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- upper layers provide nutrients and water to plants
- Plants, bacteria, insects, fungi, nematodes live in and create structures of soil
- -layers known as horizons
- -upper layer is topsoil
Name soil particles from smallest to largest (3)
what does topsoil consist of
- mineral particles
- living organisms
- decaying organic material
soils that support highly productive plant growth composed of roughly equal parts sand, silt, and clay
cations adhere to?
negatively charged soil particles
what happens during cation exchange?
- cations are displaced from soil particles by other cations
- Displaced cations enter the soil solution and can be taken up by plant roots
- Negatively charged ions do not bind with soil particles and can be lost from the soil by leaching
- •Percolating groundwater
how does agriculture impact soil
- Depletes nutrients
- –Increases erosion
- –Taxes water resources
- –Soil compaction
- –Alters soil communities
primary source of irrigation water is in these underground water reserves
the depleting of aquifiers can result in?
subsidence- the settling or sinking of land
- concentration of salts in soil as water evaporates
- irrigation can lead to this
Fertilization replaces what?
mineral nutrients that have been lost from the soil
commercial fertilizers are enriched in?
organic fertilizers are composed of?
Large monoculture farms with high fertilizers have?
bacteria dominated soil food webs
natural systems and organic farms have?
fungal based soil food webs
what does erosion of soil cause?
loss of nutrients
how can erosion be reduced
- –Planting trees as windbreaks
- –Terracing hillside crops
- –Cultivating in a contour pattern
- –Practicing no-till agriculture
when is a chemical element considered an element?
if it is required for a plant to complete its life cycle
- 9 essential elements
- -plants require them in large amounts
- 8 elements
- plants need them in small amounts
- •The layer of soil bound to the plant’s roots
- •The rhizosphere has high microbial activity because of sugars, amino acids, and organic acids secreted by roots
- •Function in the rhizosphere
- •Can enter roots
what can rhizobacteria do
- –Produce hormones that stimulate plant growth
- –Produce antibiotics that protect roots from disease
- –Absorb toxic metals
- –Make nutrients more available to roots
- •Inoculation of seeds with rhizobacteria can increase crop yields
transforms nitrogen and nitrogen-containing compounds
where does most soil nitrogen come from?
- actions of soil bacteria
- nitrogen can be an important limiting nutrient for plant growth
what do plants absorb nitrogen as?
either NO3– or NH4+
carried out by bacteria that convert NH3 into NO3–
conversion of nitrogen from N2 to NH3 through nitrogen- fixing bacteria because plants cannot directly take in the N2 from the atmosphere
plants in legume family have what with nitrogen fixing bacteria
a symbiotic relationship
- swellings along legume's roots, composed of plant cells infected by nitrogen fixing rhizobium bacteria
- The bacteria of a root nodule obtain sugar from the plant and supply the plant with fixed nitrogen
Inside the root nodule, Rhizobium bacteria assume this form called bacteroids, which are contained within vesicles formed by the root cell