Clod Size Research Articles

ロータリ耕うん後の土塊分布測定法 土塊の採土・し別法の検討

Soil pulverization is the chief aim of rotary tillage. Clod size distribution is the most commonly used index of soil pulverization. However, a method for measuring clod size distribution has not been established yet. Therefore, the present study seeks to establish a simple way of recording clod size distribution.This paper deals mainly with the following: (a) the influence on mean weight diameter of the clod when cutting with sampler and separator, (b) the probability of reducing the number of grades in sieving, namely the number of use of sieves.The results were as follows.(1) In the case of down-cut rotary tillage, clod size on the upper layer was larger than that on the middle and lower layers. On the other hand, clod size distribution by up-cut rotary tillage yielded the opposite result. Therefore, when we evaluate the clod size distribution it is necessary to sample each layer.(2) Among the three sampler sizes, statistical analysis for mean weight diameter rarely showed a significant difference between the two sampling methods. These results suggest that the separater's and the sampler's effect is no greater than that of original variance or experimental error.(3) After Synthesizing the experimental results and conducting a simulation test which used synthetic in place of dirt clods, clearly 200mm samplers should be used with cases smaller than 25mm in mean weight diameter of clods, and 400mm samplers with cases over 25mm. In other words with practical measurement of clod size distribution, we should utilize 200mm samplers in upland field and 400mm samplers in paddy field.(4) When the number of grades in sieving is properly reduced, we can, by applying a variation of Weibull's distribution, predict the clod size with an error level of 3%. These results show that we can estimate various clod size indices using on three sieves, provided that the mesh catches the largest clod.

Comparison of PRZM-2 computer model predictions with field data on the fate of napropamide and pendimethalin in soils

The ability of Pesticide Root Zone Model (PRZM-2) to simulate the movement of napropamide and pendimethalin residues in the tobacco crop was evaluated using the soil properties and amounts of rainfall and irrigation in three field trials conducted in two unsaturated zone fields in the ploughed layer (0−40 cm).The results of PRZM-2 simulation do not agree with observed field data, which also show a high variability. The cause of this discrepancy may be attributed to the 40 cm deep ploughing of the soil not followed by other agronomical practices that reduce the superficial clod size, thus generating the large voids responsible for the displacement of pesticide to the ploughing depth. For pendimethalin the discrepancy may be enhanced by the higher volatility of this pesticide.

Effects of PTO-powered disk tilling on some physical properties of Bangkok clay soil

Experiments were conducted to investigate the effects of tilling with a PTO-powered disk tiller on some physical properties of Bangkok clay soil. Tests were conducted at 1, 2, 3, 4 and 5 km h −1 forward speeds and 28° and 33° gang angles. Average moisture content of the soil was 26 g 100g −1. The effects of disk tilling were assessed in terms of changes in bulk density, total porosity, cone index, clod size distribution and soil inversion during the first and second passes. Tests were also conducted in the unpowered mode at a 28° disk gang angle setting during a single pass. The study revealed that the bulk density and cone index were reduced, and the total porosity, content of clods of < 15 mm diameter and soil inversion were increased with an increase in the number of passes and forward speed. At any given pass and forward speed, the reduction in bulk density and cone index, and increase in total porosity and content of clods of < 15 mm diameter, were greater at a 28° disk gang angle setting compared with a 33° setting. More soil inversion was recorded at a 33° than at 28° gang angle setting. A comparison of performance between powered and unpowered modes revealed that, in the unpowered mode, the tilling effects on soil physical properties were less than that obtained in the powered mode.

Tillage of compacted haul roads and landings in the boreal forests of Alberta, Canada

Ten temporary haul roads and landings in west-central Alberta were tilled with a winged subsoiler specifically designed for tilling compacted forest soils. Surface soil had been removed from all sites during construction, and spread over three of the four landings prior to tillage. Soil bulk density at the 0–10, 10–20, and 20–30 cm depths, and clod size distribution at the 0–30 cm depth were measured immediately after tillage. Bulk density of undisturbed and compacted (untilled) soil was also measured. Mean bulk density of compacted soil in haul roads was significantly greater than the bulk density of undisturbed soil, but not for landings. Tillage significantly reduced mean bulk density on three haul roads and two landings; subsurface soil was relatively dry at these sites. Most soils were difficult to fracture into small clods because these weakly aggregated soils were severely remoulded and compacted by equipment, particularly logging trucks operating on the haul roads. The degraded soil was massive and the strenght of the surface soil layers was generally much higher than was the strength of lower soil layers; this resulted in the subsoil deforming around the wings of the subsoiler rather than fracturing the surface soil. Fracturing of compacted soil into small clods was apparently enhanced by at least 2 years of frost action. The winged subsoiler was only moderately effective at fracturing recently compacted soil because of an often high soil water content, but it was observed that sites where soil was broken into large clods was loosened by frost action the following winter. Alternative methods of tilling compacted soil that insure soil fracturing over a wider range of soil water contents are needed for loosening compacted soil in northern boreal forests.

