Water Productivity for Corn as Affected by Irrigation and Nitrogen Fertilization
Daran R. Rudnick, Ph.D.Assistant Professor: Irrigation Specialist
Department of Biological Systems EngineeringWest Central Research and Extension Center
University of Nebraska-LincolnPhone: (308) 696-6709, Email: [email protected]
September 7-9, 2016
Personal Background
• Hometown: South Sioux City, Nebraska
• Education:
• B.S. Biological Systems Engineering, UNL, 2011
• M.S. Agricultural and Biological Systems Engineering, UNL, 2013
• Ph.D. Agricultural and Biological Systems Engineering, UNL, 2015
HometownSouth Sioux City, NE
WCRECNorth Platte, NE
UNLLincoln, NE
Nebraska Precipitation
Precipitation, mm
100 - 200
200 - 250
250 - 300
300 - 350
350 - 400
400 - 450
450 - 500
500 - 550
550 - 650
> 650
2000 2005
2010 Lng-Term
Avg.
Precipitation Increases West to East Irrigation Increases East to West
Source: Rudnick et al. (2015)
Why do we Irrigate??
When precipitation and soil water storage in the crop root zone cannot supply the root system with enough water to meet crop evapotranspiration (ET) demand, irrigation is required.
Insufficient Irrigation can reduce:
• Total Biomass
• Grain Yield
• Grain Quality
• Net Return ($ per ha)
Excessive irrigation can result in:
• Runoff
• Soil Erosion
• Deep Percolation of Water (and Nutrients)
• Environmental Degradation
• Anaerobic Soil Conditions (Yield Penalty)
• Increased Pumping Cost (i.e., energy cost)
Water Stress Impact on Crop Performance
The effects of water stress will depend on the timing and magnitude of water stress. Whole plant responses to water stress conditions include:
• Reduced Assimilation Flux to Growing Organs
• Decreased Photosynthesis and Respiration
• Greater Ear and Kernel Abortion
• Accelerate Leaf Senescence
• Increased Root/Shoot Ratio
• Delayed Silk Growth
• Reduced leaf area
• Stomatal Closure
Full Irrigation Limited Irrigation Rainfed
Nitrogen Stress Impact on Crop Performance
Nitrogen (N) fertilizer has a positive impact on:
• Leaf Area Index
• Leaf Area Duration
• Crop Photosynthetic Rate
• Percent Radiation Interception
• Plant Height
• Shoot Weight
• Plant N Uptake Potential
84 kg N ha-1 196 kg N ha-1
Irrigation & NitrogenStress
Source: Rudnick and Irmak (2013)
Confounding Effects between Water and Nutrient Availability.
Nutrient & Water Deficient Crops can have Lower Water Use Rates and Yields
South Central Agricultural Laboratory (SCAL)
The main plots were irrigation level: fully-irrigated (FIT), 75% of fully-irrigated (75% FIT),and rainfed and the subplots were nitrogen level: 0, 84, 140, 196, and 252 kg N ha-1.
Rainfed
75% FIT
FIT
0 20 40 6010Meters
Observations:1. Neutron Gauge Θv2. John Deere Θv3. PR1 Θv4. Matric Potential Ψm
5. Electrical Conductivity
6. Texture Analysis7. Organic Matter8. Bulk Density9. Hydraulic Properties10. Plant Height
11. Leaf Area Index12. Stomatal Resistance13. SPAD Chlorophyll Meter
Irrigation Events2011: 27 July, 4 Aug., 10 Aug., and 27 Aug.
2012: 7 July, 17 July, 1 Aug., and 12 Aug.
2013: 10 July, 26 July, and 6 Sept.
2014: 31 July and 7 Aug.
