Managing Deficit Sprinkler Irrigation of Sunflower
By Freddie Lamm & Rob Aiken
Sunflowers shorter growing season and thus lower overall irrigation needs has helped generate more interest in this crop among irrigators in the Ogallala Aquifer region. Sunflower is thought to better withstand short periods of crop water stress than are corn and soybeans; and, the timing of critical sunflower water needs is offset from those of corn and beans.
For those reasons, sunflower may be a good choice for marginal (low-volume) sprinkler irrigation systems and, as well, in those situations where crop types are split within a given center-pivot field.
While center pivot (CP) sprinklers are the predominant irrigation method in the Ogallala region, they likewise present some unique challenges when used for deficit irrigation. For example:
Center pivots cannot be effectively used to apply large amounts of water timed to a critical growth stage, as can be done with surface irrigation methods.
The CP systems cannot efficiently use small frequent events to alleviate water stress, as is the case with subsurface drip irrigation (SDI).
So with center-pivot systems, its important that available soil water in storage be correctly managed, from a timing standpoint, when it comes to additions and withdrawals so that optimum crop production economically and water-wise can be achieved.
Three easy ways to control irrigation water additions are: (1) irrigation capacity, (2) preseason management and (3) initiation date of the seasons watering program. Withdrawals, in turn, can be partially managed by altering plant populations.
The 2010 northwest Kansas study described here examined sunflower production using the three methods of controlling irrigation additions for three different targeted plant populations.
The irrigated sunflower plots, located on the Kansas State University Northwest Research-Extension Center at Colby, were planted to a short-stature hybrid on June 16. The crop emerged on June 24.
Whole-plot treatment sprinkler irrigation capacities were 1 every four, eight or 12 days. ET-based water budget irrigation scheduling was used, with the range of first irrigation dates being from July 1 to July 20. The reason for staggering the starting date was to gain information for sprinkler management in fields where the crop type is split within a given field (e.g., when the critical water needs for corn are earlier than those of sunflower).
Another whole-plot irrigation treatment in the 2010 Colby study consisted of the addition (or, for check purposes, no addition) of 5 of dormant (preseason) irrigation in early May.
Three sunflower populations 18,000, 23,000 and 28,000 plants per acre were planted. Irrigation amounts consisted of 1 applied as needed, but limited by the imposed capacity and the water budget irrigation schedule. A lateral move sprinkler was used to apply the water.
Sunflower plant canopy temperatures were measured for the highest (1 every four days ) and lowest (1 every 12 days) capacities for plots with a starting date of July 1 (for both those plots receiving and not receiving preseason irrigation). This temperature data will be used to gain an overall assessment of when deficit irrigation is resulting in critical water stresses.
Sunflower yield and yield components (plant population, seeds per head and seed mass), seed oil quality, irrigation, total crop water use and soil water depletion were determined for each plot.
The early portion of the 2010 season at Colby was wet, and irrigation needs were lower than normal. Later in the season, however, conditions were extremely dry, with just 1.08 of precipitation received between August 4 and crop maturity on October 11. The earlier wet weather meant no irrigation was required prior to July 25, so there were no differences in irrigation initiation dates. In-season irrigation totals were 11.52, 6.72 and 4.8 for the irrigation capacities limited to 1/4 days, 1/8 days and 1/12 days, respectively.
Total irrigation amounts were about 1 less than normal (based on 1972-2005 irrigation scheduling simulations at Colby).
What were the results of this study? No significant differences could be attributed to preseason irrigation on any yield component or water use parameter except for plant population, which was slightly decreased when preseason irrigation was performed (5 in late April). Why that occurred is unknown. So preseason irrigation was not an economical practice in 2010, given that the 5 of application cost about $17.50 per acre (based on a pumping cost of $3.50 per acre-inch).
The 2010 study did, however, show significant differences in yield and oil content among the range of irrigations. Significantly lower yield and oil content occurred with the lowest irrigation capacity (1 per 12 days, for a total of 4.8). The highest yields and seed mass were obtained by the lowest targeted plant population (18,000/ac) and at the greatest irrigation capacity. Oil yield (lbs/ac) for the 18,000 population was 1,357, 1,361 and 1,314 for the 1/4 days, 1/8 days and 1/12 days irrigation capacities, respectively.
Assuming a seed value of $0.213/lb and a pumping cost of $3.50 per acre-inch, the 1/8 days capacity would produce $12.73 and $17.18 greater net returns, respectively, versus the 1/4 days and 1/12 days irrigation capacities. As could be expected, increases in plant population significantly decreased seeds per head and seed mass.
As would be anticipated, water use was increased by increased irrigation capacity; but it was not affected by increases in plant population. Water productivity (yield/water use) was significantly greater with decreases in irrigation capacity, as is often the case. But that must be balanced with the effect on overall economic productivity. The smallest plant population had significantly greater water productivity due to its higher sunflower yield.
Summary Comments by Dr. Freddie Lamm
Under limited irrigation capacities (i.e., gpm/acre, inches/day), sunflower can obtain a greater percentage of its maximum yield compared to corn and soybeans. Under the right economics, sunflower can be a good candidate for deficit irrigation.
Under full irrigation, sunflower uses about 3 less irrigation than corn or soybeans. However, generally because relative yield reductions are less for sunflower, the difference in annual irrigation may be 4-5.
Sunflower irrigation needs are greatest in August, while the need is greatest in July for corn and soybeans. Producers may want to plant a portion of their production area to sunflower to better manage lower-capacity irrigation systems.
Freddie Lamm is irrigation engineer and Rob Aiken is crops research scientist with the Kansas State University Northwest Research-Extension Center at Colby.
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