Effect of Sprinkler and Border Irrigation on Topsoil Structure in Winter Wheat Field

A two-year experiment was carried out on the effect of sprinkler irrigation on the topsoil structure in a winter wheat field. A border-irrigated field was used as the control group. The total soil porosity, pore size distribution, pore shape distribution, soil cracks and soil compaction were measured. The sprinkler irrigation brought significant changes to the total soil porosity, capillary porosity, air-filled porosity and pore shape of topsoil layers in comparison with the border irrigation. The total porosity and air-filled porosity of the topsoil in the sprinkler irrigation were higher than those in the border irrigation. The changes in the air-filled and elongated pores were the main reasons for the changes in total porosity. The porosities of round and irregular pores in topsoil under sprinkler irrigation were lower than those under border irrigation. Sprinkler irrigation produced smaller soil cracks than border irrigation did, so sprinkler irrigation may restrain the development of macropore flow in comparison with border irrigation. The topsoil was looser under sprinkler irrigation than under border irrigation. According to the conditions of topsoil structure, it is preferable for crops to grow under sprinkler irrigation than under border irrigation.

Simulation of Morphological Development of Soil Cracks in Yuanmou Dry-hot Valley Region, Southwest China

Soil cracking is an important process influencing water and solutes transport in the Yuanmou Dry-hot Valley region of Southwest China. Studying the morphological development of soil cracks helps to further reveal the close relationship between the soil cracking process and water movement in such semi-arid regions. Here we report regular changes on surface morphology of soil cracks with decreasing water in four different soils (Typ-Ustic Ferrisols,Ver-Ustic Ferrisols,Tru-Ustic Vertisols and Typ-Ustic Vertisols) through simulation experiments. Our results indicate the following: 1) Different soils ultimately have different development degrees of soil cracks,according to their various values of crack area density. Soil cracks in Typ-Ustic Ferrisols can only develop to the feeble degree,while those in the other three soils are capable of developing into the intensive degree,and even into the extremely intensive degree. 2) Soil crack complexity,as expressed by the value of the area-weighted mean of crack fractal dimension (AWMFRAC),is found to continuously decrease as a whole through the whole cracking process in all the studied soils. 3) Soil crack connectivity shows a uniform trend in the studied soils,that is to say,connectivity gradually increases with soil crack development.

Surface Morphology of Soil Cracks in Yuanmou Dry-hot Valley Region,Southwest China

Surface morphology of soil cracks is one of the important factors influencing the water evaporation rate in cracked soil in Yuanmou Dry-hot Valley Region,Southwest China. Quantitative study of the complicated surface morphology of soil cracks is a prerequisite for further studies of soil-cracking mechanisms. The present paper establishes a quantitative indicator system by application of concepts and methods originating from Fractal Geometry and Network Analysis. These indicators can effectively express the complicated features of soil-crack network structure. Furthermore,a series of values related to soil-crack morphology was obtained by image processing on field photos of soil-crack quads,and gradation criteria for the degree of development of soil cracks were determined. Finally,the changes in values of the morphological indicators under different degrees of development were analyzed in detail. Our results indicate that (1) the degree of development of soil cracks can be divided into five grades,i.e.,feeble development,slight development,medium development,intensive development and extremely intensive development; (2) the values of the indicators change predictably with increasing degree of development of soil cracks. The area density (Dc) increases,and both the area-weighted mean ratio of crack area to perimeter (AWMARP),which reflects the intensity of cracking,and the index r,which is related to the connectivity of a soil crack,grow uniformly (albeit with different forms). AWMRAP increases at a geometric rate while r shows logarithm-mic growth,indicating a gradual increase in theconnectivity of a soil crack. Nevertheless,the area-weighted mean of soil-crack fractal dimension (AWMFRAC) shows a decreasing trend,indicating a gradual decline in the complexity of cracks as area density increases.

Selection of Judging Indicators for Surface Morphology of Soil Crack under Different Development Degrees in Yuanmou Arid-Hot Valley Region

Quantification of complicated surface morphology of soil crack is a prerequisite and key to soil crack study. This paper takes soil crack quads in Yuanmou arid-hot valley region as examples, selecting several morphological indicators, and analyzes the soil crack＇s morphological features under various development degrees. By statistic analysis, three quantitative indicators for surface morphology are selected, namely soil crack area density, area weighted mean fractal dimension and connectivity index R, which can not only express the development intensity of soil cracks, but also effectively describe its morphological complexity and connectivity. The research results set a good base for the establishment of soil crack assessment system in Yuanmou arid-hot valley region.