Irrigation System
Seasonal Precipitation
0
100
200
300
400
500
600
0 25 50 75 100 125 150 175
Gro
win
g Se
aso
n P
reci
pit
atio
n (
mm
)
Days After Planting
2011
2012
2013
2014
Lng-Term
𝐶𝑊𝑈𝐸 =𝐺𝑟𝑎𝑖𝑛 𝑌𝑖𝑒𝑙𝑑
𝐸𝑣𝑎𝑝𝑜𝑡𝑟𝑎𝑛𝑠𝑝𝑖𝑟𝑎𝑡𝑖𝑜𝑛
Crop Water Use Efficiency (CWUE, kg m-3)
Evaporation• Water loss to the atmosphere from the
soil & canopy interception• Dominant process early in the growing
season• Not associated with grain development
Transpiration• Water taken up by the plant and
released through the plant’s stomata• Dominant process following canopy
closure• Associated with grain development
𝐼𝑊𝑈𝐸 =𝐼𝑟𝑟𝑖𝑔𝑎𝑡𝑒𝑑 𝑌𝑖𝑒𝑙𝑑 − 𝑅𝑎𝑖𝑛𝑓𝑒𝑑 𝑌𝑖𝑒𝑙𝑑
𝑆𝑒𝑎𝑠𝑜𝑛𝑎𝑙 𝐼𝑟𝑟𝑖𝑔𝑎𝑡𝑖𝑜𝑛
Irrigation Water Use Efficiency (IWUE, kg m-3)
Crop Water Useand Uptake Dynamics
𝐸𝑇𝑎 = 𝑃 + 𝐼 + 𝑈 − 𝑅 − 𝐷𝑃 ± ∆𝑆
where:
P = Precipitation, mm
I = Irrigation, mm
U = Upward water flux, mm
R = Runoff, mm
DP = Deep Percolation, mm
∆S = Soil Water Storage Change, mm
Irrometer Watermark
Delta-T PR1-C Probe
Troxler 4302 Neutron Gauge
John Deere Capacitance Probe
Crop Evapotranspiration
Weekly Corn ET
Source: Rudnick and Irmak (2015)
Impact of Irrigation on Corn ET
0
100
200
300
400
500
600
2011 2012 2013 2014
Evap
otr
ansp
irat
ion
(m
m)
Rainfed Limited Full
Impact of Nitrogen on Corn ET
• Nitrogen has a lower effect on water use as compared with irrigation.
2011y = -0.0503x + 259.04
R² = 0.13
2012y = -0.0023x + 231.01
R² = 0.00
200
225
250
275
300
0 50 100 150 200 250 300
Ve
geta
tive
ETa
, mm
Nitrogen Fertilizer Rate, kg ha-1
2011 2012
125
175
225
275
325
0 50 100 150 200 250 300R
ep
rod
uct
ive
ETa
, mm
Nitrogen Fertilizer Rate, kg ha-1
Rainfed Limited (75% FIT) Full (FIT)
Pooled
Vegetative Growth Stage:
2011: Slope not statistically different from zero (P0.05 = 0.2352)
2012: Slope not statistically different from zero (P0.05 = 0.7659)
Reproductive Growth Stage:
Rainfed: Slope not statistically different from zero (P0.05 = 0.0505)
Limited: Slope is statistically different from zero (P0.05 = 0.0028)
Full: Slope is statistically different from zero
(P0.05 < 0.0001)
Evapotranspiration versus Nitrogen Rate
Soil Water Uptake Dynamics
0 – 0.30 m
0.30 – 0.60 m
0.60 – 0.90 m
0.90 – 1.20 m
1.20 – 1.50 m
0 20 40 6010 Meters
Soil Water Extraction, mm
0 - 25
25 - 50
50 - 75
75 - 100
100 - 125
125 - 150
150 - 175
175 - 200
200 - 225
225 - 250
250 - 275
> 275
0 – 1.50 m
Soil Water Extraction, mm
0 20 40 6010 Meters
370 - 400
400 - 430
430 - 450
450 - 470
470 - 485
485 - 500
500 - 510
510 - 520
520 - 530
530 - 545
Rainfed
75% FIT
FIT
Source: Rudnick and Irmak (2014)
0 10 20 30 40 50 60
0 - 0.3
0.3 - 0.6
0.6 - 0.9
0.9 - 1.2
1.2 - 1.5
Soil Water Extraction (%)
Soil
Dep
th (
m)
Rainfed
Lim. Irrig.
Full Irrig.
Fully Irrigated
Rainfed
Limited Irrigation
Source: Rudnick and Irmak (2014), Trans. ASABE 57(2): 445-462.
Irrigation Management can Impact Soil Water Extraction Patterns – Corn at SCAL
Individual soil layer water extraction patterns, with respect to growing degree days (GDD), days after planting, and growth development stages.
Source: Rudnick and Irmak (2014)
Temporal Trends in Corn Soil Water Extraction(Clay Center, NE – 2012)
Individual soil layer water extraction patterns, with respect to growing degree days (GDD), days after planting, and growth development stages.
Source: Rudnick and Irmak (2014)
Temporal Trends in Corn Soil Water Extraction(Clay Center, NE – 2012)
0 10 20 30 40 50 60
0 - 0.3
0.3 - 0.6
0.6 - 0.9
0.9 - 1.2
1.2 - 1.5
Soil Water Extraction (%)
Soil
Dep
th (
m)
0 kg/ha
84 kg/ha
140 kg/ha
196 kg/ha
252 kg/ha
Source: Rudnick and Irmak (2014), Trans. ASABE 57(2): 445-462.
