Lecture 2. edaphic factors


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Lecture 2. edaphic factors

  1. 1. Edaphic Factors
  2. 2. Edaphic factor • Gk ‘edaphos’= ground, soil • Abiotic factor • Relating to the physical or chemical components of the soil found in a particular area – Temperature – pH – Mineral composition
  3. 3. Soil • The biologically active, porous medium that has developed in the uppermost layer of the Earth's crust. • Natural reservoir of water and nutrients • Medium for the filtration and breakdown of injurious wastes • Foundation of all terrestrial ecosystems. – Habitat of billions of plants, animals, and microorganisms that take part in the cycling of nutrients
  4. 4. Soil • Evolved through the weathering of solid materials. The bulk of soil consists of mineral particles composed of silicate ions combined with various metal ions.
  5. 5. Soil Profile • Texturally distinct layers or horizons • Different for every area
  6. 6. Soil Classification Map
  7. 7. Tropical climate
  8. 8. Soil Temperature Color • Dark soil absorbs more energy than light colored soil. Slope • Greater absorption can be observed as the angle of incidence of the sun's rays approaches perpendicular to the soil surface. Vegetative cover of the soil • Bare soil warms and cools faster than soil with vegetation.
  9. 9. Importance of Temperature • Heat is the catalyst for many biological processes. • Soil temperature is primarily important in growing plants.
  10. 10. Soil pH • Soil pH greatly influences nutrient availability and solubility in plants. – Acidic soils are often low in nutrient concentrations. • Soil pH also determines the presence of different microorganisms • An indicator of corrosiveness of the soil.
  11. 11. Factors affecting soil pH • pH of the soil can be affected by different factors such as: – mineral content of the soil – climate – weathering – properties of rainfall – induced fertilizers
  12. 12. Soil Moisture • Water that is held in the spaces between soil particles • Related to water-holding capacity of the soil and heat-capacity of soil
  13. 13. Organic Matter • Serves as the “revolving nutrient bank account” • Serves as a reserve for many essential nutrients, especially nitrogen • Serves as an agent to improve soil fertility and hold important plant nutrients e.g. by adding organic matter to sandy soil, the ability of the soil to retain water increases
  14. 14. Organic Matter • Organic matter is related to soil color – The darker the soil, the more organic matter
  15. 15. Soil Nutrients • Nutrients are required for plants to grow and develop. • Low nutrient levels result in stunted growth, low flowering and fruit production • Can be supplied by the addition of fertilizers (inorganic or organic) • Two categories: – Macronutrients • Primary nutrients - NPK • Secondary nutrients – Ca, Mg, S – Micronutrients (B, Cu, Fe, Cl, Mg, Mo, Zn)
  16. 16. Calcium • Secondary macronutrient • Construction of cell walls and proper functioning of growing tissue • Calcium deficiency: extremely acidic soil • Necrosis around the base of the leaves
  17. 17. Nitrogen • Primary Macronutrient • Green leaf growth  chlorophyll • Nitrogen deficiency – Stunted growth – Pale green and yellow leaves
  18. 18. Phosphorus • Primary macronutrient, mobile • Cell development, promotion of good root growth, flowering, fruiting, and ripening • ATP component, biomolecules  NA, phospholipids • Limited in most soils because it is release vey slowly from insoluble phosphates • Phosphorus deficiency – Intense green color, Poor root development – Purplish leaves  abnormal increase in sugar content & anthocyanin
  19. 19. Soil Texture • Used to designate the proportionate distribution of the different sizes of mineral particles in a soil
  20. 20. Soil Pyramid 40% sand + 40% silt + 20 clay = loam 10% sand + 45% silt + 45% clay = ? 55% sand + 15% silt + 30% clay = ?