Study on Intermittent Irrigation for Paddy Rice: I. Water Use Efficiency

A field experiment was conducted in a well-puddled paddy field developed on the Tama River alluvial soil in the Farm of Tokyo University of Agriculture and Technology, Japan, to study the effect of intermittent irrigation on water use efficiency of paddy rice. Four treatments were arranged with 2 replicates: continuous flooding irrigation treatments (CFI), and three intermittent irrigation treatments Ⅱ-0, Ⅱ-1 and Ⅱ-2, in which plants were re-irrigated when the soil water potential fell below 0, -10, and -20 kPa, respectively, at soil depth of about 5 cm. Water consumption was lower in treatment Ⅱ-0 than in treatment CFI because the percolation rate was reduced by the reduction in the hydraulic head of ponded water. Intermittent irrigation led to soil repeated shrinking and swelling in Ⅱ-1 and Ⅱ-2 plots and, therefore, soil cracks developed rapidly. Since they became the major routes of water percolation, the soil cracks increased water consumption in treatments Ⅱ-1 and Ⅱ-2. There were no significant differences in dry matter production and grain yields between treatment Ⅱ-0 and treatment CFI, but the dry matter production and grain yields in treatments Ⅱ-0 and CFI were significantly higher than those in treatments Ⅱ-1 and Ⅱ-2. Therefore, the water use efficiency in the treatments was in the order of Ⅱ-0 > CFI > Ⅱ- 2 > Ⅱ- 1.

Shrinkage Characteristics of Lime Concretion Black Soil as Affected by Biochar Amendment

Studies have reported that biochar is a sustainable amendment that improves the chemical and physical properties of soil.In this study,an incubation experiment was conducted to investigate the effects of different application rates of biochar on the cracking pattern and shrinkage characteristics of lime concretion black soil after three wetting and drying cycles.Biochar derived from the corn straw and peanut shell mixture was applied to the soil at rates of 0,50,100,and 150 g kg^(-1)dry weight,representing the treatments T_(0),T_(50),T_(100),and T_(150),respectively.During the wetting and drying cycles,the cracking pattern and shrinkage characteristics of the unamended and amended soil samples were recorded.Application of biochar significantly increased soil organic carbon content in the samples.During soil desiccation,biochar significantly reduced the rate of water loss.Cracks propagated slowly and stopped due to the relatively higher water content in the soil applied with biochar.The cracking area density(ρ_c),equivalent width,fractal dimension,and cracking connectivity index decreased during the drying process with increasing application rate of biochar.Theρ_(c )value of the T_(50),T_(100),and T_(150) treatments decreased by 33.6%,52.1%,and 56.9%,respectively,after three wetting and drying cycles,whereas the T_(0) treatment exhibited a marginal change.The coefficient of linear extensibility,an index used to describe onedimentional shrinkage,of the unamended soil sample(T_(0))was approximately 0.23.Application of 100 and 150 g kg^(-1)biochar to the soil significantly reduced the shrinkage capacity by 41.45%and 45.54%,respectively.The slope of the shrinkage characteristics curve,which indicates the ralationship between soil void ratio and moisture ratio,decreased with increase in the application rate of biochar.Furthermore,compared with the T_(0) treatment,the proportional shrinkage zone of the shrinkage characteristic curve of the T_(50),T_(100),and T_(150) treatments decreased by 5.8%,13.1%,and 12.1%,respectively.Differences were not observed in the moisture ratio at the maximum curvature of the shrinkage characteristic curve among the treatments.The results indicate that biochar can alter the cracking pattern and shrinkage characteristics of lime concretion black soil.However,the effects of biochar on the shrinkage of lime concretion black soil are dependent on the number of wetting and drying cycles.

Large-Scale Test Model of the Progressive Deformation and Failure of Cracked Soil Slopes

A large-scale test bed(LWH=6 m×3 m×2.8 m)instrumented with various sensors is used to examine the effects of rainfall infiltration and evaporation on the deformation and failure of cracked soil slopes,taking the Anhui area along the Yangtze River as a field example.The results indicate that(1)during rainfall,the soil around the shallow shrinkage fissures attains transient saturation,and the attendant decrease of matric suction is the primary cause of the shallow slope failure;(2)slope deformation continues during post-rainfall evaporation;(3)if a period of evaporation is followed by heavy rainfall,soil creep is concentrated near the deepest cracks,and two zones of steep gradients in pore pressure form at the crest and toe of the slope.Finally,a saturated zone forms near each crack base and gradually enlarges,eventually forming a continuous saturated layer that induces the slope instability or failure.

Geometry and Maximum Width of a Stable Slope Considering the Arching Effect

The stability of an arching slope in deformable materials above strong rocks strongly depends on the shape and width of the span.Equations for a free surface problem that incorporate these two parameters were derived using a simplified two-dimensional arching slope model,and were validated using physical model tests under 1 g and centrifugal conditions.The results are used to estimate the maximum excavation width for a weak claystone slope in a lignite mine,for which we calculate a safety factor of 1.31.