Soil Water Extraction Patterns Affected by Nitrogen – Corn at SCAL
Improving Estimation of Crop Water Uptake
Quantifying Water Use (i.e., evapotranspiration, ET)
• Direct measurements (e.g., lysimeter, Bowen ratio energy balance system, eddy covariance, etc.)
• Expensive and challenging to deploy and maintain
• Expert knowledge required to operate, analyze, and interpret data
• Estimation methods (e.g., mathematical models)
• More practical for producers, but less accurate
• Simplified method: Two-step approach
𝐾𝑐𝑟 =𝐶𝑟𝑜𝑝 𝐸𝑇
𝐴𝑙𝑓𝑎𝑙𝑓𝑎 𝐸𝑇=𝐸𝑇𝑐𝑟𝑜𝑝𝐸𝑇𝑟𝑒𝑓
Source: Irmak (2009), NebGuide G1850.
𝐸𝑇𝑐𝑟𝑜𝑝 = 𝐾𝑐 × 𝐸𝑇𝑟𝑒𝑓
Source: High Plains Regional Climate Center (HPRCC)
• Need to be adjusted for local conditions
• Adjustments: Relative humidity, wind speed, crop height, leaf area index, & water stress.
Corn Soybean Wheat Sugar Beet Dry Beans Sorghum Sunflower
G. Stage Kc G. Stage Kc G. Stage Kc G. Stage Kc G. Stage Kc G. Stage Kc G. Stage Kc
2 Leaves 0.10 Cotyledon 0.10 Emergence 0.10 Emergence 0.10 Emerg-10% Cover 0.06 Emergence 0.10 Early Veg. 0.10
4 Leaves 0.18 First Node 0.20 Visual Crown 0.50 20-30% Cover 0.14 10-50% Cover 0.06 3 Leaves 0.15 Bud Format 1.00
6 Leaves 0.35 Second Node 0.40 Leaf Elong. 0.90 30-50% Cover 0.21 50-80% Cover 0.48 5 Leaves 0.31 Flower Initial 1.10
8 Leaves 0.51 Third Node 0.60 Jointing 1.03 50-70% Cover 0.34 80-100% Cover 0.81 8 Leaves 0.56 50% Disk Flower 1.15
10 Leaves 0.69 Beg. Bloom 0.90 Boot 1.10 70-80% Cover 0.48 Full Cover 1.00 Final leaf 0.87 Early Seed 1.15
12 Leaves 0.88 Full Bloom 1.00 Heading 1.10 80-90% Cover 0.60 Pod Elongation 1.00 Boot 1.10 Late Seed 1.15
14 Leaves 1.01 Beg. Pod 1.10 Flowering 1.10 90-100% Cover 0.73 Pod Fill 0.83 Half Bloom 1.10 Mature 0.20
16 Leaves 1.10 Full Pod 1.10 Grain Fill 1.10 Full Cover 0.83 Dry Down 0.59 Soft Dough 1.10
Silk (R1) 1.10 Beg. Seed 1.10 Stiff Doug 1.00 Max LAI 0.91 Senescence 0.30 Hard Dough 0.84
Blister (R2) 1.10 Full Seed 1.10 Ripening 0.50 Root Stg 0.91 Mature 0.09 Mature 0.10
Dough (R4) 1.10 Beg. Maturity 0.90 Mature 0.10 After Frost 0.90
Beg. Dent 1.10 Full Maturity 0.20
Full Dent 0.98 Mature 0.10
Black Layer 0.60
Full Maturity 0.10
General Crop Coefficients (Alfalfa Based)
Jensen, 1968: Crop coefficients (Kc) are “assumed” to represent the relativeamount of radiant energy available as compared to the reference surface andthe combined relative effects of resistance to:
i. Water movement from the soil to the evaporative surfaces
ii. Diffusion of water vapor from the evaporating surfaces through the laminar boundary layer
iii. Turbulent transfer to the free atmosphere
Therefore, Kc is “assumed” as an integrated factor that implicitly accounts forall factors affecting the difference in diffusion of water vapor through the soil-plant-atmosphere continuum as compared with the reference surface.
Most Kc studies are conducted under non-limiting water and nutrient (e.g.,nitrogen) conditions.
