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