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This book is dedicated to our wives and children for their love and support:
Maria, Emily, and April
JoAnn, Jennifer, and Kimberly
Amber, David, Elizabeth, Nathan, and Joshua DMH
Maria, Kimberly, Karen, and Sheryl GJH
CORN IRRIGATION MACROMANAGEMENT AT THE SEASONAL BOUNDARIES INITIATING AND TERMINATING THE IRRIGATION SEASON
KSU Northwest Research-Extension Center 105 Experiment Farm Road, Colby, Kansas Voice: 785-462-6281 Fax: 785-462-2315
Decisions about when to initiate and terminate the irrigation season are important irrigation macromanagement decisions that can potentially save water and increase net income when made correctly, but can have negative economic consequences when made incorrectly.
A combination of nine years of preanthesis water stress studies and sixteen years of post-anthesis water stress studies for corn was conducted at the Kansas State University Northwest Research-Extension Center in Colby, Kansas on a productive, deep, silt loam soil.
Overall, the pre-anthesis water stress studies suggest that corn grown on this soil type has great ability to handle early-season water stress, provided the water stress can be relieved during later stages.
A critical factor in maximizing corn grain yields as affected by pre-anthesis water stress is maximizing the kernels/area.
Maintaining a water deficit ratio greater than 0.7 to 0.8 or limiting available soil water depletion in the top 4 ft of soil profile to approximately 30% maximized the kernels/area.
Overall, the post-anthesis water stress studies suggest that corn yield is nearly linearly related to the amount of crop water use during the post-anthesis period and that total crop water use amounts may average nearly 17 inches.
Producers should plan for crop water use during the last 30 and 15 day periods that may average nearly 5 and 2 inches, respectively, to avoid yield reductions.
Management allowable depletion during the postanthesis period should be limited to 45% of the available soil water for an 8-ft profile on the deep silt loam soils of this climatic region.
Definition of Macromanagement and Scope of the Problem
Corn is the primary irrigated crop in the U.S.
Great Plains.
There are a number of efficient methods to schedule irrigation for corn on a real-time, daily, or short-term basis throughout the season.
These scheduling methods essentially achieve water conservation by delaying any unnecessary irrigation
event with the prospect that the irrigation season might end before the next irrigation event is required.
There are larger irrigation management decisions [i.e., irrigation macromanagement ] that can be considered separately from the step-by-step, periodic scheduling procedures.
Two important macromanagement decisions occur at the seasonal boundaries, the initiation and termination of the irrigation season.
Irrigators sometimes make these seasonal boundary determinations based on a traditional time-of-year rather than with sound rationale or science-based procedures.
However, a single, inappropriate, macromanagement decision can easily have a larger effect on total irrigation water use and/or crop production than the cumulative errors that might occur due to small, systematic errors in soil-, plant-, or climatic-based scheduling procedures.
This does not discount step-by-step irrigation scheduling.
To the contrary, it is an implicit assumption that improved macromanagement at the seasonal boundaries can only provide the potential for increased water conservation when used in conjunction with the step-by-step, periodic scheduling procedures.
Most of the established literature on irrigation management during the early and late corn growth stages is 35-45 years old and was written at a time when irrigated corn yields were much lower than they are today.
It is quite possible that some of the numerous yield-limiting stresses that were tolerable at the lower yield level are less tolerable today.
On the other side of the issue, there has been much improvement in corn hybrids during the period with incorporation of traits that allow water stress tolerance and/or water stress avoidance.
The corn vegetative stage is often considered the least-sensitive stage to water stress and could provide the opportunity to limit irrigation water applications without severe yield reductions.
The vegetative stage begins at crop emergence and ends after tasseling, which immediately precedes the beginning of the reproductive period when the silks start to emerge.
The potential number of ears/plant is established by the fifth leaf stage in corn.
The potential number of kernels/ear is established during the period from about the ninth leaf stage until about one week before silking.
Stresses during the 10 to 14 days after silking will reduce the potential kernels/ear to the final or actual number of kernels/ear.
Therefore, in research studies designed to examine water stresses during the first one-half of the corn crop season, both ears/plant and kernels/ear might be critical factors.
Additionally, there could be permanent damaging effects from the vegetative and early-reproductive period water stress that may affect grain filling.
Often, irrigators in the Great Plains, start their corn irrigation season after early season cultural practices are completed such as herbicide or fertilizer application or crop cultivation at the lay-by growth stage.
Crop evapotranspiration is increasing rapidly and drier weather periods are approaching, so often there is soil water storage that can be replenished by timely irrigation then for use later in the summer.
However, this
does not always mean that the corn crop required the irrigation at that point-intime.
In contrast, the post-anthesis grain filling stage in corn is considered to be highly sensitive to water stress with only the flowering and early reproductive period being more sensitive.
Plant water stress can cause kernel abortion if it occurs early enough in the post-anthesis period but is more often associated with poor grain filling and thus reduced kernel weight.
Grain kernel weight is termed as a very loosely restricted yield component , meaning that it can be manipulated by a number of factors.
The final value is also set quite late, essentially only a few days before physiological maturity.
The rate of grain filling is linear for a relatively long period of time from around blister kernel to near physiological maturity.
Yield increases of over 4 bushels/acre for each day are possible during this period.
