黄土丘陵区小流域土地覆被变化对径流产沙量的影响

为探讨黄土丘陵区小流域土地覆被变化特征及其对流域径流产沙量的影响,以黄土丘陵区吕二沟、罗玉沟及其嵌套流域(桥子沟)等3个小流域为研究对象,运用数理统计学、配对流域等方法定量分析了3个小流域不同研究时段内土地覆被变化对径流产沙量的影响.结果表明,1982~2004年间,林地面积以1.07%/a的速率快速递增是吕二沟流域土地覆被变化的最明显特征,而罗玉沟流域在国家坡改梯工程影响下,坡耕地面积大幅减少,1986~1995年间约73%坡耕地转化为梯田;结合配对流域法可知,土地覆被变化是导致流域径流和产沙减少的主要原因,在相同降雨条件下,径流深、泥沙量分别减少43.76%和35.23%.流域年径流模数与年降水量和流域森林覆被率均呈指数关系,流域森林覆被率增加5%,径流模数可减少18.43%~37.58%.     

农业污染对土壤的危害及防治措施

伴随着我国经济的高速增长,环境问题也日益突出,特别是环境污染和生态破坏日益严重。城市环境问题日益得到重视,而农村的环境保护与治理相对来说是一个薄弱环节,农村环境也正日趋恶化。农村环境污染的加剧和农业生态环境的破坏,已成为制约我国农村经济健康发展的因素之一,农业减排势在必行。结合农村实际情况,本文从环境保护的角度阐述了农业生产过程中几种典型（农药、化肥、农作物秸秆）的污染及其对农田土壤造成的危害,同时针对化肥污染和农业污染提出了防治措施。     

An economic assessment of the health effects and crop yield losses caused by air pollution in mainland China

Air pollution is severe in China, and pollutants such as PM_(2.5) and surface O_3 may cause major damage to human health and crops, respectively. Few studies have considered the health effects of PM_(2.5) or the loss of crop yields due to surface O_3 using model-simulated air pollution data in China. We used gridded outputs from the WRF-Chem model, high resolution population data, and crop yield data to evaluate the effects on human health and crop yield in mainland China. Our results showed that outdoor PM_(2.5) pollution was responsible for 1.70–1.99 million cases of all-cause mortality in 2006. The economic costs of these health effects were estimated to be 151.1–176.9 billion USD, of which 90% were attributed to mortality. The estimated crop yield losses for wheat, rice, maize, and soybean were approximately 9, 4.6, 0.44, and 0.34 million tons, respectively, resulting in economic losses of 3.4 billion USD. The total economic losses due to ambient air pollution were estimated to be 154.5–180.3 billion USD, accounting for approximately 5.7%–6.6% of the total GDP of China in 2006. Our results show that both population health and staple crop yields in China have been significantly affected by exposure to air pollution. Measures should be taken to reduce emissions, improve air quality, and mitigate the economic loss.     

麦田O3浓度的长期变化及其对冬小麦干物质和产量损失的估算

近地层臭氧污染及其对作物产量和粮食安全的负面效应已成为国内外广泛关注的焦点之一.利用2014~2016年冬小麦主要生长季期间臭氧浓度和气象因子观测资料,分析了麦田臭氧浓度、AOT40的变化特征.根据Pleijel等2007年修正的气孔导度模型,模拟了冬小麦气孔导度的变化,并与实测值进行对比验证,同时结合通量模型,计算了冬小麦气孔臭氧通量.此外,利用前期课题组建立的模型,估算了臭氧对冬小麦干物质累积和产量的影响.结果表明:臭氧浓度在冬小麦生长季期间从前期到后期逐渐增加,并呈现明显的单峰型日变化特征.从2014~2016年的每年3月1日~5月31日,平均臭氧浓度分别为36.2、37.7和33.6 n L·L~(-1),AOT40值分别为17.08、17.90和11.84μL·(L·h)~(-1).Javis气孔导度模型可以用来模拟本地区冬小麦的气孔导度,模型解释了实测气孔导度81%的变异性.2014~2016年冬小麦气孔臭氧吸收通量分别为9.36、9.32和8.65 mmol·m~(-2).在近3年臭氧浓度平均水平下,近地层臭氧会使冬小麦产量减少18.03%,干物质累积减少19.31%.     

Is there a commercially viable market for crop insurance in rural Bangladesh?

