Fertilizer Sources: Proper Selection and Management

T. Scott MurrellNorthcentral Director

Potash & Phosphate Institute

2006

Dale F. LeikamAssociate ProfessorKansas State University

Questions to be addressed: N sources for corn

• How does corn take up and use nitrate?

• How does corn take up and use ammonium?

• Is there an optimum NH4+:NO3

- ratio?

• How do N forms react prior to plant uptake?

• How do these reactions impact phosphorus management?

Corn root: horizontal cross section

Epidermis

Root hair

Russell, 1977 Zea mays root cross-section, mature root

Cortex

Endodermis

Casparian strip

PhloemXylem Pericycle

Stele

Corn root cross section

Russell, 1977 Zea mays root cross-section, mature root

Vacuole

Cytoplasm

Cell wallPlasmodesmata

Symplasmic pathway: transport of nutrients through the cytoplasm

Marschner, 2002 Zea mays root cross-section, mature root

From rootepidermisand cortexTo xylem

Getting nutrients into the symplasmic pathway

CytoplasmVacuole

Plasmamembrane

Tonoplast

Marschner, 2002

Nitrate, phosphate, chloride:co-transport via a

proton pump

Nitrate, phosphate, chloride:co-transport via a

proton pump

H+

Anion

Cell wall

H+

Proton-ATPase pump(requires energy - ATP)

Moves H+ “uphill” againstthe electrical potential gradient andthe chemical potential gradient (pH)

ATP

pH 7.3-7.6 pH 5.5

-120 to -180 mV

Getting nutrients into the symplasmic pathway

CytoplasmVacuole

Plasmamembrane

Tonoplast

Marschner, 2002

Cations (except K)Uniport

Cations (except K)Uniport

Cell wall

Cation

Uniport:“downhill” of electrical potential gradient,

but energy is still neededto maintain the gradients

-120 to -180 mV

A comparison of ammonium and nitrate assimilation

Nitrogen form

Characteristic NO3- NH4

+

Directly stored in vacuoles? yes no

Form stored NO3- amino acids, amides

Energy costs of storage lower higher

Assimilation mechanism NO3- reduction Incorporated into

amino acids, amides

Mechanism products NH3, OH- Amino acids, amides, H+

Assimilated by roots? yes yes

Assimilated by shoots? yes no

Net C fixation by roots, (NO3-) basis 1x 5x (corn)

Marschner, 2002

Early corn growth and ammonium/nitrate ratios

5

4

3

2

1

0

Dry

wei

ght

(g p

lant

-1)

Totalconcentration

(mM)5.01.0

0.2

100 75 50 25 0 NH4+

Proportion of N formMarschner, 2002

1007550250 NO3-

Ammonium and nitrate: rhizosphere pH differences

NH4+

H+

pH

Acid

Basic

NO3-

OH-

Marschner, 2002

or HCO3-

Wheat – 2wksWheat – 2wks Corn – 8 wks oldCorn – 8 wks old

ScaleScale NO3-N NH4-N

200 kg N per ha

NO3-N NH4-N

Rōmheld

Effect of Nitrogen form on Rhizosphere pH

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Bulk soil pH

Rh

izo

sph

ere

pH

NH4+ Soy NH4

+ Corn

NO3- Soy NO3

- Corn

Riley and Barber, 1971; Soon and Miller, 1977

1:1

Why is there a need for both ammonium and nitrate?

• Rhizosphere pH control

• If rhizosphere pH drops too much, ammonium uptake becomes restricted, favoring nitrate uptake

• Reverse occurs if pH increases too much from nitrate uptake

• Carbon allocation and energy regulation

• Less photosynthate is needed for nitrate assimilation

• Nitrate has lower energy storage costs since it can be stored “as is”

• So the presence of both ions helps the plant regulate rhizosphere pH, energy expenditures, and carbon allocation

Rhizosphere pH affects P uptake by corn

• 11 day old corn

• Ammonium source reduced rhizosphere pH and increased P uptake

0

1

2

3

4

5

6

3 4 5 6 7 8 9

Rhizosphere pH

To

tal P

up

tak

e, m

g P

(g

DM

)-1

Soon and Miller, 1977

Wendigo SLMCP + CaCl2MCP + Ca(NO3)2

MCP + (NH4)2SO4

Buford SiLOneida L

Starter fertilizer: NH4+ and P should be placed together

Miller and Ohlrogge, 1958

400 800 1200 1600 2000

20

40

60

0

0

20-40 lb P/acre20-40 lb P/acre + 10 lb N, mixed

20-40 lb P/acre + 10 lb N, separate

Per

cent

of

the

plan

t P

com

ing

from

the

ban

d

Phosphate added to bulk soil, lb P2O5/acre

Occurs regardlessof P soil test levelOccurs regardlessof P soil test level

Common phosphate fertilizers with ammonium

• Monoammonium phosphate (MAP)

• NH4H2PO4

• pH of 0.1M solution is 4.0

• H2PO4- ↔ HPO4

2- + H+

• Diammonium phosphate (DAP)

