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1.
Traffic and tillage induced compaction affect soil physical, chemical and biological properties and processes directly and influences plant root growth indirectly. In a pot experiment with an Entisol and an Alfisol, the effect of 0, 50, 100 and 200 kPa of compactive stress on bulk density, penetration resistance, and on root growth of maize seedlings, at the early stages of development, was studied.

Compaction resulted in a progressive increase in bulk density and penetration resistance for both soils. The Entisol reached a greater bulk density and penetration resistance than the Alfisol. Bulk density or penetration resistance were closely correlated with compactive stress. The correlation between bulk density and penetration resistance was not so close.

Increased bulk density and penetration resistance resulted in a reduction of all the root growth parameters such as number of roots, mean and total root length, rateof root elongation and fresh and dry root mass. Significant linear or curvilinear relationships were found between bulk density or penetration resistance and most of the root growth parameters studied. However, the relationships were improved when relative values (expressed as fractions of the controls) of bulk density or penetration resistance and of any one of the root growth parameters were considered. Roots grown in more compact soil had a smaller ratio of fresh to dry mass.  相似文献   


2.
Penetration resistance, bulk density, soil water content and root growth of oats were intensively studied in a tilled and an untilled grey brown podzolic loess soil. Bulk density and penetration resistance were higher in the top layer of the untilled soil compared with the tilled soil. In the latter, however, a traffic pan existed in the 25–30 cm soil layer which had higher bulk density and penetration resistance than any layer of the untilled soil. Above the traffic pan, rooting density (cm root length per cm3 of soil) was higher but below the pan it was lower than at the same depth in the untilled soil. Root growth was linearly related to penetration resistance. The limiting penetration resistance for root growth was 3.6 MPa in the tilled Ap-horizon but 4.6-5.1 MPa in the untilled Ap-horizon and in the subsoil of both tillage treatments. This difference in the soil strength-root growth relationship is explained by the build up of a continuous pore system in untilled soil, created by earthworms and the roots from preceding crops. These biopores, which occupy < 1% of the soil volume, can be utilized by roots of subsequent crops as passages of comparatively low soil strength. The channeling of bulk soil may counteract the possible root restricting effect of an increased soil strength which is frequently observed in the zero tillage system.  相似文献   

3.
The effect of soil mechanical impedance on root growth is discussed on several levels from the apex to the root system. At the individual root level, the balance of pressures on the root apex cannot account for observed reductions in root elongation rate. Furthermore, soil mechanical impedance affects the elongation rate of non-impeded organs, such as leaves or non-impeded roots. A chemical message originating in roots could account for such an effect, probably via changes in cell wall rheological properties in all growing zones of the plant. Changes in carbon allocation could also have a role. At a whole-plant level, indirect effects linked to changes in the plant structure contribute in a major way to the effect of mechanical impedance on root growth. Although only a small proportion of roots of fieldgrown plants are in contact with compact soil, geometrical characteristics of root systems are considerably affected. In particular, root deepening is delayed and roots tend to have a clumped spatial arrangement. Experimental evidence and modelling suggest that this change in root system architecture could cause water stress, even in relatively wet soil, because of an increase in resistance to the soil-root water flux. As a consequence, root water status and water flux decrease, and stomatal conductance is reduced as a consequence of a chemical message originating in the roots. This secondary message is superimposed onto the direct message linked to mechanical impedance. Under some climatic conditions, whole-plant growth rate, carbon allocation and phenologic development can then be significantly affected by a compaction in the ploughed layer, while only small changes can be expected under more favourable conditions.  相似文献   

4.
Abstract

Variations in the plant growth media were achieved by combining kaolinite clay (<lμm esd.), silt (2–50μm esd.) and sand (100–250 μm esd.) in various ratios. Peds of different sizes were separated from an Okolona clay soil and used as a growth media. A layer (3 cm thickness) of the sand, silt or clay and their combinations were intercalated between sandy loam soil material in a lucite coated cardboard carton. After 21 days the plants were harvested and analyzed for a number of growth parameters and related to the physical and micromorphology of the central control layer.

