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Four separate studies were conducted over the years 1993 through 2008 to examine the effects of post-anthesis water stress on corn.
Prior to anthesis, all treatments in each of the studies were fully irrigated according to their need.
A two-year study consisting of six irrigation treatments with three replications in a complete randomized block design was conducted in small level basins consisting of 6 corn rows each approximately 90 ft long.
Surface irrigation was used to provide irrigation amounts for each event that were between 2.5 to 3 inches to help achieve higher distribution uniformity than smaller applications would have provided.
The six irrigation treatments were termination of the irrigation season on either August 5, 10, 15, 20, 25 or 30.
The corn hybrid was Pioneer 3183.
The year 1993 was an extremely poor corn production year
characterized by very cool and wet conditions while 1994 was a good year for corn production.
A four-year study consisting of nine irrigation treatments with four replications in a complete randomized block design was conducted in small level basins consisting of 8 corn rows each approximately 90 ft long.
Surface irrigation was used in this study with event irrigation amounts of approximately 2.5 to 3 inches.
The nine irrigation treatments were termination of the irrigation season at either anthesis, anthesis plus 6, 12, 18, 24, 30, 36, 42 or 48 days.
The corn hybrid was Pioneer 3183.
Corn yields in 1995 were somewhat depressed due to a hail storm but were good in 1996 through 1998.
Another study was conducted from 1999 through 2001 using subsurface drip irrigation to more closely control soil water levels and distribution uniformity of irrigation water.
In this study, seven irrigation treatments were replicated three times in a complete randomized block with plot size of 8 corn rows by approximately 280 ft.
In this study irrigation during the post-anthesis period was managed for two distinct periods.
Four of treatments began at anthesis with one treatment receiving no irrigation after anthesis and the other three treatments only receiving irrigation if the available soil water in the top 5 foot of profile fell below approximately 68, 48 or 27% of field capacity.
Three additional treatments were no irrigation after two weeks following anthesis and soil water maintenance level treatments of either 48 or 27% of field capacity beginning also at that time.
After anthesis, irrigation amounts were generally not greater than 0.5 inches for each required event and were conducted as needed to return the available soil water to the required treatment level.
The year 1999 had above normal precipitation but 2000 and 2001 were extreme drought years.
This study utilized an subsurface drip irrigation system installed in 1999 with 5-ft dripline spacing and an emitter spacing of 24 inches.
The 2.5-ft spaced corn rows were planted parallel and centered on the driplines such that each corn row would be 15 inches from the nearest dripline.
The nominal dripline flowrate was 0.25 gpm/100 ft, which is equivalent to an emitter discharge of 0.30 gal/h for the 24inch emitter spacing.
The corn hybrid was Pioneer 3162.
The final post-anthesis water stress study was conducted on the same SDI field site as the 1999 through 2001 study but the seven irrigation treatments were the irrigation season being terminated at one week intervals beginning one week after anthesis.
This typically meant that the first irrigation treatment ceased about July 20 to 27 and the last irrigation treatment ceased about August 31 to September 7.
The crop was fully irrigated until the irrigation termination date occurred and irrigation event amounts were generally not greater than 0.5 inches.
The seven irrigation treatments were replicated three times in a complete randomized block design.
The corn hybrid was Pioneer 3162.
Post
anthesis water productivity was calculated as the crop yield in bu/acre divided by the post-anthesis crop water use.
Results for Pre-Anthesis Water Stress Studies
Statistical and tabular data analysis for pre-anthesis water stress studies
Delaying irrigation only statistically affected the yield components in three of the nine crop years and then only for the later irrigation dates.