• (NH4)2HPO4

• pH of 0.1M solution is 7.8

• HPO42- ↔ H2PO4

- + OH-

• Ammonium polyphosphate (APP)

• pH 6.0 – 6.5

• Hydrolysis reaction

Sauchelli, 1965

Photos courtesy of Agrium

Nitrification: Converts ammonium to nitrate

Important components of the reaction:

• Requires oxygen

• Reaction is acid-forming

2NH4+ + 3O2 → 2NO2

- + 4H+

Step 1: conversion to nitrite by the Nitrosomonas bacteria

Step 2: conversion to nitrate by the Nitrobacter bacteria

2NO2- + O2 → 2NO3

-

Havlin et al., 2005 Nitrosomonas (Natl. Inst. Res. Environ.)

Reaction of anhydrous ammonia

• Reaction of ammonia with water is base-forming

• Reaction is reversible at a higher pH

• Nitrification can acidify the band that was initially higher in pH

NH3 + H2O NH4+ + OH-

Ammonia hydrolysis (splits water):

Sauchelli, 1964

Nitrification

Measured pH changes after ammonia injection

3.5 in.

< 5.1

5.1 – 6.0

6.1 – 7.0

7.1 – 8.0

> 8.0

pHscale

1 day 3 weeks 10 weeks

Cochran, 1975

Laboratory experiment:Walla Walla SiLInitial pH = 5.5CEC = 17 meq/100gN rate was equivalent to 107 lb N/acre at 20 in. spacing

Acidification patterns in soil after knifed ammonia(ridge-slot plant system)

30 in.30 in.

0

10

6.7 6.1

5.5

6.7

6.7

5.8

6.46.7

0

10

6.25.6

6.8

6.86.55.9

6.8

2 months after an early May application

14 months after an early May application

Robbins and Voss, 1989 Webster clay loamWebster clay loam

Implications of soil acidification after ammonia applications

In reduced tillage systems with knifed ammonia applications, apply in the same zones each time

• The pH increases help reverse acidity resulting from nitrification from the previous applications

• Keeps subsurface acidity from spreading to other areas

Robbins and Voss, 1989

Effects of ammonia concentration on nitrification

0

50

100

150

200

250

300

0 200 400 600 800

Ammonia (NH3-N ppm)

Nit

rate

N (

pp

m)

0

1

2

3

4

5

6

7

8

9

pH

[NO3-] after 14 days

pH after 14 days

pH right after application

Eno et al., 1955

Recommendations based on ammonia reactions

• Ammonia is the preferred source for:

• Fall applications (sustained soil temp. below 50oF)

• Spring pre-plant applications on sandy soils

• Ammonia should be injected 6-10 in. deep on friable, moist soil to avoid:

• Volatilization losses

• Injury to seedlings

Reaction of urea

• Acid-consuming

• pH will not increase above 9.3

Urea hydrolysis at pH 6.5 – 8.0

CO(NH2)2 + H+ + 2H2O → 2NH4+ + HCO3

-urease

Urea hydrolysis at pH < 6.5

CO(NH2)2 + 2H+ + 2H2O → 2NH4+ + H2CO3

Koelliker and Kissel, 1988

urease

Volatilization of ammonia

The reaction NH4 ↔ NH3 + H+ is driven by:

• Difference in NH3 activity between where the fertilizer was applied and the surrounding air (windy conditions)

• Higher pH

• Higher temperature

• Lower CEC (maintains a higher solution NH4 concentration)

• Loss of CO2, which causes the pH to increase

• Contact with crop residues, which contain urease

Koelliker and Kissel, 1988

Phosphorus form affects urea volatilization

Ammonia loss

Treatment clay, pH 5.2 silty clay loam, pH 6.0

(% of urea N)

Urea 4.7 9.8

Urea + TSP 1.8 4.9

Urea + MAP 4.2 4.1

Urea + DAP 12.8 14.2

Total N was kept constant at 117 lb N/acreP rate was kept constant at 132 lb P2O5/acre

Fan and Mackenzie, 1993

Practical suggestions for urea use

• Avoid using as a preplant application on sandy soils

• Avoid contact with the seed

• Within 2 days:

• Incorporate to a depth of 2 to 4 inches or

• Receive or apply 0.25 to 0.5 in. of precipitation

• Other considerations for no-till

• Consider surface bands to reduce contact with urease

• If also applying P, band MAP or TSP with the urea at the surface

Summary

• N nutrition affects the pH of the soil surrounding the root and P uptake. Ammonium forms should be placed with P.

• When ammonia is formed, nitrification can be delayed

• In reduced tillage systems, acidification from nitrification needs to be controlled, possibly through the use of N fertilizers that are initially base-forming, repetitively banded in the same location

• Phosphorus can be a good product to co-apply with ammonium banded near the seed

• Phosphorus can be a good product to co-apply with urea banded at the surface

References

Anghinoni, I. and S.A. Barber. 1980b. Predicting the most efficient phosphorus placement for corn. Soil Sci. Soc. Am. J. 44:1016-1020.

