿的衰老,提高产草量;苜蓿地土壤干燥化明显,施用氮磷有机肥后小麦地也出现干燥化趋势;长期施磷肥有利于改善土壤磷素有效性,其中苜蓿地全磷和有效磷含量,增加了13.6%和83.8%,小麦土壤增加了22.9%和367.9%;苜蓿土壤全氮和速效氮均呈增加,而小麦地则减少;平衡施用氮磷有机肥能培肥土壤,使产量大幅度提高;在该区采取合理的轮作方式和培肥措施能有效地改善农田生态系统的生产力。

延安试区人工刺槐林地的土壤干层分析

8 0年代以来 ,以林草地地力衰退为特征的人工林草地土壤退化日趋严重 ,其中以土壤水分严重亏缺为特征的土壤干化现象愈益引起了人们的重视。土壤干化的直接后果是形成土壤干层 ,导致土壤退化 ,植物生长速率减缓 ,群落衰败以至大片死亡 ,严重地威胁到我国北方地区特别是黄土高原地区生态环境的建设。因此 ,研究和解决土壤干层问题已成为黄土高原植被建设的迫切任务。根据延安试区的土壤水分和植被生长状况调查资料 ,初步分析了不同条件下刺槐人工林地的水分状况。结果表明 :试区刺槐人工林地普遍形成了土壤干层 ,且已相当严重 ;坡向对土壤干层有明显影响 ,阳坡形成的干层较阴坡严重 ;坡度愈大 ,土壤干化愈剧烈 ;林龄对干层严重程度影响不明显。同时 ,研究指出了解决土壤干层问题的意义。

黄土丘陵林区开垦地人为加速侵蚀与土壤物理力学性质的时间变化

以子午岭土壤侵蚀与生态环境演变观测站长年观测的径流泥沙资料为基础 ,分析了林地及其开垦地不同侵蚀年限土壤的颗粒组成、>0 .2 5 mm水稳性团粒含量、抗剪强度和容重等土壤物理力学性质与土壤侵蚀强度的关系。研究结果表明 ,>0 .2 5 mm水稳性团粒含量对土壤侵蚀强度影响最大 ,其偏相关系数为 0 .972 8,其次为土壤的粗粉粒含量和抗剪强度。最后对 >0 .2 5 mm水稳性团粒含量和抗剪强度与土壤侵蚀强度的关系进行了分析 ,表明林地开垦后侵蚀第 1年和第 7年为土壤侵蚀强度加剧的转折点 ,说明了森林植被在防治黄土高原土壤侵蚀方面的作用。

黄土丘陵林区开垦地土壤抗冲性的时间变化研究

以黄土丘陵林区 10a径流泥沙观测资料为基础 ,进行土壤抗冲试验 ,分析了林地及其开垦后不同年限土壤的抗冲性能。结果表明 ,林地具有很强的抗冲性能 ,一旦被开垦后 ,随侵蚀年限的增长 ,土壤的抗冲性呈减弱趋势 ,在 3L/min流量下 ,土壤冲刷量从侵蚀 1a的 4.0 1g/L增大到侵蚀 10a的 2 5 .5 1g/L ,加剧了土壤侵蚀发展。相关分析表明 ,土壤的抗剪强度对抗冲性影响最大 ,其次为水稳性团粒和有机质含量。因此 ,退耕还林、恢复和重建植被 ,改善土壤侵蚀环境 ,提高土壤抗冲性 ,能有效地防治土壤侵蚀。

秸秆还田对灌溉玉米田土壤反硝化及N_2O排放的影响

运用乙炔抑制技术研究了不同施氮水平下秸秆还田对灌溉玉米田土壤反硝化反应和氧化亚氮(N2O)排放的影响。结果表明,土壤反硝化速率及N2O的排放受氮肥施用、秸秆处理方式及其交互作用的显著影响。与秸秆燃烧相比,不施氮或低施氮水平时,秸秆还田可刺激培养初期反硝化反应速率及N2O排放,增加培养期间N2O平均排放通量;高施氮水平时,秸秆还田可降低反硝化反应速率及反硝化过程中的N2O排放。秸秆还田可降低反硝化中N2O/N2的比例。

Assessing the consequence of land use change on agricultural productivity in China