Germination and emergence of sorghum seed were delayed in the finer aggregates. An increase in aggregate size increased the root elongation. An examination of thin sections showed that most of the roots in the finer aggregates were grown in interpedal regions whereas in the larger aggregates roots were found in both the intrapedal as well as interpedal regions.

An increase in clay content of the central layer reduced the root growth. Silt also reduced root growth but not to the extent of the clay. Maximum root growth and penetration occurred in the mixture containing about 50 percent sand. Better root growth was observed in a sandy to sandy loam texture than clay to clay loam texture.  相似文献   

5.
Soil compaction influences crop growth, movement of water and chemicals in numerous ways. Mathematical modelling contributes to better understanding of the complex and variable effects. This paper reviews models for simulating topsoil and subsoil compaction effects. The need for including both topsoil and subsoil compaction results from still increasing compactive effect of vehicular pressure which penetrates more and more into the subsoil and which is very persistent. The models vary widely in their conceptual approach, degree of complexity, input parameters and output presentation. Mechanistic and deterministic models were most frequently used. To characterise soil compactness, the models use bulk density and/or penetration resistance and water content data. In most models root growth is predicted as a function of mechanical impedance and water status of soil and crop yield—from interactions of soil water and plant transpiration and assimilation. Models for predicting movement of water and chemicals are based on the Darcy/Richards one-dimensional flow equation. The effect of soil compaction is considered by changing hydraulic conductivity, water retention and root growth. The models available allow assessment of the effects of topsoil and subsoil compaction on crop yield, vertical root distribution, chemical movement and soil erosion. The performance of some models was improved by considering macro-porosity and strength discontinuity (spatial and temporal variability of material parameters). Scarcity of experimental data on the heterogeneity is a constraint in modelling the effects of soil compaction. Suitability of most models was determined under given site conditions. Few of the models (i.e. SIBIL and SIMWASER) were found to be satisfactory in modelling the effect of soil compaction on soil water dynamics and crop growth under different climate and soil conditions.  相似文献   

6.
Abstract

Laboratory experiments were conducted under controlled conditions to determine the effect of five matric suctions (0.05, 0.10, 0.30, 1.00 and 3.00 bars) and three bulk densities (1.10, 1.30 and 1.50 g.cm?3) on the moisture content, penetrometer resistance and soybean (Glycine max L.) root growth in six different soil textural groups (sand, silt, clay and their combinations).

The different textural groups were compacted in PVC pipes 4.4 cm ID and 10 cm long and placed in pressure cells to obtain the desired matric suction. After equilibrium five pregerminated soybean seedlings were fixed on the soil surface. At the end of 48 hours root elongation was measured.

There was an increase in root growth in all the textural groups at all the bulk densities when the matric suction was increased from 0.05 to 0.30 bar. There was however a gradual decrease in root growth as the matric suction increased from 0.30 to 3.0 bars. The reduction in root growth at low and high matric suctions was related to moisture content, change in soil resistance and redox status of the soil system.

The measured penetrometer resistance values were directly related to the level of compaction, soil matric suction and also were dependent upon the texture. Close relationships were recorded between redox potentials and soil matric suction.  相似文献   

7.
Roots grow thicker in compacted soil, even though it requires greater force for a large object to penetrate soil than it does for a small one. We examined the advantage of thickening in terms of the stresses around a root penetrating with constant shape, rather than the stresses around an expanding cylinder or sphere, as has been studied previously. We combined experiments and simulations of the stresses around roots growing in compacted soils. We measured the diameter of pea roots growing in sandy loam and clay loam at four different densities, and the critical‐state properties of the soils. At a penetration resistance of about 1 MPa the diameter of the roots in the sandy loam was about 40% greater than that at 0.7 MPa, and at 2 MPa it was about 60% greater. In the clay loam, there was less thickening – about 10% greater at 1 MPa and about 20% greater at 1.5 MPa. The maximum axial stresses were predicted using a critical‐state finite‐element model to be at the very tip of the root cap. When there was friction between the root and the soil, shear stresses were predicted with smaller values at the tip than just behind the tip. When the interface between the soil and the root was assumed to be frictionless, there were by definition no shear stresses. In the frictionless case the advantage of root thickening on relieving peak stress at the root tip was diminished. The axial and shear stresses were predicted to be smaller in the clay loam than in the sandy loam and may explain why the roots did not thicken in this soil although its resistance to penetration was similar. Our results suggest that the local values of axial and shear stresses experienced by the root near its tip may be as important in constraining root growth as the total penetration resistance.  相似文献   

