Abstract: Effects of three agroforestry systems were evaluated on changes in soil chemical properties over a period of 12 consecutive crops of maize-cowpea rotation grown on a tropical Alfisol in southwestern Nigeria. Measurements of soil chemical properties for 0–5 cm depths were made over a period of 5 consecutive years from 1982 through 1986. Six treatments studied were plow-till, no-till, Leucaena hedgerows established on the contour at 4-m and 2-m spacing and Gliricidia hedgerows established at 4-m and 2-m spacings.

Abstract: Advances in Soil Mechanics of Structured Agricultural Soils - The North American Perspective.- Strength of Structured Soils Due to Loading: a Review of Processes on Macro- and Microscale European Aspects.- Soil Deformation and Fracture under Tensile Forces.- Soil Deformation under Compressive Forces.- Effective Stress in Structured Soils.- Strength of Low and Variable Charge Soils.- Effects of Dynamic and Static Loading on Compaction of Structured Soils.- Soil Cohesion Changes.- Unslaked Lime Versus Organic Soils Conditioners to Improve Soil Mechanical and Physical Properties of a Loamy Soil.- Interface Between Implements, Tillage and Soil Structure.- Modeling Soil Disturbance Due to Tillage and Traffic.- Modeling Soil Mechanical Behavior During Compaction.- Root System Responses to Soil Structural Properties: Micro and Macro Scale.- Root Activity Related to Shallow and Deep Compaction.- Tillage and Compactive Effects on Soil Hydraulic Properties and Water Flow.- Tillage and Compactive Modifications of Gaseous Flow and Soil Aeration.- Assessing the Suitability of Different Soils for New Cropping Systems in Terms of Rates of Change in Soil Structure.- Poster Paper Abstracts.- Workgroup Reports.

Abstract: (...) A replicated field study was conducted on a Webster clay loam (fine-loamy, mixed, mesic Typic Haplaquoll) in southern Minnesota and on two Ves clay loams (fine-loamy, mixed, mesic Udic Haplustoll) in southwestern Minnesota to assess the effect of surface and subsoil compaction on the growth and yield of soybean (Glycine max L. Merr.). Surface compaction treatments consisted of no interrow traffic on either side of the row at any time during the experiment and annually applied interrow wheel traffic on both sides of the row from an axle load < 4.5 Mg (...)

Abstract: Topsoil wet aggregat stability was measured during the last 13 years of an 18-year-old field trial with reduced cultivation. Soil strength and soil compressibility were analyzed by a micropenetrometer and a confined, uniaxial compression test, respectively. The trials were situated on a coarse sandy soil and a fine loam in Jutland, Denmark. During the trial period, a considerable decrease in topsoil aggregate stability was observed if the soil was ploughed annually and all plant residues were removed from the field. Shallow tillage by tine cultivation to c. 10-cm depth and especially rotovating to only 5-cm depth diminished the structure deterioration induced by the continuous growing of cereals after ploughing. A crop of Italian ryegrass (Lolium multiflorum), grown after harvest of the small grain cereal crop, also stabilized the aggregates in ploughed as well as in shallow-tilled soil, but the differences induced were less than those induced by the tillage systems. In the top layers of the loamy soil, reduced compressibility was observed in the rotovated soil compared with ploughed and tine-cultivated soil. Soil strength increased in the non-tilled layers of shallow cultivated soil compared with ploughed soil. A compact soil layer beneath the rotovation depth in the loamy soil (called a “rotovator-pan”) was found to have strength values which might depress root development.

Abstract: A quasi-theoretical soil compaction model is presented which gives good estimates (r2=0.980−0.995, P<0.001) of the complete density-stress compression line for soils of variable initial moisture content under static loads from 0 to 1.0 MPa. The 3 unknown parameter coefficients of the generalized model equation are shown to be highly correlated to several soil properties such as moisture content, pre-compression (initial) void ratio, texture, organic matter content ans the Atterberg consistenct limits. A 3-tier classification for partition consisteny limits. A-tier claasificaton for pationing soils into groupings of response to compressive stress is proposed for soil compaction modeling. This categorization is based on soil plasticity and the existence of a “compaction threshold“ sensitivity threshold” in most soils.

