3. Franzluebbers and Stuedemann (2010) Soil Sci. Soc. Am. J. 74:2131-2141
Soil Organic Carbon Sequestration (kg
.
ha
-1 .
yr
-1
)
0 200 400 600 800 1000
Total
Soil
Nitrogen
Accumulation
(kg
.
ha
-1 .
yr
-1
)
0
20
40
60
80
100
TSN = 5.7 + 0.102 (SOC)
r
2
= 0.98
Relationship between soil C and N
accumulation

4. Linkage of nitrogen with active carbon
Soil microbial
activity biologically
sequesters N into
organic matter

5. Soil process relationships
Franzluebbers et al. (1999) Soil Sci. Soc. Am. J. 64:613-623

6. Available Nitrogen (kg ha
-1
)
Relative
Yield
(fraction)
0.0
0.2
0.4
0.6
0.8
1.0
Sites with high N
availability and low N
fertilizer response
Goal of enlarging the
biologically active N
pool without causing
N leakage
Inorganic nitrogen
 Surface soil
 Residual in profile
Organic nitrogen
 Long-term stable
 Biologically active
Accounting for
Available Nitrogen (kg N ha-1)
Sites with low N
availability and high
N fertilizer response
Idealized response to nitrogen

8. Virginia Tech – essential findings
Hairy vetch cover crop increased corn yield
• more than the N credit it supplied
Soil nitrate at V4 was correlated with N uptake
of the previous cover crop
Mineralizable C (1 and 28 day tests) prior to
planting and at V4 was not predictive of
unfertilized corn yield at 4 sites
Soil nitrate at V4 was correlated with
unfertilized corn yield (r = 0.45)

9. Predicting N supply from cover crops and soil
organic matter with ecologically-based models















318.03.8,
10
):(40.0
1max0084.0 NO
NC
NN
Y
whcc
whccwhwkcc 
where,






ngmineraliziNandtillage-noif0.020,
ngmineraliziNandtillageif0.034,
ngimmobiliziNandtillageif0.12,
wh
Step 1: Cover Crop N Supply Model
Difference in unfertilized corn yield (Mg/ha) between
a cover cropped soil and a bare fallow reference
Efficiency of N supply
is controlled by tillage
and N mineralization
vs. immobilization
Pre-emptive
competition for
soil NO3
- reduces
N supply
Winterkilled and winterhardy
species have different N
supply regulators
N mineralization/ immobilization is
controlled by microbial carbon use
efficiency and biomass stoichiometry
White et al. 2016. A model data-fusion approach for predicting cover crop nitrogen supply
to corn. Agronomy Journal. doi:10.2134/agronj2016.05.0288

10. Predicting N supply from cover crops and soil
organic matter with ecologically-based models
Best Model (r2=0.67)
Unfertilized Corn Yield (Mg/ha) =
-3.6 + 3.2*Soil %C + 0.14*% sand + 0.054*% silt + 0.46*Cov.Crop N Credit
Model with CO2 Burst (r2=0.60)
Unfertilized Corn Yield (Mg/ha) =
2.9 + (0.00017 * CO2Burst2)† + 0.14*% sand + 0.48*Cov.Crop N Credit
†Term is only included in tilled soils
Step 2: Soil Organic Matter N Supply Model
• Calibrated with unfertilized corn yields from 5 cover crop experiments (119
plots)
• N supply from cover crop residues was isolated using the previously
calibrated cover crop N supply model
• Find the best predictors of N supply from soil organic matter
• Tested total soil %C, 24hr CO2 burst, soil particle size fractions, tillage
vs. no-till in a general linear model stepwise selection process

11. NC State approach
Plant N uptake in semi-controlled
greenhouse experiments being explored

12. Plant N uptake in minor relationship with
total organic C
Pershing (2016) NC State University MS thesis

13. Plant N uptake in strong relationship with
mineralizable N
Pershing (2016) NC State University MS thesis

14. Plant N uptake in reasonable relationship
with the flush of CO2
Pershing (2016) NC State University MS thesis

15. Field trials to evaluate biological N supply
Example of 3 strips
fertilized with 0, 69,
and 125 kg N ha-1 at
sidedress
- Corn grain and silage in North Carolina and Virginia

16. 1 2 3 4
Soil sampling
(8 cores from each of 4 replicate locations)
Soil analyses
Flush of CO2, net nitrogen mineralization
Routine soil testing for pH, P, K, other elements (NC Dept Agric)
Bulk density, particle size, total C-N, microbial biomass C, inorganic N

17. 20 gal/acre sidedress
36 gal/acre sidedress
No sidedress
Nitrogen treatments applied 26 June 2015
(32 rows each)

18. Yield harvest
(18’ row sections at 12 points in each strip)
Plant analyses
Dry matter yield, stand density, nutrient concentration of forage,
including protein, fiber, minerals (Ca, P, S, Mg, Na, K, Cu, Fe, Mn,
Zn), ADF, NDF, nitrate (NC Dept Agric)

19. Collected yield estimates on 21 August 2015

21. Yield Results
Sidedress N Application (lb N/acre)
0 40 80 120
Corn
Silage
Yield
(ton/acre)
[35% DM]
0
10
20
30
40
Rep 1

22. Yield Results
Sidedress N Application (lb N/acre)
0 40 80 120
Corn
Silage
Yield
(ton/acre)
[35% DM]
0
10
20
30
40
Rep 2

23. Yield Results
Sidedress N Application (lb N/acre)
0 40 80 120
Corn
Silage
Yield
(ton/acre)
[35% DM]
0
10
20
30
40
Rep 3

24. Yield Results
Sidedress N Application (lb N/acre)
0 40 80 120
Corn
Silage
Yield
(ton/acre)
[35% DM]
0
10
20
30
40
Rep 4

25. Yield Results
Sidedress N Application (lb N/acre)
0 40 80 120
Corn
Silage
Yield
(ton/acre)
[35% DM]
0
10
20
30
40
Overall (n = 12)
Average yield = 23.6 ton/acre

26. Implications
Sidedress N Application (lb N/acre)
0 40 80 120
Corn
Silage
Yield
(ton/acre)
[35% DM]
0
10
20
30
40
Overall (n = 12)

27. Wheat grain evaluations in North Carolina

28. Flush of CO2 following Rewetting of Dried Soil
(mg CO2-C kg
-1
soil)0-3 days
0 100 200 300 400 500
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Relative
Yield
Without
In-Season
Nitrogen
Wheat
Tall fescue
Corn
Preliminary results
Unpublished data
We’re getting
excited about
the potential!

30. alan.franzluebbers@ars.usda.gov