长期水耕植稻对水稻土耕层质地的影响

为了解长期水耕植稻对南方地区水田表土层颗粒组成的影响,以浙江省为研究区,采用历史资料分析、典型样区调查及定点观察相结合的方法,研究水稻土耕作层(包括犁底层)与心土层间黏粒含量的差异,分析植稻时间对水稻土不同土层颗粒组成的影响,比较植稻期间稻田排水中泥砂物质的颗粒组成与对应土壤间的差异,探讨了长期植稻对水稻土剖面质地分异的影响。对浙江省456个代表性剖面统计,与水稻土心土层比较,耕作层和犁底层黏粒含量平均下降了14%和10%。对植稻不同时间的浅海沉积物(从10～20年至80年)、第四纪红土(从5～20年至70年)和玄武岩风化物(从5～20年至35～70年)发育的水稻土比较发现,随植稻时间的增加,耕作层和犁底层土壤砂粒含量呈现增加趋势,黏粒含量明显下降,耕作层、犁底层与心土层黏粒含量的比值逐渐下降。农田排水中泥砂物质的黏粒和粉砂含量高于对应农田土壤,而砂粒含量则低于相应的土壤。分析认为,长期水耕植稻可导致耕作层土壤砂化(即砂粒含量增加,黏粒含量下降),其原因除与水耕过程中黏粒淋淀外,排水中黏粒和粉砂细颗粒的选择性流失对耕作层砂化也有较大的贡献。     

Erosion processes and erodibility of cultivated soils in North Rhine‐Westphalia under artificial rain. I. Site characteristics and results of laboratory experiments

Soil erosion by water causes substantial on‐site degradation and off‐site damages in the densely populated state of North Rhine‐Westphalia (Germany). Measures of soil conservation should be adjusted to soil erodibilities and should be based on an understanding of the processes involved in water erosion including aggregate breakdown, rainsplash erosion, surface sealing, and soil loss. For a state‐wide assessment of erosion processes and erodibilities, we tested representative cultivated soils of North Rhine‐Westphalia in laboratory and field experiments with artificial rain. In the laboratory experiments described in this paper, rainsplash erosion, sealing susceptibility, and interrill erodibility of 25 topsoils filled in 0.5 m² boxes were investigated. Results of different aggregate‐stability tests correlate with organic‐matter contents but not with parameters of rainsplash or soil loss. On most soil materials, rainsplash increases or maintains constant rates in the course of the simulation runs indicating that the soil surface did not attain a higher shear resistance. High sealing susceptibilities are found for soils of quite different textures ranging from loam sand to silt clay, whereas other silt clays, clay loams, and some clay silts maintain high infiltration rates. A trend of increasing sealing susceptibility and total soil loss with increasing clay content is observed for the loam sands to sand loams. Dynamics of soil loss is largely governed by runoff rates. Total soil loss is also determined by sediment concentration in surface runoff, which is low on most clayey soils, on loam sands poor in clay, and on a sand loam, and high in the case of highly erodible clay silts, loam sands, and sand loams. The most crust prone soils are not necessarily the most erodible. On most soils, soil‐loss rates do not stabilize until the end of the rainfall experiments. For comparing the interrill erodibilities of the soils, total soil loss is preferred instead of interrill erodibility factors (K_i, K_iq) published in the literature.     

Soil salinization of the Baer Mounds in the Volga River delta

The Baer Mounds are elongated hills arranged in parallel rows stretched from the east to the west in the Astrakhan steppe. The distance between the mounds varies from 200 to 1500 m (300 m on the average). The width of the mounds is about 250 m and their length is from 450 m to 4.5–5 km long (sometimes, up to 15–20 km). The height of the mounds varies from 7 to 10 m and increases in the southward direction. The mounds are composed of clayey sand; loamy sand; light loam; and, sometimes, loam. Their top (1–3 m) parts consist of clayey sand and loamy sand with thin interlayers of loam, clay, and argillite pebbles. The upper horizons of the brown semidesert soils are not saline. Soluble salts are leached off from them into deeper horizons. On the slopes, the deep soil horizons are saline, and salts are transported from the deep soil layers into the upper layers. This can be explained by the regular flooding of the foots of the mounds with floodwater and the capillary rise of water. Alternation of salinization and desalinization processes is responsible for the nonuniform distribution of salts in the soil profiles and along the soil catena.     

