* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Soil
Survey
Document related concepts
Arbuscular mycorrhiza wikipedia , lookup
Human impact on the nitrogen cycle wikipedia , lookup
Soil erosion wikipedia , lookup
Soil horizon wikipedia , lookup
Soil respiration wikipedia , lookup
Crop rotation wikipedia , lookup
Surface runoff wikipedia , lookup
Soil compaction (agriculture) wikipedia , lookup
Plant nutrition wikipedia , lookup
Terra preta wikipedia , lookup
Canadian system of soil classification wikipedia , lookup
No-till farming wikipedia , lookup
Soil food web wikipedia , lookup
Soil salinity control wikipedia , lookup
Soil contamination wikipedia , lookup
Transcript
Before you start the PowerPoint press F11 To maximize the screen and the button below if you need to print the work sheet Soil What is Soil? Components of Soil Soil has five components 1. Mineral particles 2. Organic matter 3. Water 4. Air 5. Living organisms 1. Mineral Particles There are five types of mineral particle in soil and these are defined by their size. Gravel greater than 2mm in size Coarse Sand between 2mm and 0.2mm Fine Sand between 0.2mm and 0.02mm Silt between 0.02mm and 0.002mm Clay less than 0. 0.002mm 1. Mineral Particles, soil texture The proportion of each type of mineral particle makes up the soil texture. A soil texture diagram can be used to calculate the type of soil on the basis of the proportion of sand silt and clay 1. Mineral Particles, texture silt clay sand A soil is composed of 30% clay 20% silt and 50% sand = Sandy,clay, loam 1. Mineral Particles, clay The most important mineral particle in soil is clay. Clay particles are very small, less than 0.002 mm, and, usually are flattened They have an enormous surface area. 1gm of clay can have a surface area between 5-250 metre2 1. Mineral Particles, clay The clay particles are charged, with many negative and some positive charges on their surface, and this gives them many important properties 1. Mineral Particles, clay Clay particles are colloidal, that is, if placed in water, they form weak hydrogen bonds with water molecules which causes them to stay in suspension. 1. Mineral Particles, clay Cations bonded to clay e.g. positively charged ions of magnesium and calcium The clay particles form part of the cation exchange capacity of soil. The clay particles bind to positively charged ions (cations) of nutrients such as magnesium and calcium. If a soil lacks clay it would inevitably be less fertile since it will lack the capacity to hold many nutrients in the soil. 1. Mineral Particles, clay and nutrients Clay particles have few positive charges so that negatively charged nutrient ions such as nitrates are much more easily leached from soils. 2. Organic Matter The majority of soils contain large amounts of dead organic matter, DOM. This comes mostly from the remains of plants, leaves, roots etc, These plant remains are broken down by decomposers and saprobionts into humus; the process is called humification. Humus is made of dead organic matter but it does not contain recognizable plant remains. The DOM and the humus are important in soil for several reasons. Plants Dead organic matter Decomposers/ saprobionts humification humus carbon dioxide Decomposers/ saprobionts mineralisation minerals carbon dioxide 2. Organic Matter, water Water forms hydrogen bonds with the dead organic matter and the humus in soil. If a soil lacks dead organic matter it is less likely to be able to retain water. In a sand dunes as succession proceeds the organic content of the soil increases and as it does so, the ability of the sandy soil to hold water increases. 2. Organic Matter, structure Soil structure is the way in which the mineral skeleton and the organic matter in the soil are aggregated together. There are a number of different types of soil structure or peds. 2. Organic Matter, structure, peds. Ped Diagram Description Crumb Typical of rich topsoils under grass or deciduous woodland. Soil organisms thoroughly mix DOM with the mineral soil. Well aerated and with good water and nutrient retention, it is an ideal soil for plant growth. Blocky Angular blocky structure is typical of deeper, clay-rich subsoils and develops as the soil cracks during dry seasons. In wet seasons the clay swells and the cracks close up again, hence this structure is only slowly permeable leading to poor drainage conditions. Platy Platy structure is not normally found in natural soils but develops as a consequence of compaction caused by inappropriate use of the soil (normally in wet conditions). 2. Organic Matter, nutrients Like the clay particles the dead organic matter forms part of the cation exchange capacity of soil. The D.O.M binds to positively charged ions, cations, of nutrients such as magnesium and calcium and retains them in the soil. 2. Organic Matter, Summary Soil Structure The organic matter interacts with the mineral particles and the living organisms to produce the soil structure, ped. Nutrients The organic matter and the clay form the cation exchange capacity of soil. Without clay and organic matter the ability of the soil to hold nutrients will be reduced. Water capacity Organic matter forms hydrogen bonds with water molecules and increases the ability of the soil to retain water. 