  21. 21. Soil particle size classification USDA System ISSS System Category Size (mm) Category Size (mm) Clay <0.002 Clay <0.002 Silt 0.002-0.05 Silt 0.002-0.02 Very fine sand 0.05-0.10 Fine sand 0.10-0.25 Fine sand 0.02-0.2 Medium sand 0.25-0.5 Coarse sand 0.5-1.0 Coarse sand 0.2-2 Very coarse sand 1.0-2.0 USDA – US Dept. of Agriculture ISSS – International Soil Science Society Milne et al. 1991. Soil Description Handbook. DSR. Land Resources. Lower Hutt
  22. 22. Soil particle size classification For large particles (Milne et al. 1991) Category Size (mm) Fine gravel 2-6 Medium gravel 6-20 Coarse gravel 20-60 Very coarse gravel 60-200 Boulders >200 USDA – US Dept of Agriculture ISSS – International Soil Science Society Milne et al. 1991. Soil Description Handbook. DSR. Land Resources. Lower Hutt
  23. 23. Soil Structure • Refers to the grouping of soil particles into porous compounds; arrangement of aggregates into larger clumps • Influenced by soil texture • Types of aggregate arrangements: – Granular – Blocky – Prismatic – Columnar – Platy – Singly grained
  24. 24. Types of Soil Structure • Granular – resembles cookie crumbs; usually less than 0.5 cm in diameter; commonly found in surface horizons where roots have been growing • Blocky – irregular blocks that are usually 1.5 – 5.0 cm in diameter • Prismatic – vertical columns of soil; usually found in lower horizons Granular Blocky Prismatic
  25. 25. Types of Soil Structure • Columnar – vertical columns of soil having salt ‘caps’ at the top; found in soils of arid climates • Platy – thin, flat plates that lie horizontally; usually found in compacted soil • Single grained – soil is broken into individual particles that do not stick together; loose consistency; commonly found in sandy soils Columnar Platy Singly grained
  26. 26. The size and shape of clumps affect the capacity of soil to hold water, air, and nutrients. GRANULAR PLATYBLOCKY
  27. 27. Field Capacity • Maximum amount of water that a particular soil can hold • Water exists in soil capillaries; pores small enough to hold water against gravity • Soil texture – Field capacity will be reached faster in coarser textured soil (loamy soil) than fine-textured soil profiles (clay) • Soil structure – Amount of aggregation determines the amount of pores available to hold water
  28. 28. • Since forces holding water are surface-attractive forces, the more surface area a soil has, the greater is the amount of water adsorbed. • Field capacity comparisons – SAND: LOWER FIELD CAPACITY lower surface area, large pores  favor rapid water infiltration and drainage – CLAY: HIGHER FIELD CAPACITY, higher SA, small pores  greater active surface for adhesion of water molecules. Field Capacity
  29. 29. Cation-Exchange Capacity (CEC) • Ability of the soil particles to adsorb and exchange cations that are loosely bound to its surface • Measure of how many negatively-charged sites are avaialble in the soil • Highly dependent on soil texture and OM content – More clay, more OM  higher CEC – Clay • weakly (-) charged: higher affinity to cations • higher surface area exposed – Organic matter • has both (+) and (-) sites
  30. 30. Cation-Exchange Capacity • Measure of fertility, nutrient retention capacity, and the capacity to protect groundwater from cation contamination • Ideally, CEC for agricultural soils is between 10 and 30 meq*/100g (sandy loam- loam) – Higher CEC – more clay – Lower CEC – more sand * Milliequivalentstakes into account both the weight and the charge of the cation
  31. 31. Determine the following parameters: • Temperature • pH • Soil moisture • Amount of organic matter • Presence of nutrients (calcium, nitrates, phosphorus) • Soil texture • Soil inhabitants Act. 2: Edaphic factors and the soil inhabitants
  32. 32. Act. 2: Edaphic factors and the soil inhabitants 1. Examine important ecological properties of soil. 2. Compare soil characteristics in various habitats. 3. Determine what organisms live within the soil medium as well as their adaptation, abundance, and over-all ecology.