Morphologic evidence of lamellae forming directly from thin,clayey bedding planes in a dune

An excavation in a sand dune in southern Michigan revealed numerous, thin (<3 mm) clay-enriched strata between otherwise weakly stratified, clean, fine sand deposits. The parallelism of both the sandy and clayey strata suggest that they have direct geologic origins, having been deposited during formation of the dune. Although the clay-enriched strata and the intervening sandy layers are both within the sand textural class, the former contained between 3.0% and 5.4% clay, and the latter <1.8% clay. In areas of preferred leaching, such as below vertical root traces, the clayey strata thin out and become absent, or “bend downward”, become wavy and contorted, and take on the appearance of typical pedogenic lamellae. These observations support a theory of lamellae genesis that is both pedogenic and geogenic. Thin sedimentary strata may be pedogenically “transformed” into features that would normally be described as (entirely pedogenic) lamellae. Thus, many thin lamellae in Pleistocene-aged soils may simply be deformed and pedogenically altered sedimentary strata. This conclusion has implications for the nature and cyclicity of clay deposition in environments where thin lamellae are common in sandy soils.     

崩岗不同土层土壤水力学特性差异性分析

为研究崩岗不同土层土壤水力学特性的差异性,采用离心法测定不同土层土壤水分特征曲线,筛选出适合的土壤水分特征曲线拟合模型,结合统计模型,推求土壤的当量孔径分布、比水容量、非饱和导水率和扩散率,分析崩岗不同土层土壤水力学参数的变化规律。结果表明,崩岗土层从红土层到砂土层的变化过程中,土壤质地由黏土向砂土变化;Fredlund&Xing模型对崩岗土壤土水特征曲线拟合效果最好;参数θs、α、n随着质地变黏重逐渐减小;随着土层深度的增加,土壤的持水性能降低;土壤比水容量、非饱和导水率和扩散率受土壤质地和基质吸力的共同影响。在低吸力阶段,3个指标随基质吸力变化比较平缓,砂土层土壤比水容量和非饱和导水率最大,扩散率最小;而在高吸力阶段,砂土层土壤的这些指标降低较快,且低于其他土层,各层土壤间导水率和扩散率差异随着基质吸力的增加而增大。     

土壤电导率对时域反射仪测定土壤水分的影响

试验通过往土壤中加入电介质溶液 ,以及在不同粘粒含量土壤上用时域反射仪 (TDR)测定土壤含水量 ,研究结果表明 :在较低含水量情况下 (砂土 <0 1 5cm3cm- 3,砂质壤土 <0 .1 8cm3cm- 3) ,电导率的增加不易引起TDR测定值的明显偏差 ;但在较高含水量下 ,当溶液电导率增加到 8dSm- 1 (砂质壤土 )和 1 1dSm- 1 (砂土 )时 ,TDR测得的含水量值明显高于实际值。在较高电导率 ( <1 6dSm- 1 )下 ,K0 .5a 与实际含水量仍呈较好的线性关系 ,但电导率引起的介电损失影响了K0 .5a ～θ线性关系的斜率和截距。本文给出了考虑电导率影响的K0 .5a ～θ线性关系的校正方程。土壤粘粒含量的增加也会引起TDR测定偏差 ,在低含水量时测定值偏低 ,在高含水量时测定值偏高。粘粒含量 <5 0 %时 ,测定偏差 <0 .0 2cm3cm- 3。     

应用Markov链理论定量描述区域冲积土壤质地层次的垂向变化特征

冲积土壤剖面质地层次的垂向变化是一个十分复杂的问题,长期以来都是定性描述而无法定量化,但土壤剖面的质地层次组合特点对土壤水分转化和溶质运移等具有重要影响,对其定量地描述和研究是进一步准确定量区域农田水转化和溶质运移的基础。马尔可夫链理论是用来描述随时间（空间）变化的一个离散状态序列的状态转移特性的,本文就其引入来研究冲积土壤剖面质地层次的垂向变化规律。研究结果表明,区域冲积土壤剖面质地层次的垂向变     

