Abstract: Ailanthus altissima (Tree-of-Heaven) seedlings were grown in compacted and non-compacted mason sand and sandy loam soil. Shoots and roots were measured to characterize seedling development and resp...

Abstract: SUMMARY A swelling stagnogley soil remained unwheeled or was uniformly wheeled by a combine harvester and a tractor in two successive autumns before direct drilling winter cereals. Combine wheeling of the soil at its wettest condition caused the largest loss of soil porosity. The autumn and spring of the second growing season for the winter cereals were wetter than long term average. The smaller porosity in the wheeled soil, created lower soil redox potential and smaller oxygen flux as well as greater soil strength and larger amounts of available water, but little difference in soil temperature. The crop in the wheeled soil had fewer plants, less root and a lighter yield than in the unwheeled soil. The wheeled soil recovered some porosity and lost strength after wetting and drying during the second growing season, whereas soil freezing had very little effect. This restructuring was sufficient to reverse some of the detrimental effects of compacting the soil.

Abstract: Large‐scale field and laboratory tests were carried out to investigate compaction characteristics of a river terrace gravel soil at the 120‐m high Sao Simao Dam in Brazil. The coarse fraction of the deposit was typically 3 in. (7.5 cm) maximum size, while the matrix (defined as material passing No. 4 sieve) was basically a clayey sand with LL=30-35%, PI=5minus;15 and 35–50% passing the No. 200 sieve. The initial objective of the compaction tests was to develop the relationship between maximum density and percentage of gravel fraction which could be used for control of compaction in the field. The scope of the investigation was later enlarged to study the effects of energy of fraction, maximum particle size, mould dimensions, gradation of coarse material and water absorption on compaction of these soils. Field compaction trials were carried out to establish procedures for embankment construction and to evaluate the efficiency of two vibratory rollers.

Abstract: SOIL compaction is known to affect crop yields. In the work reported here the residual effects of soil compaction on cotton yield reduction through diminished plant stand and increased stand variability have been established. A simple variational model is used to predict average yield from the mean values land the standard deviations of the crop stand and water use in the field. Good agreement was attained between predicted and measured average yields of seed cotton for trickle and sprinkler irrigated fields. Seed cotton yields were found to be more sensitive to stand variations than to variations in water distributions under the described experimental conditions.

Abstract: AN experiment was set up to study the effect of high axle loads on subsoil compaction and corn production in two soil textures. Treatments of 10 and 20 t/axle were applied at two soil moisture contents. Resulting changes in soil physical characteristics as compared to a control were measured to a depth of 0.60 m. Topsoil and subsoil dry density levels were significantly increased by high axle loads. Moldboard plowing of compacted plots to a depth of 0.20 m did not fully relieve topsoil compaction. Because of the small difference between them, the two soil moisture contents at the time of compaction had little effect on topsoil or subsoil bulk density in either field. The incurred soil structural changes had minimal effect on the growth and maturity of grain corn in the loam field. However, yields were significantly decreased by compactive loading. Both moisture and compaction treatments significantly modified the rate of plant growth, maturity and yields in the clay field...

Abstract: BUSH BEANS (Phaseolus vulgaris) were planted in three soil textures having varying organic matter contents that were subjected to three levels of compaction energy. Measurements were made of some plant and yield parameters in a controlled environment. Soil compaction decreased the fresh yields of the crop, the plant height, the root dry matter and increased the plant diameter. On the other hand, organic matter incorporation which tends to reduce compaction increased the fresh and dry yields of the crop, the plant height, the leaf area index and the root dry matter. The results indicate that there is a great potential for using organic matter to alleviate the problems of soil compaction in crop production.

Abstract: Little work has been published in the United States on the influence of soil compaction on increased herbicide phytotoxicity to crop seedling development. Yet, soil compaction on agricultural lands is an increasing problem, especially on certain soil types in the eastern Corn Belt region of the nation. In greenhouse studies, the effects of soil compaction of an Ockley silt loam (fine, silty, mixed, mesic Typic Hapludalf) treated with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,Ndipropyl-p-toluidine) were determined on the root and shoot development of corn. The compaction was established by compacting to the desired bulk densities 750 g soil in 600 mL stainless steel pots with a hydraulic press. Three rates of trifluralin (0, 0.38, and 0.79 µmol kg⁻¹) reduced secondary root development by 60% as the bulk density increased up to 1.66 g cm⁻³. Visual ratings of the characteristic swollen root tip injury indicated that increasing the soil bulk density from 1.50 to 1.66 g cm⁻³ resulted in an increased number of malformed roots at all herbicide rates. When compaction was made throughout the entire soil profile, the average day for emergence increased from 5.0 to 6.2 days as bulk densities increased from 1.10 to 1.66 g cm⁻³.