Three-dimensional Measurement of Loam Clods Using Machine Vision

An important objective of tillage in agriculture is to develop a desirable soil structure for a seedbed or a rootbed. Distribution of clod sizes, which indicate the final soil condition, is usually measured by sieving soil samples. But samples will break into smaller ones because of the vibration of sieve. This phenomenon often occurs when the soil is fragile, so that accurate data measurement is not possible.

Influence of clod size and method of compaction on the permeability of soils

Dans le cadre des barrieres etanches, plusieurs facteurs influencent la permeabilite des couches de sol compacte. Ces facteurs peuvent conduire a la divergence entre les resultats de permeabilite en laboratoire etin situ.

Effect of clod size on hydraulic conductivity of compacted clay : Houston, S L; Randeni, J S Geotech Test JV15, N2, June 1992, P123–128

Effect of clod size on hydraulic conductivity of compacted clay : Houston, S L; Randeni, J S Geotech Test JV15, N2, June 1992, P123–128

Depth variations in hydraulic conductivity within a single lift of compacted clay

Compacted clay liners are commonly used as components of the lower portion of composite double liner systems for hazardous waste containment. Because the overlying leachate collection and removal systems and the FMLs are not perfect leachate still comes into contact with the lower liner and thus makes it critical that the clay liner component be constructed to achieve the lowest possible hydraulic conductivity. This research was conducted to evaluate the effects of clod size on the hydraulic conductivity of compacted soils and the uniformity of conductivity with depth within a lift of compacted soil. Two subsoils, one from the Beaumont series (smectitic) and one from the Kosse series (kaolinitic), were evaluated in the laboratory and then compacted in large fixed wall permeameters using maximum clod sizes of <2.5, <5.0, and <7.5 cm to a compacted lift thickness of 23 cm. Measurements were made of the hydraulic conductivity of the entire lift, the lower two thirds of the lift, and the lower one third of the lift. The results show that the conductivity of the lower one third of the lift can be as great as 8.7 times that measured for the entire lift and indicates that liners need to be constructed using thin lifts to achieve more uniform low conductivity throughout the liner. The data also indicated that under the carefully controlled conditions of this study and with the clod sizes used, the clod size did not have a significant effect on the hydraulic conductivity of the soils tested. Soil bulk density was poorly correlated with hydraulic conductivity and indicates that measuring the bulk density of a compacted soil is an inadequate method for assuring low hydraulic conductivity. Measurements of the time to the first appearance of leachate indicated that 8 to 17 d are required for water to penetrate a 23 cm thick compacted liner with an average conductivity of 1 × 10−7 cm s−1.

Effect of Clod Size on Hydraulic Conductivity of Compacted Clay

Abstract A study has been conducted to identify the causes for field-measured values of hydraulic conductivity of clay liners being typically two orders of magnitude greater than laboratory-measured values. It has been found through laboratory testing on large specimens that the size and gradation of clods and clumps of clay, prior to compaction, can significantly affect the measured hydraulic conductivity. The results of this study are compared to existing studies on the effect of clods on hydraulic conductivity, and general agreement is found. It is concluded that, for clod sizes and gradations likely to occur in field compaction of clay liners, that differences in clod gradation and size between lab and field conditions can essentially account for the observed roughly two orders of magnitude discrepancy between lab and field-measured conductivities. Revised laboratory testing procedures for both the before-liner construction and after-liner construction cases are recommended. The revised laboratory testing procedures are designed to correct the deficiencies in conventional lab testing and to produce unbiased estimates of field hydraulic conductivity values.

Surface clod size distribution as a factor influencing soil erosion under simulated rain

The influence of five ranges of surface clod size distribution (≤2 mm; 2–10 mm; 10–20 mm; 20–50 mm and 50–100 mm) upon the rate and total amount of runoff, soil loss, percolation water and splash sediments was studied using a rainfall simulator. The equipment is described and procedures for running simulation tests are given. The method of sample preparation is discussed. For an air-dried soil sample, soil loss and runoff decreased and total percolation increased with clod sizes up to and equal to 20 mm. Similar results were obtained with a wet run made 24 h after the dry run, although total soil loss and runoff were higher, and percolation lower. No changes were observed as clod size was increased above 20 mm.

