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Biomass, Nitrogen and Carbon Decomposition of Winter Cover Crops
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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