The study aims to assess the commercial viability of a potential crop insurance market in Bangladesh. In a large scale household survey, agricultural farm households were asked for their preferences for a hypothetical crop insurance scheme using double bounded (DB) contingent valuation (CV) method. Both revenue and production cost based indemnity payment approaches were applied to assess the commercial viability of a crop insurance program assuming a partner-agent (PA) model of insurance supply. Crop insurance is found marginally commercially viable in riverine flood plain areas. The expected indemnity payable consistently exceeds the expected insurance premium receivable by the insurer for the households living in wetland basin and coastal floodplain. We conclude that a uniform structure of crop insurance market does not exist in Bangladesh. The nature of the disaster risks faced by the farm households and the socio-economic characteristics of the rural farm communities need to be taken into careful consideration while designing such an insurance scheme.

Crop residue removal and fertilizer N: Effects on soil organic carbon in a long-term crop rotation experiment on a Udic Boroll

Biofuels can be produced by converting cellulose in crop residues to ethanol. This has recently been viewed as a potential supplement to non-renewable energy sources, especially in the Americas. A 50-yr field experiment was analyzed to determine the influence of (i) removing approximately 22% of the above-ground wheat (Triticum aestivum L.) residue each crop year, and (ii) N and P fertilization on soil carbon (C) in the top 15 cm depth of a fallow–wheat–wheat (F–W–W) rotation. The study was conducted from 1958 to 2007 on a clay soil, at Indian Head in sub-humid southeast Saskatchewan, Canada. Soil C concentrations and bulk densities were measured in the 0–7.5 and 7.5–15 cm depths in 1987, 1996 and 2007 and soil C changes were related to C inputs estimated from straw and root yields calculated from regressions relating these to grain yields. Two soil organic matter models [the Campbell model and the Introductory Carbon Balance Model (ICBM)] were also used to simulate and predict the effects of the treatments on soil C change over time, and to estimate likely soil C change if 50% or 95% of above-ground residues were harvested each crop year. Crop residue removal reduced cumulative C inputs from straw and roots over the 50-yr experiment by only 13%, and this did not significantly (P > 0.05) reduce soil C throughout the experiment duration. However, after 50 yr of applying N fertilizer at recommended rates, soil C increased significantly by about 3 Mg ha⁻¹ compared to the non-fertilized treatment. The simulated effect of removing 50% and 95% of the above-ground residues suggested that removing 50% of the straw would likely have a detectable effect on the soil C, while removing 95% of the straw certainly would. Measurements and model simulations suggest that adoption of no-tillage without proper fertilization will not increase soil C. Although it appears that a modest amount of residue may be safely removed from these Udic Borolls (Black Chernozems) without a measurable effect on soil C, this would only be feasible if accompanied by appropriate fertility management.     

Parameterizing soil and weather inputs for crop simulation models using the VEMAP database

Soil and weather data are critical for the operation of crop simulation models. However, in many cases they are not readily available, especially applications at a regional or larger spatial scale. The Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) provides massive quantities of geo-referenced soil and weather data variables on a half-degree latitude–longitude grid covering the conterminous USA. The VEMAP data were derived from a range of products and analyses, including ground observations, cluster analyses, kriging interpolation, and data assimilation. The objective of this study was to convert the soil and daily weather data of VEMAP into a format that can be used in the popular modeling software Decision Support System for Agrotechnology Transfer (DSSAT). Users can select appropriate soil or daily weather information for the area of interest. The conversion of the VEMAP data resulted in 5927 unique soil profiles and 3261 unique weather station files that encompass daily data from 1895 to 1993. To demonstrate the utility of this database in DSSAT, one representative county of the state of Georgia, USA was selected and a soybean simulation model was employed to simulate final yield using the extracted soil and daily weather data for the normal year (1961–1990). Meanwhile, the extracted daily weather data were compared with ground station observations from the National Weather Service Cooperative Observer Program (COOP). The paired t-test showed that no significant differences were found between the daily weather data and between simulated yields based on VEMAP and COOP weather data for the selected location. The outcome of this research showed that the VEMAP data can be used for crop model applications. However, further research is needed to assess the accuracy of the datasets for a variety of crops at a regional or national scale.     