Large-Scale Laboratory Permeability Testing of a Compacted Clay Soil

Abstract Constant-head permeability (hydraulic conductivity) tests were performed on samples of a compacted clay soil using a 0.914 by 0.914 by 0.457-m (3 by 3 by 1.5-ft) large-scale, double-ring, rigid-wall permeameter. A naturally occurring silty clay soil was used for the permeability tests. The soil was separated into five different fractions representing five different ranges in precompaction clod sizes. Soil from each of the soil fractions was used for soil specimens. The soil for the large-scale permeameter was compacted in two 7.62-cm (3-in) lifts. Small-scale, constant-head permeability tests also were performed on soil specimens compacted into standard Proctor molds (9.44 × 10−4 m3). Comparison of the results from the two different scales of permeameters indicated that, in all cases, the permeability for a given soil fraction was higher in the large-scale permeameter than it was in the small-scale permeameter. In addition, the permeability for all soil fractions measured in the large-scale permeameter ranged from 0.6 to 2.4 orders of magnitude higher than the value measured in the small-scale permeameter. As a result of the permeability tests performed in this study, there appears to be a scale effect associated with laboratory permeability testing, especially when a significant proportion of the soil being tested consists of precompaction clod sizes which are large relative to the size of the permeameter. The scale effect in this study is thought to be due to the relationship between the compactive effort and the different degrees of confinement associated with the different scales of permeameters. The implication of the study is that a more realistic evaluation of the fieldmeasured permeability of a compacted clay soil may be possible in the laboratory if the permeameter is sufficiently large to test a representative sample of soil.

Influence of Clods on the Hydraulic Conductivity of Compacted Clay

This investigation of the influence of clod on the hydraulic conductivity of compacted clay showed that clod size during soil processing and compaction significantly influenced the compaction curve and the hydraulic conductivity of a highly plastic, compacted clay soil. The compaction curves for soils with initially large and small clods compacted with standard Proctor effort were significantly different. For smaller clods, the compaction curve was much flatter, suggesting less sensitivity to molding water content.

A comparison of moldboard plows for dry season tillage of vertisols

Performance of five moldboard plows was compared during primary tillage in a dry Vertisol. The Kirloskar plow, which is commonly used on Vertisols in India, had the highest pull requirement; a sod bottom Brazilian plow had the next highest pull requirement, followed by the Triplex and ICRISAT plows. The general purpose Mouzon plow was the easiest to pull. The Kirloskar plow created the roughest surface but in general the differences between plows in their effects on surface roughness and clod size are in practice probably not important for Vertisols.

第１報 試作機によるほ場性能 チゼル形サブソイラ付きロータリ心土破砕機の研究

The purpose of this paper aim to develop the machine being capable to break subsoil in order to prevent the soil from hardening and to accelerate the transport of water and air in the soil.The rotary tiller and subsoil breaker with a chisel type subsoiler is fabricated, and is composed of a rotary tiller with small blades and a chisel type subsoiler being able to break subsoil in advance and forced to bring the rotary tiller portion smoothly into deeper subsoil.This paper describes the field performance such as the shape, the soil hardness, the pulverization and displacement of soil disturbed by the rotary tiller and subsoil breaker with a chisel type subsoiler as influenced by the rotational speed of the rotary tiller.As a results, this machine was able to break the soil from 0.2m to 0.3m depth and from 0.2m to 0.3m width. The diagram of soil hardness indicated that the area of influenced soil was 0.45m depth. The sieve separate test indicated that the higher rotational speed of the rotary tiller made the rotary pitch smaller and pulverized the soil smaller and made clod size smaller.The higher rotational speed of the rotary tiller transported the soil farther away.

Soil Roughness Changes from Rainfall

ABSTRACT CHANGES in soil surface roughness were measured for three tillage systems following the application of a series of simulated rainstorms. Tillage systems were chisel, chisel + disking, and chisel + disking + harrowing. Rain with an intensity of 50 mm-h-i and an energy rate of 0.0275 kJ-m~2 per mm of water was applied in storms of 0.3, 0.5, 0.7, 1.5, 3.0 and 6 h durations. Soil surface roughness was expressed by a parameter R which represented the effect of clod size and frequency. Roughness changes could be described by the function R = Cj + C2 exp( C3-r) where r is the cumulative rainfall. Autocorrelation analysis showed substantial variation in the spatial dependency of (a) the roughness parameter R among tillage systems and (b) the measured elevations on a transect following different rainstorm events.

