区域土地退耕建设效益评价指标体系的初探

从建立土地退耕评价指标体系的必要性着手,以理论分析的方式,提出了一套科学的且适宜于基层一般技术人员操作的区域土地退耕建设效益评价指标体系。

农地退耕时程的土壤恢复度评估

通过测量土壤物理(密度、团聚体稳定性和入渗速率)、生物(微生物总量和土壤呼吸)和化学[表层土壤有机碳(SOC)]参数,对实施水土保持计划(CRP)的退耕土地、未受干扰和持续耕作的土地进行了比较,并利用时间函数来估计达到耕作前土壤质量所需的时间。结果显示,尽管实施CRP土地的土壤密度、入渗率、土壤呼吸和总有机碳(TOC)水平总体上趋向于受干扰前水平,但短期内任何参数都不足以恢复到受干扰前的水平。未耕作和实施30 a CRP的土壤团聚体稳定性和总微生物生物量没有显著差异,表明该参数在土地退耕30 a内得到了恢复。根据时间序列分析,估计需要53 a的时间才能使退耕土地的密度和土壤呼吸恢复到原状。入渗率和SOC的恢复时间最长,分别为75 a和128 a。结果表明,为了使土壤参数恢复到耕前状态,长期退耕是必要的。

Studies of Soil Physical Property on Different Abandoned Lands in the Minqin Oasis,Downstream of the Shiyang River

The vast area of farmland was abandoned at downstream of the Shiyang River because of decreased water recourse. To ensure the ecological safety of Minqin Oasis and to provide management basis for the abandoned land, soil physical properties were observed and studied. The authors analyzed land with abandonment time of 1 year, 2 years, 3 years, 4 years, 5 years, 8 years, 15 years, 24 years and 31 years. Samples were took at the 0-40 cm layer of soil to measure the bulk density, porosity and grain composition of soil in the different abandoned lands. Results showed that the tendency of clay content was decreasing, conversely, the fine sand increased at the layer of 0-10 cm of different abandoned lands.The changes of grain content reached a peak at the fourth year after the land was abandoned, then varied slightly. The variation of grain content of abandoned land was obvious with the extension of the abandonment year. The soil bulk density decreased and porosity increased with the extension of the abandonment year. The difference of porosity and soil bulk density at the range of 0-40 cm of different abandoned land decreased after the land abandoned for 3 years. The quality of soil was decreased, while the soil permeability was improved. The soil physical properties changed obviously in 3 to 4 years after abandonment, so it is the key time for land management.

Studies of Soil Physical Properties and Community Characteristics of Different Abandoned Lands in the Minqin Oasis,Downstream of the Shiyang River

[Objective] The aim was to explore physical properties and community characteristics of abandoned lands in different years in Minqin Oasis, downstream of the Shiyang River, [Method] The evolution of environment and plant community characteristics in different abandoned lands were analyzed after abandonment for 1, 2, 3, 4, 5, 8, 15, 24 and 31 years, and the plant community characteristics, water content, bulk density, porosity and mechanical composition of soil in the different a- bandoned lands were also researched in the Minqin Oasis, downstream of the Shiyang River. [Result] Plant of 32 species spread over 14 family live through fifty years appeared in abandoned lands in the study area. Shrubs was 6 species, herbs was 26 species among them, which were 18.75%, 81.25% respectively. The goose- foot family （6 species）, the composite family（4 species）,the grass family（4 species）, caltrop family（3 species） were 53.13% among them. Within the range of 0-40 cm of different abandoned Land, the soil moisture content showed a trend of first increase and then decrease with the increase of soil depth changes in soil bulk density and porosity of less obvious. In the range of 0-40 cm soil depth, the largest proportion of fine sand, followed by silt and clay and the smallest proportion of coarse sand in every plot, but the proportion of the each silt size varies little with the years aban- doned. [Conclusion] The research provides references for vegetation reconstruction and eco-environment construction in abandoned lands in downstream of Shiyang River.

