The influence of soil macroporosity on water retention, transmission and drainage in a clay soil

Abstract. Reductions in hydraulic conductivity and specific yield (drainable porosity) of large cores of Evesham clay soil were observed for periods up to 40 days under continuous ponding. A strong linear relationship ( r ²= 0.94) found between these two variables was used as parameter input to a layered drainage model for mole drained soils. Model results indicated that soils of lower drainable porosity and hydraulic conductivity produced higher peaked hydrographs widi faster recessions. These results are discussed in relation to the effects of soil loosening on drain response in heavy clay soils.     

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.     

黄土高原几种质地土壤的水分扩散率

本文采用水平土柱入渗法,测定了四种不同质地、不同孔隙度土壤的水分扩散率。结果表明,粘粒含量较多和孔隙度较小的土壤,单位时间内入渗水量较少,渗到既定距离需要的时间较长。各种质地土壤的扩散率D都随含水量增加而增加。当饱和度相同时,质地愈粘重,扩散率愈小。扩散率和孔隙度呈正相关。本文建立了土壤扩散率D和饱和度c的幂函数方程。将其运用到非饱和水分运动方程中,以有限差分数值计算法,所得土壤含水量的计算值和实测值比较接近,说明这些经验公式有一定的可靠性。     

Scaling the saturated hydraulic conductivity of an alfisol

Alfisols exhibit a high degree of spatial variability in their physical properties. As a result, it is difficult to use information on physical parameters measured at one location to model larger-scale hydrologic processes. In this study, the saturated hydraulic conductivity, K_S , of an Alfisol was determined on 109 undisturbed monoliths using the falling-head permeameter method. The model developed by Arya & Paris (1981) was used to calculate the pore volume from sand and clay fractions. Scaling factors were calculated from the measured K_s , sand pore-volume, clay pore-volume, clay content and effective porosity, using the similar media concept. Prediction of K_s of gravelly Alfisol using clay pore-volume is confounded by high gravel content which, when discounted, improves the prediction remarkably. The scaled mean saturated hydraulic conductivity K* for all horizons of the Alfisol was approximately l.0x 10⁻⁵ms⁻¹.     

Self-repair of compacted Vertisols from Central Queensland, Australia

Vertisols have the inherent ability to self-repair because of high clay contents and clay type that govern volume change. A study was undertaken to correlate soil inherent properties with two indicators of structure improvement based on tensile strength and clod porosity of compacted soil cores before and after wet/dry cycles. In order to minimize inter-soil differences Vertisols under similar cropping regimes and from the same climatic region in Queensland, Australia were selected. A soil repair index (R_T(1)) based on compressive strength of soil cores was related to soil inherent properties and shrinkage indices, COLE_STD and LS_MOD using multiple regression. Results showed that compressive strength of soil cores after a single wet/dry cycle after compaction was sufficient to rank Vertisols in terms of their capacity to improve structure after compaction. Clay content and clay activity (CEC/clay) on their own were poor indicators of soil repair. Fine sand was shown to be an important component in the repair process. LS_MOD and COLE_STD predicted R_T(1) equally well and indicated that Vertisols with COLE_STD values > 0.15 and LS_MOD > 12% would be expected to have sharper reductions in tensile strength compared to those with lower values after just one wet/dry cycle. Clod porosity was poorly related to soil inherent properties.     

Effects of pre-sowing compaction on soil physical properties, soil atmosphere and growth of oats on a clay soil

The effects on a number of soil physical and aeration parameters of compaction during spring pre-sowing operations were measured on a clay soil (49% clay). A soil-tyre contact stress of 200 kPa was applied by tractor tyres.
Yield of an oat crop was reduced by 30% as a result of compaction. Total porosity of the soil was reduced by 6% v/v owing to loss of pores > 60 μm, and water retention was increased. The resultant decrease in air-filled porosity greatly reduced gas diffusion and air permeability coefficients of the soil, and, for a time, O₂ content of the soil atmosphere was significantly lowered in the compacted treatment. Penetrometer resistance after sowing was 3.5 MPa in the control and 4.5 MPa in the compacted treatment; in the latter, root growth was inhibited until the soil dried and cracked. By the end of June, canopy temperature measurements indicated water stress in the oat crop on compacted soil but not in that on the control.
The results obtained indicated that air permeability, measured in the field, of 1 mm s⁻¹ provides a satisfactory single value below which crop growth is likely to be reduced.     

