SoilTestingLabw_Introduction.pdf - Ms Kaidy APES SOIL T:HE WEALTH BENEATH YOUR FEET BACKGROUND Unless you are a farmer or a gardener you probably think

SoilTestingLabw_Introduction.pdf - Ms Kaidy APES SOIL T:HE...

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Unformatted text preview: Ms. Kaidy APES SOIL: T:HE WEALTH BENEATH YOUR FEET BACKGROUND Unless you are a farmer or a gardener, you probably think of soil as "dirt" - as something you don't want on your hands, clothes, or carpet. Yet your life, and the lives of most other organisms, depends on soil, especially topsoil. Soil is not only the basis of agricultural food production, but is essential for the production of many other plant products such as wood.. paper, cotton, and medicines. ln addition, soil helps purify the water we drink, and is important in the decomposition and recycling of bio-degradable wastes. Nations, including the United States, have been built on the riches of their soils. Yet since the beginnings of agriculture people have abused this vital, potentially renewable resource: entire civilizations have collapsed because of mismanagement of the topsoil that supported their populations. Today, we are not only facing loss of soil from erosion, we are also depleting nutrients in some soils and adding toxins to others. SOIL TEXTURE Through the process of weathering, mineral rocks are broken down over long periods oftime into fine particles of clay (very fine particles less than 0.002 mm in diameter), silt (0.002 to O.OS mm) and sand (0.5 to 1.0 mm). The relative amounts of the different sizes of particles control two very important properties of soil: its fertility and its ability to hold water (see Table 1) TABLE 1: Relationship between soil components and various important properties of soil SOIL WATER · INFILTRATION WATER NUTRIENT HOLDING AERATION WORKABILITY ("TILTH') CAPACITY CAPACITY HOLDING CAPACITY CLAY POOR GOOD GOOD POOR POOR SILT MEDIUM MEDIUM MEDIIUM MEDIUM MEDIUM SAND EXCELLENT POOR POOR GOOD GOOD ORGANIC GOOD EXCELLENT EXCELLENT COMPONENT MATTER POOR TO POOR TO GOOD GOOD Soil fertility is measured by the amount of nutrients available for plant growth. These nutrients in soils are usually found in the form of positively charged ions such as NH\ Ca", or K+. Since the very small particles of clay (called micelles) often have a negative charge, these ions can be held in the soil on the surface of the micelles. The larger particles of silt and sand do not have this negative charge. Thus soils with more clay tend to be more fertile. The infiltration (absorption) and retention of water in soil are also important. Soils with low infiltration, such as clay, are more likely to have high runoff after rain and the potential for flooding. Yet these soils can retain a good deal of water. ln contrast, sandy soils have very high infiltration, rates, but are. unable to retain much water {most of the water continues to flow through the soil to the water table). High Jnflltrationcan result in leaching, the loss of. nutrient ions from the lavensofsoil where-roots are most abundant. These soils are more likely to be infertile,.arid,the,leaGhete, can ·ha't,e high.ceneentratlons of nutrients and pegicid~,s, polluting both .the watertable.and-adjacent riyer-s and lakes. •. ·:; f • ; ;'_. '·,. ~ . •. "'. ~ . . , .. !,-.-• . ' . ., . . . , . Thus, the "best" soils, called loam, are a mixture ofsand, silt, and clay. These sells 'contain the best of each ofthe.•textural components, andhave.relatlve high fertility and at the.same time , .. relatively hlgh wate1r1holding•oapê3(:ity;,\,'., " - ,.,, .. · :· /:~~·:;;. ,"lf\;'f: ·_~ ..~-~-.-\<. .· ,:t· :- ·. SOIL ORqANIC MAIT~ff Organic matter is another very important compèrieht of soils. Not only is the organ io matter the source of most nutrients (derived from the decomposition of dead plant and animal materials), but lt, tO'(!); is composed of small; negatively charged micelles. Thus, like 'clay~ organic matter in the-sbil1is)impoH:ant;in,re.taining,nuit11ient ions. ln addition, organic matter is. excellent at absorbing arrd'holdlng waterln-the soll. -ln-sorne cases, the addition of organic matter can increase the water-holding capacity ofa soil 9-fold! Peat moss is an example of organic matter that can bé added tó soil. SOIL pH The acidity (pH) of a soil is another factor determining the nutrient status of a soil. ln general, more acid soils (lower pH) have lower fertility than more basic soils because the H+ ions in the acid displace the positively charged nutrient ions in the soil micelle. These nutrient ions can then be leached from the soil. ln this exercise, you will be either "constructing" your own soil or testing an unknown soil sample. Before you do so, you must learn how to test for the infiltration rate, the waterholding capacity, and the nutrient retention of each component of the soil. You will also test to determine the percentage of each soil component in a soil sample, and will determine the type of soil in your sample from the Soil Texture Triangle. SOIL TEXTURE BY FEEL Mapted fran: st.eve J. Thien, 1979 Place approximately 2 tsp. soil in palm. Add Yater dropYise and knead soil to break doYn all aggregates. Soil is at proper consistency vhen plastic and moldable like moist putty. Does.soil remain in a ball vhen squeezed? Add dry soil to soak up water. 8 Is too too YES Place ball of soil between thumb and forefinger, gently pushing the soil with thumb, squeezing it upYard into a ribbon. Form a ribbon of uniform thickness and width. Allow the ribbon to emerge and extend over forefinger, breaking from its own weight. Does soil form ribbon? YES f sc~~e!ëil:l a weak ~ : 't¡f ~ ibbon <,l bef (·~, ..;¡~:,¡• Does soil mar.