8.
Abstract

Crops can be effectively grown on hardpan soils and water effectively used from deep in the profile if hard layers in soils can be penetrated or if they are broken up by tillage. Addition of gypsum to the soil or exploitation of genetic differences in root penetrability may help improve root penetration through hard layers with less need to depend on the energy requirements of deep tillage. To test this theory, a single‐grained Ap horizon of Norfolk loamy sand soil was compacted into soil columns to compare root penetrability of soybean [Glycine max (L.) Merr.] genotypes Essex and PI 416937 in the presence and absence of gypsum and at two soil compaction levels (columns with uniform compaction at 1.4 g cm‐1 and columns with increasing compaction with depth from 1.4 to 1.75 g cm‐1). Compaction treatments were imposed by constructing soil columns composed of 2.5‐cm‐deep, 7.5‐cm‐diameter cylindrical cores compacted to predetermined bulk densities (1.40,1.55,1.65,and 1.75 g cm.3). Soil penetration resistances were measured on duplicate cores using a 3‐mm‐diameter cone‐tipped penetrometer. Columns were not watered during the study; soybean genotypes were grown in the columns until they died. Both genotypes lived one day longer in columns with lower bulk density and penetration resistance. Although root growth was more abundant for Essex than for PI 416937, root growth of PI 416937 was not decreased by compaction as much as it was for Essex. These results suggest that PI 416937 may possess the genetic capability to produce more root growth in soils with high penetration resistance. This study suggests that genetic improvement for root growth in soils with hard or acidic layers may potentially reduce our dependence on tillage. Gypsum did not affect root growth in this study.  相似文献   

9.
During 1980, an extremely dry growing season, soybean (Glycine max L. Merrill) root morphologies were characterized at the R2 growth stage in Steele, Sharkey, Rilla, Calloway, and Stuttgart soils with a tillage pan and with a disrupted tillage pan. Results showed that the presence or absence of tillage pans resulted in dramatic changes in the soybean root morphology. Without pans, classical taproot systems tended to develop. With pans, soybean root systems tended to follow old root channels and fractures through the pan. Below the pan, soil structure manifested strong influences on root morphology. On all soils except the Steele (loamy sand), roots penetrated the tillage pan in numbers comparable to those penetrating the soil horizons with the pan disrupted. Although soil impedance to root penetration increases with drying and the 1980 growing season was exceptionally dry, mechanical impedance to soybean root penetration of tillage pans on silt loam and clay soils did not appear to be a problem. However, on the loamy sand soil mechanical impedance inhibited soybean root penetration and appeared to be a major problem.  相似文献   

10.
The decline in cotton yields in the Gezira Scheme, Sudan, has been partially attributed to deterioration in soil physical properties and the formation of a plough pan 20 cm deep as a result of the repeated use of the disc plough for land preparation. This field study was conducted during the 1990/91 season at the Gezira Research Station Farm to evaluate the effect of tillage on some soil physical properties of Vertisols, root growth and yield of cotton (Gossypium barbadense L.). Three tillage systems were used: disc harrowing (DH), three bottom disc plough (DP) and subsoiling (SS). Infiltration rates, bulk densities, soil penetration resistance, moisture depletion and root and shoot growth were measured. The results indicated that infiltration rate was not increased significantly by SS. Plant height and shoot dry matter were significantly higher with SS at later growth stages. Bulk density of the plough pan at 135 days after sowing accounted for 90% of the observed variation in subsoil root dry weight while soil penetration resistance accounted for 59% of the variation. Subsoiling increased water use efficiency 25 and 13% over DH and DP respectively. Subsoiling increased cotton yields over DH but the increase over DP was not significant.  相似文献   

