黄土高原南部3种农田土壤剖面坚实度的变化规律

为了揭示黄土高原南部地区不同质地类型土壤剖面坚实度的变化及其与土壤含水率的定量关系,以黄墡土、土娄土、裸露在地表的粘化层耕作剖面为研究对象,定位观测其0~45 cm土壤坚实度与含水率的变化。结果表明,黄墡土、土娄土、裸露在地表粘化层耕作剖面的犁底层平均坚实度均大于耕层,犁底层平均坚实度较耕层分别高194.8%,87.3%,10.4%;剖面土壤质地越粘其平均坚实度越大;土壤坚实度与含水率呈负相关关系;土壤坚实度变化速率为0时,以上3种土壤剖面临界含水率分别为0.1712,0.1757,0.1835;质地不同的土壤剖面坚实度时空变化特征有差异,其中黄墡土剖面0~20 cm土层土壤坚实度为350~500 kPa,受土壤含水率变化的影响较小;20~30 cm土层土壤的坚实度为500~1400 kPa,不易受外界环境影响;30 cm以下土层土壤坚实度为700~1600 kPa,受土壤含水率变化影响较大。土娄土剖面0~40 cm土层土壤坚实度为600~1200 kPa,受含水率变化影响较大;40 cm以下土层土壤坚实度稳定在1 800 kPa左右。粘化层剖面0~15 cm土层土壤坚实度在2000 kPa左右,受环境影响较...

渭北旱塬持续高效农田种植模式研究与示范

根据渭北旱塬自然经济特点 ,提出了该区农业持续发展的关键技术和增产新途径——农田高效优化种植模式 (以双元覆盖小麦为主 )。通过 4a的试验示范与推广 ,结果表明 :该模式可较对照增产小麦6 2 .92 % ;复种黄豆增收 1 5 0 0～ 2 2 5 0 kg/ hm2 ,较对照增产 1 0 0 %。该模式的聚水、保墒、增温和促进有机质矿化、增加土壤养分效应显著 ,可使土壤水、热环境改善 ,充分利用水资源 ,提高用水效率。

核素示踪法研究农耕地土壤侵蚀的定量模型及其评价

应用137Cs示踪技术估算农耕地土壤侵蚀量的定量模型主要有两类:径流小区上建立的经验关系式及各种理论模型。文章主要对各种主要模型作了简要介绍,并对各种模型的优点、局限性进行了比较和评价;指出今后在模型的建立和应用中注意的问题。09jgg$g2l!1Mng:44Ntd。deIH20{lse3MxBijL&:nwlxxatx*rrr。k$1lreX4各种主要模型作了简要介绍。并对各种模型的优点、局限性进行了L田获$叶平价;指出今后在模型的建立和应用中注意的问题。

中国西部退耕还林(草)面临的新问题再思考

改革开放 2 0余年来 ,在我国东部高速发展的基础上 ,党和政府审时度势提出了“西部大开发”战略 ,但西部生态环境恶劣制约我国整个国民经济发展。 2 0 0 0年在长江上游和黄河中上游的西部地区大规模实施退耕还林 ,又把可持续发展战略演绎到了新的高度。在上述背景下 ,通过对我国西部地区生态环境恶化与退耕造林所发挥作用的探讨 ,结合西部自然特点和实际情况 ,总结了建国 5 0年来 ,退耕还林和种草所经历的不平凡的 4个阶段 ,分析了退耕还林 (草 )过程中存在的主要问题 ,根据西部区情提出了保护自然资源和恢复生态环境及整治大江大河的对策。

黄土区坡面水肥条件与植被建设

在对黄土区坡耕地资源、坡面水肥资源分布和植被现状分析的基础上 ,指出在坡面上进行植被建设应根据水分和养分的植物承载能力来确定适宜的植物种类和植被建设方案时建议采取综合技术措施进行植树种草 ,最后初步提出了黄土区坡面进行植被建设的技术模式。