China's cultivated land has been undergoing dramatic changes along with its rapidly growing economy and population. The impacts of land use transformation on food production at the national scale, however, have been poorly understood due to the lack of detailed spatially explicit agricultural productivity information on cropland change and crop productivity. This study evaluates the effect of the cropland transformation on agricultural productivity by combining the land use data of China for the period of 1990-2000 from TM images and a satellite-based NPP (net primary production) model driven with NOAH/AVHRR data. The cropland area of China has a net increase of 2.79 Mha in the study period, which causes a slightly increased agricultural productivity (6.96 Mt C) at the national level. Although the newly cultivated lands compensated for the loss from urban expansion, but the contribution to production is insignificant because of the low productivity. The decrease in crop production resulting from urban expansion is about twice of that from abandonment of arable lands to forests and grasslands. The productivity of arable lands occupied by urban expansion was 80% higher than that of the newly cultivated lands in the regions with unfavorable natural conditions. Significance of cropland transformation impacts is spatially diverse with the differences in land use change intensity and land productivity across China. The increase in arable land area and yet decline in land quality may reduce the production potential and sustainability of China's agro-ecosystems. (C) 2008 Elsevier B.V. All rights reserved.

Emergy Assessment of a Wheat-Maize Rotation System with Different Water Assignments in the North China Plain

Sustainable water use is seriously compromised in the North China Plain (NCP) due to the huge water requirements of agriculture, the largest use of water resources. An integrated approach which combines the ecosystem model with emergy analysis is presented to determine the optimum quantity of irrigation for sustainable development in irrigated cropping systems. Since the traditional emergy method pays little attention to the dynamic interaction among components of the ecological system and dynamic emergy accounting is in its infancy, it is hard to evaluate the cropping system in hypothetical situations or in response to specific changes. In order to solve this problem, an ecosystem model (Vegetation Interface Processes (VIP) model) is introduced for emergy analysis to describe the production processes. Some raw data, collected by investigating or observing in conventional emergy analysis, may be calculated by the VIP model in the new approach. To demonstrate the advantage of this new approach, we use it to assess the wheat-maize rotation cropping system at different irrigation levels and derive the optimum quantity of irrigation according to the index of ecosystem sustainable development in NCP. The results show, the optimum quantity of irrigation in this region should be 240-330 mm per year in the wheat system and no irrigation in the maize system, because with this quantity of irrigation the rotation crop system reveals: best efficiency in energy transformation (transformity = 6.05E + 4 sej/J); highest sustainability (renewability = 25%); lowest environmental impact (environmental loading ratio = 3.5) and the greatest sustainability index (Emergy Sustainability Index = 0.47) compared with the system in other irrigation amounts. This study demonstrates that application of the new approach is broader than the conventional emergy analysis and the new approach is helpful in optimizing resources allocation, resource-savings and maintaining agricultural sustainability.

Impacts of socio-economic factors on sediment yield in the Upper Yangtze River

In recent years, the role of human activities in changing sediment yield has become more apparent for the construction of hydraulic engineering and water conservation projections in the Upper Yangtze River, but it has not been evaluated at the macro scale. Taking Sichuan Province and Chongqing City as an example, this paper studies the relationship between socio-economic factors and sediment yield in the Upper Yangtze River based on section data in 1989 and 2007. The results show that sediment yield is significantly correlated with population density and cultivated area, in which the former appears to be more closely related to sediment yield. Moreover, in the relation of sediment yield vs. population density, a critical value of population density exists, below which the sediment yield increases with the increase of population density and over which the sediment yield increases with the decrease of population density. The phenomenon essentially reflects the influence of natural factors, such as topography, precipitation and soil property, and some human activities on sediment yield. The region with a higher population density than critical value is located in the east of the study area and is characterized by plains, hills and low mountains, whereas the opposite is located in the west and characterized by middle and high mountains. In the eastern region, more people live on the lands with a low slope where regional soil erosion is slight; therefore, sediment yield is negatively related with population density. In contrast, in the western region, the population tends to aggregate in the areas with abundant soil and water resources which usually lead to a higher intensity of natural erosion, and in turn, high-intensity agricultural practices in these areas may further strengthen local soil erosion. It is also found that population tends to move from the areas with bad environment and high sediment yield to the areas with more comfortable environment and less sediment yield. The natural factors have greater influence on sediment yield of western region than that of eastern region. Generally, the natural factors play a dominant role on sediment yield in the Upper Yangtze River.

The single crystal-like banded textures in the films of a thermotropic liquid crystalline poly(aryl ether ketone) containing a lateral chloro group

The banded textures in the films of a thermotropic liquid crystalline poly(aryl ether ketone) containing a lateral chloro group have been studied by means of transmission electron microscopy(TEM), electron diffraction(ED) and atomic force microscopy (AFM). The crystallization-induced Landed texture without external shear can be formed when the thin films were annealed at the temperature range(320-330 degrees C) of the liquid crystalline state from the melt, The results show that the banded regions have high orientation of single crystal based on the orthorhombic packing and the growing direction of the Lands is along the b axis of the crystals, This kind of single crystal-like bands is due to the different orientation of the packing molecular chains, The molecular chains of the dark bands in the bright field electron micrograph are perpendicular to the film plane, while the ones of the bright Lands are tilt along the b axis with the tilt angle upto +/-20 degrees.

