An-Chueh ChouMaster of Science Graduate Student

John A. Ray, M.S.Research Associate

Steven E. Newman, Ph.D., A.A.F.Greenhouse Crops Extension Specialist and

Professor of Floriculture

Nitrogen Source on Bedding Nitrogen Source on Bedding Plant Growth and Water UsePlant Growth and Water Use

ProGreen EXPO – 2009

What form of N is in the bag?What form of N is in the bag?

Three forms of nitrogen– Ammonium-N NH4

+

– Nitrate-N NO3-

– Urea-N CO(NH2)2

Maximum of 40% ammonium-N and urea-N to avoid ammonium toxicity– Low pH (<5.5)– Low medium temperatures– Overly wet medium

Ammonium vs. NitrateAmmonium vs. Nitrate

Urea is considered to be the same as NH4, since urea needs to be converted to NH4 to be assimilated by plants

The NO3 form is readily taken up by the roots, is very mobile within the plant, and can be stored within the plant at high levels with no toxicity

Some NH4 can be taken up directly by roots, but most of it needs to be changed to NO3 by bacteria in the soil before root uptake can occur

Ammonium vs. NitrateAmmonium vs. Nitrate

Bacterial conversion of NH4 to NO3 is dependent on soil temperature and soil pH

Cool temperatures (less than 60°F) and low soil pH (<5.5) reduce the conversion, and NH4 toxicity can occur

Most of the NH4 taken up directly by roots has to be incorporated into organic compounds in the roots

Plants can store NH4 only at low levels without suffering from toxicity

Ammonium ToxicityAmmonium Toxicity

Lower leaves– Rolled margins– Chlorosis– Necrosis

Roots– burning

Dr. Douglas A. Cox,University of Massachusetts

Nitrate Nitrogen UptakeNitrate Nitrogen Uptake

NO3- OH-

pH goes up

Ammonium Nitrogen UptakeAmmonium Nitrogen Uptake

NH4+

H+

pH goes down

Ion Uptake and pHIon Uptake and pH

Uptake of cations (positive charge) – lowers medium pH

Uptake of anions (negative charge) – raises medium pH

True for any cation or anion uptake process More N ions are taken up than all others

combined– so N has the greatest pH effect

Common FertilizersCommon Fertilizers

Fertilizer NH4 (%) Ca (%) Mg (%)

21-7-7 100 0 0

20-20-20 69 0 0

20-10-20 40 0 0

15-5-15 22 5 2

Nitrate NitrogenNitrate Nitrogen

100% NO3-

– leaves and stems small

– plants are “hard”– may be useful for

plugs

15-40% N should be in the NH4

+ form

Older FertilizersOlder Fertilizers

20-20-20 Soil-based media Optimum pH > 7.0

– NH4+ NO3

-

– pH 6.0-7.0 had enough bacterial activity

pH < 6.0 leads to toxicities

Modern FertilizersModern Fertilizers

15-5-15 Cal Mag Soilless media

28% NH4+

5% Ca

2% Mg

How does the N-sourceHow does the N-sourceimpact plant growth?impact plant growth?

Study included two bedding plant species– Pansy– Petunia

Standard 200 ppm N– 20-10-20

Five rates or NO3:NH4– 0% NH4

– 25% NH4

– 50% NH4

– 75% NH4

– 100% NH4

Pansy, NOPansy, NO33--:NH:NH44

++=100:0=100:0

Pansy, NOPansy, NO33--:NH:NH44

++=75:25=75:25

Pansy, NOPansy, NO33--:NH:NH44

++=50:50=50:50

Pansy, NOPansy, NO33--:NH:NH44

++=25:75=25:75

Pansy, NOPansy, NO33--:NH:NH44

++=0:100=0:100

Petunia, NOPetunia, NO33--:NH:NH44

++=100:0=100:0

Petunia, NOPetunia, NO33--:NH:NH44

++=75:25=75:25

Petunia, NOPetunia, NO33--:NH:NH44

++=50:50=50:50

Petunia, NOPetunia, NO33--:NH:NH44

++=25:75=25:75

Petunia, NOPetunia, NO33--:NH:NH44

++=0:100=0:100

Pansy – Plant GrowthPansy – Plant Growth

Petunia – Plant GrowthPetunia – Plant Growth

ChlorophyllChlorophyll

Pansy - EvapotranspirationPansy - Evapotranspiration

Daily EvapotranspirationDaily Evapotranspiration

SummarySummary

Nitrogen source impacts plant growth– Species dependent

– High NH4 is detrimental

– No NH4 is detrimental

Nitrogen source impacts water use– Higher levels of NH4 increases water use of petunias– Increasing levels of NH4 increases water use of

pansies until 50% then water use decreases

ThanksThanks

Colorado State University – Horticulture and

Landscape Architecture– Agricultural Experiment

Station– Extension

Welby Gardens– Plant donations

For more information:http://ghex.colostate.edu

http://ghadvisor.blogspot.com

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