Abstract: The urban environment imposes severe stress upon vegetation The problems are many, and interactions common, making simple solutions difficult This paper on urban soils discusses basic soil physics and soil chemistry, reviews some existing literature, and describes several research efforts in Washington Particular emphasis is placed on soil compaction and ways to minimize its deleterious effects upon vegetation This year is the 200th birthday of the United States and estimates of visitation to the Washington metropolitan area range between 15- 60 million Most of these visitors will presumably descend upon Washington between Memorial Day and Labor Day Naturally National Capital Parks, National Park Service is aware of the extreme impact this number of visitors will have upon our urban parks and are taking some steps to minimize this impact At present, National Capital Parks has jurisdictional and management responsibilities for nearly 23% of the land area within the District of Columbia's boundaries, including all of the National Monuments from the White House down through the lesser important monuments

Abstract: SummaryGrowth analysis of carrots grown in water culture has shown that dry matter accumulation and growth in size are severely affected by lack of aeration of the medium, top growth being particularly affected. Exposure of the top few cm of the tap root to the air ameliorates this condition to a limited extent. Although plants grown at all times without aeration appear to adapt to such conditions to some degree, a rapid change to non-aerated conditions has disastrous effects and causes severe leaf senescence. Subsequent formation of lateral roots at the upper end of the tap root may serve to increase O2 uptake by the root system. Transfer from non-aerated to fully aerated conditions provokes a rapid increase of top growth, suggesting the involvement of root-produced cytokinins. Soil compaction also has major effects on root growth and length, very loose or highly compacted conditions being detrimental to overall growth. With high compaction normally cylindrical tap roots become sharply conical.

Abstract: SOIL density patterns were deter-mined in a clay soil field at various moisture contents using different tire sizes with varying loads and repeated passes. Laboratory tests were performed on the field samples to determine plastic and liquid limits and compaction properties of the soil. The maximum change in dry density occurred between 12-26 cm under the center of the tires. Increases in dry density reached levels up to 0.35 g/cm3 after multiple passes of the tires.

Abstract: An investigation was conducted to determine the influence of dry density and initial water content on the erosion of a compacted dispersive clay. The pinhole test developed by James Sherard and associates was used to model the erosion conditions which occur in earth dams. When the soil specimens, compacted to densities representative of standard and modified Proctor effort were eroded under a roughly constant erosional shear stress, it was found that a minimum amount of erosion occurred at a water content about 2 to 3 percent wet of optimum water content. It was also found that, at the same water content, the amount of erosion tended to decrease with an increase in the dry density. However, neither water content nor density strongly controlled the dispersiveness of the soil. A mechanism of erosion was suggested to account for the observed reactions. Also, it was found that the turbidity of the eroding water can be correlated with the concentration of suspended soil.

Abstract: A pot-culture, a field experiment and a laboratory tube-study using clay loam vertisol (0–20 cm) were conducted to study the effect of soil compaction on root cation exchange capacity (root-CEC) of one monocot and seven dicot crop plants. Over a bulk density range studied (1.10 to 1.85 g cm-3), soil compaction increased root-CEC on a unit weight basis as well as on a unit surface area basis, probably due to increase in percentage of the nitrogen content of the roots and carboxyl groups on roots of the crop plants studied. re]19760407

Abstract: Erosion studies were conducted with laboratory apparatus which produced a piping-type failure within compacted cohesive soil specimens. No artificial opening was preformed in the specimens. The erosion potential was foundto be strongly dependent upon the soil type and its chemical properties, the compaction water content, and the chemical composition of the eroding water. Interactions among the variables were important. The combination of wet side compaction and low ion concentration eroding water was found to produce extremely low resistance to erosion for some soil.

Abstract: The problem of soil compaction by rollers is complex due to influences of a great number of variables of the soil-machine system. Instead of trying to determine the influence of each variable separately, author analyzes the problem using a stochastic model, based on measurements of the maximum vertical stress and density exerted in the soil at different depths and for varying numbers of passes of the roller. The necessary number of passes is determined such that the greatest compaction of the soil at a certain depth is achieved with a probability of 95 percent at a level of significance equal to 0.05. The expected density values agreed with densities found by the Proctor method. Application of the method is illustrated by an example where the soil consists of uniform sand with an unusually high angle of internal friction. Paper is recommended for scientists and soil engineers interested in the application of probability theory. /Author/