<? a medium ribbon 1-2" long before. ·t breaks? ( onç e r befor it breaks? YES &xctsm~J tel ¡ sull 1ilc\ 01 '-lliU1 pü1/ ut rt] riü lorèl~er HI~ î ~) % Does soil feel very gritty? YES l NO HO Neither gritty nor smooth predominantly? s Q V.. . . . . . ._--,, A N D Does soil feel very gritty? Does soil. feel very gritty? Does soil feel very s111ootb? Neither gritty nor smooth predominan Neither gritty nor smooth predominantly? NO soil feel very smooth? ~ Does Does soil feel very smooth? -~ .LO---------% CLAY---~---HI l. - i I t J. iOIL TEXTURE CLASSES ,-0 ~ (l (') ..,,.... Ú'. ~ 1.--~->:--'\o\---'-_,.-~~--,bf===::;!::======-:~ · "l- - - .X- --"" - -L- - - ..::::M. - - ---" '-- - - :.(!._ - - ..){...i¡. - - ~ - - _:,¡_ - - _.:,¡_ :__ _ 'aV ~I' ~ V V Percent sand I ,• _I ~ tß & __i.o. . , Soil: The Wealth Beneath Your Feet PROCEDURES A. Testing the Percolation Rate and the Water Holding Capacity of Soil Components: a. Using a graduated cylinder, measure out 125 mL each of clay, silt, and sand. Pour each sample into a clear container /tube, and compact sample by gently bouncing the tubes on the table. b. Percolation Rate: Fill a graduated cylinder with 50 mL water. Starting with the clay tube, pour about 25 mL of water into the tube in a steady stream, trying not to disrupt the soil surface. c. Note the time when you start to pour and the volume of water poured. The stop time is when all the water has been absorbed from the surface of the soils and the water has reached the bottom of the tube, saturating the soil. If the surface water is almost gone and there is still dry material in the tube, add more water, estimating about how much will be needed to completely soak the material. Keep track of the total amount of water used. d. Calculate the percolation rate as mL/min/area (remember the equation for the surface of a circle). Record in data table l. e. Repeat procedure for the silt and sand tubes. B. Water Holding Capacity: a. Continue to add water to your samples (keep track of the total volume of water added, including the amount added in #2 above) until the sample is completely saturated and water begins to pool in the bottom of the tube. Decant off any standing water from the sand tube and/or the silt tube by placing your hand over the opening and tilting the tube over the sink to allow excess water to run off. b. Remove three samples (approximately 1 tablespoon each) from each tube and place sample in its own aluminum container or on a small piece of aluminum foil. c. Weigh each of the three samples separately, and them place either in the incubator or in the bright sunlit window to dry. d. After completely drying, weigh each sample again and calculate water holding capacity for each sample by using the following formula and record in data table 2. Wet Mass - Dry Mass x (100) Dry Mass C. Determination of Soil Composition by Separation of Layers: a. Place approximately 25 mL of field soil in 100 mL graduated cylinder. Make sure it is free of roots, stones, etc., and is well broken up. b. Add water to the 75 mL line. c. Cover the cylinder with parafilm, place the palm of your hand firmly over the opening, and invert the cylinder several times until the soil is thoroughly suspended in the water. d. Place the cylinder on the lab bench and leave it overnight. e. When the soil has settled out, there should be three reasonable distinct layers - sand, silt, and clay. Measure the volume of each layer and the total volume of the sample. f. Calculate the percent of each of the components. Be sure not to count the water. g. Record results in data table 4. D. Determination of Soil Composition by Using Soil Texture: a. Use the following flow chart to determine the percentage composition of field soil sample. b. Record results in data table 4. E. Soil Nutrient Testing: a. Follow the directions on the various kits to test soil for nitrogen levels, phosphorus levels, potassium levels, and pH levels. b. Record the results in data table 3. Soil Lab Write Up: Please read the lab background information before answering these questions. 1 c omp 1 e t e th e fo li owmg t a bl e: Component Percolation Rate Water Holding Capacity Gravel Sand Fine Sand or Silt 2. Make a summary statement regarding the data presented in the table. 3. Given the information in the soil texture triangle, and based on the knowledge you have developed about soil types and water in this lab, answer the following question: a. Which of the following soil types might you expect would support more vegetation - sandy loam or silty clay? Why? (assume that for the best vegetation both too little and too much water are problems) 4. If you were to test nutrient holding capacity in the three particle sizes, which would you expect to hold nutrients the best - sand, silt, or clay? What chemical characteristic causes these particles to bind to nutrients? Explain. 5. If you were a farmer and wanted to increase water holding capacity, what might you add to the soil to amend it? If your soil is too acidic, what could you add to adjust the pH? (you might need to research this) 6. If the A horizon in a soil sample measures 3 inches, and the rate of top soil for temperate deciduous forest (where the soil was sampled) is 1 inch/225 years, how long did it take for this horizon to develop? 7. Which of the procedures in this lab demonstrated porosity? Explain, using a definition of porosity in your explanation. 8. Which of the procedures in this lab demonstrated permeability? Explain, including a definition of permeability in your explanation. 9. List below the physical and chemical test used in this lab: Physical Tests Chemical Tests ...
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