基于分形信息维数的流域地貌形态与侵蚀产沙关系

流域地貌形态的科学准确量化是建立具有广泛适用性的流域尺度土壤侵蚀预报模型的关键科学问题之一，分形理论的提出为流域地貌形态特征的定量描述开辟了新的思路。本文基于分形理论，利用GIS技术和多元回归统计方法，以黄土高原丘陵沟壑区第一副区的岔巴沟流域为例，对该流域以分形信息维数为量化指标的流域地貌形态与降雨侵蚀产沙耦合关系进行了初步探讨。研究表明，引入地貌形态分形信息维数的岔巴沟流域降雨侵蚀产沙与地貌形态耦合关系模型可将岔巴沟各支流域差异明显的水沙关系简化为统一的数学表达，消除了由于地貌形态等下垫面因素导致的空间变异性；基于该耦合关系模型的西庄和蛇家沟流域次降雨输沙模数预测值和观测值相对误差较小、总体吻合较好；将地貌形态分形信息维数作为流域土壤侵蚀预报模型中地貌形态因子量化指标不仅可行，而且可靠。     

Yield variability related to landscape properties of a loamy soil in central Belgium

A field was investigated with precision farming techniques to delineate zones with different yield potential due to previous soil erosion. Winter wheat (Triticum aestivum L.) grain yield, straw yield, biomass and harvest index were measured with a combine harvester. Fuzzy clustering of grain and straw yield provided good delineation of zones in the field with different yield potential. Entropy and fuzziness calculations for different number of classes resulted in a division of the field into five clearly differentiated yield potential zones. Straw yield, biomass and harvest index were significantly different among zones. Grain yield was significantly different for all zones, except for two. Elevation and slope of the field were measured from a global positioning system (GPS) unit on the combine. Both were related to yield variability in the field. Average elevation, slope and soil type were calculated per cluster class. High grain yield, straw yield and biomass could be related to flat, high places in the field with little erosion. Good grain yield, low straw yield and high harvest index were found on relatively steep slopes subjected to erosion. High straw yield and low grain yield were found at low places in the field on relatively steep slopes. Lowest grain yield, straw yield and biomass were located on steepest slopes with high erosion and in depressions where accumulation of eroded soil took place and slumping and crusting of the soil were present. This information suggests that variable management on a site-specific basis would optimize yield and inputs.     

Characterization of soil profiles in a landscape affected by long-term tillage

Soil movement by tillage redistributes soil within the profile and throughout the landscape, resulting in soil removal from convex slope positions and soil accumulation in concave slope positions. Previous investigations of the spatial variability in surface soil properties and crop yield in a glacial till landscape in west central Minnesota indicated that wheat (Triticum aestivum) yields were decreased in upper hillslope positions affected by high soil erosion loss. In the present study, soil cores were collected and characterized to indicate the effects of long-term intensive tillage on soil properties as a function of depth and tillage erosion. This study provides quantitative measures of the chemical and physical properties of soil profiles in a landscape subject to prolonged tillage erosion, and compares the properties of soil profiles in areas of differing rates of tillage erosion and an uncultivated hillslope. These comparisons emphasize the influence of soil translocation within the landscape by tillage on soil profile characteristics. Soil profiles in areas subject to soil loss by tillage erosion >20 Mg ha⁻¹ year⁻¹ were characterized by truncated profiles, a shallow depth to the C horizon (mean upper boundary 75 cm from the soil surface), a calcic subsoil and a tilled layer containing 19 g kg⁻¹ of inorganic carbon. In contrast, profiles in areas of soil accumulation by tillage >10 Mg ha⁻¹ year⁻¹ exhibited thick sola with low inorganic carbon content (mean 3 g kg⁻¹) and a large depth to the C horizon (usually >1.5 m below the soil surface). When compared to areas of soil accumulation, organic carbon, total nitrogen and Olsen-extractable phosphorus contents measured lower, whereas inorganic carbon content, pH and soil strength measured higher throughout the profile in eroded landscape positions because of the reduced soil organic matter content and the influence of calcic subsoil material. The mean surface soil organic carbon and total nitrogen contents in cultivated areas (regardless of erosion status) were less than half that measured in an uncultivated area, indicating that intensive tillage and cropping has significantly depleted the surface soil organic matter in this landscape. Prolonged intensive tillage and cropping at this site has effectively removed at least 20 cm of soil from the upper hillslope positions.     