The effect of land management on carbon and nitrogen status in plants and soils of alpine meadows on the Tibetan plateau

Large-scale grassland rehabilitation has been carried out on the severely degraded lands of the Tibetan plateau. The grasslands created provide a useful model for evaluating the recovery of ecosystem properties. The purposes of this research were: (1) to examine the relative influence of various rehabilitation practices on carbon and nitrogen in plants and soils in early secondary succession; and (2) to evaluate the degree to which severely degraded grassland altered plant and soil properties relative to the non-disturbed native community. The results showed: (1) The aboveground tissue C and N content in the control were 105-97 g m(-2) and 3.356gm(-2), respectively. The aboveground tissue C content in the mixed seed treatment, the single seed treatment, the natural recovery treatment and the severely degraded treatment was 137 per cent, 98 per cent, 49 per cent and 38 per cent, respectively, of that in the control. The corresponding aboveground tissue N content was 109 per cent, 84 per cent, 60 per cent and 47 per cent, respectively, of that in the control. (2) Root C and N content in 0-20 cm depths of the control had an 2 2 average 1606 gm(-2) and 30-36 gm(-2) respectively. Root C and N content in the rehabilitation treatments were in the range of 26-36 per cent and 35-53 per cent, while those in the severely degraded treatment were only 17 per cent and 26 per cent of that in the control. (3) In the control the average soil C and N content at 0-20 cm was 11307 gm(-2) and 846 gm(-2), respectively. Soil C content in the uppermost 20 cm in the seeded treatments, the natural recovery treatment and the severely degraded treatment was 67 per cent, 73 per cent and 57 per cent, respectively, while soil N content in the uppermost 20cm was 72 per cent, 82 per cent and 79 per cent, respectively, of that in the control. The severely degraded land was a major C source. Restoring the severely degraded lands to perennial vegetation was an alternative approach to sequestering C in former degraded systems. N was a limiting factor in seeding grassland. It is necessary for sustainable utilization of seeding grassland to supply extra N fertilizer to the soil or to add legume species into the seed mix. Copyright (c) 2005 John Wiley & Sons, Ltd.

An application of the analytic hierarchy process and fuzzy logic inference in a decision support system for forage selection

Forage selection plays a prominent role in the process of returning cultivated lands back into grasslands. The conventional method of selecting forage species can only provide attempts for problem-solving without considering the relationships among the decision factors globally. Therefore, this study is dedicated to developing a decision support system to help farmers correctly select suitable forage species for the target sites. After collecting data through a field study, we developed this decision support system. It consists of three steps: (1) the analytic hierarchy process (AHP), (2) weights determination, and (3) decision making. In the first step, six factors influencing forage growth were selected by reviewing the related references and by interviewing experts. Then a fuzzy matrix was devised to determine the weight of each factor in the second step. Finally, a gradual alternative decision support system was created to help farmers choose suitable forage species for their lands in the third step. The results showed that the AHP and fuzzy logic are useful for forage selection decision making, and the proposed system can provide accurate results in a certain area (Gansu Province) of China.