Effects of soil compaction on N-mineralization and microbial-C and -N. II. Laboratory simulation

Soil compaction can affect the turnover of C and N (e.g. by changing soil aeration or by changing microbial community structure). In order to study this in greater detail, a laboratory experiment simulating total soil porosities representative of field conditions in cropped and pasture soils was set up. Soils were silty clay loams (Typic Endoaquepts) from a site that had been cropped with cereals continuously for 28 years, a permanent pasture and a site that had been cropped with maize continuously for 10 years. Soils from the three sites were compacted into cores to different total porosities (corresponding bulk densities ranging from 0.88 to 1.30 Mg m⁻³). The soil cores were equilibrated to different matric potentials (ranging from −1 to −100 kPa), yielding values for the fraction of air-filled pores of < 0.01 to 0.53 m³ m⁻³, and then incubated at 25°C for 21 days. C-mineralization was on average 15, 33 and 21 μg C g⁻¹ day⁻¹ for soils from the cropped, pasture and maize sites, respectively, and was positively correlated with soil water contents. Net N-mineralization showed a similar pattern only for well-aerated, high total porosity cores (corresponding bulk density 0.88 Mg m⁻³) from the pasture soil. Denitrification at < 0.20 m³ m⁻³ for the fraction of air-filled pores may have caused the low N-mineralization rates observed in treatments with high water content or low porosity. Microbial biomass estimates decreased significantly with increasing water contents if measured by fumigation-extraction, but were not significantly affected by water content if estimated by the substrate-induced respiration method. The degree of soil compaction did not affect the microbial biomass estimates significantly but did affect microbial activity indirectly by altering aeration status.     

Complexed organic matter controls soil physical properties

It is shown that, for mineral soils, it is not the total amount of organic carbon (or organic matter) that controls soil physical behaviour but the amount of complexed organic carbon (COC). We assume that this complex is formed by the association of unit mass (i.e. 1 g) of organic carbon with n grams of clay. Analysis of data from two French and two Polish databases shows that, for these soils, n = 10. A consequence of this is that in soils with small contents of organic carbon (OC), such as arable soils, COC is proportional to OC. However, in soils with large contents of organic carbon, such as pasture soils, COC is proportional to the clay content. This explains why we find that soil bulk density is significantly correlated with OC in French arable soils but with the clay content in French pasture soils. The use of COC instead of OC enables the arable and pasture soils to be considered on the same scale.

Water retention data were fitted to a double-exponential equation which allows both the matrix and structural porosities to be estimated. It is shown that in soils with low contents of organic carbon, the carbon content is positively correlated with the matrix porosity. In contrast, in soils with high contents of organic carbon, the matrix porosity is constant at its maximum value and the structural porosity is not significantly correlated with either the total organic carbon or the non-complexed organic carbon (NCOC). It is suggested that the complexed organic carbon can be considered as being sequestered. The soil clay content can similarly be partitioned between clay that is complexed with organic carbon and clay that is not complexed. It is shown that non-complexed clay is more easily dispersed in water than clay that is complexed with organic carbon. These findings indicate how improved pedo-transfer functions for the prediction of soil physical properties may be produced. Such functions need to use the values of complexed and non-complexed organic carbon and clay which must be determined by algorithms. The values produced by the algorithms may then be used in the improved pedo-transfer functions.     

再生水灌溉对农田土壤水流运动影响的研究进展

再生水灌溉农田既可节约宝贵的水资源、缓解农业用水紧缺,同时再生水中的多种营养元素和微量元素可促进作物生长、提高粮食产量。但再生水中的物质进入农田后将引起土壤孔隙结构、团聚体结构、黏粒分散特征和水土作用关系等一系列的变化,进而引起土壤入渗性能和导水性能的改变,增大环境污染风险。该文综述了再生水中的悬浮无机固体、大分子有机质、油脂、表面活性剂和盐分对农田土壤水流运动的影响及其作用机理,指出受灌农田土壤结构性质演化过程与驱动机制、受灌农田土壤与灌溉入渗水流之间的相互作用关系为该领域亟需开展的2个研究方向。文章对再生水农田灌溉制度制定、污染风险控制和生态环境保护均有参考价值。     

Persistence of soil compaction due to high axle load traffic. I. Short-term effects on the properties of clay and organic soils

