Ecological Intensification of Irrigated Corn and Soybean Systems
A project supported by:
University of NebraskaPotash & Phosphate InstituteFluid Fertilizer FoundationIMC GlobalNebraska Corn Board
Definitions, Concepts, Considerations
Crop Yield Potential (Yp)
What is it? Theoretically achievable yield solely determined by genetic
characteristics and climate (solar radiation, temperature).How to measure it?
(a) Calculated from components of yield and radiation use efficiency.(b) Estimated by crop simulation models.
How to achieve it? Fully-controlled, small-scale experiment to eliminate all biotic and
abiotic stresses (water, nutrients, pests).How to increase it?
(a) Breeding/germplasm improvement(b) Management: optimization of planting date in relation to variation
in Yp due to the seasonal pattern of radiation and temperature.
Variability of Crop Yield Potential
Annual variation of the simulated corn yield potential at Lincoln, NE
Source: J. Lindquist & D. Walters, UNL Ecological Intensification Project
Year1965 1970 1975 1980 1985 1990 1995 2000
Yie
ld p
ote
nti
al (
bu
/acr
e)
160
180
200
220
240
260
280
300
320
340 Yield limited by temp. and radiationmodern hybrid, 114 d to maturityPlanting: April 11, 35,000 pl./acre
Variability of Crop Yield Potential
Effect of planting date on corn yield potential at Lincoln, NE
Source: J. Lindquist & D. Walters, UNL Ecological Intensification Project
Planting date4/10 4/24 5/08 5/22 6/05
Yie
ld p
ote
nti
al (
bu
/acr
e)
230
232
234
236
238
240
242
244
246
248
250
Yield limited by temp. and radiationmodern hybrid, 114 d to maturityPlanting: 35,000 pl./acre
Attainable Crop Yield Potential (Ya)
What is it? Yield that can be achieved by minimizing abiotic and biotic stresses through the best available technology at a given site in a typical production field.
How to measure it? (a) Yield achieved in high-quality research experiments.(b) Yield achieved by yield contest winners.
How to achieve it? Optimize all soil and crop management to achieve high use efficiencies of solar radiation, water and nutrients. Minimize yield losses due to insects, diseases, weeds.
How to increase it? (a) Improve soil quality (gradual process).(b) Improve crop management (learning process)
General Relationship Between:Yield and Inputs + Management
Inputs + Management
Yield
max profit = Y/X = 0
Year or Location
Optimal Rate of Input
Average optimalrateY
X
Why is it Important to Raise Yield Potential?
Inputs + Management
Yield
Yp 2Ya 2
Yp 1Ya 1
Improved variety
Inferior variety
Yield Potential, Actual Yield, Profit and Resource Use Efficiency
A average response curveB increase in yield potential (Yp)C increase in input use efficiencyD increase in Yp and input use efficiency
Prices:Corn $1.80/buN $0.15/lb NAppl. $6.00/acre/appl.
