Abstract: Mechanization in agriculture increasingly involves the use of heavy machinery, which causes soil compaction under unfavourable moisture conditions. Soil compaction has a significant effect on root development of a crop by reducing soil aeration and by increasing soil mechanical resistance. The influence of mechanical resistance on root development and root function was studied in pot experiments, where a sandy loam soil was compacted to different pore volumes, after fertilization to different phosphate levels. Three maize plants were grown in 28 cm high and 14 cm wide pots, and harvested two and three weeks after emergence. Roots were collected from layers of 3 cm.

Abstract: Twenty-one topsoils, with texture varying from sandy loam to clay and organic matter content ranging from 1.6 to 11.9%, were submitted to compaction and settling at different moisture contents where dry bulk density was determined. Under compaction, the density curve went through a maximum while a minimum was observed in the case of settling. Optimum moisture contents corresponding to these two characteristic densities were almost the same. The most important physical properties affecting soil behavior under compaction and settling were found to be water retention properties at low matric potential which themselves depended primarily on organic matter content. Samples submitted to compaction had saturated hydraulic conductivities less than 1 cm/h, while after settling, Ksat measurements ranged from 0.8 to 234 cm/h. Organic matter played an important role in reducing the effects of compaction, and moisture content alone was not sufficient to predict the best conditions for workability in the fields.

Abstract: Measurement of soil properties and field-crop yields on cropland traversed by the Sarnia-Montreal oil pipeline indicated that pipeline isntallation detrimentally affected both crop yields and soil physical-chemical properties in the first year after construction. After 5 yr, relative yields improved although reductions still persisted at most row-cropped sites. However, alfalfa yields at two sites appeared to be unaffected by pipeline construction. Soil mixing and compaction on the right-of-way were most prevalent on medium- to fine-textured soils. Compaction did not appear to be a problem at a coarse-textured site. Soil chemical data indicated that spoil (subsoil) materials from the trench were spread across the right-of-way at most sites. Diluted soil organic matter levels in the right-of-way adversely affected nitrogen status. Medium- to fine-textured right-of-way soils had reduced porosities and hydraulic conductivities, but increased strengths compared with undisturbed adjacent soils.

Abstract: Two-thirds of the sugar-beet crop in the U.K. receives sodium chloride as part of the fertilizer programme. It is well known that the crop responds profitably on sandy soils which contain relatively little sodium and potassium, and most of these fields now receive sodium chloride. Few crops on clays, silts and organic soils are treated because the value of sodium chloride has never been clearly defined. Thus 36 field experiments were made over the 5 years 1975–9 on contrasting soil types testing five amounts of sodium chloride, 0, 100, 200, 400 and 800 kg/ha, and at two times, either autumn or spring. All the fields chosen were in continuous arable rotations where potassium chloride was applied regularly and nearly all the soils contained more than 120 mg exchangeable K/l.Sodium chloride (400 kg/ha costing £12) increased sugar yield on average by about 0·2 t/ha (worth £40) on the mineral soils but no crop responded on organic soil. Exchangeable soil sodium concentration was not a good predictive test of which fields would respond but all the large increases in yield were on fields with less than 20 mg Na/1. A few crops responded on soils with 20–40 mg Na/1 but no crop responded on soil with more than 40 mg Na/1. A survey of sodium concentrations in 800 soils showed that most mineral soils contained less than 40 mg Na/1 so it is suggested that all mineral soils regardless of texture should receive 400 kg sodium chloride/ha. Crops on organic soils did not respond to sodium chloride because the soils already contained sufficient.Autumn and spring applications of sodium chloride on mineral soils gave similar increases in yield provided the fertilizer was not applied just before sowing, when in 2 years it decreased plant establishment. This effect was particularly damaging on clays and silts where it is frequently difficult for other reasons to obtain good seed beds and full establishment. It is concluded that sodium-containing fertilizers should always be applied well ahead of sowing to allow rainfall and cultivations to incorporate them into the soil. On clays and silts it is suggested that they should be applied before ploughing to avoid soil compaction but on sands there may be advantages in post-ploughing application.

Abstract: Dry conditions intensified harmful effects of compaction to sensitive desert annual plants.

Abstract: A test of seedling growth response to several levels of soil compaction showed that root penetration depth was best correlated with soil compaction. Shoot biomass, root biomass, root elongation, and seedling height were not well correlated with compaction. The results reveal that most measurements of growth do not give a good indication of seedling response to stresses induced by compaction. In fact, selecting a growth measurement to determine seedling response may require a separate test. There were good partial correlations between mean seedling height and all other measures of growth, but relationships must be developed for each growth response. When the relationships are known, mean seedling height can be used to predict the mean value of any of the other growth variables.

