Changes in penetration resistance of Ultisols from southern China as affected by shearing

Shear stresses and soil properties modified due to stress play an important role during formation of seals in a series of rainfall events and during tillage. The objectives of the study were to evaluate the effects of the penetrometer geometry on the penetration resistance as affected by shearing under different initial soil conditions and to use the information on soil strength to elucidate shearing process. Nine homogenous air-dried soils (<2 mm) were sprayed and stored so as to obtain equilibrium soil water contents. The moist soils were sheared by horizontal displacement of layers of soil particles/aggregates in between hands in one direction. The soil cores were prepared with comparable bulk density before the measurement of maximum penetration resistance (P_max) with a small flat tip and a cone tip penetrometers. At a wide range from 0.05 to 6.2 MPa, P_max was linearly correlated between the small flat tip and the cone tip penetrometers. The conversion ratio was higher under the saturation condition irrespective of the shearing effect. The penetrometer with the small flat tip was more sensitive for the weak soils. Shearing generally increased P_max in most cases, but it decreased P_max for some sandy soils under both saturated and unsaturated conditions and for a clayey soil under the saturated condition. The soil consisting of swelling clay exerted a decrease in P_max. Rearrangement and/or sliding of particles/aggregates and increase in soil suction during shearing were attributed to the increase in P_max. Increase in porosity due to the aggregation during shearing was ascribed to the decrease in P_max. In addition, it was shown that agricultural cultivation resulted in a reduction in soil strength.     

红壤水问题及其管理

本文叙述了华中丘陵地区红壤水问题及其有效管理。指出了这一地区虽然年降雨量较多，但由于其分配极不均匀，伏旱秋旱非常严重，成为影响该地区农业生产的主要障碍因子之一。而红壤的贮水库容，特别是贮有效水的库容较低，土壤的有效含水量有限，更促进了伏秋旱的进一步发展。有计划的发展微喷灌溉，进行覆盖以及间或轮种深根植物利用深层贮水，能在相当程度上，提高红壤水资源的利用。     

陕西省几种代表性土壤NH4+吸附、解吸动力学特征研究

采用连续液流法测定了五种土壤吸附、解吸ＮＨ＾＋４的动力学性质。研究表明：（１）ＮＨ＾＋４吸附、解吸平衡时间及反应速率，平衡时的吸附、解吸量及吸附平衡常数均随土壤粘粒和ＣＥＣ不同而变化；（２）不同动力学模型及同一模型对不同土壤的拟合性不同。     

斥水土壤中的水热运动规律与数值模型

斥水土壤很难被雨水湿润，影响种子发芽出苗而造成农业减产。由于地表干燥而引起风蚀水蚀，造成土地退化。这一问题在澳大利亚、荷兰、新西兰与美国引起重视。斥水土壤中水分分布往往是无规律的“指状”，到目前为止，没有成功的数学模型。作者从研究斥水土壤地区的耕作工程实践出发，采用沟种之后，水分的分布就有了规律性。开沟播种时，耕作机械把表层斥水性特别强的土壤推到垄上而形成几乎不透水的垄，下雨时雨水只能从沟中渗入形     

Population dynamics of Enchytraeidae (Oligochaeta) in different agricultural systems

Organic matter and abiotic conditions seem to influence distribution patterns of Enchytraeidae. In this study effects of changes in management practices on population dynamics of enchytraeids were determined. At two sites (in Athens and Griffin, GA) parts of a fescue (FE) field were converted into conventional tillage (CT) and no-tillage (NT) plots and changes in densities and depth distribution of enchytraeids were followed for 3 years. A site at Watkinsville, containing various soil textures and characterised by very low organic carbon content, which was converted into no-tillage 4 years earlier, was also sampled. Significant reductions in enchytraeid densities, after conversion of fescue into CT, were only found at Griffin. The management practices affected the vertical distribution of enchytraeids. In fescue and NT more enchytraeids were found in the 0–5cm than in the 5–15cm layer. In conventional tillage fields enchytraeids were more evenly distributed over the profile or more abundant in the 5–15cm layer. Management also affected the timing of population dynamics in the different plots. At two sample dates high abundances were found in CT plots only, not in any of the other plots. Enchytraeids were larger at Athens than at Griffin and Watkinsville and contained more soil particles in their gut. At Athens enchytraeids will presumably contribute more to the development of soil structure than at the other sites. We conclude that management affects vertical enchytraeid distributions in soil and changes the timing of population dynamics. Received: 7 January 1996     