Short-term effects of high axle load traffic on soil total porosity and pore size distribution were examined in field experiments on a clay (Vertic Cambisol) and an organic soil (Mollic Gleysol) for 3 years after the heavy loading. The clay soil had 48 g clay (particle size less than 2 μm) per 100 g in the topsoil and 65 g per 100 g in the subsoil. The organic soil consisted of well-decomposed sedge peat mixed with clay below 0.2 m depth down to 0.4–0.5 m and was underlain by gythia (organic soil with high clay content). The experimental traffic was applied with a tractor-trailer combination in autumn 1981. The trailer tandem axle load was 19 Mg on the clay and 16 Mg on the organic soil. There were three treatments: one pass with the heavy axle vehicle, with wheel tracks completely covering the plot area, four repeated passes in the same direction, and a control treatment without experimental traffic. During loading, the clay was nearly at field capacity below 0.1 m depth. The organic soil was wetter than field capacity.

One and four passes with the high axle load compacted both soils to a depth of 0.4–0.5 m. On the clay soil the total porosity was reduced by the heavy loading nearly as much as macroporosity (diameter over 30 μm) to 0.5 m depth. On the organic soil, macroporosity was reduced and microporosity (under 30 μm) increased in the 0.2–0.5 m layer by the heavy loading. Total porosity did not reveal the effects of compaction on the organic soil. The compaction of the clay below 0.1 m persisted for 3 years following the treatment despite annual ploughing to a depth of 0.2 m, cropping and deep cracking and freezing. Likewise, in the subsoil (below 0.2 m) of the organic soil, differences in pore size distribution persisted for a period of at least 3 years after the heavy loading.     

Chemistry of pedogenesis in Indo-Gangetic alluvial plains

Five soil pedons–two aquic and two udic Haplustalfs and one petrocalcic Natrustalf–from the Indo-Gangetic alluvial plain of Western Uttar Pradesh were investigated to evaluate the pedogenetic processes. Sand/silt ratios indicate that parent material discontinuities are insignificant. Higher K content and lower SiO₂/R₂O₃ ratios of the non-clay fractions in Bt, rather than in the A, horizons suggest maximum weathering at or near the surface.
An almost linear relationship between decrease in molar SiO₂/R₂O₃ and % increase in clay to about 100cm depth in all the pedons, presence of clay argillans in Bt horizons (where % clay, fine/coarse clay ratio and bulk density values are greatest), all indicate that the development of argillic horizons in these soils was due, at least partly, to lessivage of clay. Fe in clay fractions decreases with depth whilst Al increases, but in the fine earth both increase steadily with depth. This, together with crystalline iron concretions in the lower Bt horizons, suggests that in Haplustalfs these horizons are gaining clay by neoformation/ reorganization of illuviated constituents, especially A1₂O₃.     

2018-2019年河南省兰考县土地利用变化对耕地风蚀的影响

[目的]探索淮河流域黄泛平原风沙预防区耕地风蚀现状、年度动态及其变化原因,为区域风蚀研究与治理提供科学依据。[方法]选取河南省兰考县为研究对象,通过高分辨率遥感影像解译2018,2019年土地利用信息,采用耕地风蚀模型计算风蚀模数,分析土地利用年度变化对耕地风蚀的影响。[结果]①2018-2019年,兰考县土地利用以水浇地为主,出现土地利用变化的区域面积为21.40 km²,水浇地动态度为-1.54%,主要变化类型为水浇地转为其他林地,面积7.19 km²。②兰考县耕地风蚀主要为微度,其次为轻度。2018-2019年,轻度侵蚀面积减少17.04 km²,动态度为-12.13%。③2018-2019年,兰考县耕地风蚀变化的主要原因是水浇地面积、空间位置的变化,因水浇地转出导致侵蚀减少的面积为3.36 km²,主要位于仪封乡、城关镇等区域;因水浇地转入造成侵蚀增加的面积为0.98 km²,主要位于仪封乡、葡萄架乡等区域。[结论]淮河流域黄泛平原风沙预防区土地利用结构、耕地风蚀特点鲜明,水浇地变化直接影响耕地风蚀。因此,区域应多关注耕地风蚀治理及耕地合理利用。     

A procedure for evaluating and mapping the erosion resistance of soils (by the example of irrigated soils of Tajikistan)

A procedure was developed on the basis of the experimental-theoretical equation for calculating the parameters of soil erosion resistance (the bottom eroding velocity of flow), the principles of the erosion resistance theory, the experimentally obtained relationships between the main erosion parameters of Tajikistan soils (the size of water-stable aggregates and their cohesion), and other properties (the initial water content, the lumpiness, the contents of physical clay and humus, the porosity ratio, and the lower plasticity limit). For practical purposes, a simpler procedure is recommended to evaluate and map the erosion resistance of irrigated lands in the areas of typical serozems and mountain cinnamonic soils of Tajikistan from minimum initial information (the texture, lumpiness, and density of the soils and the content of plant roots).     