Abstract: This paper provides a review of soil compaction principles and practice. The nonlinear relation of compaction energy to resulting density is shown. The need to consider the effect of change in moisture from the as-compacted state is pointed out. Factors that influence the reference test for specifying compaction are discussed to show the uncertainty in the resulting maximum dry density and optimum moisture content. Factors that influence field compaction are also described, and the possibility of a large variation in compaction results with field conditions is demonstrated. The need for more awareness of the effects of methods of preparation and uniformity of procedures is indicated. Limitations of density as a method of specifying compaction are pointed out. The type and magnitude of compaction measurement errors are defined and implications for compaction control are discussed. Finally, because knowledge of compactor performance in combination with observation of field procedures is a meaningful basis on which to judge compaction, some basic principles of compactor performance evaluation are described. (Author)

Abstract: The usual procedure for specification of roller equipment, lift thickness, and number of passes to compact a soil fill material of prescribed water content to an optimum density is one that heretofore has traditionally depended on empirical relations and similitude modeling--the use of laboratory-derived test data on soil compaction. In this study, soil compaction under a towed roller is predicted by using the finite-element method (FEM) of analysis. The format of the analysis encompasses the transient loading nature of the tire or roller. By expressing the compaction effort exercised by the rigid roller in terms of the amount of compaction energy required to produce a resultant unit deformation of a particular soil lift thickness, FEM analysis allows one to obtain an evaluation of the influence of soil type, lift thickness, water content, and number of passes on compaction efficiency. In addition, the format for analysis is structured to incorporate compaction of additional soil layers through a layered soil-analysis procedure. The analysis of soil compaction efficiency is supported with corresponding laboratory experiments that involve wheel tow-bin tests. (Author)

Abstract: Studies of vibratory compaction with smooth-drum rollers have indicated that the amount of compaction is highly dependent on two parameters: the magnitude of the vertical oscillatory displacement of the drum and the number of oscillations per unit of distance of travel. Model tests with small-scale rollers were carried out in the laboratroy to study the effects of these parameters on the amount of compaction. The roller had a 12-in diameter. Applied compaction forces and soil layer thicknesses were scaled down appropriately. The frequency of oscillation was reduced to eliminate the vibration effects but maintain the number of oscillations per unit of distance of travel within the range representative of full-size rollers. The mean and oscillatory components of the force applied to the soil were varied as well as the number of passes and the number of oscillations per unit of distance. The test soils were a coarse- to medium-graded silica sand and a fine clayey sand prepared with several initial density states. The results of the tests showed the relations of the test variables to the amount of compaction and to the soil stiffness and the internal damping. The stiffness and damping observations were valuable in explaining the soil-machine interaction of full-scale vibratory rollers and led to the development of an analytical model for predicting the magnitude of drum oscillation during vibration. The paper describes these model tests and presents the experimental results. The implications of the results in compacting soil with vibratory rollers are also discussed. (Author)

Abstract: Glacial till is used mainly as an impervious material in earth and rockfill dams built in Quebec. It is, in general, a well-graded mixture of sand, silt, and gravel, with 25-80 percent passing the no. 200 sieve and a natural water content at or above optimum (Proctor standard). Its natural water content, together with its very high sensitivity to atmospheric humidity, strongly influence the choice of compaction equipment, compaction procedure, and time schedule. This paper presents Hydro-Quebec's experience with this type of material, including choice of the compaction equipment, establishment of the compaction procedure, pretreatment of the borrow pit material, as well as the results and performances obtained at various sites. In addition, the paper describes the particular compaction problems and results of a manufactured material (sand and sensitive clay mixture) used as core material in certain water-retaining dikes. (Author)

Abstract: SUMMARY (1) Soil compaction is being caused by intensive use of off-road recreational vehicles in the California deserts. Vehicle tracks produced by different numbers of motorcycle and four-wheel drive passes were made on the Mojave Desert of California on both a Typic Haplargid and a Typic Torripsamment soil in an attempt to estimate minimum amounts of soil compaction which may produce significant reductions in growth of desert annual plants. (2) A motorcycle produced much smaller increases in soil strength than did a four-wheel drive vehicle. (3) Soil strength of drying compacted soil (even slightly compacted soil) increased at a much greater rate than soil strength of drying uncompacted soil. This may be an explanation for observed reductions in annual desert plant growth even on areas with a relatively small amount of compaction.

Abstract: The relation between the horizontal and vertical components of stress at a point within a soil mass depends on the physical and mechanical properties of the soil and its stress and strain histories. A series of compression tests and repeated loading tests were performed on sand and clay by using the lateral soil pressure ring MkII. This newly developed apparatus allows the laboratory determination of the lateral soil pressure response to vertical loading at rest condition or, alternatively, when limited controlled lateral strain develops. Correlations between the horizontal to vertical stress ratio (K) and the vertical load are presented. After placement of a cohesionless sample, when the material is loose, K is high and it decreases to an ultimate value. Unsaturated clay specimens exhibit somewhat different behavior--K decreases to a minimum value and then it increases with an increase in the load. During the unloading process K increases with an increase in the overconsolidation ratio, and a general relation between K and the overconsolidation ratio is suggested. However, repeated loading results in a decrease in K with an increase in the vertical load. It was also found that the grain size and distribution of grain size affect K. The present testing system does not have facilities for pore water pressure and dynamic loading measurements, which would enable more comprehensive testing and determination of soil parameters in terms of effective stress. (Author)