Delaying irrigation until July 10, 2001, July 17, 2003 and July 27, 2005 significantly reduced the number of kernels/ear and the grain yield.
These three years had an average weather-based calculated July crop ETc rate of 0.32 inches/day.
In comparison the average July crop ETc rate value was 0.26 inches/day for the other six years.
It should be noted that the years 2000 through 2003 were extreme drought years in northwest Kansas.
Delaying irrigation also significantly reduced ears/plant in 2003 and 2005.
In 2003, the reduction in kernels/ear and ears/plant for Trt 6 was partially compensated for by a statistically higher kernel weight.
Overall, these results suggest that corn grown on this soil type has great ability to handle vegetative and early-reproductive period water stress provided the water stress can be alleviated during the later stages.
The hybrid selection affected yield in only one of the four years, 2006, with the longer season Pioneer 32B33 providing significantly greater yields for the later irrigation initiation dates.
This is probably because of earlier pollination for the Pioneer 33B50 prior to receiving irrigation.
Kernels/ear was significantly less for the shorter season Pioneer 33B50 hybrid in three of four years.
Hybrid selection did not affect ears/plant in any of the four years.
In 2004, kernel weight was significantly higher for Pioneer 33B50 for some irrigation treatments, probably because of the smaller number of kernels/ear for this hybrid in that year.
It should be noted that the results do not mean that irrigation can be delayed in the Western Great Plains until mid to late July.
These plots generally started the season with reasonably full soil profiles.
Most irrigators do not have irrigation systems with adequate capacity to quickly alleviate severely depleted soil water reserves.
In addition, it is difficult to infiltrate large amounts of water into the soil quickly with sprinkler and surface irrigation systems without causing runoff problems.
Rather, look at these study results as describing the corn plant's innate ability to tolerate vegetative-period water stress.
Table 1.
Summary of yield component and irrigation data from an early season water stress study for corn hybrid Pioneer 3162, KSU-NWREC, Colby, Kansas, 1999-2003.
Year and Parameter Trt 1 Trt 2 Trt 3 Trt 4 Trt 5 Trt 6
1999 First Irrigation Date 22-Jun 29-Jun 6-Jul 13-Jul 20-Jul 27-Jul
Total Irrigation 11.2 11.2 11.2 10.0 10.0 7.6
Yield 253 a* 265 a 256 a 255 a 259 a 255 A
Plant Pop.
31073 A 32234 a 31944 a 31653 a 32234 a 32234 A
Ears/Plant 0.99 A 0.99 a 0.97 a 1.00 a 0.99 a 1.01 A
Kernels/Ear 575 A 570 a 555 a 572 a 543 a 555 A
Kernel Wt.
36.3 A 36.9 a 37.8 a 35.8 a 38.1 a 35.9 A
2000 First Irrigation Date 5-Jun 12-Jun 19-Jun 26-Jun 3-Jul 10-Jul
Total Irrigation 19.7 19.7 19.7 18.9 18.9 18.9
Yield 225 A 235 a 225 a 227 a 216 a 217 A
Plant Pop.
27878 A 28169 a 26717 a 26717 a 27007 a 27297 A
Ears/Plant 1.02 A 1.04 a 0.99 a 1.03 a 1.02 a 1.01 A
Kernels/Ear 544 A 553 a 568 a 544 a 548 a 529 A
Kernel Wt.
36.9 a 36.8 a 38.0 a 38.4 a 36.4 a 37.8 A
2001 First Irrigation Date 12-Jun 19-Jun 26-Jun 3-Jul 10-Jul 17-Jul
Total Irrigation 19.2 19.2 19.2 19.2 19.2 19.2
Yield 254 a 260 a 261 a 250 a 213 b 159 C
Plant Pop.
33977 a 34993 a 35138 a 35284 a 34413 a 33831 A
Ears/Plant 0.96 a 0.98 a 0.99 a 0.99 a 0.97 a 0.99 A
Kernels/Ear 581 a 584 a 582 a 541 a 476 b 347 C
Kernel Wt.
33.8 a 33.2 a 32.8 a 33.7 a 34.6 a 34.9 A
2002 First Irrigation Date 12-Jun 19-Jun 26-Jun 3-Jul 10-Jul 17-Jul
Total Irrigation 18.5 18.0 18.0 18.0 18.0 18.0
Yield 233 a 232 a 217 a 219 a 222 a 223 A
Plant Pop.
34558 a 34848 a 34558 a 35719 a 35719 a 34558 A
Ears/Plant 0.98 a 0.97 a 0.98 a 0.99 a 1.00 a 0.99 A
Kernels/Ear 454 a 443 a 407 a 435 a 391 a 422 A
Kernel Wt.
38.6 a 39.8 a 40.3 a 36.6 a 40.5 a 39.2 A
2003 First Irrigation Date 12-Jun 21-Jun 26-Jun 3-Jul 10-Jul 17-Jul
Total Irrigation 18.8 18.0 18.0 17.2 17.2 17.2
Yield 177 a 180 a 190 a 186 a 171 a 93 B
Plant Pop.
32815 a 33396 a 34267 a 33106 a 34558 a 32815 A
Ears/Plant 0.96 a 0.92 b 0.96 a 1.00 a 0.97 a 0.82 C
Kernels/Ear 588 a 567 a 576 a 569 a 486 b 262 C
Kernel Wt.
24.1 b 26.2 b 25.5 b 25.2 b 26.8 b 33.6 A
Values followed by the same lower case letters are not significantly different at P=0.05.

