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LABORATORY EXPERIMENTS

# LABORATORY EXPERIMENTS - SOIL PHYSICS LABORATORY...

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SOIL PHYSICS LABORATORY EXPERIMENTS The laboratory exercises are designed to supplement materials covered during the lectures and to acquaint students with methods and equipment used to obtain some of the important physical properties of soil. Due to lack of space and time, most experiments will not be duplicated. A few of the experiments will involve demonstrations of equipment only. The write up of the laboratory experiments should include: a) General Introduction b) Experimental objectives c) A list of apparatus and materials used d) A description of experimental procedures e) Data collected f) Reduced data in terms of tables and figures g) A discussion of the results and conclusions h) Brief answers to questions asked

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EXPERIMENT #1 TITLE: Soil sampling and determination of bulk density of soil. See video Lab-I. INTRODUCTION The dry bulk density of a soil is the ratio of the mass of dried solids (105°C) to its total or bulk volume (includes both solids and pore space). Bulk density is generally expressed in units of g cm-3. By definition ρb is always smaller than the soil particle density ρs which has an average value of 2.65 g cm-3 for many mineral soils. In coarse-textured soils can be as large as 1.6 g cm-3, whereas in fine textured soils it can be as low as 1.1 g cm-3 . However the structure for a soil having a given texture is a major determinant in the magnitude of ρb. For this reason ρb is often used as an approximate measure of soil structure. For example in fine-textured soil, ρb will tend to be smallest when the soil particles are highly aggregated (loose arrangement). Mechanical compaction of an aggregated soil, such as by the movement of heavy farm equipment over the surface, will tend to increase ρb. If such a soil is very wet during the passing of heavy equipment over the surface, puddling of the soil may also decrease the degree of aggregation which also tends to increase ρb. Even in extremely compacted soil, however, the bulk density remains appreciably lower than the particle density, since the particles can never interlock perfectly. Thus the soil remains a porous body, never completely impervious. In soils high in clay content, ρb is highly variable as the soil alternately swells, shrinks, aggregates, disperses, compacts and cracks. Bulk density is a widely used soil property. It is needed for converting water percentage by weight to content by volume, for calculating porosity when the particle density is known, and for estimating the weight of a volume of soil too large to weigh conveniently, such as the weight of a furrow slice, or an acre-foot. Bulk density is also needed to convert chemical contents of soil from a weight basis to a volume basis. The core method has been used for many years to determine pb in soil profiles. With this method, a cylindrical metal sampler is driven into the soil to the desired depth and is carefully removed to preserve a known volume of sample as it existed in situ. The sample is dried to 105°C and weighed. Bulk density is the oven-dried mass divided by the field volume of the
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LABORATORY EXPERIMENTS - SOIL PHYSICS LABORATORY...

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