A & B: 1 N applicationC & D 2 N applications
N rate (lb/acre)
0 50 100 150 200 250
Co
rn y
ield
(b
u/a
cre)
80
100
120
140
160
180
200
220
B
A
D
C
Yield Potential, Actual Yield, Profit and Resource Use Efficiency
N rate (lb/acre)
0 50 100 150 200 250
Gro
ss p
rofi
t ab
ove
N c
ost
($/a
cre)
180
200
220
240
260
280
300
320
340
360
Rat
e o
f re
turn
(R
OR
)($
pro
fit/
$in
pu
t)
-2
0
2
4
B
A
Max ROR Max Profit Max Y
ROR
A B increase in yield potential
Yield Potential, Actual Yield, Profit and Resource Use Efficiency
A C increase in input use efficiencyA D increase in Yp and input use efficiency
N rate (lb/acre)
0 50 100 150 200 250
Gro
ss p
rofi
t ab
ove
N c
ost
($/a
cre)
180
200
220
240
260
280
300
320
340
360
Rat
e o
f re
turn
(R
OR
)($
pro
fit/
$in
pu
t)
-2
0
2
4
Max ROR Max Profit Max Y
D
CRORA
Yield Potential, Actual Yield, Profit and Resource Use Efficiency
MAXIMUM PROFIT
A B C D
Gro
ss p
rofi
t ab
ove
N c
ost
($/a
cre)
200
220
240
260
280
300
320
340
360
A average response curveB increase in yield potential (Yp)C increase in input use efficiencyD increase in Yp and input use efficiency
Optimal N rate:A & B 162 lb/acreC & D 200 lb/acre
Yield Potential, Actual Yield, Profit and Resource Use Efficiency
A average response curveB increase in yield potential (Yp)C increase in input use efficiencyD increase in Yp and input use efficiency
lb N/acre for max yield
lb N/acre for max profit
N RATE @ Max Profit and Max Yield
A B C D0
50
100
150
200
250
Yield Potential, Actual Yield, Profit and Resource Use Efficiency
A average response curveB increase in yield potential (Yp)C increase in input use efficiencyD increase in Yp and input use efficiency
bu yield per lb N applied (PFP-N)
N Use Efficiency @ Max Profit
A B C D0.0
0.2
0.4
0.6
0.8
1.0
1.2
bu yield increase over unfertilized control per lb N applied (AE-N)
Why do we Need to Conduct Research on Understanding High Yields?
Average vs. Attainable Corn Yields
IOWA
Year1965 1970 1975 1980 1985 1990 1995 2000
Co
rn G
rain
Yie
ld (
bu
/acr
e)
0
50
100
150
200
250
300
350
400
IA, rainfed corn contest winner (4.1 bu/A/yr)IA, rainfed corn state average (1.5 bu/A/yr)
NEBRASKA
Year1965 1970 1975 1980 1985 1990 1995 20000
50
100
150
200
250
300
350
400
NE, rainfed corn contest winner (5.3 bu/A/yr)NE, rainfed corn state average (1.7 bu/A/yr)NE, irrigated corn contest winner (0 bu/A/yr)NE, irrigated corn state average (1.6 bu/A/yr)
12.1 million acres 8.6 million acres
Average vs. Attainable Soybean Yields
Source: modified from Specht et al., Crop Sci. 39 (1999), 1560-1570.
NEBRASKA
Year1970 1975 1980 1985 1990 1995 2000
So
ybea
n y
ield
(b
u/a
cre)
0
20
40
60
80
100
120NE, rainfed soybean contest winner (0.0 bu/A/yr)NE, rainfed soybean state average (0.4 bu/A/yr)NE, irrigated soybean contest winner (2.9 bu/A/yr)NE, irrigated soybean state average (0.6 bu/A/yr)Maximum yield research, USA
2.4 million acres rainfed1.1 million acres irrigated
Average vs. Attainable Corn Yields
IOWA
Year1965 1970 1975 1980 1985 1990 1995 2000
Co
rn G
rain
Yie
ld (
Mg
/ha)
0
5
10
15
20
25
IA, rainfed corn contest winner (257 kg/ha/yr)IA, rainfed corn state average (95 kg/ha/yr)
NEBRASKA
Year1965 1970 1975 1980 1985 1990 1995 20000
5
10
15
20
25
NE, rainfed corn contest winner (335 kg/ha/yr)NE, rainfed corn state average (107 kg/ha/yr)NE, irrigated corn contest winner (0 kg/ha/yr)NE, irrigated corn state average (98 kg/ha/yr)
4.9 million ha 3.5 million ha
Average vs. Attainable Soybean Yields
Source: modified from Specht et al., Crop Sci. 39 (1999), 1560-1570.
NEBRASKA
Year1970 1975 1980 1985 1990 1995 2000
So
ybea
n y
ield
(M
g/h
a)
0
1
2
3
4
5
6
7
8
9NE, rainfed soybean contest winner (0 kg/ha/yr)NE, rainfed soybean state average (27 kg/ha/yr)NE, irrigated soybean contest winner (197 kg/ha/yr)NE, irrigated soybean state average (37 kg/ha/yr)Maximum yield research
2.4 million acres rainfed1.1 million acres irrigated
How Does Soil Productivity Affect the Attainable Yield Potential?