Four separate studies were conducted over the years 1993 through 2008 to examine the effects of post-anthesis water stress on corn.

Prior to anthesis, all treatments in each of the studies were fully irrigated according to their need.

A two-year study consisting of six irrigation treatments with three replications in a complete randomized block design was conducted in small level basins consisting of 6 corn rows each approximately 90 ft long.

Surface irrigation was used to provide irrigation amounts for each event that were between 2.5 to 3 inches to help achieve higher distribution uniformity than smaller applications would have provided.

The six irrigation treatments were termination of the irrigation season on either August 5, 10, 15, 20, 25 or 30.

The corn hybrid was Pioneer 3183.

The year 1993 was an extremely poor corn production year

characterized by very cool and wet conditions while 1994 was a good year for corn production.

A four-year study consisting of nine irrigation treatments with four replications in a complete randomized block design was conducted in small level basins consisting of 8 corn rows each approximately 90 ft long.

Surface irrigation was used in this study with event irrigation amounts of approximately 2.5 to 3 inches.

The nine irrigation treatments were termination of the irrigation season at either anthesis, anthesis plus 6, 12, 18, 24, 30, 36, 42 or 48 days.

The corn hybrid was Pioneer 3183.

Corn yields in 1995 were somewhat depressed due to a hail storm but were good in 1996 through 1998.

Another study was conducted from 1999 through 2001 using subsurface drip irrigation to more closely control soil water levels and distribution uniformity of irrigation water.

In this study, seven irrigation treatments were replicated three times in a complete randomized block with plot size of 8 corn rows by approximately 280 ft.

In this study irrigation during the post-anthesis period was managed for two distinct periods.

Four of treatments began at anthesis with one treatment receiving no irrigation after anthesis and the other three treatments only receiving irrigation if the available soil water in the top 5 foot of profile fell below approximately 68, 48 or 27% of field capacity.

Three additional treatments were no irrigation after two weeks following anthesis and soil water maintenance level treatments of either 48 or 27% of field capacity beginning also at that time.

After anthesis, irrigation amounts were generally not greater than 0.5 inches for each required event and were conducted as needed to return the available soil water to the required treatment level.

The year 1999 had above normal precipitation but 2000 and 2001 were extreme drought years.

This study utilized an subsurface drip irrigation system installed in 1999 with 5-ft dripline spacing and an emitter spacing of 24 inches.

The 2.5-ft spaced corn rows were planted parallel and centered on the driplines such that each corn row would be 15 inches from the nearest dripline.

The nominal dripline flowrate was 0.25 gpm/100 ft, which is equivalent to an emitter discharge of 0.30 gal/h for the 24inch emitter spacing.

The corn hybrid was Pioneer 3162.

The final post-anthesis water stress study was conducted on the same SDI field site as the 1999 through 2001 study but the seven irrigation treatments were the irrigation season being terminated at one week intervals beginning one week after anthesis.

This typically meant that the first irrigation treatment ceased about July 20 to 27 and the last irrigation treatment ceased about August 31 to September 7.

The crop was fully irrigated until the irrigation termination date occurred and irrigation event amounts were generally not greater than 0.5 inches.

The seven irrigation treatments were replicated three times in a complete randomized block design.

The corn hybrid was Pioneer 3162.

Post

anthesis water productivity was calculated as the crop yield in bu/acre divided by the post-anthesis crop water use.

Results for Pre-Anthesis Water Stress Studies

Statistical and tabular data analysis for pre-anthesis water stress studies

Delaying irrigation only statistically affected the yield components in three of the nine crop years and then only for the later irrigation dates.

Delaying irrigation until July 10, 2001, July 17, 2003 and July 27, 2005 significantly reduced the number of kernels/ear and the grain yield.

These three years had an average weather-based calculated July crop ETc rate of 0.32 inches/day.

In comparison the average July crop ETc rate value was 0.26 inches/day for the other six years.

It should be noted that the years 2000 through 2003 were extreme drought years in northwest Kansas.

Delaying irrigation also significantly reduced ears/plant in 2003 and 2005.

In 2003, the reduction in kernels/ear and ears/plant for Trt 6 was partially compensated for by a statistically higher kernel weight.

Overall, these results suggest that corn grown on this soil type has great ability to handle vegetative and early-reproductive period water stress provided the water stress can be alleviated during the later stages.

The hybrid selection affected yield in only one of the four years, 2006, with the longer season Pioneer 32B33 providing significantly greater yields for the later irrigation initiation dates.

This is probably because of earlier pollination for the Pioneer 33B50 prior to receiving irrigation.

