Chapter 37: Soil and Plant Nutrition
Soil contains a living, complex ecosystem
o Soil particles of various sizes derived from the breakdown of rock are found in
soil. Soil particle size affects the availability of water, oxygen, and minerals in the
soil.
o A soil’s composition encompasses its inorganic and organic components. Topsoil
is a complex ecosystem teeming with bacteria, fungi, protists, animals, and the
roots of plants.
o Some agricultural practices can deplete the mineral content of soil, tax water
reserves, and promote erosion. The goal of soil conservation is to minimize this
damage.
Plant roots absorb many types of essential elements from the soil
o Macronutrients, elements required in relatively large amounts, include carbon,
oxygen, hydrogen, nitrogen, and other major ingredients of organic compounds.
Micronutrients, elements required in very small amounts, typically have catalytic
functions as cofactors of enzymes.
o Deficiency of a mobile nutrient usually affects older organs more than younger
ones; the reverse is true for nutrients that are less mobile within a plant.
Macronutrient deficiencies are most common, particularly deficiencies of
nitrogen, phosphorus, and potassium.
o Rather than tailoring the soil to match the plant, genetic engineers are tailoring the
plant to match the soil.
Plant nutrition often involves relationships with other organisms
o Rhizobacteria derive their energy from the rhizosphere, a microorganism-enriched
ecosystem intimately associated with roots. Plant secretions support the energy
needs of the rhizosphere. Some rhizobacteria produce antibiotics, whereas others
make nutrients more available for plants. Most are free-living, but some live
inside plants. Plants satisfy most of their huge need for nitrogen from the bacterial
decomposition of humus and the fixation of gaseous nitrogen.
Soil contains a living, complex ecosystem
o Soil particles of various sizes derived from the breakdown of rock are found in
soil. Soil particle size affects the availability of water, oxygen, and minerals in the
soil.
o A soil’s composition encompasses its inorganic and organic components. Topsoil
is a complex ecosystem teeming with bacteria, fungi, protists, animals, and the
roots of plants.
o Some agricultural practices can deplete the mineral content of soil, tax water
reserves, and promote erosion. The goal of soil conservation is to minimize this
damage.
Plant roots absorb many types of essential elements from the soil
o Macronutrients, elements required in relatively large amounts, include carbon,
oxygen, hydrogen, nitrogen, and other major ingredients of organic compounds.
Micronutrients, elements required in very small amounts, typically have catalytic
functions as cofactors of enzymes.
o Deficiency of a mobile nutrient usually affects older organs more than younger
ones; the reverse is true for nutrients that are less mobile within a plant.
Macronutrient deficiencies are most common, particularly deficiencies of
nitrogen, phosphorus, and potassium.
o Rather than tailoring the soil to match the plant, genetic engineers are tailoring the
plant to match the soil.
Plant nutrition often involves relationships with other organisms
o Rhizobacteria derive their energy from the rhizosphere, a microorganism-enriched
ecosystem intimately associated with roots. Plant secretions support the energy
needs of the rhizosphere. Some rhizobacteria produce antibiotics, whereas others
make nutrients more available for plants. Most are free-living, but some live
inside plants. Plants satisfy most of their huge need for nitrogen from the bacterial
decomposition of humus and the fixation of gaseous nitrogen.
