Soil Fertility Protocol Welcome Purpose Life Sciences To measure the amounts of nitrogen (N), Atoms and molecules cycle among the phosphorus (P), and potassium (K) in each living and nonliving components of horizon in a soil profile the ecosystem. Scientific Inquiry Abilities Overview Identify answerable questions. Using a NPK test kit, students mix a dry, Design and conduct sieved soil sample into a solution and an investigation. Introduction chemically extract the N, P, and K as nitrate, Use appropriate tools and techniques phosphate, and potassium. The N, P, and including mathematics to gather, K amounts in the sample are determined analyze, and interpret data. by comparing the solution to a color chart. Develop descriptions and explanations, Students describe the N, P, K amounts predictions and models using as high, medium, low, or none. These evidence. measurements are conducted three times Communicate procedures for each horizon. and explanations. Time Student Outcomes One 45-minute class period for three groups Students will be able to measure the nitrate of students to analyze one horizon. nitrogen, phosphate phosphorus and Protocols potassium contents of soils. Level Students will be able to relate soil fertility Middle and Secondary to the physical and chemical properties of Frequency the soil. Once for each soil profile Science Concepts Materials and Tools Earth and Space Sciences Soils store nutrients in different Oven-dried, sieved soil (sieved with a amounts depending on the type of Number 10 sieve with 2 mm mesh Activities Learning nutrient and the soil properties. attached to a frame) Soils have properties of color, texture, GLOBE (or equivalent) NPK kit structure, consistence, density, pH, Distilled water fertility; they support the growth of Beaker many types of plants. Teaspoon The surface of Earth changes. Clock or stopwatch Soils are often found in layers, with Soil Fertility Data Sheet (more than one each having a different chemical Data Sheet may be needed for each composition and texture. profile) Soils consist of minerals (less than 2 Latex gloves mm), organic material, air and water. Goggles Water circulates through soil Preparation changing the properties of both the Appendix soil and the water. Obtain dry, sieved soil samples. Physical Sciences Collect required equipment. Objects have observable properties. Spread out newspapers or other cover on Chemical reactions take place in every table to keep area clean. part of the environment. Prerequisites Soil Characterization Protocol GLOBE® 2014 Soil Fertility Protocol - 1 Soil (Pedosphere) Soil Fertility Protocol – The Soil Fertility Protocol measures the abundance of three nutrients: nitrate (nitrogen), Introduction phosphate (phosphorus), and potassium, in In order to grow, plants require sunlight, each horizon of a soil profile to determine if water, air, heat, and nutrients. Table SO-FE-1 the soil is fertile for plant growth. lists the macronutrients (nutrients required in Nitrogen (N) is an element found in high large amounts) and micronutrients (nutrients concentrations in the atmosphere, but relatively required in smaller quantities) required for low concentrations in soil. For nitrogen to be plant growth. The fertility of a soil indicates used by most living things, the N2 molecules the availability of these nutrients for plants must be broken apart. In soil and water, this to grow. usable nitrogen takes the form of nitrate (NO3), nitrite (NO2) and ammonium (NH4), with Table SO-FE-1 nitrate being the most common. In general, these forms of nitrogen are rapidly taken up Macronutrients Micronutrients by plants and are an important component Nitrogen (N) Iron (Fe) of plant proteins. Nitrate (NO3-), because of its negative charge, is not held by negatively Phosphorus (P) Zinc (Zn) charged soil particles and is easily removed Potassium (K) Manganese (Mn) (leached) from the soil as water passes through Sulfur (S) Copper (Cu) it. Nitrate can also be converted to nitrogen gas (N2) or ammonia (NH3) and be volatilized Calcium (Ca) Boron (B) (evaporated or removed as a gas) out of the Magnesium (Mg) Molybdenum (Mo) soil. Therefore, it is important that farmers and Chlorine (Cl) gardeners add nitrogen fertilizers when plants need the nutrient the most and can absorb it Some soil nutrients are positively charged, before it is removed from the soil by leaching. while other nutrients are negatively charged. When nitrogen is added to the soil in the form Nutrients that are positively charged, such as of organic matter, it is stored longer because potassium, calcium, and magnesium, are held it becomes available to plants slowly, as the by negatively charged soil particles. These organic matter decomposes. nutrients are removed from the soil by plants or Phosphorus (P) is used as part of the energy by weathering processes. Negatively charged pathway in the plant. Plants use phosphorus -3 particles, such as nitrogen (in the common in the form of phosphate (PO4 ). Because form of