Source: Johnson et al., 1999
Soil test K (lb/A)160 200 232 269 278
AE-N and PFP-N @ 160 lb N/A
0.2
0.4
0.6
0.8
1.0
1.2
1.4
N rate (lb/A)0 50 100 150 200 250 300 350
Yield (bu/A)
80
100
120
140
160
180
200
220
Soil test K 160 lb/A Soil test K 200 lb/A Soil test K 232 lb/A Soil test K 269 lb/A Soil test K 278 lb/A
PFP-N(bu/lb N)
AE-N(bu/lb N)
Corn, Ohio (1992-95)
What Causes the Variability of Yield in Relation to Inputs and Management?
Fertilizer N (lb/acre)0 50 100 150 200 250
Cor
n yi
eld
(bu/
acre
)
60
80
100
120
140
160
180
1996
19971999
1998
Same field in Lincoln, NE (1996-99)
Environmental Issues: Nitrate
Source: Broadbent & Carlton, 1978 N applied (kg/ha)0 100 200 300 400
Yield (bu/A) (t/ha)
0
2
4
6
8
10
12
0
30
60
90
120
150
180
N in crop or soil (kg/ha)
0
80
160
240
320
400
480
Yield
Inorganic N in soil
N in crop
Tagged N in soil
Irrigated corn, Davis, CA
Environmental Issues: Nitrate
Source: UNL, SCREC
Clay Center, NE, 18-yr LTE
0 200 400 600 800 1000 14001200 1600 1800 2000
0
2
4
6
8
10
12
1416
18
20
Cumulative Nitrate-N, kg ha-1
Dep
th,
m Continuous Corn
Corn-Soybean
Environmental Issues: C Sequestration
Source: T.O. West, ORNL, CSiTE project, 2000 (http://csite.esd.ornl.gov)
Average of long-term experiments, USA
Environmental Issues: C Sequestration
Source: Halvorson et al, Soil Sci. Soc. Am. J. 63 (1999), 912-917.
Dryland crop rotation, Akron, CO, 1984-94 (11 crops)
N rate (kg/ha)0 20 40 60 80 100 120
Mg
/ha
20
30
40
50
60
70
80
Total biomass
Total crop residues
N rate (kg/ha)0 20 40 60 80 100 120
So
il o
rgan
ic C
(M
g/h
a)
14
15
16
17
C-s
equ
estr
atio
n e
ffic
ien
cy (
%)
0
5
10
15
20
25
30
35Soil organic C
Increase in C-sequestration over control
Environmental Issues: N2O Emission
Sources: Bockman (1994), Eichner (1990)
Typical N2O emission from agricultural land:
1 to 2 kg N2O/ha per year
less than 1% of N applied
Median N2O emission (% of N applied):
Anhydrous ammonia 1.63% (range: 0.9-6.8)
Ammonium nitrate 0.40% (range: 0.04-1.7) Ammonium sulfate (chloride) 0.15% (range: 0.02-
1.7) Urea 0.11% (range: 0.01-0.6) Nitrate 0.05% (range: 0.01-1.8)
Global N fertilizer use (1999)
Million t N %World: Total N 83.0 100
Urea 39.6 48Ammonium nitrate 7.0 8Anhydrous ammonia 4.5 5Liquid N 4.2 5Other straight N 14.8 18Compound N 12.9 16
% of globalUSA: Total N 11.3 100 14
Urea 1.8 16 5Ammonium nitrate 0.6 5 9Anhydrous ammonia 3.6 32 80Liquid N 2.8 25 67Other straight N 0.3 3 2Compound N 2.2 19 17
Source: IFADATA, 2000
Kellogg Station, Michigan (1991-99)
-250
-200
-150
-100
-50
0
50
100
150C-W-S Chem & Till
C-W-S Chem, No-Till
C-W-S low inp/cov
C-W-S Organic/cov
Alfalfa
Poplar
Early Suc. (ab. 1989)
Mid Suc. (HT, ab. 1950)
Mid Suc. (NT, ab. 1959)
Forest
Relative net global warming potential (g CO2 equiv /m2/yr)*
Source: Robertson et al., Science 289 (2000), 1922-1925.