Soil organic carbon content and soil structure quality of clayey cropland soils: A large-scale study in the Swiss Jura region

Soil organic carbon (SOC) fashions soil structure, which is a key factor of soil fertility. Existing SOC content recommendations are based on SOC:clay ratio thresholds of >1:10. However, the corresponding SOC content might be considered hard to reach in clayey soils, whose structure degradation risk is assumed to be high. Here, we analysed the SOC content and soil structure quality of soils under similar cropping practices with clay contents ranging from 16% to 52%. Five undisturbed soil cores (5–10 cm layer) were collected from 96 fields at 58 farms in the Swiss Jura region. We assessed the soil structure quality visually using the CoreVESS method. Gravimetric air content and water content, and bulk density at −100 hPa were also measured, and the soil structure degradation index was calculated. We found that the relationship between SOC and clay content held over the clay content range, suggesting that reaching an acceptable SOC:clay ratio is not limited by large clay contents. This suggests that the 1:10 SOC:clay ratio may remain useful for clayey soils. In contrast to what was expected, it is not more challenging to reach this ratio in clayey soils even if it implies reaching very large SOC contents. SOC content explained the considered physical properties better than clay content. From a soil management point of view, these findings suggest that the soil texture determines a potential SOC content, while the SOC:clay ratio is determined by farming practices regardless of the clay content.     

Improved prediction of water-retention properties of clayey soils by pedological stratification

The water-retention properties of clayey soils have been studied at ?0.3 × 10⁵ and ?15 × 10⁵ Pa matric potentials using three sets of clayey horizons differing in their pedological origin. Measurements were made on small clods collected in winter when swelling is at a maximum. The results are discussed in relation to variations in the clay content and clay fabric. The bulk volume, which appears to be closely related to both clay content and clay fabric, allows the variations in water retained to be explained better than with clay content alone. With clayey horizons originating from a single soil family, differences in water retained can be explained by variations in clay content alone because clay fabric does not change greatly. These results demonstrate the significance of pedological stratification in estimating the water-retention properties when a single soil characteristic, such as clay content, is used.     

Critical limits of the degree of compactness and soil penetration resistance for the soybean crop in N Brazil

In agricultural fields soil compaction is a major cause of physical degradation. Degree of compactness (DC) is a useful parameter for characterizing compaction and the response of crops for different soils. The objectives of this study were: (1) to identify the critical DC and PR values for soybean [Glycine max (L.) Merrill] using plant growth variables and (2) to verify the relationship between DC and PR, and assess which parameter is recommended for the evaluation of soil compaction. The study was conducted in a greenhouse in a completely randomized factorial design of 4 textures × 5 compaction levels for sandy loam and sandy clay loam soils, and 3 compaction levels for the clayey and very clayey soils. Soil samples were collected from the surface of a Xantic Kandiudox from the NE region of the State of Pará, Brazil. The DC was calculated from the maximum bulk density obtained by the Proctor test, and the PR curve was determined in undisturbed samples equilibrated in different matric potentials. The growth and development of the soybean was favored in the DC range of 80 to 85%, regardless of soil texture. The critical degree of compactness for the growth of soybean was around 98% regardless of soil texture, while the critical values for penetration resistance at field capacity varied according to soil texture and bulk density and were 28.2, 5.6, 3.5, and 5.2 MPa for the sandy loam, sand clay loam, clayey and very clayey soils, respectively. The root length was the plant growth variable most susceptible to soil compaction. Change in soil penetration resistance was poorly related with change in degree of compactness showing that one parameter cannot be replaced by the other. Because PR is quickly determined in field and have a direct relationship with plant growth, for the soils evaluated in this study we recommend the use of soil PR to assess the state of soil compaction.     