Barber, S.A. 1984. Soil nutrient bioavailability: A mechanistic approach. Wiley Interscience, New York, NY.

Barber, S.A. 1978. Growth and nutrient uptake of soybean roots under field conditions. Agron. J. 70:457-461.

Cochran, V.L., F.E. Koehler, and R.I. Papendick. 1975. Straw placement: Its effect on nitrification of anhydrous ammonia. Agron. J. 67:537-540.

Edwards, J.H. and S.A. Barber. 1976. Phosphorus uptake rate of soybean roots as influenced by plant age, root trimming, and solution P concentration. Agron. J. 68:973-975.

Eno, C.F., W.G. Blue, and J.M. Good, Jr. 1955. The effect of anhydrous ammonia on nematodes, fungi, bacteria, and nitrification in some Florida soils. Agron. J. 19:55-58.

Fan, M.X. and A.F. Mackenzie. 1993. Urea and phosphate interactions in fertilizer microsites: Ammonia volatilization and pH changes. Soil Sci. Soc. Am. J. 57:839-845.

Havlin, J.L., J.D. Beaton, S.L. Tisdale, and W.L. Nelson. 2005. Soil fertility and fertilizers: An introduction to nutrient management. 7th ed. Pearson Prentice Hall, Upper Saddle River, NJ.

Koelliker, J.K. and D.E. Kissel. 1988. Chemical equilibria affecting ammonia volatilization. p.37-52. In B.R. Bock and D.E. Kissel (ed.) Ammonia volatilization from urea fertilizers. Bull. Y-206. Natl. Fert. Development Center, TVA, Muscle Shoals, AL.

Marschner, H.M. 2002. Mineral nutrition of higher plants. 2nd ed. Academic Press, New York, NY.

Mengel, D.B. and S.A. Barber. 1974. Rate of nutrient uptake per unit of corn root under field conditions. Agron. J. 66:399-402. Borkert, C.M. and S.A. Barber. 1985b. Predicting the most efficient phosphorus placement for soybeans. Soil Sci. Soc. Am. J. 49:901-904.

Miller, H.H. and A.J. Ohlrogge. 1958. Principles of nutrient uptake from fertilizer bands. I. Effect of placement of nitrogen fertilizer on the uptake of band-placed phosphorus at different soil phosphorus levels. Agron. J. 50:95-97.

Riley, D. and S.A. Barber. 1971. Effect of ammonium and nitrate fertilization on phosphorus uptake as related to root-induced pH changes at the root-soil interface. Soil Sci. Soc. Am. Proc. 35:301-306.

Robbins, S.G. and R.D. Voss. 1989. Acidic zones from ammonia application in conservation tillage systems. Soil Sci. Soc. Am. J. 53:1256-1263.

Russell, R.S. 1977. Plant root systems: Their function and interaction with the soil. McGraw-Hill, New York, NY.

Sauchelli, V. 1965. Phosphates in agriculture. Reinhold Publishing Co., New York, NY.

Sauchelli, V. 1964. Nitrogen: Chemical and physical properties. p.10-17. In V. Sauchelli (ed.) Fertilizer nitrogen: It’s chemistry and technology. ACS Monograph Ser. 161. Reinhold Publishing Co., New York, NY.

Soon, Y.K. and M.H. Miller. 1977. Changes in the rhizosphere due to NH4+ and NO3- fertilization and phosphorus uptake by corn seedlings (Zea mays L.). Soil Sci. Soc. Am. J. 41:77-80.

Maturationzone

Elongationzone

MeristematiczoneRoot cap

cells ahead of theapical meristem

Mucigel

Xylemtransports ions and

water to otherareas in the plant

Phloemtransports products of

photosynthesis to the roots

EndodermisEncases the stele

and acts as a barrier

Corn root: longitudinal cross section

Nutrient influx by roots

• Ions are not simply absorbed according to their ratios in solution

• Ions with this characteristic influx pattern require energy to be absorbed

• H2PO4-, HPO4

2-, NO3-

• K+, NH4+

• Maximum influx is reached at higher solution concentrations (Imax)

22-23 day old soybean roots22-23 day old soybean roots

Barber, 1984; Edwards and Barber, 1976

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3 4 5

Solution P, 10-6 lb P2O5/gal

Infl

ux,

10-1

4 lb

P2O

5 /

(in

s)

Imax

Fertilized soil fraction (%)

20 40 60 80 1000

Rel

ativ

e dr

y m

atte

r yi

eld

(%)

25

50

75

100

0

Corn

Soybean

10-3 lb P2O5 per pot

3.6

0.9

Anghinoni and Barber, 1980; Borkert and Barber, 1985b

P influx varies with plant age: The case for starter

-1

0

1

2

3

4

5

0 20 40 60 80 100 120

Plant age, days

Infl

ux,

10-5

lb

P2O

5 /

(in

. d

ay)

Corn

Soybean

Barber, 1978; Mengel and Barber, 1974

Corn can take in Pat a high rate early

(per unit of root)but not later

Corn can take in Pat a high rate early

(per unit of root)but not later