environmental chemistry: nitrogen (n) or….why we need healthy soils!

Environmental Chemistry:Nitrogen (N)

Or….why we need healthy soils!

N – So what??!!

• What do plants need to live and grow?

• “Nutrients” – what are they?

• 17 Essential Elements– C, H, O– N-P-K– Ca, Mg, S– Micronutrients: B, Cu, Cl, Fe, Mn, Mo, Ni, Zn

The Nitrogen Cycle

• N2 makes up 78% of troposphere (inner-most layer of atmosphere)!

• Nitrogen fixationNitrogen fixation: turning nitrogen in the atmosphere (N2) into a usable form for plants

• N2 + 3H2 2NH3 (ammonia)• Bacteria do this (in soil, or living in nodules in

special plants called legumes)• Industrial fertilizer factories do this• NH3 quickly dissolves into NH4

+ (ammonium ions)

Fig. 4.30, p. 94

NO3-

IN SOIL

NITROGEN FIXATION

by industry for agriculture

FERTILIZERS

FOOD WEBS ON LAND

NH3, NH4+

IN SOIL

1. NITRIFICATION

bacteria convert NH4+ to

nitrite (NO2-)

loss by leaching

uptake by autotrophs

excretion, death,

decomposition


NITROGEN FIXATIONbacteria convert to ammonia

(NH3) ; this dissolves to form

ammonium (NH4+)

loss by leaching

AMMONIFICATIONbacteria, fungi convert the

residues to NH3 , this

dissolves to form NH4+

2. NITRIFICATION

bacteria convert NO2- to

nitrate (NO3-)

DENTRIFICATIONby bacteria

NITROGENOUS WASTES, REMAINS IN SOIL

GASEOUS NITROGEN (N2)

IN ATMOSPHERE

NO2-

IN SOIL

The Nitrogen Cycle

• NitrificationNitrification: a two-step process• 1: Bacteria convert nitrogen in the soils

(NH3 and NH4 + ) to two different forms

– Nitrite ions (NO2-) BAD!! TOXIC! UNUSABLE!

– Nitrate ions (NO3-) GOOD NUTRIENTS FOR

PLANTS!

• 2: Bacteria convert nitrite ions (bad, NO2) to nitrate ions (good, NO3

-) that can be used by plants!

Fig. 4.30, p. 94

NO3-

IN SOIL

NITROGEN FIXATION


FERTILIZERS

FOOD WEBS ON LAND

NH3, NH4+

IN SOIL

1. NITRIFICATION


nitrite (NO2-)

loss by leaching


excretion, death,

decomposition




ammonium (NH4+)

loss by leaching




2. NITRIFICATION


nitrate (NO3-)




IN ATMOSPHERE

NO2-

IN SOIL

The Nitrogen Cycle

• Denitrification:Denitrification: special bacteria in waterlogged soil or at the bottom of lakes, oceans, or wetlands change nitrogen back into nitrite and nitrate ions, then into nitrogen gas!

• This is released into the air & atmosphere, to begin the cycle again.

Fig. 4.30, p. 94

NO3-

IN SOIL

NITROGEN FIXATION


FERTILIZERS

FOOD WEBS ON LAND

NH3, NH4+

IN SOIL

1. NITRIFICATION


nitrite (NO2-)

loss by leaching


excretion, death,

decomposition




ammonium (NH4+)

loss by leaching




2. NITRIFICATION


nitrate (NO3-)




IN ATMOSPHERE

NO2-

IN SOIL

The Nitrogen Cycle

• More important processes!• Decomposition: process of breaking down

organic material into its parts (nutrients)• Ammonification: process where bacteria and

fungi convert nitrogen wastes into NH3 which dissolves into NH4

-

• Assimilation: process where plant roots take up the useful forms of nitrogen to make DNA, amino acids and proteins in the plant tissue!

The Nitrogen Cycle

• When we “crop” the land, and take away plant material that was grown for crops, we remove N from this cycle!

• If we deplete our soils of their nutrients too quickly, the sustainability of soil for our food sources and the health of our ecosystems are put in jeopardy!

Fig. 4.30, p. 94

NO3-

IN SOIL

NITROGEN FIXATION


FERTILIZERS

FOOD WEBS ON LAND

NH3, NH4+

IN SOIL

1. NITRIFICATION


nitrite (NO2-)

loss by leaching


excretion, death,

decomposition




ammonium (NH4+)

loss by leaching




2. NITRIFICATION


nitrate (NO3-)




IN ATMOSPHERE

NO2-

IN SOIL

environmental chemistry: nitrogen (n) or….why we need healthy soils!

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