Crop Coefficients
𝐸𝑇𝑟𝑒𝑓 =0.408∆ 𝑅𝑛 − 𝐺 + 𝛾
𝐶𝑛𝑇𝑚𝑒𝑎𝑛 + 273
𝑢2 𝑒𝑠 − 𝑒𝑎
∆ + 𝛾 1 + 𝐶𝑑𝑢2
Daily grass-reference evapotranspiration (ETo) and alfalfa-reference evapotranspiration(ETr) were calculated using Penman-Monteith equation (Monteith, 1965) with a fixedcanopy resistance (ASCE-EWRI, 2005; Irmak et al., 2012):
where:
Rn = Net radiation, MJ m-2 d-1
G = Soil heat flux, MJ m-2 d-1
γ = Psychometric constant, kPa ⁰C-1
Tmean = Daily average air temperature, ⁰C
u2 = Wind speed at 2 m height, m s-1
es – ea = Vapor pressure deficit, kPa
∆ = Slope of saturation vapor pressure curve at air temperature, kPa ⁰C-1
Cn and Cd = Constants that change with reference surface
Reference Evapotranspiration (ETref)
BREBS in Clay Center, NE
Operated by Dr. Suat Irmak
Eddy Covariance System in North Platte, NE
Operated by Dr. Daran Rudnick
Climatic Data
Trends in Reference ET
Source: Rudnick and Irmak (2015)
Alfalfa Based Crop Coefficients (Kcr) for Corn:Clay Center, NE 2011-2012
Source: Rudnick and Irmak (2015)
Stress Factor (Kstress):
𝐾𝑤 =𝑇𝐴𝑊 −𝐷𝑟
𝑇𝐴𝑊 − 𝑅𝐴𝑊=
𝑇𝐴𝑊 − 𝐷𝑟
1 − 𝑝 𝑇𝐴𝑊
𝑇𝐴𝑊 = 𝜃𝑓𝑐 − 𝜃𝑤𝑝 x RZ
𝐾𝑠𝑡𝑟𝑒𝑠𝑠 =𝐾𝐶,𝑡𝑟𝑒𝑎𝑡𝑚𝑒𝑛𝑡
𝐾𝑐,𝑛𝑜𝑛−𝑙𝑖𝑚𝑖𝑡𝑖𝑛𝑔 𝑁 𝑜𝑟 𝑤𝑎𝑡𝑒𝑟
𝐴𝑠𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛: 𝐾𝑠𝑡𝑟𝑒𝑠𝑠 𝑖𝑠 𝑡ℎ𝑒 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑎𝑛𝑑 𝑁 𝑠𝑡𝑟𝑒𝑠𝑠
𝑅𝐴𝑊 = 𝑝 𝑥 𝑇𝐴𝑊
𝐾𝑛 =𝐾𝑠𝑡𝑟𝑒𝑠𝑠𝐾𝑤
Water Stress Factor (Kw):
Nitrogen Stress Factor (Kn):
Accounting for Crop Stress on ET
Source: Rudnick and Irmak (2015)
Crop Stress Factor (Kstress)
Source: Rudnick and Irmak (2015)
Monthly average Kstress, Kw, and Kn values for 0, 84, 140, 196, and 252 kg ha-1 nitrogen (N) treatments under rainfed, limited irrigation (75% FIT), and fully-irrigated (FIT) conditions in pooled 2011 and 2012.
June July August September
Irrigation N Kstress Kw Kn Kstress Kw Kn Kstress Kw Kn Kstress Kw Kn
Rainfed 0N 1.09 1.00 1.09 0.90 1.00 0.90 0.59 1.00 0.59 0.46 1.00 0.46
84N 1.01 1.00 1.01 0.81 1.00 0.81 0.79 0.93 0.85 0.53 0.90 0.61
140N 0.98 1.00 0.98 0.70 1.00 0.70 0.75 0.96 0.79 0.69 0.95 0.72
196N 1.00 1.00 1.00 0.95 1.00 0.95 0.80 0.91 0.87 0.71 0.84 0.87
252N 0.99 1.00 0.99 0.83 1.00 0.83 0.91 0.88 1.03 0.69 0.83 0.84
75% FIT 0N 1.17 1.00 1.17 0.84 1.00 0.84 0.84 1.00 0.84 0.49 1.00 0.49
84N 1.10 1.00 1.10 0.89 1.00 0.89 0.85 1.00 0.85 0.56 1.00 0.56
140N 0.97 1.00 0.97 0.92 1.00 0.92 0.95 1.00 0.95 0.88 1.00 0.88
196N 1.05 1.00 1.05 0.97 1.00 0.97 0.95 0.99 0.97 0.88 0.97 0.91
252N 1.03 1.00 1.03 0.93 1.00 0.93 0.95 1.00 0.95 0.86 0.97 0.89
FIT 0N 1.08 1.00 1.08 1.06 1.00 1.06 0.83 1.00 0.83 0.83 1.00 0.83
84N 1.00 1.00 1.00 1.05 1.00 1.05 0.97 1.00 0.97 0.80 1.00 0.80
140N 1.06 1.00 1.06 0.94 1.00 0.94 0.98 1.00 0.98 0.75 1.00 0.75
196N 1.06 1.00 1.06 0.84 1.00 0.84 1.07 1.00 1.07 0.80 1.00 0.80
• The monthly average values often experienced lower Kstress compared to Kw values; therefore, indicating that Kw alone was unable to account for the total reduction in Kc from a non-limiting water and nitrogen (N) reference.