Buffering capacity of cashew soils in South Eastern Tanzania

Abstract. Cashew soils of South Eastern Tanzania become acidified due to sulphur used for controlling powdery mildew disease ( Oidium anacardii Noack). The buffering capacity of surface and subsurface horizons of 35 soil profiles of major cashew growing areas –- the Makonde plateau, its piedmont and inland plains –- was studied. The buffering capacity of surface and subsurface horizons was strongly correlated with clay content and weakly with organic carbon content. In addition, it was only weakly correlated with total exchangeable bases and available P of the surface horizon, but strongly with soil pH, base saturation and cation exchange capacity of the clay fraction of the subsurface horizon. Highly weathered sandy soils, dominant on the Makonde plateau and common on the Piedmont, had the lowest buffering capacity. Soils from the inland plains had better buffering capacities as they are generally more clayey or are less weathered. The risk of severe acidification and of a decline in productivity of cashew and of food crops is highest on the Makonde plateau. Further development and dissemination of methods which can reduce the use of sulphur are required.     

A study of some tillage practices for sustainable crop production in India

Soil tilth has been defined in terms of a ‘Physical Index’ based on the product of the ratings of eight physical properties — soil depth, bulk density, available water storage capacity, cumulative infiltration or apparent hydraulic conductivity, aggregation or organic matter, non-capillary pore space, water table depth and slope. The Physical Index and a tillage guide were used to identify the tillage requirements of different soils varying in texture from loamy sand to clay in the semi-arid tropics. The physical index was 0.389 for a loamy sand, 0.518 for a black clay loam and 0.540 for a red sandy loam soil and the cumulative rating indices in summer and winter seasons were 45 and 44 for loamy sand, 52 and 51 for red sandy loam and 54 and 52 for black clay loam soils, respectively. The compaction of the loamy sand by eight passes of a 490 kg tractor-driven roller (0.75 m diameter and 1.00 m length) increased the physical index to 0.658 and chiselling of the red sandy loam and black clay loam increased the physical indices to 0.686 and 0.729, respectively. The grain yields of rainfed pearl millet and guar and irrigated pearl millet, wheat and barley increased significantly over the control (no compaction) yields by compaction.

The chiselling of the soils varying in texture from loamy sand to clay at 50 to 120-cm intervals up to 30–40 cm depth, depending upon the row spacing of seedlines and depth of the high mechanical impedance layer, increased the grain yields of rainfed and irrigated maize on alluvial loamy sand, rainfed maize on alluvial sandy loam and red sandy loam, rainfed sorghum on red sandy loam and black clay loam, irrigated sorghum on black clay loam and rainfed black gram on red sandy loam, pod yield of rainfed groundnut, tuber yield of irrigated tapioca and fresh fruit yield of rainfed tomato on red sandy loam and sugarcane yield on black clay soil, significantly over the yields of no-chiselling systems of tillage such as disc harrow and country plough.     

Erosion processes and erodibility of cultivated soils in North Rhine‐Westphalia under artificial rain. II. Results of field experiments and comparison with laboratory trials

In the densely populated state of North Rhine‐Westphalia, soil erosion by water causes substantial on‐site degradation and off‐site damages. The implementation of soil‐conservation measures is improved, if soil erodibilities and erosion processes are known. In a state‐wide investigation, we aimed to representatively assess soil‐erosion processes and erodibilities of cultivated soils. For this purpose, we measured surface runoff and soil‐loss rates of 28 cultivated soils with field plots under artificial rain. In the field experiments, surface runoff and soil loss indicated high sealing susceptibilities and high erodibilities on soils of quite different textures including a clay silt, a loam silt, a loam sand, a sand loam, and two standard loams. Rill formation causing high soil‐loss rates was observed on a clay silt (soil BM) and on a loam silt (soil RB), the latter yielding an empirical K‐factor of 1.66 t ha^–1 h N^–1. K‐factors of other silty soils ranged from 0.04 to 0.48, whereas sandy soils and clayey soils had K‐factors ranging from 0.00 to 0.32, and 0.00 to 0.12, respectively. Comparatively high erodibilities of two silt clays were due to saturation overland flow. Erosion processes and erodibilities of soils with similar texture varied to a large extent, possibly caused in part by seasonal differences in the timing of erosion tests. Surface runoff was different in field experiments compared with laboratory experiments (companion paper) conducted with topsoil material taken from the field plots. In addition, higher concentrations of suspended sediment were recorded on average in the field than in the laboratory. These differences might reflect the influence of the subsoil and are due to higher transport capacities on longer plots in the field. Thus, laboratory experiments can complement but not replace costly field trials for K‐factor determination. Empirical K‐factors derived from field and laboratory experiments are in general lower than K‐factors of other soils in Germany or calculated K‐factors derived from pedotransfer functions, which might be attributed to a more maritime‐type climate in North Rhine‐Westphalia. Since the temporal variability of erodibility was not assessed, the reported K‐factors should be regarded as preliminary.     