11.
Aerated solution culture is frequently used for studying plant growth. Few comparisons have been made of root growth in solution with that found in soil. The objective of this study was to compare root growth and root hair development in these two mediums. Corn (Zea mays L.) grown in aerated solution at two temperatures (18 and 25°C) and three P concentrations (2, 10, and 500 μmol L‐1) was compared with that in three soils, Raub (Aquic Argiudoll) and two Chalmers (Typic Haplaquoll) silt loams, in a controlled climate chamber over 21d. Corn plant weight and root growth were similar in solution culture and Raub soil when grown at an air and soil temperature of 18°C. At 25°C both yield and root growth were greater in Raub soil, even though P uptake by corn was 7‐fold greater in solution culture. The same difference was found when corn grown at 25°C in solution culture at 3 different P concentrations was compared with that grown in Chalmers soil at two P levels. Percentage of total root length with root hairs, root length and density and consequently root surface area, were all greater in the Chalmers soil than in solution culture. An increase in soil P, resulted in a decrease in root hair growth. No such relationship was found in solution culture. Although the recovery and measurement of plant roots and root hairs is more convenient in solution culture, results from this study indicate that the usefulness of solution culture for determining those factors which control root growth and root hair development in soil is limited.  相似文献   

12.
Current UK guidance suggests that a 'rootable' soil profile of at least 1.0 m depth should be sufficient to allow adequate rooting of the majority of tree species in a range of soil types and climatic conditions [Arboricultural Journal (1995) vol. 19, 19–27]. However, there is some uncertainty as to what constitutes a loosened soil profile in terms of penetration resistance. In this study the root development of Italian alder, Japanese larch, Corsican pine and birch was assessed after 5 years of tree growth. These data were compared to penetration resistance measured using both a cone penetrometer and a 'lifting driving tool' (dropping weight penetrometer). Tree root number and percentage were significantly reduced by increasing soil penetration resistance measured with both the cone penetrometer ( P  <   0.050) and the 'lifting driving tool' ( P  =   0.011 and 0.008 respectively). The vast majority of roots were recorded in soils with a penetration resistance of less than 3 MPa (90.7%) with a significant amount in the less than 2 MPa class (70.2%). Root development of Italian alder, Japanese larch and birch all showed a similar pattern, but Corsican pine appeared to be capable of rooting into more compact soils. The 'lifting driving tool' can be used as an alternative measure of soil penetration resistance. This equipment is more cost effective, easier to use and capable of measurements at a greater depth than the cone penetrometer. The majority of Japanese larch and birch roots (84.3%) were recorded in soils where it took less than 15 impacts to penetrate one 10 cm soil depth increment. The modelled data also suggest that a penetration resistance of 2 and 2.5 MPa relates to 10 and 15 impacts respectively.  相似文献   

13.
The balance between root and shoot growth is one of the mechanisms used by plants to adapt to a particular environment. This balance is affected by nutrient supply and water availability. The objective of this study was to understand how nitrogen (N) affects root and shoot growth of three cultivars of wheat (Triticum aestivum L.) grown under two regimes of soil moisture ('non water stressed’ and ‘stressed’ during stem elongation') in the greenhouse and growth chamber. Data showed that before stem elongation, shoot growth was less sensitive to high soil N levels than root growth. In fact, root growth was inhibited by excessive soil N concentration. The cultivar ‘Nesma’ produced more dry matter, absorbed N more rapidly and avoided the negative effect of high soil N concentrations on root growth. ‘Merchouch 8’ produced less dry matter and tolerated more water stress, and appeared to require less water. Severe water stress masked the effect of N on root and shoot growth, and the negative effect of water stress on growth was more important under high N. Plants which were water stressed during stem elongation could not fully recover when they were rewatered from boot stage to anthesis. Nitrogen application improved shoot but not root growth under this soil moisture situation. This study suggested that shoot and root growth were affected differently by N availability and that high soil N levels enhanced the negative effect of water stress on growth.  相似文献   

