Nutrient management for organic vegetable
production in NC
http://compost.tamu.edu/demos/palopinto/compost.jpg
Part I
Nitrogen Phosphorus Potassium
Average rates of N, P2O5 and K2O applied to vegetable crops in the US
Why are these rates so high ?
http://www.ers.usda.gov/publications/sb969/sb969c.pdf
(lbs/acre)
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: $4392Total fertilizer costs: $170
Fertilizer costs = 4% of total costs
N K Ca Mg P S
macronutrients micronutrientsair & water
Soil
~ 16 elements have been identified as essential for the growth of all plants
C O H Cl Fe Mn Zn B Cu Mo
Na
Co Si
V NiNeeded by
some plants
Micronutrients are critical components of enzymes
Soil solidscontain nutrients
minerals
organic matter
exchangeableions
Soil soup
Humus
Clay
-
-
--
-
-
-
-
--
Na+
Ca+2
H+
K+
Ca+2
Mg+2
K+
H20H20
H20
H20
H20H20
H20H20
H20
H20
H20
H20
H20
H20
H20
H20
H20
Soil water contains nutrients
What’s in the soil soup ??
Adapted from Brady and Weil (2002)
Ca+2
NO3-
Ca+2
K+
K+
Mg+2Ca+2
Mg+2
Ca+2
Mg+2
Ca+2
NO3-
NO3-
SO4-2
NO3-
H2PO4-
DOM
DOM
DOMCu+3
Fe+3
Zn+2
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)
Poorly bufferedHighly buffe
red
……
Nutrient availability
Cro
p
yield
DeficiencySymptoms
http://www.extension.umn.edu/distribution/horticulture/components/M1190fig1.htm
Understanding nutrient uptake
Transpirationalstream
Ro
ot g
row
th
H20
H20
Root exudatesactivate soil
microbes
?
Acute root
disease
Feed the soil vs. Feed the crop ?
Chronic root malfunction
Both strategies are important !
Healthy roots need available nutrients !
Unhealthy roots use nutrients inefficiently…
The acid infertility complex
Nutrient availability
varies with pH
Understanding aluminum toxicity
Toxic forms of Al are
bioavailableat low pHs
Aluminum toxicity is minimal above pH 5.5
http://www2.ctahr.hawaii.edu/tpss/research_extension/rxsoil/alroot.gif
Exchangeable
Al+3
Brady and Weil (2002)
100%
50%
0%
75%
25%
Percentage of m
aximum
cation exchange capacity
Avoid over-liming !!
http://www.fftc.agnet.org/library/image/bc51002p7.html
Micronutrientdeficienciesfrequently occur when
naturally acidsoils are
over-limed
http://hubcap.clemson.edu/~blpprt/acid2-chart1.gif