*Includes: soil C, N fertilizer, Lime, Fuel, N2O, CH4
Environmental Issues: Global Warming
What Do We Know About Growing Corn at Attainable Yield Potential Levels?
Yield contest winners: Continuous corn system (no rotation!) Deep soils with soil fertility built up to very high levels. Deep tillage (12-14’’). High plant density (41,000 to 44,000 plants/acre). Slow planting speed (2 mph); accurate plant spacing, less than 2%
skips. P, and K fertilizer inputs exceed average recommendations. Careful N management: Fall application for residue breakdown,
narrow band pre-plant N application (10’’ apart), starter fertilizer, sidedressing.
Frequent scouting and excellent pest control.
What Do We Know About Growing Corn at Attainable Yield Potential Levels?
Knowledge gaps:
Basic scientific understanding of yield-determining processes and how they are affected by management.
Solid scientific basis for efficient extrapolation to other locations (avoid trial and error).
Knowledge of how to design optimal systems managed at 70-80% of the yield potential.
Lack of studies that integrate productivity, profitability, and environmental consequences of high yield systems.
Research at UNL
Objectives
Quantify the yield potential of irrigated corn and soybean. Understand the physiological processes determining it.
Identify cost-effective and environmentally friendly crop management practices to achieve irrigated corn and soybean yields that approach potential levels.
Determine how changes in soil quality affect the ability to achieve yields that approach yield potential levels.
Quantify the energy use efficiency, soil C-sequestration and net radiative forcing potential of intensive corn and soybean management systems.
Ecological Intensification Project: Examples of the Questions Addressed
What is the yield and biomass potential of soybean and corn under irrigated conditions?
How much do current photosynthesis and stored carbohydrate stalk reserves contribute to grain yield at high yield levels?
Can we increase radiation and N use efficiency as we move yields up from present average yields to attainable yield levels?
What are the nutrient requirements to achieve genetic yield potential and how do they change with the yield level?
Do we need to increase soil quality to achieve optimal nutrient- and water-use efficiency at yield potential levels? How much?
What are the environmental consequences (nitrate loss, N2 emission, energy consumption, etc.) of high input systems required for achieving yields that approach yield potential levels?
What is the C-sequestration and net global warming potential of irrigated corn systems?
Key Investigators
Timothy J. Arkebauer Environmenal crop physiologyRobert M. Caldwell Soybean ecophysiology & modelingKenneth G. Cassman Crop physiology and plant nutritionRhae A. Drijber Soil microbial ecologyAchim Dobermann Soil fertility and plant nutritionJohn L. Lindquist Corn ecophysiology & modelingJohn P. Markwell BiochemistryLenis A. Nelson Plant breeding and crop production William Powers Soil physicsKenneth W. Russell Corn geneticsJames E. Specht Soybean geneticsDaniel T. Walters Soil fertility, C sequestration
Crop rotation (main plots)