基于1:5万数据库研究土壤空间分异及其影响因素——以江苏省无锡和常州市为例

土壤数据库在土壤学研究工作中作为一种存储、分析工具的重要性是不言而喻的.本研究利用ArcGIS和Visual FoxPro建立了包括8 830个图斑、269个土壤剖面数据的无锡和常州市1：5万土壤数据库,根据“土壤质量演变规律与持续利用‘973＇项目”的土壤肥力质量指标（pH、速效磷和速效钾）和全国养分分级标准（全氮）编制出土壤表层（0～15 cm）pH、全氮、速效磷和速效钾的空间分异图,从中表明pH 1～2级的土壤占整个研究区面积90%左右;土壤养分全氮、速效磷和速效钾的空间分布有明显共同特征-太滆平田区养分含量要显著高于其他地区.对不同母质和不同土壤类型（亚类级别）间的土壤表层容重、粘粒、pH、有机质、全氮、全磷、全钾、速效磷和速效钾进行了方差分析,结果显示,除全氮之外,其他属性均有显著差异.在1：5万尺度范围内,成土母质对pH、容重、全磷、有机质和速效钾起到主导作用,土壤类型对pH起到主导作用,成土母质对土壤属性的影响程度要大于土壤类型.     

农田气象条件下阿特拉津在土壤中淋溶动态的数值模拟

阿特拉津(Atrazine)是我国华北地区夏玉米田常用的除草剂,而夏玉米生育期又是该地区的主要降雨时段,对这一时段Atrazine在田间尺度的淋溶风险进行评价,对保护浅层地下水环境具有重要意义。以北京市通州区永乐店试验站一块27 m×27 m的农田为背景,通过田间采样、测试分析土壤样品并收集2001年的气象数据,基于简化土壤水三维流场的柱模型假设,在同时考虑土壤水力学参数、Atrazine运移和吸附参数空间变异性的情况下,对该农药在农田尺度下淋溶动态的空间分布进行了数值模拟。在此基础上,对夏玉米不同生育期耕层20 cm深度处的土壤水负压、水流通量和Atrazine浓度的空间变异结构进行了地质统计学分析。结果表明,在整个夏玉米生育期内这三个参量的半方差模型基本上为球状模型,它们的变程多在8~10 m。本研究案例对布设农田尺度土壤水分和Atrazine动态监控网具有一定的参考意义。     

大兴安岭不同冻土带土壤动物生态地理研究

2003年6月、8月、10月对大兴安岭不同冻土带选择沼泽、柳丛、耕地、次生林群落进行土壤动物调查，共获土壤动物39225只，隶属于4门8纲24目。由对大型、中小型及湿生三类土壤动物的数量分析可知，三类土壤动物数量的变化在群落间并不总是成正相关的关系。水平分布调查表明，中小型土壤动物的个体数量和类群数量从岛状冻土带到连续多年冻土带逐渐减少，该分布与土壤动物分布的一般规律（土壤动物分布通常符合纬度地带性分布规律，即由低纬向高纬逐渐减少）一致，但大型土壤动物的个体数量、类群数和生物量基本上从岛状冻土带到连续多年冻土带逐渐增加（即由低纬向高纬逐渐增加），湿生动物的数量也如此分布，这与土壤动物分布的一般规律不一致甚至相悖，这一特点表现出生态系统局部-区域相互关系的复杂性；土壤动物的类群数、个体数量与土壤有机质、全氮的含量呈明显的正相关；垂直分布调查表明，中小型土壤动物的个体数量和类群数量分布表现出明显的表聚性，但大型土壤动物的个体数量与生物量最大值出现在第二层；土壤动物多样性分析表明，中小型土壤动物的多样性指数从岛状冻土带到连续多年冻土带逐渐减小，而大型土壤动物的多样性指数在不同冻土带间的变化规律不明显。     

Microbial community structure in forest soils treated with a fire retardant

The influence of a fire retardant (Firesorb, an acrylic–acrylamide copolymer) on the microbial community structure determined by phospholipid fatty acid (PLFA) analysis was examined under laboratory conditions using two different textured soils under pine forest. Firesorb was added to unheated and heated soil samples (350°C for 10 min followed by reinoculation, to mimic a forest fire) at three levels of application (none, usual and three times the usual levels), and measurements were made after 12 weeks of incubation. The relative importance of the three factors considered on the PLFA profiles was as follows: soil heating ≫ soil texture ≈ Firesorb treatment. In the unheated soils, Firesorb had a larger effect than soil texture, while the opposite was found in the heated soils. Soil heating reduced the total PLFAs, while Firesorb tended to increase them in both the unheated and heated soils. Soil heating decreased the PLFAs indicative of gram-positive (G⁺) bacteria and tended to increase the fatty acids associated with gram-negative (G⁻) bacteria and, to a lesser extent, the PLFA 18:2ω6, considered to be predominantly of fungal origin. Firesorb treatment decreased the G⁻/G⁺ bacteria ratio in the heated soils but tended to increase it in the unheated soils, the effect being dose dependent.