Biology - Environment - Soil/Growing media

Return to: Biology of Horticulture

Environment - Soil/Growing media

What are six macronutrients available in the soil?

three anionic - N (nitrate), P (phosphate), and S (sulfate)

three cationic - K+ (potassium), Ca2+ (calcium), Mg2+ (magnesium)

What are some examples of micronutrients?

iron, copper, manganese etc. (mostly cations)

Give examples of elements involved in: enzyme function, cell structure, osmosis and permeability.

enzyme function - K+ and many of the micros

cell structure - N in proteins and nucleic acids, P in nucleic acids, small amounts of S in all proteins, Mg2+ in chlorophyll Ca2+ stabilizes middle lamella (calcium pectate)

osmosis, K+ is major cation in vacuole

permeability - Ca2+ stabilizes membranes

What processes lead to soil formation?

weathering rock - mineral composition

organic activity - decomposition of plant and animal, microbial activity

How do regions (horizons) of soil relate to its formation?

horizon A - organic/mineral mix where most of plant root activity occurs

hortizon B - subsoil, partially weathered rock and elements leached from above

horizon C - bedrock

What do we mean by "field capacity" and "permanent wilting percentage" and how do these vary with soil composition?

at field capacity ( 0.1 MPa), soil or growing medium holds as much water as it can after drained by gravity (low for sand, high for clay and organic soils)

at permanent wilting point (PWP) (-1.5 MPa), the plant cannot get any more water out (although a lot may still remain - half of field capacity in clay, maybe a quarter in sand and organic)

What are two important ionic properties of soil?

CEC - fixed anions (acidic) in soil (silicates in mineral fraction and carboxyls on humus) determine cation exchange capacity (CEC)

pH - degree of neutralization of these with K+, Ca2+ etc. determines pH

What are the only organisms which can fix atmospheric nitrogen?

bacteria - free living in soil

root nodules

How else can atmospheric nitrogen be fixed. happen?

lightning, volcanoes and human activity (fertilizer industry and vehicle emissions)

How do plants take up nitrogen and what must they do with it?

often as nitrate requiring reduction and incorporation into organic molecules (amino acids)

can also use ammonium which can be directly converted to organic form but is toxic at high concentration

How does this nitrogen return to the environment?

death and decomposition or consumption of plant by animal (excretion and ultimate death)

micro-organisms convert back to inorganic form and N2

Give a reason why phosphorus availability might be less of a problem for plants than nitrogen?

P (phosphorusis not lost to atmosphere like N (nitrogen)

In what way are nitrogen and phosphorus similar in terms of availability (and different from K, Mg, Ca, ect.)?

Soils do not have fixed cations to retain anions, so nitrate and phosphate tend to be leached by rain, but phosphate does form insoluble salt with Ca2+

Return to: Biology of Horticulture

	What are six macronutrients available in the soil?
	three anionic - N (nitrate), P (phosphate), and S (sulfate) three cationic - K+ (potassium), Ca2+ (calcium), Mg2+ (magnesium)

	What are some examples of micronutrients?
	iron, copper, manganese etc. (mostly cations)

	Give examples of elements involved in: enzyme function, cell structure, osmosis and permeability.
	enzyme function - K+ and many of the micros cell structure - N in proteins and nucleic acids, P in nucleic acids, small amounts of S in all proteins, Mg2+ in chlorophyll Ca2+ stabilizes middle lamella (calcium pectate) osmosis, K+ is major cation in vacuole permeability - Ca2+ stabilizes membranes

	What processes lead to soil formation?
	weathering rock - mineral composition organic activity - decomposition of plant and animal, microbial activity

	How do regions (horizons) of soil relate to its formation?
	horizon A - organic/mineral mix where most of plant root activity occurs hortizon B - subsoil, partially weathered rock and elements leached from above horizon C - bedrock

	What do we mean by "field capacity" and "permanent wilting percentage" and how do these vary with soil composition?
	at field capacity ( 0.1 MPa), soil or growing medium holds as much water as it can after drained by gravity (low for sand, high for clay and organic soils) at permanent wilting point (PWP) (-1.5 MPa), the plant cannot get any more water out (although a lot may still remain - half of field capacity in clay, maybe a quarter in sand and organic)

	What are two important ionic properties of soil?
	CEC - fixed anions (acidic) in soil (silicates in mineral fraction and carboxyls on humus) determine cation exchange capacity (CEC) pH - degree of neutralization of these with K+, Ca2+ etc. determines pH

	What are the only organisms which can fix atmospheric nitrogen?
	bacteria - free living in soil root nodules

	How else can atmospheric nitrogen be fixed. happen?
	lightning, volcanoes and human activity (fertilizer industry and vehicle emissions)

	How do plants take up nitrogen and what must they do with it?
	often as nitrate requiring reduction and incorporation into organic molecules (amino acids) can also use ammonium which can be directly converted to organic form but is toxic at high concentration

	How does this nitrogen return to the environment?
	death and decomposition or consumption of plant by animal (excretion and ultimate death) micro-organisms convert back to inorganic form and N2

	Give a reason why phosphorus availability might be less of a problem for plants than nitrogen?
	P (phosphorusis not lost to atmosphere like N (nitrogen)

	In what way are nitrogen and phosphorus similar in terms of availability (and different from K, Mg, Ca, ect.)?
	Soils do not have fixed cations to retain anions, so nitrate and phosphate tend to be leached by rain, but phosphate does form insoluble salt with Ca2+