Kernels/ear was significantly less for the shorter season Pioneer 33B50 hybrid in three of four years.

Hybrid selection did not affect ears/plant in any of the four years.

In 2004, kernel weight was significantly higher for Pioneer 33B50 for some irrigation treatments, probably because of the smaller number of kernels/ear for this hybrid in that year.

It should be noted that the results do not mean that irrigation can be delayed in the Western Great Plains until mid to late July.

These plots generally started the season with reasonably full soil profiles.

Most irrigators do not have irrigation systems with adequate capacity to quickly alleviate severely depleted soil water reserves.

In addition, it is difficult to infiltrate large amounts of water into the soil quickly with sprinkler and surface irrigation systems without causing runoff problems.

Rather, look at these study results as describing the corn plant's innate ability to tolerate vegetative-period water stress.

Table 1.

Summary of yield component and irrigation data from an early season water stress study for corn hybrid Pioneer 3162, KSU-NWREC, Colby, Kansas, 1999-2003.

Year and Parameter Trt 1 Trt 2 Trt 3 Trt 4 Trt 5 Trt 6

1999 First Irrigation Date 22-Jun 29-Jun 6-Jul 13-Jul 20-Jul 27-Jul

Total Irrigation 11.2 11.2 11.2 10.0 10.0 7.6

Yield 253 a* 265 a 256 a 255 a 259 a 255 A

Plant Pop.

31073 A 32234 a 31944 a 31653 a 32234 a 32234 A

Ears/Plant 0.99 A 0.99 a 0.97 a 1.00 a 0.99 a 1.01 A

Kernels/Ear 575 A 570 a 555 a 572 a 543 a 555 A

Kernel Wt.

36.3 A 36.9 a 37.8 a 35.8 a 38.1 a 35.9 A

2000 First Irrigation Date 5-Jun 12-Jun 19-Jun 26-Jun 3-Jul 10-Jul

Total Irrigation 19.7 19.7 19.7 18.9 18.9 18.9

Yield 225 A 235 a 225 a 227 a 216 a 217 A

Plant Pop.

27878 A 28169 a 26717 a 26717 a 27007 a 27297 A

Ears/Plant 1.02 A 1.04 a 0.99 a 1.03 a 1.02 a 1.01 A

Kernels/Ear 544 A 553 a 568 a 544 a 548 a 529 A

Kernel Wt.

36.9 a 36.8 a 38.0 a 38.4 a 36.4 a 37.8 A

2001 First Irrigation Date 12-Jun 19-Jun 26-Jun 3-Jul 10-Jul 17-Jul

Total Irrigation 19.2 19.2 19.2 19.2 19.2 19.2

Yield 254 a 260 a 261 a 250 a 213 b 159 C

Plant Pop.

33977 a 34993 a 35138 a 35284 a 34413 a 33831 A

Ears/Plant 0.96 a 0.98 a 0.99 a 0.99 a 0.97 a 0.99 A

Kernels/Ear 581 a 584 a 582 a 541 a 476 b 347 C

Kernel Wt.

33.8 a 33.2 a 32.8 a 33.7 a 34.6 a 34.9 A

2002 First Irrigation Date 12-Jun 19-Jun 26-Jun 3-Jul 10-Jul 17-Jul

Total Irrigation 18.5 18.0 18.0 18.0 18.0 18.0

Yield 233 a 232 a 217 a 219 a 222 a 223 A

Plant Pop.

34558 a 34848 a 34558 a 35719 a 35719 a 34558 A

Ears/Plant 0.98 a 0.97 a 0.98 a 0.99 a 1.00 a 0.99 A

Kernels/Ear 454 a 443 a 407 a 435 a 391 a 422 A

Kernel Wt.

38.6 a 39.8 a 40.3 a 36.6 a 40.5 a 39.2 A

2003 First Irrigation Date 12-Jun 21-Jun 26-Jun 3-Jul 10-Jul 17-Jul

Total Irrigation 18.8 18.0 18.0 17.2 17.2 17.2

Yield 177 a 180 a 190 a 186 a 171 a 93 B

Plant Pop.

32815 a 33396 a 34267 a 33106 a 34558 a 32815 A

Ears/Plant 0.96 a 0.92 b 0.96 a 1.00 a 0.97 a 0.82 C

Kernels/Ear 588 a 567 a 576 a 569 a 486 b 262 C

Kernel Wt.

24.1 b 26.2 b 25.5 b 25.2 b 26.8 b 33.6 A

Values followed by the same lower case letters are not significantly different at P=0.05.