黄淮海平原三种土壤中优势流现象的试验研究

在黄淮海平原选择三种不同质地类型的土壤（砂壤土、淤土、风沙土）,各设１．５ｍ×１．５ｍ两个小区,其中一个小区在试验开始前两癸灌水约５６ｋｇ,以获得不同的初始含水量。将１００ｍｍ含有染色剂亮蓝的水灌入小区,一天之后,开挖１ｍ×１ｍ的剖面拍照,进行图像分析处理,计算剖面中染色百分比随深度的变异,研究所形成的优势流的状况与土壤类型、土壤初始含水量的关系。结果表明：不同土壤发生优势流的程度不同,结构发育好     

红壤的物理性质及其生产意义

热带和亚热带地区广泛分布着红壤性土壤。由于该地带水热条件十分优越,促进了土壤矿物组成的强烈风化和生物物质的迅速循环,从而构成了红壤性土壤所具有的独特的化学性质和物理行为。晚近的研究表明,红壤性土壤中大量存在的高岭类粘土矿物和三二氧化物不仅决定了土壤中一系列的化学环境,而且也影响着土壤中的物理过程和力学性质的变化^[13,18],而后者的控制和改善又往往是红壤开发利用成败的关键之一^[17]。     

Some relationships between quality of irrigation waters and chemical characteristics of irrigated soils of the Nagaur district,Rajasthan

Studies were conducted on the effects of waters of different quality on the chemical characteristics of 74 surface and subsurface soils of the Nagaur district, Rajasthan. The electrical conductivity (EC) of the saturation extract of these sandy and loamy sand soils were found to be less than that of the irrigation water. Correlations were observed between EC and the constituent ions (Na⁺, Ca²⁺ and Mg²⁺ of the irrigation water and of the saturation extract of the soil samples. The pH values of the irrigation water and soil suspensions also showed a positive correlation. The carbonate and bicarbonate ion concentrations in both the irrigation water and the saturation extract of the soils correlated with their respective pH values. EC of both the irrigation water and the saturation extract from surface and subsurface soil layers correlated with total cations. Correlations between the chemical characteristics of the irrigation water and the saturation extract of the soils are of limited value for prediction purposes, due to other factors operating under field conditions.     

土壤特性对保水剂吸水性能的影响

该文测试了保水剂与砂壤土、壤砂土、砂黏壤土1和砂黏壤土2四种土壤混合后的吸水倍率,研究了土壤特性对保水剂吸水性能的影响,混合时土壤为风干土,保水剂与土壤的混合比例为0.5%。结果表明：与对照相比,保水剂与土壤混合后明显降低了吸水倍率,且随着吸水时间加长,降低幅度增大。吸水10 min后,吸水倍率下降14.4%～58.0%,70 min后,下降41.8%～90.2%。研究认为：吸水初期,吸水倍率主要受土壤孔隙特性的影响,随着吸水时间的加长,土壤溶液中离子增多,对保水剂吸水倍率产生了影响。土壤溶液中离子量与黏粒含量有关,黏粒含量高,土壤溶液中离子量大,反之则小,保水剂在黏粒含量高的土壤中的吸水倍率较在黏粒含量低的土壤中低。与土壤混合还改变了保水剂的吸水规律,对照中,吸水倍率随着吸水时间加长而加大,达到最大后趋于稳定;而在土壤中,短时间内吸水倍率达到最大,随着吸水时间加长,吸水倍率逐渐下降。     