CC Continuous corn CS Corn-soybean SC Soybean-corn
Plant population (subplots)
P1 corn: 30,000 plants/acre soybean: 150,000 plants/acreP2 corn: 37,000 plants/acre soybean: 185,000 plants/acreP3 corn: 44,000 plants/acre soybean: 220,000 plants/acre
Management intensity (sub-subplots) M1 recommend fertilizer management based on soil testing
corn: UNL recommendation for 200 bu/acre yield goal M2 intensive management aimed at yields close to yield potential
(higher fertilizer rates, micronutrients, N applied in 3 splits) Corn yield goal = 300 bu/acre
Irrigation:Drip irrigationSoil: siCL, pH 5.0-5.7, SOM 2.4-3.1%, P (Bray) 55-78 ppm, K 275-480 ppm
Experimental Details: Lincoln, NE
Experimental Design
SC CS CC CC SC CS
30,000 37,000 44,000 C|S 30,000 44,000 37,000 S|C 30,000 37,000 44,000 C|C 30,000 37,000 44,000 C|C 44,000 30,000 37,000 C|S 37,000 44,000 30,000
M1 M1 M2 | M2 M2 M1 | M2 M1 M2 | M1 M1 M2 | M2 M2 M1 | M2 M1 M2
202 204 206 | 208 210 212 | 214 216 218 | 402 404 406 | 408 410 412 | 414 416 418
30,000 37,000 44,000 | 30,000 44,000 37,000 | 30,000 37,000 44,000 | 30,000 37,000 44,000 | 44,000 30,000 37,000 | 37,000 44,000 30,000
M2 M2 M1 | M1 M1 M2 | M1 M2 M1 | M2 M2 M1 | M1 M1 M2 | M1 M2 M1201 203 205 | 207 209 211 | 213 215 217 | 401 403 405 | 407 409 411 | 413 415 417
37,000 44,000 30,000 C|S 44,000 37,000 30,000 S|C 37,000 30,000 44,000 C|C 44,000 37,000 30,000 C|S 37,000 30,000 44,000 S|C 30,000 37,000 44,000
M1 M2 M1 | M2 M2 M2 | M1 M1 M2 | M1 M2 M1 | M2 M1 M1 | M1 M1 M2
102 104 106 | 108 110 112 | 114 116 118 | 302 304 306 | 308 310 312 | 314 316 318
37,000 44,000 30,000 | 44,000 37,000 30,000 | 37,000 30,000 44,000 T 44,000 37,000 30,000 | 37,000 30,000 44,000 | 30,000 37,000 44,000
M2 M1 M2 | M1 M1 M1 | M2 M2 M1 40' M2 M1 M2 | M1 M2 M2 | M2 M2 M1101 103 105 | 107 109 111 | 113 115 117 L 301 303 305 | 307 309 311 | 313 315 317
CC CS SC SC CS CC
|--20'--|
Fertilizer Program (Corn)
Treatment Growth Stage1999 2000
C after S, M1 Pre-plant 65 103V6 65 35Total 130 138
C after S, M2 Pre-plant 105 103V6 60 100V10 60 95Total 225 298
C after C, M1 Pre-plant - 103V6 - 100Total - 203
C after C, M2 Pre-plant - 103V6 - 130V10 - 130Total - 363
M1: no other nutrients appliedM2: 44 kg P/ha, 85 kg K/ha, 21 kg S/ha
N rate (kg/ha)
Corn: Grain Yield 1999
Source: UNL Ecological Intensification Project (not for citation without permission).
Population density (plants/acre)
30000 37000 44000
Gra
in y
ield
(b
u/a
cre)
100
150
200
250
300
Gra
in y
ield
(M
g/h
a)
8
10
12
14
16
18M0 - C-S, ControlM1 - C-S, RecommendedM2 - C-S, Intensive
Source: UNL Ecological Intensification Project (not for citation without permission).
Corn: N uptake 1999
Population density (plants/acre)
30000 37000 44000
To
tal N
up
take
(kg
/ha)
50
100
150
200
250
300
350
400M0 - C-S, ControlM1 - C-S, RecommendedM2 - C-S, Intensive
Source: UNL Ecological Intensification Project (not for citation without permission).
Corn: P uptake 1999
Population density (plants/acre)
30000 37000 44000
To
tal P
up
take
(kg
/ha)
25
30
35
40
45
50
55
60M0 - C-S, ControlM1 - C-S, RecommendedM2 - C-S, Intensive
Source: UNL Ecological Intensification Project (not for citation without permission).