nitrate), phosphorus (in the common of its negative charge, phosphate is easily form of phosphate) and sulfur (in the common leached from the soil. Plants are only able to form of sulfate) are not held by negatively take up phosphate when soils are at neutral charged soil particles. These nutrients are soil pH values of 5.0-8.0. At low pH values more easily leached and removed from the (<5.0), phosphate combines with iron (Fe) and soil. When a soil loses its nutrients or does not aluminum (Al) to form phosphates that are not have the nutrients needed for plant growth, soluble and cannot be taken up by plants. At farmers and gardeners replenish nutrients by high pH values (>8.0), phosphate combines adding fertilizers to soils. with calcium (Ca) to form calcium phosphate, which is neither soluble nor available for plants Figure SO-FE-1 Soil in low pH (acidic) conditions Soil in high pH (basic) conditions K+ K+ –3 –3 PO4 PO4 – – – – – – NO3 – – NO3 – – – – Clay Particle Clay Particle – – – – – – NO – – – NO – – 3 – 3 K+ K+ AIPO4 CaHPO4 GLOBE® 2014 Soil Fertility Protocol - 2 Soil (Pedosphere) to take up from the soil. When phosphate longer may give erroneous results. occurs in one of these insoluble compounds, Welcome it becomes easy to remove from the soil when Based on previous experience with the the soil particles are eroded. Like nitrogen, GLOBE soil test kit, almost all readings for phosphorus is also more slowly and easily nitrate nitrogen result in values of none or low. available to plants when it is added as part of This may be due to the rapid removal of nitrate decomposing organic matter. from the soil once it has been added (either by plant uptake or leaching) or due to the lack of Potassium (K) plays the role of activating cell sensitivity of the kit to measure nitrate. enzymes in plants. It is readily available to plants in its elemental state (K+), and because With some soil samples, especially those of its positive charge, is easily stored on high in clay, students will need to repeat the extraction procedure more than once to obtain negatively charged soil particles. The largest Introduction source of potassium is from the decomposition enough solution for the N, P, and K analysis. of potassium containing minerals, such as mica. Managing Students In order to complete the analysis within a class period, have different students do the Teacher Support analysis for N, P, and K simultaneously after the extraction solution has been made. Preparation Make sure students understand the importance Safety Procedures of each nutrient they are measuring before they conduct the Soil Fertility Protocol. 1. Students should wear gloves when handling chemicals and the water Have students review the NPK kit instructions sample. Protocols before conducting the Soil Fertility Protocol. 2. Students should wear goggles when working with chemicals. They should Managing Materials also wear surgical masks when To measure soil fertility, students may use a opening powdered reagents. GLOBE soil test kit or an equivalent product 3. School authorities should be consulted that produces a relative value for nitrate, on the proper disposal of used phosphate, and potassium. chemicals. Measurement Procedures Questions for Further Investigation Activities Learning How might natural changes affect the fertility The basic method for measuring soil fertility of a horizon? consists of mixing a soil sample with water and chemically extracting the N, P, and K as What differences between locations could nitrate, phosphate, and potassium. The N, P, affect the fertility of a horizon? and K amounts in the sample are determined How does the soil fertility affect the types of by comparing the solution to a color chart. vegetation that can grow on a soil? How does the soil particle size distribution Using the GLOBE soil test kit to determine affect the nutrient content of a horizon? nitrogen (N), students compare the extraction solution with a pink color chart. To determine How does climate affect the nutrient content phosphorus (P), students compare the of a horizon? extraction with a blue color chart. To determine How does the type of vegetation growing on the soil affect the nutrient content of the soil? potassium (K), the students place the tube Appendix containing the extraction solution over a column of black boxes, and the amount of the blackness that can be observed through the cloudiness of the solution is compared with the column next to the tube. Students should wait no more than 10 minutes to read the color change in each tube. Waiting GLOBE® 2014 Soil Fertility Protocol - 3 Soil (Pedosphere) Soil Fertility Protocol Lab Guide Task To obtain three soil fertility readings for every horizon in a soil profile What You Need q Dried sieved soil q Distilled water q Soil Fertility Data Sheet q Pencil or pen q Plastic teaspoon q Latex gloves q GLOBE NPK test kit or equivalent kit (that q Goggles measures the relative amount of nitrate, phosphate, and potassium in a soil sample) Part 1.