The effect of soil texture and soil drainage on emissions of nitric oxide and nitrous oxide

Abstract. Agricultural soils are important sources of the tropospheric ozone precursor NO and the greenhouse gas N₂O. Emissions are controlled primarily by parameters that vary the soil mineral N supply, temperature and soil aeration. In this field experiment, the importance of soil physical properties on emissions of NO and N₂O are identified. Fluxes were measured from 13 soils which belonged to 11 different soil series, ranging from poorly drained silty clay loams to freely drained sandy loams. All soils were under the same soil management regime and crop type (winter barley) and in the same maritime climate zone. Despite this, emissions of NO and N₂O ranged over two orders of magnitude on all three measurement occasions, in spring before and after fertilizer application, and in autumn after harvest. NO emissions ranged from 0.3 to 215 μg NO-N m^–2 h^–1, with maximum emissions always from the most sandy, freely drained soil. Nitrous oxide emissions ranged from 0 to 193 μg N₂O-N m^–2 h^–1. Seasonal shifts in soil aeration caused maximum N₂O emissions to switch from freely drained sandy soils in spring to imperfectly drained soils with high clay contents in autumn. Although effects of soil type on emissions were not consistent, N₂O emission was best related to a combination of bulk density and clay content and the NO/N₂O ratio decreased logarithmically with increasing water filled pore space.     

Tillage and soil physical properties in semi-arid West Africa

In the semi-arid zone of West Africa, the growth of annual crops is severely constrained by soil and climatic conditions. Soil physical properties, specifically low porosity resulting from the particle-size distribution and predominantly low-activity clay, restricts root system development and crop growth. Using intensive mechanical tillage is an effective method in enhancing soil porosity and physical properties.

This paper summarizes the results of tillage experiments conducted for about 30 years in West Africa. Tillage methods evaluated involved deep plowing with motorized equipment or animal powered tools using tined equipment and ridgers for earthing up. Soil properties and plant characteristics evaluated were porosity, root development, microbial life, soil-water reserves, and crop yields. Results of no-tillage and minimum-tillage studies are also discussed. Application of reduced tillage techniques did not produce satisfactory results. Several mulch farming systems, using dead or living vegetative covers, were also tested in regions where annual rainfall exceeds 1000 mm.

The results obtained support the conclusion that soil tillage is an excellent means of improving soil physical properties and crop yields in the semi-arid regions of West Africa. However, adaptation of this technique by resource-poor small farmers poses several technical and logistical problems.     

Effect of potassium on soil structure in relation to hydraulic conductivity

The effect of exchangeable K⁺ on soil structure and permeability has been studied. A loamy sand, a light clay and a heavy clay soil were leached with solutions adjusted to potassium adsorption ratios (PAR) of 0.0, 0.72, 3.74 and ∞. Exchangeable K⁺ percentage (EPP) and hydraulic conductivity (HC) were measured on the leached soils. SEM observations on undisturbed soil samples were used to evaluate changes in soil structure and pore size.

EPP values for the three soils ranged as follows: 0.8–1.3, 5.5–9.2, 16.0–21.0 and 58.0–76.0 for PAR's of 0.0, 0.72, 3.74 and ∞, respectively. HC incrased slightly (20%) up to EPP values of about 20% for the loamy sand and heavy clay soil, while a decrease in HC corresponding to any increase of EPP was observed for the light clay soil. This soil was richer in illite and also exhibited higher affinity for K⁺. At the highest EPP values (58.0–76.0) HC of the three soils decreased to about 20% of the values measured for the Ca²⁺ saturated soils.

