Soil Nutrient Cycling
- Materials are broken down by macro and meso-fauna
- Nutrients are taken up and converted by lower life
forms in the soil
- They convert these nutrients to organic forms within
the cell or to inorganic forms released to soil
- These organisms die and are decomposed by other organisms
- This also releases inorganic ions
for plant or other microbe uptake and…
- The cycle starts all over
Nitrogen Cycle: Nitrogen
is the nutrient needed in largest amounts by plants and
is the most commonly applied fertilizer. Excess N can
have negative affects on plant growth and crop quality
as well as harming the environment,
especially water quality.
Nitrogen is present in one of five forms
- Organic N: 90% of N is in organic form. It must be
mineralized to become available.
- Ammonium N (NH4+): Inorganic, soluble form
- Nitrate (NO3-): Inorganic, soluble form
- Atmospheric N (N2): 80% of atmosphere but unavailable
to most plants except N-fixers
- Nitrite (NO2-): only under anaerobic conditions.
This form is toxic to plants and normally will
not be present
in significant amounts in soil.
Mineralization vs Immobilization
Mineralization - the release of organically bound
nutrients in an inorganic form usable to organisms and/or
Immobilization - the conversion of an element from the
inorganic to the organic form unavailable to plants
C:N (carbon to nitrogen) ratios
- Low C:N
ratios (<25:1) are indicative of mineralization
and rapid rates of decomposition
- High C:N ratios (>25:1) indicate
immobilization and slower decomposition rates
- Low C:N materials (high
– Undiluted manure and blood meal, grass clippings (can
get high), vegetable wastes
- Intermediate C:N materials
– Most composts, leaf mulches, cover crop residues
- High C:N materials
– Straw, bark, wood chips, sawdust, paper, cornstalks,
Composting and your garden
- Excellent source of organic matter
- Turn kitchen scraps into soil amendments
- Key is to balance air, water, and energy materials
and bulking agents.
- Four main systems:
– hot (fast), cold (slow), worm bins, or soil trenches.
- Excellent source: Backyard Composting
in the 1990s, http://cru.cahe.wsu.edu/CEPublications/eb1784/eb1784.pdf
- Add 1-2 inches of compost each year
- Compost “teas” are very
beneficial in gardens and house plants.
- One cubic yard of compost covers about 300 square
feet 1 inch deep
- Be cautious of C:N materials and watch for N deficiencies.
Next page: 13
essential nutrients & fertilizers
July 15, 2004