14.
镉诱导拟南芥根尖过氧化氢积累导致植物根生长抑制   总被引：3，自引：0，他引：3  
以模式植物拟南芥为材料研究了植物主根对不同浓度镉胁迫的响应。结果表明,随镉浓度的升高,植物主根生长受到明显抑制,胎盘兰染色表明高剂量的镉造成主根根尖细胞死亡。进一步二氨基联苯胺(DAB)染色发现镉胁迫诱导植物根尖大量积累过氧化氢,而在胁迫培养基中加入维生素C可显著改善植物根的生长、降低过氧化氢积累,并减少镉诱导的根尖细胞死亡。上述结果表明,镉胁迫诱导的拟南芥主根生长抑制很可能是由于根尖细胞过氧化物积累所致。  相似文献   

15.
利用径向生长修复算法检测玉米根系表型   总被引：2，自引：2，他引：0  
针对根系图像中的断根易导致根系表型信息难以精确获取的问题,该研究提出一种根系径向生长修复算法,并基于此进行不同抗性玉米种子根系表型对比研究。首先,采用自适应对比度增强、直方图灰度查找、椒盐去噪等对采集的根系图像进行预处理,从复杂背景中分离出根系图像;再通过YOLO-V3检测模型进行根系图像中主根根尖识别;最后,自根尖开始进行径向生长,通过分叉点主根提取策略、端点自适应修复策略实现主根图像修复,并提取主根和侧根表型信息。将普通、抗旱、抗涝、抗盐4种不同抗性的玉米种子种植于槽型扁平容器中培养14 d后取出,冲洗得到完整根系并进行图像采集。采用径向生长修复算法进行根系修复后提取根系长度和直径与根系图像修复前相比,根系长度和直径的提取精度分别由83.6%和84.4%提高至97.4%和94.8%,径向生长修复算法提取精度优于区域生长算法,适用于不同胁迫环境下玉米根系表型参数提取。在干旱环境和盐腌环境下,径向生长修复算法精度提升更明显。结果表明,本研究所提算法所提出的根系径向生长修复算法可有效提高根系图像表型信息精度,为根系表型快速提取提供参考。  相似文献   

16.
原位观察土壤中根系的生长情况是一个难题。该文提出了一种土壤栽培条件下根系生长非扰动观测根箱,并以栽种烟草为例说明其应用。该装置由生长室、水肥供应系统、图像捕获与分析系统构成。烟草根系在生长室中生长,水肥供应系统独立调节各分室的水肥供应。利用数码相机定期捕获观察面的根系图像,再用ImageJ软件分析数据,即可实现根系的定量观测。结果表明,烟草根系伸长速率在移栽后第35天和第46天出现2个增长高峰,其峰值分别为54.58和185.69cm/d。根系深度与宽度的比值随生长时间呈现"V"形曲线。根系的快速生长区域具有下移的趋势。比较生长室观察面所得数据和挖掘根箱获得的数据,结果表明,>20～40cm土层根系最多,2种方法所得到的根长在各土层的分布趋势基本一致、相关性显著,表明本装置可应用于土壤栽培条件下根系生长的非扰动观测。  相似文献   

17.
作物根系生长不仅取决于生理因素,还取决于生态环境因素,而土壤水分环境与作物根系生长之间的关系则是局部灌溉技术设计的理论依据之一。为了进一步探索影响棉花根系生长的主要因素,本文在根?冠水量平衡的基础上,结合作物系数与叶面积的关系模型、根长密度分布函数以及根系吸水效率函数,应用动态规划理论,建立了棉花根系生长模型,并以桶栽棉花试验结果进行验证。结果表明,该模型纳入了土壤水分环境、大气蒸腾力和叶面积等影响根系生长的因子,具有揭示根系生长耗水机理的作用。该模型模拟出的棉花总根长变化趋势与实测结果基本一致,当以多年月平均参考蒸散量(ET0)作为输入条件时,模拟结果总体误差为15.41%,可以用于工程设计。对模型敏感性分析结果表明,所建模型能够反映棉花根?叶生长的同步性,以及进入生殖生长期以后根—叶之间的水量平衡关系。棉花根系生长对土壤水分环境变化的敏感性高于对叶面积变化的敏感性,体现了棉花根系生长的机理,建模方法可行。本文研究成果对完善局部灌溉技术中灌溉制度的设计理论具有重要意义。  相似文献   

