黄土高原治理中的委托—代理关系及激励机制

根据委托—代理理论 ,对黄土高原治理中的参与方进行了辨析。分析了现存的委托—代理关系中存在的问题 ,设计出了新的激励与约束机制 ,使代理人能够按照委托人的意志行事     

东祁连山不同退化程度高寒草甸土壤有机质含量及其与主要养分的关系

对东祁连山金强河河谷轻度、中度、重度退化高寒草甸土壤有机质含量变化及其与土壤全磷、全氮、速效磷、速效氮含量之间的关系进行了研究。结果表明：随着退化程度的加重,020 cm层土壤有机质、全氮和速效磷含量均不断下降,全磷含量呈现出先降后升但总体呈下降的趋势,但速效氮含量则不断上升,各养分的变化差异均达到极显著水平(P<0.01)。在划分的轻度退化草地土壤中,有机质含量分别与全磷、全氮、速效磷、速效氮含量之间均不存在显著的相关关系(P>0.05),另外所划分的中度退化和重度退化草地也同样如此。但是通过把3个不同程度退化草地结合起来作为整体进行综合分析,结果表明,除了全磷,土壤有机质含量分别与全氮、速效氮、速效磷含量三者之间存在极显著的相关关系(P<0.01)。在较大尺度上,有机质可以作为土壤营养状况的主要判断指标。在研究高寒草地土壤养分状况及其综合评价中,要特别注意其时空异质性,要重视尺度问题。     

五台山高山、亚高山草甸植物种分布的环境梯度分析和种组划分

通过野外植被调查,结合景观尺度生境因子的测定与模拟,运用CCA排序分析研究区内高山、亚高山草甸地段植物物种分布与环境因子之间的定量关系,综合TWINSPAN分类结果对五台山高寒草甸植物种进行了生态种组划分。结果表明：1)五台山的高山、亚高山草甸分布地段,温度和太阳辐射是控制着草甸植物种分布的关键因子;2)依据草甸物种在CCA排序图上的分布位置,划分出高山冷干型、高山冷湿型、亚高山典型种、亚高山凉干型、亚高山凉湿型、山地暖干型和山地暖湿型几类物种,可以较好地指示研究区的生境特征;3)TWINSPAN划分结果与CCA 划分的生态种组比较吻合。     

巴音布鲁克高寒草地几种公害物综合安全的研究

采用综合安全评估法,对巴音布鲁克高寒草地六六六、敌敌畏、铅和砷的综合安全予以评估,结果表明：巴音布鲁克高寒草地土壤、地表水、饲草和肉羊中,六六六、敌敌畏和砷的生态、经济和社会综合安全率均为100%,其综合安全居于高级安全状态水平,铅的生态、经济和社会综合安全率均为94.70%,其综合安全居于中级偏上安全状态;六六六、敌敌畏、铅和砷总综合安全率达98.57%,总综合安全居于中级偏上安全水平。     

鼢鼠破坏对天祝高寒草地土壤营养的影响

对天祝高寒草地在鼢鼠破坏条件下土壤氮、磷的变化特征进行了研究。结果表明,随着时间的增长,鼢鼠破坏后的土壤全氮含量呈先下降后上升的趋势,而速效氮含量呈增加的趋势,其中,新鼠丘和旧鼠丘的土壤全氮含量均极显著低于对照（P〈0．01）,而旧鼠丘的土壤全氮含量极显著高于新鼠丘（P〈0．01）;土壤速效氮含量的变化为：对照〈新鼠丘〈旧鼠丘,对照和新鼠丘的速效氮含量均极显著低于旧鼠丘的含量（P〈0．01）,而对照和新鼠丘之间差异不显著（P〉0．05）。鼢鼠破坏后土壤的全磷含量和速效磷含量均呈现不断下降趋势,土壤全磷含量和土壤速效磷含量的变化均为：对照极显著高于新鼠丘和旧鼠丘（P〈0．01）,新鼠丘显著高于旧鼠丘（P〈0．05）。     

Dynamics of soil microbial biomass C and soil fertility in cropland mulched with plastic film in a semiarid agro-ecosystem

