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Biomass, Nitrogen and Carbon Decomposition of Winter Cover Crops

by Carol Elder — last modified November 29, 2005 03:36 PM

Research findings on residue decomposition of winter cover crops.

By M.L. Ruffo and G.A. Bollero

Rationale:

  • Temperature and moisture affect residue decomposition.
  • The use of Degree-Days and Decomposition-Days should account for the effect of temperature and moisture.
  • Estimate winter cover crops residue decomposition under realistic field conditions.

Objectives:

  • To estimate the equation parameters of biomass, C and N decomposition of winter cover crop residues expressed as a function of cumulative Degree Days and Decomposition Days.
  • Analyze the effect of locations, species and years on relative decomposition rates.

Materials and Methods:

  • Locations: Brownstown (Vertic albaqualf), Urbana (Typic endoaquoll)
  • Experimental Design: RCB 4 replications
  • Treatments: Rye (R), Hairy vetch (V) and Rye + Hairy vetch (RV)
  • Sampling: Residue biomass sampled 6 times during growing season. DM picked from 0.12 m-2 area. In the (RV) treatment, Rye and Hairy Vetch were separated. Residue analyzed for total C and total N.
  • Degree-Day: DGD = (T max + T min) / 2
  • Decomposition-Day:
  Moisture Coefficient:
  MCt = 0.5 * MCt-1 + PCt
  PCt =1, Pt > 4 mm
  PCt = Pt / 4, Pt < 4 mm 		    Temperature Coefficient:
  TC = (2 T2 322 - T4 / 324
  T (°C)= (T max + T min) / 2

The lowest of MC or TC limits Decomposition-Day accumulation. Added day by day from cover crop killing to corn harvest. Decomposition Model: Single-pool exponential decay.

Results:

Mean temperature and cumulative rainfall at Brownstown (BT) and Urbana (U), IL for 1999 and 2000.
Mean Temperature (°C)
Rainfall (mm)
 
1999
2000
 
1999
2000
 
BT
U
BT
U
 
BT
U
BT
U
May
18.2
18.1
19.3
17.9
  
110
89
120
157
June
22.5
22.1
22.0
21.1
  
89
156
169
115
July
26.2
25.7
23.4
22.7
  
99
97
92
62
August
22.3
21.7
24.1
22.9
  
56
127
146
80
Sept.
19.3
18.7
19.2
18.3
  
37
49
98
64
Mean
21.7
21.3
21.6
20.6
 Total
391
518
625
478

Brownstown:

Urbana:

View parameters of exponential decay models and goodness of fit statistics for carbon, nitrogen, and biomass decomposition as a function of degree-days.

View parameters of exponential decay models and goodness of fit statistics for carbon, nitrogen, and biomass decomposition as a function of decomposition-days.

Variance for random effects and significance level (p) for fixed effects on relative decomposition rate (k) of models using degree-days and decomposition-days.
Decomposition-Days
Degree-Days
 
C
N
Biomass
C
N
Biomass
Random
Effects
Variance Estimates
Year
0
0
0
0
0
0

Year x Location

0.0015
0.0026
0.0012
2.9 10-7
5.2 10-7
2.1 10-7
Year x WCC
0
0
0
0
0
0
Residual
0.0022
0.0048
0.0018
3.4 10-7
8.5 10-7
2.7 10-7
Fixed Effects
p>F
Location
0.64
0.70
0.54
0.78
0.86
0.62
WCC
0.02
0.04
0.028
0.006
0.018
0.006
Location x WCC
0.54
0.76
0.45
0.65
0.91
0.50

Conclusions:

  • Degree-Days and Decomposition-Days reflected weather differences between locations and years.
  • There was a significant effect of Winter Cover Crop on relative decomposition rate.
  • In Illinois, hairy vetch can be a potential source of N, while rye decomposes too slow to be a N source for corn production.
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