Providing good management during the period can help to provide a high grain filling rate and, in some cases, may extend the grain filling period a few days thereby increasing yields.
Availability of water for crop growth and health is the largest single controllable factor during this period.
However, the rate of grain filling remains remarkably linear unless severe crop stress occurs.
This is attributed to remobilization of photosynthate from other plant parts when conditions are unfavorable for making new photosynthate.
Irrigators in the Central Great Plains sometimes terminate the corn irrigation season on a traditional date such as August 31 or Labor Day based on long term experience.
However, a more scientific approach might be that season termination may be determined by comparing the anticipated soil water balance at crop maturity to the management allowable depletion of the soil water within the root zone.
Some publications say the MAD at crop maturity can be as high as 0.8.
Extension publications from the Central Great Plains often suggest limiting the MAD at season end to 0.6 in the top 4 ft of the soil profile.
These values may need to be re-evaluated and perhaps adjusted downward.
Lamm et al.
found subsurface drip-irrigated corn yields in northwest Kansas began to decrease rapidly when available soil water in the top 8 ft was lower than 5660% of field capacity for extended periods in July and August.
Lamm et al.
permitted small daily deficits to accumulate on surface-irrigated corn after tasseling, and subsequent analysis of those data showed declining yields when available soil water levels approached 60% of field capacity for a 5-ft soil profile at physiological maturity
This presentation will summarize the results from several long term field studies at the KSU Northwest Research-Extension Center in Colby, Kansas on a productive, deep, silt loam soil where irrigation treatments were either initiated or terminated at various points-intime before and after anthesis, respectively.
The studies were conducted at the KSU Northwest Research-Extension Center at Colby, Kansas, USA on a productive, deep, well-drained Keith silt loam soil during the sixteen-year period, 1993-2008.
In general, the 1990s were a much wetter period than the 2000s.
The summers of 2000 through 2003 would be considered extreme droughts.
The climate for the region is semiarid with a summer pattern of precipitation with an annual average of approximately 19 inches.
The average precipitation and calculated corn evapotranspiration during the 120-day corn growing period, May 15 through September 11 is 11.8 inches and 23.1 inches, respectively.
The corn anthesis period typically occurs between July 15 and 20.
The corn was planted in 2.5 ft spaced rows in late April to early May, and standard cultural practices for the region were used.
Irrigation was scheduled as needed by a climate-based water budget except as modified by study protocols that will be discussed in the sections that follow.
Calculated crop evapotranspiration was determined with a modified Penman equation for calculating reference evapotranspiration multiplied by empirical crop coefficients suitable for western Kansas.
Precipitation and irrigation were deposits into the crop water budget and ETc was the withdrawal.
Soil water was measured in each plot on a weekly or biweekly basis with a neutron probe to a depth of 8 ft.
in 1-ft increments.
These data were used to determine crop water use and to determine critical soil water depletion levels.
Water use values were calculated as the sum of the change in available soil water to the specified profile depth, plus the irrigation and precipitation during the specified period.
This method of calculating crop water use would also include any deep percolation or rainfall runoff that may have occurred.
Corn yield and yield components of plants/area, ears/plant, and kernel weight were measured by hand harvesting a representative 20-ft row sample.
The number of kernels/ear was calculated with algebraic closure using the remaining yield components.
Specific Procedures for Pre-Anthesis Water Stress Studies
Data from two studies where the initiation date of the irrigation season was varied were combined in the analysis.
The first study consisted of five years of data with the hybrid Pioneer 3162.
The second study during the four-year period used two corn hybrids [Pioneer 32B33 and Pioneer 33B50 ].
Both studies utilized the same field site that had a subsurface drip irrigation system installed in 1990 with 5-ft dripline spacing and an emitter spacing of 12 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 0.15 gal/h for the 12-inch emitter spacing.
The 2004-2007 study had six main irrigation treatments and the two corn hybrid split-plot treatments replicated three times in a randomized complete block design.
The 1999-2003 study used the same experimental design without the split plot.
The whole plots were 8 rows wide and 200 ft long.
The six irrigation treatments were imposed by delaying the first normal irrigation either 0, 1, 2, 3, 4, or 5 weeks.
This typically resulted in the first irrigation for Trt 1 being between June 5 and June 15 and the first irrigation for Trt 6 being around July 10 to July 24.
In some years, excessive rainfall between two adjacent treatment initiation dates would negate the need for irrigation.
In that case, the later treatments would be delayed an additional week to provide an extended data set.
After the treatment initiation date occurred, SDI was scheduled to provide 0.4 inches/day until such time that the climate-based water budget fully eliminated calculated soil water deficits.
It should be noted that this irrigation capacity of 0.4 inches/day is much greater than the typical irrigation capacity in this region.
Additionally, the procedure of eliminating the severe irrigation deficits later in the season after the plants had been stunted may lead to excessive deep percolation.
The purpose of the study was not to optimize irrigation use within the study but rather to determine what capability the corn crop had to tolerate early season water stress.
Thus, the procedures were tailored to alleviate soil water deficits relatively quickly after the treatment initiation date.
Analysis of variance of the yield and yield component data was performed for the 6 treatments for the 1999-2003 data set using a one-way AOV and using a split plot two-way AOV for the 2004-2007 data set.
Specific Procedures for Post-Anthesis Water Stress Studies

