Stickstoffumsatz in einer Lößcatena

Nitrogen turnover in a loess catena N-mineralization and mineral-N-contents were determined from spring 1993 to autumn 1995 on arable soils from loess (Luvisol, Calcaric Regosol, Gleyic-Calcaric Regosol and Cumulic Anthrosol) of a catchment area called “Bonartshäuser” farm near Gondelsheim in western Kraichgau (SW-Germany). The aim was to find out, whether the course of net-N-mineralization and mineral-N-content of the soil could be explained by the parameters soil temperature and soil moisture. Soil samples were incubated in polyethylene bags on site for mineralization and aliquots analyzed in the laboratory for the determination of the mineral-N-content. In 1993, 55 kg N ha^—1 were immobilized and up to 170 kg N ha^—1 mineralized depending on the soil type. In 1994, between 181 and 297, and in 1994, between 59 and 230 kg N ha^—1 were mineralized annually. Mineral-N-contents of the different soils throughout the experimental period (n = 45) were found to correlate much better (r² between 0.55 and 0.86) whereas net-N-mineralization (n = 44) showed coefficients of determination (r²) just between 0.08 and 0.53. Except for the Luvisol (37%) only 0 to 8% of net-N-mineralization could be explained by the combined effect of mean soil temperature and soil moisture at the beginning of the incubation using multiple linear regression analysis. Merely 1 up to 9% of mineral-N-content of the soil could be explained by the same effect. The variability and inconsistency shown by net-N-mineralization renders it inappropriate as a tool for predicting nitrogen delivery of the soil and basis for setting rules governing permissible nitrogen amounts in the soil.     

商品型生态农业系统耦合效应分析

商品型生态农业按照传统的作物系统、林果系统与草牧系统的内在关系,使其结合而形成了高一级的结构功能体—耦合系统,因而能够产生较大的耦合效应。黄土丘陵区商品型生态农业有3种模式类型,系统的耦合效应主要表现在产业结构的调整和优化、生态环境的改善、社会要素及其基础设施的改善等方面。在黄土丘陵区商品型生态农业系统的建设过程中,必须优化商品型生态农业产业结构,提高其耦合的功能效应,并扶持相关产业、措施发展。     

基于GIS的坡耕地数字高程模型的建立与应用

微地形是描述地表起伏状态的重要指标,也是地表径流和土壤侵蚀过程的重要影响因子。在微尺度上建立了不同耕作措施下黄土坡耕地的数字高程模型（DEM）,并对其空间特征进行了分析。结果表明,利用反距离加权插值法建立的微DEM模型能正确地再现坡耕地地表形态,利用其派生的微坡度、微坡向数据可作为研究土壤侵蚀空间差异的重要因子;微坡度分布特征与耕作措施密切相关,对于人工锄耕（CH）和人工掏挖（TW）措施,微坡度栅格统计数随着微坡度的增大呈先增大,后减小的变化趋势,而等高耕作（DG）措施下微坡度栅格统计数随着微坡度的增大而     

USE OF RESERVOIR DEPOSITS AND CAESIUM-137 MEASUREMENTS TO INVESTIGATE THE EROSIONAL RESPONSE OF A SMALL DRAINAGE BASIN IN THE ROLLING LOESS PLATEAU REGION OF CHINA

This paper reports the results of an investigation of the erosional response of the 3·86 km² Zhaojia Gully catchment in the rolling loess plateau region of Zichan County, Shaanxi Province, China. In the absence of direct measurements, information derived from reservoir deposits and from caesium-137 measurements on both the catchment soils and reservoir deposits was used to obtain a retrospective assessment of the longer-term (ca. 30 year) erosional response of the catchment and of the relative contributions of the rolling plateau surface and the gully areas to the sediment output from the basin. Net erosion rates on cultivated land occupying the gentle crest slopes and steeper lower slopes of the rolling plateau and the steep gully slopes were estimated to be 4500 t km⁻² year⁻¹, 8584 t km⁻² year⁻¹ and 15851 t km⁻² year⁻¹, respectively. Estimates of annual sediment yield from the study catchment based on analysis of sediment deposits in the two sediment-trap reservoirs ranged between 4627 and 32472 t km⁻² year⁻¹. Almost all the sediment transported from the catchment was contributed by 2–4 large floods each year. Measurements of the caesium-137 content of recent sediment deposits in a sediment-trap reservoir allowed the relative contributions of the total sediment yield derived from the rolling plateau and gully areas of the catchment to be estimated at 23 and 77 per cent, respectively. Analysis of the sediment deposits dating from 1973–1977 in another sediment trap reservoir allowed individual flood event couplets to be identified and indicated that the sediment associated with the first one or two floods in a season, when the soils of the plateau area were relatively dry, was derived primarily from the gully areas. The cultivated soils of the rolling plateau contributed an increased proportion of the total sediment yield during the latter stages of the flood season when the soils were wetter, and surface runoff and erosion were more widespread. Based on analysis of the caesium-137 content of the sediment deposited in this sediment-trap reservoir, the relative contributions of sediment from the rolling plateau and gully areas over the period 1973–1977 were estimated to be 21 and 79 per cent, respectively. The results obtained demonstrate the potential for using caesium-137 measurements and analysis of reservoir deposits to document the erosional response of a drainage basin. © 1997 John Wiley & Sons, Ltd.     