18.
Information is needed about root growth and N uptake of crops under different soil conditions to increase nitrogen use efficiency in horticultural production. The purpose of this study was to investigate if differences in vertical distribution of soil nitrogen (Ninorg) affected root growth and N uptake of a variety of horticultural crops. Two field experiments were performed each over 2 years with shallow or deep placement of soil Ninorg obtained by management of cover crops. Vegetable crops of leek, potato, Chinese cabbage, beetroot, summer squash and white cabbage reached root depths of 0.5, 0.7, 1.3, 1.9, 1.9 and more than 2.4 m, respectively, at harvest, and showed rates of root depth penetration from 0.2 to 1.5 mm day?1 °C?1. Shallow placement of soil Ninorg resulted in greater N uptake in the shallow‐rooted leek and potato. Deep placement of soil Ninorg resulted in greater rates of root depth penetration in the deep‐rooted Chinese cabbage, summer squash and white cabbage, which increased their depth by 0.2–0.4 m. The root frequency was decreased in shallow soil layers (white cabbage) and increased in deep soil layers (Chinese cabbage, summer squash and white cabbage). The influence of vertical distribution of soil Ninorg on root distribution and capacity for depletion of soil Ninorg was much less than the effect of inherent differences between species. Thus, knowledge about differences in root growth between species should be used when designing crop rotations with high N use efficiency.  相似文献   

19.
Shallow soil A horizon (topsoil) caused by soil erosion and soil movement from cultivation is known to reduce soil and crop productivity. The reduction may be related to limitation of root growth. A field study was conducted to investigate the effects of topsoil thickness on distributions of root density and growth. Soybeans [Glycine max (L.) Merr.] were grown on plots of Mexico silt loam (fine, montmorillonitic, mesic Mollic Endoaqualfs) with topsoil thicknesses of 0, 12.5, 25.0, and 37.5 cm above the Bt horizons. Root density was measured 60 and 90 days after planting using a minirhizotron video‐camera system. Root density was significantly reduced as topsoil thickness decreased from 37.5 to 0 cm. Mean density and net change of the density across profile between 30 and 60 days of growth had a linear function of topsoil thickness. The reduction and lower activity induced by shallow topsoil were attributed to detrimental properties in the Bt horizons. Root distribution pattern and rooting depth were not significantly affected by topsoil thickness. The roots appeared to be accumulated on the upper layers of the Bt horizons. Roots growing in thicker topsoil were more active than roots growing without topsoil. High soil moisture content during the growing season may mitigate the detrimental effects of shallow topsoil, inhibit root penetration, and enhance root activity.  相似文献   

20.
微根管法监测膜下滴灌棉花根系生长动态   总被引：3，自引：2，他引：1  
为了精细监测膜下滴灌条件下棉花(Gossypium hirsutum L.)细根生长形态,于2014年在巴州灌溉试验站开展大田试验,采用微根管法原位监测棉花根系生长,并与传统网格法作对比。分析棉花根系生长动态,构建微根管法测定的形态参数与网格法所测定形态参数的回归模型。结果表明:花期到吐絮期,利用微根管监测10~20 cm处根系生长得到的棉花根长更新速率为1.844 mm/d,期间棉花老根不断死亡和分解。微根管法与网格法测得的根系深度为50 cm,根长密度随着深度增加先增大后减少,根长密度在20~30 cm处最大。两种方法监测得的根长密度具有较好的线性相关,由微根管法测得的剖面根长密度,可通过线性回归方程换算得到实际的体积根长密度。利用微根管法能可靠地监测棉花根系的生长动态变化,今后的研究可进一步加大微根管监测范围和频率,精细监测细根生长全过程,通过构建根系生长模型分析膜下滴灌条件下棉花根系生长时空动态。  相似文献   

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