潮土区农田土体构型层次的探地雷达无损探测试验

为探究探地雷达对自然土壤土体构型进行快速无损探测的可行性,该文首先利用基于时域有限差分法的Gpr Max2D软件模拟4种具有不同介电特性差异的土壤层次的土体模型,识别雷达电磁波在具有不同土壤介电特性差异的土壤层次中传播时反射波振幅和相位的客观变化规律;然后于2016年在位于黄淮海平原潮土区的河北省曲周县选择夹黏型和底漏型2种土壤层次较明显的农田土体构型进行GPR探测试验,并挖掘土壤剖面,通过雷达图像处理软件和MATLAB编程处理雷达图像并提取波形数据,根据模拟获取的规律进行土壤层次识别,对比探测层厚与实际剖面层厚。研究结果显示,雷达电磁波在不同介质分界面处发生反射,两侧介电特性差异越大,反射波振幅越大;上层介质介电常数小于下层会发生正反射,反之发生负反射;实测波形比模拟波形杂乱;通过电磁波振幅和相位变化识别层次界面清晰的夹黏型土体构型中较厚层次的厚度的相对误差(9%)要小于识别层次界面不清晰的底漏型土体构型各层厚度的相对误差(9%);可识别的层次界面反射系数均大于0.02,两侧土壤具有较大介电特性差异;通过客观判读依据可以判别农田潮土的层次结构,但层次界面的整齐清晰程度、界面两侧介电特性差异程度和相邻层次的厚度大小影响着探地雷达探测效果。该文可以为相关研究提供参考,为实现土体构型这一重要耕地质量指标的快速监测提供借鉴。     

A comparative study of three methods of water removal prior to resin impregnation of two soils

The water in replicate samples from sub-surface horizons of a clayey and a fine-silty soil was removed either by oven-drying, freeze-drying or by acetone-replacement prior to resin impregnation. Pore space photograms (pores >60 μm diam.) from thin sections were analysed on a Quantimet 720 image analysing computer following each drying technique. During oven- and freeze-drying the clayey soil contracted considerably and subsequently satisfactory impregnation of these samples was either difficult or impossible. This macro-shrinkage caused a decrease in number and lengths of most planar pores and a decrease in size and number of all intra-aggregate pores. The loss in pore space and continuity obviously affected resin impregnation. The clayey samples in which water was replaced by acetone, and all samples of the silty soil, however pretreated, showed no measurable macro-shrinkage and all impregnated well. Oven-drying the silty soil appears to increase the porosity, causing an increase in size of all pores. A mechanism for this apparent enlargement is proposed. It is evident that acetone-replacement of the soil water prior to resin impregnation is the best of the three methods used here and should be seriously considered when image analysis is to be carried out on resin-impregnated blocks from soils of similar or related textures.     

Effect of subsurface clay on nematode communities in a sandy soil

A variety of soil properties can directly or indirectly affect nematode community structure. The effects of subsurface clay content (at 20–40 cm depth) on nematodes in the surface layer (0–20 cm depth) of a sandy soil were examined in field experiments in Florida, USA. Plots were established in a site with a relatively uniform sandy upper soil layer (88–91% sand and 5–7% clay at 0–20 cm depth) but with varying levels of clay in the subsurface layer (3–35% clay at 20–40 cm depth). Nematode numbers in the surface soil layer were affected by the amount of clay in the subsurface layer. Population densities of a number of different nematode genera were greater in the surface layer of plots with 35% subsurface clay than in plots with 3% subsurface clay. Indices of nematode community structure were largely unaffected, since effects of subsurface clay were observed across all nematode groups. Most nematodes (70–80% of total numbers) occurred at 0–20 cm depth, although Teratocephalus was more common at 20–40 than at 0–20 cm. Subsurface clay content indirectly affected soil moisture and other environmental factors in the upper soil layer in which most nematodes reside.