Lecture 3

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Nutrient elements exist in soils in various forms characterized by different accessibility to plant roots. The bulkof the nutrients is locked up in the structural framework of primary minerals, organic matter, clay, and humus.A smaller proportion of each nutrient is adsorbed in a swarm of ions near the surfaces of soil colloids (clay andorganic matter). From the swarm of adsorbed ions, a still smaller amount is released into the bulk soil solution,where uptake by plant roots can take place. (Diagram courtesy of R. Weil)
Three principal mechanisms by which nutrient ions dissolved in the soil solution come into contact with plantroots. All three mechanisms may operate simultaneously, but one mechanism or another may be mostimportant for a particular nutrient. For example, in the case of calcium, which is generally plentiful in the soilsolution, mass flow alone can usually bring sufficient amounts to the root surface. However, in the case ofphosphorus, diffusion is needed to supplement mass flow because the soil solution is very low in this elementin comparison to the amounts needed by plants. (Diagram courtesy of R. Weil)
Page 3 and 4: The many functions of soil can be g
Page 6 and 7: The soil is home to a wide variety
Page 8 and 9: The pedosphere, where the worlds of
Page 10 and 11: This road cut in central Africa rev
Page 12 and 13: Information important to different
Page 14 and 15: The light- and dark-colored soil bo
Page 16 and 17: Abundant organic matter, including
Page 18 and 19: Diagrammatic representation of acid
Page 22 and 23: Elements Essential for Plant Growth
Page 24 and 25: Quantities of Six Essential Element
Page 26 and 27: Definition• Soil is a natural thr
Page 28 and 29: Outline: Soil PhysicalProperties•
Page 31: Particle size and Soil texturalclas
Page 34 and 35: Particle and bulk density• Partic
Page 36 and 37: Soil Organic and InorganicCARBON•
Page 38 and 39: Outline: Physical Processes• Soil
Page 41 and 42: Soil Water Movement,Hydrologic Cycl
Page 43 and 44: Soil Erosion• Predicting soil ero
Page 45 and 46: Clay Minerals• Clay minerals and
Page 47 and 48: Clay minerals• Clay minerals of m
Page 49 and 50: Benefits of Organic Matter• Organ
Page 51 and 52: Soil Acidity• The pH of a soil is
Page 53 and 54: Soil Chemical Processes• Mineral
Page 55 and 56: Soil Microorganisms• Bacteria are
Page 57 and 58: Soil Microorganisms• Actinomycete
Page 59 and 60: Soil Microorganisms• Algae, like

Lecture 3

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