Residue and nitrogen dynamics Residue and nitrogen dynamics in reduced thermal and non-in reduced thermal and non-thermal Kentucky bluegrass thermal Kentucky bluegrass

seed production systemsseed production systems

Karl Umiker and Jodi Johnson-MaynardKarl Umiker and Jodi Johnson-MaynardUniversity of IdahoUniversity of Idaho

General research objectives:

1. Determine impacts of residue management strategies on nitrogen cycling.

2. Encourage timely residue decomposition.

What controls decomposition?

1. Organismsmacro to microfauna, microflora

2. Climate

3. Residue status - C:N

Approach: To understand the natural reactions that control residue decomposition.

Residue decomposition:

Residue Carbon Decomposition

• Amount of carbon

• Size of residue

• Type of carbon– % Lignin

• Availability of nitrogen– how fast and how much

C:N Ratio of Materials

Material C:N Ratio

Microbes ~8

Microbial Food ~24

Soil ~12-15

Total Residue – May ~16

Total Residue - August ~55-60

Non-standing residue - June ~22

Standing residue - June ~32

Site Descriptions

Kootenai Co. Site• Thermal vs. Non-

thermal• Annual Harvest• Variety: ‘Alene’• Treatments:

-Full Load Burn

-Bale and Burn

-Bale, Mow, and Harrow

10

20

30

40

50

60J

ul-

02

Se

p-0

2

Oc

t-0

2

De

c-0

2

Ja

n-0

3

Ma

r-0

3

Ma

y-0

3

Ju

n-0

3

Re

sid

ue

C:N

Full Load Burn

Bale and Burn

Bale, Mow, and Harrow

Kootenai Co. Site – C:N Ratio

rake/bale

burnmow/harrow

Kootenai Co. Site - %N

0.0

0.5

1.0

1.5

2.0

2.5

Jul-

02

Sep

-02

Oct

-02

Dec

-02

Jan

-03

Mar

-03

May

-03

Jun

-03

Re

sid

ue

%N

Full Load BurnBale and BurnBale, Mow, and Harrow

burnrake/bale mow/harrow

Kootenai Co Site – ‘Alene’

Fall 2002

System Bale/mow/ harrow

Bale/burn Burn

Kootenai Co. Site – ‘Alene’ Residue

0.0

1.0

2.0

3.0

4.0

5.0

Aug 8

-02

Sept 9

-02

Oct 22

-02

Nov 20-

02

May

7-03

June

23-

03

Res

idu

e (t

on

s/ac

re)

Full Load Burn

Bale and Burn

Bale, Mow, and Harrow

Wintermow/harrow bale/ burn

Summary: Residue C:N

• C:N values range from 60 – 13

• Values coalesce during the spring

• Separate fertilizer recommendations may be needed for non-thermal systems– aid in decomposition– nitrate depression

• Total residue vs. standing and non-standing

Summary:Residue Amount

• Non-thermal treatment at the Kootenai Co. site had ~1 ton/acre more residue than in the thermal treatments

• Baling may not be necessary in all systems

• Variety and/or site-specific climate conditions may influence the success of non-thermal residue management practices