3. Water, gravitational water A good soil needs to contain water. The water in soil can be divided up into a number of different categories. Precipitation Precipitation Precipitation Soil surface Gravitational water moves through the soil by gravity until it reaches the water table. As it does so, it causes the Translocation of materials through the soil. Water table 3. Water, hygroscopic water Hygroscopic water: this water is tightly joined (by hydrogen bonds) to the particles in soil particularly clay and DOM Because the hygroscopic water is so strongly attached to the clay and DOM it is difficult for plant roots to use this water 3. Water, capillary water Capillary water: water molecules can form hydrogen bonds with each other. This bonding creates surface tension which will hold the water in the soil Hydrogen bonds Because the capillary water is not strongly attached to the soil it is easy for plant roots to absorb. hygroscopic water 3. Water, drainage Feature Good Drainage Poor Drainage Pore Space * Sandy soils have large pore spaces and are well drained Clay soils have small pore spaces an are poorly drained. Humus content The presence of humus in clay soils improves drainage The presence of humus in sandy soils reduces drainage Structure Soils with a crumb ped tend to be well drained as are structurless sandy soils Clay Soils with a blocky or platy structure tend to be poorly drained Bedrock Permeability Rocks such as sandstone, limestone and chalk are highly permeable Rocks such as granite are impermeable * Please notice the difference between porosity and permeability 3. Water, soil thermal capacity Feature Effect Absorption of Solar radiation The amount of light absorbed will be related to latitude, aspect, albedo and vegetation cover. Water content Water has a high specific heat, that is it takes a lot of energy to raise its temperature, the higher the water content of the soil the more sunlight it will take to heat it Exposure In areas exposed to high winds the evaporation of water from the soil will lower the soils temperature Respiration by microorganism The decomposition of dead organic matter in soil by respiration releases heat as a waste product. 4. Soil Air, Aeration Aeration: A function of pore space determine by particle size 4. Soil Air, Aerobic conditions A good soil will contain air. The oxygen in the soil air can have a variety of different functions: It is used by the roots of plants in aerobic respiration. This provides them with energy for the active uptake of nutrients and growth. It used by decomposers and saprobionts in aerobic respiration speeding the rate of decomposition of dead organic matter and thus the recycling of nutrients. In the nitrogen cycle the presence of oxygen speeds up decomposition and nitrification by bacteria and fungi. DOM decomposition Ammonia nitrification Nitrites nitrification Nitrates 4. Soil Air Anaerobic conditions Waterlogged soils such as those found in the peat soils of Sphagnum Bog and Fen contain very little oxygen. The consequence of this is that the breakdown of dead organic matter is slow since few decomposers, such as earthworms, can survive in the anaerobic conditions. Decomposition by saprobionts such as fungi and bacteria is also slow in the absence of oxygen, since anaerobic respiration is less efficient In Anaerobic conditions denitrifying bacteria convert of nitrates to Atmospheric nitrogen. 5. Soil Organisms Soil is to a large extent formed and created by the living organisms the live in it and on it. Organisms number per teaspoonful weight (kg) per hectare Bacteria 90,000,000 1,000-2,000 Fungi 200,000 2,000-5,000 Algae 30,000 ~500 Protozoa 5,000 100-500 Nematodes 30 ~200 Earthworms <1 0-2,000 Other soil animals <1 0-500 ~ 91 million ~ 6,000 Total Which group of organisms is missing from this table? Plants 5. Living organisms Plants Pioneer species begin the process of soil formation, binding the soil particles together and reducing erosion. The plants add dead organic matter which improves structure, nutrient content and water holding capacity. As a plant succession proceeds so the soil quality improves allowing other species to come in. Fungi Fungal mycelia are found throughout soil. Fungal hyphae release enzymes which break down dead organic matter allowing the nutrients to pass to plants. Many plants form close associations with fungi, called mycorrhiza. The plants give the fungi carbohydrates in return for nutrients Animals There are many types of animals found in soil. Earthworms are important decomposers they eat dead leaves and break them down in digestion, thus they begin the process of humification, helping to recycle nutrients to plants. The passage of their bodies through the soil creates channels which develops aeration, drainage and the formation of a good crumb ped. 5. Living organisms Bacteria Bacteria are found in large numbers in soil. One metre2 of soil can contain 1011 bacteria and typically at least 5000 species. Bacteria are important saprobionts, breaking down dead organic matter. Several types are involved in the nitrogen cycle. Free living and mutualistic nitrogen fixing bacteria such as Rhizobium convert atmospheric to ammonia compounds. Nitrifying bacteria convert Ammonia to nitrites and then nitrites to nitrates. Nitrates are the main source of nitrogen for plants. Denitrifying bacteria convert nitrates to nitrogen gas in the absence of oxygen. Sandy Soils and Clay Soils Property Sandy soil Clay Soil Texture Coarse Fine Structure Structureless Forms large clods when wet Becomes hard and cracked when dry Porosity Large pore spaces, good aeration, rapid drainage Small pore spaces, poor aeration, slow drainage Water holding capacity Poor water retention, little capillary water, no waterlogging Good water retention, large amounts of capillary water, easily waterlogging Temperature Warm due to low moisture content Cold due to high moisture content Nutrient retention Low, rapid leaching High, not leached, clay particles attract nutrient cations and some anions To Find the Water Content of Soil 1. Weigh soil to find mass (mass 1) 2. Place in an Oven at 110 C0 till the soil reaches constant mass, (Final mass = mass 2) 3. Mass 1 - Mass 2 = Water content of soil To Find the Organic Content of Soil 4. Take dried soil and weigh to find mass (mass 3) 5. Place in a crucible and heat with a bunsen burner burning off the organic matter. Burn till the soil reaches constant mass, (burnt mass = mass 4) 6. Dried mass 3 – burnt mass 4 = organic content of soil To Find the pH of Soil 1. Add equal quantities of barium sulphate. (barium sulphate flocculates the colloidal particles i.e it causes the suspended particles to stick together and fall out of solution allowing you to see a colour change 2. Add universal indicator solution 3. Observe the colour change http://www.royagcol.ac.uk/soils/book/p20.htm