Water productivity of contrasting rice genotypes grown under water-saving conditions in the tropics and investigation of morphological traits for adaptation

Alternate wetting and drying (AWD) irrigation in lowland rice has been successfully implemented in farmers’ fields to reduce water input, and thereby increasing water productivity. Reported effects on grain yield were, however, contradictory: yield was reduced, maintained, or even increased when compared with continuously flooded (CF) conditions. This study was conducted in heavy clay soil to investigate yield variation among a range of genotypes grown under AWD and to determine some aboveground traits related to crop adaptation. The effect of AWD on grain yield, with a critical threshold of soil water potential for irrigation fixed at −30 kPa, varied among the 10 genotypes evaluated. Two adapted genotypes were identified with similar grain yield under CF and AWD in both experimental seasons. The grain yield of the aerobic-adapted cultivar included in the study was also maintained under AWD, however, its yield was comparatively low. The reduction in grain yield of the non-adapted genotypes ranged from 9 to 13% in the 2006 dry season and from 6 to 17% in the 2008 dry season. None of the yield components could explain by itself the variability in genotype response: in adapted genotypes, grain yield was maintained because of compensation from or maintenance of yield components, whereas, in non-adapted genotypes, grain yield reduction was not due to the decrease of one component only. Modified biomass partitioning appeared as a main driver for adaptation to AWD: adapted genotypes were characterized by larger sink size at flowering, and weaker stems and less unfilled grain number at maturity, suggesting an increase in the sink strength of the filling spikelets. The aboveground traits identified here will be of great help to further increase water productivity under the AWD strategies set up previously by IRRI water scientists.     

胶粉对混凝土抗冲磨性能的影响

选取颗粒粒径为8目的胶粉,按4种不同掺量配制胶粉混凝土,与基准混凝土、硅粉混凝土进行抗冲耐磨性能对比试验,以评价胶粉对混凝土抗冲磨性能的影响。结果表明:胶粉混凝土的抗冲磨强度大于基准混凝土和硅粉混凝土的抗冲磨强度,且抗冲磨强度随着胶粉掺量增加而增大,但其抗压土强度随着胶粉掺量的增加而降低;试件冲磨后,胶粉混凝土的破坏程度小于硅粉混凝土和基准混凝土,仅表层浆体破坏,胶粉在水泥石中分布均匀,与水泥石结合牢固,试件表面平整,显示胶粉混凝土具有较强抗冲磨性能。     

基于均匀试验的多孔混凝土的配合比研究

根据多孔混凝土的结构特点,结合多孔混凝土应用于水利护坡工程的要求,最佳配合比设计应考虑到多孔混凝土的抗压强度和孔隙率,以强度和孔隙率为目标函数,制定了均匀试验设计方法,系统研究了水灰比、骨灰比、用水量、骨料粒径对这两项指标的影响,并采用逐步回归分析法建立强度和孔隙率与各因素的数学回归模型,从而为多孔混凝土配合比设计提供分析方法。     

涌泉根灌在黄土坡地的水分运移规律试验

为了了解涌泉根灌这项微灌技术灌水后的水分运移情况,在野外黄土坡地利用剖面法对涌泉根灌在不同孔径、孔深条件下土壤水分运移规律进行了研究.结果表明,在不同孔径、孔深处理下,湿润体水平扩散半径、向上入渗距离和向下入渗深度有不同的影响,且均与时间有显著的幂函数关系;涌泉根灌停止后24 h内的土壤湿润体水平及竖直方向扩散相对变化超过了47%,湿润体平均含水量相对降低了30%;24 h后的扩散较小,平均含水量下降较小.涌泉根灌停止后24 h时的湿润体特征值可作为涌泉根灌系统设计的依据;推荐涌泉根灌适宜的孔洞深度为30~40 cm,孔径为φ6 cm.研究结果可为涌泉根灌技术的实际应用提供理论参考.     

Compaction of virgin soil by mechanized agriculture in a semiarid environment

Soil compaction was assessed in terms of soil strength as measured with a penetrometer. Penetrometer resistance was measured on virgin soil and on the same soil after one and after five passes of a 7,610 kg tractor. Also, comparative studies were made of strength profiles of soils in arable fields and in adjacent areas of virgin soil. The strength of virgin soil was increased by wheel traffic and agricultural operations in all cases. The increase in soil strength was significant down to 0.3 m, which is considerably greater than the normal depth of tillage in the area (0.05 m). Reduction in the coefficient of variation of penetrometer strengths after the passage of wheels was taken as evidence for associated losses of soil structure. Virgin soils provide important reference sites for assessing the impact of agriculture in an area.     

小麦茎秆强度关联位点及优异等位变异分析

为发掘与小麦茎秆强度紧密关联标记位点的优异等位变异和携带优异等位变异的载体资源,本研究以126份小麦种质为材料,基于混合线性模型（mixed linear model,MLM）对2011-2012、2012-2013和2013-2014三个年度的茎秆强度进行标记位点关联分析,并对关联住点等位变异的表型效应进行分析。结果表明,wmc83(2B)、gwm539(2D)、barc358(5A)、barc59(5B)和barc134(6B)均与茎秆强度显著关联,且可在3个环境下同时检测到,表型解释率均大于8%;共发掘出11种优异等位变异,分别为wmc83-A110、wmc83-A147、wmc83-A151、gwm539-A120、barc358-A179/161、barc358-A185/161、barc358-A185/179、barc358-A190/161、barc59-A182、barc59-A191和barc134-A194,其中wmc83-A110的增效效应最大。供试材料的茎秆强度随优异等位变异聚合数目的增多而增大,其中黄淮南片麦区、黄淮北片麦区、长江中下游麦区和西南麦区的供试材料中携带2（40.3%）、1（27.8%）、1（35.3%）和4（50.0%）种优异等位变异的分布频率最高。内麦10号等9份材料聚合4种及以上的优异等位变异,且茎秆强度较高,可作为相应麦区小麦茎秆强度遗传改良的种质资源。