Abstract: In a field which had been grazed by dairy cows for 26 years, the bulk density of both total soil and fine earth increased rapidly with depth down to 10–12 cm, but decreased below this depth The bulk density was approximately twice as great in the 10–12 cm as in the 2–4 cm layer Total porosity in the 10–12 cm layer was only 22%Slitting the soil to penetrate the compacted layer approximately doubled net herbage accumulation and the net uptake of N, P and K, raising herbage production and uptake of nutrients from a low level to an acceptable one Slitting tended to increase the concentrations of nitrate-N and K in herbage, but had little effect on the concentration of total N Slitting increased the weight of ash-free root in the 10–20 cm depth range

Abstract: SUMMARY 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.

Abstract: Not Available – First paragraph follows: Selection of an orchard floor management system is based on several considerations, often including its potential effect on water use, water infiltration, and soil compaction. Information on these factors has been limited, however, because many previous studies have compared only a few treatments or have produced site-specific recommendations that did not consider differences in soil characteristics or orchard management.

Abstract: Forested areas of Kanching Recreation Forest exposed to concentrated recreational use tend to show signs of deterioration as indicated by soil parameters related to soil compaction. The results of the present study clearly indicate that such a deterioration of soil conditions has already occurred, though not on an alarming scale (...)

Abstract: Wheel traffic of normal field operations is causing increasing concerns about soil compaction. Soil characteristics affecting root growth, and most easily modified by compaction, are mechanical resistance and pore size distribution. Machinery with axle loads not exceeding 5 Mg will generally cause compaction only in the surface 30 cm of the soil profile. However, a significant portion of the total root growth occurs in this surface layer. With maize, interrow wheel traffic decreased root length density in the surface 30 cm of soil by up to 90%, depending on tillage method. Total root length on a 90-cm deep profile was decreased 22% by wheel traffic under moldboard plowing, and increased 24% by wheel traffic under reduced tillage methods. Soybeans tended to show an opposite response, and also had greater compensatory root growth in the row in response to compaction between rows. Final grain yield for both maize and soybeans was positively related to the percentage of total root growth in the surface 30 cm directly under the row. Subsoil compaction from wheel traffic with axle loads greater than 9 Mg decreased rooting depth and yield of maize. Interrow tillage to a depth of 51 cm did not have any apparent effect on interrow root growth, but did increase root growth in the row.

Abstract: Characteristics of an active clay under various contents of sand are presented. The sand is an admixture used for improving properties of the active clay deposited at a marginal site. The strength of soil admixtures at various contents of sand is evaluated and compared to that of caliche soil. The experimental evidence indicates that the soil admixtures containing the sand between 25% and 30% by weight exhibit the compressive strength comparable to that of caliche soil. The soil admixture is recommended for earthwork construction based on its high strength and is more economical.

Abstract: All impacts of visitor use within the corridor of the 93-km-long (58-mile) Knobstone Hiking Trail in southern Indiana were systematically evaluated. On an areal basis, camping impacts were not extensive. When present, these impacts afected the trail environment through increased soil compaction and exposure, tree wounds, floristic dissimilarity, loss of dufl, and site development. The most striking impact was pervasive damage by of-road vehicles, including tread widening, entrenchment, and soil exposure.

Abstract: A 2-yr field study was conducted to determine the effects of soil compaction and inoculum levels of Fusarium solani f. sp. pisi on pea (Pisum sativum) root length, disease severity, plant biomass, and dry seed yields. Soil inoculum levels of F. s. f. sp. pisi were significantly reduced by fumigation with methyl bromide at the 0-20 cm depth but were not reduced below 20 cm. Use of a paraplow treatment to reduce compaction increased root density over that obtained with the conventional moldboard plow treatment. (…)

