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Nutrient management
for organic vegetable
production in NC
Part I
http://compost.tamu.edu/demos/palopinto/compost.jpg
Average rates (lbs/acre) of N, P2O5 and K2O applied to
vegetable crops in the US
Nitrogen
Phosphorus
Potassium
Why are these rates so high ?
http://www.ers.usda.gov/publications/sb969/sb969c.pdf
Most growers believe that high rates
of nutrients are needed to produce
high yields of high quality
vegetables
Jalapeno pepper production
in Fresno County, California
Total cost of production: $4392
Total fertilizer costs: $170
Fertilizer costs = 4% of total costs
~ 16 elements have been
identified as essential for
the growth of all plants
Soil
C OH
air & water
N K Ca Mg P S
Cl Fe Mn Zn B Cu Mo
macronutrients
micronutrients
V
Co
Ni
Needed by
some plants
Na
Si
Micronutrients are critical components of enzymes
minerals
Soil solids
contain
nutrients
organic
matter
H20
Soil water contains nutrients
H 20
K+
H 20
+2
Ca
- -H 20
Mg+2 H20
-
-
Humus
H+
H20
exchangeable
ions
H 20
Clay
--
H20
H 20
- Na
Ca+2
H 20
H20
+
K+
H20
H 20
H20
Soil
soup
H20
H20
H20
What’s in the soil soup ??
Cu+3
DOM
Ca+2
NO3-
Ca+2
+2
NO3- Mg
+2
H
PO
2
4
Ca
Zn+2
DOM
+
K
-
NO3
K+
+2
Ca+2 Mg
Mg+2
Fe
NO
3
+3
DOM
SO4-2
Ca+2
Adapted from Brady and Weil (2002)
Which forms of nutrients are available to
plants ?
solution
exchangeable
“active” OM
passive “OM”
weatherable minerals
Re-seasoning the soup
Modified from Havlin et al. (1999)
……
Crop yield
Deficiency
Symptoms
Nutrient availability
http://www.extension.umn.edu/distribution/horticulture/components/M1190fig1.htm
Understanding nutrient uptake
H 20
Root exudates
activate soil
microbes
Transpirational
stream
H 20
Root growth
Feed the soil vs. Feed the crop ?
Both strategies are important !
Healthy roots need available nutrients !
Unhealthy roots use nutrients inefficiently…
?
Chronic root
malfunction
Acute
root
disease
The acid infertility complex
Nutrient
availability
varies with pH
Understanding aluminum toxicity
Toxic forms
Aluminum
of Al
are
toxicity is
bioavailable
at lowminimal
pHs
above
pH 5.5
http://www2.ctahr.hawaii.edu/tpss/research_extension/rxsoil/alroot.gif
100%
Percentage of maximum cation exchange capacity
75%
50%
25%
Exchangeable
Al+3
0%
Brady and Weil (2002)
Micronutrient
deficiencies
frequently
occur when
naturally acid
soils are
over-limed
http://www.fftc.agnet.org/library/image/bc51002p7.html
Avoid over-liming !!
http://hubcap.clemson.edu/~blpprt/acid2-chart1.gif