黄土高原清水河流域土地利用/覆盖和降雨变化对侵蚀产沙的影响

近50 a来,在气候变化和生态恢复与治理工程实施的背景下,黄土高原的侵蚀产沙特征发生了明显的变化。以黄土高原典型中尺度流域清水河流域(面积436 km2)为研究对象,利用1959、1986、2007年的土地利用解译结果和1960—2005年该流域实测输沙和降水资料,采用非参数Mann-Kendall趋势分析法和滑动t检验法研究了该流域年输沙量、降雨量的变化趋势和突变点,并与通用土壤流失方程相结合分析了该流域土地利用和降雨变化对输沙量变化的贡献率。结果表明:该流域年输沙量47 a间有显著的下降趋势,突变点位于1980年;降雨量没有明显的趋势性变化,极端降雨指数下降。降雨因素对输沙量减少的贡献率为9.89%,土地利用的贡献率为90.11%,土地利用变化中工程措施淤地坝的贡献率为5.56%,植被变化的贡献率为84.55%。该流域47 a间乔木林地面积增加了944.27%,灌木林地增加了19.33%,表明清水河流域林地面积增加是导致输沙量减少的主要原因。     

Spatial and long-term variability of soil loss due to crop harvesting and the importance relative to water erosion: A case study from Belgium

The harvest of crops such as sugar beet (Beta vulgaris L.), potato (Solanum tuberosum L.), leek (Allium porrum L.) and carrot (Daucus carota L.) causes soil loss from arable land because soil adhering to the crop and soil clods that failed to be separated by the harvesting machine, are exported from the field together with these harvested crops. These soil losses can be of the same order of magnitude as soil losses caused by water erosion processes, but are often neglected in soil erosion research. In this article we developed a methodology to investigate the spatial and long-term (1846–2004) variability of soil loss due to crop harvesting (SLCH) in Belgium and the spatial distribution of the importance of SLCH relative to soil losses caused by water erosion processes in Flanders. The study is based on long-term time series of soil tare data of crop processing factories and area and crop yield statistics. Until the middle of the 20th century, potato and roots and tubers grown as second crop, had the largest share in the SLCH-crop growing area in Belgium. Sugar beet gained importance from the end of the 19th century onwards and has now, of all SLCH crops, the largest growing area. We could estimate that, partly due to increasing crop yields and the mechanisation of the harvesting process, SLCH per hectare of cropland increased from 0.4 Mg ha⁻¹ year⁻¹ in 1846 to 2.4 Mg ha⁻¹ year⁻¹ in the 1970s and early 1980s. Since then mean annual soil losses decreased again to 1.8 Mg ha⁻¹ year⁻¹ in 2004. It was assessed that total yearly SLCH in Belgium rose from more than 575,000 Mg in the middle of the 19th century to more than 1.7 × 10⁶ Mg in the 1970s and early 1980s, while current SLCH values are 1.4 × 10⁶ Mg. We estimated that since 1846, more than 163 × 10⁶ Mg soil was exported from cropland in Belgium through this erosion process, which corresponds to 109 hm³ or an average soil profile truncation of 1.15 cm. Average sediment export from cropland in Flanders was 3.7 Mg ha⁻¹ year⁻¹ in 2002, of which 46% was due to SLCH and 54% was due to water erosion processes. The relative importance of SLCH varied, depending on the agricultural region, between 38% and 94%.     

Physical characteristics of conditioned anaerobic digested sludge – A fractal, transient and dynamic rheological viewpoint

The changes in the physical characteristics of unconditioned and conditioned anaerobic digested sludge (ADS) biosolids, such as capillary suction time (CST), yield stress, average size and fractal dimensions, were investigated through a CST test, transient and dynamic rheological test and image analysis. The results showed that the optimum polymer dose range was observed when CST or its reciprocal value was employed as an indicator. There were good correlations between the yield stresses determined from both a controlled shear stress test and a strain amplitude sweep test. The yield stress and storage modulus (G′) increased as the polymer dose increased in most cases. A frequency sweep test revealed that polymer conditioning could extend the frequency sweep ranges for their elastic behaviors over viscous behaviors as well as the gel-like structure in the linear viscoelastic range. These results implied that more deformation energy was stored in this rigid structure, and that elastic behavior became increasingly dominant with the addition of the polymer in most cases. In addition, both the average sizes and two-dimensional fractal dimensions for conditioned ADS biosolids presented a similar up-climax-down variation trend as the polymer doses increased, whereas the critical polymer doses at the highest average sizes or two-dimensional fractal dimensions, were different. Correlation analysis revealed that the conditioned ADS dewaterability was not correlated with the yield stresses, while the average sizes or the two-dimensional fractal dimensions for conditioned ADS biosolids could be taken as the indication parameters for ADS dewaterability.