Abstract: Formation of new aggregates in a sandy loam soil was simulated in the laboratory. Glass beads of approximately 2-mm diameter, incorporated in artificial aggregates, served as tracers. Mixtures of five aggregate size classes of these aggregates, with diameters smaller than 10 mm and with a total oven dry weight of 360 g were treated in cylinders of 8-cm diameter and height. Soil treatments during 12 weeks represented a year cycle of events. Five different treatments were constituted from (1) application of organic matter+crop (root)-growth, (2) freezing+thawing and (3) soil compaction. Soil treatments were repeated in a second and in a third cycle. Mean weight diameter (MWD) of the aggregates and the redistribution of the tracers among the aggregate fractions were used to characterize the changes in aggregation. After the first cycle, on the average about 70% new aggregates were present. Treatments, including compaction, increased aggregate formation by an additional 9%. The effect of the different treatments was roughly the same indicating that the effects of the different basic treatments were certainly not additive. During each cycle the MWD increased, more so in treatments where freezing+thawing was absent. The MWD of treatments including compaction was relatively large, though after the third cycle the highest MWD was found in the treatment with only root growth+organic matter. The experiment indicates that, in the soil investigated, aggregates seem to have a short life.

Abstract: A comparative study in the forest of Zonien (Belgium) found that conversion of tree species and liming can be worthwhile operations in order to decrease soil compaction in beech monocultures on loamy soil. The soil restoration after introducing oak and maple can be explained to an important extent by an amelioration of the soil biological activity and the humus quality. The restoration after liming is clearly due to an increased earthworm activity. Since this action is limited by the species available at the site, it is proposed to experiment in the future with liming combined with the introduction of deep-burrowing earthworm species.

Abstract: Residual compaction in soils disturbed by differing land-use activities was examined in five southwestern Montana ghost towns. All towns had been abandoned for 46 to 77 years. Bulk density and macroporosity of the poorly sorted sandy loams and sandy clay loam soils were measured. A linear recovery model based on compaction measurements gathered at the townsites indicated that complete recovery times ranged from 50 to 145 years for soils compacted principally by human trampling, and from 79 to 227 years for soils compacted by vehicular traffic. Recovery times were strongly related to compaction intensities, percentage of organic matter in the soil, and the degree to which the soil separates were sorted. Soil loosening mechanisms of freeze-thaw heaving, clay mineral expansion and biological activity were limited at these sites, retarding soil recovery rates. [Key words: soil recovery, soil compaction, semiarid regions, ghost towns, Montana.]

Abstract: The effect of soil compaction and irrigation interval on the growth and yield of cowpea was investigated on Nkpologu sandy clay loam (Oxic Paleustult) in greenhouse pot trials. It was found that moisture stress imposed by increased irrigation interval affected growth and yield more than the compaction. Leaf area, root dry matter yield and crop water-use efficiency (WUE) were significantly reduced by high compaction (bulk density = 1.70 Mg m −3 ) relative to the medium (bulk density = 1.40 Mg m −3 ) and low (bulk density = 1.20 Mg m −3 ) compaction levels. Compaction, however, did not show significant adverse effect on shoot dry matter yield and tap root length, although each of these parameters tended to decrease with increasing compaction. Water, equivalent to the daily consumption by the crop, applied every 6 days (relative to 2- and 4-day intervals) resulted in significant reductions in leaf area, shoot and root dry matter yield ( P = 0.01), tap root length and WUE ( P = 0.05). Only leaf area and WUE were significantly reduced by the compaction/irrigation interval interaction.

Abstract: Over a 3-year period, the cumulative dry matter yield (as a measure of ground cover performance) of red clover and Italian ryegrass spring-seeded into fall-seeded winter rye was assessed using one broadcast and two drill seeding methods. Grain yield of winter rye and changes in soil physical characteristics were also assessed. Red clover was more persistent and cumulatively yielded 48% more dry mutter than ryegrass. There was no cumulative effect on soil physical characteristics due to cover species. However, during the seeding year, seeding method caused differences in soil compaction, which was reflected in cover crop yield the following year. Winter rye yield was not affected by either seeding method or cover species.

Abstract: Head losses were measured under controlled labora-tory conditions for a subirrigation system. It was found that contrary to previous findings there were no significant exit head losses in a subirrigation system. However, high divergent head losses were measured in the immediate vicinity of drain pipes. It appears from our study that divergent head losses might have been wrongly labelled as exit head losses in previous studies. It is probable that the clogging of drain envelopes with iron ochre or soil compaction around the drain pipe during installations with a trenchless plow might have been labelled as exit head losses. It was also found that divergent head losses were greater in a clay soil than in a sandy soil.