Water productivity of irrigated
corn in Nebraska
Patricio Grassini
Research Assistant Professor
University of Nebraska-Lincoln
“This cornfield, and the sorghum patch behind the barn, were the only broken
land in sight. Everywhere, as far the eye could reach, there was nothing but
rough, shaggy, red grass”
Willa Cather (My Antonia, 1918), novelist from Red Cloud NE
Water roundtable meeting
Oct 9, 2013
Water and stability
2000-2009 average yields and coefficient of variation by county for maize and
soybean in Nebraska (USDA-NASS)
Grassini et al., In Press
Grassini, unpublished
Assured water supply greatly increases yield and reduces year-to- year
variation in yield. Irrigated agriculture attracted investment in livestock feeding
operations, biofuel refineries, and manufacturing of irrigation equipment.
Water-food nexus
• We need water to produce high and
stable grain yields
• Appropriate metrics that account for
both crop production and water use
are needed in the discussion about
water & agriculture.
• Water Productivity (WP, kg grain per
inch of water supply) provides a good
framework for the discussion
Developing a WP benchmark for corn in NE
Water productivity
(WP) boundary
(11 bu ac-in-1)
Grain yield (bu ac-1)
250
200
150
Rainfed
Irrigated
100
50
Mean WP function
(8 bu ac-in-1)
0
0
5
• Yields were simulated over
20-y for 18 locations in
western Corn Belt using
Hybrid-Maize model.
• Crops assumed to grow
under optimal conditions
(no nutrient deficiencies
and no incidence of pests,
diseases, weeds).
• Model inputs based on
actual sowing date, plant
population, weather, and
soil properties at each of
the 18 locations.
10 15 20 25 30 35 40 45 50
Seasonal water supply* (in)
Grassini et al. (2009)
*Available soil water (0-5 ft) at planting + planting-to-maturity rainfall + applied irrigation
Validation of Mean Water Productivity Function
Crops grown with adequate nutrient supply and without loss from diseases, insect
pests, and weeds
WP boundary
slope = 11 bu ac-in-1
Grain yield (bu ac-1)
250
200
North Platte, NE, 1996-2006 (Payero
et al., 2006, 2008).
Mead, NE, 2001-2006. High intensive
management (Suyker and Verma, 2009)
n = 123
Progressive farmer fields in Eastern
Nebraska, 2007-2008 (Burgert, 2009)
Rainfed
150
Sprinkler
irrigation
Subsurface
drip irrigation
100
Mean WP function
slope = 8 bu ac-in-1
50
North Platte, NE, 1983-1991 (Hergert
et al., 1993).
North Platte and Clay Center, NE,
2005-2006 (Irmak and Yang,
unpublished data).
Farmer field winner of National Corn
Grower yield contest. Manchester, IA,
2002 (Yang et al., 2004).
0
0
10
20
30
40
Seasonal water supply (in)
50
Grassini et al. (2011)
Framework to diagnose and identify options to
improve water productivity in farmers’ fields
Grain yield (bu ac-1)
270
WP boundary
slope =11 bu ac-in-1
225
225 bu/ac
3) Higher yields with
less irrigation water
180
1) Higher yields, same water
supply with better crop mgmt
160 bu/ac
135
2) Less water, same yield with
improved irrigation mgmt
90
45
Mean WP function
slope = 8 bu ac-in-1
24 in
0
0
10
20
30
33 in
40
Seasonal water supply (in)
50
777 field-year observations from irrigated maize
fields in central Nebraska (2005-2007)
Tri-Basin Natural
Resources District
RIP
ST %)
(1 0
Stars indicate
weather stations ( )
or rain gauges ( )
DISK
(22%)
S
OU
INU %)
NT (38
CO IZE
MA
N)
EA
YB 61%
SO IZE (
MA
RIDGETILL
(31%) NO-TILL
(37%)
Each circle represents
a producer field
Grassini et al. (2011)
280
Water productivity (WP)
in the Tri-Basin NRD
280
Maximum yields
Grain yield (bu ac-1)
240
n = 777
~245 bu ac-1
200
WP boundary
11 bu ac-in-1
160
120
40
Mean-WP function
slope = 8 bu ac-in-1
240
200
160
WP = 6.0
bu ac-in-1
120
15
25
35
280
5
55
SURFACE
n = 261
Water requirement
for maximum yield
~ 36 in
200
160
WP = 5.3
bu ac-in-1
0
0
45
240
Average farmer’s
WP = 5.8 bu ac-in-1
80
n = 516
Grain yield (bu ac-1)
Producer-reported yields in Tri-Basin NRD,
2005-2007. Each data point corresponds to
an irrigated corn field.
PIVOT
10 15 20 25 30 35 40 45 50 55
Seasonal water supply (in)
120
15
25
35
45
55
Seasonal water supply (in)
Opportunities to reduce applied irrigation water
substantially without reducing productivity
288
11 bu ac-in-1
Optimal
irrigation
Grain yield (bu ac-1)
256
33,252 ac-ft yr-1
224
Reported yield and actual water
supply under pivot (  ) and
gravity ( Δ ) irrigation systems.
8 bu ac-in-1
■
Simulated yield under fullyirrigated conditions (irrigation
based on ETO and phenology)
20,639 ac-ft yr-1
Limited
irrigation
192
Actual
Pivot
●
Actual
Surface
Simulated yield under limitedirrigation management (75% of
fully-irrigation except during the
interval around silking when the
crop was fully-irrigated)
37,819 ac-ft yr-1
160
128
16
Total saving: 91,710 ac-ft y-1
(~32% of current water use in corn!)
Energy
saving
to annual
24
32 equivalent
40
48
electrical
usewater
of 4,300
houses
Seasonal
supply
(in) in NE!
56
Grassini et al. (2011)
Large scope to save irrigation water, without hurting yield, through replacement of
existing surface systems by pivots and fine tuning adjustment of irrigation schedule
Benchmarking yield and efficiency
of corn & soybean cropping
systems in Nebraska
Patricio Grassini, Jessica A. Torrion,
Kenneth G. Cassman, James E. Specht
Collaborators: Jenny Rees (UNL Extension Educator)
& Daryl Andersen (Little Blue NRD)
Nebraska Natural Resources Districts (NRD) data
Data on yield, N fertilizer rate, and irrigation water annually reported from 10,000+ fields since 2004
20 of 23 NRDs collaborating on this project
On-farm data survey
Data from 1030 dryland and irrigated fields in NE planted with corn and soybean in 2010, 2011, and 2012
Collected data include: field coordinates, yield, applied NPK fertilizer, lime and manure and time of
application, irrigation, type of irrigation system, tillage system, crop rotation, planting date, crop
maturity, plant density, pesticide rates and time of application, incidence of diseases and insects.
Website:
www.yieldgap.org
Thanks!
Questions?