Corn: K uptake 1999
Population density (plants/acre)
30000 37000 44000
To
tal K
up
take
(kg
/ha)
100
150
200
250
300
350M0 - C-S, ControlM1 - C-S, RecommendedM2 - C-S, Intensive
Source: UNL Ecological Intensification Project (not for citation without permission).
Nutrient Uptake Requirements
Based on 1999 data
Plant pop Management N P K S Mg
30,000 recommended (220 bu/a) 0.90 0.18 0.95 0.10 0.1244,000 intensive (260 bu/a) 0.98 0.16 1.19 0.09 0.11
30,000 recommended (220 bu/a) 0.30 0.14 0.19 0.06 0.0744,000 intensive (260 bu/a) 0.33 0.13 0.18 0.05 0.06
Nutrient uptake requirement (lb/bu)
Nutrient removal with grain (lb/bu)
July 21, 2000
July 21, 2000
Source: UNL Ecological Intensification Project (not for citation without permission).
Corn: Total Biomass 2000
Population density (plants/acre)
30000 37000 44000
To
tal a
bo
veg
rou
nd
dry
mat
ter
(Mg
/ha)
10
15
20
25
30M0 - C-S, Control M1 - C-S, Recommended M2 - C-S, Intensive M0 - C-C, Control M1 - C-C, RecommendedM2 - C-C, Intensive
Source: UNL Ecological Intensification Project (not for citation without permission).
Corn: Grain Yield 2000
Population density (plants/acre)
30000 37000 44000
Gra
in y
ield
(b
u/a
cre)
100
150
200
250
300
Gra
in y
ield
(M
g/h
a)
8
10
12
14
16
18M0 - C-S, Control M1 - C-S, Recommended M2 - C-S, Intensive M0 - C-C, Control M1 - C-C, RecommendedM2 - C-C, Intensive
Source: UNL Ecological Intensification Project (not for citation without permission).
Corn: N uptake 2000
Population density (plants/acre)
30000 37000 44000
To
tal N
up
take
(kg
/ha)
50
100
150
200
250
300
350
400M0 - C-S, Control M1 - C-S, Recommended M2 - C-S, Intensive M0 - C-C, Control M1 - C-C, RecommendedM2 - C-C, Intensive
Corn: Biomass Dynamics
Source: J. Lindquist, UNL Ecological Intensification Project (not for citation without permission).
Development stage:
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Dry
mat
ter
(kg
/ha)
0
5000
10000
15000
20000
25000 19992000
V10 Anthesis Phys. Maturity
V6
simulated total DM
simulated reprod. DM
Measured INTERCOM model37,000 plants/acreNo constraints other than T and radiation.
Possible Causes of Lower Attainable Yield in 2000 versus 1999?
Late-season high (night) temperatures causing increased maintenance respiration and shorter grain filling period?
Over-expression of vegetative biomass growth in relation to the actual yield potential?
Non-linear relationship between leaf-N, respiration rate, and temperature?
Mild water stress due to high vapor pressure deficit or imperfect irrigation?
Early insect damage? Subtle yield losses from undetected diseases?
Growth and Development
Source: J. Lindquist, UNL Ecological Intensification Project (not for citation without permission).
19992000
Emergence to anthesis 59 d 67 dAnthesis to maturity 56 d 45 d
Total growth period 115 d112 d
Average Daily Temperature
Development stage:
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Ave
rag
e T
emp
erat
ure
(C
)
10
15
20
25
30
35
19992000
V10 Anthesis Phys. Maturity
V6
Source: UNL Ecological Intensification Project (not for citation without permission).
Simulated Daily Crop Maintenance Respiration Rate
Source: J. Lindquist, UNL Ecological Intensification Project (not for citation without permission).
Development stage:
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mai
nte
nan
ce R
esp
irat
ion
(k
g d
ry m
atte
r h
a-1
d-1
)
0
100
200
300
400
500
19992000
V10 Anthesis Phys. Maturity
V6
INTERCOM model37,000 plants/acreNo constraints other than T and radiation.