Vibratory diggers for harvesting sweet potatoes in cloddy soils

A vibratory digger blade for proposed use on a sweet potato harvester was designed and tested. Investigations were conducted to evaluate the effect of peak acceleration of vibration and the combined effect of three operating variables (forward velocity, amplitude and frequency of vibration) on the geometric mean diameter (g.m.d.) of clod size and on percent reduction in soil bulk density after treatment. A dimensionless velocity ratio was formed to express the combined effect of the operating variables. A mechanical rotary soil sieve was built and used for separation and measurement of the clod sizes. Vibratory and non-vibratory operations of the digger blade were compared. Low and high-density soil conditions in a silt loam soil (1·16 g/cm 3 and 1·28 g/cm 3 ) and two levels of each of the operating variables were tested. It was found that the vibratory digger, as compared with the non-vibratory one, produced smaller soil clods and a greater reduction in the soil bulk density. Peak acceleration values greater than 3 g produced approximately the same clod break-up and reduction in soil bulk density. Peak accelerations below 1 g resulted in poorer clod break-up. Dimensionless velocity ratios greater than 3 improved the performance of the vibratory digger blade. Design specifications of the vibratory digger and the rotary soil sieve are given.

Development of a Clod Separator for Potato Packing Houses

ABSTRACT AN investigation was conducted with an experimental unit to separate clods from potatoes using the difference in their rebound trajectories. Both potatoes and clods were dropped from a feed conveyor onto a revolving steel roller and separated by an adjustable divider. The drop height was limited to 250 mm in order to prevent potato damage. The effects of roller and divider adjustment on separation efficiency were determined in relation to potato and clod size. The data were used to develop a two-stage separator for potato packing houses. Test results are presented using this machine as a precleaner in a packing house. In addition to the clods most of the loose stems and rotten tubers were also separated. A simulation model was used to study the relationship between the size distribution of the feed material and the correct separator adjustments.

Influence of Seedbed Tilth on Emergence and Root and Shoot Growth of Seedlings of Some Crops

SUMMARYWheat (Triticum aestivum), mustard (Brassica juncea), gram (Cicer arietinum) and barley (Hordeum vulgare) seedlings were raised in soils of different tilth created in microplots during 1981 and 1982. Amplitude in diurnal seed-zone temperature and soil moisture content increased with tilth coarseness. At low soil moisture levels, seedling emergence of wheat and mustard decreased with increasing clod size while that of gram and barley increased. These effects were not significant at high soil moisture levels. Shoot growth of all the crops was higher under coarse tilth than under fine tilth at both moisture levels. Root growth of wheat and mustard decreased with increasing clod size while that of gram and barley increased, at both moisture levels. Mustard had the highest seedling emergence at the low moisture level. Seedling emergence and shoot growth were higher under high moisture than under low moisture for all crops. Root growth varied depending upon the type of crop.

Studies on Evaluation Method for Clod Size Distribution of Soil Layer after Tillage (Part 1)

Studies on Evaluation Method for Clod Size Distribution of Soil Layer after Tillage (Part 1)

Soil Aggregates and Clod Strength Dependence on Size, Cultivation, and Stress Load Rates

AbstractA study was carried out (i) to determine soil clod fragmentation patterns' dependence on specific surface energy, aggregate or clod size, and stress loading rates; and (ii) to examine the hypothesis that the large clods produced during tillage operations performed on air‐dry soils are a result of soil compaction due to overtilling and machinery traffic on a moist soil during the cropping season. It was found that surface energy and specific energy required to reduce aggregate size are dependent on stress loading rates. Under a specific stress loading rate, suspected to be less than or equal to the stress wave velocity in the soil, both common methods—the unconfined compression test and the drop‐shatter test—are assumed to be equally efficient in determining the energy required for soil fragmentation. It was concluded, based on soil strength values obtained, that the fracture strength of the soils tested is attributed to CaCO3 bonding bridges and is practically uniform for all clod and aggregate size ranges tested. The observed huge clods created while tilling the air‐dry soils were size dependent on row spacing and tillage direction. These results are typical of fracturing patterns of material characterized by uniform strength. The fracture patterns for these materials follow the planes of maximal shear stresses unless obstructed by plants of lower strength (e.g., plant rows, major cracks); thus the size of fractured units depend on tillage direction, tillage implement, and row spacing.