应用Vc发酵弃渣防治保护地病害

The prevention and control of tomato plant diseases were conducted in protective ground using Vc fermentation waste residue treated by enzymolysis and ultrasonic wave. The results showed that the seedlings planted for 3 weeks on the protective ground soil continuously cropped tomato plant for 9 years and fertilized 75, 150 and 300 kg·hm -2 grew well. Their biomass were increased by 123%, 164% and 182%, and the disease incidence rates were decreased by 59%, 78% and 85%, respectively. Under application of 300 kg·hm -2 Vc fermentation waste residue, the products of tomato grown for 10 weeks on the soil continuously cropped tomato plant for 9, 6 and 2 years were increased by 60%, 43% and 14%, respectively, and the disease incidence rates were all decreased by 50%.

Spatio-temporal changes in annual accumulated temperature in China and the effects on cropping systems, 1980s to 2000

Change in thermal conditions can substantially affect crop growth, cropping systems, agricultural production and land use. In the present study, we used annual accumulated temperatures > 10 degrees C (AAT10) as an indicator to investigate the spatio-temporal changes in thermal conditions across China from the late 1980s to 2000, with a spatial resolution of 1 x 1 km. We also investigated the effects of the spatio-temporal changes on cultivated land use and cropping systems. We found that AAT10 has increased on a national scale since the late 1980s, Particularly, 3.16 x 10(5) km(2) of land moved from the spring wheat zone (AAT10: 1600 to 3400 degrees C) to the winter wheat zone (AAT10: 3400 to 4500 degrees C). Changes in thermal conditions had large influences on cultivated land area and cropping systems. The areas of cultivated land have increased in regions with increasing AAT10, and the cropping rotation index has increased since the late 1980s. Single cropping was replaced by 3 crops in 2 years in many regions, and areas of winter wheat cultivation were shifted northward in some areas, such as in the eastern Inner Mongolia Autonomous Region and in western Liaoning and Jilin Provinces.

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.

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.

Potential CO2 Emission Reduction by Development of Non-Grain-Based Bioethanol in China

Assessment of the potential CO2 emission reduction by development of non-grain-based ethanol in China is valuable for both setting up countermeasures against climate change and formulating bioethanol policies. Based on the land occupation property, feedstock classification and selection are conducted, identifying sweet sorghum, cassava, and sweet potato as plantation feedstocks cultivated from low-quality arable marginal land resources and molasses and agricultural straws as nonplantation feedstocks derived from agricultural by-products. The feedstock utilization degree, CO2 reduction coefficient of bioethanol, and assessment model of CO2 emission reduction potential of bioethanol are proposed and established to assess the potential CO2 emission reduction by development of non-grain-based bioethanol. The results show that China can obtain emission reduction potentials of 10.947 and 49.027 Mt CO2 with non-grain-based bioethanol in 2015 and 2030, which are much higher than the present capacity, calculated as 1.95 Mt. It is found that nonplantation feedstock can produce more bioethanol so as to obtain a higher potential than plantation feedstock in both 2015 and 2030. Another finding is that developing non-grain-based bioethanol can make only a limited contribution to China's greenhouse gas emission reduction. Moreover, this study reveals that the regions with low and very low potentials for emission reduction will dominate the spatial distribution in 2015, and regions with high and very high potentials will be the majority in 2030.

Generation and analysis of 5318 expressed sequence tags from the filamentous sporophyte of Porphyra haitanensis (Rhodophyta)