Nitrogen Use Efficiency: 1999
Source: UNL Ecological Intensification Project (not for citation without permission).
Corn after soybean Pop 30 Pop 37 Pop 44Partial factor productivity (PFP) M1 1.87 1.91 1.96
(bu yield/lb N applied) M2 1.15 1.20 1.26
Agronomic efficiency (AE) M1 0.49 0.54 0.59(bu yield increase/lb N applied) M2 0.36 0.41 0.47
Recovery efficiency (RE) M1 0.77 0.64 0.72(lb N uptake increase/lb N applied) M2 0.51 0.55 0.67
Physiological efficiency (PE) M1 0.64 0.84 0.82(bu yield increase/lb N uptake increase) M2 0.71 0.75 0.70
Internal efficiency (IE) M0 1.40(bu yield/lb N uptake) M1 1.07 1.18 1.16
M2 1.07 1.08 1.02
Nitrogen Use Efficiencies: 2000
Source: UNL Ecological Intensification Project (not for citation without permission).
Corn after soybean Corn after cornPop 30 Pop 37 Pop 44 Pop 30 Pop 37 Pop 44
Partial factor productivity (PFP) M1 1.83 1.90 1.88 1.16 1.17 1.15(bu yield/lb N applied) M2 0.85 0.92 0.86 0.68 0.69 0.66
Agronomic efficiency (AE) M1 0.92 0.98 0.97 0.55 0.56 0.54(bu yield increase/lb N applied) M2 0.43 0.50 0.44 0.34 0.35 0.32
Recovery efficiency (RE) M1 1.11 1.05 0.90 0.54 0.58 0.52(lb N uptake increase/lb N applied) M2 0.56 0.68 0.60 0.44 0.43 0.39
Physiological efficiency (PE) M1 0.83 0.94 1.08 1.03 0.96 1.04(bu yield increase/lb N uptake increase) M2 0.77 0.74 0.74 0.78 0.83 0.83
Internal efficiency (IE) M0 1.17 1.22(bu yield/lb N uptake) M1 0.99 1.06 1.14 1.12 1.08 1.13
M2 0.94 0.90 0.91 0.95 0.98 0.99
Nitrogen Use Efficiency: Corn 1999
Source: UNL Ecological Intensification Project (not for citation without permission).
30000 37000 44000Ag
ron
om
ic e
ffic
ien
cy o
f N
(b
u/lb
)
0.0
0.2
0.4
0.6
0.8
1.0M1 - C-S, RecommendedM2 - C-S, Intensive
Population density (plants/acre)
30000 37000 44000Rec
ove
ry e
ffic
ien
cy o
f N
(lb
/lb)0.0
0.2
0.4
0.6
0.8
1.0
1.2
Nitrogen Use Efficiency: 2000
Source: UNL Ecological Intensification Project (not for citation without permission).
Population density (plants/acre)30000 37000 44000A
gro
no
mic
eff
icie
ncy
of
N (
bu
/lb)
0.0
0.2
0.4
0.6
0.8
1.0
M1 - C-S, Recommended M2 - C-S, Intensive
30000 37000 44000Rec
ove
ry e
ffic
ien
cy o
f N
(lb
/lb)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
M1 - C-C, RecommendedM2 - C-C, Intensive
1999 Five farms in Nebraska
28,000 pl/A
155 lb N/A (all pre-plant)
sprinkler irrig.
Ecol. Int. expt. at UNL
30,000 pl/A
118 lb N/A (pre-plant+V6)
drip irrigation
Ecol. Int. expt. at UNL
44,000 pl/A
205 lb N/A (pre-plant,V6,V10) drip irrigation
Corn yield (bu/acre) 160 220 258
% of yield potential 52 73 86
Bushel yield per lb N applied (PFP N)
1.03 1.87 1.26
Bushel yield increase per lb N applied (AE N)
0.36 0.49 0.47
Recovery efficiency of applied N (%, RE N)
43 70 67
Gross return above fertilizer cost ($/acre)
291 410 461
Source: UNL Ecological Intensification Project; Prices: corn $2/bu, N $0.15/lb, $6/acre per N application
Crop Residue C After 2000 Harvest
Source: UNL Ecological Intensification Project (not for citation without permission).