Monthly Average Kstress, Kw, and Kn
Grain Yield& Efficiency Response
Diminishing Return and Efficiency
Grain yield follows a diminishing return to irrigation and N fertilizer (i.e., a lower increase in grain yield exist per unit input as the crop approaches maximum grain yield), and therefore, the efficiency of irrigation and N fertilizer can begin to decrease even as net income continues to increase.
Applied Irrigation or Nitrogen Fertilizer
Gra
in Y
ield
or
Net
Ret
urn
0
Maximum
No Benefit
Hypothetical Response Curve
Yield Response to Irrigation and Nitrogen
0
2
4
6
8
10
12
14
2011 2012 2013 2014
Gra
in Y
ield
(M
g h
a-1)
Rainfed Limited Full
y = -4E-05x2 + 0.034x + 7.3267
R² = 0.7809
0
2
4
6
8
10
12
14
16
0 50 100 150 200 250 300
Gra
in Y
ield
(M
g h
a-1)
Nitrogen Fertilizer Rate (kg ha-1)
Pooled 2011, 2012, & 2014
Water Productivity of Corn
Rainfed
y = -2E-05x2 + 0.0072x + 1.7354
R² = 0.75
Limited Irrigation
y = -5E-06x2 + 0.0054x + 1.5836
R² = 0.80
Full Irrigation
y = -3E-06x2 + 0.0051x + 1.5742
R² = 0.721.0
1.5
2.0
2.5
3.0
0 75 150 225 300
CW
UE
(k
g m
-3)
Nitrogen (kg ha-1)
Rainfed
75% FIT
FIT
Limited Irrigation
y = -7E-05x2 + 0.0383x - 3.3397
R² = 0.845
Full Irrigation
y = -3E-05x2 + 0.0198x - 1.5118
R² = 0.77
-2.5
-1.0
0.5
2.0
3.5
0 75 150 225 300
IWU
E (
kg
m-3
)
Nitrogen (kg ha-1)
Inter-Annual Economic Efficiency
Rainfedy = 41.835x - 20.766
R² = 0.72
Limited Irrigationy = 54.82x - 46.198
R² = 0.87
Full Irrigationy = 48.099x - 27.786
R² = 0.84
0
20
40
60
80
100
120
1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
Re
lati
ve N
et In
com
e (
%)
Crop Water Use Efficiency (CWUE, kg m-3)
0N 84N
140N 196N
252N
Relationship between relative net income (RNI, %) and crop water use efficiency (CWUE, kg m-3) for 0, 84, 140, 196, and 252 kg ha-1 nitrogen (N) fertilizer rates under full irrigation (FIT), limited irrigation (75% FIT), and rainfed settings for the pooled 2011, 2012, and 2014 growing seasons. Relative net income of a treatment was calculated as a percentage of the FIT-252 kg N ha-1
treatment (i.e., non-limiting water and N)
Relative Net Income vs CWUE
Source: Rudnick et al. (2016)
Limited Irrigationy = -3.1993x2 + 20.152x + 71.238
R² = 0.96
Full Irrigationy = -2.0627x2 + 22.055x + 67.921
R² = 0.86
40
50
60
70
80
90
100
110
-1.5 -0.5 0.5 1.5 2.5 3.5
Re
lati
ve N
et In
com
e (
%)
Irrigation Water Use Efficiency (IWUE, kg m-3)
84N
140N
196N
252N Limited
Irrigation
Full Irrigation
Relationship between relative net income (RNI, %) and irrigation water use efficiency (IWUE, kg m-3) for 84, 140, 196, and 252 kg ha-1 nitrogen (N) fertilizer rates under full irrigation (FIT) and limited irrigation (75% FIT) for the pooled 2011, 2012, and
2014 growing seasons. Relative net income of a treatment was calculated as a percentage of the FIT-252 kg N ha-1 treatment (i.e., non-limiting water and N).
Relative Net Income vs IWUE
Source: Rudnick et al. (2016)
Thank You!
The mention of trade names or commercial products in and during this presentation does not constitute an endorsement or recommendation for use by the University of Nebraska-Lincoln or the author.
