Determination of Moisture Content

DETERMINATION OF MOISTURE CONTENT, CONTENT WEIGHT, AND TOTAL PORE SPACE I. MOISTURE CONTENT Soil consists of three phases, namely liquid, gaseous and solid. The liquid phase is groundwater that fills part or all of the empty space between the particles soil. One of the roles of soil in the environment is as a water storage place related to cations, anions, weathering of organic matter and microbody activities. Groundwater is found in micropores or as a membrane around soil particles. The unretained water will fill the pores and then seep down due to the gravitational force. Water retention by the soil and the tendency of water to move in the soil, from soil to plants and from plants to the atmosphere are the result of potential differences, due to energy differences. Like other objects in nature, groundwater also has energy in various forms. In classical physics, 2 forms of energy are known, namely kinetic energy and potential energy. Since the movement of water in the soil is quite slow, its kinetic energy is negligible. The potential energy of groundwater determined by the internal state of the soil is very diverse. The total potential of groundwater is the sum of the influences of various forces, namely: gravitational potential, matrix potential, osmotic potential and other potential possibilities that are less important. The gravitational potential plays an important role in removing excess water. The osmotic potential is caused by the presence of dissolved materials in the soil that can reduce the free energy of water due to ions and/or solute molecules that attract water molecules. So the potential value is negative. The potential matrix is the result of the capability force and the adsorption force caused by the soil matrix. Both forces decrease the free energy of groundwater, so the potential value of the matrix will always be negative. The potential values that greatly affect the water-soil-plant relationship are matrix and osmotic potentials. Since the matrix and osmotic potentials are negative, they are often called stress or suction. The common way to express the voltage is the high or column of water. Groundwater can be classified into: (1) gravitational water, (2) capillary water, and (3) hygroscopic water. Gravitational water is water that cannot be held by the ground, but seeps downwards due to the influence of gravitational forces and exists between 0.1 and 0.5 atmospheric tensions. Capillary water is water that is squeezed, usually a layer that exists around soil particles and is in a pore space with a voltage of 0.1 and 31 atmospheres. Hygroscopic water is water that is adsorbed from water vapor in the ground air by soil particles. This water is attached to the surface of soil particles in the form of a thin membrane. This layer is held 9 strong so that it does not evaporate easily under normal conditions. Hygroscopic water cannot be absorbed by plants and is at a voltage between 31 to 10000 atmospheres. To find out the state of groundwater in relation to plant growth, it is necessary to determine the soil moisture content in several circumstances, such as (1) total moisture content, (2) field capacity, and (3) permanent wilting point. Total moisture content is the soil moisture content obtained by drying dry soil air in the oven at a temperature of 105°C until the weight is fixed. Field capacity is the amount of water retained by the ground after excess gravity water seeps down due to the force of gravity. The permanent wilting point is the content of groundwater when the plants planted on it have experienced permanent wilting in the sense that it is difficult to heal again even though a sufficient amount of water has been added. The difference between the moisture content at the field capacity and the permanent wilting point is called the available water. In the practicum, the total moisture content will be determined by gravimetric. This moisture content data will be used in the calculation of determining other soil properties. How Gravimetric Moisture Content Determination Works In the gravimetric method, the moisture content is determined directly by measuring the weight loss due to water loss due to soil drainage. The stages of the work are as follows: 1. Put a sample of soil (± 10 g) into a clean and dry weighing bottle and know the weight, then weigh it correctly. 2. Dry the soil sample in the oven (bottle lid open) at 105°C until the weight remains (± 24 hours). 3. Cool the weigh bottle and its contents in the accicator until it reaches room temperature (weigh bottle closed), then weigh it precisely. 4. Calculate the moisture content on the basis of the dry soil weight of the 105°C oven with the following equation: Water weight = bottle weight of moist soil – weight of bottle of dry soil 105°C Dry soil weight 105°C = weight of a bottle containing dry soil 105°C – bottle weight. Water weight % of soil moisture content = x 100% dry soil weight 105°C 2. Weight of Soil Contents and Total Soil Pore Space 10 Fill density is the dry weight of one unit of soil volume in an intact state. The unit of soil content weight is usually expressed in g/cm3. Fill density value 11 Soil can be used to estimate soil constituent materials (mineral materials or organic matter) and soil density. Solid soils have a high fill density and conversely, loose soils have a low fill density. The total pore space of the soil is the entire room in the whole soil occupied by air and water. The pore space of the soil is expressed in percent (%) of the volume of intact soil. The total pore space of the soil is very closely related to the density of the soil and the availability of water and air in the soil. Determination of Soil Content Weight: Materials and Tools Required: 1. Example of whole soil 2. Scales, weighing cups 3. Oven, gegep, accicator How it works 1. Weigh the example of whole soil with the tube, for example Ag 2. Take a sample of soil from inside a 20 g ± tube for moisture content determination 3. Clean the tube and weigh it, e.g. B g 4. Set the water content of the soil sample taken (item 2), e.g. C g 5. Measure the inner diameter of the tube e.g. D cm 6. Measure the height of the tube, e.g. T cm 7. Calculate the density of the contents in the following way: a. Calculate the weight of moist soil = (A – B) g b. Calculate the weight of dry soil with the formula : BL BK = KA + 1 BK = dry soil weight BL = Moist soil weight C KA = moisture content = 100 (A – B) So: BK = 12 (C/100 +1 Calculate tube volume D2 V (cm2) = II x x T 2 13 BK d. Soil content density = g/cm3 V 3. Determination of Total Soil Pore Space The determination of soil pore space (RPT) is carried out using data on content density (KI) and particle type density (KJP) with the calculation as next: Soil volume – Volume of solids RPT = x 100% Land Volume Soil volume – Volume of solids = x 100% Land Volume - Land Volume (Land weight/KJP) = 1 – x 100% (Ground weight/KI) Weight of IP land = 1- x x 100% KJP Ground weight KI = 1 - x 100% KJP Note : The density of soil particle types varies depending on the content of organic matter and the type of mineral. For mineral soils, the number 2.65 is used. If the organic matter content is more than 1%, the KJP value is reduced by 0.02 for each percent of organic matter. For peatlands, KJP measurements must be carried out directly. 14