Quantification of tillage and landscape effects on soil carbon in small Iowa watersheds

Knowledge of the long-term effects of tillage on soil organic carbon is important to our understanding of sustainable agricultural systems and global carbon cycles. In landscapes susceptible to erosion, tillage can exacerbate losses of soil and C by increasing erodibility and stimulating microbial respiration. We measured long-term changes in soil carbon and soil loss in three small watersheds located in southwest Iowa, USA. The following soil series were formed on deep loess hills: Ida and Dow (Typic Udorthents), Napier and Kennebec (Cumulic Hapludolls) and Monona (Typic Hapludolls). All watersheds were cropped to continuous corn (Zea mays L.) and two were moldboard plowed and disk tilled while the third was ridge-tilled. The ridge-tillage system had greater C contents in the surface soil than the disk tillage soils, but ridge-tillage was not different from the conventional tillage in carbon retention over time. The ridge-tillage system, however, was more effective in retaining soil within the watershed. Microbial respiration by soil microorganisms accounted for 97% of the carbon loss in the ridge-tilled watershed compared to carbon loss in eroded sediment (3%). Terrain analysis was used to segment the landscape into landform elements. Less total carbon was present in the soil profiles of backslope elements than in footslope or toeslope elements, reflecting the combined effects of soil erosion and deposition within the watersheds. Profile C content was also positively correlated with the wetness index, a compound topographic attribute, that identifies areas of the landscape where runoff water and sediment accumulate.     

黄河三角洲不同地表覆被类型和微地貌的土壤盐分空间分布

掌握不同地表覆被类型和微地貌特征下的不同深度土壤盐分空间分布规律，对土壤盐渍化防治具有重要意义。该研究以黄河三角洲入海口为研究区，在分析不同深度土壤全盐量、盐基离子（Ca2+、Mg2+、Na+、SO42-、HCO3-、Cl-）空间变异特征的基础上，通过单因素方差分析不同地表覆被类型和微地貌特征下该区土壤盐分的差异，并通过地理探测器分析地表覆被类型、微地貌对土壤盐分的交互影响。结果表明：1）表层土壤Mg2+变异系数达到1.010 8，为强变异性，其余盐基离子均为中等变异性，且均有强烈的空间相关性，全盐量与盐基离子均呈现沿海向内陆降低的趋势，约有42.57%的地区为轻度盐化土；2）不同地表覆被类型间土壤全盐量与Na+、Cl-具有显著差异；3）不同微地貌类型间Na+、Cl-具有显著差异；不同海拔的深层土壤Na+具有显著差异；4）海拔对土壤全盐量与Na+的解释力最强，地表覆被类型对土壤Cl-的解释力最强；5）坡向和海拔对土壤盐分的交互作用最强烈，q值在0.545～0.708之间，其次是地表覆被类型与坡向，q值在0.521～0.613之间。氯化钠主导该区域土壤盐分空间变异，不同地表覆被类型和微地貌特征下均呈显著差异，表层土壤盐分明显高于深层，坡向与海拔之间的交互作用能够较好地解释该地区土壤盐分空间分布。     

黄土区不同类型土壤微生物量碳、氮和可溶性有机碳、氮的含量及其关系

研究了黄土高原南部地区不同土壤类型及不同利用方式下土壤微生物摄碳、氮和可溶性有机碳、氮的含量。结果表明：不同土地利用方式下，土壤微生物量碳、氮和可溶性有机碳、氮含量均为林地〉农田，其中林地枯枝落叶层〉林地O～20cm土层。农田土壤微生物量碳、氮的含量均为红油土〉黑垆土〉淋溶褐土；农田土壤中可溶性有机碳含量为淋溶褐土〉红油土〉黑垆土，而可溶性有机氮含量则为黑垆土〉红油土〉淋溶褐土。方差分析表明，不同土壤类型土壤微生物量氮含量之间的差异达显著水平，而不同土壤类型间土壤微生物量碳、可溶性有机碳、氯含量之间的差异未达显著水平。土壤微生物量碳、氮占土壤有机碳和全氮的比例明显高于可溶性有机碳、氮占土壤有机碳和全氮的比例。相关分析发现，土壤微生物量碳与可溶性有机碳之间以及土壤微生物量氮与可溶性有机氮之间的相关性达显著或极显著水平，说明土壤微生物量碳、氮和土壤可溶性有机碳、氮之间有密切联系。     