Study on Evapotranspiration Regularity of 3 Forages in Eastern Qinghai Province

The transpiration rate and transpiration quantity＇of whole plants and foliages of Bromus innerrnis, Medicago sativa and Agropyron cristatum are measured by using improved quick and continuous weighting after being cut off method （QCWC）. The results show that transpiration rate of branches and foliages of Agropyron cristatum is highest in 3 forages, Medicago sativa is second and Bromus innermis is lowest. From July to September, the average transpiration quantity of whole plants and foliages of 3 forages is highest in August, September is second and July is lowest.

Modelling Regional Land Change Scenarios to Assess Land Abandonment and Reforestation Dynamics in the Pyrenees(France)

Over the last decades and centuries,European mountain landscapes have experienced substantial transformations.Natural and anthropogenic LULC changes(land use and land cover changes), especially agro-pastoral activities,have directly influenced the spatial organization and composition of European mountain landscapes.For the past sixty years, natural reforestation has been occurring due to a decline in both agricultural production activities and rural population.Stakeholders, to better anticipate future changes,need spatially and temporally explicit models to identify areas at risk of land change and possible abandonment.This paper presents an integrated approach combining forecasting scenarios and a LULC changes simulation model to assess where LULC changes may occur in the Pyrenees Mountains,based on historical LULC trends and a range of future socio-economic drivers.The proposed methodologyconsiders local specificities of the Pyrenean valleys,sub-regional climate and topographical properties,and regional economic policies.Results indicate that some regions are projected to face strong abandonment, regardless of the scenario conditions.Overall, high rates of change are associated with administrative regions where land productivity is highly dependent on socio-economic drivers and climatic and environmental conditions limit intensive(agricultural and/or pastoral) production and profitability.The combination of the results for the four scenarios allows assessments of where encroachment(e.g.colonization by shrublands) and reforestation are the most probable.This assessment intends to provide insight into the potential future development of the Pyrenees to help identify areas that are the most sensitive to change and to guide decision makers to help their management decisions.

Impacts of Sloping Land Conversion Program on the vegetation in loess hilly and gully area of northern Shaanxi

Aiming at alleviating the serious soil erosion, the Chinese government initiated the Sloping Land Conversion Program （SLCP） in 1999. Now; after 8 years of project implementation, the ecological recovery effects of the SLCP have become the hot issue of academic circle. This paper; raking the loess hill and gully area of northern Shaanxi as an example, presents a methodology for assessing the vegetation restoration effect of SLCP with normalized difference vegetation index （NDVI）. The key components include calculation of the Growing Season NDVI （GSNDVI）, and estimation of the NVDI change induced by climate and SLCP, respectively. Based on the method, the NDVI change between 2000 and 2006 was obtained using the GSNDVI that excluded the noise from snow and ice. After the part of total NDVI change caused to： climate variation was estimated using empiric formulae, we obtained the part induced by human factors, i.e. the SLCP The human induced part of ND VI change was considered as an approximation indicating the effect of the SLCP on the vegetation. Finally, we analyzed the ND VI change characters of the whole study area, different slope lands and different land use types by spatial statistics method. Results show that the vegetation condition is significantly improved by the SLCP, particularly land types that directly involved in the SLCP, such as steeply slope farmlands, degraded grasslands, etc.

Human Activity and Soil Fertility-Nutrients Depletion of Arable Soils in China

The reserve of soil nutrients is limited. In case of irrational use of land, nutrients would be depleted sooner. Before the 1950s the low grain production in China was maintained only by expanding the cultivated area and by recycling of nutrients in agriculture. Calculation of nutrients balance showed that in the year of 1949 there were great deficits of N, P and K elements in agriculture of China. It revealed that there would have really been danger of soil nutrients exhaustion if such a situation had continued. Things have changed since the beginning of 1950s. The nutrients balance in agriculture has been getting better and better. In the year 1987 N and P balance got rid of their great deficits. But for K the deficit grew even larger. This resulted in a rapid expansion of soil area deficient in K in China since the mid 1970s. In spite of the fact that the P balance in the arable land of the whole country was positive, the field which did not receive P fertilizer had become deficient in P. So the area deficient in P also increased. It is stressed that great attention should be paid to the depletion of soil nutrients, especially K in the northern part of China where the soil is relatively rich in K. Of course, soil sulfur and microelements should be considered next.