This book is dedicated to our wives and children for their love and support:

Maria, Emily, and April

JoAnn, Jennifer, and Kimberly

Amber, David, Elizabeth, Nathan, and Joshua DMH

Maria, Kimberly, Karen, and Sheryl GJH

CORN IRRIGATION MACROMANAGEMENT AT THE SEASONAL BOUNDARIES INITIATING AND TERMINATING THE IRRIGATION SEASON

KSU Northwest Research-Extension Center 105 Experiment Farm Road, Colby, Kansas Voice: 785-462-6281 Fax: 785-462-2315

Decisions about when to initiate and terminate the irrigation season are important irrigation macromanagement decisions that can potentially save water and increase net income when made correctly, but can have negative economic consequences when made incorrectly.

A combination of nine years of preanthesis water stress studies and sixteen years of post-anthesis water stress studies for corn was conducted at the Kansas State University Northwest Research-Extension Center in Colby, Kansas on a productive, deep, silt loam soil.

Overall, the pre-anthesis water stress studies suggest that corn grown on this soil type has great ability to handle early-season water stress, provided the water stress can be relieved during later stages.

A critical factor in maximizing corn grain yields as affected by pre-anthesis water stress is maximizing the kernels/area.

Maintaining a water deficit ratio greater than 0.7 to 0.8 or limiting available soil water depletion in the top 4 ft of soil profile to approximately 30% maximized the kernels/area.

Overall, the post-anthesis water stress studies suggest that corn yield is nearly linearly related to the amount of crop water use during the post-anthesis period and that total crop water use amounts may average nearly 17 inches.

Producers should plan for crop water use during the last 30 and 15 day periods that may average nearly 5 and 2 inches, respectively, to avoid yield reductions.

Management allowable depletion during the postanthesis period should be limited to 45% of the available soil water for an 8-ft profile on the deep silt loam soils of this climatic region.

Definition of Macromanagement and Scope of the Problem

Corn is the primary irrigated crop in the U.S.

Great Plains.

There are a number of efficient methods to schedule irrigation for corn on a real-time, daily, or short-term basis throughout the season.