Comparison of characteristics of actomyosin from white, pink, and red muscle fiber types in cultured carp

ABSTRACT: The present study compared and examined the characteristics of actomyosin among white (W), pink (P), and red (R) muscle fiber types in carp (cultured). Both the superprecipitation reaction and the Mg²⁺-ATPase activity of actomyosin became higher with increased Ca²⁺ concentration (pCa 7.0–pCa 5.0) and with decreased adenosine triphosphate (ATP) concentration (3.0–0.5 mM) in all three muscle fiber types. A comparison of the three fiber types shows that the superprecipitation reaction of actomysoin was lower in the order of W < P < R and, in contrast, was higher for Mg²⁺-ATPase activity in the order of W > P > R. A significantly positive correlation between both values was found for each of the three muscle fiber types, but these correlations were clearly different among the three muscle fiber types, and the superprecipitation reaction of actomyosin was lower in the order of W < P < R when Mg²⁺-ATPase activity was at the same level. In conclusion, the characteristics of actomyosin were remarkably different among white, pink, and red muscle fiber types.     

Distribution of potassium fractions in sweet potato (Ipomoea batatas) garden soils in the Central Highlands of Papua New Guinea and management implications

Previous studies indicated that potassium (K) deficiency is an important soil‐related factor for yield decline of the sweet potato gardens in the Central Highlands of Papua New Guinea, where sweet potato is an important staple food crop. An effort was made to characterize various fractions of K in the diverse soils of this region under sweet potato, to ascertain the probable reasons behind the observed K deficiency and its relationship to decreasing yield trends. Soils from two depths (0–10 cm) and (10–20 cm) in two types of gardens (old and new gardens) were assessed for different fractions of soil potassium in volcanic and non‐volcanic soil groups. Volcanic soils (Hydrandepts and Andaquepts) were significantly lower (P < 0.05) in exchangeable K than the non‐volcanic soils (Dystropepts, Tropoqualfs and Eutropepts). Mean exchangeable K content of the non‐volcanic soils was 95.5 mg/kg, whereas that of volcanic soils was 72.4 mg/kg. Similarly, new gardens had an average exchangeable K content of 94.1 mg/kg, which was significantly greater than 71.6 mg/kg soil of older gardens. Non‐exchangeable K content differed significantly (P < 0.001) between the soil types; mean K content was 85.9 mg/kg for the volcanic soils, whereas in non‐volcanic soils, it was 184.9 mg/kg. Garden types also differed significantly (P < 0.05) with respect to non‐exchangeable K content; new gardens registering higher average values (by almost 20%) than the older gardens. Multiple regression analysis showed that variability in the tuber yield was as a result of variability of water soluble and exchangeable K (up to 22%), non‐exchangeable K (2%), mineral K (4%) and leaf K concentrations (10%). Older gardens, which are in volcanic soil groupings, are more susceptible to the K depletion problem because of continuous sweet potato cultivation, possibly owing to their lower K reserves. Such gardens should be managed either with sufficient fallow periods for regeneration of soil fertility or with suitable application of mineral K fertilizers to enhance productivity.     

陇东地区部分冬小麦品种(系)HMW-GS的组成与遗传变异分析

本实验通过SDS-PAGE技术,对陇东地区部分冬小麦品种(系)的高分子量谷蛋白亚基组成及亚基组成频率进行了分析.结果表明陇东地区冬小麦品种(系)存在16种亚基组合类型,以N,7+8,2+12亚基含量丰富,其出现频率占品种(系)总数的36.50%,而含5+10亚基的亚基组合类型只有3种,仅占品种(系)数量的9.62%.Glu-1位点遗传多样性单一,Glu-A 1位点仅有2种等位变异形式,N亚基频率最高(71.15%);Glu-B 1位点有4种等位基因变异形式,7+8亚基频率最高(59.62%);Glu-D 1位点上有6种等位基因变异形式,2+12亚基频率最高(61.54%).通过对地方品种、育成品种(系)和引进品种HMW-GS组成比较发现,地方品种亚基的组成类型呈现出组成单一,优质亚基少的特点;而外引品种和育成品种亚基类型较为丰富,且包含一定数量的优质亚基.