Abstract: Laboratory studies were conducted to determine the effects of four levels of soil compaction and five moisture suctions on the relationship between penetrometer soil strength and emergence of maize and cowpea seedlings for five contrasting soils of Western Nigeria Compaction (bulk density) and moisture suction accounted for 75- 88% of observed variation in soil strength and affected seedling emergence at specified soil strengths The effect of compaction or moisture suction on the relation of seedling emergence to soil strength depended on soil and crop species The rate of cowpea seedling emergence, which was about two-thirds that of maize, was more adversely affected by compaction than by high moisture suction Cowpea emergence ceased when soil strengths exceeded 8 kg/cm2 in the clay loam or 10 kg/cm2 in the sandy clay loam and sandy loams, while corresponding values for maize were 14 kg/cm 2 for the clay loam and 18 kg/cm 2 for the other soils

Abstract: Pasture production and water use data are presented for a border strip irrigation trial in the Upper Waitaki Basin. Pasture development on the shallow, poorly structured Mackenzie soil was slow and irrigated pasture remained clover dominant for 6 years. With irrigation at 25% awe pasture herbage production over 3 years of this initial development stage averaged 7.2 t DM/ha/yr, 5 times more than improved dryland pasture. Grazing days (12 - 19 month old ewes) provided during the September to April growing season were 960 under dryland conditions and 5940 under irrigation at 25% awe. Of the 3 irrigation treatments (irrigation at 0%, 25%, 50% awe), irrigating at 25% awe was the most efficient giving near-maximum pasture production and the greatest herbage response per irrigation, Mean annual water use efficiency at 25% awe was high (63%) and irrigation water requirement low (470 mm) for such a naturally, highly permeable soil and was probably due to soil compaction by earthmoving machinery during border strip preparation.

Abstract: Two cultivars of common bean were grown in soil samples of an Oxisol (LR) and an Alfisol (PVp), with and without fertilizer, subjected to three compaction levels , and confined in 3.8 liter pots. The data showed that with the increase on soil compaction, there was a general tendency, in the above ground part at the end stage, to increase the nutritional efficiency of K and to decrease of the N, P, Mg, Ca, Cu and Fe. The behavior of Zn, B and Mn was influenced more intensively by the soil type, the soil fertility and the cultivar.

Abstract: The natural regeneration of soil structure following compaction was studied on a stagnogleyic paleoargillic brown earth (Albaquic Paleudalf) at Rothamsted Experimental Station. The compaction treatment was produced by wheelings, and the area between the wheelings was used as the control. The wheeled and unwheeled areas were sampled 4 times, in spring and after harvest in 1979 and 1980 The following techniques were used to monitor regeneration: measuring the profile of the soil surface in the field and laboratory measurements of air-filled pore space, water retention, shrinkage and clod density, micromorphometry and mercury intrusion. Compaction decreased the macroporosity (pores >60 μ m diameter) by over a half. Pores μ m diameter were unaffected by compaction. Natural regeneration of porosity in the top 5 cm was achieved within 18 months, but the soil below remained compacted for longer. The regenerated structure consisted mainly of planar voids induced by physical processes unlike the unwheeled soil which was characterised by packing voids and biopores.

Abstract: Soil compaction and substrate modification produced during large-scale armored military maneuvers in the early 1940s were examined in 1981 at seven sites in California’s eastern Mojave Desert Recording penetrometer measurements show that tracks left by a single pass of an M3 “medium” tank have average soil resistance values that are 50% greater than those of the surrounding untracked soil in the upper 20 cm At one site, measurements made along short segments of track that have been visually eliminated by erosion and deposition processes show a 73% increase in penetrometer resistance over adjacent, undisturbed soils Dirt roadways at three former base camp locations could not be penetrated below 5–10 cm because of extreme compaction Soil bulk density was not as sensitive an indicator of soil compaction as was penetrometer resistance Density values in the upper 10 cm of soil are not significantly different between tank tracks and undisturbed soils at most sites, and roadways at two base camps show an average increase in bulk density of only 12% over adjacent soils. Trench excavations across tank tracks show that physical modifications of the substrate can extend vertically beneath a track to a depth of 25 cm and outward from a track’s edge to 50 cm These soil disturbances are probably major factors that encourage accelerated soil erosion throughout the manuever area and also retard or prevent the return of vegetation to pre-disturbance conditions