Nitrificación y Simbiosis

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FERTILIDAD 2002FERTILIDAD 2002

Nitrificación

2NH4+ + 4O2→2NO

- + 4H+ + H2O

– Microorganismos AUTÓTROFOS OBLIGADOS

– Ellos…NO NECESITAN M.O. !!!! Como energía

– Se acelera bajo condiciones favorables

– La mayor parte del N-NH4 nitrifica en pocas

semanas

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CICLO INTERNO DE NITRÓGENO

Se diferencia por los cambios biológicos que se producen a través de

MINERALIZACIÓN e INMOVILIZACIÓN

mineralización

N ORGÁNICO NH3, NO3

inmovilización

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Nitrification• Nitrification is a two step process:

Nitrosomonas

2NH4+ + 3O2 → 2NO2

- + 4H+ + 2H2O Nitrite

Nitrobacter

2NO2- + O2 → 2NO3

- Nitrate

2NH4+ + 4O2→2NO

- + 4H+ + H2O

The second reaction is almost always faster than the first, thus nitrite does not build up in the soil.

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Nitrification• Moisture Level

– Optimum @ Field Capacity– Little nitrification in dry or waterlogged soils

• Temperature– Optimum: 25 - 35° C (75 - 95° F)– Minimal nitrification below 10° C (50° F)

• Generally assumed that there is little or no nitrification in the winter

Soil sampling for nitrate – either immediately dry or freeze the samples to keep them stable

• Aeration– O2 necessary for nitrification– Significant decrease when O2 is below

• 10% Normal atmospheric O2 ≈ 20%

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Nitrification• pH

– Nitrification bacteria sensitive to soil pH

– Nitrification will be slower at low pH

– At high pH free NH3 is toxic to nitrobacter

which may result in buildup of toxic levels

of NO2-

– Remember: Nitrification lowers soil pH

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Nitrification• Nitrification Inhibitors

Nitrosomonas

2NH4+ + 3O2 → 2NO2

- + 4H+ + 2H2O Nitrite

Nitrobacter

2NO2- + O2 → 2NO3

- Nitrate

Nitrification inhibitors block the action of nitrosomonas thus stopping the conversion of NH4

+ to NO3-

Keeps the N in the ammonium form

NH4+ won’t leach or denitrify

NO3- can leach or denitrify

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Nitrification• Nitrification Inhibitors

– Nitripyrin (N Serve)– Dicyandiamide DCD (Guardian)

• Research in PA and MD showed very little response with spring applied N on corn.

• Research on fall applied anhydrous ammonia on corn in Indiana showed a significant response.

• Same research showed much smaller response on with spring applied anhydrous ammonia on corn.

• Conditions where nitrification inhibitors would be expected to be effective:

– Poorly drained soils– Coarse textured soils– N applied way ahead of crop need

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MUTUALISMO

Se benefician ambas partes: microorganismos y plantas

1. Micorrizas: el hongo invade las células de la raíz y forma dentro de ella vescículas y arbúsculos (VA), se incrementa la absorción de nutrientes, P y Zn, y para el hongo queda energía (azúcares). El hongo a través de sus hifas explora el suelo hasta pequeñísimos espacios donde no llegarían las raíces para encontrar el fósforo para ambos

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The plant benefits because it gains nitrogen. The bacteria benefit because they get sugars and nutrients to survive.

• Legumes Most plants have to search through the soil with their roots to find nitrogen which is a critical nutrient required for growth. Legumes on the other hand form symbiotic relationships with Rhizobium bacteria. The Rhizobium live in little nodules in the roots of the legumes and fix atmospheric nitrogen into ammonium or nitrate, forms of nitrogen that can be used by the plant. In other words,

the Rhizobium turn air into fertiliser!

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Immobilization• Immobilization

– Conversion of mineral N to organic N by microbes

– Reverse of mineralization

• Organisms that decompose organic matter as an energy source require nitrogen

• Organic materials with a low N content cannot supply the needs of these organisms thus they use soil N-competition with the crop. – High C:N ratio organic matter

• Freshly immobilized N = 5-15% of soil N

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Immobilization• Low C:N ratio organic matter (<20:1)

– Organic materials with a high N content relative to carbon can supply the needs of these organisms as they decompose the OM.

– At C:N <20:1 there is a net release of mineral N ie. Mineralization

• High C:N ratio organic matter (>30:1)– Organic materials with a low N content cannot

supply the needs of these organisms thus they use soil N - competition with the crop. ie. Immobilization

• Medium C:N ratio organic matter (20-30:1)– Little net effect on nitrate

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Immobilization

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Immobilization• Other considerations

– Can result in N deficient crops– Can tie up excess N reducing losses– Immobilization is temporary– Sensitive to environmental conditions

• Temperature• Moisture• pH

– Resistance of organic material to breakdown

Technology

Nitrificación y Simbiosis