These scheduling methods essentially achieve water conservation by delaying any unnecessary irrigation

event with the prospect that the irrigation season might end before the next irrigation event is required.

There are larger irrigation management decisions [i.e., irrigation macromanagement ] that can be considered separately from the step-by-step, periodic scheduling procedures.

Two important macromanagement decisions occur at the seasonal boundaries, the initiation and termination of the irrigation season.

Irrigators sometimes make these seasonal boundary determinations based on a traditional time-of-year rather than with sound rationale or science-based procedures.

However, a single, inappropriate, macromanagement decision can easily have a larger effect on total irrigation water use and/or crop production than the cumulative errors that might occur due to small, systematic errors in soil-, plant-, or climatic-based scheduling procedures.

This does not discount step-by-step irrigation scheduling.

To the contrary, it is an implicit assumption that improved macromanagement at the seasonal boundaries can only provide the potential for increased water conservation when used in conjunction with the step-by-step, periodic scheduling procedures.

Most of the established literature on irrigation management during the early and late corn growth stages is 35-45 years old and was written at a time when irrigated corn yields were much lower than they are today.

It is quite possible that some of the numerous yield-limiting stresses that were tolerable at the lower yield level are less tolerable today.

On the other side of the issue, there has been much improvement in corn hybrids during the period with incorporation of traits that allow water stress tolerance and/or water stress avoidance.

The corn vegetative stage is often considered the least-sensitive stage to water stress and could provide the opportunity to limit irrigation water applications without severe yield reductions.

The vegetative stage begins at crop emergence and ends after tasseling, which immediately precedes the beginning of the reproductive period when the silks start to emerge.

The potential number of ears/plant is established by the fifth leaf stage in corn.

The potential number of kernels/ear is established during the period from about the ninth leaf stage until about one week before silking.

Stresses during the 10 to 14 days after silking will reduce the potential kernels/ear to the final or actual number of kernels/ear.

Therefore, in research studies designed to examine water stresses during the first one-half of the corn crop season, both ears/plant and kernels/ear might be critical factors.

Additionally, there could be permanent damaging effects from the vegetative and early-reproductive period water stress that may affect grain filling.

Often, irrigators in the Great Plains, start their corn irrigation season after early season cultural practices are completed such as herbicide or fertilizer application or crop cultivation at the lay-by growth stage.

Crop evapotranspiration is increasing rapidly and drier weather periods are approaching, so often there is soil water storage that can be replenished by timely irrigation then for use later in the summer.

However, this

does not always mean that the corn crop required the irrigation at that point-intime.

In contrast, the post-anthesis grain filling stage in corn is considered to be highly sensitive to water stress with only the flowering and early reproductive period being more sensitive.

Plant water stress can cause kernel abortion if it occurs early enough in the post-anthesis period but is more often associated with poor grain filling and thus reduced kernel weight.

Grain kernel weight is termed as a very loosely restricted yield component , meaning that it can be manipulated by a number of factors.

The final value is also set quite late, essentially only a few days before physiological maturity.

The rate of grain filling is linear for a relatively long period of time from around blister kernel to near physiological maturity.

Yield increases of over 4 bushels/acre for each day are possible during this period.

Providing good management during the period can help to provide a high grain filling rate and, in some cases, may extend the grain filling period a few days thereby increasing yields.

Availability of water for crop growth and health is the largest single controllable factor during this period.

However, the rate of grain filling remains remarkably linear unless severe crop stress occurs.

This is attributed to remobilization of photosynthate from other plant parts when conditions are unfavorable for making new photosynthate.

Irrigators in the Central Great Plains sometimes terminate the corn irrigation season on a traditional date such as August 31 or Labor Day based on long term experience.

However, a more scientific approach might be that season termination may be determined by comparing the anticipated soil water balance at crop maturity to the management allowable depletion of the soil water within the root zone.

Some publications say the MAD at crop maturity can be as high as 0.8.

Extension publications from the Central Great Plains often suggest limiting the MAD at season end to 0.6 in the top 4 ft of the soil profile.

These values may need to be re-evaluated and perhaps adjusted downward.

Lamm et al.

found subsurface drip-irrigated corn yields in northwest Kansas began to decrease rapidly when available soil water in the top 8 ft was lower than 5660% of field capacity for extended periods in July and August.