M1-CS-30 M2-CS-44
To
tal C
in b
iom
ass
(Mg
/ha)
0
1
2
3
4
5
6
7
8
9
10Root Stalk+Leaf Cob 7.3 Mg C/ha
8.2 Mg C/ha
Soil CO2 flux for 37,000 plants per acre
Source: T. Arkebauer, UNL Ecological Intensification Project (not for citation without permission).
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0 50 100 150 200 250 300 350 50 100 150 200 250 300 350Day of year
So
il C
O2
flu
x (m
g m
-2 s
-1) M2 - INTENSIVE MANAGEMENT
M1 - RECOMMENDED MANAGEMENT
1999 2000
N2O-N flux in Corn Treatments with Different
Levels of Fertility Management, 2000
Source: T. Arkebauer, UNL Ecological Intensification Project (not for citation without permission)
Control no N appliedM1 Recommended fertility management M2 Intensive fertility management
Treatment 23 May 12 July 24 August
g N ha-1 d-1
Control 0.8±0.5 a 0.6±0.6 a 1.9±0.9 a
M1 1.3±1.5 a 5.9±7.5 a 7.1±8.8 a
M2 4.2±3.3 b 24.0±19.7 b 20.6±11.4 b
Conclusions
Yield potential varies significantly from year to year.
Maximum profit is achieved at yield levels that approach the maximum attainable yield.
75 to 85% of the yield potential (220-260 bu/a) is likely to be the most efficient and profitable yield target for high-yielding systems.
Optimal plant density and N and K input depend on yield potential.
Maximum attainable yield requires higher plant density (37-44k plants/acre) and greater amounts K per bushel yield.
Some Challenges
Plant physiology & crop modeling: better understanding of processes governing fluctuation of yield potential in relation to climate and management.
Role of non-structural carbohydrates for grain filling? Quantitative estimates of root biomass and exudates. High N2O losses: how to improve N management in
combination with water management? Optimal timing and form of N? Use real-time N management?
Disease control at high yield levels. Hypothesis: maximum profit and enhanced
environmental quality are not mutually exclusive in high yield systems.
Key References
Broadbent, F.E., and A.B. Carlton. 1978. Field trials with isotopically labeled nitrogen fertilizer. p. 1-41. In Nitrogen in the environment. Vol. 1. Academic Press, New York.
Cassman, K.G. 1999. Ecological intensification of cereal production systems: Yield potential, soil quality, and precision agriculture. Proc. Natl. Academy of Science 96:5952-5959.
de Witt, C.T. 1992. Resource use efficiency in Agriculture. Agric. Systems 40:125-151.Duvick, D.N., and K.G. Cassman. 1999. Post-green revolution trends in yield potential of
temperate maize in the North-Central United States. Crop Sci. 39:1622-1630. Gifford, R.M. and L.T. Evans. 1981. Photosynthesis, carbon partitioning, and yield. Ann. Res. Plant
Physiol. 32:485-509. Greenwood, D.J., G. Lemaire, G. Gosse, P. Cruz, A. Draycott, and J.J. Neetson. 1990. Decline in
percentage N of C3 and C4 crops with increasing plant mass. Ann. Bot. 66:425-436. Loomis, R.S., and J.S. Amthor. 1999. Yield potential, plant assimilatory capacity, and metabolic
efficiencies. Crop Sci. 39:1584-1596. Specht, J.E., D.J. Hume, and S.V. Kumudini. 1999. Soybean yield potential - a genetic and
physiological perspective. Crop Sci. 39:1560-1570. Sinclair, T.R., and T. Horie. 1989. Leaf nitrogen, photosynthesis, and crop radiation use efficiency:
a review. Crop Sci. 29:90-98.