  33. 33. Soil Profile Dig at least 1 ft. below the ground Collect soil samples in each major soil horizons Take note the differences in color, structure, and thickness within the major horizons
  34. 34. Soil Temperature Equilibrate thermometer for two minutes Bury thermometer 3-6 inches below the ground and take 5 readings. Determine the soil temperature profile by plotting the soil temperature on the horizontal axis and the depth of the soil on the vertical axis
  35. 35. Soil pH Mix soil and distilled water in equal amounts (1:5 dilution; 10g with 50mL of water) Allow soil particles to settle until a clear supernate forms Take soil pH using a pH meter
  36. 36. Soil Moisture Oven dry 10g of soil placed in a pre-weighed crucible (105ºC for 24 hours) Allow to cool in a dessicator. Weigh. The dry weight sample is computed as the weight of the container with the oven-dried sample minus the weight of the container alone: (Wd = Wo – Wc)
  37. 37. Calculations Amount water = Fresh weight – Dry weight % water in sample = Fresh weight – Dry weight ____________________________ Fresh weight X 100
  38. 38. Soil Organic Matter Take 1-5 g oven-dried sample and place onto a pre-weighed crucible (Wc). Weigh (Wo). Heat in a furnace at 450ºC overnight. Cool. Weigh. (Wi) weight of the ignited soil sample (Wi – Wc). organic matter content (Wo – Wi), % of dry weight of the sample.
  39. 39. Calcium Test Combine 10 drops of soil supernate + 10 drops of 5g ammonium oxalate solution in 100mL distilled water Shake vigorously. Observe after 5 minutes. POSITIVE: milky-white precipitate NEGATIVE: no color change
  40. 40. Calcium Test Add soil and 10% HCl in a crucible POSITIVE: Effervescence. Amount is estimated using a table of determination of % CaCO3 Effervescence  carbon dioxide in the atmosphere Higher calcium carbonate present, the louder effervescence
  41. 41. % CaCO3 Audible Effect Visible Effect < 0.1 None None 0.5 Faint None 1.0 Faint-moderate Barely visible 2.0 Distinct Heard away from ear Visible from very close 5.0 Easily heard Bubbles up to 3 mm easily seen 10.0 Easily heard Strong effervescence With bubbles of 7 mm (After Clarke, 1957) Determination of % CaCO3 in soil sample
  42. 42. Nitrate Test Combine 10 drops of soil supernate + 10 drops of solution (0.33g diphenylamine in 25mL H2SO4) in a test tube Shake vigorously. Observe after 5 minutes. POSITIVE: brown - blue color
  43. 43. Phosphorus Test Combine 10 drops of soil supernate + 10 drops of solution (5g ammonium molybdate, 50mL distilled water and 50mL concentrated HNO3) in a test tube Add a piece of tin. Shake. Observe after 5 minutes POSITIVE: gray to deep blue coloration
  44. 44. Field Key To Soil Texture SAND LOAMY SAND LOAM SANDY LOAM SILT LOAM CLAY LOAM SANDY CLAY LOAM SILTY CLAY LOAM SILT CLAY SANDY CLAY SILTY CLAY Preliminary • Feeling the soil  grainy or sticky •Sandy or clayish, may color hand Moisten 10-15cm soil. Knead and try to mold into a ball. Follow key to make a rough classification.
  45. 45. Soil Inhabitants Collect litter in the site and place in a plastic bag. Add few drops of chloroform / ether. Wait for 5 minutes. Empty the contents in a white paper and look for soil invertebrates. Preserve in a small jar of alcohol or formalin.
  46. 46. Soil Inhabitants Place the collected soil sample in the Berlese-Tulgren apparatus. Observe for any organisms that will fall in the receptacle. Identify. Leave for 2 days. Continue observation and identification of soil invertebrates.
  47. 47. Berlese-Tulgren apparatus • Made up of a light bulb, aluminum foil funnel, gauze, and a test tube with formalin. • The organisms were forced to crawl downward because of the heat and light from the bulb. – Light heats and dries soil – Positive geotaxis in response to dryness
  48. 48. Berlese-Tulgren apparatus • Limitation: Biased sample of soil fauna – Based on specific avoidance behavior triggered by dryness – Best captures mobile animals and those that do not dessicate easily – Immobile larvae, endophagous nymphs and soft- bodied invertebrates such as nematodes  not extracted by a Berlese funnel.
  49. 49. Area designation Group Area 1 and 6 Lagoon 2 and 7 Old G. Silang Building 3 and 8 Water tank / Sining Lahi Headquarters 4 and 9 Gym / PE building 5 and 10 Oval
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