Porphyra haitanensis T. J. Chang et B. F. Zheng (Bangiales, Rhodophyta) is cultivated in China and widely consumed in Asia. To gain more insight into its physiological and biochemical properties, we generated 5318 expressed sequence tags (ESTs) from the sporophyte of P. haitanensis, and upon assembling into a nonredundant set, 2535 sequences were obtained, among which only 32.2% (816) shared certain similarity with published sequences (Nr and KOG). Functional classification of such ESTs revealed that most of the transcripts were related to its conservative biological metabolism, and P. haitanensis most likely possesses cyanide-resistant respiration and a C4-like carbon-fixation pathway, both of which have never been reported in a rhodophyte before. Twenty-eight percent of the nonredundant gene clusters exhibited significant similarity to those from P. yezoensis Ueda sporophytes, and 16 genes up-regulated in P. yezoensis sporophytes were also expressed abundantly in P. haitanensis. Codon usage analysis indicated that exposure to high GC pressure might occur during evolution of P. haitanensis. These findings represent the most extensive collection of ESTs from P. haitanensis to date, and all the ESTs in this study have been submitted to GenBank (accession nos. DN604790-DN608469, EG016226-EG018540).

Microprojectile bombardment of Laminaria japonica gametophytes and rapid propagation of transgenic lines within a bubble-column bioreactor

A human acidic fibroblast growth factor gene, hafgf, was successfully transferred into Laminaria japonica (kelp) gametophytes via microprojectile bombardment using the biolistic PDS-1000/He gene gun. Following phosphinothricin screening, PCR detection and Southern blot analysis, transgenic L. japonica gametophytes were cultivated in an illuminated bubble-column bioreactor to optimize growth conditions. A maximal final dry cell density of 1,695 mg l(-1) was obtained in a batch culture having an initial dry cell density of 129.75 mg l(-1). This was achieved using an aeration rate of 1.08 l air min(-1) l(-1) culture in a medium containing 1.5 mM inorganic nitrate and 0.15 mM phosphate. In addition, the relationship between different nitrogen sources and growth of transgenic gametophytes indicated that both urea and sodium nitrate were effective nitrogen sources for cell growth, while ammonium ions inhibited growth of these gametophytes.

Sequence analysis of the ITS region and 5.8S rDNA of Porphyra haitanensis

The sequences of the ITS (internal transcribed spacer) and 5.8S rDNA of three cultivated strains of Porphyra haitanensis thalli (NB, PT and ST) were amplified, sequenced and analyzed. In addition, the phylogenic relationships of the sequences identified in this study with those of other Porphyra retrieved from GenBank were evaluated. The results are as follows: the sequences of the ITS and 5.8S rDNA were essentially identical among the three strains. The sequences of ITS l were 331 by to 334 bp, while those of the 5.8S rDNA were 158 by and the sequences of ITS2 ranged from 673 by to 681 bp. The sequences of the ITS had a high level of homology (up to 99.5%) with that of P. haitanensis (DQ662228) retrieved from GenBank, but were only approximately 50% homologous with those of other species of Porphyra. The results obtained when a phylogenetic tree was constructed coincided with the results of the homology analysis. These results suggest that the three cultivated strains of P. haitanensis evolved conservatively and that the ITS showed evolutionary consistency. However, the sequences of the ITS and 5.8S rDNA of different Porphyra species showed great variations. Therefore, the relationship of Porphyra interspecies phyletic evolution could be judged, which provides the proof for Porphyra identification study. However, proper classifications of the subspecies and the populations of Porphyra should be determined through the use of other molecular techniques to determine the genetic variability and rational phylogenetic relationships.

Transforming kelp into a marine bioreactor

The past decade has seen the genetic engineering of various types of seaweed. To date, genetic transformation studies have been carried out in several seaweeds, including the red seaweeds Porphyra, Gracilaria, Grateloupia, Kappaphyclus and Ceramium and the green seaweed Ulva. A genetic transformation model system has been established in the most commonly cultivated seaweed, the brown seaweed Laminaria japonica (kelp), based on the transfer of technology used in land plant transformation and also by modulating the seaweed life cycle. This model showed the potential for application of transgenic kelp to the production of valuable products and an indoor cultivation system for transgenic kelp was proposed, taking into account necessary factors for bio-safety. In this review, the establishment at use of the kelp transformation model is introduced, highlighting the potential for transforming kelp into a marine bioreactor.