Lamm et al.

permitted small daily deficits to accumulate on surface-irrigated corn after tasseling, and subsequent analysis of those data showed declining yields when available soil water levels approached 60% of field capacity for a 5-ft soil profile at physiological maturity

This presentation will summarize the results from several long term field studies at the KSU Northwest Research-Extension Center in Colby, Kansas on a productive, deep, silt loam soil where irrigation treatments were either initiated or terminated at various points-intime before and after anthesis, respectively.

The studies were conducted at the KSU Northwest Research-Extension Center at Colby, Kansas, USA on a productive, deep, well-drained Keith silt loam soil during the sixteen-year period, 1993-2008.

In general, the 1990s were a much wetter period than the 2000s.

The summers of 2000 through 2003 would be considered extreme droughts.

The climate for the region is semiarid with a summer pattern of precipitation with an annual average of approximately 19 inches.

The average precipitation and calculated corn evapotranspiration during the 120-day corn growing period, May 15 through September 11 is 11.8 inches and 23.1 inches, respectively.

The corn anthesis period typically occurs between July 15 and 20.

The corn was planted in 2.5 ft spaced rows in late April to early May, and standard cultural practices for the region were used.

Irrigation was scheduled as needed by a climate-based water budget except as modified by study protocols that will be discussed in the sections that follow.

Calculated crop evapotranspiration was determined with a modified Penman equation for calculating reference evapotranspiration multiplied by empirical crop coefficients suitable for western Kansas.

Precipitation and irrigation were deposits into the crop water budget and ETc was the withdrawal.

Soil water was measured in each plot on a weekly or biweekly basis with a neutron probe to a depth of 8 ft.

in 1-ft increments.

These data were used to determine crop water use and to determine critical soil water depletion levels.

Water use values were calculated as the sum of the change in available soil water to the specified profile depth, plus the irrigation and precipitation during the specified period.

This method of calculating crop water use would also include any deep percolation or rainfall runoff that may have occurred.

Corn yield and yield components of plants/area, ears/plant, and kernel weight were measured by hand harvesting a representative 20-ft row sample.

The number of kernels/ear was calculated with algebraic closure using the remaining yield components.

Specific Procedures for Pre-Anthesis Water Stress Studies

Data from two studies where the initiation date of the irrigation season was varied were combined in the analysis.

The first study consisted of five years of data with the hybrid Pioneer 3162.

The second study during the four-year period used two corn hybrids [Pioneer 32B33 and Pioneer 33B50 ].

Both studies utilized the same field site that had a subsurface drip irrigation system installed in 1990 with 5-ft dripline spacing and an emitter spacing of 12 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 0.15 gal/h for the 12-inch emitter spacing.

The 2004-2007 study had six main irrigation treatments and the two corn hybrid split-plot treatments replicated three times in a randomized complete block design.

The 1999-2003 study used the same experimental design without the split plot.

The whole plots were 8 rows wide and 200 ft long.

The six irrigation treatments were imposed by delaying the first normal irrigation either 0, 1, 2, 3, 4, or 5 weeks.

This typically resulted in the first irrigation for Trt 1 being between June 5 and June 15 and the first irrigation for Trt 6 being around July 10 to July 24.

In some years, excessive rainfall between two adjacent treatment initiation dates would negate the need for irrigation.

In that case, the later treatments would be delayed an additional week to provide an extended data set.

After the treatment initiation date occurred, SDI was scheduled to provide 0.4 inches/day until such time that the climate-based water budget fully eliminated calculated soil water deficits.

It should be noted that this irrigation capacity of 0.4 inches/day is much greater than the typical irrigation capacity in this region.

Additionally, the procedure of eliminating the severe irrigation deficits later in the season after the plants had been stunted may lead to excessive deep percolation.

The purpose of the study was not to optimize irrigation use within the study but rather to determine what capability the corn crop had to tolerate early season water stress.

Thus, the procedures were tailored to alleviate soil water deficits relatively quickly after the treatment initiation date.

Analysis of variance of the yield and yield component data was performed for the 6 treatments for the 1999-2003 data set using a one-way AOV and using a split plot two-way AOV for the 2004-2007 data set.

Specific Procedures for Post-Anthesis Water Stress Studies