4/1/2024 0 Comments Density of water gcm3Moisture content measured using weight is determined by drying a moist sample to a constant weight. The moisture content of a soil can be expressed using either weight or volume. Mostly hygroscopic water held too tightly in micropores to be plant Water held at field capacity – water held at wilting point Water that drains from macropores too rapidly for plants to use Water content at saturation – water held at field capacity Classes, calculations, and explanations of soil water. Soil moisture classes and important points on the soil moisture relationship curve. Therefore, for a plant, field capacity and wilting point are most important because they determine the amount of plant-available water. The important points on the continuum include saturation, field capacity, wilting point, air dry, and oven dry. However, to understand moisture availability to plants, we break the continuum into parts and give each part a name or classification, as shown in Figure 9.2 and explained in Table 9.1. The relationship between soil moisture content and soil moisture potential is a continuum. Relationship between moisture content and moisture potential for three soils down to -100 kPa. The reason for this is that clayey soils have a higher porosity, and can hold on to more water at a given soil water potential. In general as clay content increases, the soil water content increases for a given soil moisture potential. Water content and water potential are related as shown in Figure 9.1 for five soils of differing textures. These potentials are described in units of pressure, generally kilopascals (kPa). The energy relationships between free water and soil moisture are generally expressed in terms of soil-water potentials. The retention and movement of water in soils, its uptake and translocation in plants, and its loss to the atmosphere are all energy-related phenomena. Water, which can limit plant growth, is probably most important in evaluating land use, influencing soil characteristics for most land uses. The soil-water-air continuum involves principles of physics, chemistry, and biology. How many cm of water in one bar? How many kPa in one bar? How many cm of water in one kPa?Īn understanding of soil-water relationships is essential to proper soil management for agronomic or other land use purposes. Common units used to quantify moisture potential are cm (of water), bars, and kPa.Show how to convert between these weight and volume. Compare and contrast soil water content on a weight (mass) basis and a volume basis.Identify the matric potential values (soil water potential) for saturation, field capacity, wilting point, air dry, and oven dry soil.Relate each to the different pore sizes (macro-, meso-, and micro-). Define and compare gravitational water, plant available water, and unavailable water.Define soil water potential in your own words.These definitions/questions will provide a concise summary of the major concepts to be addressed in the lab. Using the recommended reading resources and the introduction to this lab, consider the questions listed below.
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