Microbial biomass C (MBC) is one of the soil properties used as an indicator for the fertility status of a soil. A study was conducted on a semi-arid Loess Plateau in China. The field was planted with spring wheat and mulched with plastic film for various lengths of time. Our primary objectives were to (i) explore the influence of film mulching on soil MBC and soil fertility, and (ii) seek an effective approach of maintaining and improving sustainability of cropland mulched with plastic film in two growing seasons. Four treatments were tested, non-mulching (M0), mulching for 30 days after sowing (M30), mulching for 60 DAS (M60) and mulching for the whole growing period (Mw). An increasing air temperature with time within the growing season promoted soil MBC in the two growing seasons, but a severe drought led to a lower MBC in 2000 compared with the wet year of 1999. Film mulching promoted MBC significantly in the 2 years, but decreased soil organic carbon (SOC). SOC is very low in the experimental soil, accounting for the higher MBC/SOC ratio compared with ratios reported by others. The SOC is greatly reduced in the non-mulched and the Mw treatments compared to the M30 and M60 treatments. In conclusion, the benefits of film mulching in semi-arid agricultural systems are enormous but realizing their full potential depends on how long the mulching material is maintained during the growing season. In the system tested, it is desirable to mulch the plots for 30-60 DAS in order to enhance microbial biomass and cycling of nutrients and also to provide a more stable soil micro-environment that generates more residues in the rhizosphere.     

黄土高原地区森林与黄土厚度的关系

气候较干旱的黄土高原地区的植被类型和黄土高原厚度关系密切。森林植被分布于基岩山地和薄层黄土区。黄土有效水孔隙度高，水分入渗浅，土壤蒸限消耗水分较多，厚层黄土区的土壤水分条件不能满足森林植被的需要，因此厚度黄土区无森林植被分布。基岩山地和薄层黄土区的植被恢复可以林木为主，厚层黄土分布区应以 浅根草灌为主。     

高原沟壑区高效农业生态经济系统研究Ⅱ粮食生产持续发展

长武王东沟试验区通过１０多年系统田间试验，采用不同降水年型粮食作物丰产抗旱技术，在降水趋于正常的１９９３年，小麦产量为４９４４ｋｇ／ｈｍ＾２，玉米产量为９４７８．５ｋｇ／ｈｍ＾２，粮食单产６２５６．５ｋｇ／ｈｍ＾２，处历史最高水平，在世界旱作上也是罕见记录。自１９２９年以来灾情最为严重的１９９５年，年降水量２７２．２ｍｍ，占常年降水４６．６％，粮食产量仍取得１５０４．５ｋｇ／ｈｍ＾２的较好收成，与     

发展沟道人工湿地 改善基岩产沙区生态

随着沟道坝系工程建设的开展 ,黄土高原基岩产沙区出现了一些沟道湿地迹象。发展沟道人工湿地对于改善区域农业生态环境、增加生物群落、净化环境和水源等具有重要意义。鉴别和确认湿地的类属有利于湿地的研究、利用、保护和发展。依据我国湿地的定义、界定条件及类型等 ,对黄土高原基岩产沙区沟道治理形成的湿地进行了确认 ,并指出了其发展前景     

The effect of land cover/vegetation on soil water dynamic in the hilly area of the loess plateau,China

Severe soil and water loss has lead to widespread land degradation in China's loess plateau. During the past decades, a great deal of effort was made on vegetation restoration to reduce soil and water loss in the loess plateau. However, due to water shortage the efficiency of vegetation restoration was not as satisfactory as expected. As part of a vegetation restoration project, we conducted research aiming to understand the relationship between vegetation pattern and soil water dynamics. The goal was to find vegetation types appropriate for the loess plateau with scarce water resources. In 1986, fifteen plots of land were planted with five vegetation types: pine woodland, shrubland, sloping cropland, alfalfa and semi-natural grassland. Soil water content, runoff, soil erosion were measured for each plot. Environmental variables, such as rainfall, evaporation and temperature, were recorded simultaneously by an automated meteorological station. The relationship between land cover pattern and soil water dynamic was evaluated by using statistical models. We found that: (1) soil water loss occurred during the growing season, and it reached the maximum in the second half of July; (2) soil water was not fully replenished from rainfall during the rainy season; (3) pine woodland induced the largest water loss to surface runoff, followed by sloping cropland, alfalfa, semi-natural grassland and shrubland; the poor capability of pine woodland for water conservation may be attributed to soil compaction and poor ground coverage under the tree; (4) in most cases, soil water of the five vegetation types was low except for shrubland and semi-natural grassland where it was moderate-high during a few periods. These conditions inhibit sustainable vegetation growth in the semi-arid loess hilly area of the loess plateau, China.