SEM observations were performed and Ca²⁺ saturated soils compared with the K⁺ enriched ones. Ca²⁺ treated loamy sand exhibited discrete clay aggregates located in the spaces between sand particles or attached to them. K⁺ enrichment resulted in the formation of a dense network of clay microaggregates filling up the pore space. The microaggregate structure of the two Ca²⁺ clay soils changed to a dense layer composed of much smaller particles following K⁺ enrichment. Pores were mostly smaller than 10 μm in the K⁺ soil compared to several tens of microns in the Ca²⁺ form.

SEM observations and the fact that clay content did not vary with depth suggest that dispersion of clay microaggregates and their rearrangement in situ were the major mechanisms involved in HC reduction, rather than long-range clay migration and the formation of a clay enriched layer with impeded drainage.     

秸秆生物炭对黏壤土入渗规律的影响

为提高干旱半干旱区耕作土壤灌溉水的利用效率,采用秸秆生物碳对黏壤土进行改良,并用3种经典入渗模型进行入渗模拟,寻求适于描述研究区土壤入渗规律的模型及改良方案。采用双环入渗试验测定4种生物炭施用水平（10 t/hm²,20 t/hm²,30 t/hm²,50 t/hm²）的田间作物生育期内土壤含水率、入渗速率及累积入渗量,分别采用Green-Ampt模型、Philip模型和Kostiakov经验公式对试验组与对照组（CK）的入渗过程进行模拟。结果表明:施用量为30 t/hm²较CK效果最为明显,施用层（0—40 cm）入渗速率增加44.6%,耕作层土壤含水率增加8.9%,累积入渗量增加45.45%。比较3种模型的入渗过程拟合结果,认为Kostiakov经验公式拟合的效果符合实测规律,可为研究区改良土壤水分入渗过程提供理论依据。     

Soil macroporosity evaluated by a fast image‐analysis technique in differently managed soils

Abstract

Porosity, pore size distribution and a pore shape factor were measured from resin impregnated soils by means of a fast technique of image analysis. Images are directly captured by a video camera from polished impregnated blocks. Micromorphology was also used to assist in the comprehension of soil porosity changes in three differently managed soils: dry‐farming plus tillage, irrigated plus grass‐covered, steppe natural soil. Under study, alluvial soils from a semi‐arid region in NE Spain.

Even if there are no significative differences in total macro‐porosity between the differently managed soils, pore size distributions are significatively different Both natural and irrigated permanently‐covered soils have a larger amount of pores bigger than 1 mm in diameter, most of them of biological origin, greatly favouring aeration. Tillage contributes significantly to change the relative distribution of pore shape: the amount of rounded pores (vughs) decreases and elongated pores as well as fissures appear.     

Soil structural indices' dependence on irrigation water quality and their association with chromophoric components in dissolved organic matter

Irrigation with treated wastewater (TWW) may affect soil structure and stability and the characteristics of dissolved organic matter (DOM) of the soil solution. The objectives of our study were (i) to evaluate the impact of TWW irrigation, as compared with fresh water (FW) irrigation, on aggregate stability and saturated hydraulic conductivity (indices of soil structure stability) and (ii) to determine whether these indices can be associated with the chromophoric indicators of water‐extractable DOM in TWW‐ and FW‐irrigated soils. We studied aggregate stability and soil hydraulic conductivity (HC) of four different soil types irrigated with either TWW (for at least 5 years) or FW. The results were linked to earlier published data on the concentration scores of fluorescent chromophoric DOM components (obtained from excitation‐emission matrices of flouorescence coupled with parallel factor analysis), dissolved organic carbon (DOC) concentration and absorbance at 254 nm (Abs254). These were all obtained from water extracts of the same soils as those used in the current study. Irrigation with TWW decreased aggregate stability, in comparison to irrigation with FW, in the sandy clay and clay soils, while in the loamy sand TWW increased aggregate stability. The apparent steady state HCs in the TWW‐irrigated samples in the loamy sand, sandy clay and clay soils were similar to, or significantly less than, those obtained in the FW‐irrigated samples. In the sandy loam the opposite trend was noted. Results of principal component and classification analyses showed that the aggregate stability indices were directly associated with soil organic matter and DOM attributes in the coarse‐textured soils, while in the fine‐textured soils inverse associations were noted. Only in the fine‐textured soils were the HC attributes associated (directly) with some of the DOM characteristics. Our results suggest that structural indices of fine‐textured soils are more sensitive than those of coarse‐textured soils to the composition of water extractable DOM.