西南喀斯特典型坡地土壤有机碳库特征及碳同位素组成

喀斯特石漠化及其影响己经成为制约中国西南地区可持续发展最严重的生态环境问题，越来越受到人们的关注，已成为环境地球化学研究的一个重要领域。石漠化的本质就是土地退化，造成土壤肥力和生产力的下降。因此喀斯特地区现阶段主要面临如何管理好陆地生态系统，以保持原有碳储量，并尽可能沉积更多碳是当前面临的主要挑战。 峰丛洼地是喀斯特地区的典型景观，该景观的坡地是喀斯特地区自然环境最脆弱的区域，存在基岩大量裸露的情况，土地和植被退化最为严重。本文以西南喀斯特地区具有不同植被类型的典型峰丛坡地（草丛、灌草丛、稀疏灌丛和乔木林）作为研究对象，为了解喀斯特地区碳的循环机制，我们采集了4个典型坡地不同地形部位的表层和剖面土壤，主要分析了土壤可溶性有机碳（DOC）、整体土壤及不同粒径土壤组分中有机碳含量和稳定碳同位素（δ13C）值组成，同时测定了植物优势种叶片、枯枝落叶δ13C值组成。得到以下几点认识： 1、草丛和灌草丛坡地各地形部位的土壤有机碳（SOC）含量和碳氮比(C/N)值差异较大，其上坡位的土壤都具有较高SOC含量和C/N值。而稀疏灌丛和乔木林坡地SOC含量和C/N值比较稳定，其变幅较小。 2、各坡地剖面土壤中DOC含量分布和变化主要受到了有机质输入､坡地地形及土壤质量等影响｡草丛和灌草丛坡地各地形剖面中DOC含量变幅要大于乔木林和稀疏灌丛坡，对各个坡地几个剖面上层土壤（0～20cm）中DOC含量来看，其含量主要表现为：乔木林坡地＞稀疏灌丛坡地＞灌草丛坡地＞草丛坡地。但通过DOC与SOC进行比对发现，在剖面土壤中DOC/SOC值整体变化趋势主要表现为随剖面土层的加深而增加的趋势，但在土层较薄的剖面中主要呈现一直增加的趋势，而在土层较厚的剖面中则出现先增加后降低或保持稳定的现象。除了稀疏灌丛坡地最低值出现在下坡位剖面PG3外，在草丛、灌草丛和乔木林坡地最低值均出现在上坡位的剖面，其中HC1、HG1和HG2剖面的DOC/SOC值最低，范围都在0.2%以下，具有明显的高SOC和低DOC的含量特征；而乔木林坡地各剖面DOC/SOC值相对较高，范围都在0.3%以上，并且各剖面之间的差异较小。 3、草丛和灌草丛坡地上坡位HC1、HG1和HG2剖面土壤主要是基岩风化物和植物残体堆积而成的砂质新成土，砂粒含量较高，剖面土壤中有机碳含量虽然高于下坡位各个剖面土壤，但有机碳主要贮存在砂粒土壤中，其碳库处于不稳定状态。而下坡位剖面中土壤主要以粉粒和黏粒为主，土壤有机碳含量相对较低，但主要贮存在粉粒和黏粒土壤中，其碳库处于相对稳定的状态。稀疏灌丛和乔木林坡地各地形剖面中主要以粉粒和黏粒土壤为主，各个剖面之间变化幅度较小，有机碳也主要贮存在粉粒和黏粒土壤中，其碳库组成比较稳定。 4、对采样点的植物优势种叶片的碳同位素组成进行了测定。结果显示，其δ13C值主要受到遗传因素的（光合作用途经）控制，植物碳同位素组成表现出明显的差异性，C3植物的δ13C平均值为-28.2‰，C4植物的δ13C平均值为-12.7‰。另外，对不同坡地采集的同种植物叶片的δ13C值分析发现，δ13C值受环境影响因素较小。 5、对各个坡地枯枝落叶和相应表层土壤有机质δ13C值之间的相关性研究发现，灌草丛和乔木林坡地具有显著相关性，其相关系数分别为R2=0.93和R2=0.77，明显高于草丛和稀疏灌丛坡地的R2=0.28和R2=0.36。由于土壤剖面发育历史及地表植被的不同，草丛和灌丛坡地土壤有机质的δ13C值要明显高于稀疏灌丛和乔木林坡地，并且不同地形剖面的土壤有机质的δ13C值的差异较大。另外，大多数剖面的土壤有机质δ13C值在剖面深度上的变化主要表现为随土层深度的加深呈现先升高后降低或趋于稳定的变化趋势。δ13C值在土壤剖面中随深度变化，反映了作物残体输入和土壤累积特征，有助于鉴定剖面中土壤有机碳的迁移转化过程。 6、剖面中土壤δ13CDOC值与δ13CSOC值的变化规律具有相似性，表明了土壤中DOC与SOC的具有密切的关系；另外，从△(δ13CDOC－δ13CSOC)来看，大多数剖面中δ13CDOC值要高于δ13CSOC值，其中乔木林的变化幅度最低，而草丛坡地的最高。 7、对剖面中不同粒径土壤有机质δ13C值的研究发现，不同粒径土壤有机质的δ13C值在剖面深度上的差异，主要受到输入土壤中有机质变化和进入土壤后分解程度的影响。各个坡地砂粒土壤中有机质的δ13C值对地表植被的变化较敏感，同时也指示了输入土壤中较新或是分解速率较慢的有机质来源，而粉粒和粘粒土壤有机质的δ13C值则指示了土壤中分解速率较快或是分解程度较充分的有机质来源。不同粒径土壤有机质δ13C值组成特征能够较好地反映土壤有机质更新速率。